摘要:

Quenching experiments were performed to determine the effect of watt material properties on pool boiling heat transfer for downward facing convex surfaces( radius of curvature 218.5 mm) in saturated water. Experiments employed 303e-type stainless steel and copper test sections having identical dimensions ( 75 mm in diameter and 20 mm thick). Pool boiling curves were constructed on the basis of two-dimensional numerical solution of transient heat conduction in spherical coordinates( r, 9) in test sections during quenching. The measured temperature histories at nine interior locations near the boiling surface ( ∼0.5 mm) provided a time-dependent boundary condition for the numerical solution. To ensure stability and reduce both computer storage and execution time, the numerical solution used the alternating direction implicit ( ADD method with control volume representations. A sensitivity analysis was conducted to assess the effect of grid size on computation time as well as the accuracy of calculated temperatures and pool boiling heat flux values. Best results were obtained using a 20 × 20 network of control volumes and a noniterative approach, whereas the computation time on a Pentium 90-MHz PC for the entire pool boiling curve was about 7% of real time. Calculated temperatures near the top surface ( ∼5 mm) agreed with measured values to within 0.5 and 2.5 K for copper and stainless steel, respectively. The error in the overall energy balance in the test section, performed after each time interval, was less than 0.001%. The thermal diffusivity of test section material strongly affected both radial conduction within the section and lateral conduction near the boiling surface and, hence, the local pool boiling curves as well as the maximum and minimum pool boiling heat flux values.

ISSN:1040-7782    

DOI:10.1080/10407789608913806

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A comparative study is presented of two time marching schemes for simulating oscillatory natural convection of low-Prandtl-number fluids in a square cavity. Fully implicit time marching, which is first-order accurate in time, is compared with the second-order-accurate, semi-implicit (Crank-Nicolson) scheme. Both methods are implemented in a control-volume-based finite difference formulation with the central difference scheme used for advection and diffusion terms. Calculations are compared in detail for Gr = 107and Pr = 0.00S, and results for Gr = 106and 3 × 10" are briefly summarized. While both time marching schemes predict oscillatory convection at Gr = 107using an 82 × 82 grid and dimensionless time steps [( Δtα/ L2)Pr√Gr[of 1/80, the flow structure and dynamic behavior predicted by the semi-implicit scheme are more complex than those predicted by the fully implicit scheme. Moreover, it is shown that the semi-implicit calculations are independent of time step while the fully implicit calculations are not.

ISSN:1040-7782    

DOI:10.1080/10407789608913807

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A numerical analysis was carried out to study the detailed heat and mass transfer processes between a condensation liquid film and mixed turbulent moist airflow. Results show that the condensation latent heat transfer is more important for a system with higher inlet relative humidity or lower inlet Reynolds number of a moist airstream. The heat and mass transfer coefficients are higher for a system with higher inlet relative humidity and inlet Reynolds number of moist air. In addition, the aiding-buoyancy forces cause diminution in heat and mass transfer results compared with the corresponding results of forced convection.

ISSN:1040-7782    

DOI:10.1080/10407789608913808

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The incompressible unsteady flow past a channel with a pair of cylinders of rectangular cross section, placed in tandem normal to the flow, is investigated by numerical simulation. The objective is to evaluate the effect of cylinder separation distance, S / H, on the flow behavior and heat transfer on the channel walls, over a range of Reynolds numbers. Above a critical Reynolds number, these flows bifurcate to a time-periodic self-sustained oscillatory state. The results reveal for S / H = 2.0 three distinct flow patterns: steady flow ( Re = 200), time-periodic oscillatory state ( 400 < Re < 800), and quasi-periodic oscillatory flow ( Re = 1000). For S / H < 2.0 the intercylinder flow consists of a pair of steady counterrotating eddies that do not exchange fluid with the surrounding and unsteady eddies. Eddy shedding is observed only for the downstream cylinder for Re > 600.

ISSN:1040-7782    

DOI:10.1080/10407789608913809

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A study is made of steady, natural convection in a shallow horizontal porous layer, saturated by an electrically conducting fluid, to which a transverse magnetic field is applied. The enclosure is insulated on the top and bottom walls, while an end-to-end temperature difference between the vertical walls is imposed. The problem is governed by three dimensionless parameters; the Darcy-Rayleigh number Ra, the cavity aspect ratio A, and the Hartmann number Ha. On the basis of Darcy's equation, an approximate analytical solution, valid in the limit of a shallow cavity ( A→0), is developed using matched asymptotic expansions. The solution is given up to 0( A3). A numerical study of the same phenomenon, obtained by solving the complete system of governing equations, is also conducted. The study covers the range of Ra from 0 to 500, Ha from Oto5, and A from O.O5 to 1. Results are presented for the velocity and temperature profiles and heat transfer in terms of the governing parameters. Upon comparing the analytical and the numerical results, the range of validity of the approximate analytical solution is discussed.

ISSN:1040-7782    

DOI:10.1080/10407789608913810

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

In a numerical model of the directional solidification of a binary alloy, unreasonable results and/or oscillatory values of the concentration can occur when simulations of solidification scenarios with large thermal gradients approaching plane front conditions are attempted.

ISSN:1040-7782    

DOI:10.1080/10407789608913811

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor