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Applied thermal engineering
Elservier Science Ltd.
Applied thermal engineering

Elservier Science Ltd.

1359-4311

Applied thermal engineering/Journal Applied thermal engineeringISTPSCIEI
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    Flexible Bi2Te3-based thermoelectric generator with an ultra-high power density

    You, HanLi, ZhenmingShao, YuyingYuan, Xiong...
    6页
    查看更多>>摘要：Environmental energy harvesting based on flexible thermoelectric generator (f-TEG) provides an ideal micro-power source to drive the node sensors for the Internet of Things (IoT) and wearable electronics. However, the existing flexible thermoelectric devices have some disadvantages, such as low strength, large thermal resistance, complex manufacturing processes, and low reliability. Here, we report a high-performance f-TEG with a dimension of 2 x 16 x 0.6 mm(3), encapsulating 18 pairs of thermoelectric legs with the size of 0.38 x 0.38 x 0.38 mm(3). The flexible polyimide (PI) films with patterned electrodes act as the substrates, of which the upper one is cut into blocks to ensure the generator a minimum bending radius of 4.5 mm. The f-TEG can produce an open circuit voltage of 236 mV and output power of 4.19 mW under a temperature difference of 50 K, which remain almost unchanged even after 7400 times of bending tests. The power density reaches up to 13.1 mW/cm(2) at Delta T = 50 K, and the normalized output power density is 5.26 mu W/cm(2).K-2. These results are among the best performances reported for TEGs, which opens a new avenue for flexible micro-power system design and promotes the development of the next generation self-powered sensors and charge-free electronic devices.
      原文链接:
    • NSTL
    • Elsevier

    Evaluation of trans-critical transition of single- and multi-component sprays under diesel engine-like conditions

    Fu, YunpengYi, PingLi, TieChen, Run...
    15页
    查看更多>>摘要：The trans-critical transition of multi-component sprays under the ECN Spray-A conditions has attracted extensive interest. However, the drastic change of critical points of multi-components makes this controversial. In this study, the trans-critical transition of sprays before and after the end of injection is evaluated by numerical methods, and new findings have been obtained. First, the robust and accurate thermodynamic equilibrium solver and multi-component droplet evaporation model were developed and implemented into the OpenFOAM. These models have been validated against the measured phase change diagram and isolated droplet evaporation rate. Then, the mixture critical temperatures of n-dodecane/nitrogen and multi-component diesel/nitrogen were calculated under a wide range of pressures based on the thermodynamic equilibrium solver. The mixture critical temperature decreases almost linearly with the increase of the pressure. Following that, extensive sprays of ndodecane and multi-component diesel under high temperature and pressure conditions were simulated, and the predicted spray liquid penetrations were validated against the experimental data. The results found that the dilute sprays after the end of injection are more prone to transition to the supercritical mixing regime, while the trans-critical possibility of dense sprays before the end of spray decreases due to the cooling effect of extensive evaporation. Finally, the trans-critical transitions of multi-component diesel sprays before and after the end of injection were evaluated and compared with those of n-dodecane sprays. Due to the low mixture critical temperature and evaporation rate of diesel, its sprays are more likely to transition to the supercritical regime. Therefore, it can conclude that the dilute sprays after the end of injection cannot represent the thermodynamic state of dense sprays. Moreover, the multi-component diesel and n-dodecane sprays follow a different transcritical transition pathway.
      原文链接:
    • NSTL
    • Elsevier

    Comparisons of blade tip phantom cooling effectiveness for two tip structures with three tip clearances

    Li, FengWang, HaifengLiu, ZhaoFeng, Zhenping...
    14页
    查看更多>>摘要：The blade tip region of the gas turbine is exposed to an extreme operating condition with a high heat load. The conventional cooling concept that places cooling holes on the tip would consume a lot of cooling air and lead to a reduction in thermal efficiency. Whereas phantom cooling was supposed to help cool the tip region without using additional cooling air. In this paper, computational comparisons were conducted to forecast the tip phantom cooling effects caused by the blade ejections by employing the standard k-omega model. Then, phantom cooling performance was presented under the flat tip (FT) and the squealer tip (ST), with three tip clearances. Results show that the FT shows a better phantom cooling performance compared to the ST. The phantom cooling effects on the FT are distributed at the tip forepart and near the pressure side (PS). Whereas, for the ST, traces of phantom cooling are barely detected on the PS rim. Increasing the tip clearance would weaken the phantom cooling performance on the FT forepart but enhance it on the rear part. For the ST, its phantom cooling effectiveness values decrease as the tip clearance increases. A lower aerodynamic loss is obtained for the ST under any coolant MFR or tip clearance.
      原文链接:
    • NSTL
    • Elsevier

    Thermal runaway evaluation and thermal performance enhancement of a lithium-ion battery coupling cooling system and battery sub-models

