fundementals of heat and mass transfer kotandaraman (3rd edition): part 2
➤ Gửi thông báo lỗi ⚠️ Báo cáo tài liệu vi phạmNội dung chi tiết: fundementals of heat and mass transfer kotandaraman (3rd edition): part 2
fundementals of heat and mass transfer kotandaraman (3rd edition): part 2
8CONVECTIVE HEAT TRANSFERPractical Correlations - Flow Over Surfaces8INTRODUCTIONIn chapter 7 the basics of convection was discussed and the methods o fundementals of heat and mass transfer kotandaraman (3rd edition): part 2 of analysis were enumerated, correlations wore obtained for laminar flow over flat plate at uniform temperature. starting from laisic principles mid using t he concept ofboundiiry layer. The application of these correlations are limited. However these equations provide a method of correlation of exp fundementals of heat and mass transfer kotandaraman (3rd edition): part 2 erimental results and extension of these equations to practical situations of more complex nature. Though the basic dimensionless numliers used remainfundementals of heat and mass transfer kotandaraman (3rd edition): part 2
the same, the constants and power indices are found to vary with ranges of these parameters and geometries. In tills chapter it is proposed to list t8CONVECTIVE HEAT TRANSFERPractical Correlations - Flow Over Surfaces8INTRODUCTIONIn chapter 7 the basics of convection was discussed and the methods o fundementals of heat and mass transfer kotandaraman (3rd edition): part 2 er surfaces like flat plates, cylinders,, spheres and tube banks arc concerned.8.1 FLOW OVER FLAT PLATESEquations for heat, t ransfer in laminar How over Hat plate were derived from basics in Chapter 7. In tills chapter additional practical correlations arc introduced. Though several types of bounda fundementals of heat and mass transfer kotandaraman (3rd edition): part 2 ry conditions may exist, these can be approximated to three basic types. These are (i) constant wall temperature, (as may be obtained in evaporation,fundementals of heat and mass transfer kotandaraman (3rd edition): part 2
condensation etc., phase change at a specified pressure) (ii) constant heat flux, as may be obtained by electrical strip type of heating and (iii) flo8CONVECTIVE HEAT TRANSFERPractical Correlations - Flow Over Surfaces8INTRODUCTIONIn chapter 7 the basics of convection was discussed and the methods o fundementals of heat and mass transfer kotandaraman (3rd edition): part 2 able for constant wall temperature and constant heat flux. But for the third case it may bo necessary to approximate to one of the above two cases.8.1.1. Laminar flow: The condition is that the Reynolds number should be less than 5 X 105 or as may be stated otherwise. For the condition that the plat fundementals of heat and mass transfer kotandaraman (3rd edition): part 2 e temperature is constant the following equations are valid with fluid property values taken at the film temperature.Hydrodynamic boundary layer thickfundementals of heat and mass transfer kotandaraman (3rd edition): part 2
ness (from Chapter 7)0T = 5.v/J?ex° 5...(8.1)Thermal boundary layer thickness5u = 5xPr0SSS...(8.2)Displacement thickness and Momentum thickness are no8CONVECTIVE HEAT TRANSFERPractical Correlations - Flow Over Surfaces8INTRODUCTIONIn chapter 7 the basics of convection was discussed and the methods o fundementals of heat and mass transfer kotandaraman (3rd edition): part 2 ORRELATIONS-FLOW OVER SURFACES335Displacement thickness is the difference between the boundary layer thickness and the thickness with uniform velocity equal to free stream velocity in which the flow will be the same as in the boundary layer. For laminar How displacement thicknessJ’O Iu I1 —— dy 0 I0 fundementals of heat and mass transfer kotandaraman (3rd edition): part 2 ^8/3...(8.3)Momentum thickness is the difference between the boundary layer thickness and the layer thickness which at the free stream velocity will hfundementals of heat and mass transfer kotandaraman (3rd edition): part 2
ave the same momentum as in the boundary layer.Momentum thickness Sm in the laminar region is defined bydy- Ụ7...(8.4)Friction coefficient defined as 8CONVECTIVE HEAT TRANSFERPractical Correlations - Flow Over Surfaces8INTRODUCTIONIn chapter 7 the basics of convection was discussed and the methods o fundementals of heat and mass transfer kotandaraman (3rd edition): part 2 .328 7?<’£ 0 5...(8.6)The value of local Nussell number is given by (Chapter- 7)A’«, - 0.332 Ke/-51 >r*> 55...(8.7)■V u,. - 2NuL - 0.664 Ke/5 Kr1'3...(8.7 (a))This IS valid for 1’raudll number range of 0.6 to 30.For low values of Prandtl numbers as in the case of liquid metals, the local Nusselt num fundementals of heat and mass transfer kotandaraman (3rd edition): part 2 ber isNug - 0.565 (1ĩfir Pr)ữ-'ữ...(8.8)This is valid for Prandtl number less than 0.05 (liquid metals) A more general expression applicable for bothfundementals of heat and mass transfer kotandaraman (3rd edition): part 2
low and high values of Prandtl number is given by8CONVECTIVE HEAT TRANSFERPractical Correlations - Flow Over Surfaces8INTRODUCTIONIn chapter 7 the basics of convection was discussed and the methods o8CONVECTIVE HEAT TRANSFERPractical Correlations - Flow Over Surfaces8INTRODUCTIONIn chapter 7 the basics of convection was discussed and the methods oGọi ngay
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