General correlations for estimating the monthly total and direct radiation incident on horizontal surfaces in Yunnan,China

Yunnan Province, China, has the climatic characteristic of evident dry and wet seasons in November to April and May to October, respectively. Utilizing the meteorological data of these two seasons and the observed solar radiation data in seven meteorological stations in Yunnan Province, the general correlations for estimating the monthly total and direct radiation incident on any horizontal surfaces in Yunnan Province are obtained by a linear regression technique, namely Although these correlations are only applicable for estimating H and H_b in areas of Yunnan Province, it is believed that if the number of stations is large enough the general correlations can be found, which can be applied to the estimation of H and H_b in any area.     

Fluid flow and heat transfer of opposing mixed convection adjacent to vertical heated plates

Opposing mixed convective flows induced around heated vertical plates were investigated experimentally. The experiments have been carried out with air and test plates of 100 mm and 200 mm long. The flow fields over the heated plates were visualized and the local heat transfer coefficients of the plates were measured for a wide range of Reynolds and Rayleigh numbers; Re_L = 7 × 10²−1.5 × 10⁴, Ra = 9 × 10⁶−8 × 10⁸. The visualization experiments showed that the separation of the boundary layer appears first at the trailing edge of the plate when the non‐dimensional parameter of (Gr/Re) = 0.35, and that the separation point reaches the leading edge when (Gr_L^*/Re_L^2.5) = 1.0. The heat transfer experiments showed that the above flow separation retards the heat transfer significantly from that of pure forced convection. It was also revealed that the flows over the heated plates can be categorized into forced, natural, and combined convection using the above parameter, (Gr/Re), as (Gr/Re) < 0.2, (Gr/Re) > 3 and 0.2 < (Gr/Re) < 3, respectively. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(8): 595–607, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20080     

Measurement of spectra over the Bolund hill in wind tunnel

We have determined the normal Reynolds stresses and spectra of the wind velocity over a 1:115 scale mock‐up of the Bolund hill. The experiment was run in a neutral boundary layer wind tunnel using 3‐component hot‐wire velocimetry, 2‐component particle image velocimetry, and a high‐precision traversing system. Spectra have been determined at different points along transects at 2 and 5 m height above ground level. The experiment was run for 270° wind direction and for two Reynolds numbers, and , based on the maximum height of the hill and the free wind speed at this height. Our results show how the normalized power spectral density changes over the hill. The analysis of the normalized streamwise spectrum at 2 m height, just after the escarpment, reveals that part of the energy is concentrated in the interval of normalized frequencies n_h≈0.01?0.02, which could be a signature of a weakened “flapping” phenomenon described in the literature for flows over forward facing steps. The departure of the spectra slope in the inertial subrange, from the value ?5/3, was found to be correlated with the hill geometry.     

Energy storage using the reaction cycle: Methyl alcohol/acetaldehyde

The kinetics of the exothermic reaction of acetaldehyde with methyl alcohol has been studied using calorimetry in the temperature range of 263–283 K. Based on this study the reaction rate constant for the reaction was found to be and the heat of reaction was found to be These kinetics were based on the assumption of a pseudoisothermal first-order reaction.     

Numerical simulation of nanoparticle shape and thermal ray on a CuO/C2H6O2–H2O hybrid base nanofluid inside a porous enclosure using Darcy's law

In this study, the physical aspects of magnetohydrodynamic flow and heat transfer of a hybrid base nanofluid in a porous medium under the effect of the shape, thermal radiation, and Lorentz force have been examined using the finite element method. Copper oxide (CuO) of various shapes was dispersed into ethylene glycol 50%‐water 50% (likewise for Fe₃O₄). The Darcy model is chosen because of the porous medium. The effect of changeable, diverse parameters, for example, Hartmann number (Ha), volume fraction (), radiation parameter (), and buoyancy force (Ra), on the streamlines, temperature gradient, and Nusselt number are shown through contours. Outputs show that the Fe₃O₄ nanoparticles have a smaller temperature gradient than that of CuO nanoparticles. The Nusselt number decreases for a larger (Ha) number, but increases for a larger Ra, Rd. The blade shaped nanoparticle has a larger impact on increasing compared with that of other shapes.     

