Efficient Heat Removal Research Articles

Thermal–Hydraulic Performance Analysis of Combined Heat Sink with Open Microchannels and Embedded Pin Fins

An open type of microchannel with diamond pin fins (OM-DPFs) is introduced for the cooling of high-performance electronic chips. For a Reynolds number (Re) of 247~1173, a three-dimensional model is established to explore the hydrothermal properties of the OM-DPF and compare it to traditional heat sinks with closed rectangular microchannels (RMs), heat sinks with open microchannels (OMs), and the results in the existing research. Firstly, the synergy between tip clearance and pin fins on the hydrothermal properties is discussed. Secondly, the entropy production principle is adopted to analyze the irreversible losses for different heat sinks. Lastly, the total efficiencies of different heat sinks are assessed. The RMs present the worst heat transfer with the lowest friction loss. For the OMs, the temperature and pressure drop are decreased slightly compared to those of the RMs, and the irreversible loss is reduced by 4% at Re = 1173 because of the small tip clearance. But the total efficiency is lower than that of the RMs because the pressure drop advantage is offset by the weak heat transfer. For the OM-DPF, the combined structure has a noticeable impact on the multiple physical fields and hydrothermal characteristics, which present the best thermal performance at the cost of the highest friction loss. The irreversible loss of heat transfer in the OM-DPF is reduced obviously, but the friction irreversible loss significantly increases at high Re values. At Re = 429, the total entropy production of the OM-DPF is reduced by 47.57% compared with the RM. Compared to the OM and the single-pin fin structure in the literature, the total efficiency of the OM-DPF is increased by 14.56% and 40.32% at Re = 614. For a pump power of 0.1 W, the total thermal resistance (Rth) of the OM-DPF is dropped by 23.77% and 21.19% compared to the RM and OM. For a similar Rth, the pump power of the combined structure is 63.64% and 42.86% lower than that of the RM and OM. Thus, the novel combined heat sink can achieve efficient heat removal while controlling the energy consumption of liquid cooling systems, which has bright application prospects.

Experimental investigation of humidified air condensation in different rows of serpantine heat exchanger – Cooling water flow rate effect

Condensing economizers are used in the industry as they enable the acquisition of additional heat during vapor condensation. In condensing heat exchangers, water is the usual cooling agent due to its high specific heat capacity and thus efficient heat removal. Therefore, experiments of hot humid air condensation in a serpentine economizer being cooled by water were performed to reveal the effect the cooling water flow rate has on humidified air condensation in separate rows of the serpentine type economizer (with vertical tubes). The results have shown that the cooling ratio (mass flow ratio between the coolant and the humid air) had a minor effect on the distribution of the humidified air temperature along test section for inlet Reynolds number of 3000–10000. The effects on the condensation flux distribution in different rows were much stronger. The most optimal cooling ratio was determined to be 3. The results have shown that the biggest condensation efficiency is up to 35%. It was revealed that in some cases the convection was prevailing in the first rows of the economizer and this resulted in a decreased efficiency/performance of the exchanger.The obtained results from the practical point of view will provide an extended basis for the optimisation of the design of economizers for waste heat recovery in the cases of different cooling water flow rates. It could also be applied to validate computational models developed for condensation heat transfer and condensate flux numerical modelling along economizer.

Hydrodynamics in a randomly packed bed of cylindrical particles: A comparison between PR-CFD simulations and MRI experiments

Slender catalytic packed bed reactors are widely used in the chemical industry for chemical processes accompanied with significant heat liberation necessitating efficient heat removal. The employed catalyst particles are often cylindrical shaped, because these are easily manufactured via extrusion. The packing of these cylindrical particles results in a random structure of the bed causing flow maldistribution which reduces the reactor efficiency. The goal of this work is to capture the flow maldistribution with particle-resolved Computational Fluid Dynamics simulations and Magnetic Resonance Imaging experiments. By utilising the packing configuration reconstructed from the experiments, we are able to study the average fluid flow profiles and flow distribution in the bed as well as the local velocity profiles. It can be concluded that there is an overall good correspondence between the experiments and simulations. The minor deviations in the experimental and computed velocity distributions can be attributed to experimental error and slight differences in the experimental and reconstructed packing.

