Thermal Design Process Research Articles

Introduction to thermal control design process for CubeSats in Mexico

Abstract CubeSats are a popular type of spacecraft categorized as nanosatellites. In 1999, Professors first developed these devices at California Polytechnic State University and Stanford University to offer an affordable and accessible experience to students. Data information updated up to May 31st, 2023, shows that 2286 Nanosats have been launched, where 2105 were CubeSats. Moreover, 82 countries have nanosats, whereas Latin America has 44 CubeSat. The fact that Mexico just 5 launched 5 CubeSats is a consequence of the complicated space sector ecosystem in the nation that combines lack of funding and, more importantly, the absence of ¨know-how¨ design space missions from scratch. This manuscript reviews the system engineering methodology used to develop space missions, according to NASA discussing a particular methodology for CubeSat Missions. Next, a CubeSat data trend is shown, followed by a general description of its subsystems. Afterward, the design process activities of the Thermal Control Subsystem (TCS) based on the “NASA Systems Engineering Processes and Requirements” and “Thermal analysis handbook is described. The TCS is often underestimated and confused to implement. For this reason, a design methodology for the TCS accepted to Mexico context is proposed. Finally, the conclusions are presented.

Lumped Parameter Thermal Network Modeling and Thermal Optimization Design of an Aerial Camera.

The quality of aerial remote sensing imaging is heavily impacted by the thermal distortions in optical cameras caused by temperature fluctuations. This paper introduces a lumped parameter thermal network (LPTN) model for the optical system of aerial cameras, aiming to serve as a guideline for their thermal design. By optimizing the thermal resistances associated with convection and radiation while considering the camera's unique internal architecture, this model endeavors to improve the accuracy of temperature predictions. Additionally, the proposed LPTN framework enables the establishment of a heat leakage network, which offers a detailed examination of heat leakage paths and rates. This analysis offers valuable insights into the thermal performance of the camera, thereby guiding the refinement of heating zones and the development of effective active control strategies. Operating at a total power consumption of 26 W, the thermal system adheres to the low-power limit. Experimental data from thermal tests indicate that the temperatures within the optical system are maintained consistently between 19 °C and 22 °C throughout the flight, with temperature gradients remaining below 3 °C, satisfying the temperature requirements. The proposed LPTN model exhibits swiftness and efficacy in determining thermal characteristics, significantly facilitating the thermal design process and ensuring optimal power allocation for aerial cameras.

Design and thermo-enviro-economic analyses of a novel thermal design process for a CCHP-desalination application using LNG regasification integrated with a gas turbine power plant

Designing and studying processes with reduced thermodynamic irreversibility and environmental impact is imperative to improve the global applicability of the stand-alone gas turbine cycles. Hence, the present study introduces a novel cascade heat integration tool for a gas turbine cycle combined with a liquefied natural gas cold energy utilization and regasification process. A saltwater desalination subsystem, an absorption chiller, and an organic Rankine cycle are also included in the integrated system. Therefore, the developed system demonstrates an environmentally friendly combined cooling, heating, power, and freshwater production framework, improving the performance of the system in comparison to previous research. This configuration is simulated within the Aspen HYSYS software for comprehensive energy, exergy, environmental, and economic assessments. The findings demonstrate that the whole configuration yields energy and exergy efficiencies of 92.92% and 63.5%, respectively. In comparison, these efficiencies in the single-generation mode are found to be 45.92% and 43.72%, correspondingly. The environmental analysis reveals that the carbon dioxide footprint equals 0.1792 kg/kWh when operating in the multigeneration mode and 0.4591 kg/kWh in the single-generation mode. Furthermore, the economic evaluation exhibits that the cost of energy equals 67.2 $/MWh and 135.92 $/MWh for the multigeneration and single-generation operational modes, respectively.

