The effects of geometry and adjacent regenerators on shell-and-tube heat exchangers in oscillating flows

Open Access
Author:
Brady, John Feurman
Graduate Program:
Acoustics
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
December 17, 2010
Committee Members:
  • Robert Mitchel Keolian, Dissertation Advisor
  • Robert Mitchel Keolian, Committee Chair
  • Horacio Perez Blanco, Committee Member
  • Victor Ward Sparrow, Committee Member
  • Thomas B Gabrielson, Committee Member
Keywords:
  • thermoacoustics
  • heat transfer
  • oscillating flow
  • acoustics
  • heat exchangers
Abstract:
An experimental study into the effects of geometry and the presence of adjacent screens on the acoustic impedances and heat transfer performance of shell-and-tube heat exchangers in oscillating flow was conducted. Measurements of linear and nonlinear acoustic impedances were conducted simultaneously with heat transfer measurements. The results showed that rounded tube-ends produce less nonlinear resistance than flat tube-ends. A stack of screens placed adjacent to an exchanger results in nonlinear resistances that are within 5% of those that result when no adjacent screens are used. The screens also act to reduce the drop in the inertance of the exchanger at higher displacements. The length of the exchanger was found to influence the amount of nonlinear acoustic resistance. Correlations for this effect were found, but the cause is unknown. Heat transfer measurements showed that the aspect ratio of the exchanger tubes (the ratio of length to diameter) is an important parameter in predicting heat transfer. The presence of adjacent screens increases this effect. Correlations including these effects were found. It was found that when screens were placed adjacent to an exchanger, the heat transfer effectiveness dropped by as much as 20%. Likewise, when the ends of the exchanger tubes were rounded (instead of flat) effectiveness dropped by as much as 25% again. Sudden increases in effectiveness were observed at higher frequencies and displacements. It was found that these increases correspond to the onset of turbulent bursts during velocity peaks. Application of the Chilton and Colburn-J Factor analogy to oscillating flows was also investigated. It was found that at higher friction factors the analogy did not hold. Some agreement may exist at lower friction factors; however, there is insufficient data within this range to derive reliable correlations. Comparisons between measurements and the heat exchanger model in the TX segment of the DeltaEC software package were made. Comparisons to models using steady-flow heat transfer correlations (using the TASFE approximation) were also made. It was found that none of these models accurately predicted heat transfer performance. Data and correlations are presented in dimensionless form, and an explanation as to the application of the results to other exchanger sizes, different gases, and different conditions is provided.