Preliminary design and optimization of heat transfer element for calorimeter in neutral beam injection system

Abstract The calorimeter is the primary high heat flux component of the neutral beam injection (NBI) system. To meet the requirements of China’s future high-power and long-pulse NBI system for efficient heat removal from the calorimeter, this study proposes a preliminary design for a calorimeter heat transfer element (HTE) mainly formed by vacuum brazing the front plate and back plate, featuring internal hypervapotron channels to enhance heat transfer. Parametric design and numerical simulations are applied to find the optimal channel parameters, including channel height (h), fillet radius (r), and slot width (s). Response surface analysis is used to process the results of the design schemes. The thermohydraulic performance of the optimized design under different channel flow velocities and heat flux densities is further analyzed. The results indicate that the optimal parameters are as follows: h=5 mm, r=1 mm, and s=1.5 mm. The h and s mainly influence HTE’s maximum temperature and pressure drop per unit length, respectively. The optimized design can meet the design criteria with a normal channel flow velocity of 10 m/s. To prevent the HTE pressure drop from surpassing 2 MPa, the channel flow velocity should not exceed 12 m/s. The design and optimization results of this study can serve as guidance for the engineering design of the calorimeter in China’s future NBI system.

Lateral Heterostructure Formed by Highly Thermally Conductive Fluorinated Graphene for Efficient Device Thermal Management.

The continued miniaturization of chips demands highly thermally conductive materials and effective thermal management strategies. Particularly, the high-field transport of the devices built with 2D materials is limited by self-heating. Here a systematic control of heat flow in single-side fluorinated graphene (FG) with varying degrees of fluorination is reported, revealing a superior room-temperature thermal conductivity as high as 128W m-1 K-1. Monolayer graphene/FG lateral heterostructures with seamless junctions are approached for device fabrication. Efficient in-plane heat removal paths from graphene channel to side FG are created, contributing significant reduction of the channel peak temperature and improvement in the current-carrying capability and power density. Molecular dynamics simulations indicate that the interfacial thermal conductance of the heterostructure is facilitated by the high degree of overlap in the phonon vibrational spectra. The findings offer novel design insights for efficient heat dissipation in micro- and nanoelectronic devices.

Heat pipe-cooled highly-concentrated multi-junction solar cell

Concentrator photovoltaic (CPV) systems have proven the capability of competing with traditional photovoltaic (PV) systems due to their high efficiency and low area occupancy. Such CPV systems require efficient heat removal auxiliary systems, especially for medium and high optical concentration ratios. Operating a CPV system under a high optical concentration (ratio > 200 X) might require active cooling techniques, which have high operating costs and maintenance. On the other hand, heat pipes (HPs) are widely used in electronic devices for cooling purposes. This work discusses the possibility of operating a CPV system coupled with HPs as a passive cooling technique. Two different HPs with different lengths are used to compare cooling efficiency. Each HP length was tested either in a single or double configuration. Long HPs showed better heat removal compared to a traditional fin-cooling system. CVP cooling with HP systems enhanced the entire electrical output of the cell, mainly at high optical concentration ratios.

