The flow maldistribution and the effect of different inlet configuration on the flow distribution in platefin heat exchangers were studied experimentally. It is found that the flow maldistribution is serious because o...The flow maldistribution and the effect of different inlet configuration on the flow distribution in platefin heat exchangers were studied experimentally. It is found that the flow maldistribution is serious because of the defects of inlet configurations, while the inlet configuration and Reynolds number are the main factors affecting the flow distribution. The improved inlet configurations, which are the header with a two-stage distributing configuration and the guide vane with a fluid complementary cavity were proposed and tested in this paper. The experimental results show that the improved inlet configurations can effectively improve the performance of flow distribution in heat exchangers.展开更多
A two-step method for stacking arrangement of passages in multistream plate-fin heat exchanger is proposed. The first step (predict step) is to initialize the arrangement according to a local-balance principle, and th...A two-step method for stacking arrangement of passages in multistream plate-fin heat exchanger is proposed. The first step (predict step) is to initialize the arrangement according to a local-balance principle, and the second step (correct step) is to resadust the arrangement according to the results of differential computation of the temperature distribution. The computer implementation process of the local balance principle is described in detail and three examples are illustrated to show the feasibility of this principle. A subroutine program is provided to facilitate the reader to adopt this principle.展开更多
Geothermal energy,a form of renewable energy,has been extensively utilized for building heating.However,there is a lack of detailed comparative studies on the use of shallow and medium-deep geothermal energy in buildi...Geothermal energy,a form of renewable energy,has been extensively utilized for building heating.However,there is a lack of detailed comparative studies on the use of shallow and medium-deep geothermal energy in building energy systems,which are essential for decision-making.Therefore,this paper presents a comparative study of the performance and economic analysis of shallow and medium-deep borehole heat exchanger heating systems.Based on the geological parameters of Xi’an,China and commonly used borehole heat exchanger structures,numerical simulationmethods are employed to analyze performance and economic efficiency.The results indicate that increasing the spacing between shallow borehole heat exchangers can effectively reduce thermal interference between the pipes and improve heat extraction performance.As the flow rate increases,the outlet water temperature ranges from 279.3 to 279.7 K,with heat extraction power varying between 595 and 609 W.For medium-deep borehole heat exchangers,performance predictions show that a higher flow rate results in greater heat extraction power.However,when the flow rate exceeds 30 m^(3)/h,further increases in flow rate have only a minor effect on enhancing heat extraction power.Additionally,the economic analysis reveals that the payback period for shallow geothermal heating systems ranges from 10 to 11 years,while for medium-deep geothermal heating systems,it varies more widely from 3 to 25 years.Therefore,the payback period for medium-deep geothermal heating systems is more significantly influenced by operational and installation parameters,and optimizing these parameters can considerably shorten the payback period.The results of this study are expected to provide valuable insights into the efficient and cost-effective utilization of geothermal energy for building heating.展开更多
This study develops an analytical model to evaluate the cooling performance of a porous terracotta tubular direct evaporative heat and mass exchanger. By combining energy and mass balance equations with heat and mass ...This study develops an analytical model to evaluate the cooling performance of a porous terracotta tubular direct evaporative heat and mass exchanger. By combining energy and mass balance equations with heat and mass transfer coefficients and air psychrometric correlations, the model provides insights into the impact of design and operational parameters on the exchanger cooling performance. Validated against an established numerical model, it accurately simulates cooling behavior with a Root Mean Square Deviation of 0.43 - 1.18˚C under varying inlet air conditions. The results show that tube geometry, including equivalent diameter, flatness ratio, and length significantly influences cooling outcomes. Smaller diameters enhance wet-bulb effectiveness but reduce cooling capacity, while increased flatness and length improve both. For example, extending the flatness ratio of a 15 mm diameter, 0.6 m long tube from 1 (circular) to 4 raises the exchange surface area from 0.028 to 0.037 m2, increasing wet-bulb effectiveness from 60% to 71%. Recommended diameters range from 5 mm for tubes under 0.5 m to 1 cm for tubes 0.5 to 1 m in length. Optimal air velocities depend on tube length: 1 m/s for tubes under 0.8 m, 1.5 m/s for lengths of 0.8 to 1.2 m, and up to 2 m/s for longer tubes. This model offers a practical alternative to complex numerical and CFD methods, with potential applications in cooling tower optimization for thermal and nuclear power plants and geothermal heat exchangers.展开更多
Meeting the climate change mitigation targets will require a substantial shift from fossil to clean fuels in the heating sector.Heat pumps with deep borehole exchangers are a promising solution to reduce emissions.Her...Meeting the climate change mitigation targets will require a substantial shift from fossil to clean fuels in the heating sector.Heat pumps with deep borehole exchangers are a promising solution to reduce emissions.Here the thermal behavior of deep borehole exchangers(DBHEs)ranging from 1 to 2 km was analyzed for various heat flow profiles.A strong correlation between thermal energy extraction and power output from DBHEs was found,also influenced by the heating profile employed.Longer operating time over the year typically resulted in higher energy production,while shorter one yielded higher average thermal power output,highlighting the importance of the choice of heating strategy and system design for optimal performance of DBHEs.Short breaks in operation for regenerating the borehole,for example,with waste heat,proved to be favorable for the performance yielding an overall heat output close to the same as with continuous extraction of heat.The results demonstrate the usefulness of deep boreholes for dense urban areas with less available space.As the heat production from a single DBHE in Finnish conditions ranges from half up to even a few GWh a year,the technology is best suitable for larger heat loads.展开更多
As compact and efficient heat exchange equipment,helically coiled tube-in-tube heat exchangers(HCTT heat exchangers)are widely used in many industrial processes.However,the thermal-hydraulic research of liquefied natu...As compact and efficient heat exchange equipment,helically coiled tube-in-tube heat exchangers(HCTT heat exchangers)are widely used in many industrial processes.However,the thermal-hydraulic research of liquefied natural gas(LNG)as the working fluid inHCTT heat exchangers is rarely reported.In this paper,the characteristics of HCTT heat exchangers,in which LNG flows in the inner tube and ethylene glycol-water solution flows in the outer tube,are studied by numerical simulations.The influences of heat transfer characteristics and pressure drops of the HCTT heat transfers are studied by changing the initial flow velocity,the helical middle diameter,and the helical pitch.The results indicate that different initial flow velocities in the inner tube and the outer tube of the HCTT heat exchanger have little influence on the secondary flow of the fluid in the helical tubes,and the overall flow characteristics tend to be stable.The smaller helical middle diameter of the HCTT heat exchanger leads to the shorter fluid flow length,the smaller resistance along the tubes and the increase of initial pressure under the condition of constant inlet velocity,which promotes the occurrence of secondary flow.The axial flow of fluid promotes the destruction of heat transfer boundary layer and gains strength of the turbulence and heat transfer efficiency.With the increase of the helical pitch of the HCTT heat exchanger,the turbulent intensity and the heat transfer efficiency are also increased.Moreover,the improvement of the flow state of the HCTT exchanger in a longer helical pitch also enhances the heat exchange efficiency.展开更多
This study explores the effectiveness of machine learning models in predicting the air-side performance of microchannel heat exchangers.The data were generated by experimentally validated Computational Fluid Dynam-ics...This study explores the effectiveness of machine learning models in predicting the air-side performance of microchannel heat exchangers.The data were generated by experimentally validated Computational Fluid Dynam-ics(CFD)simulations of air-to-water microchannel heat exchangers.A distinctive aspect of this research is the comparative analysis of four diverse machine learning algorithms:Artificial Neural Networks(ANN),Support Vector Machines(SVM),Random Forest(RF),and Gaussian Process Regression(GPR).These models are adeptly applied to predict air-side heat transfer performance with high precision,with ANN and GPR exhibiting notably superior accuracy.Additionally,this research further delves into the influence of both geometric and operational parameters—including louvered angle,fin height,fin spacing,air inlet temperature,velocity,and tube temperature—on model performance.Moreover,it innovatively incorporates dimensionless numbers such as aspect ratio,fin height-to-spacing ratio,Reynolds number,Nusselt number,normalized air inlet temperature,temperature difference,and louvered angle into the input variables.This strategic inclusion significantly refines the predictive capabilities of the models by establishing a robust analytical framework supported by the CFD-generated database.The results show the enhanced prediction accuracy achieved by integrating dimensionless numbers,highlighting the effectiveness of data-driven approaches in precisely forecasting heat exchanger performance.This advancement is pivotal for the geometric optimization of heat exchangers,illustrating the considerable potential of integrating sophisticated modeling techniques with traditional engineering metrics.展开更多
Helically coiled tube-in-tube(HCTT)heat exchangers are widely applied to the process technology because of their compactness and higher heat transfer efficiency.HCTT heat exchangers play an important role in liquified...Helically coiled tube-in-tube(HCTT)heat exchangers are widely applied to the process technology because of their compactness and higher heat transfer efficiency.HCTT heat exchangers play an important role in liquified natural gas(LNG)use and cold energy recovery.The heat transfer characteristics,pressure distribution,and degree of vaporization of LNG in HCTT heat exchangers are numerically investigated.By comparing the simulation results of the computational model with existing experimental results,the effectiveness of the computational model is verified.The numerical simulation results show the vapor volume fraction of the HCTT heat exchanger is related to the inlet Reynolds number,inner tube diameters,and helix diameter.The vapor volume fraction increases rapidly from the fourth to the seventh equal division points of the helix tube length.On condition that the inlet Reynolds number is greater than 33500,the pressure drop rate gradually increases.When the magnitude of the vapor volume fraction is below 0.2,the heat transfer coefficient increase rate is greater than that when the vapor volume fraction is above 0.2.The heat exchange efficiency of HCTT heat exchangers increases with the decrease of the ratio of helix diameter to inner tube diameter.展开更多
Objective To investigate the flow distribution in plate fin heat exchangers and optimize the design of header configuration for plate fin heat exchangers. Methods A mathematical model of header was proposed. The e...Objective To investigate the flow distribution in plate fin heat exchangers and optimize the design of header configuration for plate fin heat exchangers. Methods A mathematical model of header was proposed. The effects of the header configuration on the flow distribution in plate fin heat exchangers were investigated by CFD. The second header configuration with a two stage distributing structure was brought forward to improve the performance of flow distribution. Results It is found that the flow maldistribution is very serious in the direction of header length for the conventional header used in industry. The numerical predictions indicate that the improved header configurations can effectively improve the performance of flow distribution in plate fin heat exchangers. Conclusion The numerical simulation confirms that CFD should be a suitable tool for predicting the flow distribution. The method has a wide variety of applications in the design of plate fin heat exchangers.展开更多
The flow characteristics of shell-side fluid in the tube-and-shell heat exchangers with trisection helical baffles with 35° inclined angles are numerically analyzed. The secondary flow distribution of the fluid i...The flow characteristics of shell-side fluid in the tube-and-shell heat exchangers with trisection helical baffles with 35° inclined angles are numerically analyzed. The secondary flow distribution of the fluid in the shell-side channel is focused on. The results on meridian planes indicate that in the shell-side channel, the center part of fluid has an outward tendency because of the centrifugal force, and the peripheral region fluid has an inward tendency under the centripetal force. So in a spiral cycle, the fluid is divided into the upper and lower beams of streamlines, at the same time the Dean vortices are formed near the left baffle, and then the fluid turns to centripetal flow near the right baffle. Finally the two beams of streamlines merge in the main flow. The results of a number of parallel slices between two parallel baffles with the same sector in a swirl cycle also show the existence of the secondary flow and some backward flows at the V-gaps of the adjacent baffles. The secondary flows have a positive effect on mixing fluid by promoting the momentum and mass exchange between fluid particles near the tube wall and in the main stream, and thus they will enhance the heat transfer of the helix heat exchanger.展开更多
