Liquid Coolant Research Articles

Method and Verification of Liquid Cooling Heat Dissipation Based on Internal Heat Source of Airborne Long-Focus Aerial Camera

The traditional passive heat dissipation method has low heat dissipation efficiency, which is not suitable for the heat dissipation of the concentrated heat source inside the long-focal aerial camera, resulting in temperature level changes and temperature gradients in the optical system near the heat source, which seriously affect the imaging performance of the aerial camera. To solve this problem, an active heat dissipation method of liquid cooling cycle is proposed in this paper. To improve the solving efficiency and ensure simulation accuracy, a dynamic boundary information transfer method based on grid area weighting is proposed. The thermal simulation results show that the liquid cooling method reduces the heat source temperature by 70.12%, and the boundary temperature transfer error is 0.015%. The accuracy of thermal simulation is verified by thermal test, and the simulation error is less than 6.44%. In addition, the performance of the optical system is further analyzed, and the results show that the MTF of the optical system is increased from 0.077 to 0.194 under the proposed active liquid cooling cycle heat dissipation method.

Cooling Performance of a Nano Phase Change Material Emulsions-Based Liquid Cooling Battery Thermal Management System for High-Capacity Square Lithium-Ion Batteries

This study investigated the application of nanophase change material emulsions (NPCMEs) for thermal management in high-capacity ternary lithium-ion batteries. We formulated an NPCME of n-octadecane (n-OD) and n-eicosane (n-E) with a mass fraction of 10%, whose phase change temperatures are 25.5 °C and 32.5 °C, respectively, with specific heat capacities 2.1 and 2.4 times greater than water. Experiments were conducted to evaluate the thermal control performance and latent heat utilization efficiency of these NPCMEs. The NPCMEs with an n-OD mass fraction of 10% (NPCME-n-OD), particularly reduced the battery pack’s maximum temperature and temperature difference to 41.6 °C and 3.72 °C under a 2 C discharge rate, lower than the water-cooled group by 1.3 °C and 0.3 °C. This suggests that nano emulsions with phase change temperatures close to ambient temperatures exhibit superior cooling performance. Increased flow rates from 50 mL/min to 75 mL/min significantly lowered temperatures, resulting in temperature reductions of 2.73 °C for the NPCME-n-OD group and 3.37 °C for the NPCME-n-E group. However, the latent heat utilization efficiency of the nano emulsions decreased, leading to increased system energy consumption. Also, it was found that the inlet temperature of the NPCMEs was very important for good thermal management. The right inlet temperatures make it easier to use phase change latent heat, while excessively high temperatures may make thermal management less effective.

Rotor-Through-Coils Toroidal-Flux Reluctance E-Motor for Aviation

Electrification of aviation propulsion is in progress. New electric motor architectures — beyond axial and radial fluxes — may be required to unlock its full potential in meeting the demanding functional requirements (in terms of power, weight and efficiency) and certification requirements (from airworthiness authorities) set for airborne operating engine. This article presents a new class of toroidal-flux reluctance electric motors, where the rotor travells inside the coils — the Rotor-Through-Coils (RTC) Reluctance E-Motor. Extensive finite element magnetic model analysis was conducted (including motor operational characteristics assessment), following from an existing validated approach. The power delivered by five series-mounted motors rivales fuel-injected engines powering existing acrobat airplanes, including similar dimensions. A further important advantage will follow in a sequel publication showing the substantial advantage of this motor architecture to be entirely and effeciently air-cooled (like high pressure turbines already do in turbofans), removing the added complexity, weight, cost and certification issues implied in using onboard liquid coolants.

Kinetics of Liquid Cooling of Bodies in Flow Devices without Phase Transition

Kinetics of Liquid Cooling of Bodies in Flow Devices without Phase Transition

Experimental study on transpiration cooling with phase change in rotating detonation engine

Transpiration cooling with phase change is an effective method for protecting high heat flux walls from ablation in combustion chambers and spaceflight vehicles. The combustion chamber walls of the rotating detonation engine (RDE) experience high heat flux, which poses significant challenges to thermal protection and limits its development. This study introduces a transpiration cooling thermal protection system for a kerosene/air RDE, where the liquid coolant absorbs heat with phase change, reducing wall temperature by more than 50% under certain conditions. The experiments investigated the effects of coolant flow rate, coolant types (water and kerosene), porosity of porous media, and fuel equivalence ratio on both transpiration cooling and detonation wave dynamics. The results show that water provides superior cooling effectiveness compared to kerosene, particularly with increased flow rates and porosity. During RDE operation, increasing flow rates of both water and kerosene initially enhances cooling efficiency but eventually leads to an overall reduction. Furthermore, higher coolant flow rates of both water and kerosene can disrupt the stability of detonation waves within the combustion chamber. Although enlarging the equivalence ratio improves cooling efficiency, maintaining continuous detonation wave generation remains challenging. The cooling efficiency in the detonation combustion mode is lower than that in deflagration. Additionally, carbon deposition was observed in the transpiration cooling system, particularly during prolonged operation. These findings provide valuable insights for the optimization and technical guidance of RDE design.

Two-Electrode Growth and Optimization of Copper Nanocone Structures for Immersion Phase-Change Liquid Cooling

Two-Electrode Growth and Optimization of Copper Nanocone Structures for Immersion Phase-Change Liquid Cooling

Research and Analysis of Liquid Cooling Heat Dissipation Equipment for Insulated-Gate Bipolar Transistor Modules of Wind Power Converters Based on the Finite Element Analysis Method

The primary objective of this study is to develop a simulation model for a liquid cooling plate (LCP) for insulated-gate bipolar transistor (IGBT) modules, with the aim of reducing the operating temperature of wind power converters (WPCs). The initial impetus for this study was the observation that the energy conversion efficiency of a WPC declines when the operating temperature of the IGBT module exceeds a critical threshold. Three LCPs, with and without heat sinks, were modelled under extreme conditions using the finite element simulation method. The effect of the number and height of the fins on the cooling efficacy was evaluated through the simulation and analysis of the LCP model with heat sinks. The results demonstrate that the optimal configuration, comprising five 10 mm fins and 13 10 mm struts, can achieve the following reductions: maximum temperature by 11.4 K, heat dissipation efficiency by 3.33%, pressure drop by 10.6 KPa, and pump power by 31.00%. Moreover, the findings suggest that the number of fins has a significant impact on temperature fluctuations, whereas the height of the fins exerts a markedly significant influence on pressure drop.

Pulsating Heat Pipe Performance Modeling with Liquid Metal Coolants Under Hypersonic Aerothermal Heating

Hypersonic heating loads concentrate at leading-edge compression areas to create excessively high local temperatures and thermally driven stresses. The fast and reliable thermal dispersion of heat pipes with significantly high thermal conductance can alleviate these localized thermal stiffness problems. The pulsating heat pipe (PHP) holds numerous advantages when compared to capillary, constant-conductance heat pipes for hypersonic thermal management applications, primarily because they lack a wicking structure. This paper numerically investigates thermal performances of a four-turn C103 niobium alloy PHP operating with lithium, potassium, sodium, and a eutectic sodium–potassium alloy (NaK-78) when exposed to heating conditions relevant to the hypersonic environment, investigating flight Mach numbers ranging from 6 to 8 and dynamic pressures ranging from 40 to 44 kPa. The robust thermofluidic properties of liquid metals, along with the powerful fluid pulsation induced in the PHP, can provide significant thermal transport from hot stagnant regions of the leading edge to the cooler trailing surfaces. Potassium showed superior thermal performance when compared to other liquid metal coolants under the presently tested conditions, with overall PHP thermal conductance as high as 34 W/K predicted for Mach 8 flight conditions. In contrast, sodium was associated with startup difficulties in the PHP; this paper attributes this to its significantly larger thermal conductivity, which can limit the vapor pressure difference over the liquid slug lengths. These predictions indicate an overall latent heat transfer dominance of around 70–95% in liquid metal PHPs.

A self-organized sandwich structure of chromium nitride for ultra-long lifetime in liquid sodium.

