Non-uniform Heat Research Articles

Performance Evaluation of an Absorber Tube of a Parabolic Trough Collector Fitted with Helical Screw Tape Inserts Using CuO/Industrial-Oil Nanofluid: A Computational Study

Improvement of the performance of renewable energy harvesters is a crucial and complicated task. Among currently utilized renewable energy harvesters, parabolic solar collectors are some of the most promising and widely used apparatuses. However, researchers are still facing some issues regarding the optimization of PTC performance, including the enhancement of heat flux absorption by the absorber tubes. Among the proposed methods to overcome this drawback, the implementation of helical screw tape (HST) and nanofluids has proven to be most effective. In the present study, the CFD simulation of an absorber tube with HST is conducted. CuO/oil nanofluid with a nanoparticle volume fraction of 1 to 3% was chosen as the working fluid. The simulation is based on the realistic operational condition of a PTC absorber tube with corresponding nonuniform solar heat flux based on the local concentration ratio. The effects of the mass flow rate (Re), HST width and nanofluid volume fraction on pumping power and heat transfer are studied. Moreover, to combine the effect of both parameters, the performance evaluation criterion (PEC), a dimensionless variable, is calculated for all of the studied cases. Enhancement of the PEC parameter by the implementation of nanofluid and HST in comparison to base fluid passing through a plain tube is also determined and reported. According to the obtained results, with the implementation of the CuO/oil nanofluid, the PEC can be enhanced by 57.3–70.8, 68.7~86.4, and 83.4~105.9% for volume fractions of 1, 2, and 3%, respectively.

Numerical Investigation of the Two-Phase Closed Thermosyphon Operating with Non-Uniform Heat Flux Profiles

The two-phase closed thermosyphon (TPCT) or wickless heat pipe has been widely considered as an extremely effective and low-cost heat removal device for various applications. A computational fluid dynamics (CFD) investigation of the TPCT can provide detailed information regarding its design and development. In this study, the effect of non-uniform heat-input profiles on a vertical TPCT has been investigated. A CFD model has been built to simulate the evaporation and condensation processes within the TPCT investigated, using a solver based on OpenFOAM which has been modified and validated against experimental data reported in the open literature. Four non-uniform heating profiles of the TPCT have been investigated, and the effects these have on the internal flow field within the pipe are discussed. Simulation results show that the non-uniform heat flux profiles can impact thermal performance depending on the overall heat loading and the heat flux profile.

Significance of radiation and chemical reaction on MHD heat transfer nanofluid flow over a nonlinearly porous stretching sheet with nonuniform heat source

This article discusses the thermal radiation significance on the 2-D laminar MHD boundary layer flow of a nanofluid, as well as the heat transfer associated with the viscous flow across a nonlinear stretching surface. The flow is produced by a nonlinearly enlarging sheet with varying temperatures in the existence of suction, radiation, and viscous dissipation. By applying suitable similarity conversions, the resultant governed PDEs are transformed to a set of nonlinear ODE’s, and then, they are solved by applying the Keller–Box approach numerically. The impact of several flow pertinent factors on heat, species concentration, and velocity fields are exposed graphically and numerically. Numerical calculations for friction factor, mass, and heat transmission rates are discussed in table form. Prior results were examined under constraining circumstances and found to be adequate. It is discovered that when the velocity slip factor is enhanced, the fluid velocity distribution declines whereas the heat and concentration gradients increase. The principal results indicate that the porosity parameter effectively decreases the velocity distribution.

MHD micro polar fluid flow over a stretching surface with melting and slip effect

Objective of the present analysis is to represent the phenomenon of Heat–mass transfer on MHD micro polar fluids caused by permeable and continuously stretching sheet along with slip impacts fostered in a porous medium. Consequently, the equation of energy includes the term of non-uniform heat source/sink. The equation regarding species concentration in cooperates the terms indicating order of chemical reaction to characterize the chemically reactive species. The application software MATLAB with governing syntax of bvp4c technique are employed to reduce equations of momentum, micro-rations, heat, and concentration into suitable required simplifications to derive necessary arithmetic manipulations of available non-linear equations. Various dimensionless parameters are portrayed in the available graphs with essential consequences. Analysis discovered that micro-polar fluid improves velocity and temperature profile while it suppresses micro-rations profile also magnetic parameter (M) and porosity parameter (K_p) reduces the momentum boundary layer thickness. The acquired deductions verify remarkable correspondence with already reported in an open literature.