Topology optimization of thermal-fluid coupling problems has received widespread attention.This article proposes a novel topology optimization method for laminar two-fluid heat exchanger design.The proposed method uti...Topology optimization of thermal-fluid coupling problems has received widespread attention.This article proposes a novel topology optimization method for laminar two-fluid heat exchanger design.The proposed method utilizes an artificial density field to create two permeability interpolation functions that exhibit opposing trends,ensuring separation between the two fluid domains.Additionally,a Gaussian function is employed to construct an interpolation function for the thermal conductivity coefficient.Furthermore,a computational program has been developed on the OpenFOAM platform for the topology optimization of two-fluid heat exchangers.This program leverages parallel computing,significantly reducing the time required for the topology optimization process.To enhance computational speed and reduce the number of constraint conditions,we replaced the conventional pressure drop constraint condition in the optimization problem with a pressure inlet/outlet boundary condition.The 3D optimization results demonstrate the characteristic features of a surface structure,providing valuable guidance for designing heat exchangers that achieve high heat exchange efficiency while minimizing excessive pressure loss.At the same time,a new structure appears in large-scale topology optimization,which proves the effectiveness and stability of the topology optimization program written in this paper in large-scale calculation.展开更多
The shell side flow fields of both sextant and trisection helical baffle heat exchangers are presented on meridian and multilayer hexagon slices.It verifies that the performance of sextant schemes is better than those...The shell side flow fields of both sextant and trisection helical baffle heat exchangers are presented on meridian and multilayer hexagon slices.It verifies that the performance of sextant schemes is better than those of the other kinds of helical baffle heat exchangers.The main mechanisms are due to the restricted leakage flow in the minimized gaps with increased baffle number and by one row of tubes dampen the leakage flow in the circumferential overlapped area of the adjacent helical baffles.The performance features were simulated on two different angled sextant helical heat exchangers and each compared with two trisection ones of either identical helical pitch or identical incline angle.The results verified that the performances of helical heat exchangers are mainly determined by the helical pitch rather than the baffle incline angle.The average values of comprehensive index hoΔpo-1/3 of the trisection helical schemes T-24.1°and T-29.7°are correspondingly 3.47%and 3.34%lower than those of the sextant ones X-20°and X-25°with identical helical pitches.The comparison results show that the average values of shell side h.t.c.hoand comprehensive index hoΔpo-1/3 of the optimal dual helix sextant scheme DX30°are respectively 7.22%and 23.56%higher than those of the segment scheme S100.展开更多
The non-uniformity of gas–liquid mixture is a critical issue which leads to the heat transfer deterioration of spiralwound heat exchangers(SWHEs).Two-phase mass flow rate and the content of gas are important paramete...The non-uniformity of gas–liquid mixture is a critical issue which leads to the heat transfer deterioration of spiralwound heat exchangers(SWHEs).Two-phase mass flow rate and the content of gas are important parameters as well as structural parameters which have prominent influences on flow distribution uniformity of SWHE shell side.In order to investigate the influences of these parameters,an experimental test system was built using water and air as mediums and a novel distributor named"tubes distributor"was designed.The effects of mass flow rate and the content of gas on two-phase distribution performance were analyzed,where the mass flow rate ranged from 28.4 to 171.9 kg·h-1 and the content of gas changed from 0.2 to 0.8,respectively.The results showed that the mixture mass flow rate considerably influenced the liquid distribution than that of gas phase and the larger mass flow rate exhibited the better distribution uniformity of two-phase flow.It was also found that the tubes distributor had the better two-phase uniformity when the content of gas was around 0.4.Tube diameter played an important role in the distribution of gas phase and slit width was more significant for the uniformity of liquid phase.展开更多
This article presents a simulated annealing-based approach to the optimal synthesis of distillation column considering intermediate heat exchangers arrangements. T-he number of intermediate condensers and/or intermedi...This article presents a simulated annealing-based approach to the optimal synthesis of distillation column considering intermediate heat exchangers arrangements. T-he number of intermediate condensers and/or intermediate reboilers, the placement locations, the.operating pressure of column, and the heat duties of intermediate heat exchangers are treated as optimization variables. A novel coding procedure making use of an integer number series is proposed to represent and manipulate the structure of system and a stage-to-stage method is used for column design and cost calculation. With the representation procedure, the synthesis problem is formulated as a mixed integer nonlinear programming （MINLP） problem, which can then be solved with an improved simulated annealing algorithm. Two examples are illustrated to show the effectiveness of the suggested approach.展开更多
Shape and quantity of helical baffles have great impact on the shell-side performance of helical baffled heat exchangers （HBHE）. In this work, three physical models of HBHE with baffles of different shape （trisecti...Shape and quantity of helical baffles have great impact on the shell-side performance of helical baffled heat exchangers （HBHE）. In this work, three physical models of HBHE with baffles of different shape （trisection, quadrant and sextant sector） were investigated. Numerical simulations were performed on HBHE at three helix an- gles （10°, 25° and 40°） by the software ANSYS CFX. Analyses of numerical results indicate that the sextant HBHE shows relatively better fluid flow performance because the leakage flow in the triangle area is evidently reduced and the fluid streamline appears much closer to an ideal spiral flow, while the trisection and quadrant HBHE show more scattered and disordered streamline distributions. The convective heat transfer coefficient and pressure drop in three types of HBHE were presented. Further investigations on the shell side performance with different helical baf- fles were implemented by the field synergy theory. Both theoretical and numerical analyses gave support on the re- lations between helical baffle shape and shell-side performance. This paper may provide useful reference for the selection of baffle shade and auantitv in HBHE.展开更多
