Dimensionless Temperature Research Articles

Thermal analysis of a moving fin using the radial basis function approximation

AbstractIn this study, the heat transfer and temperature distribution in a moving fin have been analyzed. The fin velocity was considered constant, and the thermal conductivity coefficient was variable with temperature, and the fin was under the effect of convection, radiation, and conduction heat transfer. The main equation of the problem was solved by the radial basis function method and validated by the numerical 4th‐order Runge–Kutta method. Several parameters such as thermal conductivity parameter from 0 to 1, sink temperature parameter from 0.2 to 0.8, and Nr, Nc, Pe number from 1 to 4, were examined. The outcomes illustrate that increasing the thermal conductivity by 51.5% raises the conduction heat transfers as well as the dimensionless temperature by 3.42%. Moreover, increasing the sink temperature leads to a slow rise in ambient temperature by 22.8% in the maximum state. By raising the Nc and Nr parameters, near 33.3%, the temperature distribution profile is declined by 4% and 10.5%, respectively. And increasing the Pe number by 100% results in a rise in the temperature distribution by about 7%.

Natural convection flow maxwell fluids with generalized thermal transport and newtonian heating

The objective of this article is to explore the unsteady natural convection flows of Prabhakar-like non integer Maxwell fluid. Moreover, wall slip condition on temperature and Newtonian effects on heating are also studied. The generalized memory effects are illustrated with fractional time Prabhakar derivative. Dimensionless temperature and velocity are calculated analytically with the help of Laplace transform technique. A comparison among Prabhakar fractional natural convection flows and classical thermal transport which, illustrated by the Fourier's law. As a limiting case, we recovered the solution of ordinary Maxwell and Newtonian fluids from fractional Maxwell fluids with slip and no slip conditions. The results of fractional and important physical parameters are graphically covered. Accordingly, by comparing Maxwell fluids to viscous fluids, we found out that Maxwell fluids are move rapidly than viscous fluids. Moreover, the ordinary fluids moving fast than fractional fluids.

Theoretical and experimental evaluation of temperature drop and power consumption in a cover-plate pre-swirl system for gas turbine cooling

The pre-swirl system has the ability to decrease the air supply temperature so as to improve the cooling performance and the operating life for turbine rotating blade. In this paper, a test rig was designed to reveal the aero-thermal characteristics in a cover-plate type pre-swirl system of gas turbine engines. Then, the theoretical derivation and experimental evaluation were conducted to reveal the variation of temperature drop and power consumption of a pre-swirl system with the mass flow rate ratio and rotating speed. Especially, the pressure and temperature on the rotating turbine disc were measured by a co-rotating data recorder. The theoretical and experimental analyses indicate that the temperature drop of pre-swirl system increases as the velocity coefficient of the pre-swirl nozzle outlet enhanced, but presenting a decrease with the increment of the rotating Mach number. Then, the ideal dimensionless temperature drop can be formally unified with the actual dimensionless temperature by defining the tangential velocity recovering coefficient, which is verified with the experimental results. Moreover, a linear relationship between the dimensionless temperature drop and the effective swirl ratio at the nozzle outlet can be deduced further. Especially, this relationship shows a good agreement between the predicted values and numerical results. Since the dimensionless temperature drop decreases with the increase of the dimensionless power consumption; an important discovery can be concluded that the algebraic sum of these two physical quantities is always equal to 1. Therefore, the results can offer a reference for the design and optimization of gas turbine cover-plate type pre-swirl system.

Numerical study of melting and heat transfer of PCM in a rectangular cavity with bilateral flow boundary conditions

The melting of phase change material (PCM) in a rectangular cavity with heat transfer fluids (HTFs) flowing at both sides from bottom up (bilateral flow boundary conditions) are numerically studied. A parametric study is performed by changing the Reynolds number (Re) of HTF in a range of 1 × 104, 3 × 104, 5 × 104, 7 × 104 and the Rayleigh number (Ra) in a range of 3 × 106, 4 × 106, 5 × 106, 6 × 106. The results show that the formation of natural convection is due to the impacts of non-uniform heat transfer of HTF and cooling between solid-liquid interface and liquid PCM. The asymmetric flow boundaries lead to various skew forms of the PCM melting process and effect the heat transfer and thermal energy storage. The melting process can be divided into three melting stages, the first two stages are mainly ruled by Re and the last stage by Ra. A set of introduced dimensionless parameters are analyzed to elaborate the heat transfer mechanism and the general rule of melting characteristics. The various dimensionless correlations are applied to describe the evolution of melting volume fraction, dimensionless average temperature and thermal energy storage fraction during the melting process.

