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Title: Single phase heat transfer enhancement
Author: Reddy, M. A.
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2000
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This thesis presents investigations into the enhancement of heat transfer inside tubes using HiTRAN® tube inserts manufactured by Cal Gavin Ltd. The applicability of heat transfer enhancement in vertical thermo syphon reboilers was investigated using a computer simulation. In vacuum operation, reboilers can have a significant subcooled length (as high as 60 % of the tube length). Heat transfer coefficients in this region are lower than in the two-phase region. Using tube inserts, an increase is made in the heat transfer rate occurring in the sub-cooled region and, a corresponding increase in the length of the tube subjected to two-phase heat transfer and improvement of heat transfer performance results. Geometric variables of the tube insert were investigated experimentally, to study their influence on heat transfer and pressure drop performance. Loop density, loop wire diameter, core wire diameter, loop material and uniformity of loop density were investigated. Two experimental facilities were designed, commissioned and constructed to measure the heat transfer and pressure drop performance of these tube inserts. The new rig at UMIST is located in a flameproof location and was constructed with the intention of investigating a wide range of other processes in the future. Two tube inserts were tested over a Reynolds number range of 200 to 200000 using water as the working fluid. Adiabatic, cooling and heating tests were performed using an inside tube diameter of28.25 mm. At the Cal Gavin Ltd. facility, the rig was redesigned to extend the operating range of data collection. It was enhanced by the provision of automatic data collection, improved accuracy of temperature measurement and new equipment to allow cooling experiments. Tube inserts were tested between a Reynolds number of 100 to 2000 using a viscous oil as the working fluid. Again adiabatic, cooling and heating tests were performed. An inside tube diameter of 21.18 mm was used in the maj ority of the tests, but some preliminary results using a tube diameter of 28.45 mm are also reported. Using the results of the experimental work, pressure drop performance was correlated using an approach similar to that used for packed beds. It was found that 90 % of the data were correlated between ± 15 % of the prediction using specific insert dimensions and inside tube diameter. Further investigations into the prediction of heat transfer coefficients were made. However no general correlation could be developed from a fundamental basis, to predict heat transfer across the full range of Reynolds numbers investigated in this study. A recommendation is made for a suitable correlation. The influence of the insert geometry was associated with the fundamental pressure drop and heat transfer performance of the tube insert, leading to recommendations for the optimisation of tube insert design.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (D.Eng.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available