Variable fluid properties and variable heat flux effects on the flow and heat transfer in a non-Newtonian Maxwell fluid over an unsteady stretching sheet with slip velocity

The effects of variable fluid properties and variable heat flux on the flow and heat transfer of a non-Newtonian Maxwell fluid over an unsteady stretching sheet in the presence of slip velocity have been studied. The governing differential equations are transformed into a set of coupled non-linear ordinary differential equations and then solved with a numerical technique using appropriate boundary conditions for various physical parameters. The numerical solution for the governing non-linear boundary value problem is based on applying the fourth-order Runge-Kutta method coupled with the shooting technique over the entire range of physical parameters. The effects of various parameters like the viscosity parameter, thermal conductivity parameter, unsteadiness parameter, slip velocity parameter, the Deborah number, and the Prandtl number on the flow and temperature profiles as well as on the local skin-friction coefficient and the local Nusselt number are presented and discussed. Comparison of numerical results is made with the earlier published results under limiting cases.

Effect of slip velocity on Casson thin film flow and heat transfer due to unsteady stretching sheet in presence of variable heat flux and viscous dissipation

The aim of the present paper is to study flow and heat transfer charac- teristics of a viscous Casson thin film flow over an unsteady stretching sheet subject to variable heat flux in the presence of slip velocity condition and viscous dissipation. The governing equations are partial differential equations. They are reduced to a set of highly nonlinear ordinary differential equations by suitable similarity transformations. The re- sulting similarity equations are solved numerically with a shooting method. Comparisons with previous works are macle, and the results are found to be in excellent agreement. In the present work, the effects of the unsteadiness parameter, the Casson parameter, the Eckert number, the slip velocity parameter, and the Prandtl number on flow and heat transfer characteristics are discussed. Also, the local skin-friction coefficient and the local Nusselt number at the stretching sheet are computed and discussed.

Optimization of Intermittent Variable Power Microwave Heating Process for Blueberry Pulp

To improve heating uniformity and anthocyanin content of the blueberry pulp under microwave heating,the intermittent variable power microwave heating technology was introduced in the study.The effects of technology parameters in terms of high microwave intensity heating time,intermittent time,low microwave intensity and low microwave intensity heating time on the blueberry pulp quality parameters(heating uniformity,average moisture content,the highest temperature and anthocyanin content)were investigated by using the response surface method.The results showed that the longer heating time under different microwave intensities resulted in the poorer heating uniformity.The intermittent stage promoted heat and mass transfer within the pulp and reduced the temperature difference and moisture gradient within the pulp,which enhanced desired uniformity of temperature and moisture distribution before entering the low microwave intensity heating stage.Therefore,the longer the intermittent time,the greater the heating uniformity.The optimal parameters were developed as high microwave intensity of 4 W·g^(-1),high microwave intensity heating time of 9.86 min,intermittent time of 10 min,low microwave intensity of 2.2 W·g^(-1)and low microwave intensity heating time of 6 min.This research might provide guidance for microwave heating berry fruits.

Effect of variable heat capacities on performance of 3n irreversible Miller heat engine

Based on the variable heat capacities of the working fluid, the irreversibility coming from the com- pression and expansion processes, and the heat leak losses through the cylinder wall, an irreversible cycle model of the Miller heat engine was established, from which expressions for the efficiency and work output of the cycle were derived. The performance characteristic curves of the Miller heat engine were generated through numerical calculation, from which the optimal regions of some main parameters such as the work output, efficiency and pressure ratio were determined. Moreover, the influence of the compression and expansion efficiencies, the variable heat capacities and the heat leak losses on the performance of the cycle was discussed in detail, and consequently, some significant results were obtained.

Numerical Study by Imposing the Finite Difference Method for Unsteady Casson Fluid Flow with Heat Flux

This article presents an investigation into the flow and heat transfer characteristics of an impermeable stretching sheet subjected to Magnetohydrodynamic Casson fluid. The study considers the influence of slip velocity, thermal radiation conditions, and heat flux. The investigation is conducted employing a robust numerical method that accounts for the impact of thermal radiation. This category of fluid is apt for characterizing the movement of blood within an industrial artery, where the flow can be regulated by a material designed to manage it. The resolution of the ensuing system of ordinary differential equations (ODEs), representing the described problem, is accomplished through the application of the finite difference method. The examination of flow and heat transfer characteristics, including aspects such as unsteadiness, radiation parameter, slip velocity, Casson parameter, and Prandtl number, is explored and visually presented through tables and graphs to illustrate their impact. On the stretching sheet, calculations, and descriptions of the local skin-friction coefficient and the local Nusselt number are conducted. In conclusion, the findings indicate that the proposed method serves as a straightforward and efficient tool for exploring the solutions of fluid models of this kind.

