Heat Transfer Coefficient Distributions Research Articles

Effects of rotational speed on transient cooling performance of nozzle spray with liquid nitrogen in a rotor-stator cavity

This paper presents the results of an experimental investigation into the cooling performance of a rotor-stator cavity with liquid nitrogen spraying. The experiments were conducted under varying rotational Reynolds numbers ranging from 1.70 × 106 to 5.12 × 106. The effects of rotational speed on temperature drop rate are studied and compared in detail, as well as the heat transfer coefficient distribution. Sufficient data, such as heat flux, injection rate, and injection pressure, were collected to provide a basis for further study in explaining the spray and evaporation over the cavity. It was found that the cooling performance of the rotating disc is strongly affected by the rotational speed. The short-term period exhibits a peak cooling rate of 14°C/s, in contrast to the sustained cooling rate during the spray process at rotational speeds of 500r/min, which amounts to 0.9°C/s. The occurrence of cavitation and evaporation within the nozzle results in a reduction of flow coefficient and fluctuation of the injection differential pressure. The transient cooling performance is well-explained by the temperature changes and cooling-down time under different rotational speeds. The analysis of the heat transfer coefficient is further enhanced through an evaluation of the convective and conductive heat transfer rates using a one-dimensional theoretical approach. The average temperature of the disc is expected to decrease by 100°C within a time frame no longer than 120 s. Additionally, after a duration of 120 s, the average heat transfer rate on the cold side is anticipated to surpass 8000 W/(m·K).

Analysis of billet temperature non-uniformity in a regenerative reheating furnace: Considering periodic combustion switching and misalignment contact of walking beams

Improving the billet temperature uniformity is crucial for the quality of rolled products. This paper investigated the heat and mass transfer processes in a regenerative reheating furnace by establishing typical heating unit models. The periodic combustion switching and misaligned water-cooled beams were considered. The effects of furnace temperature oscillation and skid marks on the total heat transfer coefficient distribution and billet temperature uniformity were analyzed. The results indicate that during the heating process of the billet, the periodic variation amplitude of furnace temperature decreases from 86 to 25 °C, and the depth of influence on the billet temperature is about 0.03 m. The total heat transfer coefficient on the billet bottom surface shows a wave distribution affected by beams shielding, but on the top surface, the closer it is to the furnace wall, the smaller the total heat transfer coefficient. The misalignment of water-cooled beams effectively eliminates the original skid mark and reduces the range of new skid mark. However, the cross-sectional temperature difference at the new skid marks remain at about 97 °C. Compared to extending the residence time, increasing the furnace temperature in the soaking zone is the optimal measure to reduce the influence of skid marks.

Inflatable aerodynamic decelerators for CubeSat reentry and recovery: Surface properties

In this investigation, Direct Simulation Monte Carlo Method is used to compute the surface properties of inflatable aerodynamic decelerators (IAD) applied for the reentry, recovery, and reuse of cubeSats. Surface properties calculation is of fundamental importance for flexible thermal protection system materials selection that withstand the harsh reentry environment. Furthermore, simulations are extremely important to detect possible hot spots at the IAD before design and flight. In this work, three IAD configurations are exposed to a rarefied hypersonic flow with freestream conditions that correspond to those found at reentry conditions at 105 km altitude. All geometries are assumed to be axisymmetric and have a maximum radius of 0.3 m from the center line to the shoulder edge. The main differences between the geometries are the angle between the IAD and cubeSat body and the IAD curvature for geometry 3. According to the results, all IAD geometries are effective in protecting the cubeSat during the reentry phase. It is shown that the IAD geometry has a significant influence on the heat transfer, pressure, and skin friction coefficient distribution over the flexible heat shield. The maximum heat transfer coefficient computed for geometry 1, 2, and 3 is 0.90, 0.97, and 0.84, respectively.

