Method Of Heat Removal Research Articles

Numerical Simulations of Passive Heat Removal from Mobile Microreactors

As nuclear energy becomes increasingly vital to the goals of carbon neutrality by 2050, nuclear microreactors are being researched as an option for easily transportable energy. Designed to be transportable, factory fabricated, and self-adjusting, nuclear microreactors will fill in the gaps to help make the U.S. power grid more robust. Before designs can proceed, studies must be conducted on the safety of transporting these mobile microreactors while confined within a standard International Organization for Standardization (ISO) shipping container. Because of their mobile nature, microreactors will not have access to many of the engineered decay heat removal methods that traditional reactors utilize during shutdown. Current regulations state that the surface temperature of the microreactor needs to remain below 85°C while being transported on highways. This work investigates the surface temperature profiles of a mobile microreactor while confined within an ISO shipping container that does not allow forced convection to cool the outer reactor wall. Investigations have been performed for several configurations, including different reactor sizes, power levels, and scenarios with or without shielding around the reactor pressure vessel. This conservative safety analysis restricts the power level of the reactor to be less than 1 MW(electric). A more realistic analysis with the intermittent shutdown of shipping container air circulation demonstrates that a 4-MW(electric) reactor will reach 85°C per the Code of Federal Regulations limitations after 1 h.

Efficiency Enhancement in Photovoltaic–Thermoelectric Hybrid Systems through Cooling Strategies

The integration of photovoltaic (PV) and thermoelectric (TE) modules in PV-TE systems has shown potential for expanding the utilization of the solar spectrum, enhancing the total power output, and reducing the space that is required for PV power plants. This paper discusses the characteristics of a practical PV-TE system model. Typically, to boost the power output of the TE component, a significant temperature difference is induced across the thermoelectric generator (TEG) module using various heat removal methods. These cooling techniques not only enhance the TEG module’s efficiency but may also improve the performance of the PV component. In this study, we evaluate the efficiencies of PV-TE systems that are equipped with polycrystalline silicon solar cells and seven distinct TEGs under four different conditions. Initially, the PV-TE hybrid systems are tested without a cooling mechanism at an ambient temperature of 25 °C (Standard Test Conditions EN/IEC 61215). Subsequently, we examine the systems with a passive cooling approach, employing aluminum heat sinks to facilitate improved heat dissipation. Further tests involve an active cooling system using water and then nanofluid as coolants. The results from these assessments aim to establish a benchmark for enhancing the efficiency of future PV-TE systems.

ТЕПЛОВЫЕ ПРОЦЕССЫ В ЭЛЕКТРИЧЕСКИХ МАШИНАХ: МОДЕЛИРОВАНИЕ И ОПТИМИЗАЦИЯ СИСТЕМ ОХЛАЖДЕНИЯ

The article considers thermal processes occurring in electrical machines and methods of their modeling in order to optimize cooling systems. Various heat sources, heat transfer mechanisms, and approaches to creating effective mathematical models that allow predicting the thermal behavior of machines are discussed. Based on the modeling results, the optimization of cooling systems is carried out, the advantages and disadvantages of various heat removal methods are analyzed. The presented results can be used to improve the reliability and efficiency of electrical machines.

On the Control of Elemental Composition, Macro-, and Microstructure of Directionally Solidified Additive Products from Nickel-Based Alloy

The present work establishes the influence of heat input and methods of heat removal at the wire-feed electron beam additive manufacturing (EBAM) process on the structure of an additive product made of a nickel-based alloy. The following printing approaches are considered: changes in heat input, 3D printing strategy, and heat removal conditions due to (1) heating of the substrate, (2) partial suppression of radiative heat dissipation, and (3) thermal insulation of the substrate. It is shown that epitaxial growth of dendrites occurs in each case. However, in the case of an increase in speed and a change in the 3D printing strategy, the directed dendritic growth is interrupted. Preheating of the substrate and subsequent maintenance of the temperature reached during the EBAM process, as well as partial suppression of the radiative component of heat removal, allow to obtain the most uniform directional structure.

Research on a two-phase condensation model with predictable turbulent film

Steam condensation containing non-condensable gases is the main method of heat removal under severe nuclear accidents. To investigate the condensation characteristic, several numerical simulation studies have been conducted. Previous numerical models generally assume that the condensate film is thin or even negligible owing to the existence of non-condensable gases. However, the condensation rate improved rapidly as steam concentration rises. As the condensation rate rises, the velocity and thickness of the film will also sharply increase, thereby affecting the condensation process. In this case, the film flow will transition to a turbulent regime. To consummate the condensation model, a two-phase condensation model with predictable turbulent film was proposed. The model can predict the condensation performance well in a broad range, with deviation generally within 20%. In addition, the prediction correlation and contour diagram were obtained to identify the thermal resistance ratio and the flow regime of the film according to the proposed model.

Influence of the Nozzle-to-Surface Distance on Spray Cooling Efficiency

Spray cooling is a highly effective method of heat removal that has broad practical applications, including use in modern cooling systems designed for microelectronics and microchips. It is known that spray cooling performance is influenced by a huge number of factors. This experimental research is devoted to the study of the influence of a liquid flow rate in the range of 15.1–24.2 cm3/s, heat flux up to 6.4 MW/m2, and nozzle-to-surface distance on the heat transfer rate in non-boiling mode and the distribution of the local temperature of the heat exchange surface during spray cooling. It is shown that the heat transfer coefficient weakly depends on the heat flux for all studied nozzle-to-surface distances. It is demonstrated that the nozzle-to-surface distance has a significant influence on the heat transfer and the temperature distributionon the heating surface during spray cooling in non-boiling mode. At the same time, there is an optimal distance at which the maximum heat transfer rate and uniformity of the temperature are achieved. Criteria and a ratio for determining the optimal distance from the spray nozzle to the heated surface are proposed.

Condensation heat removal due to the combined impact of natural convection and radiative cooling

The work examines the heat exchange characteristics of a condenser in which heat removal of the refrigerant condensation occurs due to natural convection and radiation cooling. The heat exchanger is designed to reduce energy costs for the removal of condensation heat. Unlike traditional air cooling condensers, it uses radiation cooling, a method of heat removal based on its transmission in the form of infrared radiation through the planet’s atmosphere into the surrounding outer space. A method for calculating the thickness of the radiating plate has been developed. To minimize material consumption and cost, the distance between the tubes is reduced to 40 mm, and the thickness of the aluminum radiating plate is reduced to 0.32 mm. The inner diameter of the coolant channels is 1 mm. For the experimental study of the condenser, an experimental stand working on R134a refrigerant was developed. Theoretical and experimental studies of heat transfer have been carried out. The heat transfer coefficient of the heat exchanger, reduced to the area of the radiating surface, was from 10.3±1.36 to 18.7±2.47 W·m–2·°C–1, when the condensation temperature was 12.8...21.9 °С higher than the temperature of atmospheric air. The operability of the condenser is shown both during the day and at night, in the presence of precipitation in the form of rain and snow, and a high level of cloudiness. The material capacity and filling of the refrigerant in the condenser are comparable to the characteristics of air-cooled condensers with forced air circulation. At the same time, it does not consume electricity. It can be used in stationary refrigeration systems (in data processing centers, commercial refrigeration equipment, air conditioners) to increase their energy efficiency

Novel Method to Improve Heat Transfer Rate Through Delta Swirl Tape for a Swirl Jet Impingement Study

With advancement of electronic equipment’s, there is a need to have an efficient method or mechanism that helps remove heat from the system. Air jet impingement is generally implied method for effective heat removal from these equipment’s. There are several types of air jet impingement techniques used and among them swirl air jet is one of most prominent and proven method. In this study, a novel method is proposed to improve heat transfer of a swirling air jet impingement. Experimental study has been performed with swirl tape and novel delta tape having twist ratio (T.R) = 2 for jet to plate distance of z/d=2 to 8 and Re varying between 1500 to 9000. This study is basically carried out to improve the heat transfer at low Re conditions. Thermal imaging technique is used to derive centerline Nu values for different jet to plate distances (z/d=2 to 8). Study shows that novel delta tape adds significant improvement in heat transfer for above mentioned conditions.

