BUSCADOR RECOLECTA

Waste heat recovery can apply to a wide range of applications, from transportation, or industries to domestic appliances. Thermoelectric generation technology applied to those cases could produce electrical energy and thus improve their efficiency. A validated computational methodology, which simulates the behavior of any thermoelectric generator and calculates the energy consumption of the auxiliary equipment involved, has been used to determine the potential of waste heat harvesting. The usable energy, the net energy, generated has to be maximized, not only the thermoelectric generation has to be maximized, but also the consumption of the auxiliary equipment has to be minimized, or if possible eliminated. Heat exchangers with a liquid as the heat carrier procure high thermoelectric generations, as their thermal resistances are very low, nevertheless when the consumption of their auxiliary consumption is borne in mind, their use is not that promising. The optimal thermoelectric energy obtained from the flue gases of a real industry using these dissipation systems is 119 MWh/year, while the maximum net energy is 73 MWh/year due to the consumption of the auxiliary equipment. The latest scenario does not only represent a 40% reduction from the optimal thermoelectric generation but also a different optimal working point. The complete elimination of the auxiliary equipment using novel biphasic thermosyphons with free convection at the same application produces a net energy of 128 MWh/year. This novel dissipation technology presents an increase on the thermoelectric generation due to its low thermal resistances, but above all due to the elimination of the auxiliary consumption., 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.

Generally, in the optimization of thermoelectric generators, only the heat exchangers or the thermoelectric modules themselves are taken into account. However, the assembly of the generator as a whole is of vital importance since a bad contact or a thermal bridge can waste the performance of an optimal generator. In this sense, the present chapter analyzes experimentally the use of different interface materials to reduce the thermal contact resistance between the modules and the heat exchangers, the influence of the pressure distribution in the assembly as well as the effect of different insulating materials in order to reduce the thermal bridge between the exchangers. Thus, it has been demonstrated that a good assembly requires the implementation of thermal interface materials to ensure the microscopic contact between the
heat exchangers and the modules, besides a uniform clamping pressure. Nevertheless, since this is normally achieved with screws, they represent a source of thermal bridges in conjunction with the small distance between the exchangers. In order to reduce heat losses due to thermal bridges, which can represent up to one-third of the incoming heat, an increment of the distance between the exchangers and the use of an insulator is recommended., The authors are indebted to the Ministry of Economy, Industry and CompetitivenessGovernment of Spain and FEDER Funds for economic support of this work, included in the
DPI2014-53158-R Research Project, as well as to the FPU Program of the Spanish Ministry of
Education, Culture and Sport (FPU16/05203).

Waste heat generation has a widespread presence into daily applications, however, due to the low-temperature grade which presents, its exploitation with the most common technologies is complicated.
Thermoelectricity presents the possibility of harvesting any temperature grade heat; besides it also includes many other advantages which make thermoelectric generators perfect for generating electric power from waste heat. A prototype divided into two levels along the chimney which uses the waste heat of a combustion has been built. The experimentation has been used to determine the parameters that influence the generation and to validate a generic computational model able to predict the thermoelectric generation of any application, but specially applications where waste heat is harvested.
The temperature and mass flow of the flue gases and the load resistance determine the generation, and consequently, these parameters have been included into the model, among many others. This computational model incorporates all the elements included into the generators (heat exchangers, ceramics, unions) and all the thermoelectric phenomena and moreover, it takes into account the temperature loss of the flue gases while circulating along the thermoelectric generator. The built prototype presents a 65 % reduction in the generation of the two levels of the thermoelectric generator due to the temperature loss of the flue gases. The general computational model predicts the thermoelectric generation with an accuracy of the ±12 %., 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.

Despite being one of the largest renewable sources, geothermal energy is not widely utilized for electricity generation. In order to leverage shallow hot dry rock (HDR) fields, the present paper proposes an alternative to enhanced geothermal systems (EGS): thermoelectric generators. Based on the conditions of Timanfaya National Park, a prototype has been built to experimentally analyze the feasibility of the proposed solution. The prototype is composed by a two phase closed thermosyphon (TPCT) as hot side heat exchanger, two thermoelectric modules, and it considers different cold side heat exchangers: fin dissipators assisted by a fan and loop thermosyphons, both with various geometries. Experiments have demonstrated that loop thermosyphons represent the best alternative due to their low thermal resistance and, especially, due to their lack of auxiliary consumption, leading to a maximum net power generation of 3.29 W per module with a temperature difference of 180 °C (200 °C in the hot side and 20 °C as ambient temperature), 54% more than with fin dissipators. Hence, there exists a new opportunity for electricity generation in shallow hot dry rock fields: thermoelectric generators with biphasic thermosyphons as heat exchangers, a patented and robust solution., The authors would like to acknowledge the support of the Spanish State Research Agency and FEDER-UE under the grants DPI2014-53158-R and RTC-2017-6628-3 ; as well as the FPU Program of the Spanish Ministry of Science, Innovation and Universities (FPU16/05203 ).

