Side Heat Research Articles

Generation of Current in Thermoelectric Generator by Absorption of Heat Using ANSYS Thermal

Thermoelectric power generation is a renewable energy conversion process that directly converts heat to electricity. This research proposes a novel fluid-thermal-electric multi-physics numerical model for predicting the performance of a thermoelectric-producing system. On the ANSYS platform, numerical simulations are done along with the exhaust temperature and mass flow rate. The range of hot end temperatures is from 100 to 450 degrees Celsius. Similarly, the cold end temperature can reach a maximum of 25 degrees Celsius and a minimum of 10 degrees Celsius. When the temperature at the generator's hot end rises, it means the temperature at the generator's cold end must fall. It means both have an inverse relation to each other. The maximum heat absorbed at the hot junction is 32.762 W and the minimum heat absorbed at the hot junction is 4.6305 W. Hence the maximum and minimum current values produced in this paper by the thermoelectric generator are 72.156 A & 10.816 A respectively. The hot side heat exchanger's position of the thermoelectric modules has a significant impact on output. Combining the benefits of many models are advised to construct an inclusive thermoelectric generator system for use in real-world applications.

Computational Fluid Dynamics for Cavity Natural Heat Convection: Numerical Analysis and Optimization in Greenhouse Application

Natural convection in cavity plays a significant role in energy-related field, including the indoor heat transfer analysis in greenhouse with integrated PV roof. In this study, mathematical model is established for two-dimensional heat transfer analysis in greenhouse air cavity, with numerical simulation through computational fluid dynamics (CFD). Main natural convection impact factors, such as system configuration parameters (tilting angle and PV panel unit number) and fluid thermal–physical properties, are investigated with indoor temperature distribution and streamline comparison by finite-volume method (FVD). Preliminary results show that with rising Rayleigh number (Ra), natural convection is enhanced with growing Nusselt number (Nu). Moreover, panel slope tilting angle (θ) highly determines inside heat transfer subregions in terms of the vertical temperature gradient declines with rising θ, improving the temperature distribution uniformity inside. The solar greenhouse example illustrates that with the increasing numbers of panel group numbers (n), the air temperature gradient differences decrease, improving the temperature distribution uniformity inside, which is preferable to built environment accurate control for greenhouse in the practical engineering. This work can provide modeling method support and reference for natural heat convection applications.

Experiment study and heat resistance analysis on heat transfer characteristics in staggered tube moving bed heat exchangers

Heat transfer of high temperature granules in the moving bed heat exchanger is an important thermal process in a blast furnace slag waste heat recovery system. Gaining a comprehensive understanding of granular side heat transfer characteristics is crucial. Here, we experimentally investigated the effects of velocity, diameter, diameter distribution, inlet temperature and granule type on granular side heat transfer and the development of heat transfer in the flow direction in a staggered tube array. Furthermore, the experimental results were analysed via the thermal resistance theory. The obtained results indicate that the heat transfer coefficient increases with increasing velocity and inlet temperature and decreases with increasing diameter. Multi-sized granules and blast furnace slag have better heat transfer than mono-sized granules and phosphorus slag, respectively. The heat transfer coefficient tends to increase and then decrease in the flow direction, with the location of the peak, depending on the ratio of the contact and penetration thermal resistance. The semi-empirical formula based on experimental results can provide a theoretical basis required to design.

Temperature Distribution in a Non-Prismatic Thermoelectric Leg and the Energy Conversion Efficiency

Abstract It has been proposed that asymmetric thermoelectric (TE) legs may enhance the TE energy conversion efficiency. This work presents an analytical model for the temperature field in non-prismatic TE legs and the energy conversion efficiency. Different from the models available in the literature, the present one-dimensional (1D) heat equation for thermal conduction in non-prismatic legs is derived from the general three-dimensional energy and charge balance laws and the thermoelectric constitutive relations considering Joule heating and the Seebeck effect on the heat flow. The temperature field in a TE leg with an arbitrary gradient of the cross sectional area is obtained using the 1D heat equation. The temperature field and energy conversion efficiency are calculated for exponential and quadratic Bi2Te3 legs as well as an exponential PbTe leg. The numerical results indicate that leg tapering has minimal effects on the temperature distribution in and energy efficiency of the non-prismatic leg under the prescribed cold and hot side temperatures boundary conditions provided that the volume of the leg remains the same. The energy efficiency of the tapered leg, however, can be significantly increased under the prescribed hot side heat flux condition. Finally, a simple estimate on the limitation of the 1D models for non-prismatic legs is discussed.

Experimental Study of the Wickless Heat Pipe Heat Exchanger by Using Nano Fluid

The use of wickless heat pipe heat exchangers has been improving a wide range of thermal applications such as solar water heaters. Therefore, more scientific research needs to be conducted to improve its performance. In the present study, a wickless heat pipe heat exchanger test rig has been designed and fabricated to investigate the effect of different parameters on its performance. Two different heat pipe working fluids have been used namely pure water and water with nanoparticles (Al2O3) using different fluid volume ratios (20%,40%,60%,80%, and 100%). The concentrations of the nanoparticles in water range between 1.3 and 7 % wt. For the heat exchanger, various inlet hot air temperatures (50, 55, and 60 oC) have been tested at the hot side (heat pipe evaporator) whereas the inlet temperature of the cold side (heat pipe condenser) has been maintained at 20 oC. The effect of airflow Reynolds number has also been examined with a range of 2583-20664. Results showed that the best heat exchanger effectiveness is achieved at a Reynolds number of 10332 and nanoparticles concentration of 7% wt. Also, the use of nanoparticles reduced the thermal resistance in the heat pipe due to the significant reduction in its surface temperature compared to that of pure water.

Heat transfer in flat tube car radiator with CuO-MgO-TiO2 ternary hybrid nanofluid

An investigation of the performance of a car radiator with CuO-MgO-TiO2 aqueous ternary hybrid nanofluid has been presented to elucidate the effect of nanoparticle concentration, flow rate, and frontal air velocity. The volume concentration of nanoparticles ranges from 0.1% to 0.5%. The effect of fluid inlet temperature, the coolant flow rate and the frontal air velocity on a flat tube radiator were investigated. The effectiveness of the radiator increases with increasing volume concentration as well as coolant flow rate. The coolant side heat transfer coefficient of 0.5% hybrid nano-coolant was 46% higher than the base fluid. The overall heat transfer coefficient was 7.65% higher than the base fluid. The friction factor and the pumping power both decrease with increasing fluid inlet temperature. The pumping power required for nano-coolant is 1.71 times the base fluid. A correlation for the overall heat transfer coefficient is also presented.

A novel two-dimensional continuum mixture theory model for paraffin wax melting in a cavity heating from side considering volume change

Paraffin wax presents a considerable potential for thermal storage technologies, given its high latent heat. Therefore, the accurate and systematic modeling of its melting process bears significant importance. Yet, existing mathematical models fail to adequately address the velocity driven by the density change during the melting process. In this research, we introduce a novel model for paraffin wax melting within a square enclosure subject to side heating. Unlike current models, our approach posits that flow within the mushy zone is dictated by the mass equation, not Darcy’s equation, and thus excludes the usage of mushy zone constant. This assumption, premised on the idea that the density-deviation-driven flow precludes the bulk flow from penetrating the mushy zone, is confirmed through a carefully designed visual experiment. Utilizing our melting model, we construct a mathematical model anchored in the continuum mixture theory. Through a comparative analysis of results acquired by numerical methods and experimental data, we find that our innovative mathematical model effectively predicts real-world scenarios with remarkable precision. Furthermore, we explore the influence of flows within the mushy zone on the melting process. Our findings indicate a significant deviation in results when assuming zero velocity in the mushy zone, suggesting that the density-deviation-driven flow is numerically negligible. However, it is crucial to note the physical relevance of the density-deviation-driven flow in accurately predicting the melting process. The absence of this consideration allows the bulk flow in the liquid region to permeate the mushy zone, thereby introducing substantial errors.

Novel distillation column retrofit combining energy integration and different tray designs

This study introduced an innovative approach for energy integration of distillation columns using side heat exchangers and parastillation. The traditional installation of side heat exchangers typically demands additional stages or an increased reflux ratio to maintain the desired separation. Here, parastillation trays replace the conventional trays below the side-reboiler or above the side-condenser. These trays enable the inclusion of more theoretical trays within the same column height compared to conventional technique. This strategic implementation allows achieving the desired separation while using energy integration and keeping the column height and reflux ratio unchanged. A comprehensive case study demonstrates how this approach effectively surpasses the limitations of existing methods. Detailed analyses of thermodynamics and exergy loss emphasize its benefits. A practical case study focusing on bioethanol purification confirms its industrial viability. This pioneering technique presents a promising solution for sustainable chemical processes, particularly advantageous for energy-intensive processes such as dilute bioproduct separation.

