Hot Side Temperature Research Articles

Self-powered wireless sensor system utilizing a thermoelectric generator for photovoltaic module monitoring application

In this work, we demonstrate a self-powered wireless PV module monitoring system that utilizes a thermoelectric generator (TEG) to convert residual thermal energy from the PV module into electrical power. We investigated the TEG performance with and without the heat sink. Results show that the temperature difference between the hot and cold sides of the TEG increased to 7.2 °C with the heat sink, compared to only 1 °C without it, at a hot side temperature of 50 °C. We integrated the TEG/heat sink with the PV module, which served as the heat source, achieving a maximum output power of 0.981 mW at a voltage of 0.06 V under a temperature gradient of 3.6 °C in a 1 sun condition. We successfully demonstrated a self-powered wireless PV monitoring sensor system by integrating a step-up voltage converter, microcontroller, IR thermometer, Bluetooth communication module, and the TEG/heat sink, which generated sufficient power for the monitoring system operation. The findings introduce a novel solution for wireless PV module monitoring that operates independently of grid connections or battery power. This innovation not only signifies advancements in renewable energy management but also opens new opportunities in the Internet of Things (IoT) sector.

High-Voltage Thermocell Modules for Direct Device Operation: Eliminating the Need for DC-DC Converters

Abstract This study explores the potential of thermocells as an efficient energy-harvesting solution that can power practical devices without the need for a DC-DC converter. We constructed thermocell devices comprising 35 legs using a modified soldering technique and electrode treatment to improve reliability. The devices achieved a peak voltage of 3.5 V at a hot-side temperature of 60°C under natural cooling conditions. These thermocells were integrated with a voltage detector integrated circuit (IC) and beacon, initiating beacon operation within 100 seconds and transmitting signals over 600 times within a 15-minute period. Our findings demonstrate the feasibility of thermocells as an alternative energy source, offering a cost-effective and streamlined approach for energy-harvesting applications without the complexity and expense of DC-DC converters.

Theoretical analysis of the optimal ejector operation and design within an ejector-based refrigeration system

Optimal operation and design of ejectors are the subject of recent concerns, especially for the enhancement of refrigeration and heat pump cycles based on natural refrigerants like carbon dioxide. In this study, a thermodynamic analysis of an ejector-based refrigeration cycle is performed to determine both what operating pressures lead to the highest physically possible performance depending on the ambient conditions, and what are the main dimensions of the ejector leading to the best performance at a given ambient temperature. A state-of-the-art thermodynamic model for the prediction of the ejector performance is for the first time utilized to generate reliable operation and performance maps of the ejector cycle. Most notably, it is found that the optimal coefficient of performance is not necessarily found when the ejector operates at critical conditions but mostly when the device is under off-design regime, depending on the ejector internal efficiency and the hot side temperature. In addition, the analysis reveals that the performance of the cycle is not highly sensitive to the throat area ratio of the ejector given that the latter lies within an acceptable range. Those findings contribute to getting a better understanding of how the cycle benefits from the ejector and define design and control strategies for the cycle.

Strong and efficient bismuth telluride-based thermoelectrics for Peltier microcoolers.

Thermoelectric Peltier coolers (PCs) are being increasingly used as temperature stabilizers for optoelectronic devices. Increasing integration drives PC miniaturization, requiring thermoelectric materials with good strength. We demonstrate a simultaneous gain of thermoelectric and mechanical performance in (Bi, Sb)2Te3, and successfully fabricate micro PCs (2×2mm2 cross-section) that show excellent maximum cooling temperature difference of 89.3K with a hot-side temperature of 348K. A multi-step process involving annealing, hot-forging and composition design, is developed to modify the atomic defects and nano- and microstructures. The peak ZT is improved to ∼1.50 at 348K, and the flexural and compressive strengths are significantly enhanced to ∼140MPa and ∼224MPa, respectively. These achievements hold great potential for advancing solid-state refrigeration technology in small spaces.

Thermoelectric generators versus photovoltaic solar panels: Power and cost analysis

In the current study, the concept of building a power plant using thermoelectric generator (TEG) modules is investigated, both technically and economically. The hypothesized thermoelectric generation power plant is a modular system, consisting of a large array of electrically connected thermoelectric generator units for generating clean electricity with-out greenhouse gas (GHG) emissions, noise, or hazardous solid wastes. The envisioned thermoelectric generation power plant (TEGPP) considered here is assumed to utilize solar radiation as a heat source, and water as a heat sink. The viability of such a concept is examined in the current study based on available specifications of a high-output thermo-electric generator module released in the market (TEG1-24111-6.0). Benchmarking is car-ried out considering a high-efficiency photovoltaic (PV) panel in the market (SunPower SPR-MAX3-400), assuming that it operates under standard solar radiation of 1,000 W, and with a standard panel temperature of 25 C, causing it to give an output electric power of 400 W (DC or direct current). It is found that in order to have an electric power of a thermoelectric generator unit similar to that of a photovoltaic panel of equal surface area, the temperature at the hot side of the thermoelectric generator unit should be about 70 C if the cold-side temperature is 30 C. However; under this output power equiva-lence, the price of the thermoelectric generator unit is about 90 times that of a photovol-taic panel of equal size (based on prices of October 2023). At an elevated hot-side tem-perature of 300 C for the thermoelectric generator unit (with the cold-side temperature being still 30 C), the thermoelectric generator unit can generate electric power that is about 25 times the power generated by a photovoltaic panel of an equal geometric area. This big boost in the output power still does not counteract the large cost difference be-tween the thermoelectric generator technology and the photovoltaic technology, where the per-watt(electric) cost in the case of thermoelectric generators is 3.5 times its value in the case of photovoltaic panels. Thus, the TEG technology in its intensified generation mode is still relatively more expensive compared to the PV technology. The practical im-plications of the current study are excluding the thermoelectric generation (based on the Seebeck effect) concept from large-scale commercial power plants, and viewing thermoe-lectric generators as sources of small electric power for waste heat management or con-venient power sources for small mobile devices.

Enhanced Peltier refrigerator using an innovative hot-side heat-rejection mechanism; Experimental study under both transient and steady-state conditions

Peltier refrigerators are an environmentally friendly cooling method, as they require no refrigerants and have no moving parts. However, effective cooling requires optimal-strong heat rejection from the hot side of the Peltier module. This research proposes and tests a self-capillary ultra-thin (0.1 mm) water-attracting coated PVC membrane (SCCP) as an innovative effective heat rejection mechanism. The SCCP cools the hot side of the Peltier module to temperatures even lower than ambient air, without external power. The cooling effect is achieved through the evaporation of a thin water film on the hot surface, driven by capillary action, which releases latent heat. This process can occur under natural or forced convection, both of which are investigated under various voltage and temperature conditions. The SCCP method was compared to traditional heatsinks and showed superior performance, with the hot side temperature being not only cooler than that in heatsink mode but also cooler than the ambient temperature in most cases. Additionally, the SCCP method demonstrated reduced sensitivity to ambient temperature changes, with only a 2–3° increase in the hot side temperature when the ambient temperature was raised by 10°. The findings suggest that SCCP is a promising technique, with further results discussed.

Operation map of a traveling-wave thermoacoustic electric generator with variable resistive-capacitive electric loads.

A toroidal-topology traveling-wave thermoacoustic electric generator (TWTEG) is developed. It consists of a traveling-wave thermoacoustic engine, two linear alternators connected in parallel, and sets of variable resistive-capacitive (R-C) external electric loads, in conjunction with accessories and instrumentation required for experimental investigations. The working medium is helium with a static absolute pressure that varies from 25 bars to 30 bars. A detailed description of the thermal design of the heat exchangers is presented. Sustainable operation of the TWTEG is achieved over a range of external R-C loads at different imposed hot-side temperatures and mean gas pressures. The performance parameters are measured for different experimental conditions and compared with a developed lumped-element model. The comparison between the experimental results and predictions reveals a good agreement. The impedance matching between the thermoacoustic engine and the linear alternators is investigated experimentally over a wide range of external R-C loads. The external R-C loads play a crucial role in the operation of the TWTEG. The mean gas pressure changes the operating frequency; however, it has no significant influence on the operating range of the TWTEG on the R-C load map. Increasing the hot-side temperature improves the thermal-to-acoustic efficiency and extends the operating region into larger regions.

Design, optimization and operation of a high power thermomagnetic harvester

Converting low temperature waste heat to electricity is vital for the green transition. Here we present how to design and optimize a thermomagnetic energy harvester that can convert a stream of waste heat to electricity through Faradays law. In optimizing the design in the traditional figure-of-eight shape, we determine the ideal size of the magnet and the beds of magnetic material using a numerical model given an overall volume constraint for each of the thermomagnetic volumes of 20 cm3. The magnet is determined to ideally be 5×5×1.25 cm, the beds should have a height of 1.09 cm and contain about 120 g of Gd spheres, and we use coils with a wire diameter of 1.8 mm and 156 windings in each coil. Following the design study, the system is realized using off-the-shelf components and tested as a function of flow rate, frequency of operation and temperature span. At a temperature span of 40 °C and a hot side temperature of 40 °C, the device produces 9 mW of power at a flow rate of 1.4 L/min.

Investigation on the linear cooling method of microfluidic chip based on thermoelectric cooler

Precise temperature regulation is a crucial guarantee for many microfluidic analyses. This study presents a linear cooling method of microfluidic chips based on a single TEC, which can achieve synchronous observation of samples. A numerical model was developed and experimentally verified to analyze the temperature responses under different driving current mechanisms of TEC. Based on simulation and experimental analysis, this study proposes to achieve linear cooling based on TEC driven by polynomial function current mechanism. The implementation process is clarified, and the iterative method to obtain the polynomial function current mechanism is provided and elaborated. Using a commercial TEC, the linear cooling of the microfluidic chip from 25.2 °C to −19.7 °C was successfully achieved through both simulation and experiment. The linear cooling rates ranging from 24 °C/min to 41 °C/min with linearity higher than 0.998 were obtained. Moreover, the influencing factors of linear cooling were discussed. It is found that the temperature of the TEC hot side has a significant impact on the linear cooling of the sample cell, while the impact of nitrogen gas temperature is almost negligible. Results also indicate that both the minimum and maximum cooling rates increase as TE-element length increases and TE-element height decreases.

Computational study of pulse current and thermal stress on thermoelectric cooler

The thermal performance of a Peltier thermoelectric cooler (TEC) can be enhanced by multi-staging, modifying the geometry of the thermoelement, and using new material with improved thermoelectric properties. This study utilizes COMSOL multiphysics to simulate thermomechanical analyses of various geometries of thermoelectric coolers under pulse current conditions. This investigation explores the influence of pulse current parameters, such as pulse width, pulse ratio, and hot-side convective heat transfer coefficient, on a thermoelectric cooler with different leg geometries. Additionally, the impact of the TEC cold-side temperature, hot-side temperature, and thermal stress on both sides is discussed. The results indicate that TEC leg shapes, such as pin and trapezoid, exhibit the minimum cold-side temperature. Increasing the pulse ratio leads to a decrease in the cold-side temperature and an increase in the hot-side temperature. A notable improvement in the cold-side temperature is also observed with higher pulse ratios, with the pin geometry achieving a minimum cold-side temperature of 276 K. Furthermore, the cooling load affects the temperature on both sides of the TEC. These findings provide valuable insights for optimizing thermoelectric coolers for electronic cooling applications using pulse current methods.

Thermal flow and thermoelectricity characteristics in a sandwich flat plate thermoelectric power generation device under diesel engine exhaust conditions