Heat transfer performance of a flexible looped heat pipe using R134a as a working fluid: Proposal for a method to predict the maximum heat transfer rate of FLHP

This paper presents the heat transfer performance of a Flexible Looped Heat Pipe (FLHP) using R134a as a working fluid. In our evaluation system, an evaporator and a condenser are connected by long flexible tubes with a diameter of 3 mm, and the total piping length of this looped heat pipe system is approximately 7500 mm. We selected porous Teflon with an effective pore diameter of 2r_cw = 1.2 µm to overcome high gravitational heads. Elevation of the evaporator above the condenser ΔH = H_e ? H_c) was changed in three conditions [ Top heat mode (ΔH = +1 m), Horizontal mode (ΔH = 0), Bottom heat mode (ΔH = ?1 m)] considering the terrestrial application and the influence of gravity on the FLHP performance was investigated. FLHP provided high thermal transport capacities over long distances through small cross‐sectional flexible tubes compared with conventional heat pipes. We also proposed an analysis method to predict the maximum heat transfer rate of FLHP. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(4): 306–318, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10093     

Mass Transfer Effects on Viscous Flow in an Expanding or Contracting Porous Pipe with Chemical Reaction

In this paper, an analysis is performed to study the effects of mass transfer and chemical reaction on laminar flow in a porous pipe with an expanding or contracting wall. The pipe wall expands or contracts uniformly at a time dependent rate. The governing equations are reduced to ordinary differential equations by using a similarity transformation. An analytical approach, namely, the homotopy analysis method is applied in order to obtain the solutions of the ordinary differential equations. The convergence of the obtained series solutions is analyzed. The effects of various parameters on flow variables have been discussed. It is noticed that the wall expansion ratio significantly increases the axial velocity and the concentration for the case of wall expansion and it decreases the axial velocity for the case of wall contraction irrespective of injection or suction. Further, it is observed that the concentration (?) decreases for a destructive chemical reaction () and increases for a generative chemical reaction (). The concentration reduces as Schmidt number () increases. The corresponding problem related to the porous pipe flow with a stationary wall can be recovered from the present analysis in the limiting case where the wall expansion ratio approaches to zero (i.e., ).     

MHD natural convection inside an inclined trapezoidal porous enclosure with internal heat generation or absorption subjected to isoflux heating

A steady laminar two‐dimensional magneto‐hydrodynamic natural convection flow in an inclined trapezoidal enclosure filled with a fluid‐saturated porous medium is investigated numerically using a finite difference method. The left and right vertical sidewalls of the trapezoidal enclosure are maintained at a cold temperature. The horizontal top wall is considered adiabatic while the bottom wall is subjected to isoflux heating. A volumetric internal heat generation or absorption is embedded inside the trapezoidal enclosure while an external magnetic field is applied on the left sidewall of the enclosure. In the current work, the following parametric ranges of the non‐dimensional groups are used: Hartmann number is varied as , Darcy number is taken as , 10^?4, and 8 × 10^?5, Rayleigh number is varied as , Prandtl number is considered constant at Pr = 0.7, the dimensionless internal heat generation or absorption parameter is varied as Δ = ?0.2, 0, 1, and 2.0, while the trapezoidal enclosure inclination angle is varied as . The results indicated a strong flow circulation occurs when the Darcy and the Rayleigh numbers are high. In addition, it is found that the Hartmann number, internal heat generation or absorption parameter and inclination angle have an important role on the flow and thermal characteristics. It is also found that when the enclosure inclination angle and Hartmann number increase the average Nusselt number along the hot bottom wall decreases. © 2012 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21013     

Raman scattering studies of the condensed phase of the HIx feed of the sulfur–iodine thermochemical cycle

The species present in the condensed phase of the HI_x, hydrogen producing, feed in the water‐splitting, sulfur–iodine thermochemical cycle have been investigated using spontaneous Raman scattering. Measurements of I₂‐containing species in the low Raman‐shift region from 50 to 400 cm^?1 in samples of the two aqueous binary systems, I₂/H₂O and HI/H₂O, and the ternary system HI/I₂/H₂O with and without the addition of H₂SO₄ have provided a consistent picture of the aqueous iodine and polyiodide chemistry. Samples were contained in sealed silica ampoules and were heated to temperatures in the range 20–300°C. The results, which cover a wide range of I₂ and HI mole fractions, and x/x_HI mole ratios, in the HI/I₂/H₂O system, reveal the co‐occurrence of H⁺I, H⁺–I^?(I₂), and H⁺–I^?(I₂)₂ solvated species in the condensed phase of HI_x. Thus, while the first is mostly evident by its strong fundamental band with Raman shift in the range from 110 to 115 cm^?1, the other two species appear convoluted in a broad prominent band whose Raman shift ranges between 153 and 172 cm^?1 depending on the x/x_HI mole ratio. These well characterized Raman features are proposed as an in situ diagnostic for process control of the cycle. Copyright © 2010 John Wiley & Sons, Ltd.     

