Conjugate mixed convection heat transfer from a vertical rectangular fin

A numerical investigation of the heat transfer from a rectangular fin by combined forced and natural convection is presented. Results are given for buoyancy parameters in the range of $\text{0 ?}\text{Gr/Re}{}^2\text{? 2}$ and convection - conduction parameters in the range of $\text{0 ? √}\text{Re k}{}_{\mathrm{f}}\text{L/k}{}_{\mathrm{s}}\text{b}\text{? 10}$. The results are compared with the conventional fin theory and it is found that concerning the fin efficiency, the latter produces acceptable results although it is not strictly correct.     

Experimental and Numerical Simulations of Flow and Heat Transfer in Heat Exchanger Elements Using Liquid Crystal Thermography

Experimental and numerical investigation of heat transfer and fluid flow were conducted for classic heat exchanger elements (flat plate with fin-tubes in-line, staggered and with vortex generators) and corrugated-undulated ducts under transitional and weakly turbulent conditions.The dependence of average heat transfer and pressure drop on Reynolds number and geometrical parameters was investigated. Distributions of local heat transfer coefficient were obtained by using liquid crystal thermography and surface-averaged values were computed. Three-dimensional numerical simulations were conducted by a finite-volume method using a low-Reynolds number k-e model under the assumption of fully developed flow. Computed flow fields provided otherwise inaccessible information on the flow patterns and the mechanisms of heat transfer enhancement.     

Experimental study of heat transfer coefficient with rectangular baffle fin of solar air heater

This paper presents an experimental analysis of a single pass solar air collector with, and without using baffle fin. The heat transfer coefficient between the absorber plate and air can be considerably increased by using artificial roughness on the bottom plate and under the absorber plate of a solar air heater duct. An experimental study has been conducted to investigate the effect of roughness and operating parameters on heat transfer. The investigation has covered the range of Reynolds number Re from 1259 to 2517 depending on types of the configuration of the solar collectors. Based on the experimental data, values of Nusselt number Nu have been determined for different values of configurations and operating parameters. To determine the enhancement in heat transfer and increment in thermal efficiency, the values of Nusselt have been compared with those of smooth duct under similar flow conditions.     

Heat transfer augmentation in a plate‐fin heat exchanger using a rectangular winglet

This study presents numerical computation results on laminar convection heat transfer in a plate‐fin heat exchanger, with triangular fins between the plates of a plate‐fin heat exchanger. The rectangular winglet type vortex generator is mounted on these triangular fins. The performance of the vortex generator is evaluated for varying angles of attack of the winglet i.e., 20, 26, and 37° and Reynolds number 100, 150, and 200. The computations are also performed by varying the geometrical size and location of the winglet. The complete Navier–Stokes equation and the energy equation are solved by the (Marker and Cell) MAC algorithm using the staggered grid arrangement. The constant wall temperature thermal boundary conditions are considered. Air is taken as the working fluid. The heat transfer enhancement is seen by introducing the vortex generator. Numerical results show that the average Nusselt number increases with an increase in the angle of attack and Reynolds number. For the same area of the LVG, the increase in length of the LVG brings more heat transfer enhancement than increasing the height. The increase in heat transfer comes with a moderate pressure drop penalty. © 2010 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/htj.20318     

Transient heat transfer in a heat‐generating fin with radiation and convection with temperature‐dependent heat transfer coefficient

The transient heat transfer in a heat‐generating fin with simultaneous surface convection and radiation is studied numerically for a step change in base temperature. The convection heat transfer coefficient is assumed to be a power law function of the local temperature difference between the fin and its surrounding fluid. The values of the power exponent n are chosen to include simulation of natural convection (laminar and turbulent) and nucleate boiling among other convective heat transfer modes. The fin is assumed to have uniform internal heat generation. The transient response of the fin depends on the convection‐conduction parameter, radiation‐conduction parameter, heat generation parameter, power exponent, and the dimensionless sink temperature. The instantaneous heat transfer characteristics such as the base heat transfer, surface heat loss, and energy stored are reported for a range of values of these parameters. When the internal heat generation exceeds a threshold the fin acts as a heat sink instead of a heat source. © 2012 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21012     

