K.N. Seetharamu

The combined effects of wall longitudinal heat conduction, inlet fluid flow nonuniformity and temperature nonuniformity in compact tube–fin heat exchangers: a finite element method

Abstract A finite element analysis of a crossflow tube–fin compact heat exchanger is presented. The analysis takes into account the combined effects of one-dimensional longitudinal heat conduction through the exchanger wall and nonuniform inlet fluid flow and temperature distributions on both hot and cold fluid sides. A mathematical equation is developed to generate different types of fluid flow⧹temperature maldistribution models considering the possible deviations in fluid flow. Using these fluid flow⧹temperature maldistribution models, the exchanger effectiveness and its deterioration due to the combined effects of longitudinal heat conduction and flow⧹temperature nonuniformity are calculated for various design and operating conditions of the exchanger. It was found that the performance deteriorations are quite significant in some typical applications due to the combined effects of longitudinal heat conduction, temperature nonuniformity and fluid flow nonuniformity on crossflow tube–fin heat exchanger.

Numerical simulation of vortex shedding past a circular cylinder under the influence of buoyancy

Flow past an isolated circular cylinder is numerically simulated, under the influence of aiding and opposing buoyancy. A modified velocity correction procedure is incorporated. Galerkin weighted residual formulation is employed for spatial discretization along with a second-order Runge–Kutta (R–K) time integration scheme. The influence of buoyancy on the Nusselt number, wake structures, temporal lift and drag forces have been studied. At low Reynolds numbers (for, e.g., Re=20–40), buoyancy opposing the flow could trigger vortex shedding. The degeneration of the Karman vortex street into twin vortices is numerically simulated for a heated cylinder. The two zones of vortex shedding and twin vortices are demarcated.

Convective heat transfer in axisymmetric porous bodies

A finite element method employing Galerkin’s approach is developed to analyze free convection heat transfer in axisymmetric fluid saturated porous bodies. The method is used to study the effect of aspect ratio and radius ratio on Nusselt number in the case of a proous cylindrical annulus. Two cases of isothermal and convective boundary conditions are considered. The Nusselt number is always found to increase with radius ratio and Rayleigh number. It exhibits a maximum when the aspect ratio is around unity; maximum shifts towards lesser aspect ratios as Rayleigh number increases. Results are compared with those in the literature, wherever available, and the agreement is found to be good.

The combined effects of longitudinal heat conduction, flow nonuniformity and temperature nonuniformity in crossflow plate-fin heat exchangers

An analysis of a crossflow plate-fin compact heat exchanger, accounting for the combined effects of two-dimensional longitudinal heat conduction through the exchanger wall and nonuniform inlet fluid flow and temperature distribution is carried out using a finite element method. A mathematical equation is developed to generate different types of fluid flow/temperature maldistribution models considering the possible deviations in fluid flow. Using these models, the exchanger effectiveness and its deterioration due to the combined effects of longitudinal heat conduction, flow nonuniformity and temperature nonuniformity are calculated for various design and operating conditions of the exchanger. It was found that the performance variations are quite significant in some typical applications.

Finite element analysis of transient natural convection in an odd‐shaped enclosure

The transient natural convective flow and heat transfer in a combined vertical and horizontal enclosure have been studied. The Galerkin’s finite element method coupled with Eulerian velocity correction scheme for pressure prediction has been employed. A detailed parametric study has been undertaken for evaluating the effects of Rayleigh number (Ra), width ratio (WR), and prescribed boundary conditions. The results indicate that the flow and isothermal patterns are strongly dependent on Ra and WR. Comparison with the results of vertical and horizontal enclosures indicates that the flow and heat transfer phenomena inside complex shaped cavities may be approximated in terms of the processes within vertical or horizontal sub‐domains. This appears to be reasonably valid if opposite walls of the enclosure are parallel. It is also observed that for certain types of boundary conditions, steady solutions do not exist at high Rayleigh numbers.

Effect of porosity on natural convective heat transfer in a fluid saturated porous medium

Abstract The effect of porosity on natural convective flow and heat transfer in a fluid saturated porous medium has been investigated using Galerkins finite element method. A generalised non-Darcy flow model with porosity as a separate parameter is used. Results indicate that the non-Darcy regime is highly sensitive to porosity changes. A variation of the order of 40% in the average Nusselt number is possible with change in the porosity, for the Rayleigh and Darcy number ranges considered.

Finite element simulation of transient laminar flow and heat transfer past an in-line tube bank

Abstract Finite element simulation of transient laminar flow past an in-line tube bank is carried out using a velocity correction procedure. The two-dimensional unsteady Navier–Stokes and energy equations are solved using an explicit and a semi-implicit algorithm for a Reynolds number of 100, a Prandtl number of 0.7, and pitch-to-diameter ratios (PDR) of 1.5 and 2.0. The Galerkin weighted residual formulation is used for the discretization in space. Numerical flow visuals are drawn, showing the time evolution of streamlines. Local and average Nusselt numbers, pressure, and shear stress distributions around the cylinders have also been determined. The results compare well with existing numerical simulations.

Solution of transient laminar natural convection in a square cavity by an explicit finite element scheme

This paper discusses the application of a finite element method based on the first-order projection scheme, which is an extension ofChorins algorithm, to transient laminar natural convection in a square cavity. Results have been presented for a fluid of Prandtl number 0.71 in the Rayleigh number range of 103-106 in terms of the variation of vertical velocity component, nondimensional temperature, and average Nusselt number with time. Various features of the scheme that render it economical in terms of CPU time and storage requirements are discussed. The steady state results have been compared with benchmark solutions, and the agreement appears to be good.

Finite element modelling of heat transfer analysis in machining of isotropic materials

Abstract A steady state 2-D and 3-D finite element analysis has been carried out for heat transfer analysis in machining of isotropic materials. Using the developed code, reassessment of available literature has been carried out. The effect of the convective heat transfer coefficient in machining has been highlighted. Using empirically available (or experimentally determined) cutting force and feed force values, a numerical model has been developed to predict the tool–chip interface temperature profile.xa0An extensive parametric study has been carried out for free cutting steels, copper and brass, using cutting data available in the literature, and the results of 3-D analysis are compared with the 2-D analysis and the available literature.

Finite element analysis of radial cooled rotating electrical machines

Accurate prediction of temperature distribution in an electrical machine at the design stage is becoming increasingly important. It is essential to know the locations and magnitudes of hot spot temperatures for optimum design of electrical machines. A methodology based on axi‐symmetric finite element formulation has been developed to solve the conduction‐convection problem in radial cooled machines using a new eight noded solid‐fluid coupled element. The axi‐symmetric model adopted is formulated purely from dimensional data, property data and published convective correlations. Steady state temperatures have been determined for 102 kW radial cooled motor at 100 percent and 75 percent loads and are validated with experimental results obtained from heat run tests. Parametric studies have been carried out to study the effect of critical parameters on temperature distribution and for optimising the design.