Stable TiO_2–water nanofluids are prepared by a two-step method, stabilities of nanofluids are investigated by precipitation method and transmittance method respectively, and thermal conductivities and viscosities ar...Stable TiO_2–water nanofluids are prepared by a two-step method, stabilities of nanofluids are investigated by precipitation method and transmittance method respectively, and thermal conductivities and viscosities are also measured. An experimental system for studying the heat transfer enhancement of nanofluids is established,and heat transfer and flow characteristics of TiO_2–water nanofluids in heat exchanger systems with a triangular tube and circular tube are experimentally studied. The effects of nanoparticle mass fractions(ω = 0.1 wt%–0.5 wt%) and Reynolds numbers(Re = 800–10000) on the heat transfer and flow performances of nanofluids are analyzed. Fitting formulas for Nusselt number and resistance coefficient of nanofluids in a triangular tube are put forward based on the experimental data. The comprehensive performances of nanofluids in a triangular tube are investigated. It is found that nanofluids in a triangular tube can significantly improve the heat transfer performance at the cost of a small increase in resistance coefficient compared with that in a circular tube, especially the resistance coefficients are almost the same between different nanoparticle mass fractions at turbulent flow. It is also found that the comprehensive evaluation index η decreases with Reynolds number at laminar flow but a critical maximum value appears at turbulent flow.展开更多
Forced convection cooling of fins on a high-temperature wall has been used to cool high-power electronic devices. We numerically calculated and experimentally measured the forced convection heat transfer coefficient a...Forced convection cooling of fins on a high-temperature wall has been used to cool high-power electronic devices. We numerically calculated and experimentally measured the forced convection heat transfer coefficient and pressure drop of a diamond-shaped fin-array with water flow in this study, which had been reported to have a self-induced flip-flop flow phenomenon. Although the flip-flop flow phenomenon occurred in calculations, it was not observed in experiments. The heat transfer and pressure drop of the diamond-shaped fin-array could be estimated with equations for turbulent flow in tubes.展开更多
Recent and constant demands for greater power densities and smaller sizes of electronic systems have stimulated the growth of new designs of different passive heat transfer methods such as heat pipes. Particularly, OH...Recent and constant demands for greater power densities and smaller sizes of electronic systems have stimulated the growth of new designs of different passive heat transfer methods such as heat pipes. Particularly, OHPs （Oscillating Heat Pipes） are relatively novel devices, capable of removing high heat rates over long and short distances with not much temperature drop. This study concentrates on the design, building and assembling a test rig in order to analyse the flow pattern ofdeionised water through a 5 turns flat plate oscillating heat pipe under different heat inputs, which was made in the school of engineering and materials science of the Queen Mary University of London by two energy M.Sc. students. The filling ratio of the water is 40%. Furthermore an experimental study on the OHP thermal performance is carried out in order to examine the effects of different surface wet conditions： super hydrophilic, hydrophilic and cleaned brass. It is demonstrated the formation of liquid slugs and vapour plugs of the water along the channels. The experimental results showed that the hydrophilic surface tends to be more energy efficient. The heat transfer performance of the super-hydrophilic and hydrophilic is higher than brass by 5-12% and 15-20% respectively.展开更多
Flow resistance and heat transfer coefficients of typical double wall laminated film cooling configuration within a turbine vane were experimentally studied.The specimen was in large scale,and made of transparent orga...Flow resistance and heat transfer coefficients of typical double wall laminated film cooling configuration within a turbine vane were experimentally studied.The specimen was in large scale,and made of transparent organic glass.Laminated configuration consisted of double wall laminates,pin-fins,staggered arrays of impingement and film holes.The number ratio of impingement holes,pin-fins and film holes was2∶1∶1.Five experiment vanes were installed in static cascade,and experiments were carried out under constant heat flux.Re of internal cooling air in the experiment was from 104 to 2×105,and Re of external fluid was from 105 to 3×105.The experiment results show that flow resistances of front channel and back channel of the vane are in the same level,and both of them decrease as Re of cooling air increases.Nuof front channel is slightly higher than that of back channel.Both of them increase as Re of cooling air increases.And experiment results were obtained from experiment vanes were compared with that obtained from laminated flat plates,and the tendency of the results agrees well.展开更多
