摘要:

Using a vectorized finite-difference marching technique, the steady-state continuity, momentum, and energy equations are solved numerically to evaluate the effects of buoyancy-induced secondary flow on forced flow in a horizontal rectangular duel with a four-row array of 12 neat sources flush mounted to the bottom wall. Secondary flows, in the form of longitudinal vortices, initially develop at spanwise positions corresponding to the edges of the heat sources. Additional plumes and vortices subsequently develop across the heater width, leading to the eventual formation of large-scale circulation patterns. For a fixed Rayleigh number and decreasing Reynolds number, the row-average Nussell numbers decrease, reach a minimum, and subsequently increase due to buoyancy effects. Thus, due to buoyancy-induced secondary flow, conditions exist for which heat transfer may be enhanced by reducing the flow rate and hence the pump power requirement. Heal transfer enhancement above the forced convection limit, as well as the Reynolds number range for which enhancement occurs, increases with increasing Rayleigh number. Appropriate scaling parameters are introduced to characterize the strength of the buoyancy-induced secondary flow and to delineate conditions for which it is significant.

ISSN:1040-7782    

DOI:10.1080/10407788908944717

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The heat transfer characteristics of a Newtonian fluid in a two-dimensional, planar, right-angled tee branch are studied over a range of inlet Reynolds numbers and Grashof numbers. The flow and heat transfer equations, subject to the Boussinesq approximation, are solved using a finite-element discretization. The effects of the branch length and the grid size on the interior flow field are examined to assess the accuracy of the solutions. Results are presented for two types of experimentally realizable boundary conditions—equal exit pressure at the outlet of each branch and specified flow split between the branches. The thermal boundary condition of uniform wall temperature is examined. The effect of increasing Reynolds number is to increase the size and strength of the recirculation zones in both the main and side branches, while that of increasing Grashof number is to decrease such an effect. For the case of equal exit pressures there is a significant flow reversal in the side branch and the exit flow rate from the main branch increases linearly with increasing Gr/Re2. For the case of specified flow split, an increasing back pressure is required to be maintained at the exit of the main branch to regulate the flow split at the desired level.

ISSN:1040-7782    

DOI:10.1080/10407788908944718

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Developing natural convection in an asymmetrically heated, open-ended vertical channel was studied both experimentally and numerically. A tightly stretched, perforated, plastic radiation shield was suspended parallel to an electrically heated aluminum plate to form a vertical channel. In order to model the heat transfer and fluid flow in the vertical channel, the unsteady, two-dimensional Navier-Stokes equations were solved using a primitive variable, finite-difference formulation. Flow through the perforated boundary was modeled using a modified form of Darcy's law. Radiative exchange between the boundaries and between the boundaries and the environment was included. The predicted mass flow was within 3% of that measured experimentally. Both the average plate temperature and the bulk exit channel air temperature were within 1·2°C of the measured values. However, the predicted average temperature of the radiation shield was 8°C higher than that measured.

ISSN:1040-7782    

DOI:10.1080/10407788908944719

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Transient laminar natural convection in a two-dimensional enclosure partitioned by an adiabatic baffle is investigated numerically, A penalty finite-element method with a Newton-Raphson iteration algorithm and a backward difference scheme dealing with the time term are adopted to solve governing equations. The effects of the baffle and Rayleigh number on the heat transfer mechanism are found to be substantial during the transient process for Rayleigh numbers of 104and 106. However, the variations of the heat transfer mechanism occur mainly in the first one-third of the time period of the transient, in spite of the presence, absence, or location of a baffle.

ISSN:1040-7782    

DOI:10.1080/10407788908944720

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

A two-dimensional finite-element nonlinear transient heat conduction model was developed and used to simulate deep-penetration keyhole laser welds in aluminum alloys. The weld thermal profiles were calculated in an arbitrary reference plane as the laser beam approached and passed the plane. From the calculated thermal profiles, three-dimensional quasi-steady-state shapes of the weld pools were determined. The predicted weld bead shape and dimensions were in good agreement with the experimental results. The experimental laser welds in aluminum alloys contained large amounts of porosity. The model predicted large mushy zones for aluminum laser welds during solidification, which in turn increase the probability of porosity formation by increased bubble entrapment.

ISSN:1040-7782    

DOI:10.1080/10407788908944721

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The discharge of sewage effluent from ports in a long diffuser pipe on the ocean bottom produces a flow pattern that may be idealized as a buoyant jet from a line source. To minimize the impact of emission of pollutants, the dispersion of wastewater should be predictable, and the prediction of the maximum height of rise is important in determining whether or not the jet will remain submerged. A buoyancy-extended K-ϵ model of turbulence has been developed for calculating the dynamical and thermal fields in forced plane plumes vertically discharged into a stably stratified environment. The predicted maximum height of rise for the linearly stratified quiescent ambient case is compared with available experimental data. An idealized two-layer situation is then considered in such a way as to simulate a thermocline in the upper part of the ocean. Numerical results are presented for a uniform horizontal cross-stream situation.

ISSN:1040-7782    

DOI:10.1080/10407788908944722

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The effects of conjugate heat transfer, vapor compressibility, and viscous dissipation in heat pipes are discussed. The accuracy of the partially parabolic versus the elliptic presentation of the governing equations is also examined. The results show that the axial wall conduction has a tendency to make the temperature distribution more uniform for heat pipes with large ratios of pipe wall to effective liquid-wick thermal conductivity. The compressible and incompressible models show very close agreement for the total pressure drop, white the local pressure variations along the heat pipe are quite different for these two models when the radial Reynolds number at the interface is high.

ISSN:1040-7782    

DOI:10.1080/10407788908944723

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor