Showing papers on "Nusselt number published in 1981"
TL;DR: In this article, two-dimensional arrays of circular jets of air impinging on a heat transfer surface parallel to the jet orifice plate are considered, and the air is constrained to exit in a single direction along the channel formed by the surface and the jet plate.
Abstract: Two-dimensional arrays of circular jets of air impinging on a heat transfer surface parallel to the jet orifice plate are considered. The air, after impingement, is constrained to exit in a single direction along the channel formed by the surface and the jet plate. The downstream jets are subjected to a crossflow originating from the upstream jets. Experimental and theoretical results obtained for streamwise distributions of jet and crossflow velocities are presented and compared. Measured Nusselt numbers resolved to one streamwise hole spacing are correlated with individual spanwise row jet Reynolds numbers and crossflow-to-jet velocity ratios. Correlations are presented for both inline and staggered hole patterns including effects of geometric parameters: streamwise hole spacing, spanwise hole spacing, and channel height, normalized by hole diameter. The physical mechanisms influencing heat transfer coefficients as a function of flow distribution and geometric parameters are also discussed.
314 citations
TL;DR: In this article, the Laminar free convection boundary layer flow of a thermomicropolar fluid past a non-isothermal vertical flat plate has been studied in detail.
262 citations
TL;DR: In this paper, a general correlating equation has been developed for all Prandtl and Dean numbers by joining the theoretical Nusselt number for a straight tube and a theoretical asymptote for the regime of creeping secondary flow.
Abstract: A general correlating equation has been developed for all Prandtl and Dean numbers. This expression was constructed by joining the theoretical Nusselt number for a straight tube, a theoretical asymptote for the regime of creeping secondary flow, a semi-theoretical expression for the boundary layer regime and an asymptotic value of Nu for the intervening regime of flow.The arbitrary coefficients and exponents in the model were evaluated using experimental and numerically computed values. Slightly differing sets of coefficients are required for uniform wall temperature and longitudinally uniform heating with uniform peripheral wall temperature. All prior theoretical results were for toroidal flow (zero pitch). A numerical solution was developed for helical flow (finite pitch). These results confirm the validity of neglecting pitch for tightly wound coils but suggest a generalization of the correlating equation for large pitch.
168 citations
TL;DR: In this paper, implicit finite-difference analysis of transient free convective flow past a semi-infinite vertical flat plate, on taking into account mass transfer, is carried out.
119 citations
TL;DR: In this article, an expression for stagnation heat transfer was derived for round, impinging jets on an electrically-heated surface in a small-scale setup characteristic of a typical turbine blade.
101 citations
TL;DR: The wall heat transfer coefficient of the gas-liquid-solid fluidized beds in the range of stable fluidization state runs correlated as a function of modified Nusselt number, modified Reynolds number and gas phase Froude number as discussed by the authors.
101 citations
TL;DR: In this article, the authors used the finite-analytic method to solve heat transfer in cavity flow at high Reynolds number (1000) for Prandtl numbers of 0.1, 1, and 10.
Abstract: Heat transfer in cavity flow is numerically analyzed by a new numerical method called the finite-analytic method. The basic idea of the finite-analytic method is the incorporation of local analytic solutions in the numerical solutions of linear or nonlinear partial differential equations. In the present investigation, the local analytic solutions for temperature, stream function, and vorticity distributions are derived. When the local analytic solution is evaluated at a given nodal point, it gives an algebraic relationship between a nodal value in a subregion and its neighboring nodal points. A system of algebraic equations is solved to provide the numerical solution of the problem. The finite-analytic method is used to solve heat transfer in the cavity flow at high Reynolds number (1000) for Prandtl numbers of 0.1, 1, and 10.
96 citations
TL;DR: In this article, the authors studied the relationship between overall heat transfer and the degrees of thermal stratification on both sides of the partition and showed that the theoretical Nusselt number calculation is in good agreement with experimental measurements.
79 citations
TL;DR: In this paper, the problem of steady film condensation outside a wedge or a cone embedded in a porous medium filled with a dry saturated vapor is investigated, where the condensate and the vapor are separated by a distinct boundary with no two-phase zone in between.
77 citations
TL;DR: In this article, measurements of Rayleigh numbers R and Nusselt numbers N have been made for a cylindrical cell having a radius to height ratio of 4·72 and containing liquid helium I.
Abstract: Measurements of Rayleigh numbers R and Nusselt numbers N have been made for a cylindrical cell having a radius to height ratio of 4·72 and containing liquid helium I. The upper surface of the cell was maintained at a constant temperature T2 near T0 = 2·178 K where the fluid density has a maximum. The heat input to the cell bottom was varied quasi-statically while the lower surface temperature T1 was recorded. The penetration parameter [Pscr ]≡(T1−T2)/(T1−T0) ranged between 0·1 and 3 for our experiments.For [Pscr ] Rc, is believed to correspond to the transition from cellular to two-dimensional flow. Near Rc and with [Pscr ] > 2 we also observed multistability, with the states believed to correspond to different numbers of convective cells.For large [Pscr ] the onset of time-dependent flow occurred much closer to Rc than is the case for Boussinesq systems.