The effects of variable specific heat on the stability of hypersonic boundary layer on a flat plate

The gas temperature within hypersonic boundary layer flow is so high that the specific heat of gas is no longer a constant but relates to temperature. How variable specific heat influences on boundary layer flow stability is worth researching. The effect of the variable specific heat on the stability of hypersonic boundary layer flows is studied and compared with the case of constant specific heat based on the linear stability theory. It is found that the variable specific heat indeed has some effects on the neutral curves of both the first-mode and the second-mode waves and on the maximum rate of growth also. Therefore, the relationship between specific heat and temperature should be considered in the study of the stability of the boundary layer.

Prediction of hypersonic boundary layer transition on sharp wedge flow considering variable specific heat

When the air temperature reaches 600 K or higher, vibration is excited. The specific heat is not a constant but a function of temperature. Under this condition, the transition position of hypersonic sharp wedge boundary layer is predicted by using the improved eN method considering variable specific heat. The transition positions with different Mach numbers of oncoming flow, half wedge angles, and wall conditions are computed condition, the nearer to the Mach number The results show that for the same oncoming flow condition and wall transition positions of hypersonic sharp wedge boundary layer move much leading edge than those of the flat plate. The greater the oncoming flow the closer the transition position to the leading edge.

Heat Transfer in MHD Flow of Maxwell Fluid via Fractional Cattaneo-Friedrich Model:A Finite Difference Approach

The idea of fractional derivatives is applied to several problems of viscoelastic fluid.However,most of these problems(fluid problems),were studied analytically using different integral transform techniques,as most of these problems are linear.The idea of the above fractional derivatives is rarely applied to fluid problems governed by nonlinear partial differential equations.Most importantly,in the nonlinear problems,either the fractional models are developed by artificial replacement of the classical derivatives with fractional derivatives or simple classical problems(without developing the fractional model even using artificial replacement)are solved.These problems were mostly solved for steady-state fluid problems.In the present article,studied unsteady nonlinear non-Newtonian fluid problem(Cattaneo-Friedrich Maxwell(CFM)model)and the fractional model are developed starting from the fractional constitutive equations to the fractional governing equations;in other words,the artificial replacement of the classical derivatives with fractional derivatives is not done,but in details,the fractional problem is modeled from the fractional constitutive equations.More exactly two-dimensional magnetic resistive flow in a porous medium of fractional Maxwell fluid(FMF)over an inclined plate with variable velocity and the temperature is studied.The Caputo time-fractional derivative model(CFM)is used in the governing equations.The proposed model is numerically solved via finite difference method(FDM)along with L1-scheme for discretization.The numerical results are presented in various figures.These results indicated that the fractional parameters significantly affect the temperature and velocity fields.It is noticed that the temperature field increased with an increase in the fractional parameter.Whereas,the effect of fractional parameters is opposite on the velocity field near the plate.However,this trend became like that of the temperature profile,away from the plate.Moreover,the velocity field retarded with strengthening in the magnetic parameter due to enhancement in Lorentz force.However,this effect reverses in the case of the temperature profile.

Hydromagnetic Nanofluid Film Flow over a Stretching Sheet with Prescribed Heat Flux and Viscous Dissipation

Thermal radiative heat transfer through a thin horizontal liquid film of a Newtonian nanofluid subjected to a magnetic field is considered.The physical boundary conditions are a variable surface heat flux and a uniform concentration along the sheet.Moreover,viscous dissipation is present and concentration is assumed to be influenced by both thermophoresis and Brownian motion effects.Using a similarity method to turn the underlying Partial differential equations into a set of ordinary differential equations(ODEs)and a shooting technique to solve these equations,the skin-friction coefficient,the Nusselt number,and the Sherwood number are determined.Among other things,it is shown that large values of the thermal radiation heat transfer rate,thermal conductivity parameter,and the Brownian motion parameter can enhance the cooling of the sheet.