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.

The nZEB standards reduce the energy demand of these buildings to a minimum, obtaining this little energy from renewable resources. Taking these aspect into consideration, a thermoelectric cooler-heat pump is proposed to achieve the comfort temperature along the whole year. The same device can provide heat in winter and it can cool down the buildings in summer just by switching the voltage supply polarity. Heat pipes are studied to work on both sides of the thermoelectric modules in order to optimize the heat transfer as these devices present really good thermal resistances and they can work in any position. However, they present pretty different thermal resistances if they work on the cold or on the hot side of the modules. A methodology to thermally characterize these heat exchangers working in both orientations is proposed and a validated computational model is developed to optimize the thermoelectric cooler-heat pump for a nZEB application. The number of thermoelectric modules, the position of the device, the ambient temperature and the air mass flow determine the operation and consequently they need to be studied in order to optimize the application., 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.

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.

La situación energética actual y todos los problemas medioambientales,
políticos y económicos asociados a ella, hacen cada vez más necesaria una
optimización de los sistemas de generación eléctrica y una incorporación de
medidas de ahorro energético a los procesos, que contribuyen en gran parte
a una reducción de la demanda de energía y a un mayor aprovechamiento de
los recursos. En este sentido, son muchos los investigadores que han puesto
el foco en la recuperación del llamado calor residual, una energía de desecho
obtenida como subproducto no aprovechado de distintos procesos.
Esta tesis doctoral estudia el aprovechamiento de energía residual a través
de generadores termoeléctricos basados en el efecto Seebeck. Estos sistemas
son capaces de producir energía eléctrica a partir de una fuente de calor y
una de las formas de optimización es mediante el diseño adecuado de los
intercambiadores de calor incluidos. Los intercambiadores tratan de acercar
la temperatura de las caras de los módulos a la de los respectivos focos y
tienen un efecto directo en la producción eléctrica.
Se propone la utilización de un intercambiador de calor pasivo con sistema
termosifón y cambio de fase como disipador de la parte fría de los sistemas
termoeléctricos. Para llevar a cabo su optimización, se ha desarrollado un modelo computacional de simulación que predice el comportamiento de estos
sistemas y permite evaluar la influencia de las características geométricas que
lo definen. Este modelo es capaz de simular estos sistemas con desviaciones
menores del ± 9%.
Tras este desarrollo, se ha utilizado la herramienta computacional para
el diseño de un termosifón bifásico que pueda ser acoplado en la parte fría
de un prototipo de generador termoeléctrico instalado en el conducto de los
gases de salida de una caldera de combustión. Los resultados experimentales
han revelado que se puede llegar a generar 240W=m2 utilizando este sistema
pasivo, lo que supone una mejora de casi un 83% frente a la utilización de un
disipador de aletas convencional con un ventilador en las mismas condiciones
de funcionamiento.
Se ha realizado, también, un estudio de la implantación de generadores
termoeléctricos en un proceso industrial real. Para ello, se ha desarrollado,
previamente, un modelo computacional que tenga en cuenta, no solo el funcionamiento
de los módulos termoeléctricos, sino que también considere el
enfriamiento que sufre la corriente de gases al circular por el conducto del
generador e integre los termosifones bifásicos como sistema de disipación del
lado frío. Una vez realizada la optimización de estos sistemas, se ha demostrado
la posibilidad de generar un total de 363MWh en un año de funcionamiento.
También se ha elaborado un análisis que pretende probar la viabilidad
económica de esta inversión alcanzándose un coste de instalación de 10€/W.
Los resultados derivados de esta tesis demuestran que la termoelectricidad
puede jugar un papel importante en el objetivo global de generación de electricidad
de forma sostenible, que permita combatir con los efectos del cambio
climático, debido a su capacidad de aprovechamiento energía residual., The current energy situation and the environmental, political and economic
issues associated to it, lead to a necessity of an optimisation in the
power generation technologies and to an implementation of energy saving
measures that could reduce the energy demand and could increase the exploitation
of resources. With this in mind, there are many investigations focused
on waste-heat recovery, byproduct energy obtained from a wide range
of processes.
This doctoral thesis tackles this by using thermoelectric generators, based
on the Seebeck effect, that can harvest waste-heat and transform it into electric
power. These devices can be enhanced by an optimisation of the heat
exchangers used at both sides of the thermoelectric modules, which have a
direct impact on the power generated.
A passive heat exchanger based on thermosyphon effect and phase change
is proposed as the heat sink for the cold part of a thermoelectric generator.
A computational model has been developed to predict the behaviour and to
optimise these kinds of systems. The model predicts the thermal resistance of
the heat exchanger with a relative error below ±9%. After this development, a new biphasic thermosyphon has been designed
and built to be installed at the cold side of a thermoelectric generator placed at
the exhaust flue in a combustion chamber. By using this kind of passive dissipater,
the experimental results show a maximum electric power generation of
240W=m2 of duct area occupied, achieving an increase of almost a 83% from
the power produced by a thermoelectric generator that uses a conventional
finned heat sink with a fan under the same working conditions.
Moreover, a computational study about the implementation of thermoelectric
generators to recover waste-heat from an industrial process in a real manufacturing
plant has been carried out. A simulation tool has been developed
considering not only the performance of the thermoelectric modules, but also
the temperature drop of the flue gasses that occurs all along the duct where
the generators are located, including biphasic thermosyphons at the cold side
of the system as well. After an optimisation of the elements, the results show
an electric energy generation potential of about 363MWh in one year. An
economic analysis has also been made, reaching an installation cost of these
generators of 10€/W.
The results obtained from this thesis prove the vital role that thermoelectric
generation can play fighting against climate change, by harnessing waste
heat to produce electricity in a more sustainable way and helping to increase
the efficiency of the processes., Ministerio de Economía y Competitividad, proyecto de investigación DPI2014-53158-R, titulado "Sistemas de Generación Eléctrica a partir de calor residual: aplicación al aprovechamiento de los humos en chimeneas domésticas e industriales (SIGER)" y enmarcado dentro del Programa Estatal de Investigación, Desarrollo e Innovación Orientada a los Retos de la Sociedad, Plan Estatal de I+D+I 2013-2016., Programa de Doctorado en Tecnologías de las Comunicaciones, Bioingeniería y de las Energías Renovables (RD 99/2011), Bioingeniaritzako eta Komunikazioen eta Energia Berriztagarrien Teknologietako Doktoretza Programa (ED 99/2011)