Magnetohydrodynamic micropolar slip flow due to an exponentially stretching sheet with chemical reaction and nonuniform heat generation

AbstractThe main focus of the current study is to examine the impact of melting heat transfer and chemical reaction on magnetohydrodynamic micropolar fluid flow over a sheet that is exponentially stretching and immersed in a porous medium. A nonuniform heat source is placed within this flow system. Other impacts like slip phenomena and thermal radiation are also taken into consideration. The governing partial differential equations are converted to a system of ordinary differential equations (ODEs) via similarity transformation and we also get the corresponding necessary boundary conditions. These nonlinear ODEs are resolved with the help of shooting technique and an Runge‐Kutta fourth order (RK‐4) iterative strategy. Also, we solve this problem using the Bvp4c approach for validating the results of the RK‐4 method. Both outcomes are consistent with previously published data. With the help of tables and graphs, we examine the influence of multiple physical parameters on velocity, thermal, microrotation, concentration, Nusselt number, Sherwood number, coefficient of skin friction, and wall couple stress. We see that the temperature distribution and velocity profiles decrease when the melting parameter increases. The temperature profile boosts when the heat source parameter is increased.

About One Mechanism of Controlling the Movement of Magnetic Particles by a Magnetic Field in a Nonuniformly Heated Liquid

About One Mechanism of Controlling the Movement of Magnetic Particles by a Magnetic Field in a Nonuniformly Heated Liquid

Effect of nonlinear thermal radiation on second order slip flow and heat transfer of Jeffrey nanofluid over a stretching sheet with non-uniform heat source/sink

The flow and heat transfer of Jeffrey nanofluid over a stretching sheet with non-uniform heat source/sink is considered in the present analysis. Effects of nonlinear thermal radiation and second order slip are taken along with uniform magnetic field. System of partial differential equations governing the described problem is reduced to nonlinear ordinary differential equations with aid of similarity transformations. Further, reduced equations are solved numerically using Runge-Kutta-Fehlberg 45 order method with shooting technique. Effects all flow pertinent parameters are recorded in terms of tables and graphs. The results are studied with help of plotted graphs, tables. Results are compared with existing one for some limiting cases and are found to be excellent agreement. It is found that both first, second order velocity slip parameters reduces the thickness of momentum boundary layer and hence decrease the velocity as a result of this one can find the increase in thermal boundary layer.

Entropy analysis of unsteady MHD nanofluid flow over a stretching surface with effects of variable viscosity and nonuniform heat generation

An unsteady two-dimensional nanofluid flow across a permeable stretched sheet is examined in terms of thermodynamic analysis. Water is utilized as the basic fluid, together with four distinct types of nanoparticles: copper (Cu), copper oxide (CuO), aluminum oxide (Al2O3), and titanium dioxide (TiO2). An external source is used to describe the heat transfer phenomena. The effects of heat generation and absorption are also taken into account. The nonlinear partial differential equations are transformed into a system of nonlinear ordinary differential equations via a similarity transformation. The spectral quasi-linearization approach is then used to numerically integrate the altered equations. Except when otherwise noted, the findings are provided for copper nanoparticle situations. A visual and detailed explanation of the effects of several physical factors on the profiles of dimensionless velocity, temperature, average entropy generation function, skin friction, and the Nusselt number are discussed. As exceptional circumstances of the current findings, there is a strong agreement between the current conclusion and the findings of the other researchers. The average entropy generation number, temperature, and velocity profiles are shown to be strongly influenced by regulating factors. It is concluded that the average entropy generation decreased in the presence of a temperature- and space-dependent heat source/sink, but it improves with enhanced viscosity parameter. The significance of the present study has frequent applications in the major area of heat transfer enhancement in renewable energy systems, industrial thermal management, and also materials processing.

