Numerical investigation of two-dimensional turbulent boundary-layer compressible flow with adverse pressure gradient and heat and mass transfer

Summary The effect of heat and mass transfer on the steady turbulent compressible boundary-layer flow with adverse pressure gradient are numerically studied. The Reynolds-averaged boundary-layer equations and their boundary conditions are transformed, in a suitable form for numerical solution, by using the compressible version of the Falkner-Skan transformation and the resulting coupled and nonlinear system of partial differential equations is solved using the Keller's-box method and a modified version of it. For the eddy kinematic viscosity the model developed by Cebeci and Smith is employed whereas for the turbulent Prandlt number model a modification of the extended Kays and Crawford's model is used. Numerical calculations are carried out for the case of air, at about free stream temperature of 300°K, and for a linearly retarded flow, known as Howarth's flow when the porous limiting surface is adiabatic, heated or cooled. The porous surface is subjected to a continuous or localized suction/injection velocity and the influence of this velocity as well as of the free-stream Mach number and of the heat-transfer parameter on the turbulent boundary-layer and the separation point is examined. It is hoped that in the absence of detailed investigations into this problem, the obtained results, presented in the figures, are very interesting and give a clearer insight into the mechanism of controlling a turbulent boundary-layer compressible flow.     

Pseudoboiling and heat transfer in a turbulent flow

Experimental data characterizing the onset of pseudoboiling in relation to flow rate, pressure, and tube diameter are presented for diisopropylcyclohexane (DICH).     

Numerical study of Soret and Dufour effects on heat and mass transfer from natural convection flow over a vertical porous medium with variable wall heat fluxes

A study has been carried out to obtain the solutions for heat and mass transfer from natural convection flow along a vertical surface with variable heat fluxes embedded in a porous medium due to thermal-diffusion (Soret) and diffusion-thermo (Dufour) effects. The buoyancy induced boundary layer adjacent to a vertical surface is analyzed using a non-Darcy flow model. The parameters for inertia, buoyancy ratio, exponent of heat flux, position and diffusion have been examined. The governing differential equations of continuity, momentum, energy and concentration are transformed into a set of coupled equations and solved using similarity analysis with numerical technique. Results show the velocity, temperature and concentration profiles related to local Nusselt and Sherwood numbers at different magnitude of Soret and Dufour numbers.     

Multicomponent heat and mass transfer during the turbulent flow of liquid films

A method is proposed for calculating the parameters of simultaneous heat and mass transfer in turbulent multicomponent liquid films which is based on solving the system of differential equations for convective heat conduction and multicomponent convective diffusion.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 57, No. 1, pp. 16–22, July, 1989.     

Kinetics of heat and mass transfer between a sprayed solution and a hot gas flow

A two-zone mathematical model is given for the process of moisture evaporation from a sprayed solution and crystallization of the salt. The computer calculations are compared with the results of experimental work.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 46, No. 5, pp. 797–804, May, 1984.     

Experimental study of turbulent single-phase flow and heat transfer inside a micro-finned tube

Single-phase heat transfer and pressure drop characteristics of a commercially available internally micro-finned tube with a nominal outside diameter of 7.94 mm were studied. Experiments were conducted in a double pipe heat exchanger with water as the cooling as well as the heating fluid for six sets of runs. The pressure drop data were collected under isothermal conditions. Data were taken for turbulent flow with 3300 ≤ Re ≤ 22,500 and 2.9 ≤ Pr ≤ 4.7. The heat transfer data were correlated by a Dittus–Boelter type correlation, while the pressure drop data were correlated by a Blasius type correlation. The correlation predicted values for both the Nusselt number and the friction factors were compared with other studies. It was found that the Nusselt numbers obtained from the present correlation fall in the middle region between the Copetti et al. and the Gnielinski smooth tube correlation predicted Nusselt number values. For pressure drop results, the present correlation predicted friction factors values were nearly double that of the Blasius smooth tube correlation predicted friction factors. It was also found that the rough tube Gnielinski and Haaland correlations can be used as a good approximation to predict the finned tube Nusselt number and ffriction factor, respectively, in the tested Reynolds number range.     

Hydraulic resistance and heat and mass exchange during turbulent flow over surfaces with slight roughness

Flow over a surface with slight roughness is examined. It is established that at high Prandtl or Schmidt numbers such roughness can markedly increase the coefficients of heat and mass exchange.     

