Heat Convection : Cylinder in Cross Flow

1. Heat Convection : Cylinder in Cross Flow P M V Subbarao Associate Professor Mechanical Engineering Department IIT Delhi A Common Industrial Application ……

2. Tube Consumption in Power Plant Heat Exchangers in US (1000 of Feet)

3. Shell And Tube Heat Exchanger A Shell and tube heat exchanger is a class of heat exchanger designs. It is the most common type of heat exchanger in power plants, oil refineries and other large chemical processes. As its name implies, this type of heat exchanger consists of a shell (a large vessel) with a bundle of tubes inside it.

4. Shell & Tube Heat Exchanger

5. Convection heat transfer with banks of tubes : Shell Side • Typically, one fluid moves over the tubes, while a second fluid at a different temperature passes through the tubes. (cross flow) • The tube rows of a bank are staggered or aligned. The configuration is characterized by the tube diameter D, the transverse pitch ST and longitudinal pitch SL.

6. Internal or External Flow !?!?! Inline Arrangement Zig-Zag Arrangement Square Pitch Triangular Pitch

7. Array of Cylinders in Cross Flow : Hydraulic Diameter • The equivalent diameter is calculated as four times the net flow area as layout on the tube bank (for any pitch layout) divided by the wetted perimeter.

8. Hydraulic Diameter : Square Pitch do PT PT

9. For square pitch: For triangular pitch:

10. the tube clearance C is expressed as: Then the shell-side mass velocity is found with Shell side Reynolds Number:

11. For tube bundles composed of 10 or more rows

12. All properties are evaluated at the film temperature.

13. For Reynolds number or If staggered and

14. If number of tubes are less than 10, a correction factor is applied as: And values for C2 are from table

15. More recent results have been obtained by Zhukauskas. All properties except Prs are evaluated at the arithmetic mean of the fluid inlet and outlet temperatures. Values for C and m.

17. Thermal resistance of an Infinitesimal adiabatic Heat Exchanger Thermal Resistance of infinitesimal Heat Exchanger

18. CONVECTION IN INTERNAL FLOWS P M V Subbarao Associate Professor Mechanical Engineering Department IIT Delhi An Essential Part of Exchanging Heat……..

19. Development of Flow

20. Hydrodynamic Vs Thermal Development of FLow • There are several fundamental problems in laminar internal flow that can be considered. • The following problems arise as a result of considering the thermal entrance length in proportion to the hydrodynamic entrance length: • L >> Lh, L >> Lt, i.e. thermally and hydrodynamically fully developed flow. • This rarely occurs in practice, but it affords many theoretical solutions. • L >> Lh, L << Lt, i.e. hydrodynamically fully developed, but thermally developing flow, sometimes called the thermal entrance problem. • This type of flow is characteristic of high Prandtl number fluids Pr >> 1, e.g. oils. • L << Lh, L << Lt, i.e. hydrodynamically and thermally developing flow, sometimes called the combined entrance problem • L << Lh, L >> Lt, i.e. hydrodynamically developing flow and thermally fully developed. • This type of flow occurs with low Prandtl number fluids Pr << 1, e.g. liquid metals.

21. Nature of Convection • In general, heat transfer is always higher in developing flows, since the thermal resistance of the boundary layer is lower. • In the thermal entrance region, heat is being transferred from a warmer wall temperature (in the case of heating) to the lowest temperature which is the inlet fluid temperature. • However, when the thermal boundary layers merge, there ceases to be a constant sink temperature and the bulk fluid temperature rises quickly. • The local heat transfer rate is: