Showing papers on "Heat transfer coefficient published in 1974"

Principles of Environmental Physics

Abstract: PREFACE TO THE SECOND EDITION LIST OF SYMBOLS 1. SCOPE OF ENVIRONMENTAL PHYSICS 2. GAS LAWS Pressure, volume and temperature Specific heats Lapse rate Water and water vapour Other gases 3. TRANSPORT LAWS General transfer equation Molecular transfer processes Diffusion coefficients Radiation laws 4. RADIATION ENVIRONMENT Solar radiation Terrestrial radiation Net radiation 5. MICROCLIMATOLOGY OF RADIATION (i) Interception Direct solar radiation Diffuse radiation Radiation in crop canopies 6. MICROCLIMATOLOGY OF RADIATION (ii) Absorption and reflection Radiative properties of natural materials Net radiation 7. MOMENTUM TRANSFER Boundary layers Wind profiles and drag on uniform surfaces Lodging and windthrow 8. HEAT TRANSFER Convection Non-dimensional groups Measurements of convection Conduction Insulation of animals 9. MASS TRANSFER (i) Gases and water vapour Non-dimensional groups Measurement of mass transfer Ventilation Mass transfer through pores Coats and clothing 10.MASS TRANSFER (ii) Particles Steady motion 11.STEADY STATE HEAT BALANCE (i) Water surfaces and vegetation Heat balance equation Heat balance of thermometers Heat balance of surfaces Developments from the Penman Equation 12.STEADY STATE HEAT BALANCE (ii) Animals Heat balance components The thermo-neutral diagram Specification of the environment Case studies 13.TRANSIENT HEAT BALANCE Time constant General cases Heat flow in soil 14.CROP MICROMETEOROLOGY (i) Profiles and fluxes Profiles Profile equations and stability Measurement of flux above the canopy 15.CROP MICROMETEOROLOGY (ii) Interpretation of measurements Resistance analogues Case studies: Water vapour and transpiration Carbon dioxide and growth Sulphur dioxide and pollutant fluxes to crops Transport within canopies APPENDIX BIBLIOGRAPHY REFERENCES INDEX

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 and mass transfer between a rough wall and turbulent fluid flow at high Reynolds and Péclet numbers

Abstract: General dimensional and similarity arguments are applied to derive a heat and mass transfer law for fully turbulent flow along a rough wall. The derivation is quite analogous to Millikan's (1939) derivation of a skin-friction law for smooth-and rough-wall flows and to the derivation of the heat and mass transfer law for smooth-wall flows by Fortier (1968a, b) and Kader & Yaglom (1970, 1972).The equations derived for the heat or mass transfer coefficient (Stanton number) Ch and Nusselt number Nu include the constant term β of the logarithmic equation for the mean temperature or concentration of a diffusing substance. This term is a function of the Prandtl number, the dimensionless height of wall protrusions and of the parameters describing the shapes and spatial distribution of the protrusions. The general form of the function β is roughly estimated by a simplified analysis of the eddy-diffusivity behaviour in the proximity of the wall (in the gaps between the wall protrusions). Approximate values of the numerical coefficients of the equation for β are found from measurements of the mean velocity and temperature (or concentration) above rough walls. The equation agrees satisfactorily with all the available experimental data. It is noted that the results obtained indicate that roughness affects heat and mass transfer in two ways: it produces the additional disturbances augmenting the heat and mass transfer and simultaneously retards the fluid flow in the proximity of the wall. This second effect leads in some cases to deterioration of heat and mass transfer from a rough wall as compared with the case of a smooth wall at the same values of the Reynolds and Prandtl numbers.

Surface heat loss from cooling ponds

Abstract: A technique is developed for accounting for the contribution of free convection to the evaporation from a cooling pond. Established formulas for forced (wind-driven) evaporation are corrected for convective effects and used in a formula for surface energy balance to estimate heat fluxes and surface temperatures of cooling ponds. The resulting expression for total heat loss agrees with observed cooling pond performance better than other formulas presently in use. Surface heat loss coefficients may be derived from the new heat loss formula for use in calculating temperature rises induced by heated discharges.

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.

Fully developed viscous—flow heat transfer in curved circular tubes with uniform wall temperature

Abstract: Fully developed forced-convective heat transfer to viscous flow of a constant-property Newtonian fluid in curved circular tubes was studied theoretically for a uniform-wall-temperature boundary condition. Numerical solutions were obtained over a wide range of Prandtl numbers for Dean numbers as large as 1,200. The curvature ratio (radius of bend/inside radius of tube) was included as an independent parameter and, for values as small as 10, was found to have a negligible effect on the peripherally averaged Nusselt number. The average Nusselt numbers for the important Prandtl number range of 0.7 to 5 were correlated by NNu = 0.836 NDe0.5 NPr0.1 for NDe ≥ 80.