Computational Fluid Dynamics Prediction of External Thermal Loads on Film-Cooled Gas Turbine Vanes: A Validation of Reynolds-Averaged Navier–Stokes Transition Models and Scale-Resolving Simulations for the VKI LS-94 Test Case

Given the increasing role of computational fluid dynamics (CFD) simulations in the aerothermal design of gas turbine vanes and blades, their rigorous validation is becoming more and more important. This article exploits an experimental database obtained by the von Karman Institute (VKI) for Fluid Dynamics for the LS-94 test case. This represents a film-cooled transonic turbine vane, investigated in a five-vane linear cascade configuration under engine-like conditions in terms of the Reynolds number and Mach number. The experimental characterization included inlet freestream turbulence measured with hot-wire anemometry, aerodynamic performance assessed with a three-hole pressure probe in the downstream section, and vane convective heat transfer coefficient distribution determined with thin-film thermometers. The test matrix included cases without any film-cooling injection, pressure-side injection, and suction-side injection. The CFD simulations were carried out in Ansys Fluent, considering the impact of mesh sizing and steady-state Reynolds-Averaged Navier-Stokes (RANS) transition modelling, as well as more accurate transient scale-resolving simulations. This work provides insight into the advantages and drawbacks of such approaches for gas turbine hot-gas path designers.

CFD simulation of the inundation effect for saturated propane vapor condensation on the surface of a horizontal tube using the volume of fluid method

The inundation of the lower tubes in a tube bundle with condensate formed on the upper tubes is among the major causes of reduced condensation rate. Experimental methods can hardly be used to get detailed information on the inundation effect, since each factor that controls the condensation process should be considered individually. However, CFD modelling using direct interface-tracking methods is an effective tool for analyzing such processes. This paper reports the results of simulation of the saturated propane vapor condensation on the surface of a horizontal tube using the Volume of Fluid method with the modified Lee model. The study presents, for the first time, the characteristics of saturated vapor condensation including the effect of inundation predicted using a 3D model. The interphase surface and the distribution of instantaneous heat transfer coefficients over the surface of the inundated pipe are presented. It has been shown that increasing the temperature of the condensate flow can substantially affect the distribution of the heat transfer rate over the tube surface due to the formation of a thermal entrance region. These results may become a starting point for modelling condensation in a tube bundle that enjoys current interest in practice.

Modelling flame-to-fuel heat transfer by deep learning and fire images

In numerical fire simulations, the calculation of thermal feedback from the flame to the solid and liquid fuel surface plays a critical role as it connects the fundamental gas-phase flame burning and condensed-phase fuel gasification. However, it is a computationally intensive task in CFD fire modelling methods because of the requirement of a high-resolution grid for calculating the interface heat transfer. This paper proposed a real-time prediction of the flame-to-fuel heat transfer by using simulated flame images and a computer-vision deep learning method. Different methanol pool fires were selected to produce the image database for training the model. As the pool diameters increase from 20 to 40 cm, the dominant flame-to-fuel heat transfer shifts from convection to radiation. Results show that the proposed AI algorithm trained by flame images can predict both the convective and radiative heat flux distributions on the condensed fuel surface with a relative error below 20%, based on the input of real-time flame morphology that can be captured by a larger grid size. Regardless of growing or decaying fires or puffing flames induced by buoyancy, this method can further predict the non-uniform distribution of heat transfer coefficient on the interface rather than using empirical correlations. This work demonstrates the use of AI and computer vision in accelerating numerical fire simulation, which helps simulate complex fire behaviours with simpler models and smaller computational costs. Highlights A total framework between AI model and fire simulation software is designed to further enhance the reliability of AI-based fire simulations. A standard pool fire simulation database is built using numerical model recommend by the IAFSS Computation Group. A deep learning model is developed to predict both the convective and radiative heat flux distributions on the condensed fuel surface using numerical images database. The demonstration showcases the application of AI and computer vision to accelerate numerical fire simulation.

