Showing papers in "Advances in heat transfer in 1970"

Heat Transfer and Friction in Turbulent Pipe Flow with Variable Physical Properties

Abstract: Publisher Summary This chapter discusses heat transfer and skin friction in turbulent pipe flow with variable physical properties. The constant properties solution has been considered only so far as is necessary for the flow and heat transfer analysis with variable physical properties. The chapter highlights analytical methods to describe heat transfer mechanisms for constant liquid properties quite satisfactorily and to take into account the influence of the variation of physical properties with temperature versus heat transfer and skin friction in a number of important cases. Disagreement between theoretical and experimental results observed in other cases, in particular, with a considerable change in physical properties over the flow cross section, may be attributed to imperfect methods of estimating the effect of the variation of physical properties on turbulent diffusivity. Important experimental material has been accumulated on heat transfer and skin friction for variable physical properties. However, certain portions of this material possess relatively low accuracy that prevents its successful use. For a number of important cases, there has been no systematic data collection or that which is available is scanty and contradictory. Therefore, the need for further experimental investigations, with a high degree of accuracy, into the fluid mechanics and heat transfer for variable physical properties is quite urgent.

Optical Methods in Heat Transfer

Abstract: Publisher Summary This chapter considers optical methods in which the temperature dependence of the refractive index is used to make the temperature field visible. The optical methods considered are divided into two groups: the shadow and schlieren techniques, utilizing the deflection of light in the measurement media, and the interference methods based on differences in lengths of the optical paths. Compared with shadowgraph and schlieren methods, the interference methods offer more detailed information about the model that is to be investigated; these allow a greater accuracy. The laws governing the propagation of light through a medium with locally varying refractive index have also been considered. The total information on the region of optical inhomogeneity being investigated comes from the deformation of a wave front, whose shape was originally known, as it passes through the region. The chapter provides examples of boundary-layer problems in the region of natural convection and combined convection. To fully demonstrate how the results are evaluated, some selected examples have been presented.

Supersonic Flows with Imbedded Separated Regions

Abstract: Publisher Summary This chapter presents illustrative data pertaining to cavities with recompression against a solid boundary rather than bluntbase wakes, because the latter are adequately covered in the other reviews. The chapter deals with recompression-controlled cavities downstream of steps (and blunt bases) that have been most thoroughly investigated both theoretically and experimentally, and presents the semiempirical model of Chapman and Korst and confronts it with evidence. The more sophisticated numerical studies, which go beyond the assumptions of the Chapman–Korst model and illustrate its insufficiencies and limitations, have been reviewed. The chapter gives an account of experimental data for cavities in notches and outlines the features of the free-interaction model that isolates the dominant mechanism governing separation-controlled cavities. Illustrative data pertaining to upstream-facing steps, ramps, and shock-induced cavities have been presented and correlated in terms of similarity parameters derived from this model. Numerical solutions of the interaction-dominated boundary-layer problem starting with either the differential equation or a multimoment approximation to the equations have been described. These constitute the most complete and sophisticated treatment of flows with imbedded separate regions, and apply, in principle, to all types of cavities.

Unsteady Convective Heat Transfer and Hydrodynamics in Channels

Abstract: Publisher Summary This chapter reviews the analysis of unsteady convective heat transfer and hydrodynamics, including the statement of the problem and the methods of investigation. The aim of the chapter, based on a review of the literature, is to analyze the available techniques and directions of research when unsteady convective heat transfer and hydraulics are studied, mainly with fluid flow in channels. The skill of reliable calculation of unsteady heat transfer and hydrodynamics has become an urgent problem in many branches of modern engineering. Due to essential differences between unsteady and steady problems, sometimes incompatible opinions appeared on the statement and methods of the theoretical and experimental investigations of unsteady problems. Besides the direct application of the development of the methods for calculating pressure losses, the study of the hydrodynamics of unsteady flows in channels has some other, no less important, purposes. The methods of calculating convective heat transfer with the use of heat transfer coefficients as well as the methods of calculating temperature fields within a wall by using the boundary conditions of the third kind, all widely applied in engineering practice for steady-state problems, may, without any major difficulties, be generalized to the solution of unsteady-state problems.