Fluid flow and heat transfer characteristics of separation and reattachment flow over a backward-facing step

In this study, a direct numerical simulation of the fluid flow and heat transfer characteristics of separation and reattachment flow at a backward-facing step is presented. A computer program of FORTRAN code is used to solve the governing equations according to finite volume method. The effects of the Reynolds number and expansion ratio on the fluid flow and heat transfer characteristics are investigated. The size of the primary recirculation zone increases with the reduction of expansion ratio and the fluctuation of isotherms increased with the increase of Reynolds number. The periodic characteristics and the dissimilarity between Nu and Cf appear in the transitional flow regime. The rotating fluids in the reattachment region increase the flow instability and the interchange of the hot and cold fluids increases heat transfer instability. The combined effects of flow instability and heat transfer instability play an important role in the formation of the dissimilarity between Nu and Cf.     

Numerical study of transient 2-D compressible flow with heat and mass transfer using the finite volume method

In this paper, we used a pressure-based finite volume method to investigate the problem of transient 2-D compressible flow with heat and mass transfer in a rectangular domain. We have used this method to solve the governing equations with given initial and wall slip boundary conditions. We implemented the SIMPLE-TS algorithm in order to compute the numerical solutions for the flow variables, viz., velocity, pressure, temperature, concentration, density. The variation of density of the fluid along the horizontal and vertical line through geometric center of the domain has been studied. The transient solutions of temperature and concentration indicate that, the transient flow though dominates initially, it finally settles down to steady states solutions after elapse of some time. Nusselt number and Sherwood numbers were used to predict the behavior of heat transfer and mass transfer, respectively, at the center line of the rectangular domain.     

Numerical investigation of three-dimensional turbulent flow and endwall heat transfer in a large-scale cascade of turbine blades

Numerical simulation is performed of three-dimensional turbulent flow and heat transfer in a cascade of turbine blades (Langston cascade), for which numerous data are available in the literature. For closing the system of Reynolds-averaged Navier-Stokes equations, use is made of two-parameter models of turbulence of the k-ω family, low-Reynolds version of the Wilcox model, and the SST model of Menter. Numerical solutions are obtained in detailed grids (over a million cells) using the finite-volume code of second-order accuracy. It is demonstrated that the predicted structure of flow and local heat transfer on the end wall are very sensitive to the choice of model of turbulence, especially in the case of a thick boundary layer at the cascade inlet. By and large, the use of the Menter model enables one to well reproduce the complex vortex structures of flow in the cascade, as well as the local and integral characteristics of loss of total pressure. The local endwall heat transfer is predicted adequately.     

Investigation of turbulent heat transfer and nanofluid flow in a double pipe heat exchanger

In present study, heat transfer and turbulent flow of water/alumina nanofluid in a parallel as well as counter flow double pipe heat exchanger have been investigated. The governing equations have been solved using an in-house FORTRAN code, based on finite volume method. Single-phase and standard k-ε models have been used for nanofluid and turbulent modeling, respectively. The internal fluid has been considered as hot fluid (nanofluid) and the external fluid, cold fluid (base fluid). The effects of nanoparticles volume fraction, flow direction and Reynolds number on base fluid, nanofluid and wall temperatures, thermal efficiency, Nusselt number and convection heat transfer coefficient have been studied. The results indicated that increasing the nanoparticles volume fraction or Reynolds number causes enhancement of Nusselt number and convection heat transfer coefficient. Maximum rate of average Nusselt number and thermal efficiency enhancement are 32.7% and 30%, respectively. Also, by nanoparticles volume fraction increment, the outlet temperature of fluid and wall temperature increase. Study the minimum temperature in the solid wall of heat exchangers, it can be observed that the minimum temperature in counter flow has significantly reduced, compared to parallel flow. However, by increasing Reynolds number, the slope of thermal efficiency enhancement of heat exchanger gradually tends to a constant amount. This behavior is more obvious in parallel flow heat exchangers. Therefore, using of counter flow heat exchangers is recommended in higher Reynolds numbers.     

凹陷阵列印刷电路板式换热器里超临界甲烷换热和流动特性模拟研究

为了强化液化甲烷在印刷电路板式微通道换热器中的换热能力,提出了一种凹陷阵列的微小通道换热器整体性能提高的被动式强化技术并进行了数值模拟验证。研究了流体温度范围125—265 K范围内的超临界甲烷在凹陷阵列结构微通道内的换热和流动特性,考察了凹陷阵列微通道和光滑微通道下,流体温度、质量流量、雷诺数和进口压力对传热系数、努塞尔数、摩擦因子和综合效益系数(PEC)的影响。此外,通过凹陷结构的局部流动特性分析强化换热机理,数值模拟结果表明相较于光滑微通道,凹陷阵列微通道的换热特性得到大大强化,且随雷诺数(由质量流量或者流体温度改变)的增大而增强,而摩擦因子只是有较弱的劣化。     

Increasing the rate of heat transfer in ducts with a turbulent gas flow

Results are shown of a study concerning the heat transfer and the hydraulic drag in an air stream through ducts of various shapes with wavy rough walls and with boundary-layer breakers.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 22, No. 6, pp. 981–986, June, 1972.     

