Geometric optimization of trapezoidal thermoelectric heat pump considering contact resistances through genetic algorithm

An alternate option for improving the performance of the thermoelectric heat pump (TEHP) is the variation in thermoelectric leg configuration. In this paper, the thermodynamic model based on first and second law of thermodynamics for an exoreversible TEHP including influence of Thomson effect as well as leg geometry on the coefficient of performance and heating load of the device has been developed and optimized. Modified expressions have been derived analytically for dimensionless heating load, irreversibilities, figure of merit, energy, and exergy efficiency. The effects of operating and geometry parameters such as shape parameter (A_c/A_h), temperature ratio (T_c/T_h), Thomson effect, thermal and electrical contact resistances on the coefficient of performance, and heating load of the TEHP have been analysed. The results indicate that the Thomson effect has adverse effect on heating load of the system. The optimal parameters obtained through GA optimization process have been compared with the optimal parameters obtained through analytical method which proved the validity of GA optimization method for optimization of TEHP. After the testing, the GA optimization has been performed to determine the optimum parameters corresponding to maximum energy efficiency and maximum heating load. It was found that the GA population converges quickly after 20 runs only which proved the GA as time and cost‐effective optimization tool. This study will be useful for designing of practical TEHP systems of different leg geometries.     

Maximum profit performance of a three‐heat‐reservoir heat pump

The operation of a three‐heat‐reservoir heat pump is viewed as a production process with exergy as its output. The relations between the optimal profit and COP (coefficient of performance), and the COP bound at the maximum profit of the heat pump are derived based on a general heat transfer law. The results provide a theoretical basis for developing and utilizing a variety of heat pumps. The focus of this paper is to search the compromised optimization between economics (profit) and the utilization factor (COP) for finite‐time endoreversible thermodynamic cycles. Copyright © 1999 John Wiley & Sons, Ltd.     

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.     

The influence of the Thomson effect on the performance of a thermoelectric cooler

The temperature distribution of a thermoelectric cooler under the influence of the Thomson effect, the Joule heating, the Fourier’s heat conduction, and the radiation and convection heat transfer is derived. The influence of the Thomson effect on the temperature profiles, on the fraction of the Joule’s heat that flows back to the low-temperature side, and consequently on the maximum attainable temperature difference and the maximum allowable heat load are emphasized and explored. The results suggest that the cooling efficiency of a thermoelectric cooler can be improved not only by increasing the figure-of-merit of the thermoelectric materials but also by taking advantage of the Thomson effect. A possible development direction for the thermoelectric materials is thus given.     

A Finite Volume Analysis of Thermoelectric Generators

ABSTRACT

The electric power produced by a thermoelectric generator (TEG) is strongly influenced by the applied heat sink. While a TEG is aimed at harvesting waste heat, the optimization of the efficiency of the heat sink is a key task for the design of waste heat recovery systems implementing TEG. A TEG model is proposed and implemented in an open source toolbox for field operation and manipulation (OpenFOAM) for the purpose of performing optimizations of the heat sink, using a commercially available TEG as basis. This model includes the multi-physics thermoelectric coupled effects. Conservation principles of energy and current are considered simultaneously. This includes the thermal and electric conduction, Seebeck effect, Peltier effect, Thomson effect, and Joule heating. Particular attention is given to a proper modeling of the boundary conditions. The thermoelectric model is implemented in such a way that it can readily be combined with other physical models in OpenFOAM. The model is validated by comparing the predictions to analytical results, measurements as well as the simulation data of other authors.     

抽凝机组耦合热电转换辅助调峰系统参数设计

  目的  为适应新能源电力并网需求,原有抽凝热电联产机组深度调峰供热改造已为重要途径之一。现有包括电热泵和电锅炉在内的热电转换装置为辅助火电机组调峰提供了潜在途径。  方法  以350 MW抽凝机组为例,建立了以热电转换装置辅助调峰参数优化模型,重点分析了热电转换设备参数对深度调峰性能的影响;其次,分别对比了电热泵和蓄热电锅炉两种典型热电转换系统在不同装置容量、不同放热速率下的调峰深度;最后,介绍了300 MW燃煤机组的煤耗率与污染物排放水平,指出本系统的节能效益,并给出热电转换装置的最优参数。  结果  结果显示:当电热泵的热功率为100 MW、放热速率与热功率相匹配也为100 MW时,机组的调峰深度达到最大值,为73 MW左右;当蓄热式电锅炉的电功率为45 MW、放热速率为100 MW时,机组的调峰深度达到最大值,为70.05 MW。蓄热式电锅炉的储热量在24 h中内略有增加,净储热量的数值为967.5 kWh。  结论  功率和放热速率是衡量热电转换装置辅助机组调峰能力的重要参数,且二者之间要有一定程度上的匹配性,针对不同情景灵活匹配热电转换装置的类型与参数可大幅提升机组的调峰深度。     

