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.
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.
The purpose of this paper is to test the validity of pulse methods to characterise the thermal properties of a fibrous non random composit material. A tridimensional numerical model shows that the influence of the contact fiber-matrix is slight except when the sample is gaz free and under vacuum; however the longitudinal diffusivity of the fiber is the most important parameter. A “flash” pulse method was used to test the validity of the model. For thick samples, the composit material is similar to an homogeneous material, the thermal properties of which depend on those of the cons tituants and on the geometrical parameters of the composit material.
Experiments were performed to determine the heat transfer characteristics of a turbulent pipe flow downstream of a flow control orifice. The orifice consisted of an orifice plate followed by an abrupt expansion. A total of fifty-four geometric variants were tested. The working fluid was water, with Prandtl number 7, and the Reynolds number range was from 50, 000 to 125, 000. The maximum Nusselt numbers observed were 3 to 5 times the value for the corresponding fully-developed flows.
Initial results are presented for double-segmentally baffled shell-and-tube heat exchangers, with leakage. The results are compared with those for a single-segmentally baffled exchanger of similar geometry, and shown to be similar to that of two such exchangers in a back-to-back parallel configuration.
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.
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.
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.
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.
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 optimal linearization method is used to obtain an approximate analytical solutions for steady state of convective fins with variable thermal conductivity. Furthermore, an approximate analytical solutions for transient state of convective fins with variable thermal conductivity is achieved by using the variational embedding method.
The entertainment by a particle laden concentric jet is theoretically determined and compared with direct measurements. Particles enhance the mixing.
This paper presents a numerical model for predicting the performance of liquid-gas mass transfer in a rotating perforated-disc type contactor. The device consists of a cylindrical section situated between two 45-degree conical sections. A liquid flows downward by gravity while a stream of air moves upward by buoyancy thus forming a counter-current flow situation in the contactor. A gas dissolved in the liquid transfers into air bubbles which are sheared to a tiny size as they rise through the perforations on the rotating disc. Both laminar and turbulent flows are treated. Utilizing the velocity distribution [10,11] and bubble trajectory [12] as the basis, the interphase mass transfer performance of carbon dioxide in the water-air system is numerically determined. It is disclosed that in both laminar and turbulent flow cases, the rate of interphase mass transfer increases significantly with a reduction in bubble size. Rotational speed does not affect mass transfer in laminar flow but causes an exponential mass transfer enhancement in higher turbulent flows. There exists an optimum through-flow rate of the liquid for the best mass transfer performance depending on the initial bubble size and disc speed. Test results [9] provide a qualitative confirmation of the theory.
An exact solution of the flow of an incompressible viscous fluid past an infinite vertical plate uniformly accelerated in the vertical direction is presented. The presence of foreign mass is also taken into account. It is observed that the skin-friction increases with increasing Sc (Schmidt number) but decreases with increasing N (buoyancy parameter) or G (Grashof number).
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.
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.
Due to the complicated geometry, the heat conduction across a bent plate has never been treated analytically before. In this paper we utilize an intrinsic coordinate system in order to obtain the temperature profile by perturbations. The curvature of the plate tends to decrease the local temperature in the vicinity of the bend.
Thermoelectric nonlinear fluctuation effects are considered by taking as an example the simple model of a conducting medium. The Nyquist formula has been generalized to include the temperature relaxation of the medium and the special density of the temperature fluctuations in the presence of the electric current flow in the medium has been determined.
An investigation of the influence of freestream turbulence on the temperature and velocity boundary layers on a circular cylinder in cross flow is presented. The investigation has been carried out for the two Reynolds numbers 5·104 and 1·105 with freestream turbulence intensities ranging from 2.5 – 11.5 % and integral scales Λf∞/D ≲ 0.14. Both experiments and numerical calculations show that for the flow ranges considered, the mean velocity field is rather unaffected by the freestream turbulence while the mean temperature field is influenced in such a way that increases in heat transfer of order 8 – 1 10 % occur.