Development of Printed Circuit Boards with High Thermal Conductivity and Low Thermal Expansion by Applying Cu-Mo Composite Materials

In recent years, electronic devices are strongly required to be smaller, lighter, and more powerful. As a result, mounted components have become smaller, more powerful, and denser, and the heat generation density on printed circuit boards (PCBs) has increased. Since rising component temperatures can lead to component failure, efficient heat removal from the generated heat has become an urgent issue. Since general PCBs have low thermal conductivity, when high heat dissipation is required, methods to increase the thermal conductivity of PCBs have been employed by increasing the copper (Cu) content in the PCB or by placing an aluminum (Al) alloy in the inner layer. However, while Cu and Al have high thermal conductivity, they also have high coefficients of thermal expansion (CTE) and young’s modulus, and the CTE of a PCB with increased thermal conductivity using these materials is high. If the thermal expansion difference between the PCB and mounted components is large, reliability against heat cycles cannot be obtained. Therefore, we have focused on copper-molybdenum (CuMo) composite materials with high thermal conductivity, high elastic modulus, and low thermal expansion. We have been utilizing Cu-Mo for the development of our PCBs and fabricated multilayered CuMo composite PCBs; therefore, this report will focus on the results regarding thermal characterization of prototype PCBs.

Heat transfer enhancement of electrospray cooling with microencapsulated phase change material slurry (MPCMS): A comprehensive numerical model and experimental study

Electrospray cooling (ESC) technology is increasingly emphasized due to its efficient heat removal capacity, minor coolant consumption and accurate thermal control. Previous articles had focused on either experimental exploration on ESC performance or numerical methods on solitary electrospray such as Volume of Fluid [1], Boundary Element Method [2] and Lagrangian model [3]. However, there is no comprehensive model characterizing the whole ESC process. Moreover, there was barely investigation on ESC enhancement using phase change materials (PCM). Herein, this study has bridged this gap by developing a new comprehensive model to explore the ESC enhancement with microencapsulated phase change material slurry (MPCMS), and conducted experiment to verify it. The influences of applied voltage, mass concentration and inlet temperature of MPCMS on the ESC were discussed. Results revealed that MPCMS offered superior cooling performance during melting process due to latent heat absorption compared to deionized water. Nevertheless, as wall temperatures increased, the deposition, higher viscosity and lower thermal conductivity of MPCMS would compromise cooling efficiency. Moreover, higher applied voltage enhanced cooling performance by increasing droplet velocity, and reducing the possibility of droplet rebound. When the inlet temperature approached the peak melting temperature, the convective heat transfer coefficient reached its maximum.

Pre-conceptual design of the fixed mirrors for the DEMO Electron Cyclotron Heating antenna

The M1 mirrors are part of the in-vessel quasi-optical Electron Cyclotron beam propagation system of the DEMO nuclear fusion reactor. These four mirrors are all non-movable and with a plane reflecting surface. Based on their functionality they are divided into two groups, the Mid-Steering Antenna (MSA) and the Multi-Beam Mirror (MBM) antenna. The MSA is responsible for controlling the neoclassical tearing modes, while the MBM is available for plasma bulk heating, current drive and thermal instability control.These mirrors are designed to withstand the thermal loads generated during operation: neutron heating, ohmic losses and stray radiation caused by the mm-wave beam reflection. To fulfil the design requirements, efficient heat removal strategies based on water cooling principles minimizing pressure drop are implemented.This paper presents the pre-conceptual design of the MBM and MSA M1 mirrors, validating the structural and geometric boundary conditions, as well as the appropriate selection of materials. Using FEA tools, thermal-hydraulic and thermo-mechanical simulations were performed with the available thermal loads to optimize the cooling parameters and perform a first stress assessment on the two M1 mirrors.

Digital Strategies to Improve Product Quality and Production Efficiency of Fluorinated Polymers: 2. Heat Removal Performance of Reactor with Internal and External Cooling Systems

This work aims to study the heat transfer performance of a sophisticated industrial suspension polymerization reactor, which is distinguished by its complex blade structure and capability in efficient heat removal,...