Dimensionless Model of Frost Roughness on Cold Flat Plate Under Forced Convection

Laboratory experiments were conducted to generate empirical dimensionless correlations for estimating surface roughness of frost formed on a cold flat plate under forced convection. Environmental variables, including wall temperature , air velocity , relative humidity , and air temperature , were considered when generating the correlations. The test conditions were chosen to simulate the environmental conditions experienced by cold-soaked fuel frost formation on the upper surface of airplane wings. Experimental conditions included wall temperatures from to , freestream temperatures from 8 to , relative humidities from 60 to 91%, and air velocities from 0.5 to . The root-mean-square height, skewness, and equivalent sand-grain roughness height of frost were correlated as functions of the Reynolds number, absolute humidity, and dimensionless temperatures. The comparison between the correlation of frost equivalent sand-grain roughness height in this study and a previous model revealed the importance of test surface geometry on frost roughness formation.

A novel spiral channel with the growing waviness on the sidewalls for compact high-efficiency heat exchanger

Spiral channels are widely used as the core heat exchangers in latent thermal storage units. This study aims to develop a novel spiral channel characterized by wavy sidewalls for high-efficiency convective heat transfer in tube side. The amplitude of the wavy sidewalls is designed to grow from the inlet to the outlet along flow direction. The thermal characteristics in the spiral-wavy channel were numerically investigated under the boundary condition of constant wall temperature, since latent heat storage units mainly work under isothermal condition. The comparison was carried out between a smooth-spiral channel and a spiral-wavy channel in terms of the heat transfer capacity, friction factor, dimensionless temperature distributions and development of boundary layers. At a given heat transfer rate, the required length of the spiral-wavy channel is only 63.5% of that of the smooth-spiral channel, which implies that the energy density and efficiency of a heat storage unit can be improved remarkably. The increase in pressure drop brought by the spiral-wave channel is less important compared with the improvement of thermal performance, suggesting its potential in heat transfer enhancement and energy saving. The present work is expected to motivate the design of compact and high-efficiency heat exchangers for thermal energy storage and extraction.

Two-and-three-dimensional analysis of Joule and viscous heating effects on MHD nanofluid forced convection in microchannels

This paper aims to study viscous heating, Joule heating and their simultaneous impacts on Al2O3-water nanofluid laminar flow and thermal characteristics in the presence of a magnetic field inside microchannels. The flow field and heat transfer are modeled two- and three-dimensionally by employing the finite volume method. To investigate the influence of viscosity variation with temperature on viscous heating, a temperature-dependent viscosity correlation specifically presented for Al2O3-water is employed. Predicted results indicate that viscosity changes due to temperature changes are negligible and although viscous heating can be reasonably ignored in the absence of the magnetic field, it must be taken into account when the magnetic field is applied. At the Hartmann number of 20, near microchannel walls, the velocity gradient rises up to 165% where the viscous dissipation significantly increases the temperature. In addition, when the magnetic field is applied, the 2D model underestimates the temperature compared to the 3D model where the effects of maximum velocity and velocity gradient on the energy equation and heat dissipation exist. The temperature profiles demonstrate that at the Hartmann number of 20, the effects of Joule heating or viscous heating increase the maximum dimensionless temperature by a factor of about 2.5 and by the rise of the Hartmann number, the dimensionless temperature increases and the effects of Joule and viscous heating become more significant. All in all, it is concluded that the heat generated by viscous and Joule heating can remarkably decrease the cooling performance of microchannels in the presence of magnetic fields.

Chebyshev collocation-optimization method for studying the Powell–Eyring fluid flow with fractional derivatives in the presence of thermal radiation

In this work, a mathematical model of the fractional-order in non-Newtonian Powell–Eyring fluid flow (PEFF) and heat transfer is presented and solved numerically. The set of nonlinear differential equations in terms of velocity, temperature which describes our proposed problem is tackled through the spectral collocation method based on Chebyshev polynomials of the third kind. This method reduces the presented model to a nonlinear system of algebraic equations. This system is constructed as a constrained optimization problem and optimized to get the unknown coefficients of the series solution. The effects of the thermal radiation, Powell–Eyring parameters; suction parameter and Prandtl number on the PEFF are discussed. The numerical values of the dimensionless velocity and temperature are depicted graphically. The results show that the given procedure is an easy and efficient tool to investigate the solution of such models. Some of findings of this important work help to govern the velocity and the rate of heat transportation through the boundary layer. At the same time, this study highlights many applications in fields of engineering and industry, where the quality of the desired product depends on the rate of heat transfer, thermal radiation phenomenon, and the composition of the material used, and manufacturing processes.