Many methods have been proposed for synthesis of heat exchanger networks in recent years, most of which consider single pass exchangers. In this study some evolutionary rules have been proposed for synthesis of multip...Many methods have been proposed for synthesis of heat exchanger networks in recent years, most of which consider single pass exchangers. In this study some evolutionary rules have been proposed for synthesis of multipass exchanger networks. The method is based on the heuristic that optimal networks should feature maximum energy recovery and have the minimum number of shells. The effectiveness of the developed evolutionary rules is demonstrated through some literature examples.展开更多
The spiral-wound heat exchanger(SWHE) is the primary low-temperature heat exchanger for large-scale LNG plants due to its high-pressure resistance, compact structure, and high heat exchange efficiency. This paper stud...The spiral-wound heat exchanger(SWHE) is the primary low-temperature heat exchanger for large-scale LNG plants due to its high-pressure resistance, compact structure, and high heat exchange efficiency. This paper studied the shell-side heat and mass transfer characteristics of vapor-liquid two-phase mixed refrigerants in an SWHE by combining a multi-component model in FLUENT software with a customized multicomponent mass transfer model. Besides, the mathematical model under the sloshing condition was obtained through mathematical derivation, and the corresponding UDF code was loaded into FLUENT as the momentum source term. The results under the sloshing conditions were compared with the relevant parameters under the steady-state condition. The shell-side heat and mass transfer characteristics of the SWHE were investigated by adjusting the component ratio and other working conditions. It was found that the sloshing conditions enhance the heat transfer performance and sometimes have insignificant effects. The sloshing condition is beneficial to reduce the flow resistance. The comprehensive performance of multi-component refrigerants has been improved and the improvement is more significant under sloshing conditions, considering both the heat transfer and pressure drop.These results will provide theoretical support for the research and design of multi-component heat and mass transfer enhancement of LNG SWHE under ocean sloshing conditions.展开更多
The traditional methods for synthesizing flexible heat exchanger networks(HENs)are not directly applicable to inter-plant HEN challenges,primarily due to the spread of system uncertainty across plants via intermedium ...The traditional methods for synthesizing flexible heat exchanger networks(HENs)are not directly applicable to inter-plant HEN challenges,primarily due to the spread of system uncertainty across plants via intermedium fluid circles.This complicates the synthesis process significantly.To tackle this issue,this study proposes a decomposed stepwise methodology to facilitate the flexible synthesis of the interplant HENs performing indirect heat integration.A decomposition strategy is proposed to divide the overall network into manageable sub-networks by dissecting the intermedium fluid circles.To address the variability in intermedium fluid temperatures,a temperature fluctuation analysis approach is developed and a heuristic rule is introduced to maintain the temperature feasibility of the intermedium fluids.To ensure adequate flexibility and cost-effectiveness of the designed networks,flexibility analysis and network retrofit steps are conducted through model-based optimization techniques.The efficacy of the method is demonstrated through two case studies,showing its potential in achieving the desired operational flexibility for inter-plant HENs.展开更多
A cell model to describe and optimize heat and mass transfer in contact heat exchangers for utilization of exhaust gases heat is proposed. The model is based on the theory of Markov chains and allows calculating heat ...A cell model to describe and optimize heat and mass transfer in contact heat exchangers for utilization of exhaust gases heat is proposed. The model is based on the theory of Markov chains and allows calculating heat and mass transfer at local moving force of the processes in each cell. The total process is presented as two parallel chains of cells (one for water flow and one for gas flow). The corresponding cells of the chains can exchange heat and mass, and water and gas can travel along their chains according to their transition ma-trices. The results of numerical experiments showed that the most part of heat transfer occurs due to moisture condensation from gas and the most intense heat transfer goes near the inlet of gas. Experimental validation of the model showed a good correlation between calculated and experimental data for an industrial contact heat exchanger if appropriate empirical equations were used to calculate heat and mass transfer coefficient. It was also shown that there exists the optimum height of heat exchanger that gave the maximum gain in heat energy utilization.展开更多
Numerical simulations were performed on flow and heat transfer performances of heat exchangers having six helical baffles of different baffle shapes and assembly configurations, i.e., two trisection baffle schemes, tw...Numerical simulations were performed on flow and heat transfer performances of heat exchangers having six helical baffles of different baffle shapes and assembly configurations, i.e., two trisection baffle schemes, two quadrant baffle schemes, and two continuous helical baffle schemes. The temperature contour or the pressure contour and velocity contour plots with superimposed velocity vectors on meridian, transverse and unfolded concentric hexagonal slices are presented to obtain a full angular view. For the six helix baffled heat exchangers,the different patterns of the single vortex secondary flow and the shortcut leakage flow were depicted as well as the heat transfer properties were compared. The results show that the optimum scheme among the six configurations is a circumferential overlap trisection helix baffled heat exchanger with a baffle incline angle of 20°(20°TCO) scheme with an anti-shortcut baffle structure, which exhibits the second highest pressure dropΔpo, the highest overall heat transfer coefficient K, shell-side heat transfer coefficient hoand shell-side average comprehensive index ho/Δpo.展开更多
基金Supported by the Doctoral Foundation of Xi'an Jiaotong University (No. DFXJTU2002-12) the Foundation for Excellent Doctoral Dissertation Author by Minister of Education, China (No. 199933).