Optoelectronic methane sensor based on two-color led module

The article proposes an optoelectronic two-wave method for monitoring the methane content in the atmosphere. Spectral characteristics are given two-color LED module LED39, LED32, photodiode PD36 and methane absorption spectrum. An optoelectronic sensor for monitoring the methane content in the atmosphere with high measurement accuracy has been developed, and its block diagram is shown. In an optoelectronic sensor for monitoring methane content in the atmosphere A two-color LED module with emission spectra of 3.2 microns (reference) and LEDs with emission spectra of 3.4 microns (working) were used . To increase the optical power of LEDs (3.2 and 3.4 microns), a design with more efficient heat removal and a parabolic reflector design for LEDs, which focuses IR radiation at an angle of 8-10 degrees, have been proposed. LED crystals with emission spectra of 3.2 microns and 3.4 microns are mounted in one housing to ensure high accuracy and sensitivity of the device.

Enhanced boiling heat transfer on three-dimensional hybrid micropillar array surfaces

Boiling heat transfer is widely used in numerous industrial systems because of its excellent heat dissipation performance. The critical heat flux (CHF) represents the upper limit of efficient heat removal. The most widely applied CHF model is Zuber's hydrodynamic instability model, which posits that the interference between vapor and liquid counterflows results in the CHF. In this paper, a three-dimensional (3D) hybrid micropillar array surface for hindering the liquid–vapor interface is proposed to enhance the CHF and heat transfer coefficient (HTC). The 3D hybrid surface comprises a tall hydrophobic (HB) pillar array surrounded by a short hydrophilic (HP) pillar array. The tall HB pillar array acts as a potential nucleation site for increasing the HTC, and the short HP pillar array acts as a wicking structure for facilitating liquid rewetting. In addition, the height difference between the HB and HP pillar arrays can potentially reduce the interference between liquid and vapor counterflows and increase the CHF. Relative to a plain silica surface, the 3D hybrid surface increases the CHF and HTC by 107% and 360%, respectively. Theoretical modeling suggests that the CHF on the 3D hybrid surface was still limited by pool hydrodynamics.

Novel integration of dual evaporator loop heat pipe for improved electric vehicle battery thermal regulation

The Battery Thermal Management System (BTMS) plays a crucial role in ensuring the efficient and safe operation of Hybrid Electric Vehicles (HEVs) and/or Electric Vehicles (EVs). Among various heat transfer techniques, Loop Heat Pipes (LHPs) have demonstrated their potential for effective heat transfer from Li-ion batteries due to their high heat transfer rates over a longer distance. The conventional design of LHPs poses challenges for constructing robust battery pack modules, particularly in electric vehicles (EVs). This complexity arises from the separation of liquid and vapor lines at either the top or bottom of the evaporator, along with the inclusion of a compensation chamber. Furthermore, the evolving requirements of BTMS highlight the necessity for efficient heat removal from multiple locations. To address these requirements, a novel Dual Evaporator Loop Heat Pipe (DE-LHP) has been developed as a BTMS solution featuring separate vapor and two liquid lines positioned at the uppermost section of each cylindrical evaporator. The developed DE-LHP is tested as a BTMS solution with a 3S4P battery module (10Ah capacity) at different charging and discharging rates (1C, 1.5C, and 2C) in surrounding temperatures ranging from 30 °C to 45 °C. When the thermal performance of the DE-LHP-equipped BTMS was compared to a module without BTMS, a drop in maximum cell temperature was noted. At an ambient temperature of 35 °C, the DE-LHP BTMS achieved temperature reductions of 22.8 %, 22.6 %, and 18.8 % at charging rates of 1C, 1.5C, and 2C, respectively. In addition, at a threshold temperature of 60 °C, the module with DE-LHP BTMS demonstrated enhanced discharging capability from 41 % State of Charge (SOC) to 0 % SOC for a 1.5C discharging rate and from 59 % SOC to 0 % SOC for a 2C discharging rate compared to the module without BTMS. Furthermore, when the module was exposed to ambient temperatures ranging from 30 °C to 45 °C, the DE-LHP BTMS maintained a temperature difference across the battery module of less than 3.5 °C for all charging rates and 1C and 1.5C discharging rates.

