Thermoelastic stress analysis of multilayered films in a micro-thermoelectric cooling device

This paper presents an analytical solution for the thermoelastic stress in a typical in-plane’s thin-film micro-thermoelectric cooling device under different operating conditions. The distributions of the permissible temperature fields in multilayered thin-films are analytically obtained, and the characteristics, including maximum temperature difference and maximum refrigerating output of the thermoelectric device, are discussed for two operating conditions. Analytical expressions of the thermoelastic stresses in the layered thermoelectric thin-films induced by the temperature difference are formulated based on the theory of multilayer system. The results demonstrate that, the geometric dimension is a significant factor which remarkably affects the thermoelastic stresses. The stress distributions in layers of semiconductor thermoelements, insulating and supporting membrane show distinctly different features. The present work may profitably guide the optimization design of high-efficiency micro-thermoelectric cooling devices.     

共线式热电发电机在侧面散热情况下的性能

热电材料是一种环境友好型功能材料,其可以实现热能与电能的相互转化,在热电发电、热电制冷中具有许多应用.传统的热电发电机为$\pi$型结构,要求热电腿的长度相等,在某些情况该结构不利于热电发电机的优化设计.热电发电机在高温工况下会引起强烈的热应力甚至应力集中,从而缩短了其工作寿命.另外,热电发电机的工作温度于环境温度,这样必然会有一部分热量散失到环境中,从而影响热电发电机的性能.针对该现象,本文建立了考虑散热的新型共线式热电发电机模型,该模型的热电腿可以独立进行优化,基于有限元方法,对考虑侧面散热的共线式热电发电机进行了仿真模拟,分析了其在狄利克雷边界条件下的热电性能和力学性能,得到了热电发电机的温度场、电势场、应力场,探究了不同强度的对流散热系数对热电发电机热电性能和力学性能的影响.结果表明,对流散热会降低热电发电机的能量转化效率,当对流换热系数达到~100W/(m$^{2}\cdot$\textcelsius) 时,效率为~0.0479,该值比绝热状态的转化效率0.066 7 低28%.对流散热使热电发电机侧面热损失增加,降低了热应力.在实际应用中,应合理优化设计隔热系统,提高能量的转化效率.      

Development of a Miniaturized Energy Converter Without Moving Parts

New developments in portable electrical and mechanical devices have created demand for increasing amounts of energy and thus new ways of supplying energy. The high energy density of hydrocarbon fuels are a possible way to solve this issue. This paper deals with the development of an adapted thermodynamic concept for a micro energy converter based on the thermoelectric effect. Developing a PowerMEMS device that does not contain any moving parts is the main design feature. In the proposed concept liquid hydrocarbon fuel, such as methanol, is evaporated in a micro evaporator, mixed with air, and combusted in a micro combustion chamber. The combustion process is assisted by catalytically coated microfibers. Electrical power can be generated by a thermoelectric generator, which is located between the hot combustion zone and the cold micro evaporator. This arrangement leads to large temperature differences between hot and cold junctions, which is necessary for efficient thermoelectric energy conversion and hence power generation. For a more detailed investigation of thermal boundary conditions and interior thermal management, in-situ temperature measurements of the combustor walls are performed using thermographic phosphors.     

Integrated microthermoelectric cooler for microfluidic channels

Precise fluid temperature control in microfluidic channels is a requirement for many lab-on-a-chip and microreactor devices, especially in biotechnology where most processes are highly temperature sensitive. We demonstrate the concept of a microthermoelectric cooler integrated into a microfluidic channel in order to give rapid and localised fluid cooling. The key aspect of this concept is the use of a second imbedded microfluidic channel that is used as a miniature heat sink. An analytical thermal model has been derived that couples thermoelectric effects with fluid heat-transfer rates from both the hot and cold connections. Using this model, the effect on cooling performance of varying the thermal resistance between the hot and cold connections and the fluid has been quantified, as well as the effect of substrate thermal conductivity. If the substrate thermal conductivity is too high, heat leakage renders the thermoelectric cooler ineffective. The optimum electrical current for cooling has been shown to be a function of the thermal resistance of the heat sink. For thermoelectric coolers there is competition between temperature reduction and cooling power. Using this fact, based on the final fluid temperature required, we have calculated the maximum flow rate that will achieve this. Finally, a prototype integrated microthermoelectric cooler has been fabricated and tested.     