Free Convection Heat Transfer from Vertical Fin-Arrays

Abstract: A simple but relatively accurate, approximate technique is presented for analyzing the heat transfer due to natural convection and radiation from parallel-fin heat sinks. This technique accounts for a nonuniform base plate temperature. The finned surfaces and the base plate have been considered to be vertical U-shaped channels and a relationship for the NusseJt number has been used which has a suitable form for both very long and very short fins. The accuracy of the technique has been demonstrated by a testing program on a representative sample of heat sinks.

Heat transfer measuring device

Abstract: A device is provided for measuring the efficiency of a heat exchanger. The device comprises a plurality of temperature sensors, a plurality of difference means and calculation means. The difference means are each responsive to a different pair of the temperature sensors to provide a signal representative of the temperature difference between the location of the sensors. The calculation means is responsive to the signals from the difference means for generating a signal representative of the efficiency of the heat exchanger. The signal is representative of either the heat transfer coefficient or the fouling factor in a heat exchanger.

Heat transport coefficients for constant energy flux models of broad leaves

Abstract: Experimental determinations of the local heat transfer by forced convection from model leaves heated by a constant energy flux were made in the laboratory under laminar and turbulent flow conditions. The results are expressed in a logarithmic dimensionless plot of the local Nusselt number, Nu d , against the local Reynolds number, Re d . For the laminar case, Nu d was only a linear function of Re d 1/2 downwind from the leading edge regions, although this relationship departed from that predicted theoretically due to the finite size and thickness of the model. For the turbulent case, a simple relationship between Nu d and Re d was found over a wide range of Reynolds numbers. The enhancement of heat transfer in the turbulent case depends primarily on the scale of turbulence rather than on the turbulent intensity. Past workers have discussed their results in relation to a factor β, defined as the ratio between the heat transfer predicted by the Polhausen equation, and that measured. The results suggest that β is not a unique parameter and may not be useful in describing the overall turbulent transfer process.

Studies of Liquid Film Flow in Two-Phase Annular and Annular-Mist Flow Regions : (Part 1, Downflow in a Vertical Tube)

Abstract: Experimental data are presented on the pressure drop, mean liquid film thickness, state of gas-liquid interface and droplet entrainment for upward annular-mist two phase flow in a vertical tube. Using these data, the relations between the shear stress at gas-liquid interface, the liquid film flow rate and the mean film thickness are investigated, and the characteristics of the mean film thickness with respect to the film Reynolds number are revealed by comparing with the analytical predictions for laminar and turbulent films. A heat transfer experiment is also performed and the results are compared with the analytical values of heat transfer coefficient for laminar and turbulent film flow. On the basis of the experimental data of heat transfer coefficient, the nondimensional thickness of the laminar sublayer of liquid film is calculated for both upflow and downflow, and correlated with the nondimensional film thickness. The result represents the difference in flow state between the upflow film and the downflow film.

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.

Individual heat transfer modes in band oven biscuit baking

Abstract: The individual modes of heat transfer, e.g., conduction, radiation and convection, are considered for the processing of products in conventional band ovens. A specific theoretical model is considered for the baking of biscuits in an indirect fired oven. Values of individual heat transfer constants in the theoretical model and major effects of the individual modes of heat transfer were determined using lab scale heating devices. Extrapolating these results to a band oven baking process, the model indicated a heat transfer profile of about 20% heat transferred by conduction, about 45% by radiation and about 35% by forced convection in the band oven, with about half the heat being absorbed as sensible heat, and about half as latent heat.

Post critical heat transfer to flowing liquid in a vertical tube. Final report. [BWR]

Abstract: The heat transfer characteristics of a liquid in vertical upflow in a tube in which the critical heat flux has been exceeded is investigated. Using a novel transient experimental technique the entire forced convection boiling curve for liquid nitrogen was obtained for a given mass flux-quality combination from which parametric effects of heater material, surface roughness and oxide scale, and dryout length on the dry wall film boiling region were determined. The results show that both increased roughness and oxide scale increase the post critical heat transfer. Increasing the dryout length decreases the heat transfer at a given mass flux-quality combination due to thermal nonequilibrium effects. No material effects were noted. (GRA)