Theoretical calculation and experimental investigation on acoustic characteristics of a regenerator in thermoacoustic apparatus

An acoustic‐driven thermoacoustic device, which is used to investigate acoustic characteristics of a regenerator, was designed and manufactured. A model of the acoustic characteristics of the regenerator is discussed. The acoustic characteristics of the regenerator, such as acoustic impedance Ẑ_n, reflection coefficient , transmission loss TL, and phase angle between incident and reflected wave at x=0, were obtained by processing the experimental results with the correlation‐spectra analysis (the auto‐ and cross‐spectra) methods theoretically. Comparisons of acoustic characteristics between two cases, A (regenerator) and B (regenerator and two additional heat exchangers), are discussed. Different heating power influence on acoustic characteristics is also investigated. The results obtained will be helpful in further investigations on the regenerator model. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(8): 539–546, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20093     

Maximum entropy generation of in‐series connected heat exchangers

Theoretical analysis of entropy generation and availability destruction of “n” similar cocurrent or counter‐current heat exchangers connected in series are presented. A criterion for comparing the relative performance of any number of in‐series connected similar heat exchangers is developed. The effect of different influencing parameters such as the number of connected heat exchangers, the individual effectiveness of each unit, the heat capacity rate ratio and flow arrangement on the quality of heat exchange are presented. It is found that, the maximum of availability destruction (maximum entropy generation) for in‐series‐connected similar cocurrent heat exchangers is obtained at ϵ^*=1/(1+δ). However, for counter‐current heat exchangers connected in‐series; ϵ=1/(∑δ^i/n). This analysis might be useful for a proper choice of the number of heat exchangers to be connected together and the choice for the best operating conditions. Copyright © 2000 John Wiley & Sons, Ltd.     

Numerical and experimental study of free convection through a horizontal open‐ended axisymmetric cavity

This paper summarizes a numerical and experimental investigation of free convective heat transfer in an open‐ended cavity between two horizontal parallel circular plates. The upper plate is maintained at an ambient temperature and the lower one is heated. Air is used as the heat transfer medium. The numerical model equations are solved using a control volume‐based finite differences method, and the experimental study was performed using holographic interferometry. Streamlines and isotherm patterns are presented and discussed for different aspect ratios (A) and Rayleigh numbers (Ra). Heat transfer at the surface of the lower plate is thoroughly inspected in the ranges and . Useful correlations of Nusselt numbers in terms of and A are given with their validity ranges. Also, an investigation of both numerical and experimental results is performed. It shows similar temperature field aspect with some differences in the radial boundary layer thickness and a small deviation in the heat transfer.     

Effect of viscous dissipation on finding dual solutions for mixed convection boundary layer flow for nanofluid

The effect of viscous dissipation on mixed convection boundary layer flow for Ag‐water nanofluid under steady‐state condition has been studied numerically for both the buoyancy assisting and opposing flows over a vertical semi‐infinite flat plate. A new co‐ordinate system has been introduced to transform the governing partial differential equations (PDEs) to facilitate the numerical calculations. Then, the local similarity method has been used for approximating the transformed PDEs to ordinary differential equations. Further, the quasi‐linearization method has been introduced to linearize the nonlinear equations and then numerical integration has been carried out using implicit trapezoidal rule along with the principle of superposition. For higher Pr, the coupled differential equations behave like stiff differential equations. To overcome the situation, orthonormalization process has been introduced. The effects of solid volume fraction of nanoparticles , the mixed convection parameter , Prandtl number , and Eckart number have been analyzed on the heat transfer and flow characteristics. It has been observed that the dual solutions are obtained for buoyancy opposing flow only and the range of dual solutions have become wider with the increases in . Further, nanofluids enhance the heat transfer process as compared to conventional heat transfer fluids . Moreover, the addition of viscous dissipation causes less heat transfer in the boundary.     

Free and forced convection boundary layer flow through a porous medium with large suction

An analytical study is made of the free and forced convection boundary layer flow past a porous medium bounded by a semi-infinite vertical porous plate. Locally similar solutions are then obtained by a perturbation method for large suction. Solutions for the velocity and temperature distributions are shown graphically for various suction velocities and values of the driving parameter G_r/R, where G_r is the Grashof number and R_e is the Reynolds number. The corresponding values of the skin friction coefficient and the Nusselt number are finally shown in tabular form.     

Tangent hyperbolic nanofluid with mixed convection flow: An application of improved Fourier and Fick's diffusion model

This article presents a tangent hyperbolic fluid with the effect of the combination of forced and natural convection flow of nanoparticle past a bidirectional extending surface. Modified Fick's and Fourier's diffusion theories are incorporated into concentration and energy equations, respectively. Convective boundary conditions and second‐order slip flow are taken in the boundary condition. Nonlinear partial differential equations result after boundary layer approximations of the mathematical formulation of the flow problem. Nonlinear high order ordinary differential equations (ODEs) are formed by applying similarity transformation on the nonlinear partial differential equations. The transformed equations are solved with the bvp4c algorithm from Matlab. The numerical solution of ODEs was obtained and the effect of interesting parameters, dimensionless velocity component along x‐ and y‐axis, temperature, and concentration particle, Re_x, Re_y, , and , were presented through tables and graphs and discussed thoroughly. The results indicated that a decrease in velocity along with the y‐axis results from the increasing behavior of S, M, and n. Decrease in both temperature and concentration results in an increase of but their elongation is a result of increase in Bi. An increase in concentration results in decrease of N and S but a decrease in concentration results in the widening of Sc, Nb, and . Furthermore, enlargement of and results in increase of and modules and elongation of both and results in increase of and (Sc and Nb), respectively. A comparison with previously published literature was performed and a good agreement was found.     

