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The thermoelastic time-dependent creep progress of a rotating annular plate with nonuniform thickness made of functionally graded piezoelectric material considering convection heat transfer and solar radiation was investigated. The nonlinear differential equation of heat transfer considering conduction, convection, and solar radiation was solved using the differential transformation method. Then, the differential equation of equilibrium for the annular plate containing creep strains was derived. Firstly, the differential equation was solved analytically for the zero time. Then, the stress and strain rates were achieved using Norton's law with Prandtl–Reuss equations. Finally, the time-dependent creep stresses and deformation redistributions were obtained employing an iterative method. [ABSTRACT FROM AUTHOR]

The purpose of this article is to study the effect of electromagnetic (EM) stimulation on the pipeline, which has an electrical and thermal effect in addition to the chemical reaction on the crude oil and makes a sinusoidal wave on the wall. Modeling the crude oil as Carreau fluid is done. EM stimulation is an effective and safe technology that can be used to improve fluid movement in a variety of industrial applications. The flow analysis by applying EM may avoid blocking the crude oil pipeline which leads to a loss of production and capital investment. The basic partial differential equations of momentum, temperature and concentration are reduced to a system of nonlinear partial differential equations, which is solved numerically by using the Rung–Kutta–Merson method with Newton iteration in a shooting and matching technique under the assumption of long wavelength and the effect of physical implanted parameters is represented through charts for velocity, temperature, and concentration and numerical application. [ABSTRACT FROM AUTHOR]

The current paper reports the impact of variation of ribs' pitch distance in the case of laminar flow and forced convection heat transfer upon flow characteristics in a rectangular channel experimentally and numerically. The thermal behavior of the ribbed channel with water as a working fluid was measured experimentally and compared to numerical simulations performed using Galerkin finite element method under the same operating and boundary conditions. Numerical analysis has been extended to investigate the entire ribbed channel with the presence of nano-particles in the base fluid to predict the performance of the heat transfer process with interaction with extended geometries. The analysis was done keeping heat flux constant at the bottom boundary condition. The impacts of the rib pitch-to-height ratio (p/e = 2.5, 3.125, 3.75, 4.375, and 5), nano-particle volume concentration (0% ≤ φ ≤ 4%), also Reynolds numbers (427.44 to 1282. 9), were all examined in the present study. The results show a good coincidence between the numerical and experimental study with a maximum deviation was nearly 3%. The main findings show that when the nano-fluid volume fraction increases from 0% to 4%, the average Nusselt number for all aspect ratios increases too. Meanwhile, the average skin friction decreases as the Reynolds number increase for different values of AR. Furthermore, the results revealed that the water – aluminum oxide nano-fluid with the concentration φ = 0.04 aid to improve the coefficient of heat transfer by 5% higher than the case of φ = 0.02, and up to 9.4% compared to pure water (φ = 0) due to an increase in viscosity. Finally, the current work shows that these extended surfaces with the use of nano-fluids can remarkably improve heat transfer properties with barely increased friction, making them suitable candidates for the development of efficient heat exchanger devices. [ABSTRACT FROM AUTHOR]

The present study involves a numerical simulation of a borehole heat exchanger (BHE) configuration that utilizes computational fluid dynamics (CFD) methodology. The BHE comprises a U-shaped pipe that facilitates the thermal exchange between water entering from one end and exiting from the opposite end. These heat exchangers are employed for both heating and cooling applications. This study concerns a system that employs water as its working fluid. The water enters a pipe at a higher temperature than that of the surrounding soil and subsequently exits with a lower temperature. The borehole wall temperature is examined in order to investigate the effects of inlet mass flow rate, backfill porosity, the presence of subterranean water, and its seepage velocity on the convection and conduction heat transfer, as well as on the system's performance. The results indicate that an increase in mass flow rate improves convection heat transfer. A porosity of 0.6 is deemed suitable under conditions of the absence of subterranean water, while a porosity of 0.2 is considered appropriate for backfill saturation and the presence of subterranean water. Also, an increase in subterranean water velocity seepage increases convection heat transfer, albeit at the expense of a decrease in system performance. [ABSTRACT FROM AUTHOR]

One of the problems in using PV cells to extract energy from sunlight is the temperature effect on PV cells. As the solar panel is heated, the conversion efficiency of light to electrical energy is diminished. Moreover, successive temperature elevations can cause dilatations in the array of cells which may also contribute to the degradation of the receiver. Some of the operating temperature mitigation approaches may include air-flow ventilation. In this study, data obtained by experimental and numerical simulations of a collector with bifacial PV cells is compared to the expressions found in the literature for the estimation of the heat transfer coefficient. Forced ventilation was applied to the studied collector as it accounts for much better heat dissipation. A new correlation for the estimation of the heat transfer coefficient is developed for such a geometry, for inlet velocities ranging between 3 and 8 m/s. Values of heat transfer coefficient estimated in the present work have been compared with studies of other researchers. [ABSTRACT FROM AUTHOR]

In this paper, two heated blocks and three flexible baffles that are alternately placed on the upper and bottom sides of a rectangular channel are used to replicate the transient heat and air movement. The novelty of this research is the use of flexible baffles to destruct the thermal boundary layer with maintaining little pressure drop, and thus reducing the required pumping capacity. The finite thickness blocks are subject to a constant heat flux, while the baffles are very thin and deforms depending on the strength of the flow of coolant (air). Finite element method with arbitrary Lagrangian–Eulerian approach is used for solving such deforming domain problem. The problem is inspected transiently by varying the dimensionless time (τ=0.0 to 10) and two salient parameters which are Reynolds number Re=10−500, and baffle elasticity parameter E=105−108. Results show that the flexibility feature of the baffles contributes not only in directing the coolant towards the hot blocks, but also contributes in reducing the skin friction and pressure drop through the channel. At Re=150, the skin friction and pressure drop of the flexible baffles are 13.2% and 16.5%, respectively lesser than the rigid baffles. The improvement of Nusselt number with flexibility parameter is marginal and within a limited low Reynolds number, where the maximal improvement is about 3.4% at Re=150.