Variability in Latent Heat Flux over the Tropical Pacific in Association with Recent Two ENSO Events

This paper analyzed the variations of latent heat flux (LHF) over the tropical Pacific in the period 1978-1988 by using COADS (Comprehensive Ocean and Atmospheric Data Set). It has been founded that the interannual variabili ty of LHF exhibits strong ENSO signal, with the significant increasing LHF during the recent two warm events, i.e., 1982 / 83 and 1986 / 87 and decreasing LHF in the cold episodes. However the longitudinal distribution of the LHF departures varies from event to event. In the eastern Pacific, the specific humidity difference at air-sea interface (qs -qa) makes a dominant contribution to the interannual variability of LHF ( r = 0.73 ), while in the western Pacific the surface wind speed, W and the qs - qa make nearly equal contribution to that of LHF.

Performance Analysis of a Solar Continuous Adsorption Refrigeration System

A study is conducted on the performances of a solar powered continuous-adsorption refrigerator considering two particular days as references cases,namely,the summer solstice(June 21st)and the autumn equinox(September 21st).The cooling capacity,system performance coefficient and the daily rate of available cooling energy are assessed.The main goal is to compare the performances of a solar adsorption chiller equipped with a hot water tank(HWT)with an equivalent system relying on solar collectors with no heat storage module.The daily cooling rates for the solar refrigerator are found to be 102.4 kWh and 74.3 kWh,respectively,on June 21st and on September 21st,using a total collector’s area of 43.47 m2.The corresponding values for the adsorption chiller equipped with a hot water tank of 2 m3(and using a total collector’s area of 72.45 m2),are 127.1 kWh and 106.13 kWh,respectively.

Experimental Study on a Multi-Evaporator Loop Heat Pipe with a Dual-Layer Structure Condenser

A loop heat pipe(LHP)is a kind of passive heat transfer device that uses the latent heat of the working fluid and the capillary forces of the capillary wicks.It demonstrates high heat transfer efficiency,long-distance heat transfer,and high pipeline flexibility.The multi-evaporator loop heat pipe(MeLHP)is a special loop heat pipe with multiple evaporators so that heat collection and emission from multiple heat sources can be achieved.In this paper,a new type of the multi-evaporator loop heat pipe prototype with a dual-layer condenser was designed,which can ensure the uniform and symmetrical layout of pipelines.The working temperature was 20℃,and propylene was used as the working fluid.The performance of the same evaporator in a single-loop LHP was considered as a reference.The experiment was conducted under two heating modes,i.e.single-evaporator heating and multi-evaporator heating,and the working stability of the prototype was verified by applying periodic heating power change and adverse elevation condition.It was observed that the prototype can be successfully started in different heating modes with a heat transfer limit of 230 W.In the test,the four loops were different in heat transfer limit due to the differences of flow resistance,and less power distribution to the loop with lowest heat transfer limit was considered to be beneficial to the prototype’s performance.Meanwhile,the prototype showed good heat sharing characteristic as the maximum temperature difference is low(smaller than 2 K in single-evaporator heating mode and 0.5 K in multi-evaporator heating mode).The prototype was of good operational reliability and found to be adaptable to the adverse elevation and cyclic variation of the heating power to a certain extent.

Prediction of hypersonic boundary layer transition with variable specific heat on plane flow

When an aircraft flies at a hypersonic speed,the temperature of gas inner boundary layer near the wall is so high that the specific heat is no longer a constant but dependent upon the temperature.It is necessary to consider its effect on transition location.In this paper,the transition locations of hypersonic plane boundary layer are predicted with the improved e N method,and the results of the specific heat dependent upon temperature are compared with those of constant specific heat.The flow parameters are taken as those corresponding to the condition at a height of 40 km and the Mach numbers of oncoming flow are 6,7,and 8,respectively.It is found that the transition locations calculated by the variable specific heat are closer to the leading edge than those by the constant specific heat.The deviations in most cases are around 30 percent.All the results prove that the real gas effect should be taken into consideration when one predicts transition location for hypersonic flow.Whether the first or second mode wave determines the transition location relies on the oncoming flow Mach number and the wall condition.

