Increase of COP in the thermoelectric refrigeration by the optimization of heat dissipation

A device for the dissipation the heat from the hot side of Peltier pellets in thermoelectric refrigeration, based on the principle of a thermosyphon with phase change is presented. The device design was accomplished by analytic calculations on the base of a semi-empirical formulation and simulations with computational fluids dynamics. In the experimental optimization phase, a prototype of thermosyphon with a thermal resistance of 0.110 K/W has been development, dissipating the heat of a Peltier pellet with the size of 40 × 40 mm, what is an improvement of 36% in the thermal resistance, with regard to the commercial fin dissipater.With the construction of the two prototypes of thermoelectric domestic refrigerators, one of them with the device developed, and the other with a conventional fins dissipater, it could be experimentally proved that the use of thermosyphon with phase change increases the coefficient of performance up to 32%.     

Development and experimental validation of a computational model in order to simulate ice cube production in a thermoelectric ice-maker

We have developed a computational model which allows the simulation of a thermoelectric device to make ice cubes in a vapour compression domestic fridge. This model solves both the thermoelectric and heat transfer equations, including the phase change equations in the ice cube production.The inputs of the model are: the thermoelectric parameters as a function of the temperature; dimensions; material properties (thermal resistances and capacities) and the boundary conditions (room temperature and voltage supplied to the Peltier module). The outputs are the values of the temperature for all the elements of the thermoelectric ice-maker and the ice production.In the experimental phase a prototype of a thermoelectric ice-maker incorporated in a vapour compression domestic fridge was constructed in order to adjust and validate the computational model, and to optimise the experimental application. This ice-maker has two Peltier modules, some aluminum cylinders, called fingers, where the ice is made, and a component that acts as heat extender and dissipater which connects the hot side of Peltier module with the freezer compartment. The ice formation on the fingers is obtained by the cooling on the Peltier modules. When the ice cubes are formed, the voltage polarity of the thermoelectric modules is switched so the fingers warm up until the ice around the fingers melts. Then the ice cubes are dropped by gravity.This paper studies the production of ice cubes using the computational model and the experiment results and analyses the most important parameters for the optimisation of the ice-maker (voltage supplied to the Peltier module, thermal resistance of the hot side dissipater and initial water temperature).     

A coupled 3D electrochemical and thermal numerical analysis of the hybrid fuel cell-thermoelectric device system

While the integration of the fuel cell (FC) and the semiconductor thermoelectric device (TED) to form a clean energy hybrid FC-TED system has been previously studied using 0-D mathematical equations, a 3-D finite element model that couples together the physics between the two devices is yet to be comprehensively studied. This paper introduces a 3-D finite element model developed in COMSOL Multiphysics that simulates both the FC and the TED subsystems where the FC electrochemical dynamics and the TED's thermoelectric effect and heat transfer physics take place between them. The studied FC stack is in direct contact with one side of the TED via the top of the gas channel structure and the other side is then convectively cooled by active air cooling. Results demonstrate that the proposed model can easily simulate the TED as both a thermoelectric generator (TEG) or as a Peltier device for cooling and heating. In the TEG mode, energy harvesting efficiency is observed at only 0.1% but expected to improve with better TED to FC relative sizing. The Peltier heating mode is also found to be advantageous in terms of quickly regulating the FC stack temperature, a valuable feature for startup processes.     

Study of the influence of heat exchangers' thermal resistances on a thermoelectric generation system

In this paper, a computational study of the influence of the heat exchangers' thermal resistances (in both the hot and cold side) on the efficiency of a thermoelectric generation device has been carried out.     

Design and experimental investigation of portable solar thermoelectric refrigerator

The main objective of this study is to design and build an affordable solar thermoelectric refrigerator for the Bedouin people (e.g. deserts) living in remote parts of Oman where electricity is still not available. The refrigerator could be used to store perishable items and facilitate the transportation of medications as well as biological material that must be stored at low temperatures to maintain effectiveness. The design of the solar-powered refrigerator is based on the principles of a thermoelectric module (i.e., Peltier effect) to create a hot side and a cold side. The cold side of the thermoelectric module is utilized for refrigeration purposes; provide cooling to the refrigerator space. On the other hand, the heat from the hot side of the module is rejected to ambient surroundings by using heat sinks and fans. The designed solar thermoelectric refrigerator was experimentally tested for the cooling purpose. The results indicated that the temperature of the refrigeration was reduced from 27 °C to 5 °C in approximately 44 min. The coefficient of performance of the refrigerator (COP_R) was calculated and found to be about 0.16.     

