Thermal Design Optimization Research Articles

Thermal Analysis of Convective-Radiative Fin with Temperature-Dependent Thermal Conductivity Using Chebychev Spectral Collocation Method

In this paper, the Chebychev spectral collocation method is applied for the thermal analysis of convective-radiative straight fins with the temperature-dependent thermal conductivity. The developed heat transfer model was used to analyse the thermal performance, establish the optimum thermal design parameters, and also, investigate the effects of thermo-geometric parameters and thermal conductivity (nonlinear) parameters on the thermal performance of the fin. The results of this study reveal that the rate of heat transfer from the fin increases as convective, radioactive, and magnetic parameters increase. This study finds good agreements between the obtained results using the Chebychev spectral collocation method and the results obtained using the Runge-Kutta method along with shooting, homotopy perturbation, and Adomian decomposition methods.

One-dimensional metal-hydride tank model and simulation in Matlab–Simulink

A model has been developed for a metal-hydride tank for hydrogen storage, based on linked modular mathematical models in Simulink®. The objective of the work was a tank-level model suitable for incorporation into a whole-of-system model, implying modest computing demands and reduced complexity. Finite-element analysis was not used. Because the apparent kinetics of a practicable metal-hydride tank is dominated by heat flow originating in the enthalpy of hydrogen absorption/desorption, particular attention was paid to modelling the effective thermal conductivity, based on a detailed description of the thermal resistance between hydride particles. The model was tested against our own experimental data for a pair of tanks with 6.4 kg total hydrogen capacity, and compared with a published 2D model and published experimental data. In all cases, the new model performed very well. The incorporation of a physical model of the effective thermal conductivity means that the tank model can also be used as a research tool to investigate ways of improving tank performance by altering the physical characteristics of the metal-hydride itself to achieve an optimal thermal design and enhanced reaction kinetics.

Research of electromagnetic and thermal optimization design on air core reactor

In this paper, the geometry‐electromagnetic character, thermal condition of the coils, and encapsulation number are coupled in the optimization design of an air core reactor, to realize the minimum usage of metal conductor. Combined with the equality constraint conditions for maximum temperature rise conservation, inductance conservation, and structure function of the reactor, the optimization design curves and results are achieved based on the initial design parameters. According to the design results, the temperature field simulation model of the reactor is established, and the results verify the correctness of the optimization method. Compared with the design method of ‘equal height and heat flux’ and thermal‐electromagnetic character without considering the change of encapsulation number, the proportionality factor of metal conductor usage is 0.73 with the optimization method. It shows that the optimization method can significantly improve the utilization ratio of the conductor. Meanwhile, the influence of regularity on the electromagnetic efficiency, thermal efficiency, and other parameters is also obtained. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Experimental study on the influence of junction temperature on the relationship between IGBT switching energy loss and device current

Accurate determination of power losses in semiconductor devices is important for optimal design and reliable operation of a power converter. The switching loss is an important component of the total device loss in an insulated-gate bipolar transistor (IGBT) in a voltage source inverter. The objective here is to study experimentally the influence of junction temperature on the turn-on switching energy loss Eon and turn-off switching energy loss Eoff. More specifically Eon and Eoff are both related to device current Ic; the influence of junction temperature on the relationship between Eon and Ic and that between Eoff and Ic is studied. As the operating environmental conditions and load conditions of power converter vary widely, a wide range of junction temperatures between −35°C and +125°C is considered here. The experimental data enable precise determination of the switching loss in each device in a high-power converter at any practical operating condition. This leads to precise estimation of total device loss and optimal thermal design of the converter. This further helps off-line and/or on-line estimation of device junction temperatures required for study of thermal cycles and reliability.

Multi-Variable Optimization of Building Thermal Design Using Genetic Algorithms

The building sector is one of the largest energy consumers in the world, comprising about 40% of the total energy consumption in numerous countries. Early design decisions have a significant impact on the energy performance of buildings. The paper presents the multi-variable optimization of the selected design parameters in a single-family building in temperate climate conditions. The influence of four types of windows, their size, building orientation, insulation of external wall, roof and ground floor and infiltration on the life cycle costs (LCC) is analyzed. Optimal selection of the design parameters is carried out using genetic algorithms by coupling the building performance simulation program EnergyPlus with optimization environment. The simulations were conducted for seven optimization cases. The analysis is performed for two variants of a building with heating and cooling systems and with a heating system only. Depending on the analyzed case, the life cycle costs decreased from 7% to 34% LCC value of the reference building. In the case of temperate climate, the building optimization (in terms of heat demand only) substantially reduces the heating costs, yet the summer thermal comfort conditions deteriorate significantly.

Model-based thermal system design optimization for the James Webb Space Telescope

Spacecraft thermal model validation is normally performed by comparing model predictions with thermal test data and reducing their discrepancies to meet the mission requirements. Based on thermal engineering expertise, the model input parameters are adjusted to tune the model output response to the test data. The end result is not guaranteed to be the best solution in terms of reduced discrepancy and the process requires months to complete. A model-based methodology was developed to perform the validation process in a fully automated fashion and provide mathematical bases to the search for the optimal parameter set that minimizes the discrepancies between model and data. The methodology was successfully applied to several thermal subsystems of the James Webb Space Telescope (JWST). Global or quasiglobal optimal solutions were found and the total execution time of the model validation process was reduced to about two weeks. The model sensitivities to the parameters, which are required to solve the optimization problem, can be calculated automatically before the test begins and provide a library for sensitivity studies. This methodology represents a crucial commodity when testing complex, large-scale systems under time and budget constraints. Here, results for the JWST Core thermal system will be presented in detail.

Thermal design optimization analysis of an intermediate fluid vaporizer for liquefied natural gas

An intermediate fluid vaporizer (IFV) is the core heat transfer equipment in a liquefied natural gas (LNG) regasification system, particularly in an offshore floating LNG receiving terminal where more efforts are focused on improving the efficiency and structure size of the vaporizer for reducing the volume and weight. By considering the constraints of both the initial velocities of the working fluids and length of the heat transfer tubes, a new numerical model based on the distributed parameter method is developed to determine the heat transfer performance and required heat transfer area (HTA) of an IFV. The effects of the intermediate fluids and their saturation parameters, inlet temperature of the seawater, and temperature drop of the seawater in the thermolator are investigated. The results show that propylene exhibits the best heat transfer performance, but its higher saturation pressure would require an increase in the wall thickness of the IFVs and therefore, limit its application. The heat transfer performances of propane and dimethylether are better than the other intermediate fluids, and are promising to be used in IFVs. With increase in the saturation temperature of propane, the required total HTA of IFVs first decreases and then increases, and the optimal saturation temperature is in the range of 250–265 K. A higher seawater temperature is beneficial for reducing the HTA, and it is also indicative of a wider optimization saturation temperature range in which the required total HTA is not sensitive to the saturation temperatures. When the temperature drop of the seawater in the thermolator varies from 0.3 K to 0.8 K, the variation in the required area is not more than 5% compared to the lowest area, and the recommended range for the corresponding heat load ratio between the evaporator and condenser is recommended is 5–15.

Multi-objective thermal design optimization of plate frame heat exchangers through Global Best Algorithm

This study deals with thermal design of plate frame heat exchangers based on Global Best Algorithm. By utilizing some basic perturbation schemes adopted from Differential Search and Differential Evolution, Global Best Algorithm aims to obtain optimum solution of any optimization problem with intensifying on exploitiation of the promising solutions rather than exploring of the unvisited paths of the search domain. Firstly, optimization performance of the proposed algorithm has been benchmarked against variety of well-known optimization algorithms by means of 16 different highly challenging optimization test functions. Then, the proposed method is put into practice to acquire the optimal values of the design variables those optimize the considered problem objectives including overall heat transfer coefficient, total cost and weight of the plate frame heat exchangers seperately as well as simultaneously. Considerable improvement in objective function values is observed as compared to preliminary design in single objective manner. Pareto frontier is constructed for dual and triple objective and best optimal solution among the curve is selected by means of the widely-known decision making methods of LINMAP, TOPSIS, and Shannon’s entropy theory. Optimal results obtained from each decision making theory are compared with respect to their corresponding deviation indexes and the best one is preferred. A sensitivity analysis is then performed to study the variational influences of some design parameters on the considered objective functions. It is observed that selected design variables has a signficant effect on problem objectives.