Exploration of highly correlated Co‐based quaternary Heusler alloys for spintronics and thermoelectric applications

The half‐metallic character of new quaternary Heusler alloys CoXMnAs (X = Ru, Rh) is established along with their thermoelectric, mechanical, and thermodynamic properties. The optimization of energy suggests that alloys are stable in Y2‐type structure with a ferromagnetic character. The electronic band profile through generalized gradient approximation and modified Becke‐Johnson potential indicates the metallic character of alloys. However, with inclusion of Hubbard potential to generalized gradient approximation, the alloys depict half‐metallic character with semiconducting nature in spin‐down state. The alloys possess high magnetic moment, CoRuMnAs has 5 μB, whereas CoRhMnAs has 6 μB, following Slater‐Pauling rule M_T = Z_T ? 24. The narrow band gap in spin‐down channel enhances the thermoelectric properties. The maximum value for thermopower (|S|) obtained is 44.3 and 53.44 μV/K for CoRuMnAs and CoRhMnAs, respectively. The variation of electrical conductivity, Seebeck coefficient, and figure of merit affirm increasing trend with temperature, which is a good indication of materials to be used in thermoelectric technology. The mechanical stability along with ductile nature of alloys is determined through elastic constants. Further, we have calculated thermodynamic properties and have established their dependence on temperature and pressure using quasi‐harmonic Debye model. The half‐metallic nature with efficient thermoelectric parameters strongly supports the possible application of alloys for spin devices and green energy generation.     

Parametrical analysis of the design and performance of a solar heat pipe thermoelectric generator unit

This paper describes a solar heat pipe thermoelectric generator (SHP-TEG) unit comprising an evacuated double-skin glass tube, a finned heat pipe and a TEG module. The system takes the advantage of heat pipe to convert the absorbed solar irradiation to a high heat flux to meet the TEG operating requirement. An analytical model of the SHP-TEG unit is presented for the condition of constant solar irradiation, which may lead to different performance characteristics and optimal design parameters compared with the condition of constant temperature difference usually dealt with in other studies. The analytical model presents the complex influence of basic parameters such as solar irradiation, cooling water temperature, thermoelement length and cross-section area and number of thermoelements, etc. on the maximum power output and conversion efficiency of the SHP-TEG. Simulation based on the analytical model has been carried out to study the performance and design optimization of the SHP-TEG.     

基于改进贪心算法的温差电器件电-热耦合效应研究

温差电器件实际工作时由于内电阻的存在不可避免地会产生焦耳热,传统的温差电研究中虽注意到温差发电过程中的焦耳热现象,但只是在等效计算热功率时消去焦耳热部分,而忽略了焦耳热对温差电器件热、冷端温度分布的影响。针对传统研究的不足,考虑实际应用中的电-热耦合效应,运用理论推导的方法建立了第三类边界条件下的温差发电负载模型,并利用改进贪心算法迭代求解,最后以SP1848-21745型温差发电片为例,通过试验验证了模型与算法的正确性。模型的数值求解与发电片实测结果对比表明,考虑了电-热耦合效应的温差发电负载模型的热电输出值更接近实测值。     

A numerical investigation of entropy generation in the entrance region of curved pipes at constant wall temperature

In this study, developing incompressible viscous flow and heat transfer in the curved pipes are studied numerically to analyze the entropy generation and thermodynamic optimization in the entrance region at a constant wall temperature. The governing equations including continuity, momentum and energy equations are solved using a second order finite difference method based on the projection algorithm. Entropy generation and optimal Reynolds number calculation based on the entropy generation minimization are carried out for two cases considering the two groups of non-dimensional parameters both numerically and analytically. The comparison of the numerical results in the entrance region with the analytical ones in the fully developed region indicates that both solutions predict nearly the same optimal Reynolds numbers, specially, for the first group of the non-dimensional parameters.     