Analytical solutions of 1-D heat conduction problem for a single fin with temperature dependent heat transfer coefficient - I. Closed-form inverse solution

Closed-form solution of 1-D heat conduction problem for a single straight fin and spine of constant cross-section has been obtained. The local heat transfer coefficient is assumed to vary as a power function of temperature excess. The dependence of the fin parameter N on the dimensionless temperature difference T_e at the fin tip for a given exponent n was derived in a form N/N₀=T_e^−μn (where N₀ is a well-known N expression for n=0). Coefficient μ was found to be equal to 5/12 according to the exact solution at T_e→1 or to 0.4 according to the fitting procedure for the data of the numerical integration. Obtained formula serves as a basis for the derivation of the direct expressions for T_e vs N at given n, fin base thermal conductance and augmentation factor presented in the second part of the study.     

Analytical solutions of the 1-D heat conduction problem for a single fin with temperature dependent heat transfer coefficient - II. Recurrent direct solution

The recurrent direct solution of the 1-D heat conduction problem for a single straight fin and spine with power-law-type temperature dependent heat transfer coefficient has been derived using inversion of the closed-form solution obtained in the first part of the study. The expression with improving convergence to calculate accurately the dimensionless temperature excess T_e at the fin tip for a given values of the fin parameter N and exponent n in heat transfer equation has been obtained by a linearization method. Equation for the temperature excess distribution throughout the fin has also been derived. The obtained formula for T_e allows to calculate the fin base thermal conductance and augmentation factor. Obtained expressions are seen to be simple and convenient for the engineering design of the fins and finned surfaces.     

Natural convection heat transfer from a thermal heat source located in a vertical plate fin

A steady state conjugate conduction–convection investigation is performed on vertical plate fin in which a small heat source is located. Heat from the fin surface is transferred to the surroundings by laminar natural convection. The governing equations for the problem are the heat conduction equation for the fin and the boundary layer equations, which are continuity, momentum and energy equations, for the fluid. A computer program is written by using the finite difference method in order to solve the governing equations which are nonlinear and coupled. The best location of the heat source in the fin for maximum heat transfer rate depends on two parameters which are the conduction–convection parameter and the Prandtl number. The obtained results have shown that for the fin with large conduction–convection parameter, a heat source location for maximum heat transfer rate exists.     

Electrohydrodynamic enhancement of heat transfer in vertical fin array using computational fluid dynamics technique

Electrohydrodynamic enhanced heat transfer of the natural convection inside an enclosure with a vertical fin array is numerically investigated via a computational fluid dynamics technique. The parameters considered in a numerical modeling are supplied voltage, Rayleigh number, inclined angle, number of electrodes, electrode arrangement, number of fins, and fin length. The results reveal that the flow and heat transfer enhancements are significantly dependent on the number and position of electrodes around the fins. Moreover, the heat transfer coefficient is substantially improved by the electric field especially at the large number of fins and the long fin length.     

MHD flow and heat transfer in a rectangular duct with temperature dependent viscosity and hall effect

In the present paper the laminar fully developed MHD flow and heat transfer through a rectangular duct of a viscous incompressible electrically conducting fluid is studied. A constant pressure gradient and an external uniform magnetic field are applied and the Hall effect is taken into consideration. The fluid viscosity is assumed to be temperature dependent with the assumption of constant wall heat flux axially and constant wall temperature peripherally. A numerical solution for the governing non-linear partial differential equations is obtained. The effect of the Hall term and the variable viscosity on the velocity and temperature fields is examined.     

Time‐dependent heat transfer coefficient of a wall

A time‐dependent coefficient of heat transfer is proposed for the computation of thermal power required, so that a room temperature reaches a desired value within a given time. A mathematical formulation of the room heating transient phenomenon is constructed in a dimensionless form. Using an integral approximate solution an analytical expression for this coefficient is provided and it is verified by diagrams adopted by DIN 4701. Copyright © 2003 John Wiley & Sons, Ltd.     

