Showing papers on "Heat transfer coefficient published in 1973"
TL;DR: In this article, a modified packet model for heat transfer between a gas-fluidized bed and an immersed surface is presented, and the model readily explains the effect of particle moisture content, shape of the immersed body and other factors on bed to immersed body heat transfer.
196 citations
TL;DR: In this article, the theory of miscible dispersion is extended to interphase transport systems, and a new exact dispersion model which accounts for dispersion with inter-phase transport is derived from first principles.
Abstract: The theory of miscible dispersion is extended to interphase transport systems. As a specific example miscible dispersion in laminar flow in a tube in the presence of interfacial transport due to an irreversible first-order reaction at the wall is analysed by an exact procedure. A new exact dispersion model which accounts for dispersion with interphase transport is derived from first principles. The new concept of an ‘exchange coefficient’ arises naturally. This coefficient depends strongly on the rate of interfacial transport. Such transport also affects the convection and dispersion coefficients significantly. A general expression is derived which shows clearly the time-dependent nature of the coefficients in the dispersion model. The complete time-dependent expression for the exchange coefficient is obtained explicitly and is independent of the velocity distribution in the flow; however, it does depend on the initial solute distribution. Because of the complexity of the problem only asymptotic large-time evaluations are made for the convection and dispersion coefficients, but these are sufficient to give useful physical insight into the nature of the problem. When the rate of the wall reaction approaches zero the exchange coefficient also approaches zero and the other two coefficients approach their proper values in the absence of interfacial transport. At the other extreme of rapid wall reaction rates, the convection coefficient is more than 50 % larger than its value in the absence of interfacial transport and the dispersion coefficient is an order of magnitude smaller than that for zero interphase transport.
185 citations
TL;DR: In this article, the authors measured the thermal conductivity of the Ga1−xAlxAs alloy system with LPE layers and found that the thermal resistivity increased with the temperature gradient in the bars with thin films of cholesteric liquid crystals.
Abstract: This paper presents the results of our measurement of the room‐temperature thermal conductivity of the Ga1−xAlxAs alloy system. The study was motivated by our need to characterize the thermal properties of cw heterostructure lasers, in which the heat generated in the optically active layer must flow through a substantial thickness of Ga1−xAlxAs to reach the heat sink. The measurement was made on LPE layers which were separated from their substrates and fashioned into rectangular bars. A steady‐state heat flow was established in the bars utilizing an argon laser as the heat source, and the conductivity was obtained by measuring the temperature gradient in the bars with thin films of cholesteric liquid crystals. The results indicate that the thermal conductivity of the alloy is well described by an existing theoretical treatment of high‐temperature lattice thermal conductivity of disordered semiconductor alloys. In the Ga1−xAlxAs system, the increased thermal resistivity of the alloy is shown to be a result...
170 citations
TL;DR: In this paper, the authors analyzed the heat transfer problem associated with pulse thermal diffusivity measurements for the cases of triangular pulses whose widths are comparable with the transit time of temperature fronts across a sample (finite pulse width effects), heat losses from sample faces, and simultaneous occurrence of heat losses and finite pulsewidth effects.
Abstract: The heat transfer problem associated with pulse thermal diffusivity measurements is analyzed for the cases of (i) triangular pulses whose widths are comparable with the transit time of temperature fronts across a sample (finite pulse width effects), (ii) heat losses from sample faces, and (iii) the simultaneous occurrence of heat losses and finite pulse‐width effects. Methods for the analysis of experimental results which are affected by these conditions are discussed. Tabular and graphical data which facilitate the analysis are given.
151 citations
150 citations
136 citations
TL;DR: In this article, an analysis of the ultimate limit of heat transfer of cylindrical heat pipes with laminar vapour flow is presented for the two limiting cases of either predominant inertia- or viscous forces (inertia and viscous flow regime), taking into consideration both the axial and radial variation of the vapour velocity.
125 citations
TL;DR: In this paper, the heat transport and vertical component of the fluid velocity in a horizontal layer of water heated from below were measured and the heat transfer results were well correlated by a simple power law relationship and indicated the possibility of flow transitions even at relatively high Rayleigh numbers.
Abstract: Measurements were taken of the heat transport and vertical component of the fluid velocity in a horizontal layer of water heated from below. The heat transfer results were well correlated by a simple power law relationship and indicated the possibility of flow transitions even at relatively high Rayleigh numbers. The velocity measurements were obtained optically and compared to predictions of Kraichnan.
