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Results for “CONVECTIVE HEAT TRANSFER”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Solution of mixed convection heat transfer from isothermal in-line fins

Transient and steady state combined natural and forced convective flows over two in-line finite thickness fins (louvers) in a vertical channel are numerically solved using two methods. The first method of solution is based on the 'Simple Arbitrary Lagrangian Eulerian' (SALE) technique which incorporates mainly two computational phases: (1) a Lagrangian phase in which the velocity field is updated by the effects of all forces, and (2) an Eulerian phase that executes all advective fluxes of mass, momentum and energy. The second method of solution uses the finite element code entitled FIDAP. In the first part, comparison of the results by FIDAP, SALE, and available experimental work were done and discussed for steady state forced convection over louvered fins. Good agreements were deduced between the three sets of results especially for the flow over a single fin. In the second part and in the absence of experimental literature, the numerical predictions were extended to the transient transports and to the opposing flow where pressure drop is reversed. Results are presented and discussed for heat transfer and pressure drop in assisting and opposing mixed convection flows.

Khalilollahi, Amir↗
NASA NTRS1979

Convective heat transfer during dendritic growth

Axial growth rate measurements were carried out at 17 levels of supercooling between 0.043 C and 2 C, a temperature range in which convection, instead of diffusion, becomes the controlling mechanism of heat transfer in the dentritic growth process. The growth velocity, normalized to that expected for pure diffusive heat transfer, displays a dependence on orientation. The ratio of the observed growth velocity to that for convection-free growth and the coefficients of supercooling are formulated. The dependence of normalized growth rate in supercooling is described for downward growing dendrites. These experimental correlations can be justified theoretically only to a limited extent.

Glicksman, M. E.↗
NASA NTRS1991

An analytical comparison of convective heat transfer correlations in supercritical hydrogen

Four correlations that cover the ranges of liquid to gas for turbulent flow convection of hydrogen are compared with CFD analysis over a range of expected design conditions for active cooling of hypersonic aircraft. Analysis of hydrogen cooling in a typical cooling panel shows how predicted design performance varies with the correlation utilized. The CFD heat transfer coefficient results for a heat spike differed significantly from all four correlations. An acceptable heat transfer coefficient can be calculated at the heat spike location by overlooking the coefficient at the spike and averaging the coefficient before and after the spike.

Dziedzic, William M.↗
NASA NTRS1988

Joule-Thomson effect and internal convection heat transfer in turbulent He II flow

The temperature rise in highly turbulent He II flowing in tubing was measured in the temperature range 1.6-2.1 K. The effect of internal convection heat transport on the predicted temperature profiles is calculated from the two-fluid model with mutual friction. The model predictions are in good agreement with the measurements, provided that the pressure gradient term is retained in the expression for internal convection heat flow.

Walstrom, P. L.↗
NASA NTRS1986

Forced convection heat transfer to air/water vapor mixtures

Heat transfer coefficients were measured using both dry air and air/water vapor mixtures in the same forced convection cooling test rig (jet array impingement configurations) with mass ratios of water vapor to air up to 0.23. The primary objective was to verify by direct experiment that selected existing methods for evaluation of viscosity and thermal conductivity of air/water vapor mixtures could be used with confidence to predict heat transfer coefficients for such mixtures using as a basis heat transfer data for dry air only. The property evaluation methods deemed most appropriate require as a basis a measured property value at one mixture composition in addition to the property values for the pure components.

Richards, D. R.↗
NASA NTRS1979

Radiative and free convective heat transfer from a containerless sphere

A mathematical model is derived for heat loss due to radiation and free convection for a small copper sphere (approximately 0.3 to 0.4 cm diameter) cooled by a helium-argon gas mixture. A FORTRAN program written to simplify calculations and extend the range of applicability to experimentation is presented. Pressures used were less than 400 torr, and resulting temperatures ranged from 500 to 4600 K. Comparison of results for initial cooling by the gas mixture with experimental data showed a 5 percent error for temperature values and a 2.7 percent error for the temperature difference caused by the cooling. Results indicate that the accuracy could be increased significantly by using better estimates for thermal conductivities.

Johnson, K.↗
NASA NTRS1990

Experimental determination of convective heat transfer coefficients in the separated flow region of the Space Shuttle Solid Rocket Motor

A series of cold flow heat transfer tests was conducted with a 7.5-percent scale model of the Space Shuttle Rocket Motor (SRM) to measure the heat transfer coefficients in the separated flow region around the nose of the submerged nozzle. Modifications were made to an existing 7.5 percent scale model of the internal geometry of the aft end of the SRM, including the gimballed nozzle in order to accomplish the measurements. The model nozzle nose was fitted with a stainless steel shell with numerous thermocouples welded to the backside of the thin wall. A transient 'thin skin' experimental technique was used to measure the local heat transfer coefficients. The effects of Reynolds number, nozzle gimbal angle, and model location were correlated with a Stanton number versus Reynolds number correlation which may be used to determine the convective heating rates for the full scale Space Shuttle Solid Rocket Motor nozzle.

