Conjugate transient heat transfer in laminar natural convection in a horizontal cylindrical annulus

The conjugate problem of natural convection in a horizontal cylindrical annulus is solved numerically, the solutions are compared with nonconjugate problems, and it is shown that the walls affect the heat transfer in the annular channel.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 51, No. 4, pp. 576–583, October, 1986.     

Natural convection flow from an isothermal horizontal circular cylinder in presence of heat generation

Natural convection laminar boundary layer flow from a horizontal circular cylinder with a uniform surface temperature at presence of heat generation has been investigated. The governing boundary layer equations are transformed into a non-dimensional form and the resulting nonlinear systems of partial differential equations are solved numerically applying two distinct methods namely (i) implicit finite difference method together with the Keller box scheme and (ii) series solution technique. The results of the surface shear stress in terms of the local skin friction and the surface rate of heat transfer in terms of the local Nusselt number for a selection of the heat generation parameter γ (= 0.0, 0.2, 0.5, 0.8, 1.0) are obtained and presented in both tabular and graphical formats. Without effect of the internal heat generation inside the fluid domain for which we take γ = 0.0, the present numerical results show an excellent agreement with those of Merkin [J.H. Merkin, Free convection boundary layer on an isothermal horizontal circular cylinders, in: ASME/AIChE, Heat Transfer Conference, St. Louis, MO, August 9–11, 1976]. The effects of γ on the fluid velocity, temperature distribution, streamlines and isotherms are examined.     

Natural convection heat transfer in air about a horizontal circular nonisothermal cylinder

Results are presented of a numerical investigation of laminar free convection heat transfer in air about a horizontal circular cylinder in the moderate Grashoff number range (10⁴ Gr_m 10⁹), for linear and quadratic laws of surface temperature variation.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 43, No. 2, pp. 209–215, August, 1982.     

超临界二氧化碳水平管内层流混合对流换热数值模拟

为得到二次流对换热的强化作用,对恒壁温冷却工况下,超临界二氧化碳在水平微细圆管内的混合对流换热进行了数值模拟.分析了重力水平、冷壁面温度、入口雷诺数Re等参数变化时管道壁面的传热系数,管内浮升力引发的二次流、范宁摩擦系数沿管道的变化规律,引入相对二次流动能将二次流的强度定量表示出来.研究发现管内流体顶部温度高于底部,上母线传热系数远高于下母线且在超临界二氧化碳的拟临界温度附近达到峰值,二次流及范宁摩擦系数在入口区域变化最剧烈,重力加速度对管内流场产生重要影响.     

Geometrical effect on laminar mixed convection in the entrance region of shrouded arrays of heated rectangular blocks

Abstract

The effect of geometric parameter on laminar mixed convection in the entrance region of shrouded arrays of heated rectangular blocks is approached numerically for large Prandtl number fluid. The problem considered is related to convective cooling of electronic components mounted on horizontal circuit boards. Typical development of streamline and isotherm, block wall temperature distribution, and local Nusselt number are presented. It is found that the secondary flow leads to a significant enhancement in heat transfer. The multiple eddies above the block, induced by the combined geometric and buoyancy effect, lead to a more uniform block wall temperature distribution and then reduce the magnitude of the highest wall temperature.     

Free convection heat transfer in horizontal channels and over a horizontal surface

Free convective heat transfer of a fluid in horizontal channels and above a horizontal surface is theoretically analyzed. The interaction of the fluid with the channel walls may be divided into two parts: formation of vortex flow cells, and heat transfer in the induced flow over the walls.     

Influence of thickness and wall thermal conductivity on heat transfer in laminar natural convection of air in a cubical cavity

Results are presented for a numerical investigation of the influence of finite thermal conductivity and wall thickness on heat transfer in a vertical cavity of rectangular cross section. Theoretical formulas are obtained for determining the total heat flux.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 35, No. 6, pp. 1130–1135, December, 1978.     

圆环腔内纳米流体自然对流的数值研究

采用Fluent软件对圆环封闭腔内的Ag-水纳米流体自然对流传热进行数值模拟,着重分析在不同瑞利数下Ag纳米颗粒的添加量和圆环内外壁半径比对圆环传热性能的影响.研究结果表明,随着瑞利数的增加,圆环间的换热强度不断加剧,换热由热传导逐渐向对流转变.添加纳米颗粒降低了换热性能,且随着颗粒浓度的增加换热效果不断恶化;同时,圆环半径比对换热有很大的影响,对一定的瑞利数而言随着半径比的减小,换热性能逐渐增强,且增大的趋势越来越显著.     