Transient temperature distribution in a multilayer semiconductor device with dynamic thermal load and non-uniform thermal contact resistance between layers

The thermal management challenge in microelectronic chips is exacerbated by their multilayer architecture and manufacturing processes that introduce non-uniform thermal contact resistance between adjacent layers. Most of the past work on development of thermal models to predict temperature distribution in microelectronic chips either does not account for such thermal contact resistance at all, or simply assumes it to be spatially uniform. This work presents an exact analytical solution for the transient temperature distribution in a multilayer chip with non-uniform thermal contact resistance between layers as well as dynamic, non-uniform heat generation. The problem is solved by first carrying out a Laplace transformation and then implementing a series solution, the coefficients of which are determined by solving a set of algebraic equations derived from the non-uniform thermal contact resistances between adjacent layers. While the problem is solved for a general M-layered chip, the solution for the practical case of a two-layer chip is also provided. Results indicate that the temperature distribution and its evolution over time is determined by the nature of the non-linear thermal contact resistance, and its overlap with the dynamic heat loads imposed on the chip. The impact of these and other relevant parameters is examined in detail. Results presented here improve the fundamental understanding of thermal transport modeling in multilayer semiconductor chips, with possible applications in other multilayer engineering systems as well.

An experimental inverse problem in determining spatially varying surface heat flux using measured temperature readings

An experimental investigation to estimate the unknown spatially dependent surface heat flux of a flat plate based on the surface temperature readings taken by a thermography camera and the conjugate gradient method (CGM) is examined in this study. In the present three-dimensional inverse problem, the functional form of the heat flux is considered to be initially unknown; thus, the functional form of the heat flux is classified as the category of function estimation. In addition, air velocity is specified as the working condition, not the heat transfer coefficient; therefore, it is defined as an inverse heat conduction-convection conjugated problem (IHCCCP). The experimental study for estimating the unknown spatially dependent surface heat flux has not been examined previously in the IHCCCP. The estimations of the inverse solutions are conducted experimentally with two designed plate heaters and various inlet air velocities and plate thicknesses, and the total heat losses are found to be approximately 5% of the original design heating power. The experimental results indicated that for a uniform heating design (Design A), the estimated heat fluxes are always very accurate if the heat losses are deducted from the design power. For the nonuniform heating design (Design B), due to the existence of two discontinuities in the heating power, the estimated relative errors for heat fluxes are found to be between 16% and 18% using 6 to 8 iterations, reflecting the nature of the inverse problem, i.e., a small measurement error will amplify the error of the estimates; in addition, the estimated heat flux becomes less accurate as the plate thickness increases. Finally, numerical simulations with errorless measurements are performed, and the results reveal that the estimated errors for heat fluxes can be decreased to approximately 8% with 150 iterations for Design B.

Investigations on boiling heat transfer characteristics in non-uniform heating U-Tube bundles under rolling motion

The development of the marine environment necessitates more rapid development of marine nuclear power plants, and the U-tube bundle heat exchangers, which exist in marine nuclear power plants, play a significant role in safety and economy. However, the radial non-uniform heating (NUH) brought on by the specific structure of the U-tube complicates the boiling heat transfer characteristics. Additionally, the environment of ocean rolling motion superimposed with NUH makes heat transfer more complex. The paper analyzes the time-averaged and transient heat transfer performance by contrasting the rolling UH experiments and rolling NUH experiments. The result demonstrates that the addition of NUH causes no impact on the influenced degree of rolling motion on the time-averaged temperature characteristics, which means a weakly coupled action of NUH and rolling motion. Based on the independence principle, considering the influencing factor of rolling motion and NUH, the developed correlation for calculating time-averaged heat transfer coefficient (HTC) can capture 96.67% of the experimental data within 15% of the error line, and the average absolute error is about 5.75%. For instantaneous fluctuated characteristics, the addition of NUH has a greater impact on the fluctuated range of water temperature than that of the wall temperature, and the fluctuation introduced by rolling motion is displayed based on the effect of NUH. Besides, the calculating method for determining the HTC fluctuation amplitude under uniform heating and rolling motion conditions also applies to situations in which NUH and rolling motion coexist, and the mean absolute error is around 13.80%, indicating that the coupled action of NUH and rolling motion is less obvious in forced circulation. The fluctuation amplitude of HTC depends more on the thermal parameters and rolling parameters. Finally, a novel computational logic approach was created and proposed to estimate transient HTC under conditions for NUH and rolling motion, which can anticipate the fluctuated amplitude and period of instantaneous HTC under corresponding conditions.