The development of fast neutron reactors with improved efficiency and sustainability, being a tangible solution to the large-scale utilization of nuclear energy, serves as a critical step prior to the commercialization of fusion energy. These reactors use liquid metal coolants, which can weaken the durability of metallic components. Conventional design of protective coatings counts upon thermodynamics, which often overlooks the kinetic factors such as structural evolutions, resulting in deteriorated coating properties. Herein, we present a novel interface-engineering strategy involving the control of the phase transformation direction and interface diffusion reaction. Through iterations of self-organization, desired surfaces and interfaces can be achieved for materials used in harsh environments. Specifically, a CrN-coated steel sample with an interfacial Cr layer was designed and fabricated. After ultra-long (up to 6000 h) immersion in liquid sodium, the CrN/Cr coating structure was converted into a sandwich Cr2N/CrN/Cr2N structure dynamically. As a consequence, the coating system exhibited enhanced properties, namely increased surface hardness (by ∼36%), reduced coefficient of friction (by ∼13%), and enhanced interfacial adhesion (by ∼37%). Thus, the proposed strategy can guide the future design of robust coatings with ultra-long service life in harsh environments.

Thermodynamic properties of perfluorooctane on the liquid-gas coexistence curve: calculation method and tabulated data

A technique has been developed for constructing a phase equilibrium line in the range from the triple to the critical point for a technically important substance, perfluorooctane (C8F18), which is currently used in various fields of industry and medicine. The proposed phase equilibrium line model includes the following equations: vapour pressure; saturated liquid density; saturated vapour density; “apparent” heat of vaporization. In this case, the vapour pressure equation satisfies the requirements of the scale theory of critical phenomena near the critical point, and the Wegner model in the vicinity of the triple point. The coexistence curve model in the vicinity of the critical point satisfies the Yang-Yang model and renormalization group theory for asymmetric systems, and in the region of rarefied gas it satisfies the linear model of average diameter. In the temperature range 246.15–496.99 K, table for perfluorooctane have been developed, including pressure and density of saturated vapor, density of saturated liquid, heat of vaporization, first and second derivatives of saturated vapor pressure. Using latest experimental data, as well as experimental data on the critical pressures of perfluoroalkanes as a function of their molecular weight, the following values of critical parameters were selected: critical pressure – 1.548 MPa, critical density – 596.4 kg/m3, critical temperature – 496.99 K. A number of statistical characteristics were calculated, including absolute mean deviation and standard deviation, characterizing the accuracy of the proposed phase equilibrium line model when describing experimental data obtained in generally recognized international thermophysical laboratories. The results obtained are useful for high-tech companies engaged in the development of innovative technologies: in the field of radio-electronic and electrical industries, in which perfluorooctane is used as a liquid dielectric and coolant; in medicine, where perfluorooctane is used as a gas transport liquid and is used for ophthalmic purposes; magnetic fluid sealers for the purpose of isolating hazardous substances from the environment and seals for devices operated in vacuum conditions or in contact with aggressive substances; magnetic fluid separators for separating non-ferrous metals by density, etc. The results of this study can also be used in developing the fundamental equation of state for perfluorooctane. The results obtained are useful for high-tech companies engaged in the development of innovative technologies: in the field of radio-electronic and electrical industries, in which perfluorooctane is used as a liquid dielectric and coolant; in medicine, where perfluorooctane is used as a gas transport liquid and is used for ophthalmic purposes; magnetic fluid sealers for the purpose of isolating hazardous substances from the environment and seals for devices operated in vacuum conditions or in contact with aggressive substances; magnetic fluid separators for separating non-ferrous metals by density, etc. The results of this study may also be useful in developing the fundamental equation of state for perfluorooctane.

Research Progress of Microchannel Liquid Cooling Technology in the Application of Thermal Management of Prismatic Lithium Batteries (Withdrawn)

Lithium-ion batteries have significant advantages such as high energy density, long cycle life and low self-discharge rate. Therefore, they are ideal for energy storage in electric vehicles. However, lithium-ion batteries are very sensitive to temperature, which affects the battery's cycle life, efficiency, reliability and safety. During the charging and discharging process, a large amount of heat is generated inside the battery due to the electrochemical reaction and resistance, causing the battery temperature to rise. When the temperature gets too high, thermal runaway, electrolyte fire and explosions may occur. As battery energy density increases, the demand for efficient thermal management continues to increase, and a compact and efficient battery thermal management system is essential. This paper introduces the development status of different thermal management technologies, reviews the application of microchannel liquid-cooling technology in the thermal management of prismatic lithium batteries, discusses the current research direction and status of microchannel technology, and finally looks forward to the future research and development direction of microchannel technology.

