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Extended surfaces
- 4. WHAT IS EXTENDED SURFACE-FINS? • In many engineering situation, means are often sought to improve heat dissipation from a surface to its surrounding
- 5. Whenever the available surface is found inadequate transfer the required quantity of heat with available temperature drop and convective heat transfer coefficient, extended surfaces or fins are used.
- 6. WORKING PRINCIPLE • In many engineering application, large quantities of heat have to be dissipated from small areas.
- 7. • The fins increases the effective area of the surface thereby increasing the heat transfer by convection.
- 8. • In other words, the shape of fins must be optimized such that the heat transfer density is maximized when the space and the materials used for the finned surfaces are constraints.
- 9. METHODS TO INCREASE HEAT TRANSFER RATE • By increasing the surface area in contact with air or providing fins. • By increasing the heat transfer coefficient for the surface.
- 10. • By increasing the temp of the hot surface or by increasing the temperature difference between hot and cold bodies
- 11. TYPES BY DESIGN • The fins are designed and manufactured in many shapes and forms. • They manufactured in different geometries, depending upon the practical applications.
- 12. • The ribs attached along the length of a tubes are called longitudinal fins. • The concentric annular disc around a tube are termed as circular or annular fins • Pin fins or spines are rods protrading from a surface.
- 13. TYPES OF FINS
- 14. ADVANTAGES • By using the fins, heat transfer rate can be increased without any preventive maintenance. It is the cheapest way for increasing the heat transferring rate from the hot bodies.
- 15. DISADVANTAGES • We know that the length of fins is directly proportional to the heat transferring rate. But the larger length is may be cause of bending in the fins and also increases the weight of engine. Therefore the overall efficiency will goes to decrease.
- 16. APPLICATIONS • Common applications of finned surfaces are with, • Cooling of electronics components • Condensers and economizers of thermal power plants
- 17. • Dry type cooling towers • Air cooled cylinders of compressors, IC engines • Evaporators and condensers of refrigeration and air conditioning system. • Electric motor and transformers
- 18. USES IN REAL LIFE
- 19. Straight Fins A straight fin is any extended surface that is attach to plane wall it may be uniform cross sectional area or its cross sectional area varies with the distance x from the wall
- 20. Annular Fins An annular fin is one that is circumferentially attached to the cylinder and its cross section varies with radius from the wall of the cylinder.
- 21. Trapazoidal Fins Heat transfer by convection between a surface and the fluid surrounding can be increased by attaching to the surface thin metallic strips.
- 22. GENERAL CONDUCTION ANALYSIS CONDUCTION THROUGH PIN EXTENDED SURFACES
- 23. qx = qx + dx + dqconv ----------- ---- (1) From Fourier Law qx = -kAc 𝑑𝑇 𝑑𝑥 qx + dx = qx + 𝑑qx 𝑑𝑥 dx qx + dx = kAc 𝑑𝑇 𝑑𝑥 - 𝑘 𝑑 𝑑𝑥 (Ac 𝑑𝑇 𝑑𝑥 ) dx
- 25. Putting values in --------------- (1) -kAc 𝑑𝑇 𝑑𝑥 = [-kAc 𝑑𝑇 𝑑𝑥 - 𝑘 𝑑 𝑑𝑥 (Ac 𝑑𝑇 𝑑𝑥 ) dx ] + hdAc (Ts – T∞) Rearranging the Equation kAc 𝑑𝑇 𝑑𝑥 - kAc 𝑑𝑇 𝑑𝑥 - 𝑘 𝑑 𝑑𝑥 (Ac 𝑑𝑇 𝑑𝑥 ) dx + hdAc (Ts – T∞) = 0 - 𝑘 𝑑 𝑑𝑥 (Ac 𝑑𝑇 𝑑𝑥 ) dx + hdAc (Ts – T∞) = 0
- 26. Dividingbothsidesby–k 𝑑 𝑑𝑥 (Ac 𝑑𝑇 𝑑𝑥 )dx - ℎ𝑑 𝑘 Ac(Ts–T∞) = 0 d2 T/dx2 ( 1 𝐴𝑐 ℎ 𝑘 𝑑𝐴𝑐 𝑑𝑥 )(Ts–T∞) = 0 ThisisgeneralFormoftheEnergyequationfor anextendedsurfaceandFins
- 27. THANK YOU