A new thermal management figure of merit for design of thermal energy storage with phase change materials

Phase Change Materials (PCMs) are frequently employed in thermal management of systems with high heat fluxes because their high latent heat of phase change limits transient temperature rises and damps temperature fluctuations. In general, detailed numerical analysis is used to design such systems. However, for an efficient thermal design process, it is desirable to have an analytic method to perform a quick quantitative comparison between all the available PCMs considering potential design configurations. The previously developed Figure of Merit (FoMc) for PCMs only depends on the thermophysical properties of the PCM and does not account for other relevant information such as geometry, melting temperature, and boundary condition. In the present work, we develop a novel performance factor (f) that works in conjunction with the material property based FoM to gauge the performance of different PCM-based thermal management systems (TMSs). The performance factor f is based on the characteristic timescales for thermal diffusion and thermal storage in a PCM system. First, this work demonstrates the range of applicability of our new FoM (fFoMc) for various PCMs (3 metallic, 4 organic, and 3 inorganic materials) across different geometrical and boundary configurations. The PCM performance is evaluated using transient numerical simulations with the metric of the maximum temperature rise in the domain after a fixed heating time. For a single PCM in different geometries, the maximum temperature rise decreases with increased f. For a general PCM-based TMS (i.e., a random combination of PCM, geometry, and boundary condition), the maximum temperature rise generally decreases with increasing the newly proposed FoM (fFoMc). Second, we extend the analysis to a composite PCM (an aluminum foam impregnated with organic PCM) to estimate the optimum porosity (ϕopt) for different geometric configurations. The analytically estimated ϕopt agrees well with the values calculated from optimizing detailed finite element simulations. Furthermore, this approach can explain the effect of expected duration of the PCM use on the ϕopt value using the proposed FoM. Overall, the proposed approach can identify the best performing geometrical configuration for a certain PCM or shortlist best performing PCM for a given setup of PCM-based TMS without detailed numerical simulations, making the design process more efficient.

The oil bath thermal cycling absorption process design and separation process research

Thermal cycling absorption process (TCAP) has been developed for years to support the separation of hydrogen isotopes, which has the characteristics of high separation efficiency and high recovery rate. The design of separation column structure, heating and cooling (H&C) system and technological parameters are the basis of TCAP technical process study and are the key points of TCAP engineering research. In this work, an improved separation system has been designed and built based on an oil bath H&C system for the first time. The separation column in this facility is 45 m long and the packing weight in the column is up to 8 kg. The separation experiments were carried out based on this facility, and the process parameters were adjusted according to the size of the separation column, which proved the superior performance of this facility. The separation experiments show that for 50% D2 - 50% H2 feed gas, the deuterium abundance can reach to 99% and the steady state extraction can be realized in production mode with the processing capacity over 400 standard L per day. Another experiment has been carried out with 1% D2 - 99% H2 feed gas, and the deuterium abundance exceeded 10%, verifying the separation ability at low abundance deuterium feed gas. Furthermore, the extraction rate can reach to 25% column capacity when the deuterium abundance in production gas is 5%.

Correlation of single-phase convective heat transfer on spray cooled plain surfaces with high Prandtl number liquids

Spray cooling with transmission oils is an innovative cooling concept for electrical machines, whereby the coolant wets the end windings directly. The thermal design process of such machines requires reliable correlations of the heat transfer coefficients obtainable. Thereby, the majority of the literature only focuses on low Prandtl number coolants at ideal nozzle distances. The transferability of the existing heat transfer models to highly viscous coolants above and below the optimal nozzle distance has yet to be investigated. Therefore, the heat transfer coefficients of spray cooling on plain surfaces with aqueous glycerol solutions (model fluid) and a transmission oil of type ATF VI was investigated. The model fluid serves the purpose of covering the entire range of material properties of commercial transmission oils with only one liquid. Prandtl numbers ranging from 80 to 340 were investigated. Various cases of spray coverage were researched by varying the nozzle distance (2mm−100mm), the spray angle (20∘−80∘) and the size of the spray cooled surface (6.35×6.35mm2;12.7×12.7mm2). Regarding the case of the optimal nozzle distance, where the spray impact area just inscribes the cooled surface, the experimental data was validated with models from the literature. Large deviations of up to 450% resulted at nozzle distances above and below the optimum. Therefore, a dimensionless correlation of the heat transfer coefficient is proposed which includes all cases of spray coverage investigated, exceeding the applicability range of the existing models. The model describes the experimental data with a mean absolute percentage error of 15%.