PCM-based passive cooling solution for Li-ion battery pack, a theoretical and numerical study

We propose in this study a novel cooling solution for Li-ion battery packs based on Phase Change Materials (PCM) and metallic fins placed around each cell. Discharging and charging processes both melt the PCM. To complete the thermal management of the batteries, an intermediary sequence is added for the PCM solidification. During a short timeframe between batteries charging and discharging, a liquid coolant flows through one small channel located within each fin. A numerical model and a theoretical analysis allow to predict the thermal behavior of the battery cells and the PCM liquid fraction changes in time. It is shown that the combination of a passive cooling solution brought by the PCM with the fast period of liquid cooling for the PCM solidification is an effective solution to control the temperature evolution within the battery cells during discharge and charge. The only external energy consumption foreseen comes from the laminar flow of the coolant for solidification during a very short period of time. The findings indicate that the proposed PCM-liquid cooling integration reduces the total energy consumption by 54.9 % (from 0.4406 kJ to 0.1963 kJ) for the 2C discharging-2C charging cycle compared to traditional liquid-cooling strategy.

Comparative Study on Heat Dissipation Performance of Pure Immersion and Immersion Jet Liquid Cooling System for Single Server

Heat dissipation has emerged as a critical challenge in server cooling due to the escalating number of servers within data centers. The potential of immersion jet technology to be applied in large-scale data center server operations remains unexplored. This paper introduces an innovative immersion jet liquid cooling system. The primary objective is to investigate the synergistic integration of immersion liquid cooling and jet cooling to enhance the heat dissipation capacity of server liquid cooling systems. By constructing a single-server liquid cooling test bench, this study compares the heat dissipation efficiencies of pure immersion and immersion jet liquid cooling systems and examines the impact of inlet water temperature, jet distance, and inlet water flow rate on system performance. The experimental outcomes show that the steady-state surface heat transfer coefficient of the immersion jet liquid cooling system is 2.6 times that of the pure immersion system, with increases of approximately 475.9 W/(m2·K) and 1745.0 W/(m2·K) upon adjustment of the jet distance and flow rate, respectively. Furthermore, the system model is streamlined through dimensional analysis, yielding a dimensionless relationship that encompasses parameters such as inlet water temperature, jet distance, and inlet water velocity. The correlation error is maintained below 18%, thereby enhancing the comprehension of the immersion jet cooling mechanism.

Experimental investigation on cooling characteristic of transpiration-film combined cooling structure using liquid coolant

Transpiration cooling has gained significant attention as a promising strategy for thermal protection in scramjet engines. However, this approach faces limitations due to its susceptible block in fuel gas environment and significant fluctuation when using liquid coolants. To address these challenges, this work proposes a novel transpiration-film combined cooling structure (CCS), where the lower porous layer could ensure sufficient heat transfer and the upper film-hole layer could keep impurities from blocking porous layer and enhance the mechanical strength. Experimental and theoretical investigation on the combined cooling structure with liquid coolant phase change are carried out, and the cooling efficiency, temperature uniformity and cooling chamber pressure of the combined structure are compared with those of the transpiration cooling structure (TCS). Remarkably, the combined structure effectively suppresses temperature fluctuations, reducing the amplitude of temperature variation to just 1/5 of that observed in the transpiration cooling system. Although the combined structure shows a modest 0.026 drop in time-averaged cooling efficiency, it significantly improves temperature uniformity and reduces pressure peaks within the cooling chamber. Furthermore, the flow characteristics of liquid film and vapor film are analyzed and the coolant utilization rate for vapor film is 6.4 times higher than that for liquid film. Consequently, the design of combined structures using liquid coolant holds great promise for achieving highly efficient thermal protection in scramjet engines.

Nanoengineering Scalephobic Surfaces for Liquid Cooling Enhancement

AbstractCrystallization fouling, a process where mineral scales form on surfaces, is of broad importance in nature and technology, negatively impacting water treatment and electricity production. However, a rational methodology for designing materials with intrinsic resistance to scaling and scale adhesion remains elusive. Here, guided by nucleation physics, this work investigates the effect of coating composition and surface structure on the nucleation and growth mechanism of scale on metallic heat transfer surfaces nanoengineered by large‐area techniques. This work observes that on hydrophilic nanostructured copper, despite its significantly enlarged surface area compared to smooth surfaces, scale formation is substantially suppressed leading to sustained, efficient cooling performance. This work reveals the mechanism through thermofluidic modeling coupled with in situ optical characterization and show that surface bubble formation through degassing is responsible for generating local hot spots enhancing supersaturation. This work then demonstrates a scalephobic nanostructured surface which reduces the accumulated surface scale mass 3.5× and maintains an 82% higher heat transfer coefficient compared to superhydrophobic surfaces with corresponding energy conversion savings. This work not only advances the understanding of fouling mechanisms but also holds promise for practical applications in industries reliant on efficient heat transfer processes.