Analysis of the effect of the number of injector nozzles on the pressure and heat transfer coefficient in a hydrogen-diesel mixture diesel engine

In reciprocating internal combustion engines, the calculation of the heat transfer coefficient (HTC) is essential to estimate the heat transfer during combustion in the combustion chamber. The HTC calculation takes into account fluid flow and combustion processes and varies as a function of crank angle and location within the chamber. The mean HTC value is commonly used to calculate the thermo-mechanical analysis of various combustion chamber components. In this study, dynamic grids for the intake port, exhaust port and chamber are created in the chamber modelling section of the AVL-Fire software. The intake and combustion processes are then simulated and the calculated pressure data are compared with experimental data at 2800 rpm with 1, 3 and 6 hole injectors. Finally, the distribution of HTC over the chamber walls was evaluated using a time step method. The research also included verification of the HTC results with theoretical data obtained by Woschni and Hohenberg. In addition, with the decreasing availability of fossil fuels and the need for lower exhaust emissions from diesel engines, the use of blends of diesel and hydrogen fuel has become widespread. In this engine, a mixture of 10 % hydrogen and 90 % diesel fuel is used. The final results show that the heat transfer coefficient increases by approximately 1.72 % when hydrogen is added to diesel fuel due to the number of collisions between hydrogen and other fuel components.

A Numerical Investigation of the Nonlinear Flow and Heat Transfer Mechanism in Rough Fractured Rock Accounting for Fluid Phase Transition Effects

The study of the seepage and heat transfer law of three-dimensional rough fractures is of great significance in improving the heat extraction efficiency of underground thermal reservoirs. However, the phase transition effects of fluids during the thermal exploitation process profoundly influence the intrinsic mechanisms of fracture seepage and heat transfer. Based on the FLUENT 2020 software, single-phase and multiphase heat–flow coupling models were established, and the alterations stemming from the phase transition in seepage and heat transfer mechanisms were dissected. The results indicate that, without considering phase transition, the geometric morphology of the fractures controlled the distribution of local heat transfer coefficients, the magnitude of which was influenced by different boundary conditions. Moreover, based on the Forchheimer formula, it was found that the heat transfer process affects nonlinear seepage behavior significantly. After considering the phase transition, the fluid exhibited characteristics similar to shear-diluted fluids and, under the same pressure gradient, the increment of flow rate was higher than the increment in the linearly increasing scenario. In the heat transfer process, the gas volume percentage played a dominant role, causing the local heat transfer coefficient to decrease with the increase in gas content. Therefore, considering fluid phase transition can more accurately reveal seepage characteristics and the evolution law.

Heat Transfer Coefficient and Adiabatic Effectiveness Measurements on a Nozzle Guide Vane With a Single Row of Cylindrical Holes

Abstract Film-cooling injection significantly affects the thermal behavior of turbine vane surfaces. In addition to the beneficial effect of the film shielding the vane from the hot gas flow, alteration of the thermal boundary layer should also be taken into account. The aim of the present work is to detail the film-cooling performance in terms of adiabatic effectiveness and external heat transfer coefficient on a 2D nozzle guide vane. A single row of cylindrical holes was tested on both pressure and suction sides of a literature vane, the VKI LS89, in a linear cascade. The employed measurement technique is a transient thermal method based on infrared thermography, which was thoroughly described and validated in a previous work. The influence of inlet freestream turbulence and blowing ratio was evaluated, and two different injection angles were considered for both pressure and suction sides. Spatially resolved distributions of adiabatic effectiveness and heat transfer coefficient (HTC) on the vane surface allow us to precisely quantify the above-mentioned aspects and highlight qualitative differences between pressure side and suction side behavior. Details regarding the generated non-uniformities in the measured parameters could be also provided, to emphasize how average quantities are not always sufficient to characterize such complex phenomena. The impact of different reference conditions to scale HTC results was also investigated. Such effect was found not negligible on the overall performance of the film-cooling system, especially on the suction side where transition plays a critical role. Ultimately, the collected results constitute a wide and detailed experimental database for numerical modeling validation in a well-studied environment as the LS89 configuration.