Deep convolutional surrogates and freedom in thermal design

A deep learning approach is presented for heat transfer and pressure drop prediction of complex fin geometries generated using composite Bézier curves. Thermal design process includes iterative high fidelity simulation which is complex, computationally expensive, and time-consuming. With the advancement in machine learning algorithms as well as Graphics Processing Units (GPUs), parallel processing architecture of GPUs can be used to accelerate thermo-fluid simulation. In this study, Convolutional Neural Networks (CNNs) are used to predict results of Computational Fluid Dynamics (CFD) directly from topologies saved as images. A design space with a single fin as well as multiple morphable fins are studied. A comparison of Xception network and regular CNN is presented for the case with a single fin design. Results show that high accuracy in prediction is observed for single fin design particularly using Xception network. Xception network provides 98 percent accuracy in heat transfer and pressure drop prediction of the single fin design. Increasing the design freedom to multiple fins increases the error in prediction. This error, however, remains within three percent of the ground truth values which is valuable for design purpose. The presented predictive model can be used for innovative BREP-based fin design optimization in compact and high efficiency heat exchangers.

Machine Learning Strategy for Wall Heat Flux Prediction in Aerodynamic Heating

The efficient and accurate prediction of the aeroheating performance of hypersonic vehicles is a challenging task in the thermal protection system structure design process, which is greatly affected by grid distribution, numerical schemes, and iterative steps. From the inspiration of the theoretical analysis and machine learning strategy, a new wall heat flux prediction framework is proposed first by establishing the relationship between the wall heat flux and the flow variables at an extreme temperature point (ETP) in the normal direction of the corresponding wall grid cell, which is named the machine learning (ML)-ETP method. In the training phase, the flow properties and their gradients at the ETP and the distance from the ETP normal to the wall are employed as feature values, and the accurate wall heat flux predicted by the converged fine grid is regarded as the tag value. With the assistance of the trained regression model, the heat flux of the same configuration with a coarse grid in the wall-normal direction could be predicted accurately and efficiently. Moreover, test cases of different configurations and inflow conditions with a coarse grid are also carried out to assess the model’s generalization performance. All comparison results demonstrate that the ML-ETP strategy could predict wall heat flux more rapidly and accurately than the traditional numerical method due to its nonstrict grid distribution requirements. The improvement of the predictive capability of the coarse-graining model could make the ML-ETP method an effective tool in hypersonic engineering applications, especially for unsteady ablation simulations or aerothermal optimizations.

Experimental evaluation of a high-temperature radial-flow packed bed thermal energy storage under dynamic mass flow rate

High-temperature thermal energy storage is recognized to be a key technology to ensure future sustainable energy generation. Packed bed thermal energy storage is a cost-competitive large-scale energy storage solution. The present work introduces the experimental investigation of an innovative 49.7 kWhth radial-flow type high-temperature packed bed thermal energy storage under dynamic mass flow rates. Various dynamic air flow rate profiles, representative of different potential applications, have been tested during the charging process to investigate their influence on the thermodynamic performance of the storage. The outlet thermal power during the discharge has been controlled by managing the air flow rate. Short operational cycles have also been performed. The results show that dynamic mass flow rates can lead to a thermal efficiency reduction between 0.5 % and 5 % with respect to static conditions. Controlling the air mass flow rate could be an efficient strategy to stabilize the thermal power output during the discharge while minimizing peaks in the pressure drop. This work testifies that specific dynamic boundary conditions should be included during the thermal storage design process since they could largely affect the unit thermodynamic performance and potential scale-up. If no specific dynamic profiles are available during the packed bed storage design stage, it is suggested to consider typical dynamic profiles of the air mass flow rate to guarantee limited efficiency reduction during operation.

