The intense thermal fluxes and aero-thermomechanical loads generated at sharp leading edges of atmospheric hypersonic vehicles traveling above Mach 5 have motivated an interest in novel thermal management strategies. Here, we use a low-temperature stainless steel-water system to experimentally investigate the feasibility of metallic leading edge heat pipe concepts for thermal management in an efficient load supporting structure. The concept is based upon a two-phase, high thermal conductance “heat pipe” which redistributes the localized thermal flux created at the leading edge stagnation point over a larger surface for effective removal. Structural efficiency is achieved by configuring the system as a wedge-shaped sandwich panel with an I-cell core that simultaneously permits axial vapor and returns liquid flow. The measured axial temperature profiles resulting from a localized thermal flux applied to the tip are consistent with effective thermal spreading that lowered the peak leading edge temperature and reduced the temperature gradients when compared with an equivalent structure containing no working fluid. A simple finite element model that treated the vapor as an equivalent, high thermal conductivity material was in good agreement with these experiments. The model is then used to design a niobium alloy-lithium system that is shown to be suitable for enthalpy conditions representative of Mach 7 scramjet-powered flight. The study indicates that the surface temperature reductions of heat pipe-based leading edges may be sufficient to permit the use of nonablative, refractory metal leading edges with oxidation protection in hypersonic environments.

Phase-change materials (PCMs) are a useful alternative to more traditional methods of thermal management of various applications. PCMs are materials that absorb large amounts of latent heat and undergo solid-to-liquid phase change at near-constant temperature. The goal of the research is to experimentally investigate the thermal properties of a novel shape-stabilized PCM/HDPE composite extruded filament. The extruded filament can then be used in a 3D printer for custom PCM/HDPE shapes. The PCM used in the study is PureTemp PCM 42, which is an organic-based material that melts around 42 °C. Four PCM/HDPE mixtures were investigated (all percentages by mass): 20/80, 30/70, 40/60, and 50/50. Preliminary findings include differential scanning calorimeter (DSC) measurements of melting temperature and latent heat as well as scanning electron microscope (SEM) pictures of filament composition.

The effect of fuel topology and control on thermal endurance of aircraft using fuel as a heat transfer agent was studied using an optimal dynamic solver (OPT). The dynamic optimal solutions of the differential equations governing the heat transfer of recirculated fuel flows for single- and dual-tank arrangements were obtained. The method can handle sudden jumps of operating conditions across different operating zones during mission and/or situations when control parameters have reached their physical limits. Although this method is robust in providing an optimal control strategy to prolong thermal endurance of aircrafts, it is not ideal for practical application because the method required iterative procedures to solve expensive nonlinear equations. The linear quadratic regulator (LQR), the feedback controller, can be derived by linearizing the adjoint equations at trim points to offer a simple control strategy, which can then be implemented directly in the feedback control hardware. The solutions obtained from both OPT and LQR were compared, and it was found two solutions were almost identical except in regions having sudden jump of operation conditions. Finally, a comparison between single- and dual-tank arrangements was made to demonstrate the importance of the flow topology. The study shows the dual-tank arrangement allows flexibility in how energy is managed and can release energy faster than a single-tank topology and hence provides improved aircraft thermal endurance.

Effects of server/rack locations and server loading configurations on the thermal performance of data center racks' array are experimentally investigated using a scaled physical model simulating real data. Front and rear rack temperatures profiles, server temperatures, and performance indices supply/return heat index (SHI/RHI) are used to evaluate the thermal management of the racks' array. The results showed that (i) servers located in high level rack cabinet have the worst thermal performance, (ii) middle racks of the rack row showed optimum thermal performance and energy efficiency, and (iii) locating the servers of high power densities in the middle of the racks row improves the thermal performance and energy efficiency of the racks array.

The increase in the number of data centers in the last decade, combined with higher power density racks, has led to a significant increase in the associated total electricity consumption, which is compounded by cooling inefficiencies. Issues, such as hot air recirculation in the data center room environment, provide substantial challenges in thermal manageability. Three operational data centers have been studied to identify the cooling issues. Field measurements of temperature were obtained and were compared to numerical simulations to evaluate the overall thermal behavior of the data centers and to identify the thermal issues.

A heat pipe utilizes liquid–vapor phase change mechanism to efficiently transfer heat. Among different heat pipes, loop heat pipe (LHP) and pulsating heat pipe (PHP) are known to be capable of high heat flux/high load heat transfer. In this article, LHP and PHP heat transfer systems are combined to achieve passive, reliable, and remote/long-distance heat transfer for thermal management of modern avionics systems. Aiming at this goal, a 2 m long LHP is developed to transport heat from the avionics chassis to the remote heat rejection site. To reduce inner saturation pressure and ensure structural safety at high operating temperature, water is used as the operating fluid in LHP. Within the avionics chassis, conduction heat transfer is enhanced by sandwiching a PHP with two printed circuit boards (PCBs) and solder-bonding them. Each PHP/PCB assembly is 20 cm long and 12.5 cm wide, with electrical heaters mounted on both sides to mimic electronic heat dissipation. Heat transfer demonstration of the LHP and PHP combo system is conducted in a lab environment with input power varying from 100 to 400 W. For all the three PHP/PCB assemblies set in the avionic chassis, heat source temperature is maintained below the required 150 °C even when heat dissipation is twice as high as the state-of-the-art (and coolant temperature is 50 °C). This combo heat transfer system reduces power consumption and increases reliability, enabling the avionic system operation in harsh environments.