Significance of the nonlinear radiative flow of micropolar nanoparticles over porous surface with a gyrotactic microorganism,activation energy,and Nield's condition

Current continuation presents the numerical study regarding stretched flow micropolar nanofluid over moving the sheet in the existence of activation energy and microorganisms. Furthermore, nonlinear aspects of thermal radiation are also utilized in the energy equation which results in the energy equation becomes highly nonlinear. This investigation has been performed by using convective Nield boundary conditions. First, useful dimensionless variables are implemented to reduce the partial differential into ordinary ones. Later on, the approximate solution of the transformed physical problem is computed by using the shooting scheme. A detailed physical interpretation of obtained results is also presented for velocity, temperature, motile microorganisms density, and mass concentration profiles. A detailed graphical explanation for each engineering parameter has been discussed for some specified range like , and The theoretical computations based presented here can be more proficient to attain the maximum efficiency of various thermal extrusion systems and microbial fuel cells.     

A numerical approach for MHD Al2O3–TiO2/H2O hybrid nanofluids over a stretching cylinder under the impact of shape factor

In this research, the heat transfer and magnetohydrodynamic stagnation point flow of a (Al₂O₃–TiO₂/H₂O) hybrid nanofluid past a stretching cylinder under the impact of heat generation, nonlinear thermal radiation, and nanoparticles shape factor has been analyzed using the Runge‐Kutta‐Fehlberg fifth order numerically method. The impact of changing diverse parameters, such as nanoparticles shape factor, named hexahedron and lamina, on temperature and velocity profiles and induced magnetic field, has been explored. The main motivation of this article is using hybrid nanoparticles to improve heat transfer. The novel findings of the current research illustrate that the Lorentz force produced by increasing magnetic field parameter () causes a decline in velocity profile; also increasing solar radiation, shape factor and the use of hybrid nanoparticles caused increment in the temperature profile. Furthermore, the lamina nanoparticle shape has more impact on Nusselt number () compared with hexahedron‐shaped nanoparticle.     

Natural convection boundary layer flow of nanofluids around different stations of the sphere and into the plume above the sphere

The main intent of the present study is to investigate the natural convection boundary layer flow of nanofluids around different stations of the sphere and eruption of the fluid from the boundary layer in to the plume above the sphere. It is pertinent to point out that in this study heated sphere is treated as point source. The system of transport boundary layer equations is based on the effects of Brownian motion and thermophoresis. The system of dimensioned boundary layer equations is transformed into nondimensional form. Later, the nondimensional form of the mathematical model is solved numerically by using implicit finite difference method. The solution of the problem depends on a controlling parameters Prandtl number P_r, Lewis number , thermophoresis parameter , and Brownian motion parameter . Particularly, it is observed that for Lewis number , Prandtl number P_r, Brownian motion parameter , and thermophoresis parameter the velocity profile is maximum at station and minimum at station . On the other hand temperature distribution is uniform at each station around the sphere and slightly reduced for . It is also observed that nanoparticles concentration is maximum at station and minimum at station We also established the result that with the increase of skin friction is reduced while the heat and mass flux are increased in the plume region‐III.     

Unsteady MHD chemically reactive double‐diffusive Casson fluid past a flat plate in porous medium with heat and mass transfer

In this paper, an attempt has been made to analyze the effects of various parameters, such as Soret and Dufour effects, chemical reaction, magnetic field, porosity on the fluid flow, and heat and mass transfer of an unsteady Casson fluid flow past a flat plate. Convective boundary conditions in heat and mass transfer and slip constant on velocity have been taken into account for analysis. The governing equations of the model have been solved numerically using the MATLAB program bvp4c. The impact of various parameters of the model on the velocity, temperature, and concentration profiles has been analyzed through different graphs. To get an insight into the physical quantities of engineering interest, viz, skin friction, Sherwood number, and Nusselt number, their numerical values have been computed for various parameters. The range of the parameters used in numerical computations are , , , , , , and . It has been noticed from the tabulated values that the skin friction gets enhanced with the increase in the thermal and solutal Grashof number, whereas its reverse effects have been observed with an increase in the Biot number. In limiting case, the present study is also compared with the available results in the literature.