57 citations
TL;DR: In this paper, an approximate solution of two-dimensional convection in the limit of low Prandtl number is presented in which the buoyancy force is balanced by the inertial terms.
Abstract: An approximate solution of two-dimensional convection in the limit of low Prandtl number is presented in which the buoyancy force is balanced by the inertial terms. The results indicate that inertial convection becomes possible when the Rayleigh number exceeds a critical value of about 7 × 103. Beyond this value the velocity and temperature fields become independent of the Prandtl number except in thin boundary layers. The convective heat transport approaches the law Nu = 0·175 R¼ for the Nusselt number Nu. These results are in reasonably close agreement with the numerical results described in the preceding paper by Clever & Busse (1980).
TL;DR: In this paper, a numerical study has been made of steady-state free convective heat transfer from a solid sphere to an incompressible Newtonian fluid for Grashof numbers of 0.05, 1,10,25 and 50 for a Prandtl number of0.72.
TL;DR: In this paper, surface tension-driven convection and buoyancy driven convection in a bounded cylindrical geometry with a free surface are studied for a range of aspect ratios and Nusselt numbers.
TL;DR: In this paper, the cooling of a low-heat-resistance sheet that moves downwards is considered and the Nusselt number associated with this process is compared with those due to other modes of heat transfer, such as radiation and forced convection.
Abstract: In this paper the cooling of a low-heat-resistance sheet that moves downwards is considered. The free-convective velocities are assumed to be much larger than the velocity of the sheet. As a result the motion of the fluid is mainly towards the point where the sheet enters the system and a ‘backward’ boundary layer ensues. It is shown that the equations can be reduced by a similarity transformation. For intermediate values of the Prandtl number the equations are solved numerically. Matched asymptotic expansions are used to treat the cases of extremely small and extremely large Prandtl number. The Nusselt number associated with this process is compared with those due to other modes of heat transfer, such as radiation and forced convection. The algebraic behaviour of the boundary-layer functions is discussed.
TL;DR: In this article, an exact method of analysis is presented for solving the low Peclet number thermal entry region problem for laminar flow inside a circular tube, including the effects of axial conduction in both the upstream and downstream directions.
TL;DR: In this article, the problem of steady natural convection film boiling about a heated isothermal vertical plate in a porous medium filled with a subcooled liquid was considered, and similarity solutions were obtained for the buoyancy-induced flow in the vapor and subcooling liquid layers with a distinct interface.
TL;DR: In this article, the decreasing influence of Ra on the Nusselt number and the effect of the aspect ratio were analyzed and then numerically verified for very high Rayleigh numbers (Ra ⪢ 106).
TL;DR: An exact analysis of Stokes' problem for an infinite vertical plate, whose temperature varies linearly with time, has been presented in this article, where it is observed that the velocity near the plate increases with the timet, and the Grashof numberGr.
TL;DR: In this article, a numerical method based on the simplified Marker and Cell technique with local cancellation of low order, diffusional truncation errors was used to study the heat transfer between the solid and liquid phases of porous media.
Abstract: Transient multidimensional natural convection in porous media has been studied using a numerical method based on the simplified Marker and Cell technique with local cancellation of low order, diffusional truncation errors. The conservation equations boundary conditions were phrased in terms of the primitive variables, velocity, and the temperature. Differences in temperature between the fluid and the solid matrix are considered. Heat transfer between the solid and liquid phases was modelled by representing the porous medium as an assemblage of spherical particles, and solving the conduction problems within the spheres at every time step. Nusselt numbers at walls were calculated from the temperature and velocity profiles. Numerical results for heat transfer through fluid saturated porous media heated from below are in agreement with published experiments. Consideration of heat transfer between the solid and fluid phase leads to Nusselt numbers that vary with the thermophysical properties of the solid material, even when the Rayleigh number and fluid thermophysical properties are kept constant. This also is observed in experiments. The calculations also show convective instabilities of the right period at high Rayleigh numbers. 15 references.
TL;DR: In this paper, the authors measured heat transfer coefficients for melting about a heated vertical cylinder embedded in a solid phase-change medium whose temperature was either at the melting point or was subcooled below the melting value.
09 Mar 1981
TL;DR: In this article, a two-dimensional arrays of circular jets of air impinging on a heat transfer surface parallel to the jet orifice plate are considered, and the air, after inpingement, is constrained to exit in a single direction along the channel formed by the surface and the jet plate.