Thermoeconomic performance and optimization of a novel cogeneration system using carbon dioxide as working fluid

A novel cogeneration power and refrigeration system using carbon dioxide as working fluid, is proposed, analyzed and optimized. The system is an internally interacting combination of a supercritical carbon dioxide recompression Brayton cycle and a transcritical carbon dioxide refrigeration cycle with an expander. The system proves to perform either as a cogeneration system producing power and refrigeration or only refrigeration system. The effects on system’s thermodynamic and economic performances are quantified of the main decision parameters. The systems performance is optimized for having either maximum first law efficiency or maximum second law efficiency or minimum total product unit cost, for both the cogeneration and refrigeration only situations. It is shown that, for the cogeneration situation, the minimum total product unit cost in cost optimal design case is 3.5% lower than that for the exergy efficiency optimal design cases. For the refrigeration only situation, it is observe that the minimum total product unit cost obtained for the cost optimal design case is 18.9% and 4.2% lower than those for the thermal and exergy efficiencies optimal design cases, respectively. The highest value of refrigeration capacity is obtained for the thermal optimal design case for the system when it produces refrigeration only. At the refrigeration only situation the lowest evaporator temperature is achieved when the system is optimized for maximum exergy efficiency.

Investigation of dynamic heat transfer process through coaxial heat exchangers in the ground

Recently, researchers are focussing on using ground coupled heat pump systems as a heat source or sink rather than air source heat pumps for HVAC needs due to the stable temperature and the high thermal inertia of the soil. The investment cost of these systems is too expensive therefore the precise thermal analysis, design and parameter optimization are essential. For an accurate design, the maximum of physical phenomena such as: axial effects, seasonal effects, underground water flow and BHE dynamic behaviour must be accounted for in order to reflect exactly the real physical situation. In the present paper thermal interferences are investigated under seasonal effects and a dynamic heat flux for a vertical coaxial borehole heat exchangers field. This enables to avoid thermal interferences by predicting efficient period of operation corresponding to the beginning of the studied phenomena (interferences) for a given separation distance between two boreholes. To reach this purpose, as a first step, a transient 2D Finite volume method (FVM) for a single borehole heat exchanger was built using MATLAB, which accounts for accurate axial and seasonal effects and a dynamic heat flux that is function of depth and time. This model has been validated against the Finite Line Source (FLS) analytical solution and good agreement between analytical and numerical methods has been obtained. Then the model has been extended to a quasi-3D model in order to investigate thermal interferences between two neighbouring boreholes. After 500 h and at the mid-point of the separating distance (1.5 m) where interferences are the strongest, the temperature is 50% (6.64 °C) lower than the case where there are no interferences.

Steady state and transient analytical modeling of non-uniform convective cooling of a microprocessor chip due to jet impingement

Heat removal from microprocessor chips with multiple regions of dynamic heat generation remains a critical technological challenge. Excessive temperature rise is undesirable for performance as well as reliability. Jet impingement cooling has been widely investigated as a potential thermal management technique due to the capability of localized cooling and of dynamically following the heat generation distribution. A jet offers large local convective heat transfer coefficient, for which theoretical models and correlations have been proposed for a variety of scenarios. However, not much work exists on using this information to determine the resulting temperature distribution. This paper addresses this need by developing analytical steady state and transient heat transfer models that account for the spatial variation in convective heat transfer coefficient and for spatially non-uniform heat flux. The solution is derived in the form of an infinite series, the coefficients of which are determined by solving a set of algebraic equations. Temperature rise predicted by the models are found to be in excellent agreement with finite-element simulations, while offering faster computation time and easier integration with design and performance optimization tools used in microelectronics. The analytical model is used for predicting temperature rise in a variety of scenarios to examine interesting optimization problems such as the cooling of multiple hotspots with a single jet, determining the optimal location of a jet, etc. Results presented here may facilitate improved thermal design and real-time performance optimization of microprocessor chips.

A simulation-based two-step method for optimal thermal design of multiple compartments

To achieve the target of temperature control with minimum power consumption, a simulation-based two-step method for optimal thermal design of multiple compartments is proposed. First, the flow passages are designed to accomplish the goal of allocating the cooling capacity based on thermal load distribution. Thermal load analysis is performed to obtain an approximate flow rate. Multiple tools, including genetic algorithm (GA), design of experiment (DOE), response surface method (RSM) and computational fluid dynamic (CFD) are coupled to find the approximate solutions of the design variables. These approximate solutions are set as an estimation of the Pareto solutions of the tradeoff between temperature targets and power consumption. Secondly, a multi-objective genetic algorithm and CFD are coupled to find the Pareto solutions. A model of multiple compartments with different thermal loads is evaluated as demonstration. The results reveal that the response surfaces based on a 200% over-determined provide a satisfactory predicting capability. The solution space is greatly reduced in the first step with less computational cost. The approximate solutions obtained from the design of flow passages are an excellent estimation of the optimal solutions. For the second step, the Pareto solutions satisfying the requirement of temperature control are acquired through the evolution of 10 generations.