In this study, the process of catalytic oxidation of methane considering radiative heat transfer was simulated using FLUENT computational software to study the effect of thermal radiation on the oxidation performance of the simulated device, and to investigate the extent to which radiative heat transfer affects the oxidation performance of the device under different operating conditions. The results show that the extent to which thermal radiation affects the oxidative performance of the equipment increases with increasing inlet temperature. When the intake temperature reaches 900K, its proportion is close to 45 %. At the same time, as the inlet gas temperature increases, the maximum reaction temperature of the oxidation unit is 1154 K, and the methane conversion rate reaches up to 89 %. The main factor affecting the oxidation performance of the unit at this time is radiation heat transfer. The extent to which thermal radiation affects the oxidative performance of the device diminishes with increasing inlet velocity. When the wind speed reaches 2 m/s, the proportion of radiative heat transfer is only 10 %, the maximum reaction temperature of the plant falls to 993 K, and the methane conversion rate drops to 68 %. At this time, the main factor affecting the oxidation performance of the plant is convective heat transfer. The influence of thermal radiation on oxidation performance gradually diminishes with an increase in intake velocity, and the proportion of radiative heat transfer decreases continuously. At methane concentrations above 1 %, the proportion of radiative heat transfer is less than 25 per cent, the maximum reaction temperature of the unit increases to 1087 K, and the methane conversion rises to 88 %. At this point, the main factor affecting the oxidation performance of the plant is convective heat transfer.

Compact heat exchangers are widely being used in various devices owing to its minimized size and efficient operation. The traditionally fitted circular tubes in heat exchanger have been modified as semi-circular tubes with slit. This newly proposed design offers added tubes surface area of 63.69% for better fluid flow and heat exchange. To investigate, two dimensional, unsteady, incompressible and isothermal computational studies have been carried out. The different confinements (BR= 1.54d, 2d and 3d) and gap ratios (g = 0.07, 0.14 and 0.21)have been preferred in order to mimic confined fluid environment in compact heat exchangers over the Reynolds numbers range of 50-200. Ansys Workbench 18 has been employed in modeling, meshing and carrying out the simulations of the problem formulated. Pressure and velocity were coupled using the SIMPLE algorithm. The convective and diffusive terms in the governing equations were discretized using second order upwind and central difference scheme. The time step size was fixed as 0.005 and the simulation was run until flow maturity. Results claim that flow sheds well nearer to tubes with slit at BR 1.54, which is not happening for circular tubes at same BR. The arrangement with the minimum BR and maximum gap ratio offers best performance. Semi-circle combination separated by 0.21d offers best heat transfer with an improvement of 10.51% as compared to circular components at a blockage (BR) ratio of 1.54 and Re of 200.The concept of tube splits instead of circular tubes is more effective in dissipating heat whenever the flow shedding is deteriorating or completely eliminated. The overall performance parameter (ɛ) for tube split is highest when BR 3 and g 0.21. [ABSTRACT FROM AUTHOR]

In the present study, the effect of taper on the lateral sides on fluid flow and heat transfer characteristics on a square cylinder has been analyzed numerically. Two-dimensional simulations have been carried out in the laminar flow regime (Re 100–800) for divergent blockage ratios (ϵ = H/D) and taper angles on the forward and backward sides of the lateral cylinder. Compared to the square cylinder, the forward tapered modification cylinders led to significant total drag reductions, pressure drop, and higher heat dissipation for low Re. The backward taper cylinder illustrates a minor increase in heat dissipation; however, the high drag coefficient and pressure drop penalty cannot be neglected. Moreover, an optimized geometry has been identified as a function of all the parameters. The reduction in blockage ratio has been determined to suppress the vortex shedding for higher Re completely. Results also indicate that the decrease in blockage ratio reduces the critical Re of the domain. The slightly tapered surfaces on either side of the square geometry significantly influence heat transfer and apply to modern industrial electronics and their cooling. [ABSTRACT FROM AUTHOR]

The process of fluid diffusion and fire dynamics in spill fires at different initial temperatures is unstable and complex, potentially leading to severe consequences. Through a series of experiments, the effects of initial fuel temperature on the combustion mechanism of ethanol spill fire were investigated. The results show that in the liquid-phase control stage, the propagation of the spill fire is greatly affected by the liquid spread, and the increasing rate of combustion area (IRCA) and the maximum combustion area (MCA) gradually increase with the increase in the initial temperature. In the gas-phase control stage, the propagation of spill fire is greatly affected by the combustion of liquid, as initial temperature increase, the IRCA and MCA gradually decrease. The increase in the initial temperature will lead to the attenuation of the pulsation phenomenon during the propagation of the flame, but will lead to the frequency of flame oscillation increases. The prediction equations of burning rate at different initial fuel temperatures are established, which show that there is a significant difference in burning rate in the liquid-phase control stage, the maximum increase in the burning rate was only 2.3%, while in the gas-phase control stage, this value is about 50%. The convective feedback is the main heat feedback mechanism of small spillage fires, and the convective feedback accounts for more than 62.5%. The higher the initial temperature, the stronger the convective feedback mechanism. [ABSTRACT FROM AUTHOR]

