美国麻省理工大学：《Thermal Energy》（热能） 10 part3

PaRT 3 INTRODUCTION TO ENGINEERING HEAT TRANSFER

PART 3 INTRODUCTION TO ENGINEERING HEAT TRANSFER

Introduction to Engineering Heat Transfer These notes provide an introduction to engineering heat transfer. Heat transfer processes set limits to the performance of aerospace components and systems and the subject is one of an enormous range of application. The notes are intended to describe the three types of heat transfer and provide basic tools to enable the readers to estimate the magnitude of heat transfer rates in realistic aerospace applications. There are also a number of excellent texts on the subject; some accessible references which expand the discussion in the notes are listen in the bibliography HT-1

HT-1 Introduction to Engineering Heat Transfer These notes provide an introduction to engineering heat transfer. Heat transfer processes set limits to the performance of aerospace components and systems and the subject is one of an enormous range of application. The notes are intended to describe the three types of heat transfer and provide basic tools to enable the readers to estimate the magnitude of heat transfer rates in realistic aerospace applications. There are also a number of excellent texts on the subject; some accessible references which expand the discussion in the notes are listen in the bibliography

Table of tables Table2.l: Thermal conductivity at room temperature for some metals and non- metals…………….HT-7 Table 2. 2: Utility of plane slab approximation HT-17 Table 9.1: Total emittances for different surfaces [from: A Heat Transfer Textbook, J Lienhard HT-63

HT-2 Table of Tables Table 2.1: Thermal conductivity at room temperature for some metals and non-metals............. HT-7 Table 2.2: Utility of plane slab approximation..........................................................................HT-17 Table 9.1: Total emittances for different surfaces [from: A Heat Transfer Textbook, J. Lienhard ]HT-63

Table of Figures Figure 1.1: Conduction heat transfer HT-5 igure2.l: Heat transfer along a bar…… Figure 2. 2: One-dimensional heat conduction HT-8 Figure 2.3: Temperature boundary conditions for a slab HT-9 Figure 2. 4: Temperature distribution through a slab HT-10 igure 2.5: Heat transfer across a composite slab(series thermal resistance).........HT-11 Figure 2.6: Heat transfer for a wall with dissimilar materials(Parallel thermal resistance).HT-12 Figure 2.7: Heat transfer through an insulated wall HT-11 Figure 2. 8: Temperature distribution through an insulated wall HT-13 Figure 2.9: Cylindrical shell geometry notation HT-14 Figure 2.10: Spherical shell Figure 3. 1: Turbine blade heat transfer configuration HT-18 Figure 3. 2: Temperature and velocity distributions near a surface HT-19 Figure 3.3: Velocity profile near a surface HT-20 Figure 3.4: Momentum and energy exchange in turbulent flow HT-20 Figure 3.5: Heat exchanger configurations HT-23 Figure 3.6: Wall with convective heat transfer HT-25 Figure 3.7: Cylinder in a flowing fluid HT-26 Figure 3. 8: Critical radius of insulation Figure 3.9: Effect of the Biot Number [hL /body] on the temperature distributions in the solid and the fluid for convective cooling of a body. Note that kody is the thermal conductivity of the body, not of the fluid.... HT-31 Figure 3. 10: Temperature distribution in a convectively cooled cylinder for different values of Biot number, Bi; r2/r,=2 [from: A Heat Transfer Textbook, John H. Lienhard] HT-32 Figure 4.1: Slab with heat sources(a)overall configuration, (b)elementary slice HT-32 Figure4.2: Temperature distribution for slab with distributed heat sources……….…HT-34 Figure 5. 1: Geometry of heat transfer fin HT-35 Figure 5.2: Element of fin showing heat transfer....... Figure 5.3: The temperature distribution, tip temperature, and heat flux in a straight one- dimensional fin with the tip insulated. [From: Lienhard, A Heat Transfer Textbook, Prentice- Hall publishers........ HT-40 Figure 6. 1: Temperature variation in an object cooled by a flowing fluid HT-41 Figure 6.2: Voltage change in an R-C circuit HT-42 Figure 8. 1: Concentric tube heat exchangers.(a)Parallel flow(b)Counterflow Figure 8.2: Cross-flow heat exchangers. (a) Finned with both fluids unmixed. (b) Unfinned with one fluid mixed and the other unmixed HT-45 Figure8.3: Geometry for heat transfer between two fluids HT-45 Figure 8.4: Counterflow heat exchanger Figure 8.5: Fluid temperature distribution along the tube with uniform wall temperature .....HT-46 Figure 9. 1: Radiation Surface Properties IT-52 Figure 9.2: Emissive power of a black body at several temperatures-predicted and observed. HT-53 Figure 9.3: A cavity with a small hole(approximates a black body) Figure 9.4: A small black body inside a cavity .HT-54 Figure 9.5: Path of a photon between two gray surfaces HT-55