Thermoelectric power generation (TEG) technology can be used to recover exhaust waste heat, but its effective application is restricted by bulky size and low thermoelectric conversion efficiency. The compactness evaluation of thermoelectric devices characterized by the power density is lacking. In this paper, a three-dimensional thermal flow and thermoelectricity multi-physics field model of a sandwich flat plate TEG device with multi-layer thermoelectric modules (TEMs) was established. An engine thermoelectric recovery bench test was carried out to verify the model and present the thermal parameters and output performance. The thermal, flow and electrical field distributions of the TEG device, as well as voltage, power and conversion efficiency with engine loads, and power density, were presented. The results show that the hot side temperatures, voltages and powers for each thermoelectric module (TEM) are greatly affected by the position occupied by the TEMs and engine loads. At full load and the coolant flow of 8.5 L/min, the device achieves the peak values of the power of 80.9 W and thermoelectric efficiency of 2.1 %, respectively. The device shows good compactness with the power density of 19.8 kW/m3, attributed to the reasonable arrangement of the collectors, coolers, and TEMs. This work can provide some insights of the relationship between the structural form and size, thermal parameters, electrical parameters and conversion efficiency of the sandwich type TEG device.

Improving the Long-Term Stability of PbTe-Based Thermoelectric Modules: From Nanostructures to Packaged Module Architecture.

Nanostructured lead telluride PbTe is among the best-performing thermoelectric materials, for both p- and n-types, for intermediate temperature applications. However, the fabrication of power-generating modules based on nanostructured PbTe still faces challenges related to the stability of the materials, especially nanoprecipitates, and the bonding of electric contacts. In this study, in situ high-temperature transmission electron microscopy observation confirmed the stability of nanoprecipitates in p-type Pb0.973Na0.02Ge0.007Te up to at least ∼786 K. Then, a new architecture for a packaged module was developed for improving durability, preventing unwanted interaction between thermoelectric materials and electrodes, and for reducing thermal stress-induced crack formation. Finite element method simulations of thermal stresses and power generation characteristics were utilized to optimize the new module architecture. Legs of nanostructured p-type Pb0.973Na0.02Ge0.007Te (maximum zT ∼ 2.2 at 795 K) and nanostructured n-type Pb0.98Ga0.02Te (maximum zT ∼ 1.5 at 748 K) were stacked with flexible Fe-foil diffusion barrier layers and Ag-foil-interconnecting electrodes forming stable interfaces between electrodes and PbTe in the packaged module. For the bare module, a maximum conversion efficiency of ∼6.8% was obtained for a temperature difference of ∼480 K. Only ∼3% reduction in output power and efficiency was found after long-term operation of the bare module for ∼740 h (∼31 days) at a hot-side temperature of ∼673 K, demonstrating good long-term stability.

Compact heat pipe heat exchanger for waste heat recovery within a low-temperature range

Heat pipe heat exchangers (HPHX) are attracting attention for being capable of effective heat exchange through phase change. Much waste heat is generated at low-temperature sources, but there has been a lack of research on this. Most previous studies focus on large HPHXs over 1 m in length. In the present study, a compact HPHX (185 × 70 × 140 mm3) with nine heat pipes was fabricated, and the potential for waste heat recovery (WHR) was investigated at low heat sources. Also, the thermal performance of the HPHX was compared with and without the fin of the heat pipe. Experiments were conducted by changing the hot-side gas temperatures (50, 75, 100, and 125 °C) and mass flow rates (0.03, 0.04, and 0.05 kg/s). The heat transfer rate and pressure loss had a linear relationship with the hot-side temperature and mass flow rate. Despite a low temperature 50 °C, more than 100 W of heat can be recovered using a compact HPHX. At least 1.8 times improved thermal performance was obtained in HPHX in which finned heat pipes were installed. These results are expected to serve as indicators for various applications that generate low-temperature waste heat, such as clothes dryers and kitchen hoods.

A novel mathematical optimization method to obtain the maximum-power electrical configuration of thermoelectric generators for energy harvesting

Waste thermal energy recovery with thermoelectric generators has been widely studied as a method to make systems that produce hot exhaust gases, such as aircrafts, ground vehicles and factories, more sustainable. In this type of applications, the mismatch in hot and cold side temperatures of thermoelectric modules (TEMs) creates a mismatch in the electrical output. For each situation, there is a certain electrical interconnection between the modules that gives the maximum global power output. Three optimization models to find what is the best way of connecting the TEMs without a trial-and-error process, as usually done in previous literature, based on mathematical programming are proposed: single branch of series-connected TEMs, multiple parallel-connected branches of series-connected TEMs, and multiple groups of independent series-connected TEMs. The main novel contributions of this paper are: (i) a mathematical optimization approach that provides how to connect the thermoelectric modules one by one, (ii) the application of the above-mentioned method in a common case study: an automotive thermoelectric generator, (iii) information about how the optimal connection between modules changes if the heat source changes its operation (iv) a method for selecting a fixed optimal connection even when the heat source operation changes, e.g. different operation modes in a thermal engine, based on introducing weighting parameters in the optimization mathematical model. The optimization approach followed here is novel and has not been applied before to thermoelectric generators.

