With forced convection

Dry Running Pump Again, no lubrication or dissipation of hear. Remove the heat with a double seal and barrier tank with forced convective flow. 

Gases and Liquids Tending to Gas Gases cannot lubricate the seal fltees. No dissipation of heat. Use a dual seal with forced convective flow. 

When the fluid displaced is accelerated by wind or artificial means the process is called forced convection. With forced convection the rate of heat transfer is increased - substantially so in many cases. 

It is not proposed to deal with forced convection here. Experimental work has yielded considerably differing results for ostensibly similar conditions. It is sufficient to note that forced convection affects small-bore pipes to a greater extent than large-bore and is dependent on temperature differences. While the heat loss from non-insulated surfaces may increase by a factor of up to 200-300 per cent, the increase in heat loss from the insulated surface would be considerably less (of the order of 10 per cent). 

Two condensers, or a condenser assembly having two separate refrigerant circuits and permitting rapair to one circuit while the other is working. If there is one assembly with forced convection, there are at least two fans. 

L6. Lee, D. H., and Obertelli, J. D., An experimental investigation of burnout with forced convection high-pressure water, Proc. Inst. Mech. Engrs. (London) 180, Pt. 3C (1965-1966). 

Sato T, Matsumura H (1964) On the conditions of incipient subcooled-boiling with forced convection. Bull Jpn Soc Mech Eng 7 392-398... 

Gunther, F. C., 1951, Photographic Study of Surface Boiling Heat Transfer to Water with Forced Convection, Trans. ASME, J. Heat Transfer 73 115-123. (3)... 

Whalley, P. B., P. Hutchinson, and G. F. Hewitt, 1973, The Calculation of Critical Heat Flux in Forced Convective Boiling, Rep. AERE-R-7520, European Two Phase Flow Group Meeting, Brussels. (5) Whalley, P. B., P. Hutchinson, and G. F. Hewitt, 1974, The Calculation of Critical Heat Flux in Forced Convection Boiling, Heat Transfer 1974, vol. IV, pp. 290-294, Int. Heat Transfer Conf., Tokyo. (5) Wichner, R. P, and H. W. Hoffman, 1965, Pressure Drop with Forced Convection Boiling of Potassium, Proc. Conf. on Applications of Heat Transfer Instrumentation to Liquid Metals Experiments, ANL-7100, p. 535, Argonne National Lab., Argonne, IL. (3)... 

For boiling in a tube, there is therefore a contribution from nucleate boiling arising from bubble formation, together with forced convection boiling due to the high velocity liquid-vapour mixture. Such a system is inherently complex since certain parameters influence these two basic processes in different ways. 

All the electrode kinetic methodology described until now has assumed a steady state (or quasi-steady state in the case of the DME). Many techniques at stationary electrodes involve perturbation of the potential or current in combination with forced convection, this offers new possibilities in the evaluation of a wider range of kinetic parameters. Additionally, we have the possibility of modulating the material flux, the technique of hydrodynamic modulation which has been applied at rotating electrodes. Unfortunately, the mathematical solution of the convective-diffusion equation is considerably more complex and usually has to be performed numerically. 

The case of combustion of an entire spherical surface with forced convection has not yet been solved. Frossling (4) originally proposed a semi-empirical relation for the low-temperature evaporation of droplets in motion. Spalding (60) has applied the equation to his heterogeneous combustion data with some success by including the term containing the transfer number ... 

As in the case with forced convective flows, there are many free convective flows that can be analyzed with sufficient accuracy by adopting the boundary layer assumption. Essentially this boundary layer assumption is that the flow consists of two regions ... 

As was done in dealing with forced convective flow over a uniform temperature plate, it is assumed that the velocity and temperature profiles are similar at all values of x, i.e., that ... 

The above equations can be solved using numerical methods, i.e., using the same basic procedures as used with forced convection. There is, however, one major difference between the procedures used in forced convection and in mixed convection. In forced convection, the velocity field is independent of the temperature field because fluid properties are here being assumed constant. Thus, in forced convection it is possible to first solve for the momentum and continuity equations and then, once this solution is obtained, to solve for the temperature distribution in tike flow. However, in combined convection, because of the presence of the temperature-dependent buoyancy force term in the momentum equation, all of the equations must be solved simultaneously. Studies of flows for which the boundary layer equations are not applicable are described in [24] to [43]. 