A study of diabatic distillation in a column with a low pressure drop

This paper examines diabatic columns with a new type of tray. The design provides effective liquid reflux flow in each column tray and a low pressure drop. The contact devices comprise a stack of multi-diameter plates with raised edges. The vertical tubes of the dephlegmator integrated into the column centre pass across all plates, and are used for heat removal. Vapors of the ascending mixture partially condense onto the plate surfaces and the dephlegmator, resulting in vapor enrichment. The liquid flow down the column forms a thin layer on the surfaces of the middle and bottom plates. When the condensate drops onto the smaller-diameter top tray, it partially evaporates, is then mixed with the liquid flow on the underlying plates, and partially evaporates again. An algorithm calculation of distillation parameters for a diabatic column, with a known reflux flow rate, vapor velocity and heat transfer coefficient, is proposed and approbated. The column separation efficiency is assessed depending on the temperature and cooling-water flow rate in the dephlegmator pipe. Several approaches for enhancing the heat transfer intensity in the column dephlegmator pipe were analysed. Several heat removal methods, including liquid film flow cooling of the inner dephlegmator pipe surface, were examined. Experimental tests were carried out using an ethanol-water binary mixture and a raw spirit complex mixture. Comparison of the characteristics of the new diabatic unit and a packed column with a spiral prismatic packing showed that the plate column with the same separation efficiency has a lower pressure drop and metal consumption. The results encourage further research on this new diabatic column design.

Effect of nozzle orientation on electrospray cooling

• The performance of electrospray cooling is similar for all spray angles from 90° (normal to target surface) down to 30°. • A sharp drop in cooling performance occurs at a spray angle of 25°due to incomplete jet-to-droplet breakup, droplet rebound from the target surface, and a reduction in the electrohydrodynamically-induced convective air flow. • Electrospray cooling is ideal for constrained environments or hard-to-reach surfaces. Two-phase cooling is an efficient method for heat removal from electronic systems. One implementation of this approach is based on electrospray atomization, where droplets of the cooling fluid are produced using high electric potentials. Electrospray cooling has several unique advantages, including low power consumption, precise delivery of coolant, and compact design. Past work has mostly focused on spray orientations where the nozzle is directed normal to the high-temperature surface. In this short communication, we examine electrospray cooling at varying spray angles, which can provide easier integration for constrained environments or hard-to-reach surfaces. Water is used as the working fluid at four different flow rates from 60 to 120 mL/hr. The nozzle orientation was varied from normal to the surface (90°) down to an acute spray angle of 25°. We found that any angle larger than 30° achieved an evaporation efficiency exceeding 100% at the critical heat flux. The efficiency dropped to 90% at an angle of 25° for all flow rates. Surface temperatures increased and the critical heat flux decreased with spray angle, with the sharpest change occurring at a spray angle of 25°. This was due to droplet rebound, incomplete droplet breakup at high flow rates, and a reduction in electrohydrodynamically-induced convective cooling. The work reported here will assist in the integration of electrospray atomization for cooling applications.