High cooling and power generation performance of α-MgAgSb with intrinsic low lattice thermal conductivity

α-MgAgSb is a promising near-room temperature thermoelectric material, characterized by its intrinsically low lattice thermal conductivity, a feature attributed to the significant atomic mass contrast and complex crystal structure. In this work, we achieved respective zTavg values of 0.58 in the temperature range of 150–300 K and 1.22 in the range of 300–550 K for α-MgAgSb, indicating exceptional potential for both cooling and power generation applications. Additionally, through the reduction of cross-sectional size, the stability of MgAgSb/Ag interface was enhanced under high temperature, which is crucial for the practical application of thermoelectric module. To verify the property of α-MgAgSb material, a 7-pair MgAgSb/Bi2Te3 module was fabricated, demonstrating a maximum cooling temperature difference ΔTmax of 60 K at hot-side temperature of 300 K and a power generation efficiency ηmax of 7.2 % with ΔT of 275 K. This work paves the way for the application of Mg-based thermoelectric materials.

ANALYSIS THE EFFECTIVENESS OF THERMOELECTRIC POWER GENERATION USING WASTE HEAT RECOVERY

Non-renewable energy resources, which account for about 85% of worlds’ energy (68% fossil fuels are used for electric power generation), are getting exhausted rapidly. As predicted by the Institute of Sustainable Energy Policies, by the year 2050, only 33% of non-renewable energy resources will be available for electric power generation. Hence, to meet the required demand, the remaining 67% has to be replaced by renewable energy sources. This demand in electric power generation has to be met by a pollution free, low-cost, clean energy resource, which is the need of the hour. The present research targets towards two main applications for generating power using the biomass energy based resources. They are domestic based application – burning biomass wood and utilizing the heat for generating power, industrial based application – combustion of gasified de-oiled Pongamia cake and utilizing the heat energy for generating power In order to achieve the proposed target, initially, the theoretical modeling on the performance of (Bi2Te3-PbTe) hybrid thermoelectric generator (TEG) composed of n-type Bismuth Telluride - p-type Lead Telluride semiconductor materials has been done. The effect of different performance parameters on the maximum conversion and power efficiencies have been theoretically analyzed by varying the hot side temperature. Key Words: Hybrid Thermoelectric Generator, Electric Power Generation, Graphene Nanoparticles.

Evaluation of energy efficiency of thermoelectric energy generator system with heat pipes, solar tracker, Fresnel lens and nano-particle fluids

This study investigated the limits of electrical energy production from a thermoelectric generator in a high thermal efficiency system using pure water and nanofluids called aluminum oxide and titanium dioxide. It was aim to provide efficient thermal performance by using a Fresnel lens, solar glass tube, heat pipe and tracking system. Experimental measurements were made between 10:00 and 14:00 on July 26 and 27 in 2023. On each measurement day, the system containing pure water and a nanofluid was compared. The values of parameters such as temperature, solar radiation, wind speed and Thermoelectric Generator (TEG) open circuit voltage were measured instantaneously during the measurements. These data were used to calculate thermal resistance, electrical efficiency and output power. The results showed that the open circuit voltage increased with increasing solar radiation and, therefore, hot side temperature. The calculations showed that the highest open circuit voltage of 2.76 V was obtained with the mechanism using pure water as the working fluid. However, the obtained electrical efficiency ηe and output power Pmax values remained at 1.06 % and 1.058 W, respectively. Numerical and Artificial Neural Network (ANN) models are widely used to save time and cost in determining the optimal operating conditions of the TEG. Therefore, in addition to the experimental study, a numerical model consisting of TEG and a cooling system, and an Artificial Neural Network (ANN) model were also developed in this study. The average absolute errors for Computational Fluid Dynamics (CFD) and electrical results were obtained in the numerical model as 3.47 % and 2.97 %, respectively. In addition, the average absolute errors in the ANN model were obtained as 0.6 %, 0.5 % and 0.27 % for water, Al2O3 and TiO2 nanofluids, respectively.

