Showing papers on "Heat transfer published in 1972"

Heat Transfer from Tubes in Crossflow

Abstract: Publisher Summary This chapter discusses the heat transfer and the hydraulic resistance of single tubes, and the banks of tubes of various arrangements in flows of gases and viscous liquids. The focus is on the important problems of the heat transfer and the hydraulic resistance of tubes, in particular with the heat transfer of single tubes, banks of tubes, and systems of tubes in crossflow. The chapter also highlights the influence of the physical properties of fluids on heat transfer. Extensive experimental data will be analyzed and will include investigations of banks of tubes of various arrangements, and a single tube in crossflow in the range of Prandtl number from 0.7 to 500 and that of Reynolds number from 1 to 2xl0 6 .

Forced convection heat transfer correlations for flow in pipes, past flat plates, single cylinders, single spheres, and for flow in packed beds and tube bundles

Abstract: Previously obtained experimental heat transfer data have been collected and are illustrated along with minor variations of the standard correlations. Analysis of data for heat transfer in randomly packed beds and compact (void fraction less than 0.65) staggered tube bundles indicates that the Nusselt number for a wide range of packing materials and tube arrangements is given by provided NRe ≥ 50. The correlations presented in this paper are not necessarily the most accurate available; however, they have wide application, are easy to use, and are quite satisfactory for most design calculations.

Extended surface heat transfer

Abstract: Preface. Convection with Simplified Constraints. Convection with Real Constraints. Convective Optimizations. Convection Coefficients. Linear Transformations. Elements of Linear Transformations. Algorithms for Finned Array Assembly. Advanced Array Methods and Array Optimization. Finned Passages. Compact Heat Exchangers. Longitudinal Fin Double-Pipe Exchangers. Transverse High-Fin Exchangers. Fins with Radiation. Optimum Design of Radiating and Convecting-Radiating Fins. Multidimensional Heat Transfer in Fins and Fin Assemblies. Transient Heat Transfer in Extended Surfaces. Periodic Heat Flow in Fins. Boiling From Finned Surfaces. Condensation on Finned Surfaces. Augmentation and Additional Studies. Appendix A: Gamma and Bessel Functions. Appendix B: Matrices and Determinants. References. Author Index. Subject Index.

Natural Convection in Enclosures

Abstract: Publisher Summary This chapter discusses the complex nature of the natural convection phenomena in enclosures. It discusses the two basic configurations of natural convection— that is, a rectangular cavity and a horizontal circular cylinder. In rectangular cavities, consideration is given to the two-dimensional convective motion generated by the buoyancy force on the fluid in a rectangle and to the associated heat transfer. The two long sides are vertical boundaries held at different temperatures and the short sides can either be heat conducting or insulated. Particular attention is given to the different flow regimes that can occur and the heat transfer across the fluid space between the two plane parallel vertical boundaries. Although heat transfer by radiation may not be negligible it is independent of the other types of heat transfer and can be fairly accurately calculated separately. To formulate the boundary value problem that describes this phenomena it is assumed that: (a) the motion is two-dimensional and steady, (b) the fluid is incompressible and frictional heating is negligible, and (c) the difference between the hot wall and cold wall temperatures is small relative to the absolute temperatures of the cold wall. In horizontal circular cylinder, consideration is given to the large Rayleigh number flow with the Prandtl number large and the Grashof number of unit order of the magnitude.

Thermal convection in a horizontal fluid layer with uniform volumetric energy sources

Abstract: Energy transport at Rayleigh numbers up to 675 times the critical (linear stability theory) value is measured in a layer of dilute electrolyte bounded horizontally by two rigid planes of constant and equal temperature; Joule heating by an alternating current passing horizontally through the layer provides the volumetric energy source. Horizontally averaged temperature profiles are determined optically. Mean temperature distributions are asymmetric at elevated Rayleigh numbers, the energy transport at the upper boundary being more than twice that at the lower boundary. Three regimes of flow are identified and discrete transitions in the energy transport appear to exist when the flow is turbulent. Extrapolation of the data to the conduction value of the Nusselt number yields a critical Rayleigh number which is within + 10·7% of linear theory values. No subcritical convection is observed when finite amplitude disturbances are introduced into the fluid at a Rayleigh number between the critical values predicted by the linear stability theory and energy theory respectively.