Channel structure has a significant effect on the heat transfer performance of PCHE.In this study,a set of rectangular straight channel PCHEs with different cross-section aspect ratios had been tested on S-CO_(2) heat...Channel structure has a significant effect on the heat transfer performance of PCHE.In this study,a set of rectangular straight channel PCHEs with different cross-section aspect ratios had been tested on S-CO_(2) heat transfer experimental platform,the effect of mass flow rate in both cold and heat sides,as well as the cross-section aspect ratio of the rectangular straight channel,on the heat transfer performance of PCHE was investigated.The results show that the comprehensive heat transfer performance of the rectangular cross-section is better than that of the semicircular cross-section;increasing the aspect ratio can improve the comprehensive heat transfer performance of PCHE,but the strengthening effect diminishes as the aspect ratio increases.Increasing the mass flow rate on both sides not only enhances the pre-cooler's cooling capacity and heat transfer,but also raises the pressure drop.In addition,an improved heat transfer correlation for rectangular cross-section PCHE was proposed,considering the effects of cross-sectional aspect ratio and pseudo-critical temperature is proposed in the range of Re from 3169 to 48474 and Pr from 0.98 to 12.5,the fited results better predict the local Nu and f magnitudes and trends in the pre-cooler under different cooling conditions,outperforming the simulated data and Gnielinski and Blasius correlation.展开更多
In recent years,bamboo,as a green building material,has attracted more and more attention worldwide.Inspired by the investigation of cross-laminated timber in structural systems,a new engineered cross-laminated bamboo...In recent years,bamboo,as a green building material,has attracted more and more attention worldwide.Inspired by the investigation of cross-laminated timber in structural systems,a new engineered cross-laminated bamboo(CLB)consisting of the cross lamination of bamboo scrimber plates is proposed in this paper.To evaluate its potential in structural applications,the thermal insulation performances of the CLB walls and CLB walls with the EPS foam plate were studied and evaluated by the temperature-controlled box-heat flow meter method.Test results indicated that the thermal insulation performance improved with the increase of thickness,but different wall configurations had little effect on the thermal insulation performance under the same thickness of the CLB wall.The thermal insulation performance of EPS-CLB composite wall was much better than that of CLB wall.In addition,a relatively acceptable accuracy of the theoretical calculations was proved.Finally,the influence of different locations of the EPS foam plate on heat transfer coefficient can be neglected as it was studied based on the validated numerical models.展开更多
Heat transfer and energy performance of Al_(2)O_(3)/water nanofluid in a 90°bend with circular cross-section are investigated in the range of Reynolds number(Re)from 5000 to 30000,particle volume concentration(Φ...Heat transfer and energy performance of Al_(2)O_(3)/water nanofluid in a 90°bend with circular cross-section are investigated in the range of Reynolds number(Re)from 5000 to 30000,particle volume concentration(Φ)from 0.005%to 4%,Schmidt number(Sc)from 9870 to 296100,Dean number(De)from 6636 to 14847.The momentum and energy equations of nanofluid together with the dynamic equation for nanoparticles are solved numerically with the particle convection,diffusion,coagulation and breakage taken into consideration.Some results are validated by comparing with the available experimental or numerical results.The effect of Re,Φ,Sc and De on the friction factor and heat transfer of Al_(2)O_(3)/water nanofluidis discussed.The results showed that the particle number decreases along the pipeline.Increasing De,Sc leads to a decrease and increase ofΦ,respectively.The mean particle diameter and particle polydispersity increase with increasing Debut with decreasing Sc.The friction factor increases with increasingΦ,Sc De and Pr but with decreasing Sc.The ratio of energy performance evaluation criterion(PEC)for the Al_(2)O_(3)/water nanofluid to the base fluid increases with increasing Re,Φand De,but with decreasing Sc.Finally,the expression of ratio of energy PEC for the nanofluid to the base fluid as a function of Re,Φ,Sc and De is derived.展开更多
基金Supported by the National Natural Science Foundation of China(51606214)
文摘Stable TiO_2–water nanofluids are prepared by a two-step method, stabilities of nanofluids are investigated by precipitation method and transmittance method respectively, and thermal conductivities and viscosities are also measured. An experimental system for studying the heat transfer enhancement of nanofluids is established,and heat transfer and flow characteristics of TiO_2–water nanofluids in heat exchanger systems with a triangular tube and circular tube are experimentally studied. The effects of nanoparticle mass fractions(ω = 0.1 wt%–0.5 wt%) and Reynolds numbers(Re = 800–10000) on the heat transfer and flow performances of nanofluids are analyzed. Fitting formulas for Nusselt number and resistance coefficient of nanofluids in a triangular tube are put forward based on the experimental data. The comprehensive performances of nanofluids in a triangular tube are investigated. It is found that nanofluids in a triangular tube can significantly improve the heat transfer performance at the cost of a small increase in resistance coefficient compared with that in a circular tube, especially the resistance coefficients are almost the same between different nanoparticle mass fractions at turbulent flow. It is also found that the comprehensive evaluation index η decreases with Reynolds number at laminar flow but a critical maximum value appears at turbulent flow.
文摘Forced convection cooling of fins on a high-temperature wall has been used to cool high-power electronic devices. We numerically calculated and experimentally measured the forced convection heat transfer coefficient and pressure drop of a diamond-shaped fin-array with water flow in this study, which had been reported to have a self-induced flip-flop flow phenomenon. Although the flip-flop flow phenomenon occurred in calculations, it was not observed in experiments. The heat transfer and pressure drop of the diamond-shaped fin-array could be estimated with equations for turbulent flow in tubes.
