Thermal Design Optimization Research Articles

Thermal Optimization Design of Heat Exchanger in Supersonic Engine with Parameters’ Fluctuation

Abstract Precooled engine is a highly expected solution to achieve supersonic transport. As the crucial component, heat exchangers protect other components from ultrahigh temperature. In traditional design methods, the nominal result is multiplied by a safety factor, whose selection entirely depends on experience, ensuring sufficient working margin to cope with fluctuation of parameters. For aero-engine, heat exchangers must work reliably with minimum weight. An advanced method of thermal optimization design with parameters’ fluctuation is proposed and proved to be effective by experimental verification. The heat transfer area can be quantitatively linked with the design confidence level, considering the coupling effect of various parameters’ fluctuation. The probability density distribution of heat transfer area has the characteristic of positive skewness distribution. With the increase of design confidence, the required heat transfer area is growing faster and faster. After optimization, the design of heat exchanger meets the requirements and the weight is effectively controlled.

Thermodynamic and exergoeconomic investigation of various SCO2 Brayton cycles for next generation nuclear reactors

In the present paper, a thermodynamic simulation platform has been established for investigating the thermodynamic and exergoeconomic behavior of six SCO2 Brayton cycle layouts used in nuclear reactors. A detailed parametric study was performed through a sensitivity analysis on the cycle efficiency and the unit cost of the total product with the fixed maximum system pressure of 20 MPa and the maximum system temperature of 550 °C. The results reveal that there exists an optimal pressure ratio corresponding to the highest cycle efficiency (thermal optimal design case) or lowest total product unit cost (cost optimal design case) for each SCO2 cycle. The intercooling cycle has highest cycle efficiency and comparable cost to the recompression cycle. Considering the exergoeconomic factors fk, it can be concluded that, for intercooling cycle, it is a more cost-effective way to reduce the capital investment of compressor at the expense of less component efficiency compared to other cycles. Whereas for the recompression cycle, it performs most outstanding in terms of total product unit cost among the studied cycles when the effectiveness of heat exchanger exceeds 0.86.

Application of metaheuristic algorithms in optimum thermal design analysis of a rectangular porous fin subjected to both insulated and convective tip conditions

In this novel optimization analysis, a rectangular porous fin subjected to convective tip conditions along with insulated end condition is studied. The aim is to optimize the important variables responsible for transferring heat from fin with insulated as well as convective tip to the surrounding in order to get a higher rate of heat transfer from the fin surface. Temperature-dependent solid and fluid thermal conductivities as well as variable internal heat generation is considered. To obtain heat dissipation rate through porous fin, the nonlinear governing equation is first solved analytically using Adomian decomposition method. Then the heat transfer rate, i.e., objective function of this problem is optimized with three powerful metaheuristic techniques, namely firefly algorithm, particle swarm optimization and gravitational search algorithm. A comparative analysis has revealed that fins with convective end show significantly higher heat transfer rate compared to their insulated end counterparts. Particle swarm optimization showed marginally higher heat transfer values compared to firefly algorithm but firefly algorithm took less computational effort to reach the optimum value.

Thermal Modeling and Design Optimization of PCB Vias and Pads

Miniature power semiconductor devices mounted on printed circuit boards (PCBs) are normally cooled by means of PCB vias, copper pads, and/or heatsinks. Various reference PCB thermal designs have been provided by semiconductor manufacturers and researchers. However, the recommendations are not optimal, and there are some discrepancies among them, which may confuse electrical engineers. This paper aims to develop analytical thermal resistance models for PCB vias and pads, and further to obtain the optimal design for thermal resistance minimization. First, the PCB via array is thermally modeled in terms of multiple design parameters. A systematic parametric analysis leads to an optimal trajectory for the via diameter at different PCB specifications. Then, an axisymmetric thermal resistance model is developed for PCB thermal pads where the heat conduction, convection, and radiation all exist; due to the interdependence between the conductive/radiative heat transfer coefficients and the board temperatures, an algorithm is proposed to fast obtain the board-ambient thermal resistance and to predict the semiconductor junction temperature. Finally, the proposed thermal models and design optimization algorithms are verified by computational fluid dynamics simulations and experimental measurements.