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.

Thermoelectric self-cooling was firstly conceived to increase, without electricity consumption, the
cooling power of passive cooling systems. This paper studies the combination of heat pipe exchangers
and thermoelectric self-cooling, and demonstrates its applicability to the cooling of power electronics.
Experimental tests indicate that source-to-ambient thermal resistance reduces by around 30% when
thermoelectric self-cooling system is installed, compared to that of the heat pipe exchanger under
natural convection. Neither additional electric power nor cooling fluids are required. This thermal
resistance reaches 0.346 K/W for a heat flux of 24.1 kW/m2, being one order of magnitude lower than
that obtained in previous designs. In addition, the system adapts to the cooling demand, reducing this
thermal resistance for increasing heat.
Simulation tests have indicated that simple system modifications allow relevant improvements in the
cooling power. Replacement of a thermoelectric module with a thermal bridge leads to 33.54 kW/m2 of
top cooling power. Likewise, thermoelectric modules with shorter legs and higher number of pairs lead
to a top cooling power of 44.17 kW/m2. These results demonstrate the applicability of thermoelectric
self-cooling to power electronics., The authors would like to thank the Spanish Ministry of Economy
and Competitiveness (DPI2014-53158-R) and FEDER Funds
(European Union) for supporting this work.

La presente tesis doctoral estudia el aprovechamiento del calor residual mediante generación termoeléctrica para la obtención de potencia eléctrica generada gracias al efecto Seebeck. Dos son las aproximaciones empleadas, la simulación computacional, empleando variables obtenidas experimentalmente y la experimentación de escenarios reales. Ambas dos han obtenido valores muy prometedores para la generación eléctrica a través de los gases residuales.
Con el desarrollo de esta tesis doctoral, se contribuye en gran medida al aumento de la eficiencia energética de los procesos industriales, así como a la reducción de la emisión de gases contaminantes al ambiente, aportando su granito de arena a la sostenibilidad del sistema energético., This doctoral thesis studies the exploitation of the waste heat to obtain electrical power by the Seebeck e˙ect that takes part inside the thermoelectric generators. Two are the approaches used, the computational simulation, through experimentally obtained variables, and the experimentation of real scenarios. Both of them have obtained really promising results in thermoelectric generation obtained from residual flue gases.
To conclude, the development of this doctoral thesis, contributes to a large degree, in the increase of the energetic eÿciency of the industrial processes, as well as reduces the polluting gases emissions to the ambient, helping to achieve a sustainable energetic model., Esta tesis doctoral ha recibido financiamiento del proyecto de investigación DPI2011-24287 "Generación Termoeléctrica con Energía Calorífica Residual (GETER)" perteneciente al Plan Nacional de I+D+I 2008-2011 y del proyecto de investigación DPI2014-53158-R "Sistemas de Generación Eléctrica a partir de calor Residual: aplicación al aprovechamiento de los humos en chimeneas domésticas e industriales (SIGER)", enmarcado dentro del Programa Estatal de Investigación, Desarrollo e Innovación Orientada a los Retos de la Sociedad, Plan Estatal de I+D+I 2013-2016., Programa de Doctorado en Ciencias y Tecnologías Industriales (RD 99/2011), Industria Zientzietako eta Teknologietako Doktoretza Programa (ED 99/2011)