Thermal distribution analysis of rectangular fin considering multiboiling heat transfer modes

In this investigation, a numerical method is used to compute the thermal distribution analysis of a rectangular fin with surface emissivity and internal heat generation. Here, the thermal conductivity, heat generation, emissivity at the surface, and coefficient of heat transfer depend on temperature linearly. The role of four distinct multiboiling heat transfer modes such as laminar film boiling (condensation), laminar convection, turbulent convection, and nucleate boiling are discussed in detail and the corresponding outcomes are displayed graphically. Isolated (insulated) and convective tip boundary conditions for the fin tip are employed in this study. The solution is obtained using shooting technique involving Runge Kutta Fehlberg method. It is emphasized that the thermal distribution shows a diminishing trend for the convective tip condition compared to the insulated tip. In addition to this, it is illustrated that laminar film boiling and laminar convection are two effective modes of heat transfer in comparison with turbulent convection and nucleate boiling for a finned surface in boiling liquids. The study on fin efficiency shows that fin efficiency increases with the increase in internal heat generation number.     

Conjugate mixed convection-conduction heat transfer along a vertical cylindrical fin in non-newtonian fluids

By considering the interaction between conduction within the fin and convection to the fluid surrounding the fin, an analysis is presented to study the heat transfer characteristics of laminar mixed convection of a non-Newtonian fluid flow over a vertical cylindrical fin. Due to the compatibility conditions of heat flux and temperature at the surface of fin, the boundary layer equations of the fluid are coupled with the heat conduction equation of the fin and should be solved simultaneously. Of interest are the effects of transverse curvature parameter, bouyancy parameter, power-law viscosity index, generalized Prandtl number and conjugate convection-conduction parameter on the local heat transfer coefficient, local heat flux and temperature distribution of the fin. Comparison of the calculated results with available data sets in the open literature for a Newtonian fluid shows a very good performance of the present numerical procedure.     

Heat transfer performances of vertical rectangular fins protruding from rectangular bases: Effect of fin length

The effects of increasing the fin length from 250 to 375 mm on (i) the steady-state rate of heat loss and (ii) the optimal uniform fin separation of vertical rectangular fins protruding from a horizontal or a vertical rectangular base, have been investigated experimentally. A constant base temperature, 40 (±0·3)°C above that of the ambient environment, was used.     

垂直矩形窄缝内的过冷流动沸腾换热性能

用高速摄像等方法研究了有压模化介质在单一垂直矩形窄缝流道内的气泡形态和传热情况 ,发现窄缝流动沸腾换热强化的原因在于流道尺寸较小 ,气泡的形状发生变化 ,增加了界面体积浓度 ,并强化了对加热面附近的扰动 ,使换热有所强化。通过与实际测量的壁温数据进行比较 ,发现用于计算大流道和池过冷沸腾换热的 Rohsenow关系式预测窄流道内高热流密度下的过冷流动沸腾换热的误差不大 ,但对于较低热流密度下的过冷流动沸腾时误差较大 ;通过最小二乘法对 Rohsenow关系式进行修正后 ,误差低于± 2 5 %。     

Parametric study of natural convection heat transfer from horizontal rectangular fin arrays

A systematic theoretical investigation of the effects of fin spacing, fin height, fin length and temperature difference between fin and surroundings on the free convection heat transfer from horizontal fin arrays was carried out. The three-dimensional elliptic governing equations were solved using a finite volume based computational fluid dynamics (CFD) code. Preliminary simulations were made for cases reported in the literature. After obtaining a good agreement with results from the literature a large number of runs were performed for a detailed parametric study. It has been shown that it is not possible to obtain optimum performance in terms of overall heat transfer by only concentrating on one or two parameters. The interactions among all the design parameters must be considered. Results are presented in graphical form together with optimum values and correlations, and compared with available experimental data from the literature.