Convective Cooling Research Articles

Convection Cooling of Power Electronics Operating in Deep-Space

Abstract Since most traditional spacecraft are designed to operate in a vacuum environment, forced convection cooling has seen limited use in space-applications. This paper considers an ideal candidate–the Dragonfly Lander, a rotorcraft being sent into Deep-space to conduct experiments on Saturn's largest moon, Titan. A forced convection based thermal management solution is presented for the Rotor Drive Electronics (RDE) unit, a high-power electronics box responsible for controlling the rotors that allow the Lander to fly on Titan. A thermal flow model was built in Solidworks Flow Simulation to evaluate the effectiveness of a fan system integrated into the packaging design and used as the primary method for cooling the RDE. The model was validated with temperature data collected from custom designed ground support equipment. It was found that utilizing forced convection allows temperatures of the electronics within the tightly packaged RDE to remain within operational limits when conductive and radiative heat transfer alone are insufficient. Titan's dense atmosphere results in greater mass flow rates through fans compared to on Earth, making forced convection a particularly efficient method of heat transfer. This research may guide the use of forced convection in future space missions, or non-traditional environments.

Convective Cooling of Blades in a Turbine Driven by Supercritical Carbon Dioxide

Convective Cooling of Blades in a Turbine Driven by Supercritical Carbon Dioxide

Research on Convective Cooling and Thermal Protection Characteristics of Integrated Dual-Sided Deflector System

Research on Convective Cooling and Thermal Protection Characteristics of Integrated Dual-Sided Deflector System

Effect of External Flow Mode on Nanofluid Mixed Convective Cooling Inside a Multi-Vented Cavity

The purpose of this paper is to study numerically laminar mixed convection in a multiple vented cavity. This enclosure is continuously heated by constant temperature from the bottom wall, while the other boundaries are presumably thermally insulated. The imposed water-Al2O3 nanofluid flow is injected or sucked. The Influences of various control parameters, e.g.: Reynolds number Re, from 200 to 5000, the solid volume fraction of nanoparticles, , from 0to 7 %, and external flow mode (injection or suction) on the thermal patterns, the flow and the heat transfer within the enclosure are studied. Numerical results revealed that the presence of nanoparticles contributes to enhancement in the heat exchange and increase in the mean temperature within a cavity. Also, it was found that the heat performance and Applying the suction mode enhances the efficiency of cooling compared to the injection mode.

Thermal performance of serpentine channel immersion cooling for lithium-ion battery 18650 with HFE-7100

This paper presents Serpentine Channel Immersion Cooling (SCIC) as a new design for battery immersion cooling applications using HFE-7100 dielectric fluid. The main objective of this research is to analyze the temperature generation characteristics of Li-ion batteries with the performance of natural convection (NC) and Serpentine Channel Immersion Cooling (SCIC) with HFE-7100 liquid. The depth of discharge (DoD) is carried out at 80% of the battery capacity during the discharge process with variations in C-rates of 1 C, 1.5 C, and 2 C. The results show that the C-rate has a greater value, the temperature value released by the battery will also be greater. The negative pole, intermediate battery, and positive pole exhibit the characteristics of the battery pack’s surface temperature in order from highest to lowest throughout the discharge process. At the negative pole of the battery, the highest temperature in NC cooling is 30.1°C, 32.3°C, and 33.3°C can reduce this temperature to 28.8°C, 29.73°C, 31.8°C by SCIC with HFE-7100 liquid at DoD 1 C, 1.5 C, and 2 C respectively. Battery surface temperature characteristics based on channel position from highest to lowest using NC in the order of 6-3-2-4-5-1 and SCIC in the order of 6-5-4-3-2-1.

Exothermic Diffusion-Reaction and Explosion Branch-Chain of an Asymmetrical Heating Channel with Convective Cooling

ABSTRACT The need to prevent uncontrollable or thermal runaway, which could potentially result in the formation of undesired reaction products or hazardous conditions, stimulated studies of thermal combustible processes. As such, this analysis focuses on the exothermic reactive species and thermal explosion of an asymmetrical heating channel with convective cooling satisfying Newton’s law of cooling. With reactant consumption, the species reaction is induced by initiation rate, branch-chain order, and chemical kinetics. A generalized Arrhenius kinetic with activation energy is considered for the energy balance model, and the system is assumed to undergo isobaric processes. The solutions to the model in graphs and tables are obtained via a semi-discretization finite difference technique, which is found to be stable and converge appropriately. The study revealed that activation energy influenced the chemical reaction without having a direct effect on heat generation. The thermal distribution is enhanced with variation in initiation rate, Biot number, and Frank-Kamenetskii terms. A variation in the initial condition strongly impacted the combustible heat distribution. Hence, in a combustion process, thermal system efficiency can be maintained by controlling excessive heat generation that can lead to unsafe conditions.