Autonomous Thermosiphon System of Passive Residual Heat Removal from the Primary Circuit of the Reactor Plant: Features of Operation, Characteristics and Basic Advantages

An autonomous system of passive removal of residual heat (PRRHS) of a reactor installation with VVER designed to ensure the safety of nuclear power plants in an accident with complete long-term blackout is considered. The system provides for the removal of heat directly from the first circuit of the reactor plant (PRRHS R). In order to increase the reliability and safety of the emergency heat sink, heat exchange equipment based on closed-type evaporation and condensation devices – two-phase thermosyphons – has been used in the system. The main feature of such heat exchangers is that their thermosiphon assemblies structurally separate the primary circuit and the auxiliary circuit of the PRRHS, which is removed outside the reactor compartment, and provide safe and efficient heat removal, reduce the risk of radioactive contamination spreading beyond safety barriers. Such autonomous passive systems will provide effective heat removal directly from the primary circuit by changing the chain of successive heat transfer sites from nuclear fuel to the final absorber and excluding from it such elements, as for example steam generators, the condition and operability of which in the emergency process of heat removal have a major impact on the safety of the reactor core. The article presents a diagram of an autonomous heat sink system; also, a description of its operation is given. The main characteristics of the course of the emergency process of removal of residual heat by the autonomous thermosiphon PRRHS R obtained by computational modeling have been considered. The advantages of an autonomous thermosiphon passive system in comparison with a passive heat removal system of a reactor installation with VVER through the second circuit are analyzed. The obtained results are proposed to solve the problems of diversification of passive safety systems of evolutionary reactor plants of nuclear power plants with VVER type reactors.

Numerical Simulation of Conjugate Mixed Convection in 3D Channel with Heat-Generating Flat Element and Symmetrical Solid Two-Fin System

This paper presents the numerical simulation results of conjugate mixed convection in a three-dimensional channel with a heat-generating element and solid fins. It should be noted that the symmetrical location of fins has been studied. The system of partial differential equations, presented in dimensionless form using velocity and vorticity vectors, has been solved by the finite difference method on a uniform grid. The central difference schemes have been used to approximate diffusive terms. In contrast, for an approximation of convective terms, the monotonic Samarskii difference schemes have been applied to improve the stable properties of central differences of the second order of accuracy. Analysis has been performed on a wide range of governing parameters, including the Reynolds number (200 ≤ Re ≤ 1000), the material of the fins (aluminum, copper, and iron), and the location of the fins on the heater surface, taking into account the identical distances between the fins and the nearest walls. Water has been considered a working cooling medium. The obtained outcomes characterize the most efficient heat removal from the surface of the energy source using the considered fin system. For example, by using copper fins, the cooling efficiency of the heating element can be increased. The average heater temperature decreases significantly with an increase in the Reynolds number. The distance between the fins also makes a significant contribution to the cooling phenomenon. It is noted that with the most successful choice of location, it is possible to decrease the temperature of the heater by more than 12%.

Metal Hydride Composite Structures for Improved Heat Transfer and Stability for Hydrogen Storage and Compression Applications

Metal alloys and intermetallic compounds offer an attractive method for safely storing hydrogen (H2). The metal alloys absorb H2 into their structure, often swelling and fracturing as a result of phase transformation during hydride formation/decomposition cycles. The absorption of H2 is an exothermic process, requiring the effective and efficient removal of heat. This can be challenging as heat transfer to/from powdered beds is notoriously difficult, and often limited by poor thermal conductivity. Hence, the observed reaction kinetics for absorption and desorption of H2 is dominated by heat flow. The most common method for improving the thermal conductivity of the alloy powders is to prepare them into composite structures with other high thermal conductivity materials, such as carbons and expanded natural graphite. Such composite structures, some also combined with polymers/resins, can also mitigate safety issues related to swelling and improve cyclic durability. This paper reviews the methods that have been used to prepare such composite structures and evaluates the observed impact on thermal conductivity.