Whitesides, R. Harold↗
NASA NTRS1982

Influence of radiant energy exchange on the determination of convective heat transfer rates to Orbiter leeside surfaces during entry

Temperatures measured at the aerodynamic surface of the Orbiter's thermal protection system (TPS), and calorimeter measurements, are used to determine heating rates to the TPS surface during atmospheric entry. On the Orbiter leeside, where convective heating rates are low, it is possible that a significant portion of the total energy input may result from solar radiation, and for the wing, cross radiation from the hot (relatively) Orbiter fuselage. In order to account for the potential impact of these sources, values of solar- and cross-radiation heat transfer are computed, based upon vehicle trajectory and attitude information and measured surface temperatures. Leeside heat-transfer data from the STS-2 mission are presented, and the significance of solar radiation and fuselage-to-wing cross-radiation contributions to total energy input to Orbiter leeside surfaces is assessed.

Throckmorton, D. A.↗
NASA NTRS1978

Convective heat transfer during dendritic solidification

Experiments on succinonitrile are described in which the dependence of dendritic growth velocity is studied as a function of orientation with respect to gravity. Growth rate measurements were carried out at a relatively small supercooling, requiring high specimen purity as well as extreme thermal stability and precision temperature measurement. The normalized growth velocity showed a dependence on orientation described by the ratio of observed growth velocity to that expected for convection-free growth being equal to 3.52 times the n-th power of Cos half the orientation angle, where n lies between 0.5 and 0.75.

Glicksman, M. E.↗
NASA NTRS2007

Preliminary Evaluation of Convective Heat Transfer in a Water Shield for a Surface Power Reactor

As part of the Vision for Space Exploration, the end of the next decade will bring man back to the surface of the moon. A crucial issue for the establishment of human presence on the moon will be the availability of compact power sources. This presence could require greater than 10's of kWt's in follow on years. Nuclear reactors are well suited to meet the needs for power generation on the lunar or Martian surface. Radiation shielding is a key component of any surface power reactor system. Several competing concepts exist for lightweight, safe, robust shielding systems such as a water shield, lithium hydride (LiH), and boron carbide. Water offers several potential advantages, including reduced cost, reduced technical risk, and reduced mass. Water has not typically been considered for space reactor applications because of the need for gravity to fix the location of any vapor that could form radiation streaming paths. The water shield concept relies on the predictions of passive circulation of the shield water by natural convection to adequately cool the shield. This prediction needs to be experimentally evaluated, especially for shields with complex geometries. NASA Marshall Space Flight Center has developed the experience and facilities necessary to do this evaluation in its Early Flight Fission - Test Facility (EFF-TF).

Pearson J. Boise↗
NASA NTRS1968

Survey of the Relationship Between Theory and Experiment for Convective Heat Transfer From Rocket Combustion Gases

The problem of predicting the distribution of heat flux in a rocket engine is complicated by a flow field and thermodynamics so perturbed by as yet indescribable combustion effects that it continues to be necessary to utilize a simplified theoretical model against which to compare experimental results in order to gain insight. The most successful model applied to this problem is that of a compressible, turbulent, accelerating boundary layer flow with an arbitrary point of origin, and chemical reaction restricted to equilibrium recombination or diffusion-limited recombination on a catalytic wall. Analysis of this model was not possible without making several assumptions about the nature of the skin friction coefficient relationship and Reynold's analogy in an accelerating boundary layer flow. The paper summarizes the analysis of this model (together with detailed treatment of the special problems of variable properties, chemical reaction, and sources of transport properties), and describes several closed-form equations that have also been developed and applied to the problem. Described are results of several experiments with hot air flow made for the purpose of checking the validity of the assumptions in the boundary layer analysis. Most significant, however, are presentations of sample distributions of local heat flux measured in rocket engines operating with a wide range of conditions, propellants, injectors and sizes. When compared with predictions, these data show the significant range of deviation in heat flux that results from the combustion effects and which precludes a generally accurate prediction theory or correlation equation until the combustion process itself is correlated.

D R Bartz↗
NASA NTRS1973

Survey of literature on convective heat transfer coefficients and recovery factors for high atmosphere thermometry

Heat transfer phenomena of rarefied gas flows is discussed based on a literature survey of analytical and experimental rarefied gas dynamics. Subsonic flows are emphasized for the purposes of meteorological thermometry in the high atmosphere. The heat transfer coefficients for three basic geometries are given in the regimes of free molecular flow, transition flow, slip flow, and continuum flow. Different types of heat phenomena, and the analysis of theoretical and experimental data are presented. The uncertainties calculated from the interpolation rule compared with the available experimental data are discussed. The recovery factor for each geometry in subsonic rarefied flows is also given.

Chung, S.↗
NASA NTRS1979

Measurements of mixed convective heat transfer to low temperature helium in a horizontal channel

A horizontal 2.85 m long, 19 mm i.d. stainless steel heated circular channel was employed to measure coefficients of heat transfer to low temperature helium flow. Experimental parameters range from 6.5 to 15 K, from 0.12 to 0.3 MPa at heat fluxes up to 1000 W/m square and Reynolds numbers from 9,000 to 20,000. A significantly nonuniform distribution of heat transfer coefficients over the tube periphery is observed. Difference between temperatures on the upper and lower surfaces of the stainless steel channel wall was found to reach 9 K. It was noted that the highest temperature on the wall outer surface is displaced from its uppermost point. Measurements of local flow temperatures revealed vortical structure of the flow. The displacement of the point with the highest temperature is attributable to the effect of vortices. The relationships for calculating local and averaged coefficients of heat transfer are proposed.

Yeroshenko, V. M.↗