Showing papers on "Nusselt number published in 1984"
TL;DR: In this article, a computational method was used to obtain solutions of the buoyancy-driven laminar and turbulent flow and heat transfer in a square cavity with differentially heated side walls.
589 citations
TL;DR: In this article, a three-part study encompassing both experiment and analysis has been performed for natural convection in an open-ended vertical channel, where one of the principal walls of the channel was maintained at a uniform temperature, while the other principal wall was unheated.
Abstract: A three-part study encompassing both experiment and analysis has been performed for natural convection in an open-ended vertical channel. One of the principal walls of the channel—the heated wall—was maintained at a uniform temperature, while the other principal wall was unheated. The experiments, which included flow visualization and Nusselt number measurements, were carried out with water in the channel and in the ambient which surrounds the channel. At Rayleigh numbers which exceeded a threshold value, the visualization revealed a pocket of recirculating flow situated adjacent to the unheated wall in the upper part of the channel. The recirculation was fed by fluid drawn into the top of the channel, adjacent to the unheated wall. Average Nusselt numbers for the heated wall were measured over a three orders of magnitude range of a single correlating parameter, which includes the Rayleigh number and the ratio of the channel length to the interwall spacing. The Nusselt numbers were found to be unaffected by the presence of the recirculation zone. Numerical solutions obtained via a parabolic finite difference scheme yielded Nusselt numbers in good agreement with those of experiment. The numerical results covered the Prandtl number range from 0.7 to 10.
184 citations
TL;DR: In this paper, two families of pin fin array geometries which have potential for improving airfoil internal cooling performance were studied experimentally and the results indicated that the use of circular pins with array orientation between staggered and inline can increase heat transfer while decreasing pressure loss.
Abstract: Modern high-performance gas turbine engines operate at high turbine inlet temperatures and require internal convection cooling of many of the components exposed to the hot gas flow. Cooling air is supplied from the engine compressor at a cost to cycle performance and a design goal is to provide necessary cooling with the minimum required cooling air flow. In conjunction with this objective, two families of pin fin array geometries which have potential for improving airfoil internal cooling performance were studied experimentally. One family utilizes pins of a circular cross section with various orientations of the array with respect to the mean flow direction. The second family utilizes pins with an oblong cross section with various pin orientations with respect to the mean flow direction. Both heat transfer and pressure loss characteristics are presented. The results indicate that the use of circular pins with array orientation between staggered and inline can in some cases increase heat transfer while decreasing pressure loss. The use of elongated pins increases heat transfer, but at a high cost of increased pressure loss. In conjunction with the present measurements, previously published results were reexamined in order to estimate the magnitude of heat transfer coefficients on the pin surfaces relative to those of the endwall surfaces. The estimate indicates that the pin surface coefficients are approximately double the endwall values.
181 citations
TL;DR: In this article, an extensive numerical study of the heat transport by 2-D steady state convection with free boundaries and temperature dependent viscosity was carried out, and the results for convection in a square box were presented in several ways.
175 citations
TL;DR: In this paper, scaling criteria for a natural circulation loop under single phase and two-phase flow conditions have been derived for a LOFT facility under one-dimensional area average forms, and preliminary conclusions on the feasibility of the facility have been obtained.
174 citations
143 citations
TL;DR: In this article, the Brinkman-Forchheimer-extended Darcy model is used as the momentum equation and the effect of porosity variation is taken into consideration.
143 citations
TL;DR: In this paper, heat transfer characteristics and flow behaviors have been made clear for an elliptic cylinder of axis ratio 1 : 3, where the testing fluid was air and the Reynolds number ranged from about 8000 to 79000.
135 citations
TL;DR: In this article, the laminar combined convection heat transfer from an isothermal horizontal circular cylinder is studied for the two cases when the forced flow is directed either vertically upward (parallel flow) or vertically downward (contra flow).
134 citations
TL;DR: In this paper, an asymptotic analysis of 2-dimensional Benard convection in a fluid of infinite Prandtl number and strongly temperature-dependent viscosity ν(T)=c e−γT is presented.
134 citations
TL;DR: In this article, the authors considered the problem of estimating the condensate film thickness in a horizontal tube with potential flow and showed that the upper part of the tube can be assumed to have no pressure gradient.
TL;DR: In this paper, two-dimensional arrays of circular air jets impinging on a heat transfer surface parallel to the jet orifice plate are considered, where the jet flow after impingement is constrained to exit in a single direction along the channel formed by the jet and heat transfer surfaces.