Topologically optimized mini-channel heat sinks for reduced temperature non-uniformity

Water-cooled mini-channel heat sinks are widely used for thermal management of electronic devices, but their flow paths are usually limited to simple designs, such as parallel channels, due to manufacturing limitations. Such designs do not distribute flow uniformly, resulting in non-uniform heat transfer across the heat sink and significant temperature gradients. A liquid-cooled heat sink with a millimeter high flow channel was designed and fabricated to cool an 86 mm x 63 mm uniformly distributed heat load. A density-based topology optimization model was implemented in COMSOL to generate a non-traditional internal geometry that minimizes temperature non-uniformity. The topologically optimized heat sink was made using a novel thermal spray additive manufacturing method in which molten aluminum was sprayed into a cavity machined in an aluminum plate through a polymer mask made in the shape of the desired flow channels by 3D printing. The cavity was closed with an aluminum plate to create a sealed heat sink. The thermal performance of the topologically optimized heat sink was compared experimentally to that of a heat sink with parallel channels. Each heat sink was placed on a uniformly heated copper block dissipating 180 – 630 W (corresponding to heat fluxes of 3.3 – 11.6 W/cm2) and its temperature measured by an array of 9 thermocouples embedded in the heated heat sink face while water flowed through it at rates of 100–1500 mL/min. The optimized heat sink maintained lower surface temperatures and reduced temperature non-uniformity on its surface at all flow rates tested. Numerical simulations demonstrated that this was due to better flow distribution by the topologically optimized flow channels.

Soret and Dufour effects on MHD mixed convection flow of Casson hybrid nanofluid over a permeable stretching sheet

The use of hybrid nanofluids can improve the engine operation and fuel efficiency in automotive engineering, as well as the efficiency of cooling systems used in food processing and preservation. This study provides insight for the development of efficient heat exchangers, thermal energy storage systems and cooling systems for various industrial applications, which can improve product quality and safety. The study aims to investigate the Soret and Dufour effects in hybrid nanofluid flow, with the goal of understanding their behaviour and potential applications in various industries. The flow is over a vertically stretched permeable sheet with porous material under convective boundary conditions and a non-uniform heat source/sink. The reduced governing equations are represented by non-linear-coupled ordinary differential equations solved by means of the shooting method based on the fourth-order Runge–Kutta method. Enhancing the Casson parameter reduces the fluid velocity while enhancing the mass and thermal Grashof numbers increases the flow velocity. The Soret and Dufour effects improve temperature and concentration, and a higher Biot number increases the temperature. The novelty of this investigation lies in its incorporation of Soret and Dufour effects, porosity, heat source/sink and a more refined definition of nanoflow, which is compared to previous results.

Significance of Navier’s slip and Arrhenius energy function in MHD flow of Casson nanofluid over a Riga plate with thermal radiation and nonuniform heat source