    Garcia, AntonioMonsalve-Serrano, JavierSari, Rafael LagoMartinez-Boggio, Santiago...
    23页
    查看更多>>摘要：This paper presents a novel simulation approach consisting of coupling fundamental and applicate aspects of Lithium-Ion battery simulations. A battery module representative of a complete battery pack is built using GT-AutoLion, consisting of a detailed electrochemical model and detailed cooling system modelled using the finite elements approach. The results show fresh and aged cylindrical cells submitted to different battery cooling flows. The cells are charged and discharged in high C(rates )to observe the performance of the proposed system in critical conditions. In addition, a battery thermal runaway code in Python is coupled to simulate the decomposition of the main components of the battery cell and their associated heat release during the battery operation. The concentration of the main species is tracked as well as the battery cells temperature distribution. The aged cells shown more probabilities of thermal runaway due to the increase of the internal resistance. However, it is possible to reduce the difference by increasing the cooling flow from 3 g/s to 50 g/s. When analysing the thermal runaway induced by a failure of a cell, the comparison shows that the mechanisms found in the bibliography shows a difference of 40 s in predicting the peak of heat release rate. Overall, the proposed framework confirms its capability of addressing the relevant phenomena during the battery operation, providing a way of improving the design phase from the battery cell to the battery pack.
      原文链接:
    • NSTL
    • Elsevier

    Experimental study on heat transfer enhancement using combined surface roughening and macro-structures in a confined double-nozzle spray cooling system

    Liu, PengfeiKandasamy, RanjithHo, Jin YaoXie, Jinlong...
    15页
    查看更多>>摘要：An experimental study is conducted to characterize the effects of surface roughness and the combined effects of surface roughening and macro-structure topology on the spray cooling heat transfer. It was found that the spray cooling thermal performances increase as the surface roughness increases. From the experimental results, a power law relationship is established between the heat flux and the magnitude of normalized roughness. On this basis, an empirical correlation is developed for spray cooling heat transfer on structured flat surfaces with varying roughness. The correlation is found to have an accuracy of 15%. In addition, the experimental results on the straight finned surfaces are compared with a region-based model with the surface roughness effect incorporated in the developed empirical correlation. The analysis reveals a decoupling relationship between the micro-roughness and macro-structure enhancing mechanisms. Furthermore, a decoupling analysis suggests that the micro-roughness enhancement and the macro-structure enhancement dominate the 0.5 mm pin finned surface and the 1.0 mm pin finned surface, respectively. However, the two types of enhancing mechanisms have a comparable contribution to spray cooling heat transfer enhancement on the straight finned surfaces. In general, spray cooling heat transfer can be enhanced by around 116% by increasing surface micro-roughness whereas heat transfer enhancement can reach as high as 136% and 288% on the surfaces with macro straight fin and pin fin structures containing micro-roughness, respectively.
      原文链接:
    • NSTL
    • Elsevier

    Approach to enhance the heat transfer of valve seats through thermal analysis

    Hassan, Mohamad Aniq Syazwan MohamedRazlan, Zuradzman MohamadAbu Bakar, ShahrimanRojan, Mohd Afendi...
    19页
    查看更多>>摘要：The valve seat insert is a component of the engine cylinder head, whose primary function is to seal the combustion chamber and absorb the valve's heat, releasing it to the engine cylinder head. The valves experience high temperatures owing to high thermal loading and low heat absorption in the valve seat, which can potentially damage the engine. Therefore, the thermal characteristics of the valve seat must be optimised to increase the heat transmission between the valve and its seat. Here, three copper alloy valve seats, brass, beryllium copper, and bronze copper, were tested against the existing sintered iron valve seat, and their temperature maps were determined using actual engine operation conditions. The instantaneous heat transfer coefficients of the valves, seats, and engine cylinder head during the four-stroke cycle were evaluated using a one-dimensional thermal simulation analysis. The values obtained were used to assess the finite-element model using a three-dimensional thermal simulation in the Ansys software. The results show that the brass, beryllium-, and bronze-copper valve seats increased the overall heat flux by 4.46%, 4.16%, and 2.06%, respectively, compared to those for sintered iron. Thus, the results are essential to improve the thermal characteristics of the copper alloy valve seat imposed on the cylinder head. For validation, an experimental engine thermal survey and uncertainty magnification factors were used to validate the model. The results indicate that the maximum difference between the simulation and experimental values is 8.42%. Therefore, this approach offers a direct and comprehensible application for evaluating the temperature distribution, heat gradient, and heat flux of the cylinder head of air-cooled sparkignition moped motorcycle engines using copper alloy valve seat materials at intermediate engine speeds. Furthermore, this method is applicable as a platform for the automotive industry to improve the heat transfer of the structural parts of internal combustion engines.
      原文链接:
    • NSTL
    • Elsevier