Publications on Thermoelectrics

Full-size prototype of active thermal window based on thermoelectricity
Antonio Arenas, Rafael Palacios, Ramón Rodríguez-Pecharromán, Francisco Luis Pagola
Proceedings of ECT2008 - 6th European Conference on Thermoelectrics. pp. O.18.1-O.18.4, July 2-4,2008, Paris, France.

Keywords: Thermoelectricity, Active thermal window, Air-conditioning

It is sometimes difficult to install air conditioning systems to control room temperature. One good example is during historic building restoration, where national or local laws may forbid installing air ducts or even just water pipes and heat exchangers. In such situation air-conditioning based on thermoelectricity may play an important role despite of a lower cooling performance compared with gas compression cycles. The proposal is to install window glasses with embedded thermoelectric elements that will transfer heat through the glass in order to heat or to cool the room.
After some previous experiences with small (20x20cm) prototypes, our team has developed and tested a full-size prototype of active thermal window (ATW) that is presented in this paper. The new prototype has been installed in a window frame (100x100cm) and would be able to generate up to 150W of cooling power while glass transparency is decreased in less than 20%.
The system includes automatic control in order to adjust voltage and current according to the measured room temperature, hence reducing electrical power consumption during normal use. Installation of the proposed air-conditioning system is as simple as replacing the current windows by the active version, in which just a pair of electric wires is required to run it in cooling or heating mode.
This project has been partially supported by the Spanish government through project no. BIA2004-06001.


Caracterización Experimental de un Paramento Transparente Activo Termoeléctrico (PTA)
Rafael Palacios, Antonio Arenas, Jorge Vázquez, Francisco Luis Pagola, Ramón Rodríguez-Pecharromán
Proceedings of 3rd Mediterranean Congress of HVAC Engineering, Climamed 2006, Vol 2, pp. 305-314, 20-21 November 2006, Lyon, France.

Keywords: Thermoelectricity applications, Peltier effect, heat pump, active window

The Active Thermal Wall based on thermoelectricity (ATW) is a heat pump system that uses Peltier effect. Classic windows (or glass walls) can be replaced by ATW for acclimatization in buildings. With a minimal reduction in glass transparency, ATW can pump heat in any direction (from inside to outside or vice versa) in order to attain the desired room temperature.
The main advantages over other conditioning technologies are: simple electronic control, and absence of fluids, pipes and pumps. Hence its use is very promising in domestic applications and mainly where installation of conventional equipment is problematic (historic building, esthetic, technical difficulties, size restriction,...).
The system in patented in Spain, E.U., and U.S.A .and it is currently being developed by a research group at the University Pontificia Comillas in Madrid, Spain. In this paper, the simulated and experimental results of a small prototype, built and tested in our laboratories, are presented. The article also summarizes the most relevant difficulties found by the research team during the development of the prototype.

El Paramento Transparente Activo (PTA) es un sistema de bombeo de calor por efecto Peltier pensado para climatización en edificación. Es instalado en las ventanas de un habitáculo en sustitución de los actuales vidrios, a los que reemplaza con una mínima reducción de transparencia, pudiendo bombear calor en cualquier dirección, de dentro hacia fuera y al revés, en orden a conseguir la temperatura deseada del habitáculo.
Las principales ventajas sobre las tecnologías actuales de climatización son: simplicidad del control electrónico y ausencia de fluidos, conductos y máquinas. Es esperanzador su uso en aplicaciones domésticas y principalmente allí donde los equipos convencionales plantean problemas (edificios históricos, estéticos, dificultades operativas, tamaño, etc…). El sistema está patentado en España, U.E. y USA y su desarrollo está siendo realizado por un grupo de investigación de la Universidad Pontificia Comillas de Madrid.
En este artículo se presentan los resultados simulados y experimentales de un pequeño prototipo construido y ensayado en nuestros laboratorios. El artículo también resume las dificultades más importantes encontradas durante el desarrollo del prototipo.