The Mutual Influence of Thermal Contact Conductivity and Convective Cooling on the Temperature Field in a Tribosystem with a Functionally Graded Strip.

An analytical model to find the temperature field that has been developed for friction systems consists of a strip and semi-space. The strip is made of a two-component functionally graded material (FGM) with an exponentially changing coefficient of thermal conductivity. In contrast, the material of the semi-space is homogeneous. An appropriate boundary-value problem of heat conduction with constant specific friction power was formulated and solved using the Laplace integral transform method. The model takes into consideration the imperfect thermal friction contact between the strip and the semi-space, and also the convective cooling on the exposed surface of the strip. The appropriate asymptotic solutions to this problem for low and high values of Fourier number were obtained. It is shown how the determined exact solution can be generalized using Duhamel's formula for the case of a linearly reduction in time-specific friction power (a braking process with constant deceleration). Numerical analysis for selected materials of the friction pair was carried out in terms of examining the mutual impact on the temperature of the two Biot numbers, characterizing the intensity of the thermal contact conductivity and convective heat exchange on the exposed surface of the strip. The obtained results can be used to predict the temperature of friction systems containing elements made of FGM. In particular, such systems include modern disc braking systems.

Comparative CFD Analysis of Forced Convection Cooling of a Gas Turbine Blade of Different Materials with Several Staggered holes

For gas turbines, the energy of the fluid can be expressed in terms of the enthalpy change, which is almost directly related to the turbine temperature. The performance of the gas turbine can be improved by continuously improving the temperature and compression ratio. In this article, for the cooling of blades, making several radial holes has been suggested to pass high cooling air at high velocity along the span of blade. CFD analysis has been used to analyse the effect of heat transfer of a gas turbine with six different models which has 6,7,8,9,10,11,12 inline one row of holes and are further compared with each other. Three different materials has been considered and heat transfer in each material has been examined and then compared. After evaluation it has been concluded that the blade with 12 staggered holes in Titanium had the minimum temperature rise. All other performances were also best in Titanium comparative to other two materials. Keywords: Gas turbine, staggered holes, CFD analysis.

Axial Ventilation and Blade Row Effects on Transient Natural Convective Shutdown Cooling in a Gas Turbine

Abstract As a large civil gas turbine is cooling down, natural convective flows cause components to cool asymmetrically – the bottom sector cools faster than the top. This can lead to a number of issues that have the potential to damage engine components and affect operability. The ability to predict this cooling cycle of a gas turbine has proven to be extremely difficult, owing to the complex nature of natural convective flow and its dependency on a considerable number of design parameters. An experimental and numerical investigation into the impact of axial ventilation (interaction between the annulus and the external air) and blade rows on the natural convective flow in a large civil gas turbine high-pressure compressor has led to some key discoveries. Axial ventilation caused a 70% increase in the peak top-to-bottom temperature difference in the cooling cycle, when compared to the baseline sealed case. The combinations of four blade rows and axial ventilation caused a 130% increase in peak temperature difference over the baseline case. Numerical simulations illuminated that the root cause of this was the cold air drawn into the lower section of the annulus led to a relatively high heat flux, coupled with a blockage effect on the natural draft in the upper section of the annulus. This study has highlighted the importance and inter-dependency of these effects in defining the level of rotor bow that is observed. Therefore, it is imperative that they are included and sufficiently captured in order for a shutdown.