108 citations
01 Jul 1973
TL;DR: In this article, the authors extended the hydrodynamic theory of the extreme pool boiling heat fluxes to embrace a variety of problems that have not previously been analyzed, such as the prediction of the peak heat flux on a number of finite heaters, the influence of viscosity on the Taylor and Helmoltz instability mechanisms with application to film boiling and to the peak flux in viscous liquids.
Abstract: The hydrodynamic theory of the extreme pool boiling heat fluxes is expanded to embrace a variety of problems that have not previously been analyzed. These problems include the prediction of the peak heat flux on a variety of finite heaters, the influence of viscosity on the Taylor and Helmoltz instability mechanisms with application to film boiling and to the peak heat flux in viscous liquids, the formalization of the analogy between high-current-density electrolysis and boiling, and the description of boiling in the low-gravity limit. The predictions are verified with a large number of new data.
104 citations
TL;DR: In this article, it was shown that the problem of perturbed free convection solution is associated with the asymptotic nature of this solution at a distance far removed from the leading edge.
100 citations
TL;DR: In this paper, the problem of heat transfer to an attached falling film has been investigated and solved numerically with a digital computer for five cases of boundary conditions, and the original problem which has three independent variables, two in space and one in time, is reduced by a similarity transformation to a two dimensional parabolic problem.
TL;DR: In this article, the heat transfer due to forced convection from an isothermal sphere in a steady stream of viscous incompressible fluid is calculated for low values of the Reynolds number and Prandtl numbers of O(1) The mean Nusselt number is compared with the results of experimental measurements.
Abstract: The heat transfer due to forced convection from an isothermal sphere in a steady stream of viscous incompressible fluid is calculated for low values of the Reynolds number and Prandtl numbers of O(1) The mean Nusselt number is compared with the results of experimental measurements At very low Reynolds numbers, both the local and mean Nusselt numbers are compared with the results obtained from the theory of matched asymptotic expansions
TL;DR: In this paper, the authors considered the effective conductivity of a dilute suspension of neutrally bouyant spherical drops which is undergoing a simple shear flow and derived the relationship between bulk heat flux and the thermal and momentum fields at the microscale of the suspended particles.
Abstract: In this paper we consider the effective conductivity of a dilute suspension of neutrally bouyant spherical drops which is undergoing a simple shear flow. The thermal conductivity, viscosity and specific heat capacity of the drops are assumed to be different from those of the suspending fluid, though it is assumed that the local Peclet and Reynolds numbers are small both inside and outside the drop. The analysis consists of three parts: a derivation of the relationship between bulk heat flux on the one hand and the thermal and momentum fields at the microscale of the suspended particles on the other; a calculation of the local temperature field near a single neutrally buoyant spherical drop in shear flow with an imposed transverse temperature gradient at large distances; and a synthesis of the general relationship for bulk heat flux and the calculated local temperature field to determine an effective conductivity for a dilute suspension of spherical drops.
TL;DR: In this article, the analytical solution to the Graetz problem with uniform wall heat flux is extended by including the viscous dissipation effect in the analysis, which reduces to that of Siegel, Sparrow and Hallman neglecting viscous disipation as a limiting case.
Abstract: The analytical solution to Graetz problem with uniform wall heat flux is extended by including the viscous dissipation effect in the analysis. The analytical solution obtained reduces to that of Siegel, Sparrow and Hallman neglecting viscous dissipation as a limiting case. The sample developing temperature profiles, wall and bulk temperature distributions and the local Nusselt number variations are presented to illustrate the viscous dissipation effects. It is found that the role of viscous dissipation on thermal entrance region heat transfer is completely different for heating and cooling at wall. In the case of cooling at wall, a critical value of Brinkman number, Br
c=−11/24, exists beyond which (−11/24 B
b > T
0 indicating overall heating effect for the fluid. The numerical results for the case of cooling at wall Br < 0 are believed to be of some interest in the design of the proposed artctic oil pipeline.
TL;DR: In this article, it was shown that these data can be relegated to four zones, depending upon the value of the ratio GfRf−2, where Gf and Rf are the Grashof and Reynolds numbers, respectively, with properties evaluated at the mean film temperature.