文摘The flow maldistribution and the effect of different inlet configuration on the flow distribution in platefin heat exchangers were studied experimentally. It is found that the flow maldistribution is serious because of the defects of inlet configurations, while the inlet configuration and Reynolds number are the main factors affecting the flow distribution. The improved inlet configurations, which are the header with a two-stage distributing configuration and the guide vane with a fluid complementary cavity were proposed and tested in this paper. The experimental results show that the improved inlet configurations can effectively improve the performance of flow distribution in heat exchangers.
文摘A two-step method for stacking arrangement of passages in multistream plate-fin heat exchanger is proposed. The first step (predict step) is to initialize the arrangement according to a local-balance principle, and the second step (correct step) is to resadust the arrangement according to the results of differential computation of the temperature distribution. The computer implementation process of the local balance principle is described in detail and three examples are illustrated to show the feasibility of this principle. A subroutine program is provided to facilitate the reader to adopt this principle.
基金support by the Shanghai Engineering Research Center for Shallow Geothermal Energy(DRZX-202306)Shaanxi Coal Geology Group Co.,Ltd.(SMDZ-ZD2024-23)+4 种基金Key Laboratory of Coal Resources Exploration and Comprehensive Utilization,Ministry of Natural Resources,China(ZP2020-1)Shaanxi Investment Group Co.,Ltd.(SIGC2023-KY-05)Key Research and Development Projects of Shaanxi Province(2023-GHZD-54)Shaanxi Qinchuangyuan Scientist+Engineer Team Construction Project(2022KXJ-049)China Postdoctoral Science Foundation(2023M742802,2024T170721).
文摘Geothermal energy,a form of renewable energy,has been extensively utilized for building heating.However,there is a lack of detailed comparative studies on the use of shallow and medium-deep geothermal energy in building energy systems,which are essential for decision-making.Therefore,this paper presents a comparative study of the performance and economic analysis of shallow and medium-deep borehole heat exchanger heating systems.Based on the geological parameters of Xi’an,China and commonly used borehole heat exchanger structures,numerical simulationmethods are employed to analyze performance and economic efficiency.The results indicate that increasing the spacing between shallow borehole heat exchangers can effectively reduce thermal interference between the pipes and improve heat extraction performance.As the flow rate increases,the outlet water temperature ranges from 279.3 to 279.7 K,with heat extraction power varying between 595 and 609 W.For medium-deep borehole heat exchangers,performance predictions show that a higher flow rate results in greater heat extraction power.However,when the flow rate exceeds 30 m^(3)/h,further increases in flow rate have only a minor effect on enhancing heat extraction power.Additionally,the economic analysis reveals that the payback period for shallow geothermal heating systems ranges from 10 to 11 years,while for medium-deep geothermal heating systems,it varies more widely from 3 to 25 years.Therefore,the payback period for medium-deep geothermal heating systems is more significantly influenced by operational and installation parameters,and optimizing these parameters can considerably shorten the payback period.The results of this study are expected to provide valuable insights into the efficient and cost-effective utilization of geothermal energy for building heating.
文摘This study develops an analytical model to evaluate the cooling performance of a porous terracotta tubular direct evaporative heat and mass exchanger. By combining energy and mass balance equations with heat and mass transfer coefficients and air psychrometric correlations, the model provides insights into the impact of design and operational parameters on the exchanger cooling performance. Validated against an established numerical model, it accurately simulates cooling behavior with a Root Mean Square Deviation of 0.43 - 1.18˚C under varying inlet air conditions. The results show that tube geometry, including equivalent diameter, flatness ratio, and length significantly influences cooling outcomes. Smaller diameters enhance wet-bulb effectiveness but reduce cooling capacity, while increased flatness and length improve both. For example, extending the flatness ratio of a 15 mm diameter, 0.6 m long tube from 1 (circular) to 4 raises the exchange surface area from 0.028 to 0.037 m2, increasing wet-bulb effectiveness from 60% to 71%. Recommended diameters range from 5 mm for tubes under 0.5 m to 1 cm for tubes 0.5 to 1 m in length. Optimal air velocities depend on tube length: 1 m/s for tubes under 0.8 m, 1.5 m/s for lengths of 0.8 to 1.2 m, and up to 2 m/s for longer tubes. This model offers a practical alternative to complex numerical and CFD methods, with potential applications in cooling tower optimization for thermal and nuclear power plants and geothermal heat exchangers.
文摘Meeting the climate change mitigation targets will require a substantial shift from fossil to clean fuels in the heating sector.Heat pumps with deep borehole exchangers are a promising solution to reduce emissions.Here the thermal behavior of deep borehole exchangers(DBHEs)ranging from 1 to 2 km was analyzed for various heat flow profiles.A strong correlation between thermal energy extraction and power output from DBHEs was found,also influenced by the heating profile employed.Longer operating time over the year typically resulted in higher energy production,while shorter one yielded higher average thermal power output,highlighting the importance of the choice of heating strategy and system design for optimal performance of DBHEs.Short breaks in operation for regenerating the borehole,for example,with waste heat,proved to be favorable for the performance yielding an overall heat output close to the same as with continuous extraction of heat.The results demonstrate the usefulness of deep boreholes for dense urban areas with less available space.As the heat production from a single DBHE in Finnish conditions ranges from half up to even a few GWh a year,the technology is best suitable for larger heat loads.