Non-Newtonian Flow and Heat Transfer:

Abstract: Various types of non-Newtonian behaviour are reviewed together with examples commonly encountered in industrial situations. The effect of such fluid properties on isothermal laminar flow in simple geometries is considered. Various problems in laminar heat transfer to non-Newtonian fluids are also discussed and the effects of temperature dependent rheological properties and viscous dissipation are considered. The relevance of these simple examples to more complex industrial problems is discussed.

A theoretical study of geothermal energy extraction

Abstract: Efficient extraction of geothermal energy from a dry well depends on the ability to establish a closed pressurized circuit of water through a large zone fractured in hot impermeable rock. Long-term perpetuation of significant power extraction depends, in addition, on the ability to extend the initial fracture zone through the effects of thermal stress cracking of the adjacent hot rocks. In support of an experimental program to test the feasibility of using this type of energy source, we have solved numerically the combined equations describing the coupled processes of fluid flow, heat transport, and rock fracture. The results show a strong dependence on the extent to which underground pressure can be maintained and the fracture zone continuously extended. They indicate that under favorable, but perhaps not unreasonably exotic, circumstances the extraction of significant thermal power from each well can be expected to continue for many decades.

Field experiment study on the convective heat transfer coefficient on exterior surface of a building

Abstract: Two identical units of heat flow meter panels were used for the experiment and were mounted side by side on the exterior surface of the building. They were maintained at slightly different temperatures and the heat flux conducted toward the surface from inside was measured. The two panels received exactly the same incident radiation so the difference in the measured heat conduction was equal to the difference in heat loss by convection and long wave emission. The convective heat transfer coefficient was calculated from the temperature of the two surfaces and the emissivity.

Theory and design of variable conductance heat pipes

Abstract: A comprehensive review and analysis of all aspects of heat pipe technology pertinent to the design of self-controlled, variable conductance devices for spacecraft thermal control is presented. Subjects considered include hydrostatics, hydrodynamics, heat transfer into and out of the pipe, fluid selection, materials compatibility and variable conductance control techniques. The report includes a selected bibliography of pertinent literature, analytical formulations of various models and theories describing variable conductance heat pipe behavior, and the results of numerous experiments on the steady state and transient performance of gas controlled variable conductance heat pipes. Also included is a discussion of VCHP design techniques.

Radiative Heating of the Global Atmosphere.

Abstract: Monthly zonal mean global radiative heating rates have been obtained from the surface to 10 mb for all twelve months. Seasonal profiles of the contribution by each constituent are presented in addition to seasonal profiles of net thermal cooling and total radiative heating. Radiation cools the troposphere almost everywhere primarily due to thermal cooling by water vapor with the cooling a maximum in the tropics. The tropical stratosphere is heated by radiation due principally to thermal and solar heating by ozone. This total radiative heating extends into the stratosphere mid-latitudes but higher latitudes exhibit cooling due primarily to thermal cooling by CO2 with the warmer hemisphere showing more cooling. Comparison with previous theory in the Northern Hemisphere shows qualitative agreement although the present study has more resolution because of the better specification of the radiative parameters, in particular, ozone and temperature.