The time-dependent creep behavior of a rotating disc composed of functionally graded material (FGM) with varying thickness was analyzed. The convection heat transfer along with internal heat generation was considered in thermoelastic analysis. The material properties were assumed to change radially as a power-law function. Also, the heat convection and heat conduction coefficients were taken as functions of temperature and radius. The nonlinear heat transfer equation was solved using the differential transformation method (DTM). Then, the equilibrium equation considering creep strains was derived. The derived differential equation was solved analytically for zero time. Considering the creep strains, the stress and strain rates were determined using Norton's law with Prandtl–Reuss equations for steady-state thermal boundary conditions. Finally, the time-dependent creep stress redistributions at any time were evaluated using an iterative method. The effects of the heat source, convection heat transfer, temperature dependency, inhomogeneity index, and angular velocity on the behavior of the disc were explored in numerical examples. [ABSTRACT FROM AUTHOR]

Bifacial photovoltaic cells can produce electricity from incoming solar radiation on both sides. These cells have a strong potential to reduce electricity generation costs and may play an important role in the energy system of the future. However, today, these cells are mostly deployed with one side receiving only ground reflection, which leads to a profound sub-optimal utilization of one of the sides of the bifacial cells. Concentration allows a better usage of the potential of bifacial cells, which can lead to a lower cost per kWh. However, concentration also adds complexity due to the higher temperatures reached which add the requirement of cooling in order to achieve higher outputs. This way, this paper focuses on the effectiveness of forced air circulation methods by comparing the thermal performance of three specific concentrating bi-facial collector designs. This paper developed a computational model, using ANSYS Fluent intending to assess the thermal performance of a covered concentrating collector with bifacial Photovoltaic (PV) cells. These results have then been validated by outdoor measurements. Results show that even a simple natural ventilation mechanism such as removing the side gable can effectively reduce the receiver temperature, thus resulting in favourable cell operation conditions when compared to the case of an airtight collector. Therefore, compared with a standard model, a decrease of 13.5% on the cell operating temperature was reported when the side gables are removed. However, when forced ventilation is apllied a 22.8% reduction on temperature is found compared to the standard air-tight model. The validated CFD model has proven to be a useful and robust tool for the thermal analysis of solar concentrating systems. [ABSTRACT FROM AUTHOR]

In this study, the reaction characteristics of reduction of calcined dolomite with ferrosilicon under argon flow to produce magnesium were studied by conducting experiments Pidgeon pellets were used to study the effect of reduced temperature, argon flow, and reduced time on the conversion of calcined dolomite reduction by ferrosilicon. The results show that the conversion significantly increases with the increase in the reduction temperature and reduction time. The conversion first increases and then decreases with the increase in argon flow. The highest conversion was obtained when the argon flow rate was 3 L·min−1, and a nearly spherical shape, nanoscale magnesium powder was obtained. Then the characters of the circulating argon entrainment process were numerically studied by ANSYS Fluent 17. A physical model of multilayer pellet arrangement was established, and a numerical calculation model of chemical reaction, radiation, heat conduction, and convection heat transfer was constructed. This confirms that high-temperature argon can effectively strengthen the heat exchange between pellets, improve the heat transfer efficiency, and facilitate the pellets to react quickly. When the conversion is 80%, the production efficiency increased by about 28.6%. In addition, the magnesium production efficiency showed an increase tendency with the increase of the argon inlet flow rate.

In this study, the reaction characteristics of reduction of calcined dolomite with ferrosilicon under argon flow to produce magnesium were studied by conducting experiments Pidgeon pellets were used to study the effect of reduced temperature, argon flow, and reduced time on the conversion of calcined dolomite reduction by ferrosilicon. The results show that the conversion significantly increases with the increase in the reduction temperature and reduction time. The conversion first increases and then decreases with the increase in argon flow. The highest conversion was obtained when the argon flow rate was 3 L·min−1, and a nearly spherical shape, nanoscale magnesium powder was obtained. Then the characters of the circulating argon entrainment process were numerically studied by ANSYS Fluent 17. A physical model of multilayer pellet arrangement was established, and a numerical calculation model of chemical reaction, radiation, heat conduction, and convection heat transfer was constructed. This confirms that high-temperature argon can effectively strengthen the heat exchange between pellets, improve the heat transfer efficiency, and facilitate the pellets to react quickly. When the conversion is 80%, the production efficiency increased by about 28.6%. In addition, the magnesium production efficiency showed an increase tendency with the increase of the argon inlet flow rate. [ABSTRACT FROM AUTHOR]

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Abstract Open-loop borehole heat exchanger (OBHE) is a single well geothermal heat exchanger with an open-loop structure that can realize the geothermal energy extraction without mining the geothermal water. In this paper, a sandbox experiment is designed to simulate the convective heat transfer process in the reservoir area of OBHE. The mechanism of convective heat transfer in the reservoir area is studied, and the key factors that affect the convection heat transfer intensity are analyzed. The results show that the convection heat transfer of OBHE in the reservoir area is affected by both the driving effect of fluid flow inside the screen tube and the buoyancy effect. In the forward flow mode, the two effects have the opposite direction. While in the backward mode, the two effects have the same direction. The backward flow mode is more conducive to convective heat transfer. In addition, many factors influencing significantly the convective heat transfer of OBHE include inlet temperature, inlet flow rate, reservoir temperature, fluid flow direction and inner tube diameter.