基金supported by Innovative Team Introduction Projects for New Universities in Jinan City(No.2021GXRC075).
文摘As compact and efficient heat exchange equipment,helically coiled tube-in-tube heat exchangers(HCTT heat exchangers)are widely used in many industrial processes.However,the thermal-hydraulic research of liquefied natural gas(LNG)as the working fluid inHCTT heat exchangers is rarely reported.In this paper,the characteristics of HCTT heat exchangers,in which LNG flows in the inner tube and ethylene glycol-water solution flows in the outer tube,are studied by numerical simulations.The influences of heat transfer characteristics and pressure drops of the HCTT heat transfers are studied by changing the initial flow velocity,the helical middle diameter,and the helical pitch.The results indicate that different initial flow velocities in the inner tube and the outer tube of the HCTT heat exchanger have little influence on the secondary flow of the fluid in the helical tubes,and the overall flow characteristics tend to be stable.The smaller helical middle diameter of the HCTT heat exchanger leads to the shorter fluid flow length,the smaller resistance along the tubes and the increase of initial pressure under the condition of constant inlet velocity,which promotes the occurrence of secondary flow.The axial flow of fluid promotes the destruction of heat transfer boundary layer and gains strength of the turbulence and heat transfer efficiency.With the increase of the helical pitch of the HCTT heat exchanger,the turbulent intensity and the heat transfer efficiency are also increased.Moreover,the improvement of the flow state of the HCTT exchanger in a longer helical pitch also enhances the heat exchange efficiency.
基金supported by the National Natural Science Foundation of China(Grant No.52306026)the Wenzhou Municipal Science and Technology Research Program(Grant No.G20220012)+2 种基金the Special Innovation Project Fund of the Institute of Wenzhou,Zhejiang University(XMGL-KJZX202205)the State Key Laboratory of Air-Conditioning Equipment and System Energy Conservation Open Project(Project No.ACSKL2021KT01)the Special Innovation Project Fund of the Institute of Wenzhou,Zhejiang University(XMGL-KJZX-202205).
文摘This study explores the effectiveness of machine learning models in predicting the air-side performance of microchannel heat exchangers.The data were generated by experimentally validated Computational Fluid Dynam-ics(CFD)simulations of air-to-water microchannel heat exchangers.A distinctive aspect of this research is the comparative analysis of four diverse machine learning algorithms:Artificial Neural Networks(ANN),Support Vector Machines(SVM),Random Forest(RF),and Gaussian Process Regression(GPR).These models are adeptly applied to predict air-side heat transfer performance with high precision,with ANN and GPR exhibiting notably superior accuracy.Additionally,this research further delves into the influence of both geometric and operational parameters—including louvered angle,fin height,fin spacing,air inlet temperature,velocity,and tube temperature—on model performance.Moreover,it innovatively incorporates dimensionless numbers such as aspect ratio,fin height-to-spacing ratio,Reynolds number,Nusselt number,normalized air inlet temperature,temperature difference,and louvered angle into the input variables.This strategic inclusion significantly refines the predictive capabilities of the models by establishing a robust analytical framework supported by the CFD-generated database.The results show the enhanced prediction accuracy achieved by integrating dimensionless numbers,highlighting the effectiveness of data-driven approaches in precisely forecasting heat exchanger performance.This advancement is pivotal for the geometric optimization of heat exchangers,illustrating the considerable potential of integrating sophisticated modeling techniques with traditional engineering metrics.
基金supported by Innovative Team Introduction Projects for New Universities in Jinan City(No.2021GXRC075).
文摘Helically coiled tube-in-tube(HCTT)heat exchangers are widely applied to the process technology because of their compactness and higher heat transfer efficiency.HCTT heat exchangers play an important role in liquified natural gas(LNG)use and cold energy recovery.The heat transfer characteristics,pressure distribution,and degree of vaporization of LNG in HCTT heat exchangers are numerically investigated.By comparing the simulation results of the computational model with existing experimental results,the effectiveness of the computational model is verified.The numerical simulation results show the vapor volume fraction of the HCTT heat exchanger is related to the inlet Reynolds number,inner tube diameters,and helix diameter.The vapor volume fraction increases rapidly from the fourth to the seventh equal division points of the helix tube length.On condition that the inlet Reynolds number is greater than 33500,the pressure drop rate gradually increases.When the magnitude of the vapor volume fraction is below 0.2,the heat transfer coefficient increase rate is greater than that when the vapor volume fraction is above 0.2.The heat exchange efficiency of HCTT heat exchangers increases with the decrease of the ratio of helix diameter to inner tube diameter.
文摘Objective To investigate the flow distribution in plate fin heat exchangers and optimize the design of header configuration for plate fin heat exchangers. Methods A mathematical model of header was proposed. The effects of the header configuration on the flow distribution in plate fin heat exchangers were investigated by CFD. The second header configuration with a two stage distributing structure was brought forward to improve the performance of flow distribution. Results It is found that the flow maldistribution is very serious in the direction of header length for the conventional header used in industry. The numerical predictions indicate that the improved header configurations can effectively improve the performance of flow distribution in plate fin heat exchangers. Conclusion The numerical simulation confirms that CFD should be a suitable tool for predicting the flow distribution. The method has a wide variety of applications in the design of plate fin heat exchangers.