If the Darcy assumptions are used then with forced convective flow over a surface in a porous medium, because the velocity is not assumed to be 0 at the surface, there is no velocity change induced by viscosity near the surface and there is therefore no velocity boundary layer in the flow over the surface. There will, however, be a region adjacent to the surface in which heat transfer is important and in which there are significant temperature changes in the direction normal to the surface. Under many circumstances, the normal distance over which such significant temperature changes occur is relatively small, i.e., a thermal boundary layer can be assumed to exist around the surface as shown in Fig. 10.9, the ratio of the boundary layer thickness, 67, to the size of the body as measured by some dimension, L, being small [15],[16]. 

Our development in this chapter is primarily analytical in character and is concerned only with forced-convection flow systems. Subsequent chapters will present empirical relations for calculating forced-convection heat transfer and will also treat the subjects of natural convection and boiling and condensation heat transfer. 

The foregoing analysis of free-convection heat transfer on a vertical flat plate is the simplest case that may be treated mathematically, and it has served to introduce the new dimensionless variable, the Grashof number, which is important in all free-convection problems. But as in some forced-convection problems, experimental measurements must be relied upon to obtain relations for heat transfer in other circumstances. These circumstances are usually those in which it is difficult to predict temperature and velocity profiles analytically. Turbulent free convection is an important example, just as is turbulent forced convection, of a problem area in which experimental data are necessary however, the problem is more acute with free-convection flow systems than with forced-convection systems because the velocities are usually so small that they are very difficult to measure. Despite the experimental difficulties, velocity measurements have been performed using hydrogen-bubble techniques [26], hot-wire anemometry [28], and quartz-fiber anemometers. Temperature field measurements have been obtained through the use of the Zehnder-Mach interferometer. The laser anemometer [29] is particularly useful for free-convection measurements because it does not disturb the flow field. 

Thus, we find that the overall heat-transfer coefficient is almost completely controlled by the value of h . We might have expected this result strictly on the basis of our experience with the relative magnitude of convection coefficients free-convection values for air are very low compared with forced convection with liquids. 

B. Single sphere, creeping flow with forced convection Nsh = = [4 ° + 1-21 [T] Use with log mean concentration difference. Average over sphere. Numerical calculations. (.NReNSc) < 10,000 Nrs < 1.0. Constant sphere diameter. Low mass-transfer rates. [46] [88] p. 114 [105] [138] p. 214... 

B. Single sphere, creeping flow with forced convection... 

This value would be even smaller when the radiation effects are considered. The critical radius would be much less in forced convection, often less than 1 mm, because of much larger h values associated with forced convection. Therefore, we can insulate hot-water or steam pipes freely without worrying about the possibility of increasing the heat transfer by insulating the pipes. 

Fig. 21. Film boiling with forced convection. The liquid flow was normal to a horizontal tube at one atmosphere. Velocity = 0 to 14 ft./sec. Diameter = 0.387 to 0.637 inch (B5).

Now we are ready for the dimensional analysis of convection problems. We begin with forced convection because of its relative simplicity. 

Having learned the dimensionless numbers associated with forced convection we now proceed to those for natural convection. 

In Chapter 5, we learned the foundations of convection. Integrating the governing equations for laminar boundary layers, we obtained expressions for the heat transfer associated with forced convection over a horizontal plate and natural convection about a vertical plate. We also found analytically, as well as by the analogy between heat and momentum, that the thermal and momentum characteristics of laminar flow over a flat plate are related by... 

Dobson [144] developed an additive model that combined film condensation (i.e., a modified Nusselt analysis) at the top and sidewalls of the tube with forced convection condensation in the stratified pool at the bottom of the tube. 

General empirical correlations. In this approach, no attempt is made to base the correlations on nucleate pool-boiling correlations combined in some way with forced convective correlations. Rather, the data are correlated independently using a number of dimensionless groups. 

For the saturated boiling region, the power-law interpolation method has been used by, for instance, Steiner and Taborek [259] and Wattelet [262]. Steiner and Taborek deal with forced convective boiling in the quality region and hence use Eq. 15.226 as a basis. Their expression is as follows ... 

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