Modelling and Temperature Control of Liquid Cooling Process for Lithium-Ion Battery

Modelling and Temperature Control of Liquid Cooling Process for Lithium-Ion Battery

Liquid Hydrogen Cooling System for 100 kW-Class HTS Rotor Thermal Design

Liquid Hydrogen Cooling System for 100 kW-Class HTS Rotor Thermal Design

Advanced Thermal Management of Cylindrical Lithium-Ion Battery Packs in Electric Vehicles: A Comparative CFD Study of Vertical, Horizontal, and Optimised Liquid Cooling Designs

Advanced Thermal Management of Cylindrical Lithium-Ion Battery Packs in Electric Vehicles: A Comparative CFD Study of Vertical, Horizontal, and Optimised Liquid Cooling Designs

Liquid Cooling of Fuel Cell Powered Aircraft: The Effect of Coolants on Thermal Management

Abstract Electric propulsors powered by Proton Exchange Membrane Fuel Cells (PEMFCs) offer a net zero solution to aircraft propulsion. Heat generated by the PEMFCs can be transferred to atmospheric air via a liquid cooling system; however, the cooling system results in parasitic power and adds mass to the propulsion system, thereby affecting system specific power. The design of the cooling system is sensitive to the choice of liquid coolant and so informed coolant selection is required if associated parasitic power and mass are to be minimized. Two approaches to selection of coolants for PEMFC-powered aircraft are presented in this paper for operating temperatures in the range 80-200°C (this covers low, intermediate, and high temperature PEMFCs). The first approach uses a Figure of Merit (FoM) alongside minimum and maximum operating temperature requirements. The FoM supports the selection of coolants that minimize pumping power and mass while maximizing heat transfer rate. The second approach uses a cooling system model to select ȜPareto efficientȝ coolants. A hybrid-electric aircraft using a PEMFC stack is used as a representative case study for the two approaches. Hydrocarbon-based coolants are shown to be favorable for the case study considered here (aromatics for PEMFCs operating at <130°C and aliphatics for PEMFCs operating at >130°C). As the PEMFC operating temperature increases, the parasitic power and mass of the TMS decreases. Operating at elevated temperatures is therefore beneficial for liquid cooled PEMFC-powered aircraft. Nevertheless, there are diminishing performance gains at higher operating temperatures.

Simulations With Compressible Multiphase Formulation on Heat Transfer Studies in a Rocket Thrust Chamber With Experimental Validation

Abstract In the combustor for rocket engines, liquid film cooling is a widely adopted technique for restricting the structural components to the acceptable bounds for the successful operation of the propulsion systems. Multiple cooling techniques for thrust chamber walls are favored along with the coolant film in propulsion systems operating at higher chamber pressures by incorporating an ablative cooling mechanism for the nozzle. The adoption of combination will result in challenges in simulation studies due to the presence of multiphase phenomenon in the system. The current article presents the effects of these two cooling methods on a thrust chamber wall studied through compressible multiphase formulations. A majority of the previous studies have used incompressible flow equations to model coolant film behavior and associated heat transfer. The present study utilizes an approach utilizing compressible multiphase flow to simulate the behavior of the compressible hot gas flow and the incompressible coolant liquid film accounting for phase change effects, vapor diffusion into hot gas, radiation effects on coolant surface, liquid entrainment, and blowing effects due to vapor formation at interface. Film-cooling effects on ablative nozzle accounting for pyrolysis phenomenon due to material decomposition governed by Arrhenius expression are also emphasized. The outcome of the numerical model showed good agreement with available test data in literature, and results from the tests done in-house. The model described in the present study was able to support the actual evidence of liquid film cooling being able to preserve the walls of the thrust chamber from severe internal thermal environment and prevent ablation on surface of nozzle.