D. Astrain

Numerical modelling and a design of a thermoelectric dehumidifier

A prototype dehumidifier was designed and built based on thermoelectric cooling technology. A computational calculation model based on electric analogy was used in the devices design and optimisation (AERO), meaning that effects occurring inside the equipment, such as heat transfer, thermoelectric effects and the phase change which occurs during condensation and evaporation could be solved simultaneously. The thermoelectric dehumidifier prototype was built after performing several simulations using this calculation model. Numerous tests were carried out in order to optimise the Peltier pellet and fan supply voltages in experimental conditions. The prototype was also compared to conventional vapour-compression systems, thermoelectricity showing significant potential in the field.

Computational Study on Temperature Control Systems for Thermoelectric Refrigerators

Thermoelectric refrigeration has the outstanding advantage of allowing accurate temperature control. However, on the market there are thermoelectric refrigerators which include on/off temperature control systems, because of their simplicity and low cost. The major problem with this system is that, when the thermoelectric modules are switched off, the heat stored in the heat exchanger at the hot end of the modules goes back into the refrigerator, forming a thermal bridge. In this work, we use a computational model, presented and validated in previous papers, to study alternative control systems. A new system is introduced based on idling voltages; that is, once the temperature of the refrigerator reaches the lower limit, the thermoelectric modules are not switched off but supplied with minimum voltage. Computational results prove that this system reduces the electric power consumption of the refrigerator by at least 40% with respect to that obtained with on/off control systems, and the coefficient of performance increases close to the maximum provided by any other control system.

Reduction in the Electric Power Consumption of a Thermoelectric Refrigerator by Experimental Optimization of the Temperature Controller

Most thermoelectric refrigerators used for food conservation are operated by on/off temperature controllers, because of their simplicity and low cost. This type of controller poses a major problem: when the inner temperature reaches the lower setpoint and the thermoelectric modules are switched off, a great amount of the heat stored in the heat exchanger at the hot end of the modules goes back into the refrigerator, by heat conduction through the modules and the heat extender. This effect significantly increases the electric power consumption of the refrigerator. This work studies experimentally the influence of different temperature control systems on the electric power consumption and coefficient of performance of a thermoelectric refrigerator: an on/off controller, a proportional–integral–derivative controller, and a novel operating system based on idling voltages. The latter provides voltage to the modules once the inner temperature reaches the lower setpoint, instead of switching them off, preventing heat from going back. A prototype has been constructed to compare these operating systems. Results prove that the controller based on idling voltages reduces the electric power consumption of the refrigerator by 32% and increases the coefficient of performance by 64%, compared with the on/off controller.

Thermoelectric Self-Cooling System to Protect Solar Collectors from Overheating

Solar collectors for water heating have spread rapidly in recent years, as their use saves significant amounts of fuel and electricity. One of the main problems with these systems is overheating of the internal fluid, which takes place when an enormous amount of heat is collected but the demand for hot water is low, resulting in high-pressure, high-temperature conditions that damage some of the components. Nowadays, most such systems include either static or dynamic dissipators that remove excess heat. This paper presents a thermoelectric self-cooling system designed to dissipate excess heat from a solar-collector system and prevent overheating of the internal fluid. Thermoelectric self-cooling (TSC) is a novel thermoelectric application, proven to enhance the cooling of any heat-generating device without electricity consumption. This paper presents the design and computational study of a TSC system, pointing out that the most important parameters are the thermal resistances of the heat exchangers, and that their reduction significantly improves the performance of the thermoelectric system. The final design outperforms currently used static and dynamic dissipators, increasing the heat transfer coefficient by more than 50% and requiring no electricity, representing a promising alternative to prevent overheating of solar collectors.

Study of Complete Thermoelectric Generator Behavior Including Water-to-Ambient Heat Dissipation on the Cold Side

Reduction of the thermal resistances of the heat exchangers of a thermoelectric generation (TEG) system leads to a significant increase in TEG efficiency. For the cold side of a thermoelectric module (TEM), a wide range of heat exchangers have been studied, from simple finned dissipators to more complex water (water–glycol) heat exchangers. As the Nusselt number is much higher in water heat exchangers than in conventional air finned dissipators, the convective thermal resistances are better. However, to conclude which heat exchanger leads to higher efficiencies, it is necessary to include the whole system involved in the heat dissipation, i.e., the TEM-to-water heat exchanger, the water-to-ambient heat exchanger, as well as the required pumps and fans. This paper presents a dynamic computational model able to simulate the complete behavior of a TEG, including both heat exchangers. The model uses the heat transfer and hydraulic equations to compute the TEM-to-water and water-to-ambient thermal resistances, along with the resistance of the hot-side heat exchanger at different operating conditions. Likewise, the model includes all the thermoelectric effects with temperature-dependent properties. The model calculates the net power generation for different configurations, providing a methodology to design and optimize the heat exchange in order to maximize the net power generation for a wide variety of TEGs.

Experimental Study and Optimization of Thermoelectricity-Driven Autonomous Sensors for the Chimney of a Biomass Power Plant

In the work discussed in this paper a thermoelectric generator was developed to harness waste heat from the exhaust gas of a boiler in a biomass power plant and thus generate electric power to operate a flowmeter installed in the chimney, to make it autonomous. The main objective was to conduct an experimental study to optimize a previous design obtained after computational work based on a simulation model for thermoelectric generators. First, several places inside and outside the chimney were considered as sites for the thermoelectricity-driven autonomous sensor. Second, the thermoelectric generator was built and tested to assess the effect of the cold-side heat exchanger on the electric power, power consumption by the flowmeter, and transmission frequency. These tests provided the best configuration for the heat exchanger, which met the transmission requirements for different working conditions. The final design is able to transmit every second and requires neither batteries nor electric wires. It is a promising application in the field of thermoelectric generation.