• Energy Research

Abstract This paper sets out to describe the design, construction and testing of a thermoelectric-based conditioned mattress intended to reduce the human-mattress interface temperature, in order to increase the user’s sleep quality and thermal comfort in warm locations of Spain. A prototype is constructed and tested, which includes a mattress and a thermoelectric system that cools the inner air and governs the human-mattress interface temperature. This temperature results 2.1 °C lower than that of the room ambient, for 90 W of supplied electric power to the thermoelectric modules, with a coefficient of performance of 0.34. Under this scenario, the comfort perceived by the user is expected to improve compared to that provided by a no-conditioned mattress. The prototype is modified so that the inner air is pumped directly to the human body. With this improvement, the relevant temperature is now that of the inner air, which results 3.4 °C lower than the room ambient temperature, thus expected to increase even more the comfort perceived by the user, with 0.58 of coefficient of performance. In order to simulate both the transient and steady state of the global system, a lumped-capacitance model is devised specifically for this application. The validation process is conducted comparing simulated and experimental values of electric current, temperature difference between ends of the modules, temperature difference between the inner air and the ambient, and coefficient of performance. In steady state, the theoretical model predicts the experimental results with deviations below ±9%. Computational results indicate that the inner air temperature increases by only 1 °C, when air humidity increases from zero to 100%. Under the 100%-humidity scenario, the inner air temperature is still 2.4 °C lower than the room ambient temperature, reducing slightly the coefficient of performance to 0.47.

Abstract Thermoelectric refrigeration (TEC) exhibits several advantages compared to vapour-compression, since this technology presents accurate temperature control systems and higher levels of compactness, robustness and noiselessness. However, its low efficiency is acting as a deterrent for it to spread in the refrigeration market. One of the factors determining the efficiency of a thermoelectric refrigerator is the temperature difference between the hot and cold sides of the thermoelectric modules (TEMs). This is dependent on the thermal resistances of the heat exchangers used. This paper discusses the results of an experimental study of different types of heat exchangers for the thermoelectric module hot side: a water–air system comprising a cold plate, pump and fan coil; a finned heat sink with fan; a heat pipe with fan. Expressions of thermal resistance have been obtained for these three types as a function of the air and water mass flows and the number of TEMs per unit of surface area of heat exchanger (occupancy ratio, δ), as well as expressions of the power consumed by the fans and the pump. Finally, a computational study has been carried out on a thermoelectric refrigerator of 15 m3 of interior volume, in order to obtain the influence of the heat exchanger studied, on the total consumption of the refrigerator and its efficiency. The results have demonstrated that relevant improvements can be made in TEC efficiency by the proper optimisation of the heat exchangers.

Abstract Thermoelectric self-cooling systems hold good prospects for the future, since they improve the cooling of any heat-generating device without electricity consumption. The potential number of applications seems to be enormous, hence the necessity of a specific model to simulate this type of thermoelectric application. This paper presents a computational model for thermoelectric self-cooling applications, capable of simulating both the steady and the transient state of the whole system. Supported by fluid-dynamics software and based on the implicit finite differences, the model solves the system of equations composed of the Fourier's law and the thermoelectric effects Seebeck, Peltier, Joule and Thomson, including temperature-dependant properties. Furthermore, the model architecture allows the inclusion of new analytical expressions and/or procedures in order to simulate any component with higher accuracy or include more complex ones. Statistical studies indicate ±12% of maximum deviation between experimental and simulated values of the main outputs. Furthermore, the model simulates the performance of the system under abruptly changing conditions. In conclusion, the computational model turns out to be a powerful tool that will play a key role in the design and development of thermoelectric self-cooling applications.

Thermoelectric devices hold significant promise for generating electricity from geothermal heat, enabling the powering of measuring equipment in remote locations without the need for moving parts. Nevertheless, most developed geothermal thermoelectric generators employ fans and pumps to enhance heat transfer, thereby compromising the robustness and reliability inherent to thermoelectricity. Furthermore, there is a lack of research on passive heat exchangers for geothermal thermoelectric generators, particularly in studying their operation under a wide range of meteorological conditions. Therefore, this paper conducts a comprehensive analysis of passive heat exchangers for the cold side of the generators. Phase-change-based heat exchangers differing in their length and fluid are studied experimentally, along with a fin dissipator. Additionally, the influence of wind velocity on heat transfer and mechanical requirements is further explored through a Computational Fluid Dynamics model. The most significant outcome is quantifying the impact of the design parameters and operational variables on the electrical production of the thermoelectric generator. Accordingly, this research aims to broaden the application of these generators to extreme environments, such as Deception Island in Antarctica. Under average operational conditions, generators incorporating 400 mm water heat pipes generate 0.95 W per thermoelectric module, while those incorporating heat pipes with methanol achieve an average of 0.70 W. Moreover, water and methanol-based systems produce 120% and 60% more power than generators using a fin dissipator. Nonetheless, for temperatures beyond -6.5 °C, water might freeze and the methanol-based heat exchangers become more suitable. The authors would like to acknowledge the support of the Spanish State Research Agency and EFEDER-UE, Spain for funding under the PID2021-124014OB-I00 research project.

