Letters in Heat and Mass Transfer最新文献

A closed model for slug flow pattern, which permits the prediction of all slug characteristics (for given gas and liquid rates) is presented. Aerated slugs (non-zero void fraction) and pure liquid slugs are considered. The model is based on new concepts of boundary-layer relaxation in a mixing region at the slug front and its recovery at the slug back.

It is shown that for given gas and liquid rates, the model can, in principle, be applied for a wide quasi-steady frequency range in the developing region. However, stability analysis indicates that there exists a preferable (narrow) frequency range, associated with minimum pressure drop, where slug pattern stabilizes. Comparison with available experimental findings is satisfactory.

In the framework of the Tchen's theory of the dispersion of discrete particles in turbulrnt flows, it is shown that discrete particles can disperse faster than fluid particles, even if the Lagrangian r.m.s. velocity for discrete particles is smaller than the Lagrangian r.m.s. velocity for fluid particles. Examples are given, assuming a Frenkiel's family of Lagrangian correlations for fluid particles velocities.

It is shown that in certain cases the explicit similarity solution for the binary alloy solidification problem exhibits an artificial mushy zone. Although this solution satisfies all of the explicit mathematical conditions of the problem, there can exist a region just in front of the solid/liquid interface where the temperature and concentration it defines lie in the region between the solidus and liquidus curves. A numerical example is given which shows the mushy region, and a condition on the data is derived whose satisfaction will guarantee its occurrence. The anomaly is interpreted to be a shortcoming of the mathematical formulation, which does not explicity state all of the assumptions.

For one-dimensional transient heat conduction, a procedure is developed to estimate the temperature at one boundary when both the temperature and heat flux are measured at the other boundary. The Laplace transform technique is employed and the inverse Laplace transform is carried out by using a novel technique. Exact and noisy data are used to infer the unknown boundary temperature. It is shown that the present procedure is accurate and also stable to measurement errors.

One dimensional heat conduction equation has been analysed for periodic heat transfer in an inhomogeneous bounded medium. Exact analytical solutions for some typical thermal conductivity profiles have been obtained. Also an approximate solution has been attempted for the first time for heat conduction problems which is applicable for any arbitrary variation of thermal conductivity, Numerical appreciation for a parabolic thermal conductivity profile shows that results from approximate approach are in excellant agreement with those obtained by the exact analytical approach.

Liquids with properties βpv/c_p ⪡ 1 and p²vκ/c_pT ⪡ 1 are defined as “incompressible liquids”. The compression work in motion of incompressible liquid is negligibly small. The change in the internal energy of incompressible liquids with respect to the temperature is, however, proportional to c_p. Motions of perfect gases in open systems under appropriate conditions and in closed systems with no net heat addition (or removal) are prescribed by the energy equation with c_p as the appropriate specific heat. Otherwise, either no reduction is possible or both c_p and c_v may become the appropriate specific heats in the energy equation.