On the stability of the isoflux Darcy–Bénard problem with a generalised basic state

The scope of this study is to determine the conditions for the onset of the instability in a horizontal porous layer subject to isoflux boundary conditions and with an infinitely wide single–cell basic flow. When the circulation in the basic cellular flow is absent, one recovers the usual Darcy–Bénard conduction basic state. The governing parameters are the Rayleigh number associated with the uniform wall heat flux, and the dimensionless horizontal temperature gradient. The latter parameter controls the magnitude of the basic cellular circulation flow in the horizontal direction. The modal analysis of the instability is carried out numerically by employing a pseudo–spectral method, as well as the shooting method for the solution of the stability eigenvalue problem. Neutral stability and the critical conditions for the onset of the convective instability of the basic state are investigated.

Theoretical Study of Mixed Convection Cooling of Microprocessor Using CuO Nanofluid. (Dept. M)

Cooling of electronic equipments is playing an important role in the last decades as a world experiences a technological boom in all fields. In this study, a numerical study for mixed convection cooling of microprocessor is investigated by the use of pure water and CuO-water nanofluid at six different volume concentrations. The model is built, meshed and simulated by Ansys Fluent Package 16.0 and a mesh independence test is carried out. The study is performed by changing heat load (115W, 130W), inlet velocity, at different concentrations of nanofluids (Pure water, 0.5%, 0.86%, 1.5%, 2.25%, 3.5%, 5%). The present results showed that using CuO-water nanofluids over pure water provides an enhancement in heat transfer characteristics. The dimensionless parameters such as Nusselt number, Archimedes number, Prandtl number, friction factor and dimensionless temperature are studied and correlated. An enhancement of 36.5% in thermal hydraulic performance is found at 0.50% volume fraction at Re = 1679.212. The data are correlated with maximum error of 4.1%.

Non-similarity solutions of radiative stagnation point flow of a hybrid nanofluid through a yawed cylinder with mixed convection

In this new-fangled research, the mixed convective stagnation point flow of a hybrid nanofluid over a yawed cylinder with radiation impact is considered. In reality, the perception of mixed convection in the study of yawed cylinder rises in heat exchangers. To explore the heat diffusion through the system of mixed convection, the mathematical problem is formed in the form of partial differential equations which are coupled and nonlinear. A solution technique is applied and described for indulgencing non-similar thermal boundary layers. The non-similar terms involving in the transformed equations are held without approximations. The non-similar equations are solved numerically using the bvp4c technique. The exploration divulges numerous significant results involving yaw angle, hybrid nanoparticle volume fraction, mixed convection, radiation, and non-similarity phenomena. The impact of the yaw angle in enhancing the velocity of the hybrid nanofluid in the span-wise and chord-wise directions in the aiding buoyancy flow and decelerating in the opposing flow, while the contrary behavior is noticed for the dimensionless temperature profile. Also, the hybrid nanoparticles reduce the velocity in both directions in case of assisting as well as opposing flow, whereas the dimensionless temperature augments.

Impacts of Uniform Magnetic Field and Internal Heated Vertical Plate on Ferrofluid Free Convection and Entropy Generation in a Square Chamber.

The heat transfer enhancement and fluid flow control in engineering systems can be achieved by addition of ferric oxide nanoparticles of small concentration under magnetic impact. To increase the technical system life cycle, the entropy generation minimization technique can be employed. The present research deals with numerical simulation of magnetohydrodynamic thermal convection and entropy production in a ferrofluid chamber under the impact of an internal vertical hot sheet. The formulated governing equations have been worked out by the in-house program based on the finite volume technique. Influence of the Hartmann number, Lorentz force tilted angle, nanoadditives concentration, dimensionless temperature difference, and non-uniform heating parameter on circulation structures, temperature patterns, and entropy production has been scrutinized. It has been revealed that a transition from the isothermal plate to the non-uniformly warmed sheet illustrates a rise of the average entropy generation rate, while the average Nusselt number can be decreased weakly. A diminution of the mean entropy production strength can be achieved by an optimal selection of the Lorentz force tilted angle.

