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Thermal and Fluid Study of the Effect of Fluid Flow Maldistribution in the Structure of Plate Fin Heat Exchanger

Sherafat, Mohammad | 2022

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 58096 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Afshin, Hossein
  7. Abstract:
  8. Plate-fin heat exchangers are mainly used in cryogenic air separation and liquefaction, liquefaction of natural gas, helium, nitrogen, ethylene, propane, propylene, etc., production of chemicals such as ethylene, and exhaust gas filtration. Cryogenic temperature conditions are required to liquefy gases like helium. Plate-fin heat exchangers need the efficiency of above 85% in cryogenic conditions, making their design and evaluation a highly complex and sensitive process. These designs have been associated with assumptions such as constant properties and uniform flow distribution. However, it has been realized that variable properties, header configuration, and flow distributor of a heat exchanger can significantly affect its performance. To this end, this study seeks to choose a header for a plate-fin heat exchanger based on velocity maldistribution (β ,SV) and temperature maldistribution (ΔT ,ST) parameters. Various headers were assessed, and it was found that the SV value for any type-C header was 0.106, which was 428.3% better than simple header. The maximum-to-minimum ratio (β) was 1.70, indicating a 369.4% improvement. Thus, type-C headers were the best choice. A particular flow distributor was evaluated at different angles to determine the optimal case. The best distribution was achieved at a 45-degree angle for both normal and cryogenic temperature ranges. For normal temperatures, the velocity distribution obtained by the 45-degree distributor was improved by 0.85 and 0.32% compared to 30 and 60-degree distributors, respectively. The 45-degree distributor also enhanced the temperature distribution by 4.9 and 9.4% and 60-degree distributors, respectively. For cryogenic temperatures, the velocity distribution of the 45-degree distributor was improved by 7.8 and 3.4% than that of 30 and 60-degree distributors. Using the 45-degree distributor, the temperature distribution was also enhanced by 1.07 and 9.1% compared to 30 and 60-degree distributors, respectively. It can be concluded that a type-C header with a 45-degree flow contributor offered the optimal flow distribution and the highest performance for a plate-fin heat exchanger
  9. Keywords:
  10. Cryogenic ; Plate Fin Heat Exchanger ; Variable Properties ; Temperature Maldistribution ; Velocity Maldistribution

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