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Test bench for measuring the electrical properties of commercial thermoelectric modules
Jorge Vázquez, Rafael Palacios, Miguel Angel Sanz-Bobi, Antonio Arenas
Proceedings of Twenty-Second International Conference on Thermoelectrics - ICT 2003, Aug 2003, Montpellier, France

One of the most promising applications of thermoelectricity is the recovery of waste heat for the production of electrical energy. Nowadays, several thermoelectric companies manufacture commercial thermoelectric modules (TEMs) based on Bi2Te3 compounds specially designed to perform as Seebeck modules.
This paper describes a test bench (geometry, materials, measuring equipment) to analyse the behaviour of this type of modules working under several temperature differences (?Ts). This allows to estimate the potential electric power generated in an application where the optimum ?T cannot be achieved because the amount of heat supplied by the heat source is too small, or there is a limitation in the heat dissipation capacity at the cold side. The paper also shows the results obtained using two commercial modules tested under different working conditions. Plots of voltage, electrical power generated, and efficiency versus electric current generated are also included.


Thermoelectric device to allow diesel engine start-up at cold weather conditions
Jorge Vázquez, Rafael Palacios and Miguel Angel Sanz-Bobi
Proceedings of the 7th European Workshop on Thermoelectrics, Poster #2, Oct 2002, Pamplona, SPAIN.

Keywords: Thermoelectricity, Peltier Effect, Cold Engine Start-up, Diesel

Sometimes diesel engines cannot be started under low temperature conditions. The main reason is the obstruction of the fuel filter as a consequence of gasoil becoming solid paraffin as the temperature lowers. This paper describes a device based on thermoelectricity and eutectic compound that attached to the outside of the filter can melt paraffin quickly. While the engine is running and the fuel is warm, heat is stored in the eutectic compound. Then, when the user is about to start the engine at low temperature conditions, thermoelectric modules are used to transfer stored heat from the eutectic compound into the fuel, dissolving paraffin thus unblocking the filter. Thermodynamic simulations based on 3D finite element models show that just two minutes after connecting the device, the filter is ready to allow engine start-up. These results are obtained for standard gasoil, which solidifies at -5ºC, and starting the simulations at extreme initial conditions where the filter interior is considered a solid block of paraffin at -20ºC.


Performance Analysis of Thermoelectric Pellets with Non-Constant Cross Sections
Antonio Arenas, Jorge Vázquez, Rafael Palacios
Proceedings of the 7th European Workshop on Thermoelectrics, Paper #26, Oct 2002, Pamplona, SPAIN.

Keywords: Thermoelectricity, Optimal Design, Pellets

Thermoelectricity theory has stated that both, heat absorbed and rejected at the cold and hot sides of a thermoelectric pair by Peltier effect only depends on the thermoelectric properties of the semiconductors, the absolute temperature in the unions, and the electrical current through the pair. However, the irreversible phenomena, Joule and Fourier effect, are volumetric effects. That is to say, they can be affected by the geometry of the pellets, and furthermore, they have an influence on the temperature at the surfaces where the Peltier effect takes place. As consequence, the net heat power pumped by a thermoelectric pair can be modified when non-constant cross section pellets are used. In this paper, variable cross section pellets are studied, analysing the influence on the heat power absorbed, and on the coefficient of performance. Firstly the study of the effect just on the irreversible phenomena, and secondly, taking into account the influence on the irreversible effects together with Peltier effect. This problem has been conveniently studied fixing the volume of the pellets and when the lateral surfaces of pellet are not adiabatic. In this paper the problem has been analysed on a different way. Different geometrical characteristics of the pellets are analysed in order to improve the exchange of heat power at the ends of the pellets evaluating the effect produced in other variables, specially in the volume of the pellets. The lateral surfaces are considered adiabatic taking into account the efforts done by the manufactures of commercial thermoelectric modules to reduce these thermal losses. The results are compared with typical values obtained using constant cross sections. The conclusions obtained in this work can be of interest in the design of thermoelectric pairs in applications where the size of the pellets allows for the use of variable cross sections, or the thermolectric properties are extremely sensitive to temperature variations.