Performance Analysis of Nanofluid-based Photovoltaic Thermal Collector with Different Convection Cooling Flow

Using solar energy through photovoltaic (PV) panels has excellent potential as an alternative energy source. However, the problem of high operating temperatures causing a reduction in work efficiency needs to be addressed. This study aimed to analyze the development of a cooling system to increase PV panels' electrical and thermal efficiency. The research involved analyzing the use of TiO2, Al2O3, and ZnO working fluids by adding 0.5 vol% to water in an active cooling method. The cooling system involved a rectangular spiral and a rectangular tube behind the PV panel. A solar simulator simulated solar radiation with intensity variations to analyze the cooling system's performance in different working conditions. The results showed that the heat exchanger with a nanofluid configuration reduced the panel temperature by 14 oC, which increased the electrical efficiency by up to 4.7% in the ZnO nanofluid. In the rectangular spiral configuration, the ZnO nanofluid reduced the panel temperature from 60 to 45 oC, increasing the Isc value from 2.16A to 2.9A and the Voc value from 21.5V to 23V. This resulted in a maximum power increase of the panel to 53W. Doi: 10.28991/CEJ-2023-09-08-08 Full Text: PDF

Natural Convection Cooling of a Heat Source Placed at the Bottom of a Square Cavity Filled with Water-Based Nanofluid

The present work deals with the cooling process of a heat source, placed in the center of the bottom wall of a square cavity. A numerical resolution using finite volume method was carried out. The cavity is filled with a water-based Nanofluid, where four different types have been assumed. The vertical and top walls are under low temperature TC. Two thermal conditions were assumed at the source (q-imposed or T-imposed), while the remaining parts of the same wall are isolated. The effects of Rayleigh number (Ranf), source length (SL), volume concentration of nanoparticles (Φ) and their types were analyzed. The case of pure water (Φ = 0%), studied first, served as a reference case. The results obtained for this case, showed the increase of disturbances in the dynamic and thermal fields, in addition to the average rate of heat transfer (Nu) when Ra increases and SL decreases. SL = 1.0 case showed exception. These effects are more important for the T-imposed case than the other. Subsequently, the Al2O3-Water Nanofluid is considered with 0 <Φ≤ 10%. An increase in circulation intensity with improvement of local (Nu) and average (Nu) heat exchange rates have been recorded when Φ increases, although mentioning that its effect is significantly stronger for the q-imposed case. In the last part of the work, three other types of Nanofluids were assumed, where the obtained results showed the main improving effect of higher thermal conductivity on the heat transfer intensity. An important result which can be summed up in the great rapprochement of the heat exchange intensities for strong Ranf and Φ for SL close to 1.0, for the two heating types. In other words, the condition on the source loses its importance for such considerations.

Effect of Convective Cooling on the Temperature in a Friction System with Functionally Graded Strip.

An exact solution of the boundary-value problem of heat conduction was obtained with consideration of heat generation due to friction and convective cooling for the strip/semi-space system. Analytical solutions to this problem are known for the case with both friction elements made of homogeneous materials or a composite layer with a micro-periodic structure. However, in this study, the strip is made of a two-component functionally gradient material (FGM). In addition, the exact, asymptotic solutions were also determined at small and large values of the Fourier number. By means of Duhamel's theorem, it was shown that the developed solution for a constant friction power allows to obtain appropriate solutions with a changing time profile of this value during heating. Numerical analysis in dimensionless form was carried out for the FGM (ZrO2-Ti-6Al-4V) strip in combination with the cast iron semi-space. The influence of the convective cooling intensity (Biot number) on the temperature field in the considered friction system was investigated. The developed mathematical model allows for a quick estimation of the maximum temperature of systems, in which one of the elements (FGM strip) is heated on the friction surface and cooled by convection on the free surface.

Numerical Simulation of Mixed Convection Cooling of Electronic Component within a Lid-driven Cubic Cavity Filled with Nanofluid

Abstract This study investigates the effect of the movement of a moving lid on the heat transfer and cooling of three isothermal blocks inside a cubic enclosure filled with a Cu-water nanofluid. The study's geometry is three-dimensional with three blocks which are assumed to have a fixed hot temperature TH. The study considers two cases for the movement of the upper lid: one where the lid moves in the longitudinal direction, and another where it moves in the transverse direction. The dimensionless governing equations considering the boundary conditions are solved by implementing the finite volume approach with the power low as a resolution scheme. The study varies several factors such as the shape of the nanofluid, the shape factor of the blocks (3L/4, L/2, and L/4), the number of cold walls, the Richardson number (0.01 to 10), the volume fraction of nanoparticles (0 to 0.06), at a fixed Grashof number (104). The results indicate that decreasing the Richardson number improves the heat transfer coefficient's performance. Also, the study finds that longitudinal movement provides better block cooling compared to transverse movement. Additionally, changing the height of the blocks from L/4 to 3L/4 resulted in a decrease in heat transfer inside the cavity. As stated, the research aimed to investigate the impact of different directions of lid movement on the cooling of heater blocks, with the goal of enhancing the thermal performance and heat transfer efficiency of various technical engineering equipment.