Local heat-transfer coefficient estimation in cross-helix corrugated tubes under turbulent regime

In a wide variety of engineering applications, convection heat transfer enhancement plays a major role in reducing the heat exchanger’s size and costs and increasing their efficiency. The passive methods for increasing convective heat transfer are the most interesting since they don’t require any external power to achieve the desired enhancement. For this reason, this approach is preferred in the industrial sector of heat exchangers. For the enhancement of the performances of these apparatuses, in particular, the tubular ones used in the pharmaceutical, food, and chemical, the most adopted passive solution is the corrugation of their tube walls. Two pipes characterized by cross-helix corrugation have been experimentally analyzed both investigating the global heat transfer performance and studying the local heat transfer coefficient distribution to profoundly examine the thermal performance enhancement mechanisms of this passive technique. It has been observed that at Re = 16,000, the heat transfer rate in the smaller pitch tube is 18.18% higher than that in the larger pitch tube. The inverse heat conduction problem in the tube wall is addressed to achieve the local coefficient distribution method by using temperature readings collected from an infrared camera on the outer surface of the tube as the initial data.

Coupled fluid-thermal-structural analysis during the air cooling for glass tempering

The tempering process of plate glass involves rapidly cooling the high-temperature glass using an array of impinging air jets, inducing desired stress during cooling. Consequently, the formation of tempering stress results from the coupled interaction among flow, heat transfer, and stress. However, most previous studies have commonly neglected the influence of the flow field by assuming a uniform and constant distribution of heat transfer coefficients at different positions on the glass plate, which deviates from actual situations. This study employed a fluid-thermal-structural coupled simulation approach to predict the non-uniform residual stress distribution in tempered glass and investigate the interaction mechanisms among flow, heat transfer, and stress. Simultaneously, to validate the reliability of the method and model, this study experimentally investigated the single-nozzle jet impingement cooling for glass tempering. The study concluded that the simulation results were consistent with the experiment. Subsequently, a comparative analysis was performed between the fluid-thermal-structural coupled simulation results based on real boundary conditions and the thermal-structural coupled simulation results based on ideal uniform heat transfer coefficient boundary conditions. The results revealed non-uniform distributions of both heat transfer coefficient and temperature due to varying localized flow characteristics. Consequently, the ratio of surface compressive stress to internal tensile stress along the width direction of the glass was not a fixed value but ranged from 1.63 to 2.38. Furthermore, significant differences were observed in the stress distribution under the simulations of fluid-thermal-structural coupling and thermal-structural coupling. Therefore, it is recommended to employ the fluid-thermal-structural coupling method when predicting localized stress distribution.

Study on flow and heat transfer characteristics of salt solution ice slurry

As a phase change material, ice slurry allows the storage of thermal energy in the form of latent heat. This has great advantages in terms of reducing energy consumption and environmental protection, and is being widely used. In this study, based on the Eulerian-Eulerian CFD model and the Population Balance Model (PBM), the flow and heat transfer characteristic of salt solution ice slurry was simulation studied, which included the pressure drop, friction coefficient, volume fraction, distribution of ice crystals and local heat transfer coefficient during the flow and solidification of salt solution ice slurry in different conditions. And the experimental system is set up to verify the results of the model and analyze the variation rules of these parameters. The results showed that in salt solutions with different concentrations, when the flow rate and solid phase volume fraction increase, the pressure drop and local heat transfer coefficient of the ice slurry will increase. The surface heat transfer coefficient reached to 2.5 × 103 W m-2 K-1, 2.9 × 103 W m-2 K-1, and 3.2 × 103 W m-2 K-1 when ice crystal volume fraction was 5 %, 10 %, and 15 %, respectively. The study will contribute to understanding of the changes in basic characteristics of salt solution slurry during the flow and phase transition processes.