Simultaneous Optimization of Component Layout and Thermal Design for CubeSat under Limited Power Resources

Simultaneous Optimization of Component Layout and Thermal Design for CubeSat under Limited Power Resources

Optimal Design of Integrated Heat Pipe Air-Cooled System Using TLBO Algorithm for SiC MOSFET Converters

Optimal thermal management system design is critical for power electronic converters to ensure the reliability of power semiconductor switches. Medium power density inverter systems are often air-cooled to ensure an efficient and cost-effective thermal management solution. In addition, using heat pipes as the heat transfer medium between the heat sources and the heat sink can provide lower volume for the entire inverter. This paper investigates the effectiveness of Teaching Learning Based Optimization (TLBO) for finding the optimal forced-air heat sink with heat pipe cooling system to achieve higher fan efficiency and lower inverter packaging volume. The optimal design is found utilizing commercially available fans and heat pipes. The TLBO design optimization is also compared to the highly implemented Particle Swarm Optimization (PSO) and it is found that TLBO uses 20 times fewer iterations than PSO to converge, and that the TLBO results are more robust for different design constraints.

Research on thermal design control and optimization of relay protection and automation equipment

Relay protection devices and power automation systems are an important product in the power equipment manufacturing industry. They are customarily divided into secondary equipment for the transmission and distribution industry, and are responsible for protecting and controlling the primary equipment of the power grid and measuring the load of the power grid system. Thermal design is a major research topic for the reliability study of relay protection devices. The paper introduces the thermal design process of the relay protection device processing equipment, from the single-chip, module level, etc. to construct and isolate the airway facilities, and uses the FLOTHERM software to simulate the relay protection device model. Thermal simulation can guide the structural design, optimize the structure, make the single-machine structure more reasonable, and the heat dissipation more effective, improving the reliability of the single machine.

Hybrid composites in reusable space vehicles wing structures

The study is dedicated to the solution of a complex problem – development of an optimal thermal design of the tourist class reusable space vehicle (RSV TC) wing structure. The complexity of the problem resides in the necessity to consider critical factors of the suborbital flight and in a number of nesting tasks,that need to be solved. The authors implemented a multiscale modeling approach covering design of hybrid composite material thermal properties (i.e. mesoscale level), determination of thermal loads and thermal state analysis of a composite wing (i.e. macroscale and structural scale levels). Analysis of thermal fields demonstrated the necessity of thermal protection (TP) application for the wing structure. Consequently, optimal from the weight efficiency point of view TP thicknesses were determined. Summing up, the results of a RSV TC wing structure development are presented in the current paper.

Thermo-Mechanical Analysis and Its Effect on Rf Behaviour of A Tapered Cavity of the W-Band Gyrotron Oscillator

Thermo-mechanical analysis of a tapered cylindrical RF interaction cavity of a TE6,2, 95 GHz, 100 kW gyrotron has been carried out to study the effect of ohmic loss generated due to radiated microwave energy. For stable device operation, with the help of design relationships, describing the approach, an optimum thermal system design has been presented and performances got analyzed using a commercial simulation code “COMSOL Multiphysics”. For various cavity thicknesses, and convective heat transfer coefficient values under without fins and with radial fins conditions system performance have been investigated. Taking water as coolant at ~293 K, hydraulic diameter and flow rate range has been determined for the optimum convective heat transfer coefficient values. An optimized simple cooling system thus designed keeps the maximum RF cavity radius deformation (increase) ~ 3.2 μm maintaining the average cavity outer surface temperature of 308 K. Further, using nonlinear time-dependent multimode analysis, a decrease of 48 MHz in resonance and a decrement of 20 in diffractive quality factor of the interaction cavity along with reduction of 2 kW of the device output power have been observed in the case for the deformed cavity from those of the initial cavity gyrotron device, which are found within the tolerance limit of such devices.