Research on Panel Flutter Considering the Effect of Convective Active Cooling

The aeroelastic characteristics of the panel under the action of coolant are obviously different from the flutter characteristics of the traditional panel. In order to solve this problem, the dynamics model of the panel flutter was established in this paper based on von Karman’s large deformation theory and the Kirchhoff–Love hypothesis. The panel dynamics equations were discretized into constant differential equations with finite degrees of freedom by Galerkin’s method, and solved by the fourth Runge–Kutta method in the time domain. The nonlinear modified piston theory was used to predict the unsteady aerodynamic loads, and the accuracy of the flutter analysis model was verified. On this basis, the effects of the head-panel pressure of coolant, the pressure drop ratio, the coolant injection direction, and the inertial resistance and viscous resistance on panel stability and flight stability were investigated, respectively. The results showed that reducing the pressure drop ratio, and reducing or increasing the head-panel pressure (valuing away from the freestream pressure) can improve the critical dynamic pressure when bifurcation occurs. At M∞=5.0, the pressure drop ratio causes a 22.1% increment in the critical dynamic pressure. The influence of the coolant injection direction on the panel bifurcation is mainly influenced by the head-panel pressure. The inertial resistance slows down the convergence process of the panel response, increases the limit cycle amplitude, and reduces the critical dynamic pressure of the panel, while the viscous resistance plays the opposite role. Based on these conclusions, this paper finally proposes the suppression method of panel fluttering from head-panel pressure, inertial resistance, viscous resistance, etc.

Chip Morphology and Surface Integrity in Turning AZ31 Magnesium Alloy under Dry Machining and Submerged Convective Cooling

Magnesium alloys have broad applications, including medical implants and the aerospace sector owing to their great density and high strength-to-weight ratio. Dry cutting is a frequent technique for machining this material. However, it always leads to an excessive rise in temperature due to the absence of cooling at the cutting zone, which affects the machined surface integrity and chip morphology. In this study, chip morphology and surface integrity of the AZ31 magnesium alloy were investigated in the turning process using an internal cooling method called submerged convective cooling (SCC) to overcome the absence of cooling in dry cutting. This method can exploit the advantage of the high specific heat capacity of water as a cooling fluid without any reaction between water and magnesium to create a cooling element in the cutting zone. The chip morphologies and surface integrity were analyzed experimentally with varying cutting speeds under SCC and dry cutting. The experimental results revealed that SCC and dry cutting produced saw-tooth or serrated chip formation. The chips produced in dry cutting were continuous, while SCC was short and discontinuous as a result of a severe crack on the back surface of the chip. It was discovered that the grain refinement layer on the machined samples was thinner under SCC turning. SCC machining increased the microhardness of the AZ31 magnesium alloy by 60.5% from 55 HV to 88.3 HV, while dry turning exhibited a 49% increase in microhardness. The result revealed that surface roughness improved by 10.8%, 9.4% and 4.7% for cutting speeds (V) of 120, 180, and 240 m/min, respectively, under the SCC internal cooling. Based on the result obtained, SCC cutting outperformed dry cutting in terms of chip breakability, grain refinement, microhardness, and surface roughness.

Nonlinear Mixed Convection in a Reactive Third-Grade Fluid Flow with Convective Wall Cooling and Variable Properties

Energy management and heat control whenever a reactive viscous fluid is the working medium has been one of the greatest challenges encountered by many in the field of chemical and industrial engineering. A mathematical approach to thedetermination of critical points beyond which the working environment becomes hazardous is presented in the present investigation together with the entropy generation analysis that guarantees the efficient management of expensive energy resources. In this regard, the nonlinear mixed convective flow behavior of a combustible third-grade fluid through a vertical channel with wall cooling by convection is investigated. The mathematical formulation captures the nonlinearities arising from second-order Boussinesq approximation and exponential dependence of internal heat generation, viscosity, and thermal conductivity on temperature. The resulting nonlinear boundary value problems were solved based on the spectral Chebyshev collocation method (SCCM) and validated with the shooting-Runge–Kutta method (RK4). The nonlinear effects on the flow velocity, temperature distribution, entropy generation, and Bejan heat irreversibility ratio are significant. Further analyses include the thermal stability of the fluid. Findings from the study revealed that flow, temperature, and entropy generation are enhanced byincreasing values of the Grashof number, the quadratic component of buoyancy, and the Frank-Kameneskii parameter, but are reducedbyincreasing the third-grade material parameter. Moreover, it was shown that increasing values of the third-grade parameter encourages the thermal stability of the flow, while increasing values of the linear and nonlinear buoyancy parameter destabilizes the flow. The present result is applicable to thick combustible polymers with increased molecular weight.