Investigation on the heat transfer characteristics of flexible vacuum glass based on cross-laminated microcavities

Vacuum glass is a key component of energy-efficient buildings. At present, the traditional vacuum glass (VG) has some problems, such as side edge heat transfer, poor thermal insulation in small sizes, high cost of indium alloy edge sealing, and poor adaptability to the rigid structure to environments, which limits its application in buildings. Vacuum interlayer heat transfer is thickness-independent. Therefore, increasing the transfer path and thermal resistance of the support structure under micrometer gaps achieves effective thermal insulation. In this study, a vacuum glass with a cross-laminated microcavity structure was proposed. The cross-laminated structure has a total thickness of several hundred micrometers and is made of polycarbonate. The heat transfer and stress-strain of the cross-laminated vacuum glass (CLVG) and VG are investigated. The results indicate that the CLVG accomplished a lower heat transfer coefficient compared with the VG at a size smaller than 30 × 30 cm2. In addition, the CLVG is edge-effect-free. As a flexible structure, the CLVG can be easily applied to existing buildings. This study contributes to the exploration of new structures for the vacuum glass.

The extreme high cooling capacity thermoelectric cooler optimal design for kilowatts scale thermoelectric air-conditioner of high-speed railway carriage

In recent 20 years, the rapidly development of thermoelectric materials promotes thermoelectric s application in large scale cooling area, i.e. air-conditioner. To provide quiet working environment for the driver of high-speed railway, a kilowatt scale air-conditioner was designed. Firstly, a novel thermoelectric cooler with maximum cooling capacity of 450 W was designed with 199 thermoelectric elements, and the cooling performance were investigated under different cold and hot side heat exchange capacity. Second, the hot and cold side heat exchangers were optimized adopting genetic algorithm. Finally, a high coefficient of performance (COP) thermoelectric air conditioning (TEAC) system was designed for high-speed railway locomotive. The TEAC system comprising 16 TECs achieved a cooling capacity of 2342 W with a COP of 0.5 in cooling mode, and meets one 1HP TEAC requirements. The temperature field inside the locomotive was uniform and exhibited a linear correlation with the supplied air temperature. This research demonstrates the utility of high-power TEAC in high-speed railway carriages, providing valuable insights for the application of TEAC technology.

PERFORMANCE EVALUATION OF HOT AIR THERMOELECTRIC GENERATOR USING BIOMASS ENERGY SOURCE

Thermoelectric generators are solid-state devices that convert heat into electricity using the Seebeck effect, when there is a temperature difference across a thermoelectric material. This research designed an experimentally tested a thermoelectric hot air generator using sixteen SP1848-27145 modules in two parallel strings. The system consists of a biomass combustion chamber, hot air exhauster, hot and cold side heat exchangers. Voltage, current and temperatures in the combustion chamber, hot air heat exhauster, hot side heat exchanger and cold side heat sink were measured. The hot air exhauster, hot side heat sink and cold side maximum temperatures are 178.3°C, 69.2°C and 44.5°C respectively yielding an open circuit voltage of 64 V and current of 1.99 A in the course of the experiment. The thermal performance of the designed hot air exhauster, hot side heat exchanger and cold side heat were simulated using ANSYS Fluent, for pictorial representation of their temperature contours.

Design and performance analysis of hot side heat sink of thermoelectric cooler device based on simulation and experiment

AbstractAs for improving the heat diversion capacity of the hot side heat sink of the thermoelectric cooler (TEC), thereby improving the operational performance of the TEC, this study designed a type of double‐embedded flat heat pipe (EFHP) finned heat sink and compared with a standard aluminum (Al) heat sink. In experimental studies, TEC under two heat sinks were placed under different operating currents for heat transfer analysis and performance comparison. The experimental results demonstrated that the EFHP heat sink had better heat diversion ability, effectively improving the operational performance of TEC. When the TEC was input with a current of 6A, the thermal resistance of the double EFHP finned heat sink decreased by 19% compared to the Al heat sink; cooling capacity and coefficient of performance increased by 8.3% and 9.46%, respectively. Further, TEC's cold and hot surface temperatures decreased by 10.83% and 10.2%, respectively, and the heat uniformity of the heat sink improved. In addition, the CFD software Icepak was used to analyze the effects of double flat heat pipe spacing and length on the heat sink and TEC and the performance of two heat sinks and TEC under different heat dissipation conditions and obtained good agreement. This study can provide further guidance and assistance in designing the TEC cooling system.

Calibration methods and power cycling of double-side cooled SiC MOSFET power modules

Reliability analysis depends heavily on accurate measurements of junction temperatures for power semiconductors. It forms the foundation for precise reliability tests such as power cycling tests. One of the most established methods for junction temperature measurement in MOSFETs is the VSD(T) method. With the introduction of new module configurations such as the DSC (double-side cooled) module with cooling on both sides, conventional calibration methods for single side cooling require a critical review regarding their applicability. This article will highlight various calibration options and analyse them in regard to sensitivity and reproducibility for DSC modules. Subsequently, the most promising methods are evaluated experimentally. It was found that by heating the modules on both sides, a better temperature uniformity can be achieved than from single side heating alone. This allows to apply the VSD(T) method on DSC modules also during power cycling. A power cycling test with in situ mechanical force measurement was conducted to verify the results.