Parametric study of evacuated tube collector solar air heater with inserted baffles on thermal network for low-temperature applications

The great challenge in the evacuated tube solar air heater for the industrial application is choosing the optimum thermal networks to get target temperature for the desired air flow rate. In this work, theoretical analysis is done to investigate the influence of the significant design parameters such as evacuated tube length, diameter and number of tubes in a collector on the thermal performance and to design a thermal network model for achieving the desired temperature at specified flow rate of air for industrial process heat applications. Further, establishing an empirical correlation to simplify the thermal network design process. Based on the results of design parametric study, optimal parameters identified for a collector system are 20 numbers of evacuated tubes having dimensions of 1.8 m length, 58 and 47 mm outer and inner diameters. It is noticed that a considerable drop in temperature rise attained in each collector while increasing the number of collectors in series network. The enviro-economic analysis reveals that the overall useful energy gain per annum can be achieved around 8252 kWh which will reduce 17.16 tonne of carbon dioxide emission through the utilization of a thermal network comprising six modules working at 500 kg/h mass flow rate of air. The correlation relates the attainable effective thermal with the non-dimensional operating parameters such as mass flow number, temperature ratio, and number of collectors. The correlation can be used to design a solar evacuated tube thermal network and the proposed solar evacuated tube thermal network can be effectively employed for fulfilling the industrial process heating applications require hot air between 80 and 120 °C.

Thermal and Structural Performance of a Small Satellite with Networked Oscillating Heat Pipes

Typically, spacecraft development is costly and time-consuming because of the many iterations usually needed to reach optimal design solutions. This paper presents an innovative approach that eliminates the need to iterate the thermal design process using a network of variable conductance oscillating heat pipes (VC-OHPs) on every structural panel. The temperatures of the panels where components are mounted would thus be maintained at constant levels by VC-OHPs, even if the instruments’ locations or heat dissipation changes. A structural thermal model was built to verify the proposed thermal and structural design in a simulated deep space environment and in a launch environment. It consisted of two VC-OHPs and six aluminum honeycomb panels. A thermal vacuum test was conducted to demonstrate the temperature control by the VC-OHPs. The test results showed that temperature control by VC-OHPs could maintain the panels operating as evaporators at stable temperatures and follow the reservoir temperature. A vibration test was conducted under the launch environment of a Japanese H2A rocket. The results confirmed that the structural thermal model met requirements for resistance to mechanical launch environment. The VC-OHPs functioned after the vibration test. The structural thermal model showed that the proposed thermal control architecture is feasible in an actual spacecraft in terms of thermal and structure design.

Optimization of Thermal Design and Mold Flow Process for 3D SiP Structure

Abstract With the advent of the 5G era, major package and testing plants have been taking frequent action recently. Obviously, with higher and higher performance requirements, SiP is a functional package integrated multiple functional chips, including processor, memory into one package. However, thermal design is an important issue to be addressed at this time. This paper mainly presents a 3D SiP structure based on the combination of two substrates, integrating 4 components in a single package, total power consumption is 30 Watt. To address thermal management difficulties of this 3D SiP, a method is designed to increase the thermal path between the two boards. The Effects of the structure, number of via, and changing location of components aspects of the thermal performance are studied. The thermal vias was designed in between the two boards provide are direct heat dissipation, connecting the metal studs above passive components to improve thermal performance. Thermal performance with 240 vias is improved by 0.4%, while the number of vias increases from 240 to 912, the temperature decreases only 1.0%, 0.6% respectively. The difference of thermal resistance (θJB) comparison is 1.9%, 1.5% and 1.0%. There are limits to the improvement of vias, the effect of increasing the number of via is not as good as expected. However, increasing the thermal conduction path may have an effect on the void of mold flow. s 3D mold flow modeling of the transfer molding process with molded underfill (MUF) using Moldex3D is applied to optimize design and process parameters that can reduce device defects. There is one important challenge that faced air voids entrapment in molding area. Generally, the experiments involve a lot of design of experiment (DOE) matrixes which spend a lot of time to solve air void issue. As above reasons, the mold flow simulation can be used to apply molding parameters to find out optimum solutions for air void risk free of SiP, which can reduce development cycle time before mass production. From the mold flow simulation results, when the number of plunger segments increases and the tail flow rate decreases, the void issues can be effectively improved.

