Showing papers in "Journal of Heat Transfer-transactions of The Asme in 1974"

Natural Convection Adjacent to Horizontal Surface of Various Planforms

Abstract: Natural convection adjacent to horizontal surfaces of circular, square, rectangular, and right triangular planforms has been studied experimentally. Electrochemical techniques were employed involving a fluid with a Schmidt number of about 2200. The results encompass a wide range of Rayleigh numbers thus providing information on both the laminar and the turbulent regimes. The data for all planforms are reduced to a single correlation in the laminar and turbulent regimes using the characteristic length, as recommended by Goldstein, Sparrow, and Jones. L* = A/p, where A is the surface area and p is the surface perimeter. The laminar data for all planforms are correlated by the expression Sh = 0.54 Ra1/4 (2.2 × 104 ≤ Ra ≤ 8 × 106) and the data for the turbulent regime are correlated by the expression Sh = 0.15 Ra1/3 (8 × 106 ≤ 1.6 × 109) Transition is found to occur at about Ra = 8 × 106 . The present work thus significantly extends the Rayleigh number range of validity for the use of L* through the 1/4 power laminar regime into the turbulent 1/3 power regime. It also demonstrates the validity of the use of L* to correlate natural convection transfer coefficients for highly unsymmetrical planforms, which heretofore had not been demonstrated. Comparisons to analytical solutions and other experimental heat and mass transfer data are presented.

An Experimental Study of Heat Transfer and Film Cooling on Large-Scale Turbine Endwalls

Abstract: Experiments were conducted to determine the film cooling effectiveness and convective heat transfer coefficient distributions on the endwall of a large-scale turbine vane passage. The vane test models employed simulated the passage geometry and upstream cooling slot geometry of a typical first-stage turbine. The test models were constructed of low thermal conductivity foam and foil heaters. The tests were conducted at a typical engine Reynolds number but at lower than typical Mach numbers. The film cooling effectiveness distribution for the entire endwall and the heat transfer distribution for the downstream one-half of the endwall were characterized by large gapwise variations which were attributed to a secondary flow vortex.Copyright © 1974 by ASME

Heat Transfer and Film Cooling Following Injection Through Inclined Circular Tubes

Abstract: Film cooling effectiveness and heat transfer are measured downstream of injection through discrete holes into a turbulent mainstream boundary layer. Air is injected through both a single hole and a row of holes spaced at three-diameter intervals and inclined at an angle of 35 deg to the main flow. There is little difference between the heat transfer coefficient with blowing and without blowing at low blowing rates (mass flux ratios). In fact, at low blowing rates, injection is found to decrease somewhat the heat transfer coefficient from that measured without blowing. As the mass flux ratio increases past unity, the heat transfer coefficient increases, especially with injection through a row of holes. The peak heat transfer is usually found at the edge of the spreading jets (i.e., between two holes). At a blowing rate near two, the lateral average of the heat transfer is as much as 27 percent higher than the heat transfer with no blowing. The increase in heat transfer is attributed to the interaction between the jets and the free stream, causing high levels of turbulence.

The Effects of Radiative Heat Transfer Upon the Melting and Solidification of Semitransparent Crystals

Abstract: Employing the assumptions of one-dimensional energy transfer, equilibrium phase change, and negligible convection in liquid regions, the time-dependent conservation of energy equation is formulated for the general situation of n semitransparent contiguous liquid and solid phases The dimensionless parameters governing phase change are identified and the effects of their variation are ascertained by a finite difference solution of the rigorously formulated energy and radiative transfer equations The chief conclusions of this investigation are that for the range of parameters encountered in the melting and solidification of many optical materials, radiant transfer has a significant effect, and that during solidification, radiation can force the temperature profile within the liquid phase to assume a shape which leads to unstable interfacial growth

Radiative Transfer in Packed Spheres

Abstract: Radiative transfer through a packed bed of microspheres is analyzed on the basis of a new conceptual model, which combines the continuous and discontinuous models in predicting the scattering and absorption properties of packed microspheres. The basic elements of the formulation consist of the determination of the scattering diagram of a unit cell, the optical properties of a series of thin microsphere layers, and the solution of the two-flux equations. Results show a strong dependence of these radiative properties on the particle diameter and emissivity. Qualitative agreement is shown in the comparison of the predictions with existing experimental data.