基金The National Natural Science Foundation of China (No.50976022)the National Key Technology R&D Program of China during the 11th Five-Year Plan Period (No.2008BAJ12B02)
文摘The flow characteristics of shell-side fluid in the tube-and-shell heat exchangers with trisection helical baffles with 35° inclined angles are numerically analyzed. The secondary flow distribution of the fluid in the shell-side channel is focused on. The results on meridian planes indicate that in the shell-side channel, the center part of fluid has an outward tendency because of the centrifugal force, and the peripheral region fluid has an inward tendency under the centripetal force. So in a spiral cycle, the fluid is divided into the upper and lower beams of streamlines, at the same time the Dean vortices are formed near the left baffle, and then the fluid turns to centripetal flow near the right baffle. Finally the two beams of streamlines merge in the main flow. The results of a number of parallel slices between two parallel baffles with the same sector in a swirl cycle also show the existence of the secondary flow and some backward flows at the V-gaps of the adjacent baffles. The secondary flows have a positive effect on mixing fluid by promoting the momentum and mass exchange between fluid particles near the tube wall and in the main stream, and thus they will enhance the heat transfer of the helix heat exchanger.
基金supported by the Aeronautical Science Foundation of China(Grant No.2020Z009063001)the Fundamental Research Funds for the Central Universities(Grant No.DUT22GF303).
文摘Topology optimization of thermal-fluid coupling problems has received widespread attention.This article proposes a novel topology optimization method for laminar two-fluid heat exchanger design.The proposed method utilizes an artificial density field to create two permeability interpolation functions that exhibit opposing trends,ensuring separation between the two fluid domains.Additionally,a Gaussian function is employed to construct an interpolation function for the thermal conductivity coefficient.Furthermore,a computational program has been developed on the OpenFOAM platform for the topology optimization of two-fluid heat exchangers.This program leverages parallel computing,significantly reducing the time required for the topology optimization process.To enhance computational speed and reduce the number of constraint conditions,we replaced the conventional pressure drop constraint condition in the optimization problem with a pressure inlet/outlet boundary condition.The 3D optimization results demonstrate the characteristic features of a surface structure,providing valuable guidance for designing heat exchangers that achieve high heat exchange efficiency while minimizing excessive pressure loss.At the same time,a new structure appears in large-scale topology optimization,which proves the effectiveness and stability of the topology optimization program written in this paper in large-scale calculation.
基金Supported by the National Natural Science Foundation of China(51776035).
文摘The shell side flow fields of both sextant and trisection helical baffle heat exchangers are presented on meridian and multilayer hexagon slices.It verifies that the performance of sextant schemes is better than those of the other kinds of helical baffle heat exchangers.The main mechanisms are due to the restricted leakage flow in the minimized gaps with increased baffle number and by one row of tubes dampen the leakage flow in the circumferential overlapped area of the adjacent helical baffles.The performance features were simulated on two different angled sextant helical heat exchangers and each compared with two trisection ones of either identical helical pitch or identical incline angle.The results verified that the performances of helical heat exchangers are mainly determined by the helical pitch rather than the baffle incline angle.The average values of comprehensive index hoΔpo-1/3 of the trisection helical schemes T-24.1°and T-29.7°are correspondingly 3.47%and 3.34%lower than those of the sextant ones X-20°and X-25°with identical helical pitches.The comparison results show that the average values of shell side h.t.c.hoand comprehensive index hoΔpo-1/3 of the optimal dual helix sextant scheme DX30°are respectively 7.22%and 23.56%higher than those of the segment scheme S100.
基金Supported by the research funds from MIIT program on High Technology Research Program of Ship(2013K4181).
文摘The non-uniformity of gas–liquid mixture is a critical issue which leads to the heat transfer deterioration of spiralwound heat exchangers(SWHEs).Two-phase mass flow rate and the content of gas are important parameters as well as structural parameters which have prominent influences on flow distribution uniformity of SWHE shell side.In order to investigate the influences of these parameters,an experimental test system was built using water and air as mediums and a novel distributor named"tubes distributor"was designed.The effects of mass flow rate and the content of gas on two-phase distribution performance were analyzed,where the mass flow rate ranged from 28.4 to 171.9 kg·h-1 and the content of gas changed from 0.2 to 0.8,respectively.The results showed that the mixture mass flow rate considerably influenced the liquid distribution than that of gas phase and the larger mass flow rate exhibited the better distribution uniformity of two-phase flow.It was also found that the tubes distributor had the better two-phase uniformity when the content of gas was around 0.4.Tube diameter played an important role in the distribution of gas phase and slit width was more significant for the uniformity of liquid phase.
文摘This article presents a simulated annealing-based approach to the optimal synthesis of distillation column considering intermediate heat exchangers arrangements. T-he number of intermediate condensers and/or intermediate reboilers, the placement locations, the.operating pressure of column, and the heat duties of intermediate heat exchangers are treated as optimization variables. A novel coding procedure making use of an integer number series is proposed to represent and manipulate the structure of system and a stage-to-stage method is used for column design and cost calculation. With the representation procedure, the synthesis problem is formulated as a mixed integer nonlinear programming （MINLP） problem, which can then be solved with an improved simulated annealing algorithm. Two examples are illustrated to show the effectiveness of the suggested approach.
