G. Comini

Thermal Aspects of Cryosurgery

Tissue reactions to cryosurgical procedures depend on temperature variations and on rates of temperature variations induced by freezing probes. In this paper thermal responses of biological systems undergoing freezing are obtained through the application of the finite element method to the solution of the nonlinear bio-equation. This model allows realistic predictions of isotherm fields and of rates of freezing in practically any cryosurgical procedure.

CFD simulation of refrigerated display cabinets

Abstract The finite element method is employed for the analysis of velocity and temperature distributions in refrigerated open display cabinets. The CFD code is based on the streamfunction-vorticity formulation, and incorporates a LES turbulence model. As an example of application, a vertical multi-deck cabinet is investigated under different operating conditions. The numerical results have been validated by comparison with experimental tests performed in accordance with the EN441 Standard. The influence of various design parameters has been investigated.

FINITE-ELEMENT SOLUTION OF THE INCOMPRESSIBLE NAVIER-STOKES EQUATIONS

A finite-element procedure is presented for the calculation of two-dimensional, viscous, incompressible flows of a recirculating nature. As in finite-difference procedures, velocity and pressure are uncoupled and the equations are solved one after the other. Velocity fields are determined by first calculating intermediate velocity values based on an estimated pressure distribution and then obtaining appropriate corrections to satisfy the continuity equation. Illustrative examples involving flow in the entrance region between parallel plates, lid-driven cavity flow, and flow around an obstacle demonstrate the accuracy and capabilities of the proposed technique.

AN EQUAL-ORDER VELOCITY-PRESSURE ALGORITHM FOR INCOMPRESSIBLE THERMAL FLOWS, PART 1: FORMULATION

Abstract A finite-element algorithm is presented for the solution of two- and three-dimensional incompressible laminar thermal flows. The algorithm is cast in a time-dependent form and can be classified as a projection finite-element method. However, the procedure utilized for handling Ike velocity-pressure coupling shares many features with the SIMPLER finite-difference method. In fact, given an initial or guessed velocity field, the pseudo-velocities, i.e., the velocities that would prevail in the absence of the pressure field, are found first. Then, by enforcing continuity on the pseudo-velocity field, the tentative pressure is estimated and the momentum equations are solved in sequence for the velocity components. Afterward, continuity is enforced again to find corrections that are used to modify the velocity field and the estimated pressure field. Finally, if required, the energy equation is solved before moving to the next step.

Finite-element analysis of convection problems in spatially periodic domains

The finite-element method is used to solve fully developed convection problems in spatially periodic domains. Symmetric and antisymmetric periodicity in temperature is imposed in an original way that allows for different thermal boundary conditions at the walls. The formulation is first validated by comparing the numerical results with the analytical solutions for fully developed velocity and temperature distributions in a parallel-plate channel. Afterward, the accuracy and the capabilities of the procedure are demonstrated by two examples involving laminar flow and heat transfer in a periodic corrugated channel and in a parallel-plate channel with staggered fins.

EFFECT OF ASPECT RATIO ON CONVECTION ENHANCEMENT IN WAVY CHANNELS

Pressure drop and heat transfer characteristics are investigated in the fully developed region of three-dimensional wavy channels whose aspect ratios (width over height) range from one to infinity. Numerical simulations show that Nusselt numbers and friction factors increase with decreasing aspect ratios, in such a way that global performances improve. In all the channels considered, friction factors always increase with the Reynolds number, while Nusselt numbers significantly increase only above the critical value of the Reynolds number at which self-sustained flow oscillations begin. In turn, the critical value of the Reynolds number decreases with the aspect ratio, down to a minimum that is reached asymptotically.

Convective heat and mass transfer in wavy finned‐tube exchangers

The paper adopts a simplified two‐dimensional approach to deal with convective heat and mass transfer in laminar flows of humid air through wavy finned‐tube exchangers. The computational domain is spatially periodic, with fully developed conditions prevailing at a certain distance from the inlet section. Both the entrance and the fully developed flow region are investigated. In the fully developed region, periodicities in the flow, temperature and mass concentration fields are taken into account. The approach is completely general, even if the finite element method is used for the discretizations. In the application section, velocity, temperature, and mass concentration fields are computed first. Then apparent friction factors, Nusselt numbers, Colburn factors for heat and mass transfer, and goodness factors are evaluated both in the entrance and in the fully developed region.

A STREAMFUNCTION-VORTICITY-BASED FINITE-ELEMENT FORMULATION FOR LAMINAR-CONVECTION PROBLEMS

Abstract The finite-element method is used to solve mixed-, farced-, and natural-convection problems in two-dimensional incompressible laminar flows. The streamfunction-vorticity equations are uncoupled and solved in sequence with the energy equation. The wall vorticity is evaluated in the framework of the streamfunction equation, and particular care is taken to specify inflow and outflow boundary conditions properly. The resulting scheme achieves convergence without the traditional need for upwinding, even for very high values of the Reynolds and the Rayleigh numbers. Stability and accuracy of the approach are demonstrated by the solution of three well-known test problems concerning mixed and forced convection downstream of a backward-facing step, and natural convection in a heated square cavity.

LAMINAR FORCED CONVECTION IN THREE-DIMENSIONAL DUCT FLOWS

A finite-element procedure for the prediction of laminar forced convection in three-dimensional parabolic flows is presented. The procedure, based on the parabolized simplification of the complete Navier-Stokes equations, is first validated by comparing computed results with the available literature data for thermally and hydrodynamically developing flows in flat channels. Then, new results are presented for simultaneously developing flows in square duels, with

Convective heat transfer in ribbed square channels

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