Abstract: Two-dimensional arrays of circular air jets impinging on a heat transfer surface parallel to the jet orifice plate are considered The jet flow, after impingement, is constrained to exit in a single direction along the channel formed by the jet orifice plate and the heat transfer surface In addition to the crossflow which originates from the jets following impingement, an initial crossflow is present which approaches the array through an upstream extension of the channel The temperature of the initial crossflow air may differ from the jet air temperature The configurations considered are intended to model the impingement cooled midchord region of gas turbine airfoils in cases where an initial crossflow is also present Nusselt numbers and dimensionless adiabatic wall temperatures resolved to one streamwise jet hole spacing were experimentally determined for ratios of the initial crossflow rate to the total jet flow rate ranging from zero to unity These are presented and discussed relative to the flow and geometric parameters
TL;DR: In this article, a vertical boundary of a horizontal plate-like solid initially at the fusion temperature with adiabatic upper and lower surfaces was subjected to a step-wise temperature increase.
TL;DR: In this paper, two different degrees of corrugation-peak roundedness were used in addition to sharp (i.e. unrounded) corrugations peaks. But the results showed that the Nusselt number was relatively insensitive to whether the peaks were sharp or rounded.
TL;DR: In this article, the transient natural convection heat transfer problem between two horizontal isothermal cylinders is formed within the Boussinesq approximation and solved numerically through the vorticity-stream function approach.
TL;DR: In this paper, the boundary-layer flow over semi-infinite vertical and horizontal flat plates, heated to a constant temperature in a uniform free stream, is studied when the buoyancy forces either aid or oppose the development of the boundary layer.
TL;DR: In this paper, the natural convection motion and heat transfer rate in an inclined rectangular air layer, in which two opposing isothermal rigid-boundaries were kept at different temperatures, were investigated experimentally for various angles of inclination.
TL;DR: In this paper, both constrained and unconstrained cavity geometries were studied and detailed velocity profiles were obtained using laser doppler velocimetry for Rayleigh numbers between 3 x 10/sup 10/ and 2 x 10 /sup 11/, corresponding to a constant elevated wall temperature boundary condition.
Abstract: Experimental results for natural convection in a cavity are reported. Both constrained andd unconstrained cavity geometries were studied. Detailed velocity profiles were obtained using Laser doppler velocimetry for Rayleigh numbers between 3 x 10/sup 10/ and 2 x 10/sup 11/, corresponding to a constant elevated wall temperature boundary condition. Characteristics of two-dimensional and three-dimensional flows obtained with dye flow visualization are discussed, including boundary layer transition to turbulence, flow patterns in the cavity, and flow outside of the cavity. Local Nusselt number is correlated with local Rayleigh number for constrained and unconstrained cavities.
TL;DR: In this paper, a theoretical analysis of the combined heat and mass transfer process taking place in the absorption of a gas or vapor in a turbulent liquid film is presented, where Eddy diffusivity correlations have been used to describe the transport near the wall and the interface and in the bulk of the film.
TL;DR: The Navier-Stokes and energy equations have been solved numerically for a pair of spheres in tandem at Re = 40 for two different spacings using bispherical coordinates as discussed by the authors.
TL;DR: In this article, the authors studied the condensation of steam on a subcooled water layer in a cocurrent horizontal channel at atmospheric pressure, and found that 50 to 90 percent of the steam condensed within 1.2 m from the entrance.
Abstract: Condensation of steam on a subcooled water layer was studied in a cocurrent horizontal channel at atmospheric pressure. The heat transfer coefficients were found to vary from 1.3 kWS/m/sup 20/C to 20 kW/m/sup 20/C, depending on whether the liquid interface was smooth or wavy, increased with increasing steam flow rates and water flow rates. For all cases, 50 to 90 percent of the steam condensed within 1.2 m from the entrance. The average Nusselt numbers were correlated with average steam and water Reynolds numbers an average liquid Prandtl numbers, for both smooth and wavy interface flows. Finally, a correlation of the average heat transfer coefficient and condensation rate for wavy interface flow was obtained as a function of inlet conditions and distance downstream.
TL;DR: In this article, the effects of wall conduction and radiation heat exchange between surfaces on laminar natural-convection heat transfer in a two-dimensional rectangular cavity were investigated.
Abstract: Numerical results have been obtained for the effects of wall conduction and radiation heat exchange between surfaces on laminar natural-convection heat transfer in a two-dimensional rectangular cavity. Parametric heat transfer calculations have been performed and results are presented In graphic and tabular form. Local and average Nusselt numbers along the cavity walls are reported for a range of parameters of physical interest. The findings suggest that the local or the average Nusselt number may not be a meaningful parameter for use in conjugate heat transfer problems. The results indicate that natural-convection heat transfer in the cavity is reduced by heat conduction in the walls and radiation exchange among surfaces.
TL;DR: For the past 25 years, there has existed in the Thermosciences Laboratory of the Mechanical Engineering Department of Stanford University a research program, primarily experimental, concerned with heat transfer through turbulent boundary layers.
Abstract: For the past 25 years, there has existed in the Thermosciences Laboratory of the Mechanical Engineering Department of Stanford University a research program, primarily experimental, concerned with heat transfer through turbulent boundary layers. In the early phases of the program, the topics considered were the simple zero-pressure-gradient turbulent boundary layer with constant and with varying surface temperature, and the accelerated boundary layer. Later equilibrium boundary layers were considered along with factors affecting the boundary layer, taking into account transpired flows, flows with axial pressure gradients, transpiration, acceleration, deceleration, roughness, full-coverage film cooling, surface curvature, free convection, and mixed convection. A description is provided of the apparatus and techniques used, giving attention to the smooth plate rig, the rough plate rig, the full-coverage film cooling rig, the curvature rig, the concave wall rig, the mixed convection tunnel, and aspects of data reduction and uncertainty analysis.
TL;DR: In this article, a numerical analysis of laminar flow and heat transfer in a tube bank is described, where the two-dimensional Navier-Stokes and energy equations are solved numerically for successive subregions from the inlet to the exit of the bank by a procedure catted the one step forward and half step backward iteration method.
Abstract: A numerical analysis of laminar flow and heat transfer in a tube bank is described. The two-dimensional Navier-Stokes and energy equations are solved numerically for successive subregions from the inlet to the exit of the bank by a procedure catted the “one step forward and half step backward iteration method” and by using a hybrid grid system. Calculations are carried out for an in-line square tube bank up to five rows deep, with pitch-to-diameter ratios 1.5 × 1.5, under the conditions of uniform tube wall temperature, Re = 60, 120, and 300, and Pr = 0.7. Stream, isovorticity, and isothermal lines through the whole tube bank, local and average Nusselt numbers, pressure distributions along the tube walls and in the flow directions, and friction factor are presented. The friction factor and average Nusselt number agree well with published experimental results. An analogous relation between an in-line tube bank and parallel plates with respect to developing heat transfer characteristics is presented.
TL;DR: In this paper, three fundamental theoretical flow models including Oseen type rectilinear flow, potential flow, and Oseen's viscous flow approximation are developed for forced convection heat transfer to parabolic cylinders and paraboloids of revolution which are relevant to dendritic growth.
TL;DR: In this paper, a case of very high heat conductance of the particle is considered and the velocity field around the sphere is assumed to be steady and of the Stokesian type.
TL;DR: In this article, the authors used a regular perturbation expansion in terms of the Darcy-Rayleigh number (R) for thermal convection in a saturated porous medium.
01 Jan 1984
TL;DR: In this article, local heat transfer coefficients were obtained on irregular cylindrical shapes which typify the accretion of ice on circular cylinders in cross flow and averaged axially to obtain a nominal shape of constant cross section for the heat transfer tests.
Abstract: Local heat transfer coefficients were obtained on irregular cylindrical shapes which typify the accretion of ice on circular cylinders in cross flow. The ice shapes were grown on a 5.1 cm (2.0 in.) diameter cylinder in the NASA Lewis Icing Research Tunnel. The shapes were 2, 5, and 15 min accumulations of glaze ice and 15 min accumulation of rime ice. Heat transfer coefficients were also measured around the cylinder with no ice accretion. These icing shapes were averaged axially to obtain a nominal shape of constant cross section for the heat transfer tests. Heat transfer coefficients around the perimeter of each shape were measured with electrically heated copper strips embedded in the surface of the model which was cast from polyurethane foam. Each strip contained a thermocouple to measure the local surface temperature. The models were run in a 15.2 x 68.6 cm (6 x 27 in.) wind tunnel at several velocities. Background turbulence in the wind tunnel was less than 0.5 percent. The models were also run with a turbulence producing grid which gave about 3.5 percent turbulence at the model location with the model removed. The effect of roughness was also simulated with sand grains glued to the surface. Results are presented as Nusselt number versus angle from the stagnation line for the smooth and rough models for both high and low levels of free stream turblence. Roughness of the surface in the region prior to flow separation plays a major role in determining the heat transfer distribution.
TL;DR: In this paper, the authors used a mesh transformation technique coupled with the introduction of false transient parameters for the steady state solution of the problem of fluid motion and heat transfer in an incompressible fluid contained in a nonrectangular inclined enclosure.
TL;DR: In this article, a double-pipe heat-exchanger with an annular duct of streamwise-periodic-varying cross-sectional area is investigated analytically for Reynolds numbers 50-1000 and Prandtl numbers 2-10.
Abstract: The fully developed laminar-flow and temperature fields of a double-pipe heat-exchanger with an annular duct of streamwise-periodic-varying cross-sectional area are investigated analytically for Reynolds numbers 50-1000 and Prandtl numbers 2-10. Numerical results are presented graphically and discussed. At Re 1000 and Pr 10, the Nusselt number is found to be four times that of a similar configuration with constant cross section the pressure drop is increased by a factor of two. Nusselt numbers for two different boundary conditions (constant wall temperature or uniform wall heat flux) are shown to differ by only 10-15 percent. 8 references.