The increasing complexity and miniaturization of electronic applications necessitate the development of efficient and compact heat sink designs for effective heat dissipation. This study presents a numerical investigation of heat transfer performance in circular pin-fin heat sinks featuring notches of varying sizes. Five distinct heat sink models are analyzed, with the first model comprising a solid fin, while the remaining four incorporate notched fins of different dimensions. Results indicate a significant influence of notch size on heat transfer performance, particularly for larger notches. The Nusselt number for a heat sink with a 4 mm notch size exhibits an increase of approximately 9% compared to that of a solid-fin heat sink. Additionally, the average temperature of heat sinks decreases with the introduction of notched fins, resulting in a temperature difference of 2.15℃ between solid-fin and 4 mm-sized notch heat sinks. An assessment of overall efficiency and overall effectiveness reveals that all notched heat sinks are viable options, with the 4 mm-sized notch heat sink demonstrating optimal performance in this study. This investigation provides valuable insights for the design of highperformance heat sinks in compact electronic applications. [ABSTRACT FROM AUTHOR]

The heat transfer characteristics of the vibrating blades of different shapes were numerically modeled in the present work. A single blade was arranged in a channel with vertical or horizontal alignment. Both the static environment and the channel flow were considered. Four types of blades, rectangular, trapezoidal, serrated, and folding, were comparably modeled. The results showed that the vibrating blade could effectively enhance the convection heat transfer of the heated surface with a smaller increase of pressure drop. For the static environment, the heat transfer performance of the vertical alignment of the blade is better than the horizontal alignment. For channel flow, the opposite conclusion is obtained. For the inlet velocity of channel flow vinlet=2 m/s and vinlet=6 m/s, the maximum improvement of the local convection heat transfer coefficient is about 98% and 12%, respectively. The corresponding pressure drops were reduced and increased by 9.5% and 8.8%, respectively. The vibrating blade can effectively improve the convection heat transfer at lower inlet velocity. Under the same working conditions, the pressure drop difference between the four shapes of fan blades is less than 1%, and the folding blade has the best local heat dissipation performance. [ABSTRACT FROM AUTHOR]

Microscale electronic devices offer promising application capabilities in various fields, such as information, aeronautics and astronautics, energy, and chemical engineering. Specifically, the exceptional performance of high-integration and high-frequency devices leads to a significant heat flux enhancement. Conventional air and liquid cooling techniques struggle to meet the efficient heat dissipation requirement, affecting the reliability and safety of microscale electronic devices significantly. Many types of passive heat transfer process intensification strategies have been proposed recently, such as those based on adjusting element structure, surface roughness, surface hydrophobicity, and channel dimension. However, these passive strategies increase flow resistance to some extent, limiting their applicability. Ultrasound has several unique characteristics, including low cost, simple operation, flexible control, strong penetrability, and good biocompatibility. These characteristics make ultrasound a promising candidate for use in national defense, biomedical theranostics, agriculture, food, the environment, and materials. Researchers have paid considerable attention to the integration of ultrasound with heat transfer techniques, which has gradually become one of the key research directions for heat transfer enhancement. This paper aims to provide a comprehensive overview of the research progress on the intensification of the ultrasound-excited heat transfer process. First, the principles of ultrasound-excited heat transfer enhancement are introduced, and two major acoustic phenomena, acoustic cavitation and acoustic streaming, are highlighted. Theoretical and experimental studies on ultrasound-excited single-phase gas convection, single-phase liquid convection, pool boiling, and flow boiling heat transfer process intensification are then summarized, and typical studies in these fields are categorized and discussed in depth. Finally, current challenges and future directions are presented, such as simple numerical simulation models that should consider multiphysics and multidomain constraints for accurately representing the practical heat transfer process, lack of sufficient characterization methods that should develop new and integrated visualization techniques for precisely monitoring heat transfer performance, limited focus on other acoustic phenomena other than acoustic streaming and acoustic cavitation that should provide a comprehensive analysis for revealing the in-depth heat transfer mechanisms, and few attempts and pathways to industrialization that should demand researchers from different disciplines to work together and collaboratively. It is hoped that this review article will not only reveal the unprecedented functionality of ultrasound for heat transfer enhancement but will also provide critical guidelines for the rational and practical design of robust ultrasound heat transfer platforms.

In this study, the heat transfer of nanofluids as single-phase, incompressible, laminar, permanent in a two-dimensional sinusoidal channel under the influence of a magnetic field with a porous medium is investigated. Alternating heat flux is applied to the channel walls. The governing equations are discretized using Fluent software with finite volume method (FVM) and velocity and pressure coupling is performed using SIMPLE algorithm. The Reynolds number range is 500 ≤ Re ≤ 200. Water is considered as the base fluid and magnesium oxide nanoparticles have been added to it. The volume percentage of nanofluid is 0.04. Nanofluid flow in 4 different Darcys (0.00001, 0.0001, 0.001, and 0.01) and magnetic field application in 4 Hartmann numbers (0, 4, 7 and 10) have been investigated. The results show that in all cases, with increasing Hartmann number, the heat transferred improves and the pressure drop increases. By increasing the Darcy number from 0.00001 to 0.01 under the same conditions (Reynolds 500 and Hartmann 10), the Nusselt number equals 4.392. Also, with increasing the Darcy number, the viscous resistance decreased and the pressure drop was always lower, so that the numerical pressure drop ratio was less than 1.

