Advanced Heat Transfer Devices for Aerospace Applications

This paper reviews advanced heat transfer devices utilizing advanced manufacturing technologies, including well-established thermal management applications. Several factors have recently contributed to developing novel heat transfer devices. One of the potential technologies revolutionizing the field of energy conversion is additive manufacturing (AM), colloquially known as three-dimensional (3D) printing. This technology permits engineers to develop a product with a high level of freeform features both internally and externally within a complex 3D geometry. Among different AM approaches, selective laser melting (SLM) is a well-used technique for developing products with a lower cost-to-complexity ratio and quicker time production compared to other manufacturing processes. The integration of SLM technology into heat exchangers (HXs) and heat sinks (HSs) has a strong potential, especially to fabricate customized and complex freeform shapes. The aim of this research is to review the advancement in design complexities of different industrial heat transfer devices incorporating metal SLM fabrication. The review is not meant to put a ceiling on the AM process, but to enable engineers to have an overview of the capabilities of SLM technology in the field of thermal management applications. This review presents the opportunities and challenges related to the application of SLM technology in connection to novel HXs and HSs, as well as heat pipes (HPs). The latter are passive heat transfer devices utilized in many thermal control applications, especially related to electronics cooling and energy applications.

Improved thermal management is needed to increase the power density of electronic and more effectively cool electronic enclosures that are envisioned in future aircraft, spacecraft and surface ships. Typically, heat exchanger cores must increase in size to more effectively dissipate increased heat loads, this would be impossible in many cases, thus improved heat exchanger cores will be required. In this Phase I investigation, MRi aimed to demonstrate improved thermal management using graphite foam (Gr-foam) core heat exchangers. The proposed design was to combine Gr-foams from POCO with MRi's innovative low temperature, active metal joining process (S-Bond{trademark}) to bond Gr-foam to aluminum, copper and aluminum/SiC composite faceplates. The results were very favorable, so a Phase II SBIR with the MDA was initiated. This had primarily 5 tasks: (1) bonding, (2) thermal modeling, (3) cooling chip scale packages, (4) evaporative cooling techniques and (5) IGBT cold plate development. The bonding tests showed that the ''reflow'' technique with S-Bond{reg_sign}-220 resulted in the best and most consistent bond. Then, thermal modeling was used to design different chip scale packages and IGBT cold plates. These designs were used to fabricate many finned graphite foam heat sinks specifically for two standard type IC packages, the 423 and 478 pin chips. These results demonstrated several advantages with the foam. First, the heat sinks with the foam were lighter than the copper/aluminum sinks used as standards. The sinks for the 423 design made from foam were not as good as the standard sinks. However, the sinks made from foam for the 478 pin chips were better than the standard heat sinks used today. However, this improvement was marginal (in the 10-20% better regime). However, another important note was that the epoxy bonding technique resulted in heat sinks with similar results as that with the S-bond{reg_sign}, slightly worse than the S-bond{reg_sign}, but still better than the standard heat sinks. Next, work with evaporative cooling techniques, such as heat pipes, demonstrated some unique behavior with the foam that is not seen with standard wick materials. This was that as the thickness of the foam increased, the performance got better, where with standard wick materials, as the thickness increases, the performance decreases. This is yet to be completely explained. Last, the designs from the thermal model were used to fabricate a series of cold plates with the graphite foam and compare them to similar designs using high performance folded fin aluminum sinks (considered standard in the industry). It was shown that by corrugating the foam parallel to fluid flow, the pressure drop can be reduced significantly while maintaining the same heat transfer as that in the folded fin heat sink. In fact, the results show that the graphite foam heat sink can utilized 5% the pumping power as that required with the folded fin aluminum heat sink, yet remove the same amount of heat.

<div class="section abstract"><div class="htmlview paragraph">Advancements in additive manufacturing (AM) technology have enabled the use of Triply Periodic Minimal Surface (TPMS) lattice structures to integrate thermal and structural functions into a single component. These structures offer advantages such as weight reduction, compactness and enhanced heat dissipation, making them promising for automotive, aerospace and electronics applications. TPMS structures, characterized by zero mean curvature and periodic crystalline geometry, have recently gained significant research attention thanks to their potential in thermal management. Among various TPMS geometries, the gyroid and diamond structures stand out for their thermal and fluid dynamic performance. This study explores the influence of cell geometry, unit cell size, and wall thickness on the efficiency of TPMS-based heat exchangers, as these parameters are crucial for their technical feasibility. Using Computational Fluid Dynamics (CFD) simulations, a comparative analysis is conducted for a case study represented by a heat exchanger. The numerical approach relies on a steady-state Reynolds-Averaged Navier-Stokes (RANS) approach with the Reynolds Stress Transport (RST) Elliptic Blending model, while heat transfer is analyzed through the Conjugate Heat Transfer (CHT) technique. The results indicate that reducing the unit cell size enhances heat transfer but also increases pressure drop at a fixed flow rate. Similarly, increasing the wall thickness raises pressure losses, though its effect on heat transfer is minimal. Overall, the diamond structure outperforms the gyroid in both thermal efficiency and flow permeability, making it a more effective choice for TPMS-based heat exchangers. These findings offer valuable insights for optimizing TPMS geometries in high-performance heat transfer applications, guiding future research and industrial implementations.</div></div>