Blade tip leakage flow and heat transfer characteristics over a gas turbine blade at subsonic and transonic exit conditions

The present study numerically investigates the blade tip leakage flow (TLF) over a gas turbine blade cascade at low speed ( M ex = 0.1) and transonic ( M ex = 0.92) blade exit Mach numbers, with and without shroud motion. Various blade tip flow phenomena like flow separation and reattachment, flow choking, shock-boundary layer interaction (SBLI), and tip leakage vortex (TLV) are studied, and their influence on the heat transfer coefficient (HTC) distributions over the blade tip and near tip blade suction surface is investigated. The study has found some new zones of heat transfer due to the interaction of horseshoe vortices (HSV) with the blade tip. In addition to the primary TLV, a secondary TLV is formed, which increases near tip blade suction surface heat transfer. The flow transitions to supersonic speed in the aft portion of the blade tip for the transonic case resulting in complex heat transfer distribution due to SBLI, compared to near-uniform distribution for the low speed case. This supersonic flow results in a smaller flow separation zone near the aft portion of the pressure side tip edge for the transonic case compared to the low speed case. The qualitative nature of HTC near the leading edge of the blade tip resembles for low speed and transonic cases. However, near the trailing edge of the blade tip, the qualitative nature of HTC for the transonic case shows a substantial difference due to supersonic flow compared to the low speed case.

A numerical study on fluid flow and heat transfer characteristics of oily wastewater falling film outside an elliptical tube

Falling film heat exchangers have recently been widespread as a heat transfer technique for oily wastewater. Researching the characteristics of fluid mechanism for heat transmission is crucial. In this research, numerical models are applied to simulate the heat transmission and flow of falling film outside ellipse tube. In order to emulate fluid flow and heat transmission, the oily wastewater falling film is analyzed utilizing the VOF approach under circumstances of constant thermal flow. On the flow properties and heat transfer coefficient distribution of liquid film, the impacts of the input height, contact angle, liquid film flow rate, and oil content are examined. These computational outcomes are attained: (1) More so than film thickness, according to the simulation results, increasing liquid film flow significantly affects velocity;(2) One of the main causes of how oil concentration affects heat transmission is the complex disturbance process of liquid film and the force change around tube structure;(3) Around 40°, inlet height has the greatest impact on local heat transfer coefficient;(4) The overall heat transmission will deteriorate due to the hydrophobic impact brought on by increased contact angle.

Numerical and experimental analysis of air-cooled Lithium-ion battery pack for the evaluation of the thermal performance enhancement

The main objective of this study is to assess the thermal performance of an air-cooled Lithium-ion battery pack. This involves analyzing the heat dissipation characteristics and temperature distribution within the battery pack at different operating conditions. Here, the thermal performance of the battery pack is evaluated numerically and experimentally. The experimental platform allows adjusting numerous control factors, like air velocity (0.5 to 2.0 m/s), air temperature (282.0 to 315.0 K), and battery pack discharge rate (0.5 to 2.5C). The temperature distribution is studied in longitudinal and transverse directions of the battery pack and circumferentially for a cell. The numerical simulations involve the solution of Shear Stress Transport (SST) k- ω model-based Navier-Stokes (N-S) equation using the ANSYS FLUENT R19.2 software. The numerical results were found to closely match the experimental findings with maximum error to be within 3.12%. The evaluation parameters used to assess the thermal performance of BTMS are maximum temperature(Tmax), maximum temperature difference (∆Tmax), average temperature (Tavg.), and standard deviation of the temperature σT within the battery pack. The numerical and experimental analyses show a reduction in both the maximum and mean temperature of the battery pack and improved temperature uniformity, with the increase in air velocity, lowering the discharge rate and decreasing the ambient temperature. The correlation between air inlet velocity and temperature drop is stronger at higher discharge rates than lower discharge rates. The effect is due to high heat transfer coefficient and uniform air distribution at high velocities, less heat generation and more time to dissipate heat at low discharge rates, and lower temperature of air at cold ambient conditions. The reduced temperatures and temperature uniformity minimizes the occurrence of localized hotspots within the battery pack. Further, for any given air inlet temperature, an increase in temperature is observed parallel to the direction of airflow. Under severe operating conditions, the inlet-to-discharge temperature difference reached a maximum of T = 22.14 K whereas, under mild conditions, it dropped to T = 0.21 K. The circumferential temperature non-uniformity of cells lying in high-temperature zone of the battery pack reduces with increasing velocity. The work presented here can help in the identification of potential hotspots and design better cooling strategies for the battery pack at different operating conditions.