Commercial freezers are commonly used the outer wall as a heatsink. This heatsink needs surrounded ambient air for cooling, which is the natural convection mechanism. However, in theory the force convection provides more heat transfer than the natural convection. Therefore, energy consumption of the force convection is generally less than the natural convection. This study aims at testing and comparing the heat transfer between the natural convection and force convection of the heatsink of the commercial freezer. Moreover, this study investigated the potential of energy reduction of the freezer by using the natural convection and the force convection of the heatsink. In this study, the unmodified commercial freezer installed with the wind tunnel over the heatsink of the freezer was made. The necessary parameters such as heatsink surface temperature, cooling air temperature, ambient air temperature, velocity of cooling air, and power consumption of the freezer were collected. The testing conditions were varied the internal heat load of the freezer by using water as 0, 3, and 6 kg, and varied the cooling air velocity as 0, 1, 2, and 3 m/s. The results showed that the convection mechanism was significantly affected by energy consumption. Furthermore, it was clearly found that the heat transfer for the force convection was higher than the natural convection. Moreover, the use of force convection resulted in a lower energy consumption. In particular at the internal heat load of 6 kg, the energy consumption of the force convection decreased by 17.5%, 17.7%, and 20.5% as compared to the natural convection at the cooling air velocity of 1, 2, and 3 m/s, respectively. Based on the results obtained it can be concluded that the force convection for the freezer heatsink can be used to reduce energy consumption, which could be efficiently applied in the future works.

The inverse solution to the heat flux identification during the vertical plate cooling in air has been presented. The developed solution allowed to separate the energy absorbed by the chamber due to radiation from the convection heat losses to air. The uncertainty tests were carried out and the accuracy of the solution has been estimated at a level of 1%-5% depending on the boundary condition model. The inverse solution was obtained for the temperature measurements in the vertical plate. The stainless-steel plate was heated to 950°C and then cooled in the chamber in air only to about 30°C. The identified heat transfer coefficient was compared with the Churchill and Chu model. The solution has allowed to separate the radiation heat losses and to determine the Nusselt number values that stay in good agreement with the Churchill and Chu model for a nearly steady-state air flow for the plate temperature below 100°C.

Open-loop borehole heat exchanger (OBHE) is a single well geothermal heat exchanger with an open-loop structure that can realize the geothermal energy extraction without mining the geothermal water. In this paper, a sandbox experiment is designed to simulate the convective heat transfer process in the reservoir area of OBHE. The mechanism of convective heat transfer in the reservoir area is studied, and the key factors that affect the convection heat transfer intensity are analyzed. The results show that the convection heat transfer of OBHE in the reservoir area is affected by both the driving effect of fluid flow inside the screen tube and the buoyancy effect. In the forward flow mode, the two effects have the opposite direction. While in the backward mode, the two effects have the same direction. The backward flow mode is more conducive to convective heat transfer. In addition, many factors influencing significantly the convective heat transfer of OBHE include inlet temperature, inlet flow rate, reservoir temperature, fluid flow direction and inner tube diameter. [ABSTRACT FROM AUTHOR]

In this work, the superheated vapor effect on liquid film condensation in a saturated porous medium using Forchheimer's model has been investigated analytically and numerically. The applied governing equations, the continuity equation, the Forchheimer equation, and the energy equation were transformed using the similarity transformation technique into a dimensionless form using a set of suitable variables and then solved numerically using the Runge–Kutta method. Results obtained were graphically drawn to illustrate the effects of superheated vapor and subcooled liquid on the liquid film condensation, temperature, and heat transfer rate through the porous medium. It was found that the film thickness is a function of dimensionless parameters related to the degree of subcooling and Grashof number without a superheating effect. Consequently, the Nusselt number depends on the square root of the Rayleigh number, the Grashof number, and the dimensionless film thickness. It was also found that if superheating exists, the liquid film thickness then depends on four dimensionless parameters related to the Grashof number, the degree of subcooling of the liquid, the extent of the superheating of the surrounding vapor, and a property ratio of the liquid and the vapor phase. [ABSTRACT FROM AUTHOR]

The heat transfer simulations of turbine blades with internal cooling are faced with so many uncertainties, of which some originate from the secondary air system, including the inlet hot gas temperature and pressure and the cooling side boundary conditions, and the blade material. The main objective of this work is to carry out a suitable sensitivity analysis on a specific novel turbine vane to improve the thermal performance of its internal cooling system and to quantify how the uncertainties on the designed/calculated values can desirably/undesirably affect the maximum blade surface temperature, which can consequently affect the gas turbine engine efficiency. Furthermore, the sensitivity analysis is carried out to find the effects of uncertainties of a number of key parameters on the resulting blade temperature distribution. To arrive at trustworthy conclusions, the conjugate heat transfer (CHT) method is used to analyze the heat and fluid flow behavior. This work suitably develops a CHT-based method/solver to perform the proposed study. This method/solver uses a segregated iterative procedure, in which the outer hot gas region is simulated using the computational fluid dynamics (CFD) solver, the flow passing through the connected internal cooling passages is calculated using a 1D correlated-based solver, and the vane conduction is predicted using a 3D finite-element solver, which are fully coupled. The results show that the cooling channel wall temperature has a direct impact on the convective coefficient magnitude; especially in lower temperature regions. As a novel contribution, this work takes into account the cooling wall temperature influence on the 1D code calculations. To implement this, an artificial neural network is suitably trained to predict better convective coefficient. The results of this developed CFD-CHT code are validated against experimental data available for a benchmark vane. Eventually, the sensitivity analysis is carried on the present specific novel turbine vane. [ABSTRACT FROM AUTHOR]