Development of a thermoelectric refrigerator with two-phase thermosyphons and capillary lift

A thermoelectric domestic refrigerator has been developed, with a single compartment of 0.225 m³, for food preservation at 5 °C. The cooling system is made up of two equal thermoelectric devices, each composed of a Peltier module (50 W) with its hot side in contact with a two-phase and natural convection thermosyphon (TSV) and a two-phase and capillary lift thermosyphon (TPM), in contact with the cold side.The entire refrigerator has been simulated and designed using a computational model, based on the finite difference method. Subsequently an experimental optimization phase of the thermosyphons was carried out, until thermal resistance values of R_TSV = 0.256 K/W and R_TPM = 0.323 K/W were obtained. These values were lower than those obtained with finned heat sinks.Finally, a functional prototype of a thermoelectric refrigerator was built, and the results which were obtained demonstrate that it is able to maintain a thermal drop (Ambient Temperature–Inside Temperature) of 19 °C. The electric power consumption at nominal conditions was 45 W, reaching a COP value of 0.45. The study demonstrated that by incorporating these two-phase devices into thermoelectric refrigeration increases the COP by 66%, compared with those which use finned heat sinks.     

Power generation characteristics of a sandwich‐type self‐heating thermoelectric generator with spatially varying embedded heat source

Power generation characteristics of a sandwich‐type thermoelectric generator in which the heat source is embedded into thermoelectric elements are investigated. Our previous work on a similar concept only considered a uniform heat source distribution inside thermoelectric elements. In this work, the effect of the spatial distribution of a heat source is examined. In particular, the effect of the concentration of heat source near the one end, that is, the hot end, is intensively studied as a potential means of improving the efficiency of the device. Although the effects of heat source concentration in impractical cases without heat transfer limitations on the cold side remain ambiguous, it become clear that heat source concentration indeed has positive effects in more realistic cases with finite heat transfer coefficients imposed on the cold side. Because of the relatively low efficiency of typical thermoelectric generation, a significant amount of heat must be dissipated from the cold end of the thermoelectric element. Greater heat source concentration near the hot end leads to more effective utilization of available heat source, reduces the amount of heat rejected at the cold end, and lowers the hot end temperature of the thermoelectric element. Overall, it is suggested that heat source concentration can be used as a method to achieve more efficient operation and better structural integrity of the system. Copyright © 2015 John Wiley & Sons, Ltd.     

Computational model for refrigerators based on Peltier effect application

A computational model, which simulates thermal and electric performance of thermoelectric refrigerators, has been developed. This model solves the non-linear system that is made up of the thermoelectric equations and the heat conduction equations providing values for temperature, electric consumption, heat flow and coefficient of performance of the refrigerator. Finite differences method is used in order to solve the system and also semi empirical expressions for convection coefficients.Subsequently a thermoelectric refrigerator with an inner volume of 55 × 10⁻³ m³ has been designed and tested, whose cold system is composed of a Peltier pellet (50 W of maximum power) and a fan of 2 W. An experimental analysis of its performance in different conditions has been carried out with this prototype, which, in his turn, has been useful for assessing the accuracy of the developed model. The built thermoelectric refrigerator prototype, offers advantages with respect to vapour compression classical technology such as: a more ecological system, more silent and robust and more precise in the control of temperatures which make it suitable for camping vehicles, buses, special transports for electro medicine, etc.     

Thermodynamic modelling of a solid state thermoelectric cooling device: Temperature–entropy analysis

This article presents the temperature–entropy analysis, where the Thomson effect bridges the Joule heat and the Fourier heat across the thermoelectric elements of a thermoelectric cooling cycle to describe the principal energy flows and performance bottlenecks or dissipations. Starting from the principles of thermodynamics of thermoelectricity, differential governing equations describing the energy and entropy flows of the thermoelectric element are discussed. The temperature–entropy (T–S) profile in a single Peltier element is pictured for temperature dependent Seebeck coefficient and illustrated with data from commercial available thermoelectric cooler.     