Development of thermal hydraulic design code for SFR steam generators

Sodium heated once-through steam generator (OTSG) is a critical component of Sodium cooled Fast Reactor (SFR). It is a counter current heat exchanger. It transfers heat from hot sodium to water. Therefore, the steam generator is a necessity for the operation of the plant. However, due to the phase change exists in water side, it becomes challenging to design a steam generator for SFR. After the successful construction of CEFR (China Experiment Fast Reactor), a power-up demonstration SFR is being developed in China. For the design and analysis of the steam generator of the demonstration SFR, a thermal hydraulic Design Code of Once-through Steam generator for Sodium cooled fast reactor (DeCOSS) has been developed based on the movable mesh method. The DeCOSS code has been benchmarked based on the design data of OTSGs reported. The tube lengths and temperature distributions calculated by DeCOSS showed general agreements with published data. The influences of tube diameters on heat transfer capacity have been analyzed. The results indicated that the heat transfer capacity is determined by the thermal resistance of tube wall under the condition of fixed heat transfer coefficient of water side. In addition, under the same flow area of water and sodium, the heat transfer capacity could be enhanced by decreasing the tube diameters with constant tube wall thickness. Hence, the code can be utilized to do the sensitivity analyses and optimum thermal design of OTSGs. Moreover, it can support the design work of once-through steam generator of SFR.

Entropy generation rate minimization for hydrocarbon synthesis reactor from carbon dioxide and hydrogen

The process of hydrocarbon synthesis from carbon dioxide and hydrogen in a fixed-bed reactor, a novel approach of converting renewable and distributed energy to high-energy-density liquid hydrocarbon fuels, is designed and optimized thermodynamically in the present study. With the minimum entropy generation rate (EGR) due to heat transfer, frictional flow and chemical reactions as objective function, finite time thermodynamics (or entropy generation minimization) and optimal control theories are applied to find the minimum EGR along with the corresponding optimal paths of the carbon dioxide hydrogenation reactor. The results show that a reduction up to 26.29% can be achieved by optimizing the profile of the heat reservoir temperature outside the tube and inlet conditions, which is mainly due to a compromised decrease in the irreversibilities of chemical reactions and heat transfer. The chemical driving forces of the FT (Fischer-Tropsch) reactions in the optimal reactors decrease considerably compared with those of the reference reactor under the operation of constant heat reservoir temperature. The results obtained in the present study can provide some theoretical guidelines for the optimal thermal design of the real-world reactor of hydrocarbon synthesis process from carbon dioxide and hydrogen.

Thermal design optimization of passive cooling capability in a dry-storage system by adding wall undulations or semi-circular fins

Thermal design investigation of a novel liner inner wall surface geometry alteration of a ventilated concrete cask used for spent nuclear fuel storage is carried out through three-dimensional Computational Fluid Dynamics (CFD) simulations. The present study reveals that the new proposal returns values for the convective heat transfer coefficient that are almost three orders of magnitude higher than the base case. Hence, proving that even making such a rather simple alterations to the smooth walls geometry, i.e. adding undulations or semi-circular fins, can result in a significant convective heat transfer enhancement, therefore, further reducing the risks of structural damages caused by the dry-storage system overheating. Before conducting the design optimization study mentioned above, two validation test cases have been considered in order to examine the Reynolds Averaged Navier-Stokes (RANS) models’ capability to predict the flow under buoyancy driven and low turbulence levels such is the case in the passively cooled dry cask system. The test cases considered in the validation study sections are the experimental measurements of Betts and Bokhari for turbulent natural convection in an enclosed tall cavity and the temperature measurements in concrete-shielded spent fuel storage cask system reported by McKinnon. The models selected for the validation study are namely the k-ω SST model, the v2-f model, the low-Reynolds k-ε model, and the recently formulated elliptic blending k-ε model. It has been found that out of these models, the low-Reynolds k-ε model was found to provide a good combination in returning both; physically realistic and conservative solution. The present validation using well-resolved RANS simulations has shown that a more quantitative and detailed comparison of the predictions is required in order to clearly highlight the discrepancies between the models’ predictions in terms of velocity, turbulent kinetic energy and, in particular, convective heat transfer coefficient profiles. The commonly adopted methodology in limiting the validation process to temperature profiles comparison only, would cover up these differences as the temperature variation is affected by the combined effects of the convective and the radiation heat transfer modes.