Scaling of Transient Natural Convection Cooling in Side-Cooled Cavity: The Effect of Variable Viscosity

The transient natural convection of variable and constant viscosity fluids in a side cooled cubical cavity is studied experimentally. The convective flow in the cavity is visualized by the shadowgraph technique. The fluid was initially preheated and enough time is allowed to assure uniform temperature distribution. Temperature difference is introduced by a sudden cooling of the two side walls. The results indicate that the transient flow development is characterized by the following distinct processes: the initial growth of the vertical boundary layer and horizontal intrusions, the interaction of the horizontal intrusions and the stratification. New scaling relations are introduced to include the effect of the viscosity variation with temperature. The new suggested scalings showed good agreement with the measurements based on the shadowgraph images.

A Ducted Photovoltaic Façade Unit with Forced Convection Cooling

This paper explores the potential of forced convection cooling in a ducted photovoltaic façade unit. Where a photovoltaic panel is backed by a 5 cm thick insulated duct at a depth of 50 cm. The potential of heat removal from the photovoltaic unit due to forced convection is investigated with a range of fan speeds from 1 m/s to 6 m/s. It is found that the ΔT between the inlet and outlet of the duct ranged from 2.6–24.6 °C. A fan speed of 4 m/s yielded the highest cooling potential by removing 550 W with a cooling efficiency of 51%. Whereas a fan speed of 6 m/s yielded the lowest mean PV cell temperature of 62.7 °C. This would improve the cell’s efficiency by 17.53%. This very experimental setup has been tested previously with natural convection cooling, which removed 529 W with a maximum efficiency of 48.98% This improves PV panel efficiency by 12.69%. The addition of heat removed and power recovered by the ducted system was 68.53% of the former (i.e., forced convection), while it was 61.67% for the latter. A 12 V DC fan with a variable speed electric circuit powered by a fraction of the PV generated power (i.e., 0.75 W) yielded better cooling that translated into nearly 19 W of further energy generation.

A Free-Standing, Silent, Micro/Mesoscale Combustion-Powered Thermoelectric Generator Based on Natural Convection Cooling

Abstract In recent years, the world has become increasingly interested in power generation using thermoelectric generators (TEG) because of the advantage of converting heat directly to electricity. In this work, experimental studies have been carried out on micro/mesoscale combustor-powered thermoelectric generators (MCP-TEG) to evaluate the influence of different types of heat sinks on the cold side of MCP-TEG. The micro/mesoscale combustor was connected with Bi2Te3 based TEG1-12708 thermoelectric modules from both sides along with a heat sink on the cold side of the modules. The system uses natural convection cooling with a flat-plate aluminum heat sink. The MCP-TEG generates electrical power of 0.242 W with an overall efficiency of 0.3% at a hot-end temperature of 351 K. Power load feature and time history tests are conducted to evaluate the performance of the MCP-TEG system and comparisons of various related studies were made.

Analysis of Hydromagnetic Double Exothermic Chemical Reactive Flow with Convective Cooling through a Porous Medium under Bimolecular Kinetics

In this study, the analytical solution of steady hydromagnetic double exothermic combustible reaction fluid flow in a porous medium with convective cooling wall is presented. The viscous heating reactive liquid is totaling exothermic without consumption of material. The combustion reaction of the fluid takes place in a Poiseuille device, and it is been propelled by pressure gradient and pre-exponential bimolecular kinetics. The device is exposed to convective cooling to keep the reactive hydromagnetic fluid from distortion. The weighted residual method (WRM) is analytically used to get the numerical values for the dimensionless nonlinear governing equations. The solution to temperature and velocity distribution is carried out and the result is graphically depicted. The Nusselt number and skin friction coefficient is also showed for some significant parameters engrained in the flow and the solution obtained is compared with numerical method. As obtained in the study, the second exothermic reaction term increases the combustion process; hence the term will assist in reducing toxic discharge from the engines that pollute the environment. The Frank-Kamenetskii parameter contributes highly to system thermo-fluid destruction; as such it must be monitored.