State of the Art of Thermoelectric Generators Based on Heat Recovered from the Exhaust Gases of Automobiles
Jorge Vázquez, Miguel A. Sanz-Bobi, Rafael Palacios, Antonio Arenas
Proceedings of the 7th European Workshop on Thermoelectrics, Paper #17, Oct 2002, Pamplona, SPAIN.

Keywords: Thermoelectricity, Seebeck Effect, Waste Heat, Thermoelectric Generator, Exhaust Gases

The recovering of heat from exhaust gases in automobiles is a typical application of electricity generation using thermoelectricity. This paper is focused on reviewing the main characteristics and evolution of the different investigations performed over the last three decades concerning the use of thermoelectric generation using the heat from the exhaust gases produced in the combustion process of an automobile. The use and evolution of different kinds of thermoelectric materials (silicon germanium, lead telluride and bismuth telluride alloys) will be presented. Also, several main characteristics of the different structures proposed for the thermoelectric generators (TEGs) will be compared. In the review included in this paper, it would be useful to update the potential of thermoelectric generation in the automobile industry nowadays. The results presented can be considered as references of the minimum goals to be reached. Better results can be expected due to the continuous improvement in thermoelectric, thermal and insulating materials.


Cooling system for hermetic devices based on thermoelectricity
Rafael Palacios, Jorge Vázquez, Miguel A. Sanz-Bobi
Sixth European Workshop on Thermoelectrics. Freiburg, Germany. Sep/2001

Cooling systems based on a continuous flow of fresh air are typically used in electronic devices. For applications in adverse environment such us underwater applications of industrial applications using air with a great amount of dust, hermetic devices are needed. The major problem when designing hermetic devices is to provide a proper cooling system. This paper describes different alternatives for cooling hermetic devices. The study was done for a personal computer, evaluating the amount of heat produced during sleep condition and busy condition. Different cooling alternatives are presented: natural convection using standard radiators (for a noiseless system), and forced convection using radiators and fans. Both configurations are compared with the equivalent ones using thermoelectricity to increase the heat transfer between the inside of the hermetic box and the outside environment. It is demonstrated that without thermoelectricity, it is almost impossible to evacuate enough heat because the box of the PC has to be full of radiators. While applying the Peltier effect the heat transfer is highly increased.


An Active Thermal Wall Based on Thermoelectricity
Jorge Vázquez, Miguel A. Sanz-Bobi, Rafael Palacios, Antonio Arenas
Sixth European Workshop on Thermoelectrics. Freiburg, Germany. Sep/2001

This paper describes the basic principles of a new concept for an active thermal wall able to improve the current practice of design and installation of air conditioning for enclosed spaces. The wall is a translucent or transparent flat wall which separates two environments (indoor and outdoor environments) at different temperatures allowing for the control of the desired temperature in one of these environments. This objective is reached using thermoelectric modules imbibed between translucent or transparent materials, such as glass windows, allowing for the transport of heat between the two environments at different temperatures. The most important applications to which the new active wall would be aimed are included within the sector of the thermal conditioning of spaces and heat transmission controlled in industrial machines or environments, substituting the usual installations.

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Bidimensional Analysis of a Thermoelectric Module using Finite Element Techniques
Antonio Arenas, Jorge Vázquez, Rafael Palacios
XIX International Conference on Thermoelectrics.  Cardiff, Wales, United Kingdom. Aug 2000

In this paper an analysis is performed on a thermoelectric module using finite element techniques taking into account the following two hypothesis: thermal and electrical flows are present in two dimensions.
The commercial software tool named ANSYS has been used in order to develop this analysis. This software includes the possibility to analyse jointly the Fourier and Joule effects, but not the Peltier effect. Additional software has been developed in order to include the Peltier effect. The consideration of the three effects at the same time will allow for a better simulation and analysis of the performance of a thermoelectric module.
The ANSYS model developed very closely represents the real configuration of a thermoelectric module. It takes into account the thermoelements, and their electrical bridges and junctions. All the properties of the materials have been considered constant.
Several simulations have been performed using the proposed model. In all cases, the model has become a powerful and flexible tool of analysis able to present detailed numerical and graphical results. Furthermore, the possibility to use this model in more complex structures is a very attractive feature now available. The comparison between the results of this model and the performance of an elemental thermoelement allows the observation of the influence of every component in a thermoelectric module. The model and the main tests performed will be presented in this paper.