Compressed air energy storage (CAES) is an important technology in the development of renewable energy. The main advantages of CAES are its high energy capacity and environmental friendliness. One of the main challenges is its low energy density, meaning a natural cavern is required for air storage. High-pressure air compression can effectively solve the problem. A liquid piston gas compressor facilitates high-pressure compression, and efficient convective heat transfer can significantly reduce the compression energy consumption during air compression. In this paper, a near isothermal compression method is proposed to increase the surface area and heat exchange by using multiple tube bundles in parallel in the compression chamber in order to obtain high-pressure air using liquid-driven compression. Air compression with a compression ratio of 6.25:1 is achieved by reducing the tube diameter and increasing the parallel tube number while keeping the compression chamber cross-sectional area constant in order to obtain a high-pressure air of 5 MPa. The performances of this system are analyzed when different numbers of tubes are applied. A system compression efficiency of 93.0% and an expansion efficiency of 92.9% can be achieved when 1000 tubes are applied at a 1 minute period. A new approach is provided in this study to achieve high efficiency and high pressure compressed air energy storage. [ABSTRACT FROM AUTHOR]

A validated CFD by ANSYS model is built for a melting process of PCM (gallium), inside rectangular enclosure heated from one side and cooled from another. This was carried out by enabling the solidification and melting model in addition energy model of ANSYS. Regression model of melting front results from CFD model by ANSYS is utilized and integrated inside numerical approach by MATLAB to generate constants for Nusselt correlations and effective conductivity during different melting stages that can be used to define melting front locations and temperature at grid different locations. In addition, effect of the wall temperature and model aspect ratio variation on melting process have been simulated by ANSYS and analyzed in details. Enthalpy method and conduction equations for 2-D model were used to describe the predicted share of convection in melting process, with trial and error by assuming the constants automatically. Accordingly, melting process can be predicted in a simple and a conservative time way at the same time, the results are mainly indicating that convection heat transfer affects the melting process and melting behavior which is in coherence with previous experimental and analytical literature. Also, the effect of aspect ratio were investigated to assure that the more the aspect ratio, the better is the temperature homogeneity. [ABSTRACT FROM AUTHOR]

With the help of commercial software, we have discussed the novel numerical simulations for a two-dimensional rectangular cavity with two square rotating obstacles, Fig. 1, that has fixed dimensions from the reference point (0, 0) placed in it, and we have interpreted a detailed convection analysis for fluid flow that highlights the physical, mathematical and numerical aspects of this system. The square obstacles having an anti-clockwise rotation are heated to a certain temperature, respectively, where the behavior of the fluid distribution depends upon the values of Reynolds number. We have conducted this research by fixing Reynolds number at four different positions like Reynolds 10, 30, 50 and 80. The prime effects of Reynolds number and Prandtl number are highlighted for convection analysis. Finally, we have analyzed the results of velocity, pressure, vorticity and temperature from the viewpoint of numerical simulations. Heat transfer has a huge dependence on the Reynolds number and Prandtl number. [ABSTRACT FROM AUTHOR]

The present work performs a numerical analysis of the geometrical investigation of a two-dimensional channel with two alternated isothermal rectangular blocks subjected to turbulent forced convective flows. Constructal Design associated with Exhaustive Search is used to investigate the influence of the geometry of the isothermal blocks over the performance of the cooling convective flows in a multi-objective viewpoint, i.e., considering the pressure drop and heat transfer rate. The time-averaged equations of continuity, momentum, and energy conservation are solved with the finite volume method. The k– ω shear stress transport model is used for the closure of turbulence. The effect of the two proposed degrees of freedom, the height/length ratio of the two blocks ( H 1 / L 1 and H 2 / L 2) , is analyzed in relation to the proposed objectives. Regarding the thermal purpose, the geometry with the highest insertion into the channel led to the best performance, while the opposite configuration led to the best fluid dynamic performance. This behavior was similar to that previously found in the literature for forced convective laminar flows. For a multi-objective perspective, the use of technique for order preference by similarity to ideal solution indicated that asymmetric blocks led to the best multi-objective performance when both performance indicators had the same weight. [ABSTRACT FROM AUTHOR]

In this study, the effect of stationary and oscillating blades on the forced convection heat transfer in a channel is studied numerically. Simulations are performed in a fully-developed, laminar, unsteady, and incompressible flow with Reynolds number and Prandtl number equal to 100 and 1, respectively. The effects of the blade geometry, oscillating speed and oscillation angle on heat transfer and pressure drop are studied. The results are presented in terms of time-averaged Nusselt number, temperature, and vorticity distribution and the pressure drop. The results indicate that the oscillation angle, oscillating speed of the blade, and the number of the blades, affect the thermal performance of the channel. In most cases, it is observed that the effect of the oscillation angle is more than that for the oscillating speed on heat transfer enhancement. However, increasing the number of blades does not necessarily help to enhance the heat transfer, but it can slightly decrease the pressure drop.