600 MW双机热电联供系统智能优化方法研究

以600 MW双机热电联供系统为研究对象,引入基于灰狼捕食行为模拟的群智能优化算法,针对其繁琐更新机制导致热电负荷分配时效性差的问题,进一步提出改进的灰狼优化算法(GGWO),利用前3等级狼的位置和高斯采样进行种群进化机制更新。通过EBSILON平台开展仿真试验,揭示600 MW双机热电联供系统的热电耦合特性和系统运行特性,并将改进的灰狼优化算法应用于该系统的热电负荷优化分配。结果表明：两台机组电负荷一定时,尽可能增大抽凝机组的抽汽供热量可减小系统总热耗量;通过智能热电负荷运行优化,可有效降低系统总热耗量,提高系统经济效益。     

A Numerical Study of Entropy Generation in the Entrance Region of Curved Pipes

In this study, developing incompressible viscous flow and heat transfer in curved pipes are studied numerically considering a constant heat flux at the wall to analyze the entropy generation. The governing equations including continuity, momentum and energy equations are solved using a second order finite difference method based on the projection algorithm. Entropy generation and thermodynamic optimization are investigated through the entrance region of the curved pipes with circular cross section by a general non-dimensional analysis both numerically and analytically. Optimal Reynolds number calculation based on the entropy generation minimization are carried out for two cases considering the two groups of non-dimensional parameters. The comparison of the numerical results in the entrance region with the analytical ones in the fully developed region indicates that both solutions predict nearly the same optimal Reynolds numbers.     

Influence of massive heat‐pump introduction on the electricity‐generation mix and the GHG effect—Belgian case study

To evaluate the environmental impact of massive heat‐pump introduction on greenhouse gas (GHG) emissions, dynamic simulations of the overall electricity‐generation system have been performed for Belgium. The simulations are carried out with Promix, a tool that models the overall electricity‐generation system. For comparison, three heating devices are considered, namely conventional boilers, heat pumps and electrical resistance heating. The introduction of electric heating at the expense of classic heating increases the demand for electricity and generates a shift of emissions from fossil‐fuel heating systems to electrical power plants. The replaced classic fossil‐fuel‐fired heating represents emissions of about 300 kton. With regard to the heat‐pump scenarios, both direct heat‐pump heating with a coefficient of performance (COP) of 2.5 and accumulation heat‐pump heating with a COP of 5 are investigated. The results of the simulations reveal that the massive introduction of heat‐pump heating is favourable to the environment. In Belgium, the largest reductions in GHG emissions occur with heat pumps for direct heating, combined with newly commissioned combined cycle (CC) gas‐fired plants or with accumulation heat‐pump heating. These scenarios bring about overall GHG emission reductions of approximately 200 kton compared with the reference case with conventional heating for the years 2000 and 2010. The amount of additional electricity‐related emissions depends on the considered heating device. In 2010, the scenario with accumulation heat pumps results in an overall decrease of Belgian GHG emissions by 0.15% compared with the reference scenario. The expansion of the electricity‐generation system with new CC plants has an important favourable impact on GHGs as well. In most cases, the combination of higher electricity demand and the construction of new gas‐fired CC plants will lead to lower overall GHG emissions. Copyright © 2007 John Wiley & Sons, Ltd.     

On the ‘reaction in chain’ in the thermoelectric conversion of energy through thermocouples: Theoretical implications of the phenomenon

It is shown, experimentally, that in certain initial conditions of temperature, and for certain parameters, a ‘reaction in chain’ may start in a thermocouple, and produce a ‘permanent regime’, through which heat from a single course is converted into electrical energy. It is shown, theoretically, that the phenomenon occurs when compensation of heat losses due to thermal conduction, through Peltier and Thomson heat is realized, so that the efficiency is affected only by the Joule effect, and may attain much higher values than through conventional operation of these thermoelectric devices, conventional peration requiring two heat sources, a hot and a cold one.     

Effect of Mach number on thermoelectric performance of SiC ceramics nose-tip for supersonic vehicles

This paper focus on the effects of Mach number on thermoelectric energy conversion for the limitation of aero-heating and the feasibility of energy harvesting on supersonic vehicles. A model of nose-tip structure constructed with SiC ceramics is developed to numerically study the thermoelectric performance in a supersonic flow field by employing the computational fluid dynamics and the thermal conduction theory. Results are given in the cases of different Mach numbers. Moreover, the thermoelectric performance in each case is predicted with and without Thomson heat, respectively. Due to the increase of Mach number, both the temperature difference and the conductive heat flux between the hot side and the cold side of nose tip are increased. This results in the growth of the thermoelectric power generated and the energy conversion efficiency. With respect to the Thomson effect, over 50% of total power generated converts to Thomson heat, which greatly reduces the thermoelectric power and efficiency. However, whether the Thomson effect is considered or not, with the Mach number increasing from 2.5 to 4.5, the thermoelectric performance can be effectively improved.     