Balancing Thermal and Electrical Packaging Requirements for GaN Microwave and Millimeter-Wave High Power Amplifier Modules

A method for balancing thermal and electrical packaging requirements for gallium nitride (GaN) high power amplifier (HPA) modules is presented. The goal is to find a design approach that minimizes the junction temperature of the GaN so that it is reliable and has interconnects that meet electrical performance requirements. One benefit of GaN is that it can simultaneously achieve high power density and operate at microwave and millimeter-wave frequencies. However, the power density can be so high that the necessary thermal solutions can have negative impact on electrical performance. This is especially a concern for the electrical interconnects required for the input/ output ports on high power amplifier devices. This is because the signal interconnects must operate at GHz frequencies, which means that special care must be taken to avoid problems such as undesired signal coupling and ground path inductance. Therefore, this work focuses on GaN packaging and its integration into a module. The results show that an optimum thickness for the GaN heat spreader exits for thermal performance but the electrical design is impacted negatively if the optimum thermal design is chosen. Therefore, a balanced design is chosen which meets overall system level requirements.

A compactly integrated cooling system of a combination dual 1.5-MW HTS motors for electric propulsion

The high temperature superconducting (HTS) contra-rotating propulsion (CRP) systems comprise two coaxial propellers sited on behind the other and rotate in opposite directions. They have the hydrodynamic advantage of recovering the slipstream rotational energy which would otherwise be lost to a conventional single-screw system. However, the cooling systems used for HTS CRP system need a high cooling power enough to maintain a low temperature of 2G HTS material operating at liquid neon (LNe) temperature (24.5 - 27 K). In this paper, a single thermo-syphon cooling approach using a Gifford-McMahon (G-M) cryo-cooler is presented. First, an optimal thermal design of a 1.5 MW HTS motor was conducted varying to different types of commercial 2G HTS tapes. Then, a mono-cryogenic cooling system for an integration of two 1.5 MW HTS motors will be designed and analyzed. Finally, the 3D finite element analysis (FEA) simulation of thermal characteristics was also performed.

Numerical analysis of a plain-fin type heat exchanger with two tubes in a crevice-type heat pipe

This paper employs numerical tools to obtain an optimal thermal design of a heat exchanger with plain-fins. This heat exchanger is located at the condensing section of a crevice-type heat pipe. The plain-fins in the heat exchanger are radically mounted to two tubes in the condensing section. To obtain the optimal design parameters, a computational fluid dynamics technique is introduced and applied to different placement configurations in a system module. Owing to its effects on the heat pipe performance, the temperature difference between the tube surfaces and ambient air is investigated in detail. A greater heat dissipation rate occurs when the plain-fin offsets change from 2 to 3 mm. When this temperature difference is ΔT=70°C, the upper part of the plain-fins undergoes an accumulation of heat. At below 70 °C, the dissipation of heat is accepted. A rectangular plain-fin geometry with varying widths and heights does not have a significant impact on the heat dissipation throughout the overall system. In addition, the temperature distributions between different plain-fin pitches show an equal profile even with different fin pitches.

Degradation modeling of satellite thermal control coatings in a low earth orbit environment

Thermal control coatings are widely used in passive thermal control systems of satellites. These coatings ensure that the temperatures remain within the safe operating limits. The purpose of this paper is to present a degradation modeling method for thermal control coatings used in satellites in a low earth orbit (LEO). The materials investigated in the present study include the S781 white paint and the F46 second surface mirror. The LEO environmental factors that cause the degradation of these materials and the corresponding failure mechanisms are discussed first. With in-orbit telemetry temperatures, an energy balance equation is used to calculate the solar absorptance of the coatings on several LEO satellites. Results show that the solar absorptance of the coatings degrades significantly over time and can thus be used as a crucial performance parameter for the characterization of coating degradation. A Wiener process with time transformation is used to model the nonlinear degradation characteristic of solar absorptance. The first hitting time is employed to model failure time with consideration of a critical degradation level. The degradation modeling method is accurate, and the results provide insight into the life prediction and thermal design optimization of LEO satellites.