Analysis of energy saving effect of green building exterior wall structure based on ANSYS simulation analysis

For the accuracy of the results of this research, this article only studies some buildings in areas with extremely low temperatures. In extreme weather, these buildings require external wall structures with good thermal insulation to achieve the effect of cold protection. How to make the exterior wall structure of these buildings energy-saving and environmentally friendly is the key issue of our research, and it is also an urgent issue in architectural design. Although the exterior wall occupies a small area in the overall building, the exterior wall plays a major role in the design and thermal insulation of the entire building. Effectiveness, energy consumption and other aspects play an important role. In order to clarify the thickness of the cold-proof system of the concrete foam external wall, we used ANSYS to model the parameter model and predict the special situation, and compared with the original cold-proof material, to study the thermal insulation effect of the foam concrete cold-proof wall. We have obtained through experiments and calculations that when the thickness of the concrete foam is 145 mm, the cold protection effect of the concrete foam exterior wall cold protection technology is very similar to that of the 50 mm thick polystyrene board exterior wall cold protection system. We compared and analyzed the envelope structure of the existing buildings, and did a lot of experiments and tests to provide some information support and solutions for the changes of the envelope structure. After weighing the pros and cons, we chose the cold protection method of the envelope. After changing the structure of the building, after testing, we found that this method is effective in preventing cold and heat preservation, and the speed of cold current transmission is greatly slowed down, so there will be no freezing of the internal structure. And the concrete material can make the internal structure more stable, will not break due to the huge temperature difference between indoor and outdoor, and enhance the effect of heat preservation. This article focuses on the study of CPU automatically discharging heat during operation, and decomposes and observes the internal structure of the ANSYS system, observes how these systems perform heat rejection and cooling, and we also analyze the characteristics of the cold aisle open IDC system. Based on the research, we compared and analyzed two heat removal methods.

Investigation on subcooled flow boiling heat transfer characteristics in ICE-like conditions

AbstractThe increasing demand of cooling in internal combustion engine (ICE) may require the shift of heat removal method from traditional single phase liquid convection to subcooled flow boiling in order to fulfill the desired functional temperature. Thus, the characteristics of subcooled flow boiling heat transfer should be studied exclusively considering the practical conditions in ICEs. Accordingly, in this article, subcooled flow boiling experiments were conducted in a rectangular channel using 50/50 volume mixture of ethylene glycol and water coolant (EG/W) as working fluid. Aluminum and cast iron surfaces were selected as the heated surfaces to simulate the material of cylinder head in gasoline and diesel engines, respectively. Experimental results showed a trend that the aluminum surface had a better performance than the cast iron surface in terms of heat transfer coefficient in the boiling region. The difference between these two surfaces was concluded as results of different surface thermophysical properties. A modified wall heat flux model was proposed based on the power-type addition method. The proposed model modified the nucleation boiling contribution by introducing a new parameter which accounts for the influence of thermophysical properties of heated surface on the boiling process. Thus, one such modified model could be useful for practical engine cooling applications.

Experimental analysis of a metal hydride hydrogen storage system with hexagonal honeycomb-based heat transfer enhancements-part B

This study is a continuation of the computational analysis of the reactor equipped with hexagonal honeycomb based heat transfer enhancements, performed in Part A of the study. In the present study, the performance of the metal alloy and the reactor is investigated experimentally. The gravimetric capacity and reaction kinetics of the alloy La0.9Ce0.1Ni5 are determined. The performance of the reactor under different external environments is noted. The influence of operating conditions such as supply pressure, heat transfer fluid, heat transfer fluid temperature on the reactor performance is investigated. Evaporative cooling as a heat removal technique for metal hydride based hydrogen storage reactors is tested for the first time and compared to conventional heat removal methods. It is found to improve the heat transfer from the alloy bed significantly.

Speedy Hydration of Carbon Dioxide Hydration in an Immediate Coolant of Ice Granules.

Hydrate-based carbon capture (HBCC) has been considered as a promising technique in recent times. However, large exothermic heat of hydration and lower solubility of the gas in water cause a slower hydration rate and poor gas uptake during hydration. In the present work, a phase change heat removal method was applied, in which ice granules surrounded by normal alkanes were used as an immediate coolant and quick nucleation center to intensify the carbon dioxide capture through hydrate formation. Normal alkanes have great potential to enhance gas–water contact due to their high solubility with CO2 and thus may enhance the hydration rate. The slurries of ice in normal alkanes from cooling three different W/O emulsions were prepared to perform all the hydration experiments in a batch autoclave at a constant temperature of 267.15 K and pressure range of 1.9–2.5 MPa with a stirring speed of 600 rpm. Kinetics of CO2 hydrate formation such as induction time, hydration duration, molar gas uptake, and hydrate growth rate were determined using a mole balance (PVT) model. Compared to earlier investigations of hydrate formation, in present work, the hydrate growth rate increased by 7–39 times and enlarged to 352 times as compared to pure water while gas uptake per mole of water increased by 1.6–10 times.