Experimental design and analysis for film boiling heat transfer in a circular tube

In order to study the heat transfer of water during film boiling, stable film boiling heat transfer experiments are conducted in a circular tube. As the temperature of the heater surface sharply increases in a short period of time when critical heat flux (CHF) occurs, hot-patch technology is adopted to prevent damage to the test section. A complete experimental design, including the experimental facility, test section, experimental procedures, and the measurement of parameters, is developed. Two experimental schemes are used for testing, namely the post-CHF test and the quench test, respectively. These two schemes have been verified to achieve stable film boiling and yield consistent results. The effect of various parameters, including heat flux, pressure, mass flow and inlet subcooling, on the heat transfer coefficient has been analyzed. The experimental parameters range from an inlet subcooling of 10–50 K, a pressure of 0.1–2.5 MPa, and a mass flux of 100–1000kg/m2s. Through the analysis of the distribution of heat transfer coefficient along the axial location, three distinct heat transfer regions can be identified. Combined with heat transfer characteristics, three types of flow are considered: smooth inverted annular flow, rough inverted annular flow and inverted slug flow. Most of the data in this study is concentrated in the first two regions, namely the inversed annular flow. The data obtained in these tests is expected to provide important information for the study of inverted annular flow.

Numerical study of heat and mass transfer during drying process of barley grain piles based on the pore scale

AbstractDrying conditions greatly affect the quality of grains, and efforts should be made to minimize the loss of grains during the drying process. In this study, numerical simulations were conducted to investigate the drying behavior of barley at both the particle and grain pile scales by solving the coupled heat and moisture equation. The model was validated using thin‐layer drying experimental results from the literature, and it was found that the simulated values of average moisture content of the grain had a maximum relative error of 7.73% compared to the experimental values. Furthermore, the impact of air temperature and relative humidity on drying was analyzed. The results showed that the heat and mass transfer coefficients of barley grains varied along the surface, the irregularity of the barley grains resulted in an asymmetric distribution of the surface heat transfer coefficient. Regions with lower porosity in the grain pile exhibited lower rates of heat and moisture transfer, particularly in the central area. Moisture transfer within the grain pile dominated the drying time compared to heat transfer. It was also observed that air temperature and relative humidity were the main variables influencing the drying rate of the grains. As the inlet air temperature increased from 45 to 70°C, the drying rate of the grain pile increased from 0.068% to 0.085%(d.b.)/min. Similarly, reducing the relative humidity from 40% to 18% resulted in an increase in the drying rate from 0.062% to 0.075%(d.b.)/min (within the first 10 min).Practical ApplicationsThis study employed numerical simulations to investigate the drying behavior of barley at both the particle scale and grain pile scale. The developed model was validated using experimental data from thin‐layer drying studies, confirming a significant agreement between the simulated and experimental values. Moreover, the study unveiled the impact of air temperature and relative humidity on the drying process. It was observed that regions with lower porosity within the grain pile experienced reduced rates of heat and moisture transfer. Notably, moisture transfer dominates the drying time. Additionally, the study emphasized the substantial influence of air temperature and relative humidity on the drying rates. These findings offer valuable insights for optimizing drying parameters, including air temperature and relative humidity, in order to enhance the efficiency and quality of the barley grain drying process.

