Esmaeil Yousefi's research while affiliated with Shahrood University of Technology and other places

Thermoelectric generator systems are often evaluated and studied in open circuit and close circuit modes. In the open circuit case, minimum heat flux passes across the thermoelectric module and the module does not have any thermal losses. Moreover, in the close circuit system, the external consumer is connected to the module and higher heat is pumped from its hot side to cold side. Hence, investigating the effect of external load resistance as the consumer connected to the module on its response is a significant issue in thermoelectric systems. In this study, to evaluate the effect of various consumers (4, 8, 10, 15, 20 and 30 Ω) over the module on discharge time, output voltage and temperature on both sides of the module, thermoelectric systems lacking and containing phase change material as the useful means for energy storage and thermal management of thermoelectric system were designed and exposed to constant heat loads. Results of this study show that the power consumption of the internal resistance of the module (connected to the consumer) led to an increase in the temperature of both sides of the module compared to open circuit systems. Therefore, the thermal balance and temperature distribution over the module changes and more affected. The maximum output power and discharge time were obtained at the external resistance of 4 Ω (close to the average internal resistance of the module) in the studied systems. The phase change material prevented excessive temperature on the hot side during the charging process and provided proper thermal management to enhance voltage generation and discharge time. The thermoelectric generator is an effective technology in starting consumers with low resistance, such as light bulbs and remote controls.

Active cooling of thermoelectric generators (TEGs) by fans or water pumps imposes cooling energy reducing net power generation in TEG systems. This study aims to make zero-cooling energy TEG systems by integration of low temperature phase change material (PCM) and porous copper foam on cold side of the TEG. In this design, air fan is eliminated. To study the proposed system under transient heat input, the TEG system was exposed to continues and dynamic heat flows. Results of this study show that, the proposed fanless heat sink is an effective and alternative cooling solution for TEG systems. Utilization of the copper foam in the PCM not only reduced cold side temperature of the TEG by 11.3 %, but it also prevents hot side of the TEG from overheating. With this cooling technique, output power of the TEG increased 53.5 % compared to conventional TEG systems operating with fan. The results of this study provide a guideline for design of self-sufficient and autonomous TEG systems with zero-cooling energy used for energy harvesting for sensors and actuators under dynamic heat sources.

Phase change materials (PCMs) are useful means for energy storage and thermal management of thermoelectric generators (TEG) systems. Nevertheless, energy storage rate under transient heat loads is slow due to low thermal conductivity of PCMs. In this study, copper and nickel porous metal foams are applied in a PCM on hot side of a TEG to accelerate storage of fusion heat and power output of the TEG under transient boundary conditions. Therefore, continuous and fluctuating heat flows were imposed to the system initiating from ambient room temperature. Results of this study show that, adding the metal foams enhances heat flux through the PCM by reducing overall thermal resistance in the energy storage box. The PCM with copper foam makes higher percentage of increase of temperature in the box and higher power generation until the melting point, while the PCM with nickel provides higher storage temperature after the melting process. The metal foams improve the thermal conductance between the heat source and the TEG creating higher temperature difference across the module and making higher electrical power compared to the case with PCM-only. The corresponding power enhancement is 26.2% and 62.5% by the TEGs with the nickel and copper foams, respectively.

Thermoelectric generator (TEG) systems are often exposed to unstable heat loads with transient temperature boundary conditions. TEG behavior recognition in thermal fluctuations is necessary to increase its efficiency and protection. This research deals with the experimental study of thermoelectric module’s performance under transient thermal boundary conditions. Therefore, three types of novel prototypes of transient heat loads including rectangular, triangular, and sinusoidal were suggested. Also, a phase change material (PCM) was applied inside an aluminum box on the hot side of the module. In the mentioned system, the effect of PCM on the module performance in the unstable heat loads was investigated. Applying PCM led to the protecting the module against temperature fluctuations, storing the energy, and generating effective voltage for a long time after turning the heat source off. Voltage generation lasted for 59.5 min with 90 W input power in 3-min periods in the rectangular heat load. Meanwhile, after switching the heaters off, 42.8- and 50-min voltages were received from triangular and sinusoidal loads, respectively, each with the power ranging from 0 to 90 W in four periods, lasted for 3 min.