Reducing Domain Density Enhances Conversion Efficiency in GeTe.

Incorporating dilute doping and controlled synthesis provides a means to modulate the microstructure, defect density, and transport properties. Transmission electron microscopy (TEM) and geometric phase analysis (GPA) have revealed that hot-pressing can increase defect density, which redistributes strain and helps prevent unwanted Ge precipitates formation. An alloy of GeTe with a minute amount of indium added has shown remarkable TE properties compared to its undoped counterpart. Specifically, it achieves a maximum figure-of-merit zT of 1.3 at 683 K and an exceptional TE conversion efficiency of 2.83% at a hot-side temperature of 723 K. Significant zT and conversion efficiency improvements are mainly due to domain density engineering facilitated by an effective hot-pressing technique applied to lightly doped GeTe. The In-GeTe alloy exhibits superior TE properties and demonstrates notable stability under significant thermal gradients, highlighting its promise for use in mid-temperature TE energy generation systems.

Analysis and optimization of effect factors of refrigeration performance of portable micro-refrigerator

The objective of this study was to ascertain an efficient portable cold container, considering the constrained space, low airflow velocity, and uneven heat distribution of a micro-refrigerator, which lead to in insufficient heat dissipation and low refrigeration efficiency. A thermoelectric micro-refrigerator model with a volume of 9083.8 cm3 was established under forced convection heat transfer conditions. Through single-factor and response surface experiments, the impact of thermoelectric elements configuration on refrigeration efficiency was identified. These elements include the input current of the Thermo Electric Cooler (TEC), the derating factor (actual power) of the cooling fan, and the height of the heat sink fin.The results indicate that optimizing the refrigeration conditions significantly enhances the refrigeration efficiency of the micro-refrigerator. At an ambient temperature of 25℃, with a fan derating factor of 0.77 (corresponding to an actual power of 0.8218 W), a heat sink fin height of 59.15 mm, and a TEC input current of 5.09A, under stable conditions,the cold side temperature can reach −11.3 ℃. The hot side temperature is 38.2 ℃, consistent with the response surface experiment result. Numerical simulation under these conditions reveals a cold side temperature of −12.4 ℃ and a hot side temperature of 41.9 ℃, showing a 9.7 % difference from the experimental results. The simulation data further demonstrate that the vertical arrangement of the cooling fan and heat sink can achieve a cold side temperature of −12.9 ℃, effectively maintaining the hot side temperature below 40 ℃. The thermoelectric system investigated in this paper holds promising potential for applications in portable fresh-keeping and refrigeration.

Enhancing the performance of thermoelectric generators using novel segmental arrangement of multi-functional gradient materials

Enhancing the performance of thermoelectric generators at wide range of operating temperatures is of great importance to maximize the output power. Thus, different updated semiconductor materials with different values of figure of merit are used. Accordingly, a modified design of the TEG system based on the multi-functional gradient (MFG) technique is developed. A comprehensive three-dimensional modeling and optimization analysis was developed and numerically simulated. The numerical predicted results were validated using the available measurements and numerical data. The results showed that when compared to low operating temperature semiconductor material of traditional (Bi2Te3) at a hot side temperature equals 227 °C, the updated material improved the output power and efficiency by 18.8% and 58%, respectively. At high operating temperature at Th = 620 °C, the upgraded material outperformed the Silicon–germanium (SiGeT) traditional semiconductor material by about 71% in the output power and 100% in the efficiency. Using the MFG-TEG, the performance improvement over the conventional design at Tc = 27 °C, and Th of 477 °C was around 315% for output power and 503% for efficiency. The current findings introduce a brand-new, innovative technique that allows scientists to create thermoelectric generators that are incredibly efficient.