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PLATE HEAT EXCHANGER

PLATE HEAT EXCHANGER

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PLATE HEAT EXCHANGER

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  1. PLATE HEAT EXCHANGER engineering-resource.com

  2. GROUP MEMBERS • Nadeem Akhtar (2006-chem-22) • Matloob Ahmed (2006-chem-26) • Zohaib Atiq Khan (2006-chem-40) engineering-resource.com

  3. Introduction to PHE • Second abundantly used HEX after STHE. • Fall in the category of compact heat exchangers. • Mostly used in food industry like milk, beverages and juices industry. • Is usually comprised of a stack of corrugated or embossed metal plates in mutual contact. engineering-resource.com

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  6. Facts and figures on Plate Heat Exchanger engineering-resource.com

  7. 1-Size range for unit and plates • For unit engineering-resource.com

  8. 1-Size range for unit and plates (b) For plates engineering-resource.com

  9. 2-Standrad performance limits engineering-resource.com

  10. 2-Standrad performance limits engineering-resource.com

  11. Mechanical parts of PHE • Plates (provide heat transfer area) • Gasket (prevents leakage of fluids). • Frame (for enclosure, on front). • Pressure plate (to press the plates on rare side). • Support column (to support the exchanger). • Splitter (plate dividing the PHE in parts in case of multi-streaming) • Tightening bolts engineering-resource.com

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  13. Multi streaming using splitter plate engineering-resource.com

  14. Material of construction (1) Plates As plates are very thin (0.5 – 1.2mm) So we can not compromise on material of construction plates are usually made of very strong materials, depending on operatin conditions (a) stainless steel AISI 304 (b) stainless steel AISI 316 (c) Hastelloy B (d) Hastelloy c-276 (e) alluminium brass 76/22/2 (f) incoloy 825 engineering-resource.com

  15. Material of construction (2) Gaskets engineering-resource.com

  16. Classification of PHES Plate heat exchangers can be classified based on • Joints • Plate corrugations. • Flow arrangements. engineering-resource.com

  17. Classification of PHES • Based on joints PHES are classified in to three types • Gasketted. • Brazed. • Welded. engineering-resource.com

  18. Classification of PHES (1) gasketted. engineering-resource.com

  19. Classification of PHES (2) brazed. engineering-resource.com

  20. Classification of PHES (3) Welded plate. engineering-resource.com

  21. Classification of PHES Based on corrugation two types of PHES exist (a) Wash board. (b) Chevron. engineering-resource.com

  22. Classification of PHES Based on flow arrangement • Series flow • U-arrangement engineering-resource.com

  23. Advantages of PHE • A PHE offers very high heat transfer coefficient. Increase in H.T coefficient is three to five times. • Is suitable even for a close approach temperature as low as 2 oC, and for a large temperature cross. • Offers ease of inspection, cleaning and maintenace. • Heat transfer area can be increased or decreased by adding or removing some plates. • Conveniently performs multiple heat exchange duties in a single exchanger. • Requires much less floor soace. • Costs less than shell and tube heat exchanger especially when expensive material of construction is used. engineering-resource.com

  24. Disadvantages • Effect of fouling because of scaling, deposition of solids by crystallization, corrosion, and even by biological materials is quite significant in PHES • Large over design is required. For example in an STHEX for a fouling resistance of 1.76*10-4 will increase the required surface area by 35% in case of STHEX but will increase the required surface area of a PHE by about 100%. • The allowable fouling resistance in PHE is one tenth of that in STHEX. engineering-resource.com

  25. Applications • Dairy industry • Pharmaceuticals • Food processing • Petroleum and chemical industries • Pulp and paper industry • Power generation • Reboiling or condensing services engineering-resource.com

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  27. Applications for which PHES are not recommended • Gas-to-gas applications • Fluids with very high viscosities may pose to distribution problems, flow velocities less than 0.1m/s are not used because of low H.T coefficient. • Less suitable for vapours condensing under vacuum engineering-resource.com

  28. Design of Plate Heat Exchanger engineering-resource.com

  29. Thermal Design Steps Step # 1 • Calculate properties of fluids i.e density, viscosity, thermal conductivity, specific heat • Also determine fluids unknown inlet and outlet temperatures and flow rates engineering-resource.com

  30. Step # 2 • Calculate heat duty, the rate of heat transfer required Qc = (mcp)c (t2-t1) Qh = (mcp)h (T2-T1) engineering-resource.com

  31. Step # 3 • Calculate the log mean temperature difference, LMTD LMTD = (T1-t2) – (T2-t1) ln(T1-t2)/(T2-t1) engineering-resource.com

  32. Determine the log mean temperature correction factor, Ft NTU = ( To- Ti ) LMTD Where Ti = stream inlet temperature °C To = stream outlet temperature °C LMTD = log mean temperature difference °C Step # 4 engineering-resource.com

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  34. Step # 5 • Calculate the corrected mean temperature difference ∆Tm= Ftx LMTD engineering-resource.com

  35. Step # 6 • Select specific construction of the plates suitable for the required service like • Plate material • Port diameter • Gasket material engineering-resource.com

  36. Step # 6 cont’d • Corrugation type Washboard pattern Chevron pattern engineering-resource.com

  37. Step # 6 cont’d • Effective length • Width • Plate pitch engineering-resource.com

  38. Step # 7 • Estimate the overall heat transfer coefficient engineering-resource.com

  39. Step # 8 • Calculate the surface area required Q = UA (Ft x LMTD ) A = Q U (Ft x LMTD ) engineering-resource.com

  40. Step # 9 • Determine the number of plates required • Number of plates = Total surface area Area of one plate engineering-resource.com

  41. Area of one plate • A = (L – D) x W engineering-resource.com

  42. Step # 10 • Decide the flow arrangement and number of passes engineering-resource.com

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  44. Step # 11 • Calculate the film heat transfer coefficients for each stream Nu = C Ren Prm (µ/µw)x Typical reported values are C = 0.15-0.40 n = 0.65-0.85 m = 0.30-0.45 (usually 0.333) x = 0.05-0.20 engineering-resource.com

  45. Step # 11 continued • Most popular correlation for preliminary estimate of area is (hde/kf) = 0.26 Re0.65 Pr0.4 (µ/µw)0.14 • Also we can use general relation (hde/kf) = Ch Ren Pr1/3 (µ/µw)0.17 engineering-resource.com

  46. Ch & n values engineering-resource.com

  47. Step # 12 • Calculate the overall coefficient, allowing for fouling factors 1 = 1 + 1 + t + Rfh + Rfc Ud hh hc kw engineering-resource.com

  48. Step # 13 • Compare the calculated with the assumed overall coefficient. • If satisfactory, say - 0% to + 10% error, proceed. If unsatisfactory return to step 7 and estimate another value of overall heat transfer coefficient U engineering-resource.com

  49. Hydraulic Design Pressure Drop Calculations engineering-resource.com

  50. Step # 14 • Check the pressure drop for each stream • Channel pressure drop ∆Pc = 8 f Lpρup2 de 2 f = 0.6 Re-0.3 engineering-resource.com