Sensitivity analysis of the effects of the thermal parameters of exhaust gases on the output of a thermoelectric generator

Recovering the dissipated heat from exhaust is a useful means of reducing the energy consumption level as well as cutting down on environmental pollution. An efficient technique for recovering this lost heat is the use of thermoelectric generators, which directly convert the dissipated heat into useful electrical energy. In this paper, a whole thermoelectric generator system installed on the exhaust pipe of a vehicle has been modeled, and the effects of thermal parameters on the output of this thermoelectric generator have been measured and evaluated by means of sensitivity analysis. The E‐Fast sensitivity analysis method has been used in this study. The sensitivity analysis results indicate that, among the thermal parameters examined, the temperature of gases entering the heat sink installed at exhaust pipe outlet () has the greatest influence (37%) and the flow rate of fluid entering the heatsink installed on the cold side of thermoelectric modules () has the second greatest influence (17%) on the output power of the considered thermoelectric generator. By using these results, the best cases of hot exhaust gases from various industries and vehicles with the highest potential of recovering the dissipated energy and heat from them by thermoelectric generators can be identified.     

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。     

Development of a temperature-controlled car-seat system utilizing thermoelectric device

A thermoelectric device was used to control the temperature of the car-seat surface: the warm temperature in the summer and cold temperature in the winter. The characteristics of the thermoelectric device for the car-seat were analyzed in relation to the input voltage and output temperature of the device. To install the device inside the car-seat, an air conditioning system was designed, consisting of a fan and duct to regulate the warm side of the thermoelectric device. To analyze and control the temperature of the car-seat system, a mathematical model of the car-seat system is proposed, and a robust control algorithm based on the sliding mode control is applied, respectively. A portable control system implementing the sliding mode control algorithm was developed by using a one-chip microprocessor and power driving system. The good performance of the developed control system for the constructed car-seat system was validated by actual tests. The test results are presented.     

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.     

Performance analysis of a double-pass thermoelectric solar air collector

The thermoelectric (TE) solar air collector, sometimes known as the hybrid solar collector, generates both thermal and electrical energies simultaneously. A double-pass TE solar air collector has been developed and tested. The TE solar collector was composed of transparent glass, air gap, an absorber plate, thermoelectric modules and rectangular fin heat sink. The incident solar radiation heats up the absorber plate so that a temperature difference is created between the thermoelectric modules that generates a direct current. Only a small part of the absorbed solar radiation is converted to electricity, while the rest increases the temperature of the absorber plate. The ambient air flows through the heat sink located in the lower channel to gain heat. The heated air then flows to the upper channel where it receives additional heating from the absorber plate. Improvements to the thermal and overall efficiencies of the system can be achieved by the use of the double-pass collector system and TE technology. Results show that the thermal efficiency increases as the air flow rate increases. Meanwhile, the electrical power output and the conversion efficiency depend on the temperature difference between the hot and cold side of the TE modules. At a temperature difference of 22.8 °C, the unit achieved a power output of 2.13 W and the conversion efficiency of 6.17%. Therefore, the proposed TE solar collector concept is anticipated to contribute to wider applications of the TE hybrid systems due to the increased overall efficiency.     

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.     

Low cost stove-top thermoelectric generator for regions with unreliable electricity supply

During the winter months in regions where constant electric power supply cannot be relied upon, power may be derived parasitically from heating stoves. A proportion of heat from these 20–50 kW wood or diesel-heated stoves may be utilized to drive a thermoelectric generator (TEG) consisting of several commercially available low-cost modules. These are Peltier modules operating in a power generating mode and adapted to the low-flux regime coupled with hot side temperatures of 100–300 °C. Two commercially available modules are considered. The generator is then theoretically re-evaluated with the Peltier modules re-designed in order to produce maximum power in a simple and cheap manner allowing easy commercial production using existing technology. A current power target is set at 100 W for a minimum domestic use.     

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.     

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.     

Performance review of a novel combined thermoelectric power generation and water desalination system

A novel combined thermoelectric power generation and water desalination system is described with a system schematic. The proposed system utilises low grade thermal energy to heat thermoelectric generators for power generation and water desalination. A theoretical analysis presents the governing equations to estimate the systems performance characteristics combined with experimental validation. Experimental set-up consists of an electric heat source, thermoelectric modules, heat pipes, a heat sink and an evaporator vessel. Four heat pipes are embedded in a heat spreader block to passively cool the bottom side of the thermoelectric cells. The condenser of these four heat pipes is immersed in a pool of saline water stored in an evaporation vessel which is maintained at sub-atmospheric pressure. The liquid to vapour phase change cooling method achieve low saturation temperature and offers a high heat transfer coefficient for the cooling of the thermoelectric generators. At the same time this method utilises the low temperature heat extracted from the cold side of the thermoelectric generator for water desalination. It was observed that at low saturation temperatures greater heat flux could be supplied to the thermoelectric generators with less heat losses to the atmosphere.