Effects Viscous Dissipation on the Asymptotic Behaviour of Laminar Forced Convection for HerscheI-Bulkley Fluid in a Circular Duct

The asymptotic behaviour of laminar forced convection in a circular duct, for a Herschel-Bulkley fluid with constant properties, is analysed by taking into account the viscous dissipation effects. The axial heat conduction in the fluid is neglected. The asymptotic temperature field and the asymptotic value of the Nusselt number are determined for every boundary condition that allows a fully developed region. Comparisons with other existing solutions for Newtonian and non-Newtonian cases are presented.

Effects of different heating patterns on the decomposition behavior of white pine wood during slow pyrolysis

This study investigated the effect of different heating rates on the pyrolysis behavior of the white pine wood residues.The raw materials were tested via two heating patterns with variable heating rates and compared with three other heating patterns with constant heating rates.The yields and characteristics of products such as char,pyrolysis oil and non-condensable gases under different heating rates were also determined.The gas,liquid,and solid phase yields of the products via heating with decreasing heating rates were similar to the yields obtained from constant heating rate at 2.3℃/min.The pyrolysis process by decreasing heating rates resulted in 30.04% char,44.53% bio-oil,and 25.43% non-condensable gases,which displayed higher char yield and pyrolysis gas than the other heating patterns.The results of thermo-gravimetric analysis showed that variable heating rate significantly changed the weight loss profiles during pyrolysis.It was observed during gas chromatography test that CO and CO_(2) were released earlier than CH_(4) and H_(2).The analysis of the chemical components confirmed that the bio-oil produced by heating process with decreasing rates contains less macromolecular organic matter content than the other patterns.

Analysis on capabilities of density-based solvers within OpenFOAM to distinguish aerothermal variables in difusion boundary layer

Open source feld operation and manipulation（OpenFOAM）is one of the most prevalent open source computational fluid dynamics（CFD）software.It is very convenient for researchers to develop their own codes based on the class library toolbox within OpenFOAM.In recent years,several density-based solvers within OpenFOAM for supersonic/hypersonic compressible flow are coming up.Although the capabilities of these solvers to capture shock wave have already been verifed by some researchers,these solvers still need to be validated comprehensively as commercial CFD software.In boundary layer where diffusion is the dominant transportation manner,the convective discrete schemes＇capability to capture aerothermal variables,such as temperature and heat flux,is different from each other due to their own numerical dissipative characteristics and from viewpoint of this capability,these compressible solvers within OpenFOAM can be validated further.In this paper,frstly,the organizational architecture of density-based solvers within OpenFOAM is analyzed.Then,from the viewpoint of the capability to capture aerothermal variables,the numerical results of several typical geometrical felds predicted by these solvers are compared with both the outcome obtained from the commercial software Fastran and the experimental data.During the computing process,the Roe,AUSM＋（Advection Upstream Splitting Method）,and HLLC（Harten-Lax-van Leer-Contact）convective discrete schemes of which the spatial accuracy is 1st and 2nd order are utilized,respectively.The compared results show that the aerothermal variables are in agreement with results generated by Fastran and the experimental data even if the1st order spatial precision is implemented.Overall,the accuracy of these density-based solvers can meet the requirement of engineering and scientifc problems to capture aerothermal variables in diffusion boundary layer.

Direct numerical simulation methods of hypersonic flat-plate boundary layer in thermally perfect gas

High-temperature effects alter the physical and transport properties of air such as vibrational excitation in a thermally perfect gas,and this factor should be considered in order to compute the flow field correctly.Herein,for the thermally perfect gas,a simple method of direct numerical simulation on flat-plat boundary layer is put forward,using the equivalent specific heat ratio instead of constant specific heat ratio in the N-S equations and flux splitting form of a calorically perfect gas.The results calculated by the new method are consistent with that by solving the N-S equations of a thermally perfect gas directly.The mean flow has the similarity,and consistent to the corresponding Blasius solution,which confirms that satisfactory results can be obtained basing on the Blasius solution as the mean flow directly in stability analysis.The amplitude growth curve of small disturbance is introduced at the inlet by using direct numerical simulation,which is consistent with that obtained by linear stability theory.It verified that the equation established and the simulation method is correct.