Aero-Thermal Analysis of Rarefied Flow Over Inverse Cone Shaped Objects Using Direct Simulation Monte Carlo Analysis

Abstract When an object undergoes atmospheric entry, it experiences drag and heat load over its surface which determines its trajectory and ability to survive the hostile flow conditions. This work performs numerical analysis using direct simulation Monte Carlo (DSMC) simulations to study key flow features and properties on a cone-shaped body. The cone is created by varying the angle of extrusion (α) of the flat-nosed face of a cylinder in positive and negative directions. Detailed analysis of the key flow features is conducted, and the results of the distribution of surface heat transfer and drag coefficient on each of the negative α are contrasted against the results obtained for zero and positive α for which compressible flow physics are well defined. For α≤45 deg, heat flux increases with an increase in α, while the total drag experienced by the body decreases. Meanwhile, when α is increased in the negative direction, an inverse cone is formed, which creates a cavity inside the body, and the body decelerates more with an increasing magnitude of α. In contrast, the wall heat flux inside the cone remains quite low. These conditions allow the body to maintain a significantly low temperature during high-speed flow, like in the case of planetary entry, in comparison with the high temperature resulting in α≤0 deg cases. The present study also helps to improve the understanding of optimum cone-shaped space objects from the perspective of drag and heat flux.

The effect of coupled combustion reaction on conjugate heat transfer in boundary layer of a segregated oxidizer/fuel solid motor

Combustion reaction plays an important role in heat transfer of boundary layer of solid rocket motor. In the present study, a transient numerical model is developed to investigate the influence of coupled combustion reaction on heat transfer in boundary layer of the segregated oxidizer/fuel solid motor (SOFSM). The results show that conjugate heat transfer characteristics of non-reacting flow are distinct from those of the reacting flow with coupled combustion. The reacting flow with coupled combustion renders higher and more homogeneous temperature and velocity compared with the non-reacting flow. Due to the effect of combustion heat release on thermophysical properties of the gas phase species, the heat transfer coefficient and effective thermal conductivity of the reacting flow are much higher than those of the non-reacting flow. When the combustion time increases, the heat transfer coefficients decrease in the reacting and non-reacting flows due to reduced flow velocity and lower O2 concentration. The Nusselt number (Nu) of the reacting flow is also higher than that of the non-reacting flow. Significant decrease of Nu is found in the non-reacting flow with combustion time. However, the Nu varies very slightly along the flow direction in the reacting flow. As pressure increases from 1.5 MPa to 5.0 MPa, the high-temperature area becomes narrower and the flow velocity decreases in the combustion channel. The diffusion and mixing of the oxidizer and fuel gas along the radial direction are thus weakened in the coupled combustion flow. The total heat transfer coefficient decreases from 295.88 W m−2 K−1 to 46.52 W m−2 K−1 and Nu decreases from 36.27 to 16.56 with increase of pressure. The distribution of total heat transfer coefficient is found to be highly synchronous to the distribution of regression rate of coupled combustion process. The distribution of heat transfer coefficient directly affects parallel regression and coupled combustion of the TAGN propellant. The fitting relationship of Nu, i.e., Nu = 0.058Re0.6Pr0.424 is obtained for the coupled combustion flow in the motor, which provides better insight into the heat transfer in the SOFSM system.

A numerical investigation of hydrogen impingement-effusion array jet for a heat sink cooling using solid/porous fins: A thermo-hydrodynamic analysis

Increasing the aim of hydrogen use as fuel in vehicles motivates applying it to other critical requirements, such as cooling, owing to its thermal properties. Therefore, the effect of applying hydrogen impingement jets for cooling a hot surface of electrical devices, such as a prismatic battery, is investigated in this numerical study. The dependent variables are the volumetric flow rate, the jet distance from the target to the jet diameter, the coolant type, and the fins configuration, called in-line and staggered, and types, as solid or porous. The convective heat transfer coefficient, thermal resistance, pressure drop, and temperature and velocity distribution for the studied cases are considered. The simulation is conducted using the SST k-ω turbulence model, SIMPLE algorithm, and second-order method for discretization differential equations. Applying hydrogen as the coolant decreases the maximum temperature up to 2% and increases heat transfer by about 10%, while it mitigates the pressure drop by a factor of 1/12 if compared to air coolant. Further, inserting porous fins improves heat transfer by about 10% and 17%, respectively for air and hydrogen coolant in comparison with the case without fins. The fin decreases the temperature on the root and makes the recirculation zones.