In this work, the effect of acoustic waves on vortex shedding and convective heat transfer of two tandemly arranged cylinders is investigated using experiments and numerical simulations. This paper focuses on the average Reynolds number Re = 200, the sound pressure level ranges from 127dB to145dB, and the sound frequency ranges from 100Hz to 1000Hz. Different acoustic wave frequencies and particle vibration velocity amplitudes were set as the entrance conditions. The average heat transfer in the upstream and downstream cylinders was enhanced due to the increase in the particle velocity amplitude of the fluid around the cylinder by acoustic oscillations. Moreover, with the increase in the acoustic frequency, the flow mixing is enhanced and irregular vortices appeared in the cylindrical wake. With regards to the particle velocity amplitude, the values of the Nusselt number of the two cylinders increase with the increase in particle velocity amplitude. With the increase in the particle velocity amplitude, the forced mixing and heat transfer of the gap flow between the two cylinders are enhanced. The comparison between the experimental and numerical results shows that acoustic waves can enhance convective heat transfer of two tandemly arranged cylinders in the cross-flow.

This research investigates the effects of employing nanofluids in a tubular heat exchanger on the heat transfer process. The performance of employing water as a base fluid and multi-wall carbon nanotubes (MWCNTs) with a varying concentration nanofluid as operational fluids was investigated in an experimental investigation. The current study makes use of an Armfield Heat Exchanger (HT31) and an Armfield heat exchange service unit (HT30X). Five volumetric concentrations of nanomaterials were used to make nanofluids (0.22%, 0.33%, 0.66%, 1.1%, 1.53%). The Reynolds number of the flow inside the tube ranged from 1598 to 8000. By measuring the variables, the overall heat transfer coefficient, pressure drop, friction factor, and mean Nusselt number are computed. The overall heat transfer coefficient increases as the concentration of MWCNTS and the mass of flow increase, according to the experimental data. In comparison to distilled water, the Nusselt number value has increased by 68%, this increase is due to the nanoparticles' volume concentration. Pressure drop values increase significantly when nanofluids are used. The friction factor increases as the volume concentration of nanoparticles increases. A relationship between Reynolds number and MWCNT volume concentration is proposed for computing the Nusselt number. An acceptable agreement may be found by comparing the results of the current investigation to the literature. [ABSTRACT FROM AUTHOR]

Experiments on the convection heat transfer and pressure drop of supercritical carbon dioxide in a mini vertical upward flow were investigated in a smooth tube with an inner diameter of 2 mm. The experiments were conducted with pressures ranging from 7.62 to 8.44 MPa, mass fluxes ranging from 600 to 1600 kg·m−2·s−1, and heat flux ranging from 49.3 to 152.3 kW·m−2. Results show that the peak of heat transfer occurs when the bulk fluid temperature is below the proposed critical temperature and the wall temperature is above the proposed critical temperature. For the 2 mm vertical upward flow, the radial buoyancy effects are relatively weak, and the axial thermal acceleration effect cannot be negligible. In this study, a new modified Jackson correlation for the supercritical carbon dioxide is proposed for convective heat transfer. To reflect the effect of flow acceleration on heat transfer, a dimensionless heat flux was introduced to construct a new semi-correlation of heat transfer. The new correlation of friction factor taking into account the variation of density and dynamic viscosity was proposed with 146 experimental data within a ±20% error band. [ABSTRACT FROM AUTHOR]

In this study, the process of catalytic oxidation of methane considering radiative heat transfer was simulated using FLUENT computational software to study the effect of thermal radiation on the oxidation performance of the simulated device, and to investigate the extent to which radiative heat transfer affects the oxidation performance of the device under different operating conditions. The results show that the extent to which thermal radiation affects the oxidative performance of the equipment increases with increasing inlet temperature. When the intake temperature reaches 900K, its proportion is close to 45 %. At the same time, as the inlet gas temperature increases, the maximum reaction temperature of the oxidation unit is 1154 K, and the methane conversion rate reaches up to 89 %. The main factor affecting the oxidation performance of the unit at this time is radiation heat transfer. The extent to which thermal radiation affects the oxidative performance of the device diminishes with increasing inlet velocity. When the wind speed reaches 2 m/s, the proportion of radiative heat transfer is only 10 %, the maximum reaction temperature of the plant falls to 993 K, and the methane conversion rate drops to 68 %. At this time, the main factor affecting the oxidation performance of the plant is convective heat transfer. The influence of thermal radiation on oxidation performance gradually diminishes with an increase in intake velocity, and the proportion of radiative heat transfer decreases continuously. At methane concentrations above 1 %, the proportion of radiative heat transfer is less than 25 per cent, the maximum reaction temperature of the unit increases to 1087 K, and the methane conversion rises to 88 %. At this point, the main factor affecting the oxidation performance of the plant is convective heat transfer., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Authors.)

During the construction of tunnels subjected to high temperatures (here called high-temperature tunnels), ventilation cooling is an essential requirement. A high-temperature section of a construction tunnel on the Sichuan-Tibet Railway was used as a test case to study the heat exchange on both sides of the ventilation duct during active cooling. We used theoretical analysis and numerical simulation to establish a model for calculating the temperatures associated with the ventilation duct, and studied the influence of different factors on the convection heat exchange on the inside and outside the duct during the ventilation cooling process. According to simulation and field measurement results, the airflow temperature inside the duct rose with the distance from the inlet, and the temperature near the duct's wall was higher than the temperature in the center. After analyzing different influencing factors, it was found that duct material and thickness have little effect on the convection heat transfer inside the duct. But the convection heat transfer intensity would rise when the temperature difference between the inside and the outside of the duct increased, and the heat flux (q) through the wall increased by 1.5 W/m2. The average air temperature trend of the ventilation duct section was stable as the ventilation distance increased. It increased linearly as ventilation distance increased. While the effect of ventilation cooling gradually declined, and the overall temperature of the air of the tunnel rose when the ventilation distance increased. As a result, heat exchange along the duct should be fully considered in the design and application of the ventilation cooling process to ensure that the airflow temperature reaching the excavation face at the head of the tunnel meets the operational requirements.

