Showing papers in "Advances in heat transfer in 1977"

Heat and Mass Transfer between Impinging Gas Jets and Solid Surfaces

Abstract: Publisher Summary Heating or cooling of large surface area products is often carried out in devices consisting of arrays of round or slot nozzles, through which air impinges vertically upon the product surface. This chapter presents a comprehensive survey emphasizing the engineering applications and empirical equations, presented for the prediction of heat and mass transfer coefficients within a large and technologically important range of variables. The local variations of the transfer coefficients are based on the experimental data for single round nozzles (SRN), arrays of round nozzles (ARN), single slot nozzles (SSN), and arrays of slot nozzles (ASN). The variation of local transfer coefficients is graphically represented. It also explores how to apply these equations in heat exchanger and dryer design as well as in optimization. The flow field of impinging flow is diagrammatically represented. External variables influencing heat and mass transfer in impinging flow depends on mass flow rate, kind and state of the gas and on the shape, size, and position of the nozzles relative to each other and to the solid surface. The design of high-performance arrays of nozzles is also discussed.

Simultaneous Heat, Mass, and Momentum Transfer in Porous Media: A Theory of Drying

Abstract: Publisher Summary The well-known transport equations for continuous media are used to construct a rational theory of simultaneous heat, mass, and momentum transfer in porous media. Several important assumptions regarding the structure of the gas–liquid system in a drying process are made that require theoretical or experimental confirmation. This chapter presents a general theory that provides a starting point for the construction of special theories so that various drying processes can be studied analytically without recourse to an enormous computational effort. It analyzes the motion of a liquid and its vapor through a rigid porous media. The development of the relevant volume averaged transport equations, which describe the drying process, is also focused. The transport of momentum in the gas phase and the laws of mechanics are applied to the drying process. The thermal energy equations are considered by forming the total thermal energy equation, and the problem of determining the mass average velocities in the gas and liquid phases are also discussed.

Viscous Dissipation in Shear Flows of Molten Polymers

Abstract: Publisher Summary Heat transfer in flowing molten polymers is largely influenced by rheology–– the rheological properties of the polymer and by the flow geometry. The rheology of steady shear flow can treat most of the heat transfer problems completely. This chapter discusses the heat transfer problem, and classifies the heat transfer and viscous dissipation in molten polymers. The heat transfer in shear flow is analyzed and a large emphasis is laid on replacing the commonly used idealized boundary conditions–– constant wall temperature or constant wall heat flux by more general conditions. The heat transfer at the wall is described by an outer temperature difference and the Biot number that is used successfully for describing the boundary conditions for temperature calculations in solids. The Biot number is appropriate for describing the boundary conditions between isothermal and adiabatical, as they occur in real processes. A unifying concept is developed that makes it possible to comprise the most important shear flow cases into a single one that can be solved with one numerical program. The nonviscometric flow in channels and flow with free boundaries is also discussed. An example of heat transfer in unsteady unidirectional shear flow is also provided.

Heat and Mass Transfer in Rivers, Bays, Lakes, and Estuaries

Abstract: Publisher Summary Transfer of heat in rivers, bays, lakes, and estuaries, the acronym THIRBLE is employed. Mass transfer in natural waters is regarded as a part of the same set of phenomena, the detailed numerical modeling of axisymmetrical jets are discussed. It is useful to remember that jet-mixing phenomena can be very simply described and quantitatively predicted, by way of well-established algebraic formulas. This chapter explains how can one extend the number of practically interesting THIRBLE processes that can be represented by simple numerical models, specifically those that involve only one-dimensional storage in the computer and marching integration. The number of practically interesting THIRBLE processes include: two-dimensional parabolic, hyperbolic, or partially parabolic, is very large. Most THIRBLE processes are three-dimensional and unsteady; and the geometries of practical rivers, bays, lakes, and estuaries are highly nonuniform. An accurate description of the geometries of both the water-mass boundaries and of the injection devices, a very large number of grid points are needed, larger than is commonly available on existing computers. A range of THIRBLE problems that can be solved by means of computational procedures involving only one-dimensional storage for each variable is also considered.