Natural convection heat transfer of cold water in an eccentric horizontal cylindrical annulus — a numerical study

A numerical study of the natural convection heat transfer of cold water, having the density inversion between two isothermal eccentric horizontal cylinders is studied. A general code is developed for the body fitted coordinate system. This procedure transforms an arbitrarily shaped physical domain into a rectangular (square) domain. The governing equations in this computational domain are solved by the upwind finite difference scheme. The numerical solutions are obtained for a Rayleigh number (Ra) ranging between a Prandtl number (Pr) 12.0 and inversion parameter (γ) 0,−1 and −2. The affect of the radius ratio (R) on the flow patterns and heat transfer coefficients is studied by taking the Radius ratio as 1.5 and 2. The eccentricity affect is studied by moving the center of the inner cylinder horizontally and vertically (both positive and negative directions) with respect to the center of the outer cylinder. For the cases considered in the present study, it is again for the minimum heat transfer is observed like in the case of concentric annulus.     

Computation of laminar flow in mixed turbulent convection and its influence on heat transfer

Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 62, No. 3, pp. 366–372, March, 1992.     

混合工质水平管内流动凝结换热研究进展

从实验和模型两个方面,综述了国外对混合工质在水平光管和强化管内流动凝结换热的研究。对多种公开发表的混合工质凝结换热关联式的适用性和准确性进行了讨论。同时,指出了现有研究方法和研究内容的不足,以及应进一步深入研究之处。     

Experimental investigation of heat transfer with drop condensation inside horizontal tubes

The authors describe the method and present results of an investigation of heat transfer with drop condensation of water vapor, generated by injecting fluoridecontaining bisulphide into the condensate of a closed system.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 58, No. 3, pp. 488–492, March, 1990.     

Intensification of heat transfer in the condensation of water vapor on horizontal tubes with annular grooves

Results are presented from an experimental study of the mean heat-transfer coefficient in the film condensation of water vapor on the external surface of tubes with transverse periodic grooves of smooth configuration.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 55, No. 5, pp. 789–794, November, 1988.     

Theoretical study of heat transfer on horizontal tubes in the condensation of a descending vapor flow

A theoretical solution is proposed for a problem of heat transfer on horizontal tubes in the condensation of a descending vapor flow. Results are presented from calculation of theoretical heat transfer and are compared with experimental results.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 42, No. 3, pp. 376–382, March, 1982.     

Augmentation of two-phase heat transfer and pressure drop of refrigerants in horizontal tubes

Passive methods to improve the heat transfer characteristics of two-phase refrigerant flows by altering the tube-side geometry are reviewed and categorized for use in performing system studies and defining future research efforts. The information presented includes available correlations and data for the prediction of the two-phase, heat transfer coefficient and the pressure drop in six different geometries under various combinations of operating conditions and refrigerant selection.     

The effect of the horizontal vibrations on natural heat transfer from an isothermal array of cylinders

A numerical investigation is carried out to study an unsteady laminar natural convection heat transfer caused by an array of isothermal oscillating circular cylinders. Under oscillating conditions, flow and thermal fields are categorized into a class of moving boundary problems. In this study, the moving interfaces between the fluid and cylinders have been considered. The numerical model used in the present paper, is based on a 2D Navier–Stokes momentum and energy equations for an incompressible flow solver on an unstructured grid. Discretization of the governing equations including continuity, momentum and energy equations is achieved through a finite element scheme based on characteristic based split algorithm using the arbitrary Lagrangian–Eulerian approach to satisfy boundary movement. Besides a dual time stepping method is employed to capture unsteady flow and thermal characteristics. The working fluid is designated a Prandtl number of 0.71(air) and assumed to be incompressible with constant physical properties. The radiation, viscous dissipation and pressure work are also assumed to be negligible throughout this investigation. Fluid flow and heat transfer characteristics are examined in the domain of the Rayleigh number, cylinders spacing, amplitude, and frequency of oscillations such that: 10³ ≤ Ra ≤ 10⁵, 2 ≤ s/d ≤ 4, 0.5 ≤ l ≤ 2, and 0.1 ≤ f ≤ 0.4. The obtained results reveal that increment of Rayleigh number and cylinders’ spacing augment the average Nusselt of each cylinder as well as higher oscillation amplitude and frequency. Moreover, it was found that horizontal vibration makes vortices appear in the left and right area of the cylinders. These vortices reduce heat transfer from two upper cylinders.     

Condensation heat transfer of R410A inside internally grooved horizontal tubes

Heat transfer coefficients were measured for the condensation of R410A and R22 inside internally grooved horizontal tubes. The experiment was performed for five different kinds of internally grooved tubes of about 8.00 mm o.d. the shapes of which were conventional helical grooved and herring-bone grooved ones. To measure the local heat transfer coefficients, the test section was subdivided into 10 small sections having 1 m working length. The ranges tested are as follows: the refrigerant mass velocity was from 130 to 400 kg/(m²/s) for R410A and R22, and the vapour pressure was 2.4l MPa for R410A and 1.53 MPa for R22. The obtained heat transfer data of R410A and R22 indicate that the values of the local heat transfer coefficients of the herring-bone grooved tube are about twice as large as those of helical one. All measured local heat transfer coefficients of condensation were compared with the predicted values from previous correlations proposed by other researchers, and were well correlated with the empirical equation using the frictional coefficients for each tube proposed by the author.