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Thermoelectricity Applied to Heating of a Fuel Filter of a Car in a Cold Starting

Jorge Vázquez, Miguel A. Sanz-Bobi, Rafael Palacios, Antonio Arenas
XIX International Conference on Thermoelectrics.  Cardiff, Wales, United Kingdom. Aug 2000
This paper presents the results of an investigation about the use of thermoelectricity in a car fuel filter in order to prevent the problems associated to its obstruction due to the creation of paraffins when the car is stopped for a long time in an environment where the temperature is very low. Also, it describes the main features of a redesign of a conventional car filter in order to include thermoelements able to transfer heat, precisely at the moment of  the car starting, from an eutectic fluid to the cold fuel contained in the filter. Several numerical simulations and performance tests of the new designed car filter will be presented.
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Performance of a Thermoelectric Module Using the Thermodynamic Relationship Temperature-Entropy (T-S)

Antonio Arenas, Jorge Vázquez, Miguel A. Sanz-Bobi, Rafael Palacios
XIX International Conference on Thermoelectrics.  Cardiff, Wales, United Kingdom. Aug 2000

In this paper, the performance of a thermoelectric module is analysed using the thermodynamic diagram Temperature-Entropy. This diagram can be used as a graphical tool which allows for the analysis of thermoelectric processes, both reversible and non-reversible, in an elemental pair or thermoelectric elements.
A similarity is found between the Seebeck coefficient and entropy per unit of electrical charge.  This allows for the use of the Seebeck coefficient and absolute temperature as coordinates in a representative Cartesian system. All processes, both reversible and non-reversible, in a pair of thermoelectric elements can be represented in the above mentioned system.
This analysis is completed with the identification of several graphic elements such as lines and areas, and their association to different equations and thermodynamic relationships of the thermoelectric module performance. This approach is very useful in the analysis of thermoelectric modules as it is performed from an engineering point of view in classical thermodynamics.

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Potential use of small waste heat sources based on thermoelectricity: application to an overhead projector and a battery charger

Miguell A. Sanz-Bobi, Rafael Palacios
Fifth European Workshop on Thermoelectrics, ETS'99. September 1999. Pardubice, Czech Republic. Pg 58-65

A general overview of the potential use of waste heat sources for the generation of energy will be described in this paper. Attention will be specially placed on low and medium levels of heat sources, in particulaar in appliances that are used almost daily. In order to demonstrate the effectiveness of the use of such waste heat sources, two applications are described: the generation of electricity from the heat of an overhead projector and the use of heat sources to charge batteries of domestic equipment such as telephones, radios and security systems.

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Electrical Properties of Commercial Thermoelectric Modules

Rafael Palacios, Ming Zhu Li
Fourth European Workshop on Thermoelectrics, ETS'98. September 1998. Madrid, Spain. Pag. 159-162

One of the most promising applications of thermoelectricity is the recovery of waste heat for the production of electrical energy.  The best performance in electrical power generation is obtained using specially designed TE elements [7][11], but the mass production of Peltier modules leads to an important reduction in prices.  Commercial thermoelectric modules do not have a very high performance but are cheap, robust and easy to install.  TE modules are appropriate for waste heat recovery at low temperatures [8].
This paper shows the results of testing a commercial thermoelectric module for electrical power generation.  All the results have been obtained experimentally using a test bench designed to study commercial TE modules.  Several working conditions have been tested, obtaining voltages up to 2.4 V and currents up to 0.45 A for a single module.  Plots of voltage as a function of the current are shown for different heat transfers (up to 28 W).  Typical VI plots for alkaline batteries and NiCd rechargeable batteries have also been obtained to compare the behavior of the TE module as a voltage generator.