Quantitative review on recent developments of flat-plate solar collector design. Part 1: Front-side heat loss reduction

Several studies demonstrated novel and effective design solutions for the FPC thermal performance enchantment by the front side heat loss reduction. However, these design improvements were tested under different climatic and operating conditions. This fact makes it almost impossible to compare these design improvements. The following study quantitatively analyses the current flat-plate solar collector design developments, focusing on reducing front-side heat loss. It also performs a simulation analysis to demonstrate the thermal performance improvement of the chosen design solutions for three specific applications. The literature review was performed to identify the most promising design solutions. Then, the considered design solutions were modelled using the validated detailed theoretical model of a flat-plate solar collector (FPC). Finally, the modelling results were used to perform the thermal performance simulation analysis for Würzburg (Germany) climatic conditions and constant mean fluid operating temperatures of 50, 75, and 100 °C. The simulation results indicated that applying the considered design solutions to decrease the front-side heat losses could significantly increase the FPC thermal performance. Moreover, for high-temperature applications, where the front-side heat loss is a crucial factor determining the FPC thermal performance, there is more than a significant potential for the FPC thermal performance enchantment. To sum up, our findings indicate a significant thermal performance improvement potential that could increase the application range of FPCs and make them more competitive for a broader application area.

Performance assessment of a real water source heat pump within a hardware-in-the-loop (HIL) testing environment

Over the last decade, the global fight against climate change through electrification has led to an increase in research on building heating, ventilation, and air conditioning (HVAC) systems that utilize intelligent control algorithms to provide demand-side grid service while also maintaining the thermal comfort of building occupants. As the pivotal point between building electricity consumption and indoor thermal comfort, high-efficiency electrical vapor-compression heat pumps are at the center of these emerging studies, and various grid-interactive and occupant-comfort control algorithms have been developed for them. The impact of these algorithms on heat pump operation and performance when subjected to different weather conditions, building loads, and grid requests calls for investigation and verification via experimental testing with actual heat pumps integrated with real-time building and grid responses. This study introduces a Water-Source Heat Pump (WSHP) Hardware-in-The-Loop (HIL) Test Facility that is the first of its kind. This testbed utilizes a 2-ton variable speed water-to-air heat pump that is capable of interacting with a virtual environment currently comprised of an EnergyPlus (E+) building simulation, an agent-based occupant behavioral model, and a single U-tube ground-loop heat exchanger (GLHE) model. Detailed descriptions of the testbed’s physical design and operation, virtual environement, as well as their mutual communication is provided. An uncertainty analysis is also performed under manufacturer specified heating and cooling design conditions. This analysis shows that the total load across the WSHP’s demand side heat exchanger, i.e., the sum of its latent and sensible components, can be measured with a relative uncertainty of ± 10.4% and ± 3.6% in cooling and heating mode respectively. The WSHP’s coefficient of performance (COP) can be measured with relative uncertainties of ± 10.4% in cooling mode, and ± 3.7% in heating mode. A preliminary 24-h experimental demonstration is then performed utilizing the DOE prototype small commercial office building model in E+. The simulation takes place in Atlanta, GA on the date of 08/26/15 from 12:00 AM to 11:59 PM using TMY3 weather data. . The results from this demonstration show that over the course of this experiment the simulated outputs of zone dry-bulb temperature, zone humidity ratio, and WSHP inlet water temperature can be tracked by testbed emulators up to a root mean squared error (RMSE) of ± 0.27 °C, ± 0.376 g/kg, and ± 0.85 °C respectively. The WSHP’s dynamic behavioral characteristics and performance are also captured, and correspond well with the authors’ previous understanding of heat pump efficiency as a function of evaporator and condenser fluid inlet conditions respectively.

Linear and Nonlinear Stability Analysis of Molten Salt Natural Circulation Loop

Abstract A molten salt natural circulation loop (MSNCL) has been setup to study the steady-state, transient, and stability characteristics of molten nitrate salt, mixture of sodium nitrate, and potassium nitrate in 60:40 ratios by weight. Natural circulation experiments in a temperature range of 290 °C–600 °C have been performed. A semi-analytical linear model was derived for stability analysis of rectangular natural circulation loops with conventional localized surface heating and cooling. The developed model includes the effect of wall thermal inertia, variable internal heat transfer coefficient, finite secondary side heat transfer coefficient at cooler, and heat losses for predicting the stability map. These effects are incorporated considering their significant role in modeling high-temperature molten salt-based natural circulation systems. The developed model has been first validated with the experimental data of water loop available in literature. The developed model is then validated with the experimental data generated in MSNCL. Validation of in-house developed nonlinear model has also been performed against the same experimental data. The comparison of both linear and nonlinear stability analysis with the experimental data shows good agreement and articulates the importance of various parameters which have been included in the developed model.