Experimental on the liquid cooling system with thermoelectric for personal computer

In the present experimental investigation, the liquid cooling in the micro channel fin heat sink with and without thermoelectric for central processor unit (CPU) of personal computer. The micro channel heat sinks with two different channel height are fabricated from the aluminum with the length, the width and the base thickness of 28, 40, 2?mm respectively. The de-ionized water is used as coolant. Effects of channel height, coolant flow rate, and run condition of PC on the CPU temperature are considered. The liquid cooling in micro-rectangular fin heat sink with thermoelectric is compared with the other cooling techniques. The thermoelectric has a significant effect on the CPU cooling of PC. The experiments are performed at no load and full load conditions within 60?min after steady state, which the mass flow rate are 0.023, 0.017 and 0.01?kg/s. The results heat transfer rate increase with increasing coolant flow rate and higher channel. When comparing with the other cooling system, cooling system with thermoelectric gives the highest efficiency. However, thermoelectric has the high or low heat transfer rate from heat rejected and cooling capacity conditions.     

含空心纤维热电复合材料的能量转换效率及力学性能

空心纤维常用于热电复合材料的结构设计。纤维附近产生的不均匀温度场会引起局部热应力集中,威胁材料的可靠性并可能导致结构失效。本文采用圆环夹杂模型,研究了含空心纤维热电复合材料在均匀远场电流和能流作用下的力学响应。基于非线性全耦合的热电本构方程,利用复变函数中的级数法得到了纤维和基体中热电场和应力场的解析解。通过数值算例,分析了空心纤维的传导能力和几何尺寸对温度场、应力场和局部热电转换效率的影响。结果表明：随着空心纤维内径和界面热阻的增大,界面周围的应力场增大,但并不改变应力场的分布趋势。此外,我们发现：温度分布和应力场对几何参数比对界面热阻更为敏感。     

Fracture mechanics analysis of delamination in a thermoelectric pn-junction sandwiched by an insulating layer

A fracture mechanics analysis is conducted for a delamination problem of a multilayered thermoelectric material (TEM) that consists of an n-type layer and a p-type layer sandwiched by an insulating layer. A time-varying energy release rate is presented when the n-type layer delaminates from the insulating layer. Effects of the temperature difference across the system and the applied electric current on the energy release rate are identified. The influence of the thickness ratio of the insulating layer to the thermoelectric (TE) layer is also examined. Based on the energy release rate criterion, the critical temperature difference for delamination propagation is obtained. Some useful conclusions are given.     

Experimental investigation of the performance of a thermoelectric generator based on Peltier cells

An experimental investigation is carried out to characterize the performance of thermoelectric modules used for electric power generation over a range of different resistance loads. The performance of a Peltier cell used as a thermoelectric generator is evaluated in terms of power output and conversion efficiency. The results show that a thermoelectric module is a promising device for waste heat recovery.     

The thermoelectric transistor a possible batteryless amplifying semiconductor device

Summary A signal, modulating by carrier emission the concentration of free carriers in a semiconductor wafer containing a temperature gradient, is reproduced by the thermoelectric voltage between output electrodes at different temperatures. The conditions for power amplification are discussed. Criteria are derived for the choice of material, geometrical shape and heat flow through an amplifying device. The use of Ge seems to be possible, though difficult. New semiconducting materials show promising properties. Formerly Department of Physics, University, Oslo, Norway.     