A Comprehensive Heat Transfer Study Inside a Steam Turbine Valve: Experiment, Numerical Simulation, and Simplified Model

Abstract In a steam turbine system, one of the main factors limiting the operational flexibility is the thermal stress associated with a high-temperature gradient within the control valves, which often leads to structural damage during frequent startup and shutdown cycles. One possible solution is to utilize an electric heating system with appropriate insulation to decrease the warm-up time. Here, an experiment and a numerical simulation were performed using a scaled turbine valve equipped with an electric heating system to understand the heat transfer process. The experiment, which was conducted at Shanghai Jiao Tong University, had a duration of 100 h and included three heating–cooling cycles and two heat preservation states. The results showed that the temperature distribution of the scaled valve was uniform, which is due to the high thermal conductivity of the valve body and the low conductivity of the insulation layer. The simulation, which used the commercial software ansysfluent 2019 R1, was performed to model the experimental heat transfer process and showed less than 10% deviation from the measured temperatures. A sensitivity study revealed that the valve temperature is very insensitive to the heat transfer coefficient of the outer surface of the insulation layer, which is attributed to the negative feedback regulation of radiation heat transfer. To further improve the computing efficiency, a simplified model based on the lumped parameter method and the quasi-steady-state assumption was proposed and validated. This model can predict the 100 h valve temperature history in less than 1 min and showed good agreement for all of the studied cases. The ability of the simplified model to simulate the valve heating–cooling cycles at a high efficiency could accelerate the thermal design process to improve the operational flexibility of steam turbines in the future.

Characteristic Thermal Parameters in Electric Motors: Comparison Between Induction- and Permanent Magnet Excited Machine

The thermal modeling and design process of highly utilized electric machines is a complex task. The main heat paths within an electric drive are influenced by a variety of different thermal interfaces, that can mainly be described by thermal conduction and convection. The proper selection and estimation of these design parameters is challenging especially in the early design stage. This paper provides a systematic investigation evaluating inaccuracies and design influences of single thermal resistances, such as the convective heat transfer in the rotor-stator annulus, in the cooling jacket or interfaces between different machine components. Within the study, electromagnetic finite element models and thermal lumped parameter models of two traction drives are developed and validated using test bench measurements. The thermal design parameters are varied in a range resulting from intensive literature research and own laboratory experience. The influence of the design parameters in different operational points of the drives are studied in a sensitivity analysis.

Numerical and Analytical Investigation of Heat Transfer Mechanisms and Flow Phenomena in an Intermediate Pressure Steam Turbine Blading During Startup

Abstract As a result of an ever-increasing share of volatile renewable energies on the worldwide power generation, conventional thermal power plants face high technical challenges in terms of operational flexibility. Consequently, the number of startups and shutdowns grows, causing high thermal stresses in the thick-walled components and thus reduces lifetime and increases product costs. To fulfill the lifetime requirements, an accurate prediction and determination of the metal temperature distribution inside these components is crucial. Therefore, boundary conditions in terms of local fluid temperatures as well as heat transfer coefficients (HTCs) with sufficient accuracy are required. As modern numerical modeling approaches, like 3D-conjugate-heat-transfer (CHT), provide these thermal conditions with a huge calculation expense for multistage turbines, simplified methods are inevitable. Analytical heat transfer correlations are thus the state-of-the-art approach to capture the heat transport phenomena and to optimize and design high efficient startup curves for flexible power market. The objective of this paper is to understand the predominant basic heat transfer mechanisms such as conduction, convection, and radiation during a startup of an intermediate pressure (IP) steam turbine stage. Convective heat transport is described by means of heat transfer coefficients as a function of the most relevant dimensionless, aero-thermal operating parameters, considering predominant flow structures. Based on steady-state and transient CHT simulations, the heat transfer coefficients are derived during startup procedure and compared to analytical correlations from the literature, which allow the calculation of the heat exchange for a whole multistage in an economic and timesaving way. The simulations point out that the local convective heat transfer coefficient generally increases with increasing axial and circumferential Reynolds' number and is mostly influenced by vortex systems such as passage and horseshoe vortices. The heat transfer coefficients at vane, blade, hub, and labyrinth-sealing surfaces can be modeled with a high accuracy using a linear relation with respect to the total Reynolds' number. The comparison illustrates that the analytical correlations underestimate the convective heat transfer by approximately 40% on average. Results show that special correlation-based approaches from the literature are a particularly suitable and efficient procedure to predict the heat transfer within steam turbines in the thermal design process. Overall, the computational effort can be significantly reduced by applying analytical correlations while maintaining a satisfactory accuracy.