On the Solution of Linear Diffusion Problems With Variable Boundary Condition Parameters

Abstract: A method of solution is presented for the treatment of a class of boundary value problems of linear diffusion theory for finite homogeneous media which have applications in transient heat conduction (or mass diffusion) in a finite medium subjected to convective type boundary condition with time and space dependent coefficient, in the processes of neutron slowing in a finite medium with absorbing boundaries that exhibit energy-dependent cross sections, and in many related areas.

Augmentation of Heat Transfer in Tubes by Use of Mesh and Brush Inserts

Abstract: This paper summarizes the results of a study to determine the heat transfer and pressure drop characteristics of two types of tube inserts developed specifically for augmenting heat transfer and accommodating high heat fluxes. The best performing mesh-insert tubes exhibited heat transfer coefficients nine times the coefficients with empty tubes while brush-insert tubes had coefficients averaging five times the empty tube values, both comparisons being made at equal mass velocity. Both inserts produced very large pressure drops. Subcooled boiling curves and burnout points are presented; burnout heat fluxes are two to three times the empty tube values at equal mass velocity. For single-phase conditions and for burnout, the mesh and brush tubes have favorable performance characteristics, based on pumping power, which suggest use of these inserts in certain special cooling systems.

The Distortion of Turbulent Velocity and Temperature Profiles on Heating, for Mercury in a Vertical Pipe

Abstract: Measurements were made in mercury, for turbulent flow and constant flux heating in a vertical pipe, in order to determine the extent to which the velocity and temperature distributions are affected by buoyancy forces. With increasing heat flux, velocity profiles at Reynolds numbers of 20,000 to 60,000 were found to be markedly distorted in comparison with the isothermal velocity profile. Even very low heat input caused significant distortion, while at high heat input a limiting profile shape was approached, with the center velocity well below the mean and the maximum occurring in the vicinity of the wall. Eddy diffusivities of heat and momentum calculated from the measured profiles exhibit a considerable variation with heat input, indicating that buoyancy forces not only change the radial shear stress distribution but also alter the nature of the turbulence in the pipe.

Radiative Transfer in Homogeneous Nongray Gases With Nonisotropic Particle Scattering

Abstract: A perturbation technique is presented to treat the problem of radiative transfer in homogeneous, plane parallel, nongray gases with nonisotropic particle scattering. The technique allows use of nongray narrow-band or wide-band models as well as Mie and Rayleigh scattering coefficients and asymmetry factors. Results are obtained in the form of monochromatic transmittance, reflectance, and absorptance of water clouds typical of those in the earth’s atmosphere.

An Experimental Investigation of the Temperature Field Produced by a Cryosurgical Cannula

Abstract: Liquid crystals, a material that exhibits brilliant changes in color over narrow temperature bands, have been successfully used to study the temperature field that is produced by a cryosurgical cannula (cryoprobe). Cryoprobe tip temperatures ranging from −36 to −117 C were used to produce frozen regions in a clear gel. Experimental results compare within experimental uncertainty with results of a one-dimensional analytical solution for predicting ice growth rates.

Peak pool boiling heat flux in viscous liquids

Abstract: The stability of a gas jet in a surrounding viscous liquid is studied. An expression is developed for the critical velocity at which the jet becomes unstable in a returning viscous liquid. The stability analysis is made to correspond with the geometrical configuration of gas jets and liquid columns similar to those observed near the peak pool boiling heat flux. The critical velocity of the gas jet is then used to obtain the functional form of the peak heat flux on flat plates and cylindrical heaters. The expressions are compared with original observations of the peak heat flux in very viscous liquids on flat plate, and cylindrical, heaters at both earth-normal, and elevated, gravities.

A Generalized Prediction of Heat Transfer Surfaces

Abstract: A new way of presenting the heat transfer data is shown. This leads to a dimensionless performance plot between a “heat transfer performance factor” and a “pumping power factor” with a nondimensional “flow length between major boundary layer disturbances” as a varying parameter. This approach leads to the possibility of approximately presenting all surface geometries on a single “idealized” performance plot, the nondimensional “flow length” being a geometrical characteristic of each surface. The method can be used to predict approximately the heat transfer performance characteristics of a new, untested surface. The plot permits the rapid assessment and comparison of various heat transfer geometries for a given application. The performance plot is valid only in the turbulent flow regime. The method will prove invaluable in optimizing a design accounting for space limitations, economic restraints, and system considerations such as pumping power and effectiveness tradeoffs.