Experimental investigation on heat transfer performance of the grooved spiral wound heat exchanger

To enhance the heat transfer efficiency of the spiral wound heat exchanger, a grooved spiral wound heat exchanger (GSWHE) was proposed. A test platform was accomplished to experimentally investigate the heat transfer performance with the comparison of a spiral wound heat exchanger (SWHE). The uncertainty analysis of the experiment was conducted, with the maximum relative error being not more than ±5%. The comprehensive heat transfer coefficient of the GSWHE is higher than that of the SWHE when the cooling water flow rate is low. To determine the heat transfer coefficient of both sides, the Wilson plot method was applied. The tube side heat transfer coefficient in the SWHE is found to have an error of about ±30% compared to the empirical correlations. The results also clearly suggest that grooves enhance the heat transfer of the shell side in the GSWHE. By employing effectiveness as a criterion, the comprehensive performance of the GSWHE was found to be 1.23 times higher than that of the SWHE.

Study of the geometry and structure of a thermoelectric leg with variable material properties and side heat dissipation based on thermodynamic, economic, and environmental analysis

Thermoelectric generator (TEG) without moving parts, refrigerants, and direct carbon emissions is the most promising way to reduce carbon dioxide. The economy and thermal efficiency of TEG are seriously inhibited by geometry and structure, while existing studies have not investigated the effect of geometric and structure on output characteristics when the model considers the effect of side leg dissipation and variable properties. This paper proposes a one-dimensional model considering the effect of Peltier heat, conductive heat, Joule heat, Thomson heat, side leg dissipation, and temperature dependence for variable and conventional geometric and structures for 8 different materials. The effects of operation parameters, geometry parameters, and structures on thermodynamic, economic, and environmental performances are studied. The higher hot source temperature and shorter leg length benefit comprehensive performance. Increasing side leg dissipation decreases efficiency. When the fin parameter (L(heP/λA)0.5) is below a specific value, increasing side leg dissipation can promote the output power, economic and environmental performance. Compared to the traditional structure, the output power and efficiency of new configurations are increased by 1.01–3.59 and 1.03–4.57 times, respectively; The cost and CO2 emission reduce by 1.0–72.1% for low hot source temperature and figure of merit (ZT) material.

Flow Characteristics and Heat Transfer Performances of Quadrant Helical Baffle Heat Exchanger with Grooved Joint

Helical baffle heat exchanger has a wide application in many industrial fields because of its high efficiency and low resistance. A new structure of the grooved helical baffle is proposed to strengthen the stability between the overlapped baffles during the spiral flow of fluid. Based on this structure, the liquid water was selected as the working medium in the tube side and shell side, the flow field characteristics and heat transfer performances of the quadrant helical baffle heat exchanger are numerically analyzed using software FLUENT 2017. The results show that when the helical angle is large (50°) and the overlapped amount is small (0.5), the comprehensive performance of the heat exchanger is the best. Therefore, the heat exchanger performance can be improved by choosing the appropriate combination of helical angle and overlapped amount. The correlation formula of the shell side heat transfer coefficient with helical angle, overlapped amount and mass flow rate is obtained by means of regression analysis, which can provide a reference for engineering application and optimal design of grooved helical baffle heat exchanger.

Experimental and numerical investigation on the melting behavior of paraffin in a shell and tube latent heat storage unit

In order to reduce the melting time of an improved shell and tube latent heat energy storage unit, the melting behaviors of phase-change material (paraffin) in the unit are investigated through visualization experiments. And a two-dimensional simulation model is established to explore the strengthening mechanism of the melting process by distinct heating methods and non-heat source wall. Results show that the complete melting time of outside heating method is 70.2% less than that of inside heating method at same heat flux. Eliminating the influence of heat transfer area (equal total heat input), the outside heating can generate more extensive and stronger natural convection, and the complete melting time can be shortened by 20.2%. In addition, the heat transfer bridge built by the non-heat source wall between the high temperature liquid phase-change material zone and the dead zone can effectively enhance the natural convection and accelerate the melting process. Especially considering the non-heat source wall, the melting time can be reduced by 44.2% through using the inside heating method.