Shell & tube heat exchangers are commonly used in process industries and power generation. They consist of a bundle of tubes contained within a cylindrical shell. Baffles inside the shell direct fluid flow and support the tubes. Key factors in design include tube layout, materials selection, baffle type, and fluid allocation between shellside and tubeside. Proper design considers factors like heat transfer rates, pressure drops, fouling resistance, size requirements, and cleaning needs.

1. SHELL & TUBEHEAT EXCHANGER DESIGN By Khairpur Group Waqas Ali Tunio (07ME34) (G.L) Khalil RazaBhatti (07ME40) (A.G.L) AyazAli Soomro (07ME31) Muhammad FarooquePirzado(07ME56) Zain-ul-AabideenQureshi (07ME57) Quaid-e-Awam University of Engineering, Science & Technology, Nawabshah - Pakistan HEAT and MASS TRANSFER

3. They are used in process industries, in conventional and nuclear power tations, steam generators, etc

4. They are used in many alternative energy applications including ocean, thermal and geothermal.

5. Shell & tube heat exchangers provide relatively large ratios of heat transfer area to volume.

8. Baffles used both to support the tubes and to direct into multiple cross flow

9. Gaps or clearances must be left between the baffle and the shell and between the tubes and the baffle to enable assemblyShell Tubes Baffle

10. Construction

11. TEMA Standard The design and construction is usually based on TEMA 9th Edition 2007 Supplements pressure vessel codes like ASME and BS 5500 Sets out constructional details, recommended tube sizes, allowable clearances, terminology etc. Provides basis for contracts Tends to be followed rigidly even when not strictly necessary Many users have their own additions to the standard which suppliers must follow

12. Shell & Tube Heat Exchangers Shell & tube type heat exchangers are built of tubes (round or rectangular in general) mounted in shells (cylindrical, rectangular or arbitrary shape). Many variations of this basic type is available. The differences lie mainly in the detailed features of construction and provisions for differential thermal expansion between the tubes and the shell.

13. Shell Types

14. Tube to Header Plate Connection Tubes are arranged in a bundle and held in place by header plate (tube sheet). The number of tubes that can be placed within a shell depends on Tube layout, tube outside diameter, pitch, number of passes and the shell diameter. When the tubes are to close to each other, the header plate becomes to weak. Methods of attaching tubes to the header plate

15. Baffle Type & Geometry Baffles serve two functions: Support the tubes for structural rigidity, preventing tube vibration and sagging Divert the flow across the bundle To obtain a higher heat transfer coefficient.

16. Segmental Cut BafflesBaffle Type & Geometry The single and double segmental baffles are most frequently used. They divert the flow most effectively across the tubes. The baffle spacing must be chosen with care. Optimal baffle spacing is somewhere between 40% - 60% of the shell diameter. Baffle cut of 25%-35% is usually recommended. The triple segmental baffles are used for low pressure applications.

17. Disc & Ring BafflesBaffle Type & Geometry Disc and ring baffles are composed of alternating outer rings and inner discs, which direct the flow radially across the tube field. The potential bundle-to-shell bypass stream is eliminated This baffle type is very effective in pressure drop to heat transfer conversion Disc

18. Orifice BaffleBaffle Type & Geometry In an orifice baffle shell-side-fluid flows through the clearance between tube outside diameter and baffle-hole diameter.

20. Available pressure drop.

21. The number of tubes is selected such that the

23. The lower velocity limit corresponds to limiting the fouling, and the upper velocity limit corresponds to limiting the rate of erosion.

25. Requirement for low cost, light weight, high conductivity, and good joining characteristics often leads to the selection of aluminum for the heat transfer surface.

26. On the other side, stainless steel is used for food processing or fluids that require corrosion resistance.

27. In general, one of the selection criteria for exchanger material depends on the corrosiveness of the working fluid.

30. From the heat transfer viewpoint, smaller-diameter tubes yield higher heat transfer coefficients and result in a more compact exchanger.

31. However, larger-diameter tubes are easier to clean and more rugged.

32. The foregoing common sizes represent a compromise.++ For mechanical cleaning, the smallest practical size is 19.05 mm. ++ For chemical cleaning, smaller sizes can be used provided that the tubes never plug completely.

33. Tube Layout pitch Rotated square 45o Triangular 30o Rotated triangular 60o Square 90o

35. Two standard types of tube layouts are the square and the equilateral triangle.

36. • Triangular pitch (30o layout) is better for heat transfer and surface area per unit length (greatest tube density.)

37. Square pitch (45 & 90 layouts) is needed for mechanical cleaning.

38. Note that the 30°,45° and 60° are staggered, and 90° is in line.

40. The square pitch (90° or 45°) is used when jet or mechanical cleaning is necessary on the shell side. In that case, a minimum cleaning lane of ¼ in. (6.35 mm) is provided.

41. The square pitch is generally not used in the fixed header sheet design because cleaning is not feasible.

42. The triangular pitch provides a more compact arrangement, usually resulting in smaller shell, and the strongest header sheet for a specified shell-side flow area.

44. Fouling Shell and tubes can handle fouling but it can be reduced by keeping velocities sufficiently high to avoid deposits avoiding stagnant regions where dirt will collect avoiding hot spots where coking or scaling might occur avoiding cold spots where liquids might freeze or where corrosive products may condense for gases High fouling resistances are a self-fulfilling prophecy

45. Size of Heat Exchanger The initial size (surface area) of a heat exchanger can be estimated from

49. JazakALLAH-o-Khaira