Isotropic Thermal Cloaks with Thermal Manipulation FunctionSupported by the National Natural Science Foundation of China (Grant No. 51406168).

By extending the conventional scattering canceling theory, we propose a new design method for thermal cloaks based on isotropic materials. When the objects are covered by the designed cloaks, they will not disturb the temperature profile in the background zone. In addition, if different inhomogeneity coefficients are selected in the thermal cloak design process, these cloaks can manipulate the temperature gradient of the objects, i.e., make the temperature gradients higher, lower, or equal to the thermal gradient in the background zone. Therefore, thermal transparency, heat concentration or heat shield effects can be realized under a unified framework.

Optimization of thermal systems considering time-varying availability: a case study of the CGAM problem

One of the most important steps of the thermal systems design process can be economic optimization. In the conventional methods of this optimization, most of the time system’s availability, amount of production, and maintenance costs are considered to be constant throughout the system’s lifetime. However, factors such as changing of the components’ failure rate due to degradation or repairing, and stops in operation because of overhauls could lead to a change in the availability and the amount of production. Also, in multi-product systems, upstream components’ failures would stop production in downstream parts. In this paper, a method is proposed regarding the consideration of these factors to economic optimization. Hence, the optimal system design and its economic analysis would be more accurate than conventional methods. In terms of a case study, the CGAM cogeneration system is studied. The first step of this optimization is calculating instantaneous availability employing the state-space method by considering the overhauls and time-varying failure rate for the components. Then, the average availabilities for power and heat generation in each year are estimated. As costs and incomes appear to be variables, the net present value of benefits is considered as an objective function and the optimum system properties are achieved through solving the optimization problem.

Thermal Modeling of Outdoor Digital Displays Under Different Brightness Outputs

The thermal design process for electronic products often minimizes the use of computational fluid dynamics and heat transfer (CFD/HT) software in favor of quick prototyping and testing to determine the thermal characteristics of the product. For large-scale products with many thermal challenges, such a strategy can be impractical due to the high cost of prototyping cycles, time constraints, and inevitable iterations involved. In such cases, thorough CFD/HT models developed early in the design process are valuable for driving the product design. Based on this idea, the study examines thermal performance of 55” outdoor digital displays using CFD/HT tools and a prediction under hazardous outdoor condition is made for two different brightness outputs. The prediction is extrapolated and validated through the outdoor testing and simulation comparisons. It is shown that CFD/HT software can be used as a means of making conservative design choices.

Thermal design of dual circulating fluidized bed reactors for a large-scale CO2 capture system

A dual circulating fluidized bed reactor has been studied for carbon dioxide (CO2) capture. It is important to maintain the reaction temperature of the adsorbent in the carbonation–regeneration cycle. The dual circulating fluidized bed reactor will be used ultimately in the large reactors of industrial-sized power plants to control CO2 emissions. However, to date, studies have considered only small-scale reactor models, due to the limitations associated with two-phase flow dynamics and changes in the heat transfer characteristics with reactor size. In this study, we investigated the thermal design of a feasible pilot-scale reactor through thermal-fluid analysis of the reactor and heat transfer in two-phase flow. Based on our thermal-fluid experimental results for a laboratory-scale dual circulating fluidized bed reactor with an amine-functionalized silica sorbent 0.37EB-PEI, a thermal design process was carried out to increase the reactor scale. In consideration of the heat of reaction and the sensible heat for a continuous process, the increase in total heat duty at the reactor scale has been determined. In the overall heat transfer process of the reactor, consisting of three heat transfer mechanisms, the bed-to-wall heat transfer by gas-solid fluidization was identified as the dominant mechanism. The scale-up of the fluidized bed resulted in a change in gas-solid behaviors and a lower heat transfer coefficient. Ultimately, through the thermal design process, the heat exchange area required for a large-scale carbonation reactor and regeneration reactor were derived; specifically, for the pilot-scale reactor to accommodate > 2000 m3/h flue gas, the required reactor height was estimated to be about two times compared to not taking the scale-up effect into account. We proposed a multi-tube reactor with the high heat transfer coefficient and the large heat transfer area for an efficient large-scale CO2 capture system.

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.