刚性圆形压头作用下热电材料半平面的无摩擦接触问题

热电材料可以将热能转化为电能,反之亦然,这一优良的性质将有助于研发更具成本效益的设备和器件。本文研究了刚性圆形压头作用在热电材料半平面的无摩擦接触问题。假定压头为电导体、热导体,且压头压入深度及与材料的接触区域宽度未知。首先求解电场和温度场,利用傅里叶变换得到了电势函数、温度、电流密度和能量通量的解析表达式。然后求解弹性场,利用积分变换和边界条件,将该热弹性接触问题转化为第一类奇异积分方程并数值求解。数值结果讨论了压头半径和热电载荷对法向接触应力、电流强度因子和能量通量强度因子的影响。结果表明,对于圆压头,热电材料的法向电流密度、法向能量通量在接触边缘表现出奇异性,而表面法向接触应力在接触边缘为零。本文建立的研究模型有助于更深层次的了解热电材料的接触行为。     

DNA stretching modeled at the base pair level: Overtwisting and shear instability in elastic linkages

Stretching experiments on single DNA molecules indicate that, counterintuitive to expectations, DNA overwinds when stretched and, at large forces, undergoes a transition into an overstretched form indicated by a plateau on the force–displacement diagrams. It is believed that these effects are the result of non-linearities in the elastic response of DNA. We use a discrete, base pair level model to simulate the behavior of short DNA molecules, taking into account the sequence dependent physical properties of DNA alongside with the coupling between the kinematical step parameters, yet retaining the quadratic form of local elastic energy function. By constructing bifurcation diagrams of equilibrium configurations and studying the dependence on base pair combinations we show that the quadratic model is capable of explaining the overtwisting as a result of coupling between modes of deformation and overstretching as a result of shear instability.     

The application of 2D base force element method (BFEM) to geometrically non-linear analysis

Based on the concept of the base forces by Gao, a new finite element method – the base force element method (BFEM) on complementary energy principle for two-dimensional geometrically non-linear problems is presented. A 4-mid-node plane element model of the BFEM for geometrically non-linear problem is derived by assuming that the stress is uniformly distributed on each sides of a plane element. The explicit formulations of the control equations for the BFEM are derived using the modified complementary energy principle. The BFEM is naturally universal for small displacement and large displacement problems. A number of example problems are solved using the BFEM and the results are compared with corresponding analytical solutions and those obtained from the standard displacement finite element method. A good agreement of the results, and better performance of the BFEM, compared to the displacement model, in the large displacement and large rotation calculations, is observed.     

State space approach to thermoelectric fluid with fractional order heat transfer

A new mathematical model for electromagnetic thermofluid equation heat transfer with thermoelectric properties using the methodology of fractional calculus is constructed. The governing coupled equations in the frame 11 of the boundary layer model are applied to variety problems. Laplace transforms and state space techniques (Ezzat Can J Phys Rev 86:1241–1250 in 2008) are used to get the solution of a thermal shock problem, a layer problem and a problem for the semi-infinite space in the presence of heat sources. According to the numerical results and its graphs, a parametric study of time-fractional order 0 < α ≤ 1, on temperature and the thermoelectric figure of merit are conducted.     

A device to achieve low Reynolds numbers in an open surface water channel

When investigating flow structures, and especially flow transitions, research projects often seek to increase insight using complementary numerical and physical experiments. Obtaining exact Reynolds number correspondence can frequently be difficult in experiments, particularly when relatively low values are required. Often, available test facilities were designed and optimised for a specific velocity range, meaning they have restrictions on the minimum flow velocity. This study describes a device to reduce the flow velocity locally in an open surface water channel. The underlying idea is to divert a controlled fraction of the incoming flow from the working section by increasing the pressure there, resulting in reduced velocity. This idea is realised using a ‘sub-channel’ that can be inserted into the main test chamber, with a variable porosity perforated screen at its downstream end. This study assesses and optimises the flow quality inside this structure, such as usable test section length, uniformity of the velocity profiles and turbulence intensity. The results demonstrate that the device creates high quality low Reynolds number flows, which is exemplified with the canonical circular cylinder in cross-flow.     