Recently energy saving is most important concept for all electric products and production. Especially, in Data-Center cooling system, power consumption of current air cooling system is increasing. For not only improving thermal performance but also reducing electric power consumption of this system, liquid cooling system has been developed. This paper reports the development of cold plate technology and vapor chamber application by using micro-channel fin. In case of cold plate application, micro-channel fin technology is good for compact space design, high thermal performance, and easy for design and simulation. Another application is the evaporating surface for vapor chamber. The well-known devices for effective heat transfer or heat spreading with the lowest thermal resistance are heat pipes and vapor chamber, which are two-phase heat transfer devices with excellent heat spreading and heat transfer characteristics. Normally, vapor chamber is composed of sintered power wick. Vapor chamber container is mechanically supported by stamped pedestal or wick column or solid column, but the mechanical strength is not enough strong. So far, the application is limited in the area of low strength assembly. Sometime the mechanical supporting frame is design for preventing deformation. In this paper, the testing result of sample is described that thermal resistance between the heat source and the ambient can be improved approximately 0.1°C/W by using the micro-channel vapor chamber. Additionally, authors presented case designs using vapor chamber for cooling computer processors, and proposed ideas of using micro-channel vapor chamber for heat spreading to replace the traditional metal plate heat spreader.

Evaluation of innovative thermal performance augmentation techniques in heat sinks & heat pipes: Electronics & renewable energy applications

Application of machine learning to thermal management of solid-state hydrogen storage: A comprehensive review

A novel phase change material-based thermal management of electric machine windings enabled by additive manufacturing

Heat pipe is a self‐contained heat transfer device based on the evaporation and condensation of a working fluid, with passive pumping of the condensate back to the evaporator; it has no mechanical moving parts and requires no external power other than the heat that flows through it. Heat pipes ensure good heat spreading capability and geometric flexibility. Heat pipes are used to perform several important heat transfer and thermal management roles in the chemical and linked industries. Examples include separation of hazardous streams associated with heat source and sink, heat recovery, temperature flattening or isothermalization of processes, temperature control in chemical reactions, and spot cooling. In its simplest function, the heat pipe possesses the property of extremely high effective thermal conductivity (several hundred times that of metals), for that reason they are sometimes referred to as “thermal superconductors.” As a result, the heat pipe can produce nearly isothermal conditions making an almost ideal heat transfer element. In another form, the heat pipe can provide positive, rapid, and precise control of temperature under conditions that vary with respect to time.

Investigation of neutronic and thermal–electric coupling phenomenon in a 100 kWe-level nuclear silent heat pipe-cooled reactor

Heat exchangers with mini- and micro-channel components are capable of high energy exchange due to their incumbent large surface area to volume ratio. Concurrently, recent advances in additive manufacturing simplify the creation of metallic minichannels that incorporate turbulators for heat transfer enhancement. As part of the development of a minichannel heat exchanger with turbulators, this study analyzes the three-dimensional conjugate heat transfer and laminar flow in a minichannel heat exchanger equipped with rectangular winglet vortex generators (VGs) through numerical simulation. The minichannels have a hydraulic diameter of 2.86 mm and are assumed to be made from aluminum alloy AlSi10Mg. This material is one of the popular alloys in the additive manufacturing industry (three-dimensional (3D) printing) because of its light weight and beneficial mechanical and thermal properties. The working fluid is distilled water with temperature-dependent thermal properties. The minichannel is heated by a constant heat flux of 5 W cm−2 and the Reynolds number is varied from 230 to 950. The simulations are performed using the COMSOL® platform, which solves the governing mass, momentum, and energy equations based on the finite element method. The effect of the VG design parameters, which include VG angle of attack, height, length, thickness, longitudinal pitch, and distance from the sidewalls, is investigated. It is found that the generation of three-dimensional vortices caused by the presence of the vortex generators can notably boost the convective heat transfer, at the cost of increased pressure drop, potentially reducing the heat exchanger size for a given heat duty. A sensitivity analysis indicates that the angle of attack, VG height, VG length, and longitudinal pitch have the most significant effects on the heat transfer and flow friction characteristics. In contrast, the VG thickness and distance from the sidewalls only had minor influences on the heat exchanger performance over the studied range of design parameters.

