Vertical Narrow Channel Research Articles

Forced liquid helium flow transient heat transfer in a narrow channel under step heat flux

The paper presents experimental data on transient heat transfer in forced flow two-phase helium in a narrow vertical channel. Two principal mechanisms of heat transfer deterioration have been found. The first is due to increasing pressure reaching supercritical values. The second is the crisis when the liquid microlayer near the channel wall is evaporating completely. The influence of flow rate, quality and initial heating upon heat transfer and crisis have been studied and are discussed.

The experimental study of liquid nitrogen boiling heat transfer in vertical narrow channel of porous layer surface

The observation of boiling flow pattern in narrow channel of sintered aluminium powder surface and the measurement of the boiling heat transfer indicate that major flow pattern in narrow channel is annular flow pattern with liquid guttae. The thinner liquid film and the smaller flow velocity, the stronger boiling heat transfer. The lag of annular flow is caused by that of bubble flow. The boiling heat transfer coefficient of the porous surface is 3–6 times as large as that of the smooth surface.

Evaporative heat transfer and pressure frop in a rib-roughened flat channel. Effects of rib height and spacing of transverse rib roughness.

The purpose of this study is to investigate the effects of repeated transverse rib roughness on forced convection evaporation in a narrow vertical channel. Five channels which have the same cross section measuring 2mm by 50mm (aspect ratio 25) and have different rib heights (e=0.6 and 1.0) and rib spacings (P=7, 10, 15, 20mm) were investigated. Experiments were conducted using R12 as a working fluid for vertical upward flow at mass velocities between 50 and 130kg/m2s and mass qualities between 0.2 and 0.8. Comparison of these data indicates that the heat transfer coefficient has a tendency to increase with reducing rib spacing and to decrease with reducing rib height. The highest heat transfer coefficient, which is obtained by the channel with P=7mm and e=1mm, is about three times higher than the smooth channel. This ribbed channel was also found to be best in these five channels under the same pumping power condition.

Heat Transfer Characteristics in Narrow Vertical Rectangular Channels Heated from Both Sides

The effects of gap size on heat transfer characteristics were investigated experimentally for a vertical rectangular flow channel with gaps of 2.5mm, 6mm and 18mm. As a result, the following was revealed. The flow shows a nature of forced convective heat transfer when Grx/Re(21)/18xPr1/2 is less than 2.5×10-4, and a free-convective heat transfer when Grx/Re(21)/18xPr1/2 is higher than 1.8×10-3, for all three gap sizes of the flow channel. As for the data for a gap of 2.5mm in the transition region between forced convection and free convection, it was confirmed that the heat transfer coefficient higher than that predicted by the heat transfer correlation for turbulent forced convection along a flat plate was due to the acceleration of the main flow through the development of the boundary layer, not to buoyancy force.

Enhancement of heat transfer due to bubbles passing through a narrow vertical rectangular channel

A theoretical analysis has been made of heat transfer enhancement due to bubbles passing through a narrow vertical channel. The mechanism of enhancement for a constant heat flux is: heat is first transported by a latent heat of evaporation on the bubble interface covering the heated surface and is followed by sensible heating of the succeeding liquid. The latent heat transport is calculated using an integral method and the sensible heating is determined exactly. For low heat fluxes, the calculated heat transfer coefficients are in fairly good agreement with the experiments; at high heat fluxes, however, the calculated values are approximately half the experimental values, since flow along the heated surface is not taken into account.

Enhancement of heat transfer due to bubbles passing through a narrow vertical rertical rectangular channel. Theoretical analysis without evaporation on an interface.

A theoretical analysis has been made to elucidate the mechanism of the enhancement of heat transfer due to bubbles passing through a narrow vertical channel. This analysis is introduced based on a change in heated surface temperature with a time during which the bubble passes through it. The characteristics of enhancement are given for a constant heat flux and a constant temperature, having a similar tendency to those obtained in the experiment. The heat transfer coefficients obtained are about 2 times as large as those predicted by the analysis. The difference between the results arises from the effect of the flow which is not taken into account in the analysis. In addition, the thickness of the liquid film, which plays an essential role in the enhancement of heat transfer due to the passing bubbles, is 71.7 μm within the experimental range of qw=1.3×104-2.8×105 w/m2, T0=0.1-1.0 sec, and lb=10, 20, and 30 mm.