Thermal explosion of a reactive gas mixture at constant pressure for non-uniform and uniform temperature systems

In this study, the approximate and exact solutions for the stationary-state of the solids model with neglecting reactant consumption for both non-uniform and uniform temperature systems were applied on gas ignition under a constant pressure condition. The criticality conditions for a slab, an infinite cylinder, and a sphere are determined and discussed using dimensionless temperatures under constant ambient and surface temperatures for a non-uniform temperature system. Exact solution for a Semenov model with convection heat loss was also presented. The solution of the Semenov problem for constant volume or density as a solid and constant pressure were compared. The critical parameter δ is calculated and compared with those of Frank-Kamenetskii solution values. The validation of the calculated ignition temperatures with other exact solution and experimental results were offered. The relation between critical parameters form Semenov and F.K. models solution was introduced.

Mixed Convection of a Radiating Magnetic Nanofluid past a Heated Permeable Stretching/Shrinking Sheet in a Porous Medium

This paper analyzes the collective effects of buoyancy force, thermal radiation, convective heating, and magnetic field on stagnation point flow of an electrically conducting nanofluid past a permeable stretching/shrinking sheet in a porous medium. Similarity transformations are used on the resulting nonlinear partial differential equations to transfer into a system of coupled nonlinear ordinary differential equations. The fourth-fifth-order Runge–Kutta–Fehlberg method with shooting technique is applied to solve numerically. Results are obtained for dimensionless velocity, temperature, and nanoparticle volume fraction as well as the skin friction and local Nusselt and Sherwood numbers. The results indicate the existence of two real solutions for the shrinking sheet in the range of λ c < λ < 0 . The fluid flow stability is maintained by increasing the magnetic field effect, whereas the porous medium parameter inflates the flow stability. It is also noted that both the skin friction coefficient and the local Sherwood number approximately decline with the intensification of thermal radiation within the range from 9.83% to 14% and the range from 48.86% to 78.66%, respectively. It is also evident in the present work that the local Nusselt number upsurges with the porous and suction/injection parameters.

Nonlinear Mixed Convective Flow over a Moving Yawed Cylinder Driven by Buoyancy

The fluid flow over a yawed cylinder is useful in understanding practical significance for undersea applications, for example, managing transference and/or separation of the boundary layer above submerged blocks and in suppressing recirculating bubbles. The present analysis examines nonlinear mixed convection flow past a moving yawed cylinder with diffusion of liquid hydrogen. The coupled nonlinear control relations and the border restrictions pertinent to the present flow problem are nondimensionalized by using nonsimilar reduction. Further, implicit finite difference schemes and Quasilinearization methods are employed to solve the nondimensional governing equations. Impact of several nondimensional parameters of the analysis on the dimensionless velocity, temperature and species concentration patterns and also on Nusselt number, Sherwood number and friction parameter defined at the cylinder shell is analyzed through numerical results presented in various graphs. Velocity profiles can be enhanced, and the coefficients of friction at the surface can be reduced, for increasing values of velocity ratio parameters along chordwise as well as spanwise directions. Species concentration profile is reduced, while the Sherwood number is enhanced, for growth of the Schmidt number and yaw angles. Furthermore, for an increasing value of yaw angle, skin-friction coefficient in chordwise direction diminishes in opposing buoyancy flow case, whereas the results exhibit the opposite trend in assisting buoyancy flow case. Moreover, very importantly, for increasing magnitude of nonlinear convection characteristic, the liquid velocity and surface friction enhance in spanwise direction. Further, for increasing magnitude of combined convection characteristics, velocity profiles and coefficient of friction at the surface enhance in both spanwise and chordwise directions. Moreover, we have observed that there is no deviation for zero yaw angle in Nusselt number and Sherwood number.

Consequence of Modified Boundary Condition On Natural Convection in a Porous Medium Saturated by Nanofluid – A Computational Approach

In the present numerical simulation, steady, laminar, two-dimensional flow in a porous medium saturated by nanofluid [1] along an isothermal vertical plate is presented. Here we have studied a more realistic situation where the nanoparticle volume fraction at the plate (boundary condition) is passively controlled by assuming that its flux there is zero. We employ Boungiorno model [2] that treats the nanofluid as a two-component mixture, incorporating the effects of Brownian motion and thermophoresis. Darcy model is utilized for the presence of porous medium. With the help of appropriate similarity variables, the governing nonlinear partial differential equations of flow are changed to a bunch of nonlinear ordinary differential equations. Afterwards, they are reduced to a first order system and integrated using Newton Raphson and adaptive Runge-Kutta methods. The computer codes are developed for this numerical analysis in Matlab environment. Dimensionless stream function (s), longitudinal velocity (s’), temperature (θ) and nanoparticle volume fraction (f) are figured and outlined graphically for various values of four dimensionless parameters, namely, Lewis number (Le), buoyancy-ratio parameter (Nr), Brownian motion Parameter (Nb), and thermophoresis parameter (Nt). The dependence of the reduced Nusselt number on these parameters is illustrated.

Heat Transfer at a Particle‐Tube Wall Contact Point: Impact of Catalyst Configuration on Hot Spots

AbstractHot spots tend to cause serious problems owing to probable damages to the reactor wall in intense endothermic reactions leading to safety concerns and enormous repairing costs. The heat transfer of a single cylindrical particle is studied empirically and numerically to evaluate hot spot creation close to the bed wall. Computational fluid dynamcis (CFD) methodology is used to solve the momentum, continuity, and energy equations simultaneously. The newly developed experimental method is applied to validate simulation data using the Chilton‐Colburn analogy. The particle rotation over the X, Y, and Z axes is studied and analysis of variance (ANOVA) is employed to statistically investigate the particle rotation effects on the dimensionless maximum temperature of the reactor wall.

Experimental study on the thermal performance of a novel physically separated chilled water storage tank

Naturally stratified chilled-water storage is widely used to offset the peak electrical demand caused by air-conditioning, but the mixing between cold and warm water greatly influences its thermal performance, especially for a low aspect ratio tank. In this study, a novel physically separated chilled water storage tank is proposed to take place traditional membrane tanks. The thermal performance of this novel tank is evaluated by static and dynamic experiments. The temperature distribution, outlet temperature, figure of merit (FOM1/2/FOM), and percent cold recoverable (PCR) are analyzed when the cold water temperature is approximately 2 °C and 4 °C, and the temperature difference ranges from 7.91 to 13.86 °C. The results demonstrate the excellent thermal performance of the novel tank under a large temperature difference. Compared with conventional temperature conditions, the stability of the outlet temperature under low-temperature conditions is better during the discharging process with the dimensionless temperature increasing by 10% at the end of the process. The full-cycle FOM increases significantly and the PCR decreases slightly with increasing temperature difference. When the FOM reaches its maximum of 93.2%, the PCR exceeds 91%. Therefore, this research work exhibits great application potential of this novel tank due to its ability to improve the thermal performance for a low aspect ratio tank, which provides a new direction for chilled water storage tank design.

Enhancement of Heat Transfer for Electronic Components in Horizontal Channel by Passive Cooling.(Dept.M)

In this study, numerical investigation on heat transfer by mixed convection for air-cooling through a rectangular horizontal duct with three heat sources is conducted. These heat sources are rectangular ribs with different small aspect ratios and every heat source emits uniform heat flux with small space between each other. The investigation is to enhance forced convection that produced from fan through a rectangular horizontal duct with natural convection using perforated holes between each heat source. The study shows the effect of air entering through the holes at different open hole ratio β (0.01472, 0.02618, 0.04091, 0.05891, 0.08017) and with Reynolds number Re in the range (376, 900, 2073, 3428 and 6170) and at Grashof number Gr = 0.371 x 107 on the temperature of each heat source. The results show the best performance at open hole ratio 0.04091 for which the dimensionless temperature decreased by 5% for the first heater, 15% for the second one and 6% for the third one.

The Effect of Fin Length on Free Convection Heat Transfer in Annular Space of Concentric Arrangement Using Shear-Thinning Fluids as a Thermal Medium

The two-dimensional steady-state natural convection of shear-thinning fluids is studied numerically between two concentric horizontal cylinders with different constant temperatures. The inner cylinder was put eccentrically into the outer one. The inner cylinder are held at constant temperatures with the inner one heated isothermally at temperature (Th) and the outer cylinder have one fin cooled isothermally at temperature Tc (Th > Tc). The simulations have been taken for the parameters 102 ≤ Ra ≤ 104, = 0.71 ≤ Pr ≤ 10 and 0.6 ≤ n ≤1.The effects of Rayleigh number and Prandtl number on the dimensionless velocity and temperature are investigated for both shear-thinning and Newtonian fluids. Also the mean Nusselt number for various values of governing parameters is obtained and discussed. Although huge researches were conducted for natural convection in non-circular enclosures, researches for annular enclosures are very limited, especially finned enclosures. The length of the fin is also studied. The results show that increase in the length of fin increases the effectiveness of heat transfer. Also, the increase in Ra number increases the heat transfer effectiveness.