A Review of the Recent Development of Photovoltaic/Thermal (PV/T) Systems and Their Applications

Hybrid photovoltaic/thermal systems have become an important energy technology due to their capacity of producing electrical and thermal energy simultaneously, their ease of integration into buildings and good overall performance. Conventional PV systems generate waste energy in the form of heat during the conversion of solar radiation into electricity. It has been shown that the electrical efficiency of PV panels decays with the rise in the PV cell temperature. Therefore, PV performance can be optimised if this heat is removed. Air and water are the most common media used for heat removal and the energy can then be used for heating applications in buildings. In the last five decades, researchers worldwide have carried out experimental studies, simulations and numerical modelling of different types of PV/T systems. In addition to water and air, heat removal methods such as refrigerants, PCM, heat pumps and nanofluids have been analysed. This work presents an overview and discussion of the research of the different PV/T thermal control systems of the last five years. The present study highlights key points of the different techniques that exist, such as overall efficiencies, parameters and configurations, type of system, the nature of work, country of development and applications. Based on this study, it was concluded that the PV/T systems are auspicious technology and that further work should be focused on the aesthetics of the systems to promote acceptance and improvement of the efficiency.

Additive Manufactured Impinging Coolant, Low Electromagnetic Interference, and Nonmetallic Heat Spreader: Design and Optimization

Abstract With the increase of electronic device power density, thermal management and reliability are increasingly critical in the design of power electronic systems. First, increased density challenges the capability of conventional heat sinks to adequately dissipate heat. Second, higher frequency switching in high voltage, high current, wide bandgap power modules is creating intensified electromagnetic interference (EMI) challenges, in which metallic heat removal systems will couple and create damaging current ringing. Furthermore, mobile power systems require lightweight heat removal methods that satisfy the heat loads dissipated during operation. In this effort, we introduce an additive manufacturing (AM) pathway to produce custom heat removal systems using nonmetallic materials, which take advantage of impinging fluid heat transfer to enable efficient thermal management. Herein, we leverage the precision of additive manufacturing techniques in the development of three-dimensional optimized flow channels for achieving enhanced effective convective heat transfer coefficients. The experimental performance of convective heat removal due to liquid impingement is compared with conventional heat sinks, with the requirement of simulating the heat transfer needed by a high voltage inverter. The implementation of nonmetallic materials manufacturing is aimed to reduce electromagnetic interference in a low weight and reduced cost package, making it useful for mobile power electronics.

The Effects of Heat Generation on Cutting Tool and Machined Workpiece

Metal cutting processes usually cause heat generation at the cutting zone (around the workpiece-tool intersection). The heat generated during these processes may cause different effects on both the workpiece and tool, this in turn may affect the finished product and the general performance of the machined piece. In this study, a review was done on various types of machining conditions available, effects of heat generated on the workpiece and tool, and the approaches adopted to reduce this heat at cutting zones. This study also focuses on the simulation of percentage ratio of heat removal. To handle the simulation, various approaches of heat removal methods were used to get the percentage ratio using the ansys version 19.1 software. It was discovered that heat generation causes two major types of wear on the tool, crater and flank wear, resulting in the reduction of cutting tool life as well as dimensional inaccuracy, surface damage and severe corrosion cases on the workpiece. Various heat reduction methods and coolant application types were as well studied and their merits and demerits were discussed.