The transient thermal response of a 15-cell, 48 V, lithium-ion battery pack for an unmanned ground vehicle (UGV) was simulated using ANSYS fluent . Heat generation rates and specific heat capacity of a single cell were experimentally measured and used as input to the thermal model. A heat generation load was applied to each battery, and natural convection film boundary conditions were applied to the exterior of the enclosure. The buoyancy-driven natural convection inside the enclosure was modeled along with the radiation heat transfer between internal components. The maximum temperature of the batteries reached 65.6 °C after 630 s of usage at a simulated peak power draw of 3600 W or roughly 85 A. This exceeds the manufacturer's maximum recommended operating temperature of 60 °C. We present a redesign of the pack that incorporates a passive thermal management system consisting of a composite expanded graphite (EG) matrix infiltrated with a phase-changing paraffin wax. The redesigned battery pack was similarly modeled, showing a decrease in the maximum temperature to 50.3 °C after 630 s at the same power draw. The proposed passive thermal management system kept the batteries within their recommended operating temperature range.

In this paper, passive thermal management of an electric vehicle (EV) battery pack with phase change material (PCM) is studied numerically. When the temperature in the cells increases, and consequently in the submodule also, the heat is absorbed through melting of the cooling jacket which surrounds the cells. This, in turn, creates cooling effects in the cell and the battery pack. A finite volume based numerical model is used for the numerical simulations. The effects of different operating conditions are compared for the submodule with and without the PCM. The present results show that a more uniform temperature distribution is obtained when the PCM is employed which is in agreement with past literature and experimental data. The results also imply that the effect of PCM on cell temperature is more pronounced when the cooling system operates under transient conditions. The required time to reach the quasi-steady state temperature is less than 3 h, and it strongly depends on the heat generation rate in the cell. The maximum temperature of the system decreases from 310.9 K to 303.1 K by employing the PCM and the difference between the maximum and minimum temperatures in the submodule decreases in this way. The temperature differences are 0.17 K, 0.68 K, 5.80 K, and 13.33 K for volumetric heat generation rates of 6.885, 22.8, 63.97, and 200 kW/m3, respectively.

In this paper, exergy analysis of a hybrid electric vehicle thermal management system (TMS) is initially investigated in order to find the areas of inefficiencies and exergy destruction within each system component. In the analysis, advanced exergy modeling is utilized to study both endogenous/exogenous and avoidable/unavoidable exergy destructions for each component of the system and further understand the interactions among the TMS components and determine the underlying reasons behind the exergy destructions. Moreover, this approach is also used to enhance exergoeconomic analyses by calculating the endogenous/exogenous and avoidable/unavoidable portion of the investment and exergy destruction costs (so-called advanced exergoeconomic analysis) in order to improve the cost effectiveness of the system and provide information on how much of the cost can be avoided for each component. Based on the analysis, it is determined that exogenous exergy destruction is small but significant portion of the total exergy destruction in each component (up to 40%, in the chiller and thermal expansion valves) and that large portion of the exergy destruction within the components (up to 70%, in the compressor) could be potentially avoided. Moreover, it is determined that electric battery, compressor, and chiller are dominated by investment cost, whereas the condenser and evaporator are dominated by the cost of exergy destruction in the system.

The need for low profile, sustainable thermal management solutions is becoming critical in information and communications technology applications ranging from consumer products to server cabinets. This work presents a finless thermal management solution that utilizes fluidic structures generated within an empty cavity to enhance the heat transfer coefficient. The finless thermal management solution can be manufactured to have a height of less than 5 mm when using low profile motors. Particle image velocimetry (PIV) combined with infrared (IR) imaging techniques are used to explain the underlying flow physics that results in increased heat transfer rates compared to typical laminar flows. It is found that the local heat transfer coefficients in the finless design are up to 500% greater than those achieved at the same Reynolds number using conventional boundary layer theory. The design is compared to an existing commercial solution and is found to provide benefits in terms of cost, reliability, weight, acoustics, and fan power consumption. These advancements over current state of the art lead to a more sustainable solution for low cost, low profile cooling applications.