Riga plate is known to create a crossing electric and magnetic field to generate a wall-parallel Lorentz force. The significance of Casson nanofluid flow past a Riga plate is observed in the sphere of engineering, such as polymer extrusion, food manufacturing, plastic films, oil reserves and geothermal manufacturing. Researchers are interested in this model because of its potential use in biological rheological models. As Casson nanofluid flows are of great interest, this study aims to investigate the three-dimensional magnetohydrodynamics (MHD) flow with heat and mass transport of Casson nanofluid over a flat Riga plate. As a novelty, this study also includes the effectiveness of wall velocity slip, activation energy, nonlinear radiation, and temperature and space-dependent heat source/sink. Suitable similarity transformations have been employed to generate the dimensionless ordinary differential equations (ODEs) from the partial differential equations (PDEs) regulating the fluid flow problem. The transformed nonlinear boundary value problem is then solved numerically using the in-built routine “bvp4c” in MATLAB. The visual demonstrations are provided for the effects of various significant physical factors on the flow, heat and mass distributions. On the other hand, wall shear stress and rates of heat and mass transport at the surface are measured and displayed numerically in tabular form. The findings indicate that the fluid velocity in both directions slows as the velocity slip parameter increases. However, the velocity profile is escalated with the boost of modified Hartmann number. An increase in heat source parameters leads to decrease the heat transmission rate at the wall. The higher values of the radiation parameter result in a better wall heat transmission rate. Further, the rate of mass transport drops when the activation energy parameter is hiked.

Heat Transfer and Flow Structure Characteristics of Regenerative Cooling in a Rectangular Channel Using Supercritical CO2

At an extremely high Mach number, the regenerative cooling of traditional kerosene cannot meet the requirement of the heat sink caused by aerodynamic heating and internal combustion in a scramjet propulsion system. As a supplement of traditional regenerative cooling, supercritical CO2 is regarded as an effective coolant in severe heating environments due to its excellent properties of heat and mass transportation. In this paper, the heat transfer and flow structure characteristics of regenerative cooling in a rectangular channel using supercritical CO2 are analyzed numerically using a validated model. The effect of heat flux magnitude, nonuniform heat flux, acceleration and buoyancy and flow pattern are considered to reveal the regenerative cooling mechanism of supercritical CO2 in the engine condition of a scramjet. The results indicate that the heat transfer deterioration phenomenon becomes obvious in the cooling channel loaded with relatively high heat flux. Compared with the cooling channels loaded with increased heat flux distribution, the maximum temperature increased for the channel loaded with decreased heat flux distributions. When larger acceleration is applied, a relatively lower wall temperature distribution and higher heat transfer coefficients are obtained. The wall temperature distribution becomes more uniform and the high-temperature region is weakened when the coolants in adjacent channels are arranged as a reversed flow pattern. Overall, the paper provides some references for the utilization of supercritical CO2 in regenerative cooling at an extremely high Mach number in a scramjet.

Impacts of variable viscosity and chemical reaction on Ohmic dissipative fluid flow in a porous medium over a stretching sheet with thermal radiation

AbstractThis study investigates the chemical reaction influence on heat transfer flow of viscous Newtonian fluid over a moving surface under the intensity of nonuniform heat source/sink. Variable fluid viscosity and ohmic heating effects are considered in the model equation. The uniqueness of the present investigation is to scrutinize the significance of nonuniform heat source/sink and ohmic heating on the heat transfer flow of optically thin radiative fluid in a permeable medium. The flow equations of continuity, momentum, thermal and solutal fields are converted by invoking relevant dimensionless variables. Also, the converted nonlinear equations are analyzed numerically by using the fourth order Runge–Kutta Fehlberg approach. The significance of model parameters are scrutinized and discussed in detail via graphs and tables. The important findings of this study are the effects of Joule heating , viscous dissipation parameter , variable fluid property parameter and radiation parameter on fluid flow, energy profile and solutal field. The results show that the thermal field depreciates as the Prandtl number increases but escalates against higher values of Joule heating parameter and Brinkman number. Also, the outcome of this study reveals that an enhancement in the values of variable viscosity parameter declines velocity distribution. Concentration distributions behave as a growing function of the Soret number and diminishing function of the Schmidt number. Furthermore, contrasting this study with existing results reveals excellent agreement.

