Document JNXMKMwpOORqLbJ5k3GZXLkeK

88 CHAPTER 4 1955 Guide * Fluid Meiers, Their Theory and Application (American Society of Mechanical Engineers, 4th Edition, 1937). 1 Flow Measurement, Power Test Codes, Part 5, Chap. 4 (American Society of Me- chanical Engineers, 1949) . J 4 Standards for Discharge Measurement {National Advisory Committee for Aero- i nautics, NACA Tech. Mem. 952, 1940) (Translation of German Industrial Standard 1932). , * Gas Measurement Committee Report No. 2, Natural Gas Department (Amer ican Gas Association, 1948). , 6 The Flow Mechanism and Performance of the Rotameter, by E. M. Schoenborn, Jr. and A. P. Colburn (Institute of Chemical Engineers, Transactions, 35, 1939, 359- 381). CHAPTER 5 HEAT TRANSFER Conduction, Convection, Radiation; Equations for Conduction, Convection, Radi ation and Combined Convection and Radiation; Heat-Flow Resistance, in Series and Parallel; Practical Heat Transfer Problems; Periodic and Transient Heat Flow BIBLIOGRAPHY EAT is the form of energy that is transferred by virtue of an existing temperature difference. The temperature difference is the potential HYf. - [A] Thermodynamics, by EdwaTd F. Obert (McGraw-Hill Book Company, 1948). which causes the transfer, the latter in turn being resisted by the thermal K, [B] Thermodynamics of Fluid Flow, by Newman A. Hall (Prentice-Hall, Inc., properties of the material combined in a single term known as the resist i) 1951). [C] Fluid Mechanics, by Russell A. Dodge and Milton J. Thompson (McGraw- Hill Book Co., 1937). [D] Fluid Mechanics, by R. C. Binder (Prentice-Hall, Inc., 2nd Edition, 1949). ance. Energy exchange associated with evaporation, condensation, etc., is treated elsewhere such as in the section on cooling lower design in Chapter 35. The objectives of this chapter are to: i* [E] The Physics of Solids and Fluids, by P. P. Ewald, H. Poschl and L. Prandtl 1. Describe the mechanisms and present the rate equations for the different modes (Blackie, 1936). of heat transfer. [F] A Study of the Data on the Flow of Fluids in Pipes, by Emory Kemler, Hy- Idraulic Paper HYD-55-2 (A.S.M.E. Transactions 65, No. 10, 7-22, 1933; Discussion, idem., 55, No. 10, 23-32, 1933). 2. Illustrate the application of the basic concepts to steady-state problems (tem perature independent of time or a cyclic variable thereof) by means of several typical solutions of heat transfer systems. [G] The Flow of Fluids in Closed Conduits, by R. J. S. Pigott (Mechanical Engi neering 55, 1933, 497-501, 515). 3. Present concise summaries of available methods of analysis for transient and periodic heat transfer problems. [H] Fluid Meters, Their Selection and Installation (American Society of Mechanical Engineers, 1933). [H The Orifice Meter for Measurement of Flow of Gases and Liquids, by Allen D. Further applications to specific systems will be found throughout The Guide. MacLean (Pittsburgh Equitable Meter Co., 1938). [J] Pitot Tube Practice, by Edward S. Cole (A.S.M.E. Transactions 57, 1935, 281- CONDUCTION, CONVECTION AND RADIATION 294; Discussion, idem. 58, 1936, 146-156). [K] Pitot Tubes in Large Pipes, by Edward S. Cole and E. Shaw Cole (A.S.M.E. Transactions, 61,1939, 465-473; Discussion, idem. 61, 1939, 473-475). j 1.1 Investigation of Errors of Pitot Tubes, by C. W. Hubbard (A .S.M.E. Trans actions, 61, 477-497; Discussion, idem. 61, 1939, 497-506). \MJ Piping Arrangements for Acceptable Flowmeter Accuracy, by R. E. Sprenkle Thermal conduction is the term applied to the mechanism of heat trans fer whereby the molecules of higher kinetic energy transmit part of their energy to adjacent molecules of lower kinetic energy by direct molecular action. Since the temperature is proportional to the average kinetic energy of the molecules, thermal transfer will occur in the direction of ! ':t (A.S.M.E. Transactions, 67, 345-357, 1945; Discussion, idem. 67, 357-360, 1945). decreasing temperature. The motion of the molecules is random-, there is no net material flow associated with the conduction mechanism. In the case of flowing fluids, thermal conduction is significant in the region very close to a solid boundary or wall, for in this region the flow is laminar, parallel with the wall surface, and there are practically no cross currents in the direction of the heat transfer across the solid fluid boundary. In solid bodies the significant mechanism of heat transfer is always thermal conduction. Contrasted to the thermal conduction mechanism, thermal convection involves energy transfer by eddy mixing and diffusion1 in addition to conduction. This is shown schematically in Fig. 1 which exhibits transfer from a pipe wall at surface temperature U to a colder fluid at a bulk tem perature L. (Bulk temperature is that which would be attained if the fluid stream were drawn off at a certain section and mixed. It is therefore somewhat higher than the lowest temperature in the stream.) In the laminar sublayer, immediately adjacent to the wall, the heat transfer occurs by thermal conduction; in the transition region, which is called fhe buffer layer, eddy mixing as well as conduction effects are significant; 89