An important issue in thermoelectric generators is the thermal design of the heat exchangers since it can improve their performance by increasing the heat absorbed or dissipated by the thermoelectric modules. Due to its several advantages, compared to conventional dissipation systems, a thermosyphon heat exchanger with phase change is proposed to be placed on the cold side of thermoelectric generators. Some of these advantages are: high heat-transfer rates; absence of moving parts and lack of auxiliary con- sumption (because fans or pumps are not required); and the fact that these systems are wickless. A com- putational model is developed to design and predict the behaviour of this heat exchangers. Furthermore, a prototype has been built and tested in order to demonstrate its performance and validate the compu- tational model. The model predicts the thermal resistance of the heat exchanger with a relative error in the interval [?8.09;7.83] in the 95% of the cases. Finally, the use of thermosyphons with phase change in thermoelectric generators has been studied in a waste-heat recovery application, stating that including them on the cold side of the generators improves the net thermoelectric production by 36% compared to that obtained with finned dissipators under forced convection. The authors are indebted to the Ministry of Economy, Industry and Competitiveness-Government of Spain and FEDER Funds for economic support of this work, included in the DPI2014-53158-R Research Project.

One of the options to reduce industrial energy costs and the environmental impact is to recover the waste-heat produce in some processes. This paper proposes the use of thermoelectric generators at a stone wool manufacturing plant to transform waste-heat from a hot gas flow into useful electricity. A combination of two computational models, previously developed and validated, has been used to perform the optimization from a double point of view: power output and economic cost. The proposed thermoelectric generator includes fin dissipaters and biphasic thermosyphons as the hot and cold side heat exchangers respectively. The model takes into account the temperature drop along the duct where the gases flow, the electric consumption of the auxiliary equipment, and the configuration and geometry of the heat exchangers. After the simulations a maximum net power production of 45 838 W is achieved considering an occupancy ratio of 0.40 and a fin spacing of 10 mm. The installation cost is minimized to 10.6 €/W with an occupancy ratio of 0.24. Besides, the Levelised Cost of Electricity, LCOE, is estimated for a thermoelectric generator for the first time. It is necessary to use standar methodologies to compare this technology to others. The LCOE estimated for the proposed design is around 15 c€/kWh within the ranges of current energy sources, proving, in this way, the capabilities of waste-heat recovery from industrial processes at reasonable prices with thermoelectric generators. The authors are indebted to the Government of Navarre funds for economic support of this work, included in the 0011-1365-2018-000101 Research Project; and the Spanish Ministry of Economy and Competitiveness for the economic support thanks to the DPI2014-53158-R project.

Abstract Computational models emerge as essential tools in the challenge of developing competitive thermoelectric refrigerators for the domestic sector. This paper presents a computational model for thermoelectric refrigerators that simulates the entire system under transient state, including the thermoelectric modules, heat exchangers, insulated compartments, and hot and cold reservoirs. Also, temperature-dependent Peltier, Seebeck, Thomson and Joule effects are implemented. A prototype of a thermoelectric refrigerator has been built and tested to conduct the verification and validation of the computational model. The most important outputs are predicted with deviations lower than ±10%. The effect on the outputs of temperature-independent properties has been assessed. Results indicate that deviations are up to twice as high as those obtained for temperature-dependent properties, so these simplifications are invalid in the simulation of thermoelectric refrigerators under real operation.

Thermoelectric generation contributes to obtain a more sustainable energetic system giving its potential to harvest waste heat and convert it into electric power. In the present study a computational optimal net generation of 108.05 MWh/year was produced out of the flue gases of a real tile furnace located in Spain (the equivalent to supply the energy to 31 Spanish dwellings). This maximum generation has been obtained through the optimization of the hot and cold heat exchangers, the number of thermoelectric modules (TEMs) installed and the mass flows of the refrigerants, including the temperature loss of the flue gases and the influence of the heat power to dissipate over the heat dissipators. The results are conclusive, the installation of more TEMs does not always imply higher thermoelectric generation, so the occupancy ratio (δ) has to be optimized. The optimal generation has been achieved covering the 42 % of the surface of the chimney of the tile furnace with TEMs and using heat pipes on the cold side, which present smaller thermal resistances than the finned dissipators for similar consumptions of their fans. Moreover, the high influence of the consumption of the auxiliary equipment shows the importance of considering it to obtain realistic usable electric energy from real applications. The authors are indebted to the Spanish Ministry of Economy and Competitiveness for the economic support to this work, included in the DPI2014-53158-R research project.