SL-90-01-3 -- An Experimental Investigation of Heat Transfer Characteristics of Spirally Fluted Tubes in Confined Cross-Flow PDF

Presents the results of an experimental investigation of confined cross-flow around spirally enhanced tubes. Confined cross-flow was simulated by placing a bank of spirally fluted tubes in a transparent channel that facilitated viewing of the flow around the tubes. This test section was used as a cross-flow heat exchanger in which cold water flowing in a confined cross-flow mode outside the tube bank was tested by steam condensing on the inside of the tube. Overall heat transfer coefficients, cross-flow heat transfer coefficients, and tube-side heat transfer coefficients were calculated directly from measured mass flow rates and fluid temperatures. Measurement of the tube temperature at the flute crest trough at several axial locations allowed the evaluation of individual heat transfer coefficients directly without the need for tedious, and sometimes error-prone, Wilson plots. Heat transfer coefficients were used to develop a correlation for the Nusselt number in terms of geometric and flow variables. Approximately nondimensionalised variables, such as the number of tubes in the bank, flute pitch, flute depth, number of flute starts, Reynolds number, and Prandtl number, were used as independent variables in the correlation. An attempt was made to explain the dependence of the Nusselt number on each of these variables on the basis of the flow mechanisms observed by using flow visualisation techniques.

KEYWORDS: experiment, heat flow, properties, extended surfaces heat exchangers, cross flow heat exchangers, tubes, spiral heat exchangers, heat transfer coefficient, calculating, measuring, flow rate, temperature, Nusselt number, Reynolds numbers, Prandtl number.