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Index

HEDH
A B C D E F G H I J K L M N O P Q R S
Saddle supports, for heat exchangers, Safety factors, Safety, of heat exchangers: Salicyl aldehyde: Salts, heat transfer, as heat transfer media, Sand roughness, equivalent, Santotherm, heat transfer media, Sastri and Rao correlation for surface tension, Saturated boiling: Saturated density: Saturated fluids, tables of physical properties, Saturation pressure, Saturation temperature, Saunders, E A D Sauer, H J Jr, Scale formation in heat exchangers, Scaling approximations, in nonisothermal gas radiation, Scattering bed models, for radiative heat transfer from surfaces, Scattering, interaction phenomena with, Scattering coefficient, Schack wide-band model, for gas radiation properties, Schick and Prausnitz method, for critical volume of mixtures, Schlunder, E U Schmidt, F W Schmidt correlation, for heat transfer in in-line banks of high fin tubes, Schmidt number, Schneider, G E, Schrock and Grossman correlations, for forced convective heat transfer in two-phase flow, Schunk, M Schwier, K, Scraped surfaces: Scaling devices, in shell-and-tube heat exchangers, Seawater physical properties, Seider-Tate equation, for heat transfer in heat exchangers, Selection of heat transfer equipment: Semiconductors, thermal conductivity, Separated flow model: Separation, exergy analysis for, Separators, for use in association with evaporators, Series solutions, for one-dimensional transient conduction, Serrated fins, in plate fin heat exchangers, Shah correlation for boiling, Shah correlation, for boiling in horizontal tubes, Shape factor, in radiative heat transfer between diffuse surfaces, Shear flow, of non-Newtonian fluids, Shear free flow, of non-Newtonian fluids, Shear rate, in fluid, Shear stress: Sheffield, J W, Shelf dryer, Shell-and-tube heat exchanger: Shell-to-baffle clearance, in shell-and-tube heat exchangers, Shells, for shell-and-tube heat exchangers: Sherwood number Shipes, K V, Short-tube vertical evaporator, Sigma phase embrittlement, of stainless steels, Silicate scales, in heat exchangers, Silicone oils, as heat transfer media, physical properties of, Silver method, for calculation of multicomponent condensation, Similarity theory, Simonis, V, Single-phase fluid flow: Single stage flash evaporation (SSF): Singularities, two-phase gas-liquid pressure drop across, Sink, in radiation: Skid-mounted units, specification of, Skin friction coefficient, Skrinska, A, Slab: Sleeves, internal, for expansion bellows, Slot: Slug flow: Slugging, in fluidized beds, Smith, A A, Smith, R, Smith, R A Smith, O, Snell's law, in radiation, Software, for code design, Solar absorber, Solar reflector, Soldered fins, in double pipe exchangers, Solid fuels, properties of, Solids circulation, in fluidized beds, Solid-gas flow: Solid-liquid flow: Solidification: Solids: Solids circulation, in fluidized beds, Soot blowing, Sound velocity: Source, in radiation: Spacers, in shell-and-tube heat exchangers, Spalding, D B, Sparging: Specific enthalpy, Specific entropy: Specific heat capacity, Specific internal energy, Specific volume: Specification of heat exchangers, Spectral absorptivity: Spectral emissivity, in gases, Specular surface, Specular-walled passages, radiative heat transfer in, Spheres: Spherical coordinates, for finite difference equations for conduction, Spherical shells: Spheroids (oblate and prolate), free convective heat transfer from, Spine fins: Spiral heat exchanger: Spirally fluted tubes: Sponge rubber balls, in fouling mitigation, Spray dryers, Sprays, in heat exchangers, Square ducts: Stable equilibrium, of vapor and liquid, Staggered tube banks: Stainless steels, Stanton number Startup: State diagram, for fluidized beds, Static mixers, in heat exchangers, Statically stable foams, Steam, dropwise condensation of, Steam tables, Steam turbine exhaust condensers, Steels, as material of construction, Stefan-Boltzmann constant, Stefan's law, for blackbody radiation, Stegmaier, W, Steiner and Taborek correlation, for forced convective boiling, Stephan and Korner correlation, for boiling of binary mixtures, Stiffeners, PD5500 code guidelines for, Stiffeners, against external pressure, EN13445 guidance on, Stirred beds, heat transfer to, Stirred reactor model, for furnaces, Stone's strongly implicit method, Straight fins (longitudinal fins): Stratified gas-liquid flow: Stratified liquid-liquid-gas flow: Steam analysis methods, for shell-side heat transfer and pressure drop in shell-and-tube heat exchangers, Stress, compressive, in heat exchanger tubes, Stress corrosion cracking, of stainless steels, Stress equation models, for turbulent boundary layers, Stress-strain curve, for solids, Stress tensor: Stresses: Strip baffles, in tube bundles with longitudinal flow, Strouhal number, Subchannel analysis, for critical heat flux in rod bundles, Subcooled boiling: Subcooling: Sublayer, viscous, Submerged combustion, Successive over-under relaxation method for solution of implicit equations, Suction: Suction line exchangers in refrigeration, Sulfur: Sulfur compounds (organic): Sulfur dioxide: Sulfur hexafluoride: Sulfur trioxide: Supercritical fluids: Superficial velocity, in multiphase flow, Superheated gases: Superheated liquid, in metastable state, Superheated vapor, condensation of, on vertical surface, Supersaturation, as cause of fogging in condensers: Suppression of nucleate boiling, Surface catalysis, in augmentation of heat transfer, Surface condensers, Surface finish: Surface, hydraulically smooth, Surface material, effect on fouling, Surface models, in radiative heat transfer, Surface modification for drag reduction, Surface temperature, effect on fouling, Surface tension: Surfactants, in drag reduction, Suspension, radiation interaction phenomena in, Sutherland formula, for viscosity variation with temperature, Sutterby fluid (non-Newtonian), free convective heat transfer to, Swirling flow, in augmentation of heat transfer, Synthetic heat transfer media, Synthetic mixture heat transfer media,
T U V W X Y Z

