Letters in Heat and Mass Transfer最新文献

A modified Schmidt equation is proposed which includes the influence of a non-linear thermal Kapitza resistance on nucleate boiling at solids immersed in liquid helium I. Data of transient nucleate boiling heat transport, at increasing heat flux, are in good agreement with the equation.

The effect of vibration on natural convection heat transfer from vertical rectangular fin arrays of different fin spacings and fin lengths was investigated experimentally. It was seen that up to a certain threshold value of the product of amplitude and frequency (15 mm/s), the imparting of vibration did not have any significant effect on heat transfer from the fin array: Beyond this value, however, the heat transfer rate increased considerably with the increase in the intensity of vibration, the maximum increase obtained being 250% when the vibrational energy input was 90 W.

A simple integral method has been developed for laminar film condensation on plane and axisymmetric bodies. The method retains the acceleration terms in the momentum equation so as to account for the Prandtl number effect. The results appear to be in close accord with those of the complete boundary layer equations. The discussions extend over a wide range of Prandtl numbers and the temperature difference across the film, with an emphasis on the low Prandtl number case.

Full Navier-Stokes equations have been solved numerically to investigate the laminar free convective heat transfer from a cone with a closed end. It is shown that the elliptic nature of the flow contributes significantly toward the augmentation of the local heat transfer rate.

The vorticity effect on the forced convection problem of a viscois flow over a semi-infinite non-isothermal wedge is analysed. A solution is found using the method of matched asymptotic expansions up to the order of $\text{1}\text{Re}$. Numerical solutions for wedge semi-angle of 0 and 18 degrees, as well as Prandtl numbers 0.7, 1 and 10 are shown. The results indicate that the vorticity can increase or decrease considerably the heat flux and that the second order terms may introduce significant corrections for low Reynolds numbers (less than 10³).

Two recently developed simplified models of multicomponent mass transfer are employed to determine the composition profiles during the condensation of a binary vapor (methanol-water) from an inert gas (air or helium). It is found that the profiles and the predicted outlet conditions are in excellent agreement with the results obtained using an exact solution of the Maxwell-Stefan equations to predict the mass transfer rates. It is concluded that the simplified approach to multicomponent mass transfer calculations will probably be adequate for many design problems, thereby realising important savings in computational time and computer program complexity.

Experimental observations of boiling in a water-saturated porous medium are reported. The porous medium is contained in a vertical circular cylinder of diameter D and height H which is heated from below and cooled from above. Single-cell thermal convection occurs prior to the onset of boiling. With the onset of boiling, an isothermal two-phase zone forms above the bottom in regions of ascending convection. The size of the two-phase zone increases with increasing heat flux. At high heat fluxes the cellular convertion flow disappears; a horizontal water layer is then observed to overlie a two-phase layer. A vertical countercurrent flow of liquid and vapor dominates heat transfer in the two-phase layer. In the layered state, an oscillatory boiling mode can develop which is attributed to the periodic formation of a vapor layer at the heating surface.

The mechanism of Nusselt number oscillation at the junction of a straight and helical tube is examined experimentally. The heat transfer behavior in this development region is used as the basis for heat transfer enhancement in a coil in which the curvature is repeatedly reversed.