Thermohydraulic performance comparison of 3D printed circuit heatsinks with conventional integral fin heatsinks

Additive manufacturing has enabled the fabrication of intricate geometries and structures of numerous sizes at high accuracy, which has attracted researchers towards its application as 3D-printed heatsinks. In this context, current work is focused on exploring the potential of periodic lattices of cellular materials as heat sinks and their comparison with conventional thermal management systems. Thermohydraulic characteristics of the heatsinks with channel designs of cellular structures, namely, simple cubic and body-centered cubic, are evaluated and compared with the performance of conventional heatsinks with integral fins. The heatsinks' conjugate heat transfer and flow are solved numerically, employing a validated model built on 3D Reynolds averaged Navier Stokes with the Shear Stress Turbulence model. Water and critical CO2 are used as coolants in this study. Results show that the SC design performs best compared to the classic finned design with an overall performance evaluation criterion of around 4.45 times higher at a flow rate of 1.5 L/min using water as a coolant. In addition, body-centered cubic lattice performs with a PEC of 4.33 at the same flow rate and working fluid. The computed results demonstrate that the performance of 3D-printed heatsinks geometries is significantly superior to the classic designs making them an ideal candidate for designing further compact and efficient heat removal systems for electronic devices.

Growth of elongated vapor bubbles during flow boiling heat transfer in wavy microchannels

Flow boiling within microchannels is an efficient heat removal mechanism by utilizing the latent heat of the fluid. Numerical simulations can resolve the small temporal and spatial scales of the vapor bubbles in the flow boiling process, thus accessing many details of the flow which is unattainable experimentally. Most of the previous studies of flow boiling heat transfer used straight microchannels, even though curved microchannels have potential to further enhance the heat transfer performance. In this study, the flow boiling heat transfer in wavy microchannels is studied via numerical simulation by focusing on the growth of the vapor bubbles. Straight and wavy microchannels are considered for comparison and analysis. The numerical simulations are conducted using the finite volume method to solve the flow and the heat transfer, and the volume of fluid (VOF) method to capture the interface dynamics. The effects of key dimensionless numbers on bubble growth rate and wall heat transfer are quantified, including the Weber number, the Capillary number, and the Jakob number. The results indicate that the wavy structure of the microchannel has a strong effect on the bubble growth and the wall heat transfer in microchannels. As the waviness of the microchannel increases, the bubble grows faster because of the bubble deformation by the wavy channel, the bubble moves faster due to the bubble expansion, and the heat transfer is enhanced by the perturbation of the bubble to the flow. With the large velocity perpendicular to the channel flow direction induced by the waviness, the local Nusselt number of the wavy channel could be high up to 2.6 times higher than the straight channel.

GaN-полевой транзистор с эффективным теплоотводом на Si-подложке

A simple design of a GaN field-effect transistor on a Si substrate with efficient heat removal through polydiamond layers formed on the walls of grounding holes is proposed. According to calculations, as a result of the introduction of such a heat sink with the same average distance between the gate sections, the maximum temperature in the channel of the GaN transistor on the Si substrate decreases significantly and becomes comparable to the maximum temperature in the channel of the GaN transistor on the SiC substrate.

GaN field-effect transistor with efficient heat dissipation on Si substrate

A simple design of a GaN field-effect transistor on a Si substrate with efficient heat removal through polydiamond layers formed on the walls of grounding holes is proposed. According to calculations, as a result of the introduction of such a heat sink with the same average distance between the gate sections, the maximum temperature in the channel of the GaN transistor on the Si substrate decreases significantly and becomes comparable to the maximum temperature in the channel of the GaN transistor on the SiC substrate.. Keywords: GaN FET, ground hole, channel temperature, polydiamond.