Turbulent transfer mechanisms in the atmospheric surface layer

Abstract: The objective of this study was to investigate the turbulent transfer mechanism near the surface. ‘Direct’ measurements of the turbulent fluxes of momentum, heat, and moisture were made in the atmospheric surface layer 2 m above a grass surface at Ladner, Canada. The spectral correlation coefficients were considered to be a measure of the transfer efficiency as a function of scale size. For momentum transfer the efficiency decreased at all scales as instability increased. It is postulated that this was due to greater amounts of momentum being transferred in bursts of short duration, thus making the spectral correlation coefficient, averaged over sufficient time, smaller. The Ladner results for heat transfer showed that its transfer efficiency increased at all scales when instability increased. The ratio of the transfer efficiency of heat to that of momentum was greater than 1 for most scales, even for near neutral stratifications, and increased to between 2 and 3 for more unstable conditions. The efficiency of moisture transfer was usually smaller than that for heat transfer and was found to depend on the correlation between moisture fluctuations and those of temperature.

Heat Flow and Convection Demonstration Experiments Aboard Apollo 14

Abstract: A group of experiments was conducted by Apollo 14 astronaut Stuart A. Roosa during the lunar flyback on 7 Fehruary 1971 to obtain information on heat flow and convection in gases and liquids in an environment of less than 10-(6)g gravity. Flow observations and thermal data have shown that: (i) there are, as expected, convective motions caused by surface tension gradients in a plane liquid layer with a free upper surface; (ii) heat flow in enclosed liquids and gases occurs mainly by diffusive heat conduction; and (iii) some convective processes, whose characteristics are not fully known, add to the heat transfer.

A Critical Discussion of Theories of Flame Spread across Solid and Liquid Fuels

Abstract: Mathematical descriptions of flames spreading over liquid and solid fuels are obtained, using basic assumptions derived from observations or physical reasoning. A review of existing theories shows that they are incomplete in that they either treat an uncoupled problem of the condensed phase where the spreading rate and heat flux at the surface are given, or they merely determine the spreading rate in terms of a new vaguely defined eigenvalue. An important difference between the liquid and solid cases, due to convection, is pointed out, and it is shown that solid-fuel flame-spread theories which claim to apply to the liquid case, in reality do not apply to it. A mathematical formulation and a method of solution are presented for the phenomenon of flame spread over solid fuels with forward heat conduction in both the solid and the gas. The method uses an energy integral over the field to determine the spreading rate in terms of the basic properties of the fuel and air.

Method of extracting heat from dry geothermal reservoirs

Abstract: Hydraulic fracturing is used to interconnect two or more holes which penetrate a previously dry geothermal reservoir, and to produce within the reservoir a sufficiently large heat-transfer surface so that heat can be extracted from the reservoir at a usefully high rate by a fluid entering it through one hole and leaving it through another. Introduction of a fluid into the reservoir to remove heat from it and establishment of natural (unpumped) convective circulation through the reservoir to accomplish continuous heat removal are important and novel features of the method.

Thermal properties of granulated materials.

Abstract: Review of the thermophysical properties of granular materials or silicates believed to simulate the lunar surface layer. Emphasis is placed on thermal conductivity data and the effects of material and environmental variables on the thermal conductivity. There are three basic mechanisms of heat transfer in particulate materials: conduction by the gas contained in the void spaces between the particles; conduction within the solid particles and across the interparticle contacts; and thermal radiation within the particles, across the void spaces between particle surfaces, and between void spaces themselves. Gas and solid conduction, thermal radiation, and the interaction between conduction and radiation are considered.

Incipient Separation of a Supersonic, Turbulent Boundary Layer, Including Effects of Heat Transfer

Abstract: An experimental study of the interaction of a turbulent boundary layer with a compression corner has been conducted at a Mach number of 29, Reynolds number based upon boundary-layer thickness of 22 to 59 x 104, and ratio of wall-temperat ure-to-recovery-temperature of 105 to 047 Adiabatic wall data showed an incipient separation angle of 65°, as determined by the liquid line method The static pressure distribution was found to be insensitive to the presence of small regions of separated flow The present results, combined with other data, shown an increasing trend of incipient separation angle with Reynolds number The effect of wall cooling was to increase the incipient separation angle and reduce the separation distance