Second Law Efficiency Analysis of Heat Exchangers

Analytical analysis of unbalanced heat exchangers is carried out to study the second law thermodynamic performance parameter through second law efficiency by varying length‐to‐diameter ratio for counter flow and parallel flow configurations. In a single closed form expression, three important irreversibilities occurring in the heat exchangers—namely, due to heat transfer, pressure drop, and imbalance between the mass flow streams—are considered, which is not possible in first law thermodynamic analysis. The study is carried out by giving special influence to geometric characteristics like tube length‐to‐diameter dimensions; working conditions like changing heat capacity ratio, changing the value of maximum heat capacity rate on the hot stream and cold stream separately and fluid flow type, i.e., laminar and turbulent flows for a fully developed condition. Further, second law efficiency analysis is carried out for condenser and evaporator heat exchangers by varying the effectiveness and number of heat transfer units for different values of inlet temperature to reference the temperature ratio by considering heat transfer irreversibility. Optimum heat exchanger geometrical dimensions, namely length‐to‐diameter ratio can be obtained from the second law analysis corresponding to lower total entropy generation and higher second law efficiency. Second law analysis incorporates all the heat exchanger irreversibilities. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21109     

Performance analysis on a novel micro‐channel heat pipe evacuated tube solar collector‐incorporated thermoelectric generation

In China, because of the emergence of a large number of high‐rise buildings, the solar hot water heater system often uses the balcony wall‐mounted method for installation. The thermoelectric energy converter is proposed as one of the possible technologies to incorporate solar water heater to produce electricity for building application. In this paper, the conceptual development and theoretical analysis of a novel micro‐channel heat pipe evacuated tube solar collector‐incorporated thermoelectric generation are all proposed. The new system takes into account many advantages, including the high heat transfer, low convective heat loss, and low contact thermal resistance. The exergy analysis method based on the second law of thermodynamics is also introduced to evaluate the performance of this system. The results show that a novel micro‐channel heat pipe evacuated tube solar collector‐incorporated thermoelectric generation has a high thermal performance with addition of electricity production. Copyright © 2016 John Wiley & Sons, Ltd.     

Multiobjective thermo‐economic and thermodynamics optimization of a plate–fin heat exchanger

In the present work, a multiobjective heat transfer search (MOHTS) algorithm is proposed and investigated for thermo‐economic and thermodynamic optimization of a plate–fin heat exchanger (PFHX). Heat exchanger effectiveness and total annual cost (TAC) are considered as thermo‐economic objective functions. Similarly, entropy generation rate and heat exchanger effectiveness are considered as thermodynamic objective functions. Six design variables including flow length of cold and hot streams, no flow length, fin height, fin pitch, and fin offset length are considered as decision variables. Effectiveness and accuracy of the proposed algorithm are evaluated by analyzing application examples of a PFHX. The results obtained using the proposed algorithm for thermo‐economic considerations are compared with the available results of NSGA‐II and TLBO in the literature. Results show that 3.56% to 10.29% reductions in TAC with 0.48% to 0.81% higher effectiveness are observed using the proposed approach compared to TLBO and NSGA‐II approaches. Additionally, the distribution of each design variable in its allowable range is also shown for thermo‐economic consideration to identify the level of conflict on objective functions. The sensitivity analyses of design variables on the objective functions value are also performed in detail.     

First and second law investigations of a new solar‐assisted thermodynamic cycle for triple effect refrigeration

This investigation is persuaded for the first and second law analyses of a new solar‐driven triple‐effect refrigeration cycle using Duratherm 600 oil (Duratherm Extended Life Fluid, NY, USA) as the heat transfer fluid is performed. The proposed cycle is an integration of ejector, absorption, and cascaded refrigeration cycles that could produce refrigeration output of different magnitude at different temperature simultaneously. Both exergy destruction and losses in each component and hence in the overall system are determined to identify the causes and locations of the thermodynamic imperfection. The effects of some influenced parameters such as hot oil outlet temperature, refrigerant turbine inlet pressure, and the evaporator temperature of ejector and cascaded refrigeration cycle have been observed on the first and second law performances. It is found that maximum irreversibility occurs in central receiver as 52.5% and the second largest irreversibility of 25% occurs in heliostat field. The second law efficiency of the solar driven triple effect refrigeration cycle is 2%, which is much lower than its first law efficiency of 11.5%. Analysis clearly shows that performance evaluation based on the first law analysis is inadequate and hence, more meaningful evaluation must be included in the second law analysis. Copyright © 2013 John Wiley & Sons, Ltd.