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Thermal properties of commercial thermoelectric modules
Rafael Palacios, Miguel Angel Sanz-Bobi
ICT'97, XVI International Conference on Thermoelectrics. Dresden, Germany, 1997

Thermoelectric semiconductors and the mass production of thermoelectric modules have experienced a big development in the last years, making thermoelectricity attractive for industrial and commercial applications. The design of industrial applications requires deep knowledge about how thermoelectric modules behave. Even in the case of an application designed to work at a certain operating point of the module, it is interesting to evaluate how would it behave at different working conditions. The thermal and electrical characteristics of the commercial thermoelectric modules, provided by the manufacturers, usually represent the optimal working condition or a few points in a narrow area around that point. But the characteristics can not be considered constant, the modules are specially sensitive to the temperature, which is very changeable in real applications and in fact depends on the heat transferred.
This paper shows the results of testing two commercial thermoelectric modules, one is the typical 12V, Tmax=80°C and the other, designed for high temperature, is a 50W, Tmax=200°C. All the results have been obtained experimentally using a test bench designed and built for this purpose. Special procedures were applied in order to be able to control the temperature in both sides of the thermoelectric module during the experiments. A description of the test bench (which is very easy to build for any laboratory) and the procedures for testing modules in a convenient way are also included. The results obtained correspond to a wide range of working conditions: a temperature from 15°C to 190°C, a range of heat power from 10W to 50W, and electric power from 0.1W to 80W.

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Numerical results

Thermoelectricity applied to the cryoconcentration of orange juice
Miguel A. Sanz-Bobi, Rafael Palacios, Antonio Arenas
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Prototype of heat pump based on Peltier effect. Results of performance tests
Rafael Palacios, Miguel A. Sanz-Bobi, José Villar, Antonio Arenas
Second european workshop on thermoelectrics. Nancy, France. Nov/95

Air conditioning based on the Peltier effect has many theoretical advantages over other air conditioning techniques, such us reliability, control... This idea encouraged the development of a research project oriented to study the feasibility of this technique to industrial and domestic applications. In this project an experimental heat pump has been designed and built to study the behavior of Peltier cells in a real application. In this paper experimental results are shown. A brief description of the heat pump, external equipment and sensors used during the tests is included. The methods used to measure physical magnitudes like flows, heats and temperatures are also described. Several working conditions have been tested to study the performance of the heat pump. We mainly regulated the current supplied to the Peltier cells to different levels. Successful experiments, reaching steady temperatures and power exchange, have been carried out for heating and cooling modes. Results of the most relevant experiments, including the values of steady temperatures, flows and heat power, are shown in this paper.

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Application of thermoelectricity to the precess of cryoconcentration of orange juice
Miguel A. Sanz-Bobi, Rafael Palacios
Second european workshop on thermoelectrics. Nancy, France. Nov/95

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Prototype of heat pump based on Peltier effect for applications in ambient temperature conditioning
Miguel A. Sanz-Bobi, Rafael Palacios, José Villar, Antonio Arenas
Proceedings of the XI International Conference on Thermoelectrics. University of Texas, 1992

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Prototipo de bomba de calor por efecto Peltier para aplicaciones de climatización
Miguel A. Sanz-Bobi, Rafael Palacios, José Villar, Antonio Arenas
X Congreso Nacional de Ingeniería Mecánica, Madrid, ESPAÑA. Anales de ingeniería mecánica. Año 9, No.3, sep/92, Pag. 251-253

La refrigeración por efecto Peltier cuenta con grandes ventajas, lo que ha llevado a realizar un proyecto de investigación para estudiar la utilización de estas técnicas en aplicaciones industriales y domésticas. En este proyecto se ha diseñado y construido una bomba de calor experimental con objeto de estudiar el comportamiento de las células Peltier. Actualmente el proyecto se encuentra en fase de experimentación, este artículo describe los criterios de diseño de la bomba.

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Rafael Palacios
Instituto de Investigación Tecnológica
Escuela Técnica Superior de Ingeniería ICAI