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This study investigates the thermal performance of composite ultra-thin heat pipes (UTHPs). UTHPs are fabricated by flattening cylindrical heat pipes with outer diameter of 2 mm. The thickness and width were 0.8 mm and 2.7 mm, respectively. The composite wick structure is made of sintered copper foam-mesh wick (CFMW). CFMW combines the good heat transfer performance of copper foam and the high mechanical strength of mesh. The manufacturing process of UTHP was studied and the thermal performance of UTHP samples were investigated experimentally. The results indicate that the optimum filling ratio of UTHPs is 100% and the maximum temperature difference is 3.7 °C under the maximum heat transport capacity of 5 W. The thermal resistances of UTHPs increase gradually with the heat power before drying out. Too low or too high filling ratios will reduce the heat transfer efficiency of UTHPs by increasing the thermal resistances. With the optimum filling ratio of 100%, the evaporation thermal resistance of UTHP is found to be 0.29 K/W and the condensation thermal resistance is 0.45 K/W at the heat load of 5 W.

This study investigates the thermal performance of composite ultra-thin heat pipes (UTHPs). UTHPs are fabricated by flattening cylindrical heat pipes with outer diameter of 2 mm. The thickness and width were 0.8 mm and 2.7 mm, respectively. The composite wick structure is made of sintered copper foam-mesh wick (CFMW). CFMW combines the good heat transfer performance of copper foam and the high mechanical strength of mesh. The manufacturing process of UTHP was studied and the thermal performance of UTHP samples were investigated experimentally. The results indicate that the optimum filling ratio of UTHPs is 100% and the maximum temperature difference is 3.7 °C under the maximum heat transport capacity of 5 W. The thermal resistances of UTHPs increase gradually with the heat power before drying out. Too low or too high filling ratios will reduce the heat transfer efficiency of UTHPs by increasing the thermal resistances. With the optimum filling ratio of 100%, the evaporation thermal resistance of UTHP is found to be 0.29 K/W and the condensation thermal resistance is 0.45 K/W at the heat load of 5 W.

This study proposes three composite wick structures (copper power or mesh sintered on grooved tube), namely, single arch-shaped sintered–grooved wick (SSGW), bilateral arch-shaped sintered–grooved wick (BSGW), and mesh–grooved wick (MGW), to improve the thermal performance of ultra-thin heat pipes (UTHPs). Phase-change flattening technology is employed to fabricate UTHPs. The morphologies of the wick structures after flattening are observed. An experimental apparatus is setup to investigate the thermal performance of UTHP samples under incremental heat loads. The heat transfer limits of UTHP are theoretically and experimentally analyzed. Capillary limit is found to be the main heat transfer limit, and the theoretical values of the samples with SSGW and BSGW are in good agreement with the experimental results. Results indicate that the maximum heat transport capacities are 12 W, 13 W and 14 W, under the corresponding optimum filling ratios of 70%, 70%, and 80%, for the SSGW, BSGW and MGW UTHPs, respectively. Evaporation and condensation thermal resistances of UTHP samples increase with the increase in the filling ratio before the occurrence of dry-out. UTHPs with SSGW have the least evaporation thermal resistance whereas UTHPs with MGW have the least condensation thermal resistance.

This study proposes three composite wick structures (copper power or mesh sintered on grooved tube), namely, single arch-shaped sintered–grooved wick (SSGW), bilateral arch-shaped sintered–grooved wick (BSGW), and mesh–grooved wick (MGW), to improve the thermal performance of ultra-thin heat pipes (UTHPs). Phase-change flattening technology is employed to fabricate UTHPs. The morphologies of the wick structures after flattening are observed. An experimental apparatus is setup to investigate the thermal performance of UTHP samples under incremental heat loads. The heat transfer limits of UTHP are theoretically and experimentally analyzed. Capillary limit is found to be the main heat transfer limit, and the theoretical values of the samples with SSGW and BSGW are in good agreement with the experimental results. Results indicate that the maximum heat transport capacities are 12 W, 13 W and 14 W, under the corresponding optimum filling ratios of 70%, 70%, and 80%, for the SSGW, BSGW and MGW UTHPs, respectively. Evaporation and condensation thermal resistances of UTHP samples increase with the increase in the filling ratio before the occurrence of dry-out. UTHPs with SSGW have the least evaporation thermal resistance whereas UTHPs with MGW have the least condensation thermal resistance.