Performance investigation of convective and radiant heat removal methods in large spaces

Reducing the energy used for removing heat from solar radiation, high-temperature walls and air infiltration is becoming increasingly important in large space buildings. This paper proposes an analysis method to distinguish the performances of different heat removal methods in raising the cooling efficiency as well as reducing the heat flux. Firstly, the features of heat sources in large spaces are identified and proper parameters (heat flux or temperature) are selected to reflect their characteristics in heat transfer. Based on the goals of maximizing the cooling temperature and minimizing the heat flux, the influencing coefficients are defined to evaluate the influences or active forces of each type heat source and removal method on indoor environment and heat flux, and a simplified analysis model is established to reflect the character of different heat removal processes in large spaces with equivalent thermal resistance. On this basis, the influences of heat sources on indoor environment and the active forces of heat removal methods (e.g., jet ventilation and radiant floor cooling) are weighted quantitatively. By comparison, when the radiant floor cooling method is adopted, the operative temperature influencing coefficients that correspond to solar radiation and high-temperature envelope are lower than those in the case of jet ventilation, and the heat flux influencing coefficients are also smaller due to relatively lower degree of vertical air mixing. Therefore, radiant floor cooling method is more suitable for large spaces for its specialty in handling the heat from solar radiation and high-temperature envelope.

Comparison of methods of heating a rotary-film apparatus for the production of vegetable concentrates

The object of research is the temperature field of the working surface of the rotor-film apparatus (RFA) when heated by a nichrome spiral with a different coolant layer or using a flexible film resistive radiating type electric heater (FFREHRT). Since the concentration of vegetable purees using RFA is a promising solution, due to a significant reduction in processing time and high quality of the resulting products. Today, most RFAs use electric heating of nichromes with spirals with intermediate coolants, to process a uniform heat flow, which is determined empirically for the thickness of the coolant layer depending on the flow of raw materials, it is processed. Such methods make it possible to obtain qualitative indicators of the uniformity of the temperature field, but the problem is an increase in the metal consumption of the apparatus due to the presence of pumps for the movement of coolants, which generally complicates the operating conditions. Therefore, it is important to improve the RFA heating system using FFREHRT, which is also a thermally insulated surface with a uniform distribution of the temperature field over the entire radiation plane. In the course of the study, the uniformity of the temperature distribution in the RFA model sample is determined for various heating methods (nichrome wire with an intermediate coolant, PFMS-4 organosilicon liquid or FFREHRT). The obtained comparison of heat removal methods made it possible to establish that heating with a nichrome spiral is optimal when the thickness of the coolant layer is 4 mm with a temperature difference of 1.2...2.4 °C . Under conditions of using FFREHRT, a temperature difference of 0.5...0.7 °C. This confirms the prospects of using FFREHRT in the RFA heating system in the conditions of a change in the feed rate of 0.5...1.5•10 3 kg/s. Thanks to the use of FFREHRT for RFA heating, operational conditions will be improved by simplifying the structural properties, reducing resource costs compared to heating with a heating shell with a coolant and the optimal temperature difference on the working surface of the apparatus.

Study on reactor residual heat removal method based on steam controllable discharge in station blackout accident

The design of passive residual heat removal system (PRHRS) has the problems of uncontrollable coolant cooling rate and incomplete matching between the heat removal capacity and the reactor residual heat. To solve these problems, a residual heat removal method is proposed in this paper, which is controllable release of secondary steam into the environment at the early stage of reactor shutdown when the residual heat is large. The feasibility of this method is verified by the thermohydraulic analysis code. The results show that this method can discharge the residual heat in a period of time after the reactor shutdown, and the coolant system can establish a stable natural circulation. But when the steam generator is empty, the residual heat must be removed by other ways. After that, based on the critical flow theory of nozzle, a simplified method for calculating the steam discharge power and estimating the safety-related parameters by steam pressure is proposed, which can be a reference for operators to control the cooling rate, analyze the system status and handle the accident. The conclusions can also provide references for the study and improvement of residual heat removal method.