Thermal design optimization of novel modular power converter assembly enabling higher performance, reliability and availability

An alternative integration scheme for a half-bridge switch using 70μm thin Si IGBTs and diodes is presented. This flat switch, which is designed for high-frequency application with high power density, exhibits high strength, high toughness, low parasitic inductance and high thermal conductivity. Such a novel assembly approach is suitable to optimize performance, reliability and availability of the power system in which it is used. The paper focuses on the thermal performance of this assembly at normal and extreme operating conditions, studied by means of FEM thermo-fluidynamic simulations of the module integrated with connectors and liquid cooler, and thermal measurement performed on an early prototype. Improved solutions are also investigated by the FE model.

The simulation methods based on 1D/3D collaborative computing for the vehicle integrated thermal management

The vehicle integrated thermal management containing the engine cooling circuit, the air conditioning circuit, the turbocharged inter-cooled circuit, the engine lubrication circuit etc. is the important means of enhancing power performance, promoting economy, saving energy and reducing emission. In this study, a 1D/3D collaborative simulation method is proposed with the engine cooling circuit and air conditioning circuit being the research object. The mathematical characterizations of the multiple thermodynamic systems are achieved by 1D calculation and the underhood structure is described by 3D simulation. Through analyzing the engine compartment integrated heat transfer process, the model of the integrated thermal management system is formed after coupling the cooling circuit and air conditioning circuit. This collaborative simulation method establishes structured correlation of engine-cooling and air conditioning thermal dissipation in the engine compartment, comprehensively analyzing the engine working process and air condition operational process in order to research the interaction effect of them. In the calculation examples, to achieve the integrated optimization of multiple thermal systems design and performance prediction, by describing the influence of system thermomechanical parameters and operating duty to underhood heat transfer process, performance evaluation of the engine cooling circuit and the air conditioning circuit are realized.

High Temperature Shear Horizontal Electromagnetic Acoustic Transducer for Guided Wave Inspection.

Guided Wave Testing (GWT) using novel Electromagnetic Acoustic Transducers (EMATs) is proposed for the inspection of large structures operating at high temperatures. To date, high temperature EMATs have been developed only for thickness measurements and they are not suitable for GWT. A pair of water-cooled EMATs capable of exciting and receiving Shear Horizontal (SH0) waves for GWT with optimal high temperature properties (up to 500 °C) has been developed. Thermal and Computational Fluid Dynamic (CFD) simulations of the EMAT design have been performed and experimentally validated. The optimal thermal EMAT design, material selection and operating conditions were calculated. The EMAT was successfully tested regarding its thermal and GWT performance from ambient temperature to 500 °C.

Envelope Thermal Design Optimization for Urban Residential Buildings in Malawi

This study sought to optimize the envelope thermal design of free-running urban residential buildings in Malawi. It specifically set out to improve the urban residential buildings’ thermal comfort and suggest optimal envelope thermal design features for these buildings. The research study was primarily dependent on computer simulations in EnergyPlus to replicate the typical Malawian urban residential building’s thermal behaviour and then study the impacts of various envelope configurations on the thermal comfort conditions registered in the building. The simulation model was experimentally validated to check its appropriateness to the climatic design conditions prevalent in Malawi and out of the three major cities that were considered, the model was found to be appropriate for use in the two cities of Mzuzu and Lilongwe leaving out the city of Blantyre. The optimization methodology that was employed involved the use of orthogonal arrays, statistical analyses and the listing method. It was found that the optimal envelope thermal design, which registered up to 18% lower discomfort hours than that of the typical urban residential building, consists of a 50 mm concrete floor slab, 230 mm burnt brick walls with an external layer of 19 mm EPS, tiled roof with an internal layer of sarking and 50 mm EPS, double Low-E Glazing with a transparency ratio of 45% and 0.2408 m2 of adaptable operational surface area for the air bricks. Out of all the envelope features that were studied, air infiltration registered the most significant contribution towards the ultimate residential building thermal performance. It was demonstrated that controlled air infiltration through the use of operable air bricks whose operational surface area is adaptable can be very effective in enhancing the building’s comfort levels. It was further observed that excessive insulation of the building envelope generally has a detrimental effect on the indoor space thermal comfort levels.