Study on Thermal Distortion and Thermal Design Optimization of Satellite Antenna Reflector during Orbit Period

Reflector thermal distortion status is essential to performance stability of communication satellite antenna in geosynchronous orbit, and should be carefully validated in design period. Thermal distortion simulation of current satellite antenna reflector is usually conducted by numerical calculation of extreme temperature field condition from thermal analysis results. However, telemeasuring result shows that, the worst performance time of antenna is not usually under these extreme temperature conditions, and it is necessary to analyze the thermal distortion features of satellite antenna during the whole orbit period to provide efficient instructions for design of the antenna thermal control.

Multiobjective and Multicase Optimization of a Spacecraft Radiator

Optimization is now an established tool for obtaining better solutions in engineering design. Nevertheless, the multiplicity of possible applications and the continuing search for better computational performance has motivated researchers in continuing to propose new methods, as well as improvements on existing ones. Not only optimization has allowed a better exploration of the design space, it also can significantly reduce the time of the design process. In this paper the advantages of using a fully multiobjective and multicase approach for the design of space radiators is presented. The optimization of Amazonia-1 satellite batteries panel thermal design is investigated. Instead of conventional space radiators, in this work an innovative solution considering the fin as heat absorber is analyzed. The results have shown that there are several viable configurations regarding to fin coating material, heater power consumption and additional mass, and the choice of the appropriate radiator configuration shall be evaluated based on system impact. The possibility of testing automatically different coatings and sizes for the fin, allowed by the optimization approach, increased significantly the probability of finding viable solutions on the design space.

A quantity-quality-based optimization method for indoor thermal environment design

This paper proposes a quantity-quality-based optimization method of indoor thermal environment design that emphasizes entransy and exergy analysis. We scrutinized the different focuses of entransy and exergy in examining an energy-related phenomenon or process, and pointed out the need for integrating entransy and exergy for the optimization of indoor thermal environment design. The proposed method contributes to identifying the most energy-efficient solution for attaining the same level of indoor thermal comfort for end users by quantifying the entransy and exergy efficiency of active technologies. With this method, a benchmark technical solution was properly determined and benchmarks for entransy dissipation and exergy loss during the process of thermal environment design were quantified. Entransy dissipation and exergy loss under common technologies were compared with the benchmark values. The concepts of relative entransy savings and relative exergy savings were defined as the evaluation indexes of technical energy efficiency. Referencing winter indoor thermal environment design for residential buildings in hot-summer and cold-winter (HSCW) regions in China, the proposed method was applied to assess the energy efficiency of different heating methods, including an inverter air conditioner, an “air source heat pump + floor radiation,” a “wall-hanging gas heater + floor radiation,” a “wall-hanging gas heater + radiator,” and an oil-filled radiator. This paper recommended that the “air source heat pump + floor radiation” be used for residential buildings in winter in HSCW regions to improve energy efficiency. In addition, the optimization results of the proposed method were compared with that of traditional energy and exergy analysis methods. The results showed that the new method more accurately analyzed the energy flow in indoor thermal environment design, and therefore can serve as an improved way of thinking about follow-up studies on the optimization of heat pump units and the operation strategies of floor radiant heating systems.

Thermal simulation analysis and optimization design of miniaturized traveling wave tube amplifier

This paper introduces the thermal simulation analysis and optimization design method of the miniaturized traveling wave tube (TWT) amplifier. Firstly, the thermal loss of TWT is analyzed. Then, based on the thermodynamic theory and ANSYS Icepak software, the TWT amplifier is modeled and simulated. According to the characteristics of the miniaturized TWT, the thermal optimization design of the water-cooled plate and the slow-wave structure are carried out respectively. On this basis, the comprehensive optimization design of the water-cooled plate and the slow-wave structure is carried out. Finally, the experimental verification is executed. The experimental results are in agreement with the simulation results. The overall and local temperature distribution characteristics of the TWT amplifier have been significantly improved.

Thermal design optimization and analysis on heating load of rural buildings in northern China

The envelope of rural buildings has been lack of effective and reasonable thermal insulation method and therefore its energy consumption has always been high. In order to address this problem, this paper aims to optimize the thermal design of building envelope. The simulation using DesignBuilder software for modeling and analyzing, using the orthogonal experimental design method to study the effects of external wall, external window and roof on heating load, and optimal thermal insulation scheme was obtained, which was 100mm PUF (external wall), 6mm+12mm+6mm low-E glass (external window) and 100mm PUF (roof). Results revealed that the addition of sunspace can significantly reduce the heating load and thus the selection of window thermal insulation material is very important. Compared with the condition of highest heating load, the energy-efficient rate of optimal scheme reached to 21.4%. The results of this study will serve as the idea for optimal design of rural buildings envelope.

Thermal resistance modelling and design optimization of PCB vias

Various reference printed circuit board (PCB) thermal designs have been provided by semiconductor manufacturers and researchers. However, the recommendations are not optimal, and there are some discrepancies among them, which may confuse electrical engineers. This paper aims to develop an analytical thermal model for PCB vias, and further to find the optimal design for thermal resistance minimization. Firstly, the vertical thermal resistance of a PCB via array is analytically modelled. Then the dependence of the thermal resistance on multiple design parameters is analysed, and the optimal via diameter is found for different PCB specifications. Finally, the developed thermal model and optimal trajectory are verified by computational fluid dynamics (CFD) simulations and experiments.

Three-dimensional X-ray thermography using phase-contrast imaging

Thermal management is a key technology to desterilize unused energy sources for building sustainable societies. However, conventional temperature measurement methods such as infrared thermography can detect only the surface temperature of objects because they use infrared light. We thus present a novel three-dimensional X-ray thermography using a phase-contrast X-ray imaging technique, which enables non-destructive observations of the inner thermal distribution of samples. The sensitivity of phase-contrast X-ray imaging is about 1000 times higher than that of conventional X-ray imaging. Therefore, temperature changes can be detected by using density changes caused by thermal expansion. We applied X-ray interferometric imaging (XI) that detects phase-shift by using a crystal X-ray interferometer. The highest sensitivity of XI was utilized to successfully obtain the first three-dimensional image that visualizes the thermal distribution in heated water nondestructively. Additionally, projection images visualizing the dynamic thermal flow in heated water were also obtained, and their distribution and diffusion velocity agreed well with those of the calculated images obtained by computational fluid dynamics analysis. These results show that the novel thermography enables nondestructive observations of inner temperature and thermal flow and can provide solutions for optimum thermal design of electrical devices, motors, and engines.

Thermal design optimization of evaporator micropillar wicks

Heat pipes and vapor chambers act as efficient heat spreaders since they rely on phase change of the coolant. The evaporator design is critical and typically high performance is characterized by the high heat dissipation capability with low thermal resistance. In the past, there have been numerous experimental and modeling studies focused on the design of evaporator wicks of different geometries, but systematic studies to simultaneously optimize both the heat flux and thermal resistance have been limited. In this work, we developed a comprehensive model that considers both aspects to provide design guidelines for evaporator micropillar wicks. We show that capillary limited heat dissipation is best captured with a recently developed numerical model as compared to previous analytical models. We also developed a numerical model to obtain the effective wick thermal conductivity, which is a function of pillar diameter, pitch, and height. Smaller diameters with smaller pitches of the pillars had more thin film area and had larger effective wick thermal conductivities. Our parametric investigations show that trade-offs between lowest thermal resistance and maximum heat carrying load exists, and the actual wick geometry will be dictated by application specific requirements. Finally, we highlight the importance of accurately obtaining the accommodation coefficients to predict the effective wick thermal conductivity. The present work would enable in optimal design of micropillar wicks (with low thermal resistance and high dry-out heat flux) and the same methodology can be extended to other types of wick structures as well.