01 Sep 1973
TL;DR: In this paper, experimental data on and methods for calculating heat transfer coefficients with nucleate boiling of liquids on metallic heating surfaces are discussed with emphasis on the problems created by the surface conditions of the heating surface.
Abstract: Translated fmm Teploenergetika; 19: No. 9, l4-99(1972), Experimental data on and methods for calculating heat transfer coefficients with nucleate boiling of liquids on metallic heating surfaces are discussed with emphasis on the problems created by the effects of the surface conditions of the heating surface. It is concluded that, at the present time, a sufficiently reliable method is available for calculating the mean heat transfer level when boiling normal (nonmetallic) liquids in the region of moderate pressures. However, allowing for the effects of surface conditions remains unsolved and must be further investigated in order to improve the accuracy of design calculations for heat exchangers for thermal and nuclear power plants. (LCL)
TL;DR: In this article, the equations of motion and energy for flow and heat transfer in curved tubes have been solved numerically by the alternating direction-implicit techni�¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯481€1.0 + [8.279 × 10−4 + 7.964×10−3λ]
TL;DR: In this paper, the heat transfer of fully developed laminar flow in internally finned tubes is investigated analytically, and the highest Nusselt number is obtained for the tube with 22 fins extended to about 80 percent of the tube radius.
Abstract: The heat transfer of fully developed laminar flow in internally finned tubes is investigated analytically. If there is no heat generation in the fluid, the highest Nusselt number is obtained for the tube with 22 fins extended to about 80 percent of the tube radius. Its value is almost 20 times that for the finless tube. When there is heat generation at sufficiently large rate, the number of fins is reduced from 22 to 16 in order to obtain the highest Nusselt number.
TL;DR: It was found that the assumption of negligible resistance between food and teeth overestimates greatly the resulting temperature gradients and heat transfer coefficients during drinking and mastication are below 7.0 X 10 -2 calorie/cm2 second°C.
Abstract: Experiments were conducted to determine the thermal resistance between food and teeth during mastication processes and the drinking of beverages. It was found that the assumption of negligible resistance between food and teeth overestimates greatly the resulting temperature gradients. Also, heat transfer coefficients (reciprocal thermal resistance) during drinking and mastication are below 7.0 X 10 -2 calorie/cm2 second°C.
TL;DR: In this paper, local heat transfer coefficients and fully developed temperature profiles were measured in NaK eutectic mixture in a pipe at uniform wall temperature, where Reynolds numbers ranged from 26 000 to 302 000 and flow was fully developed.
TL;DR: In this article, the surface area of a sphere or cylinder was analyzed and the total buoyant force on the sphere and total drag force on a cylinder was estimated. But the authors did not consider the effect of the velocity of the sphere on the cylinder.
TL;DR: In this paper, the authors examined liquid immersion techniques for cooling minute heat sources and found that nucleate boiling may introduce mechanical stresses, contamination and physical design problems, and two alternatives to boiling (forced convection and bubble induced mixing) were also investigated which reduced or bypassed some of these problems.
TL;DR: A sonic anemometer, lyman alpha humidiometer, and thermistor thermometer were operated on ice at 75°N, 15°W in March-April 1972 as part of the Aidjex pilot study as mentioned in this paper.
Abstract: A sonic anemometer, lyman alpha humidiometer, and thermistor thermometer were operated on ice at 75°N, 15°W in March-April 1972 as part of the Aidjex pilot study. Spectra of temperature and humidity fluctuations and cospectra for the sensible and latent heat fluxes were similar to those published for neutral conditions over sea and land. Bulk transfer coefficients were CT = 1.2 × 10−3 and CQ = 0.55 × 10−3, respectively. The Bowen ratio of sensible to latent heat fluxes ranged from 1 to 15 and can be obtained from values of the temperature and humidity spectra at low frequencies except when the latent heat flux is very small. These data were recorded at the spring equinox, and the dominant feature of the heat fluxes is their diurnal variation. Evaporation continued for several hours after the sensible heat flux changed to the downward direction. Over Robeson Channel in July 1972 the heat transfer coefficient was CT = 1.0 × 10−3 for stable conditions.
TL;DR: In this paper, the problem of laminar combined forced and free-convection heat transfer from a vertical thin needle in a variable external stream is considered, and the similarity solutions for needles with isothermal walls and needles with uniform wall heat fluxes have been obtained.