Numerical study for the effects of thermophoresis and variable thermal conductivity on heat and mass transfer over an accelerating surface with heat source

A modified numerical solution scheme, for local similarity boundary layer analysis, is used to study the effects of thermophoresis and variable thermal conductivity on heat and mass transfer over an accelerating surface with heat source in the presence of suction and blowing. This numerical scheme is efficient and accurate and it can be programmed and applied easily and its application is illustrated, step by step, by studying the above mentioned problem. The resulting boundary layer equations are solved numerically by Chebyshev finite difference method. Numerical results for the velocity, temperature and concentration as well as for the skin friction, Nusselt and Sherwood numbers are obtained and reported graphically for various parametric conditions to show interesting aspects of the solution.     

Experimental study of heat and mass transfer characteristics in a cross-flow heating tower

A heating tower heat pump (HTHP), as a novel integrated heating and cooling unit, is drawing more and more attention due to its high efficiency, low limitation of topographical conditions and no frost problems. The heating tower which can take advantage of energy from air is a significant unit of HTHP system and greatly affects system performance. This paper experimentally studies the heat and mass transfer characteristics of a cross-flow heating tower, which uses PVC structured packing and takes glycol as cycling fluid. Heat and mass transfer capacities, as well as heating efficiency, are adopted as performance indices. The effects of the inlet parameters, including air and solution flow rates, air inlet temperature and humidity ratio, solution inlet temperature and concentration, on the indices are investigated. Besides, a coupled heat and mass transfer model is developed and solved with finite difference method without the assumption of Lewis number. Correlation expressions of heat and mass transfer coefficients are proposed, which are in good agreement with the experimental data.     

倾斜热管湍流床的气固流动特性

为了探明间壁式流化床换热器内热管对气固流动状态的影响,采用欧拉双流体模型,并应用能量最小多尺度(energy minimization multi-scale, EMMS)曳力模型,对可实现2种物性相近催化剂热管间壁换热的湍动流化床流动特性进行模拟研究。结果表明:通过与实验数据进行比较,证明模型是有效的;比较热管对床内固含率轴向分布的影响,发现热管的设置可减小气泡尺寸、有效降低颗粒被夹带量;热管对固含率的影响主要位于热管末端,其仅存在于热管所在区域,且随着径向位置靠近隔板逐渐减小;沿热管轴向存在隔板影响区和主换热区,主换热区随着轴向高度的增加而减小,随着表观气速的增大而增大。     

声波作用下的单圆柱绕流及传热特性数值研究

为了研究声波对单圆柱绕流流动和传热特性的影响,建立了流场、声场、对流传热多物理场耦合的二维数学模型,并利用有限元软件COMSOL进行数值模拟。结果表明:(1)当频率f=50 Hz、声压级L_SP=123～149 d B时,斯特劳哈尔数Sr随声压级增大而减小,圆柱表面压力系数C_P随声压级增大而增大;(2) L_SP=143 d B、f=20～80 Hz时,斯特劳哈尔数Sr、压力系数C_P均随频率f增大而增大;(3)对比f=50 Hz、L_SP=143 d B声波作用与无声波作用的情况,阻力系数C_DF和升力系数C_DL都呈周期性变化,但有声波作用时振幅增大;(4)声波作用会促进圆柱表面热量传递,但当L_SP>143 d B,圆柱表面局部努塞尔数Nu_θ开始减小。该研究结果为强化圆柱绕流传热提供了理论研究基础。     

Numerical evaluation of the heat transfer and the friction drag in a pipe with a turbulent flow of a gas with variable physical properties

The temperature field and the velocity field as well as the local coefficients of heat transfer and friction are determined in the entrance segment of a pipe where a turbulent flow of a gas with variable physical properties stabilizes thermally.Translated from Inzhenerno-Fizteheskii Zhurnal, Vol. 24, No. 4, pp. 730–734, April, 1973.     

Experimental study on the heat and mass transfer characteristics in a refrigerated truck

An experimental study on the heat and mass transfer characteristics in the body of a refrigerated truck for cases without an air curtain, with a fan air curtain and with a plastic strip curtain have been carried out. The variations in temperature and relative humidity inside the stationary truck during a short duration after the door is opened are the present focus. The average air temperature inside is found to increase to 14, 7 and 8°C from an initial temperature of −10°C, for cases without an air curtain, with a fan air curtain and with a plastic strip curtain, respectively, within 2 min after the door is opened. It is found that using an air curtain can have energy savings up to 40 and 11%, respectively, compared to the cases without an air curtain and using plastic strip curtain. Comparison between the experiment and numerical results also shows reasonable agreement in terms of average temperature inside the body.