Review of heat transfer enhancement techniques for single phase flows

Lithium ion battery thermal management by using coupled heat pipe and liquid cold plate

The lithium-ion battery, a key technology for electric vehicles, is an electrochemical power source with complex ion flow and heat transfer processes. Temperature is one of the main parameters affecting the performance of these battery systems, as high temperatures may accelerate the degradation rate of a battery cell and shorten its lifespan. Low temperatures can also reduce the battery efficiency and affect its discharge capacity, and subsequently, its life cycle. In addition, uneven temperature distribution within a battery pack could exacerbate the inconsistency between cells and cause life cycle decay. A suitable working temperature window for the lithium-ion battery is usually between 25°C to 40°C, and the temperature difference among the cells should be maintained below 5°C to ensure the cells performance and durability. Therefore, battery thermal management (BTM) is required to keep the battery temperature within the desirable operating range and maintain temperature uniformity. This paper provides a review of two aspects: The significance of BTM and current BTM strategies, and the research status of heat pipe-based BTM systems. Firstly, the thermal characteristics of the lithium-ion power battery are introduced, and the significance of BTM are expounded. Then, the advantages of heat pipe technology are introduced, and the research status of BTM based on heat pipes is evaluated in detail. In this study, the heat transferred in a heat pipe-based thermal management system was divided into three processes: The heat generation process, which is determined by the operating condition; the heat transfer process of a heat pipe, which is related to its structural design and its arrangement in the system; and the heat dissipation strategy on the condensation section. With respect to heat generation, researchers have studied the effect of operating conditions on the heat generation characteristics of the system. Results show that the temperature is closely related to the dynamic operating conditions. Further research should be combined with the actual vehicle operating conditions to formulate effective real-time control strategies to achieve a high efficiency and low energy consumption BTM system. Researchers have evaluated various factors that affect heat transfer performance. This study concludes that both the internal structure of heat pipe and its arrangement in the battery pack should be considered in the design of the BTM system to achieve optimum heat transfer performance. Future studies should focus on the analysis and optimization of flat plate heat pipes, which have good application prospects in BTM systems. Concerning heat dissipation enhancement, air cooling, direct liquid cooling, and indirect liquid cooling are the most common strategies for heat pipe cooling. However, most designs aim to reduce the temperature rise and temperature difference, and the system parameters are seldom taken into consideration. Further investigation into the heat dissipation enhancement of heat pipes should focus on the multi-objective optimization of the system including, synthesizing the thermal and electrical characteristics, improving energy consumption, and making the system lightweight. In addition, the heat pipe is also a highly efficient heat transfer element for battery heating. Current research has verified its heating rate and heating efficiency. Notably, the heating strategies are now in the pilot testing stage and have not been used in battery pack productions. One of the key elements for future research may involve the heating characteristics of a BTM based on heat pipes in different operating environments. Another aspect could be researching the heating strategy in low temperature environments.

A comprehensive review of heat transfer enhancement of heat exchanger, heat pipe and electronic components using graphene

With the advancement of sophisticated technology, it has become a prime concern to design electronic and mechanical equipment having a very compact assembly. The cooling technology associated with such equipment has become one of the bottleneck problems. Mini-channel heat sink having the benefit of high surface area to volume ratio could be the solution for effective heat transfer in the miniature devices. However, the pressure drop penalty of this mini-channel heat sink is significantly high. The thermal performance of the mini-channel profoundly depends on the geometry and its arrangement like shape of the cross sectional area, channel flow path, surface roughness, obstacles in the flow direction etc. Flow with redeveloping thermal boundary layer results in higher heat transfer rate. In this research work, several heat transfer enhancement techniques have been studied numerically considering redeveloping boundary layer. Rectangular mini-channel having a hydraulic diameter of 1.53 mm has been considered in this study. Air is taken as the working fluid which is supplied to the heat sink at an inlet temperature of 293 K and at velocity of 0.7 m/s, 1.2 m/s, 1.5 m/s, 2 m/s and 2.5 m/s. Temperature of the bottom surface of the channel is kept fixed at 340 K. The thermal performance of the mini-channels have been evaluated and compared based on Nusselt number, thermal resistance and pumping power requirements. Once the simulation is completed for the conventional mini-channel, the channel has been modified by incorporating different heat transfer enhancement schemes, like introducing bump of different size inside the channel, implementing cross connection of the channels by placing converging or diverging nozzles side by side. From the numerical results, it has been found that introduction of bump enhances heat transfer rate compared to the simple rectangular channel. Modifications of the channel with the converging or diverging nozzle and cross connection between channel and nozzle introduce cross flow of the coolant at a higher rate compared to the rectangular mini-channel, resulting in increased Nusselt number compared to the all of the configurations. Requirement of the pumping powers for the converging and diverging arrangements are found higher than the conventional rectangular mini-channel in order to ensure the same thermal performance.