Experimental Development of Tubeside Heat Transfer Correlations for Laminar Flow with and without Inserts.

摘要

An experimental study of laminar flow heat transfer of an ethylene glycol/water mixture in an electrically heated horizontal tube using wire mesh (HEATEX) and twisted tape inserts was investigated. Twelve thermocouples, inserted in the tube wall at four longitudinal locations, enabled a mean inside experimental heat-transfer coefficient to be accurately measured. A constant wall heat flux boundary condition was placed on the wall by wrapping six 200 W flexible heater tapes tightly around the tube. The ethylene glycol/water mixture provided a coolant Reynolds number between 200-5000 and a Prandtl number between 30-140. Two smooth inside diameters and a roped tube profile were tested with and without the inserts. Heat-transfer correlations for tubes without inserts were developed and compared with theory for both thermally and hydrodynamically developing flow. Correlations were also developed for the two types of inserts. Nusselt numbers for fully developed flow were found to be a function of Reynolds and Prandtl numbers for the wire mesh insert and a function of tape twist ratio, Reynolds and Prandtl numbers for the twisted tape insert. Heat transfer enhancements of over 7 for the wire mesh insert and over 4 for the twisted tape insert at high Reynolds numbers were obtained over the empty tube.