Abstract: Two-dimensional arrays of circular jets of air impinging on a heat transfer surface parallel to the jet orifice plate are considered. The air, after inpingement, is constrained to exit in a single direction along the channel formed by the surface and the jet plate. The downstream jets are subjected to a crossflow originating from the upstream jets. Experimental and theoretical results obtained for streamwise distributions of jet and crossflow velocities are presented and compared. Measured Nusselt numbers resolved to one streamwise hole spacing are correlated with individual spanwise row jet Reynolds numbers and crossflow-to-jet velocity ratios. Correlations are presented for both inline and staggered hole patterns including effects of geometric parameters: streamwise hole spacing, spanwise hole spacing, and channel height, normalized by hole diameter. The physical mechanisms influencing heat transfer coefficients as a function of flow distribution and geometric parameters are also discussed.Copyright © 1981 by ASME
01 May 1981
TL;DR: In this article, a series of forced convection steam cooling tests at low Reynolds numbers and bundle boiloff tests were conducted in the unblocked bundle task of the FLECHT SEASET program.
Abstract: A series of forced convection steam cooling tests at low Reynolds numbers and bundle boiloff tests were conducted in the unblocked bundle task of the FLECHT SEASET program. The COBRA-IV-I computer code was utilized to simulate the steam cooling tests, so that the effects of the housing, disconnected heater rods in the bundle, and subchannel mixing were accurately accounted for. After careful data screening, a steady-state forced convection steam cooling heat transfer correlation was developed using the measured heater rod power, heater rod surface temperatures calculated from the measured cladding inner surface temperature by an inverse conduction code, and the vapor temperatures at various subchannels calculated by the COBRA-IV-I code The new correlation was found to give higher heat transfer than the conventional Dittus-Boelter correlation in the low Reynolds number region. At higher Reynolds numbers, the data begin to merge with the Dittus-Boelter correlation.
TL;DR: In this article, a special subgrid scale heat flux model for liquid metal flows is deduced together with a method of calculating the model coefficients, and the numerical results confirm Lawn's theory, giving reasonable heat flux correlation coefficients which depend only weakly on the problem marking parameters.
TL;DR: In this paper, a semi-empirical entrainment theory was used to determine the NPSH requirements for a pump by the combined effects of cavitation, fluid properties, pump geometry, and pump operating point.
Abstract: The net positive suction head (NPSH) requirements for a pump are determined by the combined effects of cavitation, fluid properties, pump geometry, and pump operating point. An important part of this determination is the temperature depression (Delta T). Correlations are presented of the temperature depression for various degrees of developed cavitation on venturis and ogives. These correlations, based on a semi-empirical entrainment theory, express Delta T in terms of the dimensionless numbers of Nusselt, Reynolds, Froude, Weber, and Peclet, and dimensionless cavity length (L/D). The Delta T data were obtained in Freon 114, hydrogen and nitrogen for the venturis and in Freon 113 and water for the ogives.
TL;DR: In this article, natural convection in a rectangular cavity is considered for the problem where one vertical wall is heated and the other is cooled using a modified Oseen technique in a manner similar to Gill's solution.
TL;DR: In this article, temperature profiles were measured in air beneath isothermal plate surfaces at Rayleigh numbers ranging from 4×10 4 to 1.5×10 6, in excellent agreement with predictions based on approximate analytical solutions to the heat transfer problem.
TL;DR: In this paper, the influences of property variations in natural convection were investigated. Butler et al. showed the influence of properties variations on heat transfer from a vertical isothermal, heated surface to gaseous nitrogen and the ambient temperature, Tinfinity, was varied in order to cover a large range of the Rayleigh number and also the generation of large values of this parameter.
Abstract: The objective of this paper is to show the influences of property variations in natural convection. Heat transfer from a vertical isothermal, heated surface to gaseous nitrogen is experimentally investigated. The ambient temperature, Tinfinity, is varied in order to cover a large range of the Rayleigh number and also the generation of large values of this parameter. The range 80 K
TL;DR: In this paper, the stability of three-dimensional convection in rectangular boxes of fluid-saturated porous material with square horizontal cross-section heated from below is investigated and the properties of a special class of solutions exhibiting a high degree of symmetry are determined as a function of box size and Rayleigh number.
Abstract: Steady, three-dimensional convection in rectangular boxes of fluid-saturated porous material with square horizontal cross-section heated from below is found to be non-unique. The properties of a special class of solutions exhibiting a high degree of symmetry are determined as a function of box size and Rayleigh number. The stability of these solutions to general three-dimensional perturbations is also determined. In some cases, when these solutions are found to be unstable, the alternative forms of three-dimensional convection are presented. Multiple three-dimensional steady states are given for a few particular values of box size and Rayleigh number.
TL;DR: In this article, a conjugate internal-external natural convection problem was solved numerically for Grashof numbers between 103 and 107 and for a Prandtl number of 0.7.