Letters in Heat and Mass Transfer最新文献

Solution for two-phase flow with low Reynolds number and low Capillary number in two-dimensional divergent-convergent channel is presented. The method consists in (1) solving separately in each fluid domain the Navier-Stokes and continuity equations for some velocity conditions on the interface and (2) choosing the solution which appears physically as the most satisfactory relatively to the equality of tangential stresses on both sides of the interface. So, for a given interface, it is possible to determine the pressure drop in such a channel for various viscosity ratios.

Heat transfer coefficient is measured between a 25.4 mm outer diameter smooth vertical tube immersed in 0.254 m internal diameter fluidized beds of sand (d_p = 265, 507 and 787 μm), glass beds (239, 357 and 412 μm), silicon (368 μm) and alumina (267 μm) as a function of bed temperature (335 – 528 K) and fluidizing velocity. The solids movement and mixing in the bed is investigated by measuring the heat transfer coefficient at two radial positions in the bed for various values of fluidization velocity and bed temperature. The minimum fluidization velocity, bed voidage and maximum heat transfer coefficient are also reported for different experimental conditions. The qualitative variation of h_o with different operating and system parameters is found consistent with the known mechanisms of heat transfer for an immersed surface in a fluidized bed. Quantitative correlation of h_o and h_omax will be reported in a future publication.

The present investigation deals with a theoretical analysis of direct contact sensible heat transfer between two immiscible liquids in a countercurrent spray column. The non-dimensional parameters governing the heat transfer process are identified and a study of the effects of the variation of these parameters is made. The predicted column heights and the temperature profiles of both the phases along the column compare favourably with the available experimental data.

This paper presents an experimental investigation of film breakdown heat flux for water film flowing over a heat dissipator tube inside which hot fluid flows. Data for clean tubes and with continuously falling water for long period are reported. Influence of flow rate on dryout heat flux for both type of tubes and on heat transfer prior to dryout for tube with longer usuage is presented. The effect of temperature difference between hot fluid and falling water film on the film breakdown heat flux and heat transfer coefficients prior to film breakdown is also reported.

We propose a very simple model of a mushy zone which admits of an explicit solution. To our knowledge, it is the only instance where an actual observation of the mushy zone width and structure is used as a partial basis for the model definition. The model rests upon two unknown parameters. The first determines the relation between the equilibrium temperature gradient and the mushy zone width. The second depends upon the dendritic structure in the mushy zone, and is related to the solid fraction. Both can be estimated from experiments. We define the model, present its closed form solution, and give tables from which the solution can be found explicitly. It is seen that in most cases the predicted mushy zone is of very small width.

By making use of local equilibrium assumption, a calculation has been made on $\text{vθ}$, temperature distribution, Nusselt number and thermal eddy diffusivity for liquid metal turbulent heat transfer in a circular tube and the calculated results are discussed in comparison with available experimental data.

The addition of small amount of soluble polymer makes the boiling behavior significantly different from that of pure water. The polymer additives reduce the tendency of coalescence between vapor bubbles. Consequently, they become smaller in size, larger in number, and tend to stay on the heating surface in a relatively orderly manner. No significant improvement in heat transfer rate caused by the polymer additives was observed in this work; the critical burn out heat flux was reduced slightly.