A continuum model of micro-cracks in concrete

The aim of this study is to propose a model describing the evolution of the mechanical properties of micro-cracked bodies under slow mechanical loading. To do so, we consider each material element of the body as a domain of finite size comprising one single crack. The size and orientation of the latter are treated as Lagrangian coordinates that are complementary to those usually describing the translations of the material elements. As such, their evolution is driven by some balance equations that are provided by the theory of continua with microstructure and by fit constitutive equations. To deal with the latter, we then call upon fracture mechanics. The model is applied to concrete within some simplifying assumptions and the case of a bar tensioned by a hard device is studied. Crack propagation and stiffness loss are determined when the loading increases, they are compared to experimental results.     

Influence of the electron and phonon temperature and of the electric-charge density on the optimal efficiency of thermoelectric nanowires

In this paper we study the thermodynamic efficiency of thermoelectric generators in which the heat transport is driven by phonons and electrons. It is assumed that the phonon temperature and the electron temperature are different, and that the electric-charge density is nonuniform. The mean temperature is defined by observing that the internal energy of the system is the same either in the presence of two temperatures, or of one temperature. In steady states, we determine the influence of the gradients of the mean temperature and of the electric-charge density on the theoretical values of the thermoelectric efficiency. The physical conditions under which such efficiency is optimal are determined as well.     

Intelligent design of waste heat recovery systems using thermoelectric generators and optimization tools

Optimal design of thermal systems that effectively use energy resources is one of the foremost challenges that researchers almost confront. Until now, several researches have been made to enhance the performance of major thermal systems. In this investigation, the authors try to make a conceptual design to maximize the electricity demand of Damavand power plant as the biggest thermal system in Middle East sited in Iran. The idea of designing is laid behind applying a number of thermoelectric modules within the condenser in order to recover the waste heat of the thermal systems. Besides, the authors have developed some intelligent tools to elaborate on the performance of their proposed model. Firstly, an artificial neural network has been utilized to estimate the potential power generation of the thermoelectric modules. At the second step, computational fluid dynamic solver, FLUENT is used to determine the variation of the temperature through the length of the thermoelectric module assembly. Based on the gained results, an intelligent multi-objective optimization algorithm called Pareto based mutable smart bee is developed to optimize the properties of the thermoelectric component.     

Wide spectrum solar energy harvesting through an integrated photovoltaic and thermoelectric system

This paper proposes a power system concept that integrates photovoltaic （PV） and thermoelectric （TE） technologies to harvest solar energy from a wide spectral range. By introduction of the ＇spectrum beam splitting＇ technique, short wavelength solar radiation is converted directly into electricity in the PV cells, while the long wavelength segment of the spectrum is used to produce moderate to high temperature thermal energy, which then generates electricity in the TE device. To overcome the intermittent nature of solar radiation, the system is also coupled to a thermal energy storage unit. A systematic analysis of the integrated system is carried out, encompassing the system configuration, material properties, thermal management, and energy storage aspects. We have also attempted to optimize the integrated system. The results indicate that the system configuration and optimization are the most important factors for high overall efficiency.     

基于遗传算法的温差发电系统模块布局优化设计

温差发电在航空航天等极端环境供电和汽车余热利用等领域具有重要的应用,然而低的热电转换效率严重限制了其发展.目前主要从提高材料本身性能和优化热电模块结构两方面提升性能.本文从整体出发,建立了基于遗传算法的温差发电系统模块布局优化设计方法.融合已有的解析模型,发展了能够快速获得系统电输出功率的性能评估方法;通过遗传算法,以...     

Experimental and computational study of the developed flow field in a flat plate integrated collector storage (ICS) solar device with recirculation

The flow structure in a flat plate integrated collector storage device, with recirculation of the storage water, is studied experimentally and theoretically. To facilitate flow visualization, an experimental device was constructed by transparent material (Plexiglas). Flow velocities and fluctuations are measured, using a LDV system. A three-dimensional CFD-model was developed using the FLUENT code. The standard k–ω model is selected as the most appropriate. The model is validated, with good agreement, against experimental measurements. Furthermore, copper tubes, in the form of embedded heat exchanger, are placed inside the device and another similar 3D model was developed. The model was used to examine the behavior of the system, when the service water enters the heat exchanger, thus being indirectly heated by the stored hot water. It is shown that the outlet temperature of the service water is enough higher, when recirculation occurs.