摘要:

Mixed convection flow fields and heat transfer of partially enclosed axial and radial laminar jets impinging on a heated flat plate have been investigated from the numerical solution of incompressible unsteady Navier-Stokes and energy equations with a Boussinesq approximation. For mixed convection flow at Re = 200, steady flow has not been observed for either the radial or the axial jet. For the smallest Crashof number (Gr = 10,000), periodic solutions have been obtained. With Gr = 40,000, nonsteady nonperiodic (chaotic) flow appears. Free convection may increase the heat transfer by more than 200 %.

ISSN:1040-7782    

DOI:10.1080/10407789408955984

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A numerical model is developed to determine convective heat transfer distributions for an array of submerged planar jets impinging on a uniform heat flux or constant temperature moving surface where the surface motion is directed perpendicular to the jet planes. Unlike prior related work, the model accounts for the interaction between neighboring jets in the array without imposition of an imposed cross flow. The effects of surface speed, nozzle separation distance within an array, nozzle height, and Reynolds number on the flow field, coefficient of friction, and Nusselt number are investigated. Results suggest that neglecting surface motion effects can lead to overestimates of heat transfer.

ISSN:1040-7782    

DOI:10.1080/10407789408955985

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

This work deals with the problem of transient conjugated mixed convection heat transfer in a vertical pipe maintained at either uniform heat flux (UHF) or uniform wall temperature (UWT). The effects of the ratio of Grashof number to Reynolds number Gr / Re, conductivity ratio K, diffusivity ratio A, and dimensionless wall thickness Δ on the interfacial heat flux, velocity, and temperature profiles are discussed in detail. Three conditions of wait effects were examined, i.e., zero wall thickness (case A), effect of heat capacity (case B), and dual effects of heat capacity and wall conduction (case C). The prediction shows that the results of case C give a longer thermal lag than those of case B. Additionally, for the case of UWT, the time for the system to reach the steady state condition is indistinguishable for the system having K and A ≥ 100 or Δ ≥ 0.2.

ISSN:1040-7782    

DOI:10.1080/10407789408955986

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A two-dimensional finite difference computer program in cylindrical coordinates has been developed to solve the case of laminar natural convection in a vertical tube open to a large reservoir. Such a device, the open thermosyphon, is used in a number of applications, including the cooling of gas turbines, geothermal energy extraction, and thermosyphon solar water heaters. The objectives of this work were to study the nature of fluid flow and the heat transfer rate along the tube wall. A semi-implicit, time marching, finite difference solution procedure was used, satisfying continuity, momentum, and energy equations for incompressible flow. Results show three well-defined flow regimes appearing as functions of the tube length-to-radius (aspect) ratio. Fluid motion in the tube and heat transfer rates became oscillatory at long time intervals. Plots of streamlines and isotherms at selected times for different aspect ratio tubes are also presented to show the transient behavior of fluid motion.

ISSN:1040-7782    

DOI:10.1080/10407789408955987

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Methods that predict heat transfer rates in thermally developing flows, important in engineering design, are often compared with the classical Graetz problem. Surprisingly, numerical solutions to this problem generally do not give accurate results in the entrance region. This inaccuracy stems from the existence of a singularity at the tube inlet. By adopting a fundamental approach based upon singular perturbation theory, the heat transfer process in the tube entrance has been analyzed to bring out the asymptotic boundary layer structure of the generalized problem with non-Newtonian flows. Using a standard finite difference method with only 21 radial nodes, results within 0.3% of the exact solution to the Graetz problem (Newtonian limit of generalized power law fluid flows) are obtained. Compared with previous numerical solutions reported in the literature, these results are an order of magnitude improvement in the accuracy with an order of magnitude decrease in the required number of radial nodes. Also, the number of radial nodes does not have to be increased in the present method to maintain this high level of accuracy as the initial singularity is approached. Solutions for power law, non-Newtonian fluid flows are presented, and generalized correlations are given for predicting Nusselt numbers in both the thermal entrance region and fully developed flows with 0 < n ≤ ∞.

ISSN:1040-7782    

DOI:10.1080/10407789408955988

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A computational procedure is described to study the mixing flow in a multilobe turbofan mixer. The predictions have been obtained using a finite volume method to solve the density-weighted time-averaged Navier-Stokes equations. Turbulence is characterized by the k-ε eddy viscosity model. To fit the irregular boundaries of the flow field, the curvilinear nonorthogonal coordinates are employed. The robustness of the computational procedure is enhanced by making use of nonstaggered grids. Results show that the streamwise vortex generated at the exit of the lobes dominates the performance of the mixing process. Comparison with experimental data indicates that good predictions can be obtained provided that sufficient inlet conditions are given.

ISSN:1040-7782    

DOI:10.1080/10407789408955989

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Laminar fluid flow and forced convection heat transfer over equally spaced linear arrays of spheres are analyzed using the finite element package FIDAP. For the arrays, sphere spacings of 1.5, 2, and 3 diameters are examined at Reynolds numbers of 40, 80, and 120 and Prandtl numbers ranging from 0.73 to 7.3. Average Nusselt numbers and drag coefficient data for a linear array of eight spheres (as an approximation to the developing region) and a single sphere with periodic boundary conditions (as an approximation to fully developed flow) are presented and correlated.

ISSN:1040-7782    

DOI:10.1080/10407789408955990

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor