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Development of an Analytical Code for Simulation and Design of Spiral Wound Heat Exchanger in Cryogenic Applications

Mostafazadeh Abolmaali, Ali | 2022

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 54911 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Afshin, Hossein
  7. Abstract:
  8. This research aims to develop a numerical tool for design and performance evaluation of spiral wound heat exchanger (SWHE) in the cryogenic temperature range. This type of heat exchangers are used in gas liquefaction cycles due to their compact structure and ability to achieve high effectiveness values. High sensitivity of liquefaction cycles yield to heat exchanger effectiveness, effect of some physical phenomena in cryogenic temperature range, and complicated shell-side flow structure of SWHEs, turns the design and performance evaluation of cryogenic SWHEs into a challenging issue. Consequently, first of all, the geometrical parameters of SWHE were introduced and made dimensionless. In this regard, main dimensionless parameters were recognized as start factor, number of tubes in the first layer, number of layers, longitudinal pitch to tube outside diameter ratio, and radial pitch to tube outside diameter ratio. Then, a 1D numerical code was developed which is able to evaluate the performance of counter-flow or parallel-flow heat exchangers taking into account the effects of variation of thermo-physical properties with temperature, heat transfer with surrounding environment, longitudinal heat conduction, and external heat sources. The 1D code performance has been verified through comparison with several analytical solutions that are available in the literature. Afterwards, an analytical sizing algorithm which finds the optimum geometrical parameters of SWHE considering given velocity, Reynolds number, and pressure drop limits was developed. Since Nusselt number and friction factor correlations for shell-side flow were required by performance evaluation and also sizing codes, 3D computational fluid dynamics (CFD) has been used to realize the mechanism of flow and heat transfer in the shell-side of SWHEs. To this end, two simulation scenarios were implemented. In the first scenario, the shell-side flow and also mechanism of heat transfer between shell-side fluid and helical tubes have been studied. Using multiple regression analysis, the Nusselt number and friction factor correlations were established based on the simulation results. In the second scenario, the mechanism of heat transfer between shell-side fluid and shell-wall have been investigated. On the basis of simulation results, the SWHE was divided into two regions known as entrance and fully developed regions and local Nusselt number correlations were established for both regions using multiple regression analysis. Finally, the sizing algorithm and performance evaluation algorithm are combined to form a design model which is able to design SWHE for gas liquefaction cycles. Then, the performance of design model is investigated by means of some examples. It is shown that the variation of thermo-physical properties with temperature and heat-in-leak have 20% and 15% impact on the SWHE performance, respectively. On the other hand, it is concluded that longitudinal heat conduction through tube walls and shell wall has negligible impact on the final results. Moreover, other input parameters of the design problem like the allowable pressure drop in the shell-side of SWHE play an important role in the design process so that decreasing the shell-side allowable pressure drop from 10 kPa to 2 kPa doubles the length of SWHE, approximately
  9. Keywords:
  10. Spiral-Wound Heat Exchanger ; Cryogenic ; Computational Fluid Dynamics (CFD) ; Property Variational ; Heat Leakage ; Longitudinal Heat Conduction

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