Impinging Jets

DOI 10.1615/hedhme.a.000173

2.5.6 Impinging Jets

A. Introduction

Heating or cooling of large-surface-area products is often carried out by means of arrays of round or slot nozzles. A fluid (typically, air) impinges upon the product surface. Impinging flow devices allow short flow paths to the surface small boundary layers and, therefore, relatively high heat and mass transfer rates. For these reasons impinging jets are used in the fields of paper drying, the drying of functional films, thin film coating applications (such as optical foils), battery electrodes, and many other industrial applications. The fluid temperature, fluid flow rate, diameter (or slot width) of the impingement nozzles, distance to the surface, and spacing and alignment between the nozzles are the main variables, which can be adjusted for a given heat or mass transfer problem. As shown by Schrader (1961), Glaser (1962 and 1963), and other authors (Lohe, 1967; Petzold, 1968; Kumada and Mabuchi, 1970; Romanenko and Davidzon, 1970), the flow pattern of impinging jets from single round and slot nozzles can be subdivided into three characteristic regions: the free jet region, the stagnation flow region, and the region of lateral (or radial) flow outside the stagnation zone, also called the wall jet region after the basic theoretical work of Glauert (1956). The velocity field of an impinging jet is shown schematically in Figure 1. The free jet, at the exit of the nozzle, a, with diameter D or slot width B, in general will be turbulent (for typical industrial application conditions). By intensive exchanger of momentum with the surrounding gas over the free boundaries, b, the jet broadens linearly with its length, z', up to a limiting distance, zg, from the solid surface, c. The velocity profile, d, being nearly rectangular at the nozzle exit, spreads toward the free boundaries and, for sufficient length of the free jet, approaches a bell shape. Toward a substrate, stagnation flow begins relatively close to the surface [ according to Schrader (1961), limiting distance zg is about 1.2 times the nozzle diameter ]. Here, the vertical velocity component is decelerated and transformed into an accelerated horizontal one. Analytical solutions of the Navier–Stokes equations are known for the idealized limiting case of the infinitely extended plane and axisymmetric laminar stagnation flows [ see Schlichting (1958), pp. 76–81 ]. Because of the finite range of the jet and the exchange or momentum with its motionless surroundings, the accelerated stagnation flow finally must transform to a decelerated wall jet flow. Thus, the wall parallel velocity component wg (wr), initially increasing linearly from zero, must reach a maximum value at a certain distance xg (rg) from the stagnation point, and finally tends to zero with xn (rn) in the fully developed wall jet. Exponent n is about −0.5 for the plane (Glauert, 1956; Seban and Back, 1961; Schwartz and Cosart, 1961) and about −1 for the axisymmetric (Glauert, 1956; Seban and Back, 1961; Bakke, 1957) turbulent wall jet. While the stabilizing effect of acceleration keeps the boundary layer laminar in the stagnation zone, transition to turbulence generally will occur immediately after xg (or rg) in the decelerating flow region. The wall boundary layer and free jet boundary grow together, forming the typical wall jet profile where the boundary layer, σ, is defined as the locus of the maxima of the velocity [ z(wx,max) ] (see f in Figure 1). In principle, the impinging flow from arrays of nozzles shows the same three flow regions: free jet, stagnation zone, and wall jet. However, in addition to that, secondary stagnation zones occur where the wall jets of neighboring nozzles impinge upon each other. These secondary stagnation zones are characterized by boundary layer separation and eddying of the flow at the substrate position where the neighboring jets interact.

Figure 1 Velocity field of impinging flow

B. Local Heat and Mass Transfer Coefficients

(a) Single Round Nozzles (SRNs) and Single Slot Nozzles (SSNs)

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