The thermal management of high density power electronics can be extremely challenging due to high power loads paired with small device footprints. When these power electronics are used in systems, which require extremely high reliability, the design of the thermal abatement system takes on increasing importance. In this study, the thermal response of a solid state fault current limiter is analyzed in steady-state and failure mode to develop a thermal solution which is both economical and reliable. The solid state fault current limiter is used in electric distribution systems to prevent a current surge from reaching sensitive equipment downstream of a power plant in the event of a disturbance on the line. A parametric study on several design variables including power loading, device spacing, and system flowrate is completed to give insight into the development of an optimal design. A coldplate design using dielectric mineral oil, which minimizes both system footprint and operating cost, is developed. This analysis and thermal management solution is applicable not only to this situation but also to the other high density power electronics applications.

The current paper presents the results of an analytical study of steady state heat conduction in a rectangular tube with eccentric hot spots on both the top and the bottom surfaces. The rectangular domain is assumed to be adiabatic on the lateral surfaces and a single or multiple eccentric hot spots can be applied on the top and bottom surfaces. Isothermal, heat flux, or convection boundary conditions can be applied on the hot spots. Because the hot spots are eccentric, the spreading resistance becomes a dominant factor in heat conduction in the tube. The multiple hot spots, multiple layers and combination problems are also studied in the current paper. The solutions can be applied to the thermal management of three-dimensional stacks of electronic devices, the interconnect layers and the thermoelectric devices.

With the seamless advancements in modern electronics and shrinking thermal real estate, a number of candidate thermal technologies have been developed. As system designers evaluate these methods, they require unambiguous comparisons in order to properly assess the positives and negatives of advanced solutions. The most commonly used metrics, particularly thermal resistance, are limited in their applicability, especially because they account for only for single factors like the temperature of the heated device. To improve these comparisons, a new volumetric enhancement factor, EF v , is proposed, which can be justified based on lumped capacitance arguments. When coupled with the thermodynamic coefficient of performance, EF v allows a simple comparison that relates thermal performance, system input needs, and system size simultaneously. Using these metrics, several advanced technologies are compared, demonstrating that liquid cooling using microchannels can be in excess of 1000 times more effective than air cooling methods.

The thermal management of power electronics presents a significant challenge to thermal engineers due to high power loads coupled with small footprints. Inadequate thermal dissipation of these loads can lead to excessively high equipment temperatures and subsequent system failure. In this study, a unique power electronics-based transformer, called the intelligent universal transformer (IUT), is thermally analyzed using the computational fluid dynamics software ICEPAK . The objective of this work is to examine the use of a finned heat pipe array for the power electronics in the IUT. A design sensitivity study was performed to determine the effect of the number of fins attached to the heat pipe array, the number of heat pipes in the heat pipe array, and the fin material on the steady-state operating temperature of the power electronics. It was determined that a set of 33 copper fins attached to an array of 36 heat pipes on each side of the containment unit is sufficient for continuous operation of the power electronics. This analysis and thermal management solution will be applicable not only to this situation but also to other high density power electronics applications.

Carbon nanotube (CNT) suspensions have shown promise as a heat transfer nanofluid due to their relatively high thermal conductivity and ability to remain in stable suspension for long durations. To assess their potential as a phase change material for thermal management systems, the stability of such suspensions under repeated phase change cycles is investigated. Electrical resistance testing was used to monitor stability of the CNT network during freeze-thaw cycling. With distilled water as the base fluid, the effects of CNT size and type, CNT concentration, surfactant type and concentration, and processing parameters were investigated. Nanofluids tested included laboratory-prepared and commercially supplied samples. Experiments showed breakdown of the nanofluid in less than 12 phase change cycles for all samples tested. Ultrasonication after breakdown was shown to restore resistance values to prebreakdown levels. The results suggest the use of CNT-enhanced water as a phase change material presents a significant operational challenge due to instability of the CNT network during phase change cycling. Should the use of such nanofluids be warranted as a phase change material, electrical resistance testing along with repeated ultrasonication may be considered as a means to control and monitor stability of the nanoparticle suspension in service.

Increasingly, military and civilian applications of electronics require extremely high-heat fluxes on the order of 1000 W / cm 2 . Thermal management solutions for these severe operating conditions are subject to a number of constraints, including energy consumption, controllability, and the volume or size of the package. Calculations indicate that the only possible approach to meeting this heat flux condition, while maintaining the chip temperature below 65 ° C , is to utilize refrigeration. Here, we report an initial thermodynamic optimization of the refrigeration system design. In order to hold the outlet quality of the fluid leaving the evaporator to less than approximately 20%, in order to avoid reaching critical heat flux, the refrigeration system design is dramatically different from typical configurations for household applications. In short, a simple vapor-compression cycle will require excessive energy consumption, largely because of the additional heat required to return the refrigerant to its vapor state before the compressor inlet. A better design is determined to be a “two-loop” cycle, in which the vapor-compression loop is coupled thermally to a pumped loop that directly cools the high-heat-flux chip.