The inverse solution to the heat flux identification during the vertical plate cooling in air has been presented. The developed solution allowed to separate the energy absorbed by the chamber due to radiation from the convection heat losses to air. The uncertainty tests were carried out and the accuracy of the solution has been estimated at a level of 1%-5% depending on the boundary condition model. The inverse solution was obtained for the temperature measurements in the vertical plate. The stainless-steel plate was heated to 950°C and then cooled in the chamber in air only to about 30°C. The identified heat transfer coefficient was compared with the Churchill and Chu model. The solution has allowed to separate the radiation heat losses and to determine the Nusselt number values that stay in good agreement with the Churchill and Chu model for a nearly steady-state air flow for the plate temperature below 100°C. [ABSTRACT FROM AUTHOR]

The clutch temperature rise characteristics in successive shifting conditions are crucial to its thermal stability and thermal safety. In the present paper, a comprehensive numerical model is proposed to investigate the temperature change of separator discs during successive shifting with the consideration of convection heat transfer in disengaged friction pair gaps, which is validated by repeated shifting experiments on the SAE#2 test bench. Since the second separator disc near the piston has the widest disengaged gaps and double-sided heat input, its temperature rise and temperature drop are the highest. The temperature rise gradually equals the temperature drop with the increasing working cycle, then the maximum clutch temperature no longer increases. The longer the shifting interval, the better the heat dissipation is, thus the lower the accumulated temperature rise. Moreover, the increasing lubrication oil temperature reduces the convection heat transfer and increases the temperature rise in an engaging process, but the accumulated temperature rise does not increase due to the widened friction pair gaps. This paper can obtain the temperature rise characteristics of a wet multi-disc clutch concerning its disengaged gaps during successive shifting, which is a promising candidate for investigating its overall performance. [ABSTRACT FROM AUTHOR]

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Global warming is increasing as CO 2 emissions from the use of conventional fossil fuels continue to rise. The development of geothermal energy is gradually becoming the key to the sustainable development of human society in the future. Enhancing the heat transfer performance of circulating heat transfer fluids is one of the effective means to efficiently exploit deep geothermal resources. In this study, a self-developed circulating heat exchange experimental setup was established. The convection heat transfer characteristics of nanofluids in high-temperature rocks were experimentally investigated. Al 2 O 3 nanofluid and CuO nanofluid were used as the working medium for heat transfer in high temperature granite samples. The effects of the Reynolds number (1000–6000) and parameters such as nanoparticle type (CuO & Al 2 O 3), size (20 nm & 40 nm) and mass fraction (0 wt%-2wt%) on the heat transfer intensity were analyzed. The effect of nanoparticle accumulation on the rock surface on the local heat transfer strength was also investigated. The results indicate that the increase of Reynolds number enhances the heat transfer strength of nanofluids in rocks. Nanofluid containing 20 nm Al 2 O 3 nanoparticles has better heat transfer performance in rock than nanofluid containing 20 nm CuO nanoparticles. Meanwhile, the heat transfer performance of nanofluid containing 20 nm Al 2 O 3 nanoparticles in rock is better than that of nanofluid containing 40 nm Al 2 O 3 nanoparticles. The heat transfer intensity increases and then decreases as the nanoparticle mass fraction increases. The heat transfer coefficient at Reynolds number 6000 is 52.2 % higher than that of water. For nanofluids and water, the local heat transfer intensity decreases with increasing distance from the inlet. Meanwhile, accumulation of nanoparticles on rock surfaces during convective heat transfer enhances heat transfer intensity. The results show that nanofluids have the potential to be applied to deep geothermal resource extraction. This paper provides data and technical support for the application of nanomaterials in medium and deep geothermal systems to enhance heat transfer efficiency. [ABSTRACT FROM AUTHOR]

The convection heat transfer in a countercurrent double-tube heat exchanger with various fins in a turbulent flow is investigated. The suitable heating or cooling process of fluids is the effective use of the double-pipe heat exchanger. We use water-aluminum oxide nanofluid and water-titanium dioxide at four concentrations (0.4%, 2%, 4%, 6%) as the cold fluid in the inner tube and water as the hot fluid in the annular space. The single-phase model for nanofluid modeling and the standard k-ε model with scalable wall function for simulating the turbulent flow is utilized. To better examine this novel geometry, its performance is compared with simple and rectangular-finned geometries. The results show that the water aluminum oxide nanofluid has a better convection heat transfer coefficient than water titanium dioxide and pure water. Raising the nanofluid concentration from 0.4% to 6% increases the convection heat transfer coefficient by 12%. Heat exchangers with a rectangular and curved fin have 81% and 85% better efficiency than the heat exchanger without a fin. The novel geometry causes a smaller pressure drop despite its higher convection heat transfer coefficient. Also, it is shown that with raising the Reynolds number and nanofluid concentration, the pressure drop increases.