Heat transfer characteristics in narrow vertical rectangular channels heated from both sides.

The effects of gap size on heat transfer characteristics were investigated experimentally for a vertical rectangular flow channel with gaps of 2.5 mm, 6 mm and 18 mm

Characteristic of Heat Transfer Enhancement Due to Bubbles Passing Through a Narrow Vertical Channel

Characteristic of Heat Transfer Enhancement Due to Bubbles Passing Through a Narrow Vertical Channel

New apparatus for measuring steady-state diffusion

A steady concentration gradient is maintained in a narrow vertical diffusion channel making it possible to determine the concentration dependence of the diffusion coefficient in one single experiment. The gradient is sustained by a simple transport system and is observed interferometrically. The apparatus is tested using calcium chloride and sugar. The method is rapid and the results agree fairly well with those reported in the literature. Analyses of the flow velocity and the time to reach the steady state are given.

High Rayleigh number convection in shallow enclosures with different end temperatures

Buoyancy-driven laminar convection in shallow horizontal enclosures (width/height ⪢1) with adiabatic horizontal walls and isothermal vertical walls of different temperatures has been investigated for very high Rayleigh numbers ( Ra ⪢ 10 6). It is found that this flow regime, which is characterized by boundary layers lining both the vertical and horizontal walls, differs qualitatively from the low- Ra flow regime, in which the horizontal boundary layers are absent. The decreasing influence of Ra on the Nusselt number and the effect of the aspect ratio are analytically shown and then numerically verified. Comparison is made with existing experimental and numerical data, and a new correlation is proposed for the Nusselt number in this flow regime. An explanation is also advanced regarding the current controversy about the power dependence of the Nusselt number on Ra in narrow vertical channels.

Energy dissipation and geometric structure at spreading plate boundaries

A simple analytical model of injection of solid material under ocean ridge axes and of shearing action under transform faults is presented on the basis of high temperature creep laws. The orthogonality between ridge axes and transform faults is explained by the principle of least-energy dissipation in the plastic flow at diverging plate boundaries and it is shown that this striking surface geometry implies the existence of a narrow vertical injection channel under oceanic ridges.

Static heat transfer to liquid helium in open pools and narrow channels

The transfer of heat to boiling liquid helium has been measured in open pools and narrow channels. In open pools a marked dependence of heat transfer on the orientation of the heated surface is observed. The maximum heat flux for nucleate boiling varies from 1 W/cm 2 with the heated surface horizontal facing upwards to about 0·1 W/ cm 2 with the surface horizontal facing downwards. In a narrow vertical channel the maximum heat flux is reduced to about 0·15 W/ cm 2 for a rectangular channel 10 mm × 1 mm (50 cm length), and appears to decrease linearly with the channel dimension. The heat transfer is considerably increased in the narrow channel when the fluid is pressurized.

APPLICATION OF ELECTROPHORESIS-CONVECTION TO THE FRACTIONATION OF BOVINE γ-GLOBULIN

A method of fractionation of proteins in solution in which an electrophoretic adaptation of the principles of the Clusius column is utilized was suggested by Kirkwood in 1941 (1) and tested experimentally by Nielsen and Kirkwood (2) several years later. Recently an electrophoresis-convection apparatus of improved design has been described and successfully used in the fractionation of the pseudoglobulin of horse diphtheria antitoxin (3) and bovine serum proteins (4). Fractionation occurs in a narrow vertical channel between two semipermeable membranes, connecting an upper and lower reservoir. Separation depends upon the superposition of diflerential horizontal electrophoretic transport of the components on vertical convective transport of the solution as a whole. The vertical convective transport is controlled by the horizontal density gradient produced by the electrophoretic migration of the proteins across the channel. The result of the superposition of horizontal electrophoretic transport and vertical convective transport is movement of the mobile components from the top reservoir to the bottom reservoir at rates depending on their mobilities, with a relative enrichment of the top reservoir with respect to the slow components and the bottom reservoir with respect to the fast components. The separation of a protein mixture possessing discrete mobility and isoelectric point spectra, e.g. serum, into its constituent proteins is accomplished by successive immobilization of the components at their respective isoelectric points and transport of the mobile components from the top reservoir of the apparatus.