HT-3 Table of Figures Figure 1.1: Conduction heat transfer ......................................................................................... HT-5 Figure 2.1: Heat transfer along a bar ......................................................................................... HT-6 Figure 2.2: One-dimensional heat conduction ........................................................................... HT-8 Figure 2.3: Temperature boundary conditions for a slab............................................................ HT-9 Figure 2.4: Temperature distribution through a slab .................................................................HT-10 Figure 2.5: Heat transfer across a composite slab (series thermal resistance)............................HT-11 Figure 2.6: Heat transfer for a wall with dissimilar materials (Parallel thermal resistance)........HT-12 Figure 2.7: Heat transfer through an insulated wall ..................................................................HT-11 Figure 2.8: Temperature distribution through an insulated wall................................................HT-13 Figure 2.9: Cylindrical shell geometry notation........................................................................HT-14 Figure 2.10: Spherical shell......................................................................................................HT-17 Figure 3.1: Turbine blade heat transfer configuration ...............................................................HT-18 Figure 3.2: Temperature and velocity distributions near a surface. ...........................................HT-19 Figure 3.3: Velocity profile near a surface................................................................................HT-20 Figure 3.4: Momentum and energy exchange in turbulent flow. ...............................................HT-20 Figure 3.5: Heat exchanger configurations...............................................................................HT-23 Figure 3.6: Wall with convective heat transfer .........................................................................HT-25 Figure 3.7: Cylinder in a flowing fluid .....................................................................................HT-26 Figure 3.8: Critical radius of insulation ....................................................................................HT-29 Figure 3.9: Effect of the Biot Number [hL / kbody] on the temperature distributions in the solid and in the fluid for convective cooling of a body. Note that kbody is the thermal conductivity of the body, not of the fluid.........................................................................................................HT-31 Figure 3.10: Temperature distribution in a convectively cooled cylinder for different values of Biot number, Bi; r2 / r1 = 2 [from: A Heat Transfer Textbook, John H. Lienhard] .....................HT-32 Figure 4.1: Slab with heat sources (a) overall configuration, (b) elementary slice.....................HT-32 Figure 4.2: Temperature distribution for slab with distributed heat sources..............................HT-34 Figure 5.1: Geometry of heat transfer fin .................................................................................HT-35 Figure 5.2: Element of fin showing heat transfer......................................................................HT-36 Figure 5.3: The temperature distribution, tip temperature, and heat flux in a straight one￾dimensional fin with the tip insulated. [From: Lienhard, A Heat Transfer Textbook, Prentice￾Hall publishers].................................................................................................................HT-40 Figure 6.1: Temperature variation in an object cooled by a flowing fluid .................................HT-41 Figure 6.2: Voltage change in an R-C circuit............................................................................HT-42 Figure 8.1: Concentric tube heat exchangers. (a) Parallel flow. (b) Counterflow.......................HT-44 Figure 8.2: Cross-flow heat exchangers. (a) Finned with both fluids unmixed. (b) Unfinned with one fluid mixed and the other unmixed ....................................................................................HT-45 Figure 8.3: Geometry for heat transfer between two fluids.......................................................HT-45 Figure 8.4: Counterflow heat exchanger...................................................................................HT-46 Figure 8.5: Fluid temperature distribution along the tube with uniform wall temperature .........HT-46 Figure 9.1: Radiation Surface Properties..................................................................................HT-52 Figure 9.2: Emissive power of a black body at several temperatures - predicted and observed..HT-53 Figure 9.3: A cavity with a small hole (approximates a black body).........................................HT-54 Figure 9.4: A small black body inside a cavity .........................................................................HT-54 Figure 9.5: Path of a photon between two gray surfaces...........................................................HT-55

Figure 9.6: Thermocouple used to measure temperature IT-59 Figure 9.7: Effect of radiation heat transfer on measured temperature HT-59 Figure 9.8: Shielding a thermocouple to reduce radiation heat transfer error Figure 9.9: Radiation between two bodies HT-60 Figure 9.10: Radiation between two arbitrary surfaces HT-61 Figure9.11: Radiation heat transfer for concentric cylinders or spheres HT-6 Figure 9.12: View Factors for Three-Dimensional Geometries [from: Fundamentals of heat Transfer, F P. Incropera and D P. DeWitt, John Wiley and Sons] HT-64 Figure 9.13: Fig 13.4--View factor for aligned parallel rectangles [from: Fundamentals of heat Transfer, F P Incropera and D P. DeWitt, John Wiley and Sons .HT-65 Figure 9.14: Fig 13.5--View factor for coaxial parallel disk [from Fundamentals of Heat Transfer F P Incropera and D P. De Witt, John Wiley and Sons HT-65 Figure 9.15: Fig 13.6--View factor for perpendicular rectangles with a common edg HT-66

HT-4 Figure 9.6: Thermocouple used to measure temperature...........................................................HT-59 Figure 9.7: Effect of radiation heat transfer on measured temperature. .....................................HT-59 Figure 9.8: Shielding a thermocouple to reduce radiation heat transfer error ............................HT-60 Figure 9.9: Radiation between two bodies................................................................................HT-60 Figure 9.10: Radiation between two arbitrary surfaces.............................................................HT-61 Figure 9.11: Radiation heat transfer for concentric cylinders or spheres...................................HT-62 Figure 9.12: View Factors for Three - Dimensional Geometries [from: Fundamentals of Heat Transfer, F.P. Incropera and D.P. DeWitt, John Wiley and Sons]......................................HT-64 Figure 9.13: Fig. 13.4--View factor for aligned parallel rectangles [from: Fundamentals of Heat Transfer, F.P. Incropera and D.P. DeWitt, John Wiley and Sons]......................................HT-65 Figure 9.14: Fig 13.5--View factor for coaxial parallel disk [from: Fundamentals of Heat Transfer, F.P. Incropera and D.P. DeWitt, John Wiley and Sons].....................................................HT-65 Figure 9.15: Fig 13.6--View factor for perpendicular rectangles with a common edge .............HT-66