空气横掠矩形翅片椭圆管束换热规律的数值研究

采用Fluent软件对矩形翅片椭圆管束空气侧的对流换热情况进行了三维数值模拟，获得了不同流速下翅片表面温度分布，分析了迎面风速与换热系数之间的关系，随着速度的增大，空气侧的换热系数增加，并拟合了换热计算公式。同时分析了不同翅片间距对换热的影响因素，随着翅片间距的增大，空气侧换热系数增加，而且随着Rg数的增加，换热的强化更加明显。     

超临界CO2布雷顿循环中冷却器的夹点分析

针对超临界CO_2布雷顿循环中冷却器的夹点问题,采用传热单元模型,对夹点产生条件和影响因素进行了理论研究和计算分析。结果表明:冷却器内超临界CO_2的参数接近临界参数,产生夹点的可能性大;夹点的主要影响因素是超临界CO_2与水的流量比,随着流量比的增大,夹点温差逐渐减小;夹点温差对冷却器的换热面积和压降具有直接影响,随着夹点温差的增大,换热面积逐渐减小、压降逐渐增大;当夹点温差由2.9℃增大至4.4℃时,冷却器的换热面积减小了50%,但压降增大了约150%。     

翅片形式对强化换热影响的研究及其效应评价

本文就翅片形式对换热特履和流动特性的影响进行了实验研究，并综合上述两方面影响，以热力系统Ｙｏｎ分析为基础，对不同形式的翅片强化换热的效果进行了评价。     

车载板翅式油冷却器的实验研究

某型车载板翅式油冷却器采用锯齿翅片强化油侧传热。利用风洞实验台对该油冷却器进行实验,测试其不同空气和油流量条件下的传热和流阻性能,并拟合了传热性能经验关联式。采用对数平均温差法建立油冷却器性能模型,以分析其空气侧部分遮挡工况下的实际性能。为提高油冷却器性能模型预测精度,借助FLUENT模拟得到了其锯齿翅片传热和流阻的特性数据。研究表明,正常工况下,油冷却器基于油侧表面积的总传热系数为49～74 W/(m2·℃),空气侧遮挡将显著降低油冷却器传热性能。     

高温温差发电装置集热器结构数值仿真研究

设计了一种针对高温烟气的圆筒式温差发电装置,在装置中设置分流桶增强烟气侧的换热效果。利用Ansys Fluent软件对装置的温度场、速度场及排气压降进行仿真模拟,分析了不同分流桶的桶直径、端盖孔直径和分流孔直径对热电模块冷热端温度分布的影响。仿真结果表明：温差发电系统集热器通道中设置分流桶可以实现高效温差发电,分流桶端盖未开孔时装置的换热效果优于端盖开孔结构;适当减小分流孔直径或增大分流桶直径会提升热电模块的冷热端温差,分流孔直径为2 mm时的换热效果最优,分流桶直径过大会使热电模块温度分布及温差的均匀性降低;系统烟气压降会随着分流孔直径的增大或分流桶直径的减小而降低。     

换热网络优化的研究进展

换热流程中换热器、加热器、冷却器、混合器和分流器等组合构成换热网络。国内外对如何优化换热网络已有大量研究,提出了不同的优化方法。本文介绍夹点设计法、双最小换热温差法、人工智能法、神经网络模型法、遗传算法等具有代表性的研究进展情况。     

光伏背板翅片散热器自然对流特性分析

聚光光伏等的快速发展都会面临散热问题,本文对翅片散热装置的散热特性作了相关分析。基于Fluent数值模拟软件,对矩形片状翅片散热器在定温加热、自然对流条件下的温度分布和速度分布进行了模拟;在温差50℃≥ΔT≥100℃、翅片高度140 mm≥H≥60 mm、翅片间距14 mm≥S≥6 mm范围内对翅片尺寸优化,得出翅片表面平均对流换热系数的变化趋势。结果表明,50~100℃内温差越大,对流换热系数越大;H取100 mm时,散热量最大,较H=80 mm时提高了32.15%;S取12 mm时散热量最大,较S=10 mm时提高了27.44%。     