This paper presents the novel designs of a concentric cylindrical thermoelectric generator (CCTEG) and an annular thermoelectric module (ATEM). The simulations are carried out to compare the performance of ATEM and the conventional square-shaped thermoelectric module (STEM). The heat pipe technology is introduced into the heat sink system in order to enhance the heat transfer in the radial direction of exhaust gas flow. A new index termed as the heat transfer filling factor ff has been introduced which quantities the level of space utilisation for thermoelectric modules (TEMs). The correlation between the coolant flow rate and TEM performance is also carried out. Experimental work is also carried out to demonstrate the viability of using the heat pipes for heat transfer enhancement as well proving the viability of the design. The simulations indicate that the open circuit electric potential of the ATEM is 17% more than that of the STEM. The experimental results show that the CCTEG system performs well under various conditions. This results also demonstrate that the concept of adding heat pipes to the heat sink system is a practical solution to achieve higher thermoelectric generator (TEG) performance while maintaining the compactness of the TEG system. A heat transfer filling factor of 0.655 is achieved for the CCTEG system which is higher compared to the existing TEG systems. Moreover, a higher coolant flow rate contributes to obtaining a better performance of the TEG system. It is important to note that the introduced index can give guidance for further optimisation design of TEG systems.

This paper presents the novel designs of a concentric cylindrical thermoelectric generator (CCTEG) and an annular thermoelectric module (ATEM). The simulations are carried out to compare the performance of ATEM and the conventional square-shaped thermoelectric module (STEM). The heat pipe technology is introduced into the heat sink system in order to enhance the heat transfer in the radial direction of exhaust gas flow. A new index termed as the heat transfer filling factor ff has been introduced which quantities the level of space utilisation for thermoelectric modules (TEMs). The correlation between the coolant flow rate and TEM performance is also carried out. Experimental work is also carried out to demonstrate the viability of using the heat pipes for heat transfer enhancement as well proving the viability of the design. The simulations indicate that the open circuit electric potential of the ATEM is 17% more than that of the STEM. The experimental results show that the CCTEG system performs well under various conditions. This results also demonstrate that the concept of adding heat pipes to the heat sink system is a practical solution to achieve higher thermoelectric generator (TEG) performance while maintaining the compactness of the TEG system. A heat transfer filling factor of 0.655 is achieved for the CCTEG system which is higher compared to the existing TEG systems. Moreover, a higher coolant flow rate contributes to obtaining a better performance of the TEG system. It is important to note that the introduced index can give guidance for further optimisation design of TEG systems.

Transport represents over a quarter of Europe's greenhouse gas emissions and is the leading cause of air pollution in cities. It has not seen the same gradual decline in emissions as other sectors. Recently, the thermoelectric power generation (TEG) technology emerges as an alternative solution to the emission reduction challenge in this area. In this paper, we present an innovative pathway to an improved heat supply into the concentric shape-adapted TEG modules, integrating the heat pipe technologies. It relies on a phase changing approach which enhances the heat flux through the TEG surface. In order to improve the heat transfer for higher efficiency, in our work, the heat pipes are configured in the radial direction of the exhaust streams. The analysis shows that the power output is adequate for the limited space under the chassis of the passenger car. Much effort can also be applied to obtain enhanced convective heat transfer by adjusting the heat pipes at the dual sides of the concentric TEG modules. Heat enhancement at the hot side of the TEG has an effective impact on the total power out of the TEG modules. However, such improvements can be offset by the adjustment made from the coolant side. Predictably, the whole temperature profile of TEG system is subject to the durability and operational limitations of each component. Furthermore, the results highlight the importance of heat transfer versus the TEG power generation under two possible configurations in the passenger car. The highest power output per repeat unit is achieved at 29.8 W per 0.45 L with a ZT value 0.87 for a Bi2Te3-based thermoelectric material in our studies. The study provides an insight into a structurally achievable heat exchanger system for other high-temperature thermoelectric materials.

Transport represents over a quarter of Europe's greenhouse gas emissions and is the leading cause of air pollution in cities. It has not seen the same gradual decline in emissions as other sectors. Recently, the thermoelectric power generation (TEG) technology emerges as an alternative solution to the emission reduction challenge in this area. In this paper, we present an innovative pathway to an improved heat supply into the concentric shape-adapted TEG modules, integrating the heat pipe technologies. It relies on a phase changing approach which enhances the heat flux through the TEG surface. In order to improve the heat transfer for higher efficiency, in our work, the heat pipes are configured in the radial direction of the exhaust streams. The analysis shows that the power output is adequate for the limited space under the chassis of the passenger car. Much effort can also be applied to obtain enhanced convective heat transfer by adjusting the heat pipes at the dual sides of the concentric TEG modules. Heat enhancement at the hot side of the TEG has an effective impact on the total power out of the TEG modules. However, such improvements can be offset by the adjustment made from the coolant side. Predictably, the whole temperature profile of TEG system is subject to the durability and operational limitations of each component. Furthermore, the results highlight the importance of heat transfer versus the TEG power generation under two possible configurations in the passenger car. The highest power output per repeat unit is achieved at 29.8 W per 0.45 L with a ZT value 0.87 for a Bi2Te3-based thermoelectric material in our studies. The study provides an insight into a structurally achievable heat exchanger system for other high-temperature thermoelectric materials.