Showing papers on "Film temperature published in 1988"

Free Convection Flow of Non-Newtonian Fluids Along a Vertical Plate Embedded in a Porous Medium

Abstract: The problem of free convection flow of a non-Newtonian power law fluid along an isothermal vertical flat plate embedded in the porous medium is considered in the present study. The physical coordinate system is shown schematically in Fig 1. In the present study, it is assumed that the modified Darcy law and the boundary layer approximation are applicable. This implies that the present solutions are valid at a high Rayleigh number. With these simplifications, the governing partial nonlinear differential equations can be transformed into a set of coupled ordinary differential equations which can be solved by the fourth-order Runge-Kutta method. Algebraic equations for heat transfer rate and boundary layer thickness as a function of the prescribed wall temperature and physical properties of liquid-porous medium are obtained. The similarity solutions can be applied to problems in geophysics and engineering. The primary purpose of the present study is to predict the characteristics of steady natural convection heat transfer using the model of the flow of a non-Newtonian power law fluid in a porous medium given by Dharmadhikari and Kale (1985). Secondly, the effects of the new power law index n on heat transfer are investigated.

Falling film heat transfer analysis on a bank of horizontal tube evaporator

Abstract: Heat transfer analysis of falling film evaporation on a bank of horizontal tubes is investigated in this study. Liquid falling from one tube to the next lower one is considered as a thin liquid jet impinging on the top of the tube with a uniform free falling velocity. The hydrodynamic and thermal solutions are obtained by a finite difference method. In these solutions the heat transfer coefficients are modified to account for waviness. Liquid film thickness and local and average heat transfer coefficients are obtained for the constant heat flux and isothermal boundary conditions. Convective heat transfer effects are shown to be dominant as Peclet number increases. Heat transfer coefficients for the tubes in a tube bank decrease from the first tube onwards until the fully developed region is reached. The present predictions agree favorably with the reported heat transfer data.

Transient temperature fields in crossflow heat exchangers with finite wall capacitance

Abstract: Solutions are provided in non dimensional form for the transient analysis of direct-transfer crossflow heat exchangers, with both fluids unmixed and finite wall heat capacity. The two-dimensional transient temperature distributions of core wall and both fluids are determined by analytical methods for any externally applied variation of the primary fluid inlet temperature. The general solutions are derived by the local energy balance equations, and are presented as simple integrals of the Green's functions, which represent the pulse response following a deltalike perturbation in the inlet temperature of the primary fluid, and are deduced using the Laplace transform method. The Green's functions are expressed as integrals of modified Bessel functions, in terms of the heat capacity ratios, number of transfer units, heat transfer resistance and flow capacitance ratios.

Analysis of the friction (spin)-welding process for thermoplastics

Abstract: The friction (spin)-welding process for thermoplastics is known to consist of four phases: (1) initial heating of the interface to the melting temperature by Coulomb friction, (2) unsteady melting and flow in the transverse direction, (3) steady-state flow, and (4) unsteady flow and solidification after the spin motion is stopped. Simple analytical models, which are based on an analysis of the vibration welding process, have been developed for the first three phases. These models have been used for analysing spin-welding data for poly (methyl methacrylate), poly(vinyl chloride), acetal and nylon 66. Estimates have been obtained for the film thickness, the film viscosity and the film temperature as functions of the weld process parameters. In particular, it has been shown that an increase in the weld velocity can result in a significant reduction of the film viscosity. The film viscosity is shown to be less sensitive to the weld pressure.

Method and apparatus for measuring the distribution of heat flux and heat transfer coefficients on the surface of a cooled component used in a high temperature environment

Abstract: Heat flux distribution and heat transfer coefficient distribution over a surface of a component used in a high temperature environment are determined by supplying coolant of predetermined characteristics to the component and measuring a temperature distribution over a predetermined surface The heat flux at each temperature measurement point on the surface of the component is determined from heat flux calibration data obtained before the component is placed in service and while it is being operated at in-service cooling conditions The heat transfer coefficient at various locations on the surface of the component is determined from the heat flux indicated by the heat flux calibration data, the temperature of the surface, and the temperature of the environment in which the component is situated

Effect of pressure gradient of friction and heat transfer in a dusty boundary layer

Abstract: Approximate analytic expressions for the local friction and heat transfer coefficients in a dusty laminar boundary layer are obtained and tested in the case of an incompressible carrier phase, power-law variation of the external gas flow velocity and small velocity and temperature phase disequilibrium. These expressions supplement the numerical analysis of the dusty boundary layer on a blunt body [1, 2] and the asymptotic calculation of the friction and heat transfer in a quasiequilibrium dusty gas boundary layer on a plate [3]. The combined effect of dustiness and pressure gradient on the friction and heat transfer coefficients is discussed. The results obtained can be used for the practical calculation of the friction and heat transfer in a quasiequilibrium dusty laminar boundary layer and for interpreting the corresponding experimental data.