汽轮发电机气体冷却器性能试验研究

气体冷却器是汽轮发电机的重要设备之一。其传热与阻力性能将直接影响汽轮发电机的运行经济性和可靠性。为实现汽轮发电机气体冷却器的优化设计,对不同翅片间距的翅片管冷却器的传热和阻力性能进行了试验研究,得到了Re在3 000~190 000之间换热器翅片侧的传热和阻力特性,并分析了风速和翅片间距对气体冷却器传热和阻力性能的影响规律。研究成果对汽轮发电机气体冷却器的结构与性能优化具有重要的指导作用。     

海洋温差发电系统热力学及热经济性分析

以热力学基本原理为基础,建立了海洋温差发电系统仿真模型,对比分析了亚临界状态下R717、R134a和R600三种工质系统在约束蒸发器窄点温差条件下优化目标函数随蒸发温度的变化规律。结果表明:蒸发温度越高,不同系统换热器的热负荷以及冷、热海水泵功率越小,最佳蒸发压力和工质泵功率越大;不同系统的热效率和单位换热面积输出电量与蒸发温度的相关性较大,随蒸发温度的增加近似线性递增。蒸发器的换热面积与循环工质种类的相关性较小,但冷凝器的换热面积与循环工质种类的相关性较大。R717循环更接近于卡诺循环,R717的系统热效率最大,热负荷及泵功率最小,且其热经济性目标函数值在合适的范围内,是海洋温差发电系统较为理想的循环工质。研究结果可为海洋温差发电系统的设计、试验及设备选型提供理论参考。     

小管径穿片式翅片管三种间距下的换热与阻力特性

对3种基管外径(10 mm)和管间距相同、翅片间距不同的穿片式空气-水换热器的换热与阻力特性进行了试验研究,翅片间距分别为1.0、1.6、1.9 mm.得出了不同翅片间距下的管外换热系数和流动阻力系数以及相应的计算关联式,利用评价指标对3种试件的综合换热性能进行了评价.结果表明:翅片间距对管外换热性能的影响很大;在选择具有合理翅化比的换热器的翅片间距时还需考虑经济性和紧凑度等方面的因素.     

Development of an energy-saving module via combination of solar cells and thermoelectric coolers for green building applications

A solar-driven thermoelectric cooling module with a waste heat regeneration unit designed for green building applications is investigated in this paper. The waste heat regeneration unit consisting of two parallel copper plates and a water channel with staggered fins is installed between the solar cells and the thermoelectric cooler. The useless solar energy from the solar cells and the heat dissipated from the thermoelectric cooler can both be removed by the cooling water such that the performance of the cooling module is elevated. Moreover, it makes engineering sense to take advantage of the hot water produced by the waste heat regeneration unit during the daytime. Experiments are conducted to investigate the cooling efficiency of the module. Results show that the performance of the combined module is increased by increasing the flow rate of the cooling water flowing into the heat regeneration water channel due to the reductions of the solar cell temperature and the hot side temperature of the thermoelectric coolers. The combined module is tested in the applications in a model house. It is found that the present approach is able to produce a 16.2 °C temperature difference between the ambient temperature and the air temperature in the model house.     

Examination of the Cooling Performance of a Two-Stage Thermoelectric Cooler Considering the Thomson Effect

The cooling performance of two-stage thermoelectric coolers test modules for different types (serial, parallel, and separate) are examined in this study. Thomson heat is taken into account in order to discuss its effect on temperature prediction and the internal heat transfer mechanism. Three different Seebeck coefficient models (constant Seebeck model, quadratic polynomial Seebeck model, and log-linear Seebeck model) are examined through experimental investigation and numerical simulation for suitability and accuracy. Results show that the best Seebeck coefficient model is the quadratic polynomial Seebeck model (PSM). Thomson heat can enhance the cooling performance of thermoelectric cooler under specific conditions.     

A novel thermoelectric refrigeration system employing heat pipes and a phase change material: an experimental investigation

This paper presents results of tests carried out to investigate the potential application of heat pipes and phase change materials for thermoelectric refrigeration. The work involved the design and construction of a thermoelectric refrigeration prototype. The performance of the thermoelectric refrigeration system was investigated for two different configurations. The first configuration employed a conventional heat sink system (bonded fin heat sink) on the cold side of the thermoelectric cells. The other configuration used an encapsulated phase change material in place of the conventional heat sink unit. Both configurations used heat pipe embedded fins as the heat sink on the hot side. Replacement of the conventional heat sink system with an encapsulated phase change material was found to improve the performance of the thermoelectric refrigeration system. In addition, it provided a storage capability that would be particularly useful for handling peak loads and overcoming losses during door openings and power-off periods. Results showed that the heat sink units employing heat pipe embedded fins were well suited to this application. Results also showed the importance of using a heat pipe system between the cold junction of the thermoelectric cells and the cold heat sink in order to prevent reverse heat flow in the event of power failure.     

Multi‐objective genetic algorithm optimization of thermoelectric heat exchanger for waste heat recovery

A model is developed to simulate a cross‐flow heat exchanger, including fins, in the wall of which thermoelectric generators are sandwiched. Such a system could be used for waste heat recovery. The model is used to optimize the device based on several objective functions: total volume, total number of thermoelectric modules, power output, and pumping power. The design variables are the local distribution of modules and of current, the shape of the fins, and the division of the heat exchanger in sub‐channels. Pareto fronts are achieved with a multi‐objective genetic algorithm, and are presented here. The results show that the number of sub‐channels in the heat exchanger has a larger impact on the overall performance than the fin geometry for this particular problem. Also, the net power output is mostly correlated to the number of thermoelectric modules, and less to the heat exchanger volume. Various relations between the different competing objectives are shown and analyzed. Copyright © 2011 John Wiley & Sons, Ltd.     

Numerical investigation of thermal and electrical management during hydrogen reversible solid-state storage using a novel heat exchanger based on thermoelectric modules

In order to reduce the costs generated by the hydrogen solid storage tank's accessories such as the heat exchanger, this work was carried out. It shows thermal and electrical investigations of transient hydrogen (H₂) solid storage in a tank filled with porous medium (LaNi₅) to activate a potential PEM automotive fuel cell. For this purpose, we use a novel heat exchanger with a heat sink combined with thermoelectric modules (TEMs). We realize a simulation that helps us verify if thermoelectric exchanger will be an alternative to the conventional ones. The main results are that a thermoelectric cooler and heater with 127 couples of semiconductors coupled with 19 fins heat sink could be used during the reversible hydrogen solid storage. Also, results show that we can avoid the water freezing at negative temperatures when using a conventional heat exchanger by using TEM during hydrogen absorption. Finally, during the endothermic desorption of the hydrogen, TEG use can avoid boiling water used in the heating system. Also, the hydrogen tank will be lighter and compact without fins and water tubes.     

Integrating high-temperature proton exchange membrane fuel cell with duplex thermoelectric cooler for electricity and cooling cogeneration

To harvest the waste heat from exothermic reaction processes, a novel hybrid system model mainly incorporating a high-temperature proton exchange membrane fuel cell (HT-PEMFC) and a duplex thermoelectric cooler is conceptualized to theoretically predict the potential performance limit. The duplex thermoelectric cooler is composed of a thermoelectric generator (TEG) and a thermoelectric cooler (TEC), where the TEG harvests the waste heat to generate electricity and the TEC utilizes the generated electricity for cooling production. A mathematical model is established to estimate the proposed system performance from both exergetic and energetic perspectives considering various irreversible effects, from which effectiveness and practicality of the proposed system can be examined. The hybrid system maximal output power density allows 14.1% greater than that of the basic HT-PEMFC, whereas the according destruction rate density of exergy is decreased by 7.7%. The feasibility and effectiveness of the proposed system configuration are verified. Moreover, substantial parametric analyses indicate that the proposed system performance can be improved by elevating the HT-PEMFC operating temperature, inlet relative humidity and doping level while worsened by enhancing the leak current density, electrolyte thickness and Thomson coefficient. The results acquired may be helpful in designing and optimizing such an actual hybrid system.     

Exergy analysis of single‐stage and multi stage thermoelectric cooler

Thermoelectric devices are solid‐state devices. Semiconductor thermoelectric cooling, based on the Peltier effect, has interesting capabilities compared to conventional cooling systems. In this work second law analysis of thermoelectric coolers has been done with the help of exergy destruction. In the first part, performance of single‐stage thermoelectric coolers and multi stage thermoelectric coolers has been compared for same number of thermoelectric elements i.e. 50. The performance parameters considered to compare their performance are rate of refrigeration, coefficient of performance, second law efficiency and exergy destruction. In second part, multi stage thermoelectric coolers have been analyzed for three different combinations of number of elements in two stages of thermoelectric coolers. The result of the analysis shows that the performance of a multi stage thermoelectric cooler which has total 50 elements gives best performance when it has 30 elements in hotter side and 20 elements in colder side out of the three cases considered. The comparison of single‐stage thermoelectric cooler and multistage thermoelectric cooler shows that for same number of elements rate of refrigeration (ROR) of single‐stage thermoelectric cooler is much higher than that of multi stage thermoelectric cooler. The COP remains same for both of them but the peak value of cop is obtained at much lower value of current supplied in multi stage thermoelectric cooler. Exergy destruction has constant values in single stage as well as multi stage thermoelectric cooler when the two stages have equal number of elements but it decreases with increase in x. The result of comparison of multistage thermoelectric cooler for three values of x i.e. 0.5, 1, 1.5 shows that the COP, ROR and second law efficiency improve and exergy destruction degrades with increase in x and the best performance has been obtained for x = 1.5 out of the three values considered. Copyright © 2013 John Wiley & Sons, Ltd.     

Design Optimization of a New Hot Heat Sink with a Rectangular Fin Array for Thermoelectric Dehumidifiers

The objective of this research was aimed at conducting an experimental investigation to study the heat sink performance of a new rectangular fins array. Various operating conditions were considered, namely the distance between the fan and the fins, varied from 0 mm to 40 mm, heat supplied to the sink and the fan voltage. It was concluded that a fan installed at 30 mm height from the fins is recommended as the hot side temperature was the lowest. Next a pre-experimentation of small scale prototype of thermoelectric Dehumidifier (TED) was designed and constructed. It was composed of two thermoelectric (TE) cooling modules, MT2-1, 6-127, (two in serial) mounted between the rectangular fin heat exchangers with dimension 140 × 240 × 35 mm. The hot side was cooled by a ventilation fan whereas the air flow on the cold side was free convection. The effect of position of fan was investigation experimentally. Preliminary tests confirmed the good performance of the hot heat sink design for the intended thermoelectric application.     

Thermoelectric water-cooling device applied to electronic equipment

This article investigates the thermal performance of a thermoelectric water-cooling device for electronic equipment. The influences of heat load and the thermoelectric cooler's current on the cooling performance of the thermoelectric device are experimentally and theoretically determined. This study develops a novel analytical model of thermal analogy network to predict the thermal capability of the thermoelectric device. The model's prediction agrees well with the experimental data. The experimental result shows that when heat load increases from 20 W to 100 W, the lowest overall thermal indicator increases from − 0.75 KW^− 1 to 0.62 KW^− 1 at the optimal electric current of 7 A. Besides, this study verifies that the thermal performance of the conventional water-cooling device can be effectively enhanced by integrating it with the thermoelectric cooler when the heat load is below 57 W.     

Analysis on the cooling performance of the thermoelectric micro-cooler

Numerical analysis has been carried out to figure out the performance of the thermoelectric micro-cooler with the three-dimensional model. A small-size and column-type thermoelectric cooler is considered and Bi₂Te₃ and Sb₂Te₃ are selected as the n- and p-type thermoelectric materials, respectively. The thickness of a thermoelectric element considered is 5–20 μm. The effect of parameters such as the temperature difference, the current, the thickness of a thermoelectric element, and the number of thermoelectric pairs on the performance of the cooler has been investigated. The predicted results show that the performance can be improved for the thick element with the large number of thermoelectric pairs or the small cross-sectional area of the element.