Experimental study on friction pressure drop and circumferential heat transfer characteristics in helical tubes

Helical tubes are widely used in nuclear plants, heat recovery process, and refrigeration technology. The fluid is influenced by centrifugal force flow through the helical tube, accompanied by secondary flow which is conducive to the enhancement of heat transfer. However, the uneven circumferential heat transfer caused by the secondary flow was seldom reported, while the pressure drops and heat transfer characteristics of helical tubes under single-phase and two-phase flow conditions need to be supplemented. This paper investigated the friction pressure drop and circumferential heat transfer characteristics based on the experiments on helical tubes with the coil diameter to the tube diameter varying from 28.5 to 128.5 and lift angle varying from 3° to 10°. The results showed that the coil diameter was the key parameter affecting the pressure drop and non-uniform circumferential heat transfer, compared with the lift angle. At the same cross section, the heat transfer coefficient at the outside tube wall was the highest, which was more obvious under small coil diameter conditions. Correlations of flow resistance and heat transfer were proposed for the single-phase and saturated boiling two-phase flow, respectively, and the predicted values were improved compared with the prediction results of correlations in the existing literature.

Heat transfer and hydraulics for a novel receiver pipe of solar parabolic trough: a computational approach.

The effect of symmetrical convex-concave corrugations on receiver pipe of a parabolic trough solar collector is numerically investigated. Twelve distinct geometrically configured receiver pipes with corrugations have been examined for this purpose. The computational study is conducted for varying corrugation pitch (4mm to 10mm) and height (1.5mm to 2.5mm). Heat transfer enhancement, flow behavior, and overall thermal performance of fluid moving through a pipe under non-uniform heat flux condition are all determined in this work. The Reynolds number ranges from 5000 to 50,000. The findings reveal that presence of corrugations leads to axial whirling and vortices in the receiver pipe, thus enhancing the heat transfer. The receiver pipe having corrugations of 8mm pitch and 2mm height gave the best results. The maximum enhancement in average Nusselt number over smooth pipe has been observed as 28.51%. In addition, relationships of Nusselt number and friction factor against selected design parameters and operating conditions are also displayed as correlations.

Numerical study of axisymmetric hybrid nanofluid MgO-Ag/H2O flow with non-uniform heat source/sink

The physical strength, mechanical resistance, chemical stability, thermal conductivity, and other properties of hybrid nanoparticles are more satisfactory than those of individual nanofluids. The thermal performance of hybrid nanofluids has been the subject of an increasing number of studies in the literature. A significant research is done on theoretical correlations for estimating the thermophysical characteristics of nanofluids. The performance of hybrid nanofluids for heat transmission is investigated in the present work through a comparative analysis. For this, a mathematical model is formulated by considering the impact of thermal radiation and irregular heat source/sink in a porous medium. In this study, the magnetized flow of nanofluid MgO/H2O and hybrid nanofluid MgO-Ag/H2O are studied numerically. The controlling flow model of PDEs is transformed into ODEs by using the similarity transformation. The results revealed that the hybrid nanofluid fluid's thermal conductivity is more effective than the nanofluid's thermal conductivity. Further, the use of high suction strengths higher the heat transfer for both solutions while the opposite trend occurred for friction drag.

Numerical analysis of pyrolysis and coking of aviation kerosene in a rectangular U-bend tube under one-side heating

Pyrolysis and coking of Chinese aviation kerosene RP-3 in a rectangular U-bend tube of nonuniformly heating was numerically simulated. Discussion was held regarding how the bending structure affected temperature distribution, thermal cracking, and pyrolytic deposition. Results indicated that the secondary flow induced by centrifugal forces effectively promoted thermal convection between near-wall and core regions. This effect further decreased the fuel temperature of near-wall region. Furthermore, nonuniform distribution of temperature in the U-bend tube was reduced. More RP-3 reacted along the heated wall in the straight tube, which significantly accelerated the average reaction rate in the cross section and increased the yield of coke precursors formed by secondary reactions. Notably, the curved structure promoted heat transfer and anticoke deposition performance. Under the same inner surface area, the total amount of pyrolytic deposition of U-bend tube was reduced by 17.77 mg during coking duration of 5 min.