Heat Transfer by Natural Convection of Helium Between Horizontal Isothermal Concentric Cylinders at Cryogenic Temperature

Abstract: An experimental study was performed of the heat transfer by natural convection of helium between horizontal isothermal concentric cylinders at cryogenic temperatures. Time-averaged temperature profiles at various locations in the annulus and overall heat transfer rates were measured as the Rayleigh number was varied from 6 {times} 10{sup 6} to 2 {times} 10{sup 9} and the expansion number from 0.20 to 1.0 for a constant Prandtl number of 0.688 and diameter ratio of 3.36. It was found that the heat transfer rate depends on the magnitude of the expansion number as well as on the magnitude of the Rayleigh number. With gas properties evaluated at a volume-weighted reference temperature, a correlation equation is presented that correlates the heat transfer data with maximum deviations of {minus}8.2 and +8.5 percent. The results of this study are compared with previously published studies of other investigators.

On the generalization of the Weinbaum-Jiji bioheat equation to microvessels of unequal size; the relation between the near field and local average tissue temperatures.

Abstract: The extensive series of experiments reported in Lemons et al. [1] show that measureable local tissue temperature fluctuations are observed primarily in the vicinity of the 100-500 micron countercurrent vessels of the microcirculation and thus strongly support the basic hypothesis in the new bioheat equation of Weinbaum and Jiji [2] that these countercurrent microvessels are the principal determinants of local blood-tissue heat transfer. However, the detailed temperature profiles in the vicinity of these vessels indicate that large asymmetries in the local temperature field can result from the significant differences in size between the countercurrent artery and vein. Using the superposition techniques of Baish et al. [9], the paper first presents a solution to the classic problem of an unequal countercurrent heat exchanger with heat loss to the far field. This solution is then used to generalize the Weinbaum-Jiji bioheat equation and the conductivity tensor that appears in this equation to vessels of unequal size. An asymptotic analysis has also been developed to elucidate the relationship between the near field temperature of the artery-vein pair and the local average tissue temperature. This analysis is used to rigorously prove the closure approximation relating the local arterial-venous temperature difference and the mean tissue temperature gradient which had been derived in [2] using a more heuristic approach.

The near-wall temperature profile of turbulent boundary layers

Abstract: Solutions of t h e energy equation are presented for perturbed flows where the boundary layer displays s constant stress region near the wall. The analysis applies (0 flms with and without heat transfer, a t all Mach numbers. It is shown that the widely quoted forms of the velocity and temperature log-laws for low Mach number flows apply only in the limit of very low heat transfer rates. For compressible boundary layers with heat transfer, the relationships presented here can be used to determine the skin friction and heat transfer rate for perturbed boundary layers with a constant stress region near the wall. As a demonstration of the method, the skin friction and heat transfer -fficienta were determined for a Mach 2.3 turbulent boundary layer experiencing a step change in wall temperature.

An Analytical Solution Countercurrent Heat Transfer Between Parallel Vessels With a Linear Axial Temperature Gradient

Abstract: Presented in this paper is a solution for countercurrent heat exchange between two parallel vessels embedded in an infinite medium with a linear temperature gradient along the axes of the vessels. The velocity profile within the vessel is assumed to be parabolic. This solution describes the temperature field within the vessels, as well as in the tissue, and establishes that the intravessel temperature is not uniform, as is generally assumed to be the case. An explicit expression for the intervessel thermal resistance based on the difference between cup-mixed mean temperatures is derived.

Natural Convection Heat Transfer in Hemisphere

Abstract: Natural convection in a hemisphere was studied with bottom surface heated and hemispherical surface cooled. Heat transfer and flow visualization experiments were performed. The range of Rayleigh number and Prandtl number were 9 × 106 1 × 109), the effect of the hot thermal plumes was con...