文摘Recent and constant demands for greater power densities and smaller sizes of electronic systems have stimulated the growth of new designs of different passive heat transfer methods such as heat pipes. Particularly, OHPs （Oscillating Heat Pipes） are relatively novel devices, capable of removing high heat rates over long and short distances with not much temperature drop. This study concentrates on the design, building and assembling a test rig in order to analyse the flow pattern ofdeionised water through a 5 turns flat plate oscillating heat pipe under different heat inputs, which was made in the school of engineering and materials science of the Queen Mary University of London by two energy M.Sc. students. The filling ratio of the water is 40%. Furthermore an experimental study on the OHP thermal performance is carried out in order to examine the effects of different surface wet conditions： super hydrophilic, hydrophilic and cleaned brass. It is demonstrated the formation of liquid slugs and vapour plugs of the water along the channels. The experimental results showed that the hydrophilic surface tends to be more energy efficient. The heat transfer performance of the super-hydrophilic and hydrophilic is higher than brass by 5-12% and 15-20% respectively.
文摘Flow resistance and heat transfer coefficients of typical double wall laminated film cooling configuration within a turbine vane were experimentally studied.The specimen was in large scale,and made of transparent organic glass.Laminated configuration consisted of double wall laminates,pin-fins,staggered arrays of impingement and film holes.The number ratio of impingement holes,pin-fins and film holes was2∶1∶1.Five experiment vanes were installed in static cascade,and experiments were carried out under constant heat flux.Re of internal cooling air in the experiment was from 104 to 2×105,and Re of external fluid was from 105 to 3×105.The experiment results show that flow resistances of front channel and back channel of the vane are in the same level,and both of them decrease as Re of cooling air increases.Nuof front channel is slightly higher than that of back channel.Both of them increase as Re of cooling air increases.And experiment results were obtained from experiment vanes were compared with that obtained from laminated flat plates,and the tendency of the results agrees well.
基金supported by the National Natural Science Foundation of China(52276150).
文摘Channel structure has a significant effect on the heat transfer performance of PCHE.In this study,a set of rectangular straight channel PCHEs with different cross-section aspect ratios had been tested on S-CO_(2) heat transfer experimental platform,the effect of mass flow rate in both cold and heat sides,as well as the cross-section aspect ratio of the rectangular straight channel,on the heat transfer performance of PCHE was investigated.The results show that the comprehensive heat transfer performance of the rectangular cross-section is better than that of the semicircular cross-section;increasing the aspect ratio can improve the comprehensive heat transfer performance of PCHE,but the strengthening effect diminishes as the aspect ratio increases.Increasing the mass flow rate on both sides not only enhances the pre-cooler's cooling capacity and heat transfer,but also raises the pressure drop.In addition,an improved heat transfer correlation for rectangular cross-section PCHE was proposed,considering the effects of cross-sectional aspect ratio and pseudo-critical temperature is proposed in the range of Re from 3169 to 48474 and Pr from 0.98 to 12.5,the fited results better predict the local Nu and f magnitudes and trends in the pre-cooler under different cooling conditions,outperforming the simulated data and Gnielinski and Blasius correlation.
基金from the National Natural Research and Development Fund(9Z05000049D0)Integrated Key Precast Components and New Wood-bamboo Composite Structure(2017YFC0703502).
文摘In recent years,bamboo,as a green building material,has attracted more and more attention worldwide.Inspired by the investigation of cross-laminated timber in structural systems,a new engineered cross-laminated bamboo(CLB)consisting of the cross lamination of bamboo scrimber plates is proposed in this paper.To evaluate its potential in structural applications,the thermal insulation performances of the CLB walls and CLB walls with the EPS foam plate were studied and evaluated by the temperature-controlled box-heat flow meter method.Test results indicated that the thermal insulation performance improved with the increase of thickness,but different wall configurations had little effect on the thermal insulation performance under the same thickness of the CLB wall.The thermal insulation performance of EPS-CLB composite wall was much better than that of CLB wall.In addition,a relatively acceptable accuracy of the theoretical calculations was proved.Finally,the influence of different locations of the EPS foam plate on heat transfer coefficient can be neglected as it was studied based on the validated numerical models.
基金Projects supported by the National Natural Science Foundation of China(Grant No.91852102).
文摘Heat transfer and energy performance of Al_(2)O_(3)/water nanofluid in a 90°bend with circular cross-section are investigated in the range of Reynolds number(Re)from 5000 to 30000,particle volume concentration(Φ)from 0.005%to 4%,Schmidt number(Sc)from 9870 to 296100,Dean number(De)from 6636 to 14847.The momentum and energy equations of nanofluid together with the dynamic equation for nanoparticles are solved numerically with the particle convection,diffusion,coagulation and breakage taken into consideration.Some results are validated by comparing with the available experimental or numerical results.The effect of Re,Φ,Sc and De on the friction factor and heat transfer of Al_(2)O_(3)/water nanofluidis discussed.The results showed that the particle number decreases along the pipeline.Increasing De,Sc leads to a decrease and increase ofΦ,respectively.The mean particle diameter and particle polydispersity increase with increasing Debut with decreasing Sc.The friction factor increases with increasingΦ,Sc De and Pr but with decreasing Sc.The ratio of energy performance evaluation criterion(PEC)for the Al_(2)O_(3)/water nanofluid to the base fluid increases with increasing Re,Φand De,but with decreasing Sc.Finally,the expression of ratio of energy PEC for the nanofluid to the base fluid as a function of Re,Φ,Sc and De is derived.
