Intensity Of Convective Heat Transfer Research Articles

Cross-flow transport and heat transfer enhancement in laminar pulsed flow

Abstract An experimental investigation to examine the influence of flow pulsation in a rectangular finned channel on cross-flow transport and convective heat transfer intensification was carried out. The fins were arranged in equal spacing and on the insulated wall opposite to the smooth flat heat transfer surface to avoid heat transfer enhancement by conduction. Pulsation amplitude A ranging from 0.28 to 0.53 mm and pulsation frequencies f in the range of 16 ≤ f ≤ 54 Hz were investigated. A steady flow Reynolds number in the laminar range of 50–1140 was studied. Recirculation eddies and complex flow structures formed within the modules were characterized by a mean cross-flow velocity using PIV. The intensification of the heat transfer coefficient due to the flow pulsation becomes more significant with increasing pulsation amplitude. The heat transfer enhancement was found to match with the cross-flow velocity. Maximum heat transfer enhancement, E = 2.5, was achieved at relative fin height, i.e. ratio of fin height to hydrodynamic boundary layer thickness of 29. No significant heat transfer was obtained at very low and very high flow rates.

The Results of Experimental Investigation into Rational Intensification of Convective Heat Transfer in Rectangular Channels with Protrusions and Grooves Having a Smoothly Rounded Two-Dimensional Cross Section

The Results of Experimental Investigation into Rational Intensification of Convective Heat Transfer in Rectangular Channels with Protrusions and Grooves Having a Smoothly Rounded Two-Dimensional Cross Section

The Effect of Plate Size on the Natural Convective Heat Transfer Intensity of Horizontal Surfaces

Natural convective heat transfer from flat horizontal isothermal plates has been investigated for more than a century. In the present study, the influence of the size of the plate on the heat flux is investigated. Two ranges of the heat transfer intensity are proposed for this problem: for the plates with characteristic length smaller than 0.1–0.2 m, the heat transfer coefficient is inversely proportional to the plate width; for plates wider than 0.2 m, the heat flux is not influenced by the plate width. The explanation for the discrepancy between the two ranges of natural convective heat transfer based on analysis and comparison of experimental data available in the literature has been proposed.

Natural convective heat transfer from isothermal cuboids

The paper presents results of theoretical and experimental investigations of the convective heat transfer from isothermal cuboid. The analytical solution was performed taking into account complete boundary layer length and the manner of its propagation around isothermal cuboid. It arises at horizontal bottom surface and grows on vertical lateral surface of the block. After changing its direction, the boundary layer occurs above horizontal surface faced up and next it is transformed into buoyant convective plume. To verify obtained theoretical solution the experimental study has been performed. The experiment was carried out for three possible positions of the same tested cuboid. As the characteristic linear dimension in Nusselt–Rayleigh theoretical and experimental correlations we proposed the ratio of six volumes to the cuboids surface area, for the analogy to the same ratio using as the characteristic dimension for the sphere, which is equal to the sphere’s diameter. It allowed performing the experimental results independently from the orientation of the block. The Rayleigh numbers based on this characteristic length ranged from 10 5 to 10 7. The Nusselt number describing intensity of convective heat transfer from the cuboid can be expressed by: Nu= XRa 1/5+ YRa 1/4, where X and Y are coefficients dependent on the cuboid’s dimensions. For the range of provided experiment the experimental Nusselt–Rayleigh relation can be presented in the form: Nu=1.61Ra 1/5 or 0.807Ra 1/4 with the good agreement with the theoretical one recalculated for the tested cuboid dimensions.

Intensification of Convective Heat Transfer

Intensification of Convective Heat Transfer

Natural convective heat transfer from isothermalconic

Theoretical considerations on convective heat transfer from isothermal upward conicalsurfaces have been presented. The physical model of this phenomenon consists of an isothermalcone of inclination angle (φ) between the cone generating line ( X) and the radius ( R) of the cone base. The angle is a parameter of conical surface which varied from ( φ = 0−circular horizontal plate) to ( φ = π/2—vertical cylinder) . Onthe basis of Navier–Stokes equations, assuming the parabolic temperature profile in the boundarylayer, the velocity profile tangent to the surface has been calculated. Introduction of the meanvelocity value in the boundary layer into the balance of energy and mass equations andcomparison with the Newton equation leads to the dependence describing the boundary layerthickness. Next the relation of Nusselt and Rayleigh numbers, including a function expressingthe influence of the inclination angle ( φ) on the heat transfer process, has been derived.The obtained solution describes the natural convective heat transfer process for threecharacteristic cases of the conical surface. For the boundary cases φ = π/2 (vertical cylinder) and φ = 0 (circular upward facing horizontal plate), the solution describing convective heat transferintensity is Nu X=H = 0.668 · Ra 1/4 X=H for φ = π/2 and Nu X=R = 0.932 · Ra 1/5 X=R for φ = 0. For the case (0 < φ < π/2) (cones), the solution has the form Nu X = 1.680 · Φ 1/4 · Ra 1/4 X where (Φ) is a function of the inclination angle ( φ) of the generating line of theconical surface to the base of radius ( R) .

Intensification of convective heat transfer in channels with a porous high-thermal-conductivity filler II. Forced heat-transfer regime

Results are presented from an analytical study of intensification of convective single-phase heat transfer in a channel with a porous high-thermal-conductivity filler in the case of intensive external heating.

Intensification of convective heat transfer in the local swirling of an anomalously viscous fluid flow by an axial-flow bladed swirling unit

The intensification of convective heat transfer in anomalously viscous media with local swirling of the flow by axial-flow bladed swirling units is investigated experimentally.

Intensification of convective heat transfer in the local swirling of a flow of an anomalously viscous fluid by screw swirlers

Intensification of convective heat transfer in the local swirling of a flow of an anomalously viscous fluid by screw swirlers

Mechanism of heat and mass transfer during sublimation in a forced flow of rarefied gas

The interaction of a flow of rarefied gas with the flow of vapor close to a surface undergoing sublimation is studied by a visualization method. The rate of sublimation and the intensity of convective heat transfer are expressed as functions of the velocity of the incident flow of rarefied gas.