• Energy Research

The power generated from TEG is relatively unstable owing to temperature variations at its hot and cold side terminals. The dc-dc converters can provide more stable power output thereby improving the overall efficiency of TEG system. However, to facilitate better performance improvement, maximum power point tracking (MPPT) algorithm can be applied to extract maximum power from TEG system. Therefore, parameter analysis of a TEG/dc-dc converter system in different modes is being carried out. A TEG-dc-dc boost converter model is analysed in both MPPT and direct pulse width modulation (PWM) modes subjected to a variable load. To further study the capability of dc-dc converters to stabilise the TEG power output, increasing ramp and random hot side temperature is applied to the MPPT and direct PWM based modes so that the effect on output parameters i.e. voltage and power, can be analysed. It is noted that even for the random temperature input to the TEG, the output voltage resulting from the converter is almost constant. Therefore dc-dc converters are able to stabilise the power generated from TEG. It is also observed that dc-dc converter with MPPT based model is able to effectively extract the maximum power without having to adjust any component from the MPPT algorithm as it is the case with direct PWM based model. From the study, it has been established that proper selection of converter components is necessary to reduce converter losses as well interferences on the load connected to TEG-dc-dc converter system.

This paper suggests a type of quantitative research method with the application of Computational Fluid Dynamics (CFD) and EcoTect tools for a sustainable urban design project. This paper is part of a funded research study and was completed in 2010. This study is part of the larger project for planning and development of Cao Fei Dian eco-city development in North-Eastern China; one of the first eco-city development projects in the first batch of pilot eco-cities in China. The research programme addresses the main aspects of good practice in terms of eco-design and sustainability. These aspects include wind flow analysis around buildings, insolation analysis of open spaces, pollutant dispersion in water systems and noise control on urban highways. This study aims to explore a range of research methods in order to enhance the performance of integrated design with a comprehensive planning stage. The integration in evaluation across professions and subject boundaries is emphasised to identify the key gaps between sustainability and design. The main method of this study is the application of CFD and EcoTect tools for environmental performance of a larger urban area than the common use for architectural interventions or immediate outdoor spaces of a project. This study suggests an integrated urban design model with the application of computational tools (i.e. CFD and EcoTect in here) and how these could inform, from a technical dimension, a more comprehensive approach to executing best practice in design and planning. The paper concludes by suggesting an integrated model of urban design to achieve urban sustainability.

Abstract Thermal stress in IGBT power module can lead to sever thermal reliability problems such as module deformation, performance degradation and even permanent damage. So, it is important to develop innovative and efficient IGBT cooling technologies. In this paper, a novel thermal management system is developed for cooling IGBT power module. The module is integrated with a vapour chamber-based heat sink to reduce thermal resistance and improve temperature uniformity significantly. 3D FEM modelling is conducted to investigate the effect of vapour chamber on temperature distribution, thermal stress, energy strain dissipation density and lifetime under power cycle. The simulation results show that the proposed thermal management system is superior to traditional cooling solution regarding cooling capacity, thermal stress, creep and plastic strain energy dissipation and thermal fatigue life. The study of failure mechanism of solder layer under power cycling suggests that creep causes the main is damage in the power cycling and cracks induced by thermal loading can be expected to initiate at the edge.

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.

AbstractAn overview of current thermal challenges in transport electrification is introduced in order to underpin the research developments and trends of recent thermal management techniques. Currently, explorations of intelligent thermal management and control strategies prevail among car manufacturers in the context of climate change and global warming impacts. Therefore, major cutting-edge systematic approaches in electrified powertrain are summarized in the first place. In particular, the important role of heating, ventilation and air-condition system (HVAC) is emphasised. The trends in developing efficient HVAC system for future electrified powertrain are analysed. Then electric machine efficiency is under spotlight which could be improved by introducing new thermal management techniques and strengthening the efforts of driveline integrations. The demanded integration efforts are expected to provide better value per volume, or more power output/torque per unit with smaller form factor. Driven by demands, major thermal issues of high-power density machines are raised including the comprehensive understanding of thermal path, and multiphysics challenges are addressed whilst embedding power electronic semiconductors, non-isotropic electromagnetic materials and thermal insulation materials. Last but not least, the present review has listed several typical cooling techniques such as liquid cooling jacket, impingement/spray cooling and immersion cooling that could be applied to facilitate the development of integrated electric machine, and a mechanic-electric-thermal holistic approach is suggested at early design phase. Conclusively, a brief summary of the emerging new cooling techniques is presented and the keys to a successful integration are concluded.

Abstract In this work, a novel wickless heat pipe fabricated using the roll-bond process and called the roll-bond flat thermosyphon was proposed for electronic component cooling due to its slim and large-size configuration, low-cost, and mass-production capable. The thermal performance of roll-bond flat thermosyphon was investigated through the tests in terms of 3 typical structures (stagger, cross and align) and 4 filling ratios (5%, 10%, 20%, and 40%) under the increasing heat power, and evaluated with the effective thermal conductivity and the maximum heat transfer capacity. The phenomena of boiling regime evolution, geyser effect, liquid entrainment and dry-out, can be found through the temperature responses in the cases of progressive filling ratios and heating powers. The cross-structured sample was found to behave the worst among the three structures due to its blocked up-flowing inflated circuits. The highest effectivity thermal conductivity of 22404 (W/K·m) was found in the 5%-align sample, however, accompanied with early dry-out. The heat transfer capability is positive correlated to the filling ratio, and maximum heat transfer capacity of 100 W (heat flux of 14.9 (kW/m2)) was recorded in the stagger-40% sample. The 20%-stagger sample is recommended as the optimum design, due to its more stable and relative high thermal conductivity, which is peaked to 16019 (W/K·m), and averaged at 12616 (W/K·m) in the range of 0–90 W.

Abstract The performance of thermoelectric generation (TEG) systems is significantly dependent on the hot side temperature of thermoelectric legs and the temperature difference between the hot side and cold side of the legs. To keep the TEG module working at an optimal condition, a high heat flux over 10 W/cm2 through the TEG needs to be maintained. Due to the low heat transfer coefficient of the gas flow to the exhaust pipe wall surface, typically at a high temperature ranging from 400 °C to 800 °C, the actual heat flux into the TEG heat exchanger is limited significantly, resulting in relatively low efficiency of the TEG conversion. In the present study, an effective solution for enhancing the heat transfer of gas flow in the radial direction to the TEG is proposed by means of immersing high temperature heat pipes perpendicularly into the exhaust flow. Similarly, conventional heat pipes are radially inserted into a concentric coolant jacket in order to enhance heat transfer performance at the cold side of TEG modules. Overall, the TEG assembly is configured as a compact and scalable heat pipe heat exchanger. The simulation results show that the hot side temperature of the TEG can reach and be maintained as high as 300 °C while the cold side temperature of the TEG can be maintained at approximately 85 °C for a normal engine coolant loop. The results also show that the closer to the heat source in the pipeline the TEG system is located, the better the power generation that is expected. Moreover, better thermoelectric generation can be expected at a higher engine speed. By installing the TEG heat exchanger between catalytic converter and muffler, the best power output in the thermoelectric heat exchanger can be achieved at 450 W and 5000 rpm. If the TEG heat exchanger is adjacent to the outlet of a catalytic converter, the best-simulated performance at 6000 rpm is 705 W for a single sub pipeline. Therefore, a total power generation of 1410 W is achievable since the existing exhaust pipe is a dual pipeline system.