基金Supported by the National Natural Science Foundation of China(51106090)the National Key Basic Research Program of China(2013CB228305)the Independent Innovation Foundation of Shandong University(2012TS190)
文摘Shape and quantity of helical baffles have great impact on the shell-side performance of helical baffled heat exchangers （HBHE）. In this work, three physical models of HBHE with baffles of different shape （trisection, quadrant and sextant sector） were investigated. Numerical simulations were performed on HBHE at three helix an- gles （10°, 25° and 40°） by the software ANSYS CFX. Analyses of numerical results indicate that the sextant HBHE shows relatively better fluid flow performance because the leakage flow in the triangle area is evidently reduced and the fluid streamline appears much closer to an ideal spiral flow, while the trisection and quadrant HBHE show more scattered and disordered streamline distributions. The convective heat transfer coefficient and pressure drop in three types of HBHE were presented. Further investigations on the shell side performance with different helical baf- fles were implemented by the field synergy theory. Both theoretical and numerical analyses gave support on the re- lations between helical baffle shape and shell-side performance. This paper may provide useful reference for the selection of baffle shade and auantitv in HBHE.
文摘Many methods have been proposed for synthesis of heat exchanger networks in recent years, most of which consider single pass exchangers. In this study some evolutionary rules have been proposed for synthesis of multipass exchanger networks. The method is based on the heuristic that optimal networks should feature maximum energy recovery and have the minimum number of shells. The effectiveness of the developed evolutionary rules is demonstrated through some literature examples.
基金funded by the National Natural Science Foundation of China(No.51806236,No.51806239)the Fundamental Research Funds for the Central Universities(No.2015XKMS059)+1 种基金Shaanxi Postdoctoral Fund Project(No.2018BSHEDZZ56)Foundation of Key Laboratory of Thermo-Fluid Science and Engineering(Xi'an Jiaotong University),Ministry of Education(No.KLTFSE2017KF01)。
文摘The spiral-wound heat exchanger(SWHE) is the primary low-temperature heat exchanger for large-scale LNG plants due to its high-pressure resistance, compact structure, and high heat exchange efficiency. This paper studied the shell-side heat and mass transfer characteristics of vapor-liquid two-phase mixed refrigerants in an SWHE by combining a multi-component model in FLUENT software with a customized multicomponent mass transfer model. Besides, the mathematical model under the sloshing condition was obtained through mathematical derivation, and the corresponding UDF code was loaded into FLUENT as the momentum source term. The results under the sloshing conditions were compared with the relevant parameters under the steady-state condition. The shell-side heat and mass transfer characteristics of the SWHE were investigated by adjusting the component ratio and other working conditions. It was found that the sloshing conditions enhance the heat transfer performance and sometimes have insignificant effects. The sloshing condition is beneficial to reduce the flow resistance. The comprehensive performance of multi-component refrigerants has been improved and the improvement is more significant under sloshing conditions, considering both the heat transfer and pressure drop.These results will provide theoretical support for the research and design of multi-component heat and mass transfer enhancement of LNG SWHE under ocean sloshing conditions.
基金financial support provided by the National Natural Science Foundation of China(22378045,22178045).
文摘The traditional methods for synthesizing flexible heat exchanger networks(HENs)are not directly applicable to inter-plant HEN challenges,primarily due to the spread of system uncertainty across plants via intermedium fluid circles.This complicates the synthesis process significantly.To tackle this issue,this study proposes a decomposed stepwise methodology to facilitate the flexible synthesis of the interplant HENs performing indirect heat integration.A decomposition strategy is proposed to divide the overall network into manageable sub-networks by dissecting the intermedium fluid circles.To address the variability in intermedium fluid temperatures,a temperature fluctuation analysis approach is developed and a heuristic rule is introduced to maintain the temperature feasibility of the intermedium fluids.To ensure adequate flexibility and cost-effectiveness of the designed networks,flexibility analysis and network retrofit steps are conducted through model-based optimization techniques.The efficacy of the method is demonstrated through two case studies,showing its potential in achieving the desired operational flexibility for inter-plant HENs.
文摘A cell model to describe and optimize heat and mass transfer in contact heat exchangers for utilization of exhaust gases heat is proposed. The model is based on the theory of Markov chains and allows calculating heat and mass transfer at local moving force of the processes in each cell. The total process is presented as two parallel chains of cells (one for water flow and one for gas flow). The corresponding cells of the chains can exchange heat and mass, and water and gas can travel along their chains according to their transition ma-trices. The results of numerical experiments showed that the most part of heat transfer occurs due to moisture condensation from gas and the most intense heat transfer goes near the inlet of gas. Experimental validation of the model showed a good correlation between calculated and experimental data for an industrial contact heat exchanger if appropriate empirical equations were used to calculate heat and mass transfer coefficient. It was also shown that there exists the optimum height of heat exchanger that gave the maximum gain in heat energy utilization.
基金Supported by the National Natural Science Foundation of China(50976022,51276035)the Provincial Science and Technology Innovation and Transformation of Achievements of Special Fund Project of Jiangsu Province(BY2011155)
文摘Numerical simulations were performed on flow and heat transfer performances of heat exchangers having six helical baffles of different baffle shapes and assembly configurations, i.e., two trisection baffle schemes, two quadrant baffle schemes, and two continuous helical baffle schemes. The temperature contour or the pressure contour and velocity contour plots with superimposed velocity vectors on meridian, transverse and unfolded concentric hexagonal slices are presented to obtain a full angular view. For the six helix baffled heat exchangers,the different patterns of the single vortex secondary flow and the shortcut leakage flow were depicted as well as the heat transfer properties were compared. The results show that the optimum scheme among the six configurations is a circumferential overlap trisection helix baffled heat exchanger with a baffle incline angle of 20°(20°TCO) scheme with an anti-shortcut baffle structure, which exhibits the second highest pressure dropΔpo, the highest overall heat transfer coefficient K, shell-side heat transfer coefficient hoand shell-side average comprehensive index ho/Δpo.
