Chart correlation for saturated boiling heat transfer: Equations and further study

TLDR

CHAPT, a graphical correlation introduced in 1976 for estimating saturated boiling heat transfer coefficients in tubes and annuli, has attracted wide attention due to its broad fluid and orientation applicability but remains difficult to use in computer calculations. The paper aims to provide accurate equations that represent the CHART correlation, responding to inquiries about its availability. The author derived analytical equations for CHART and validated them against extensive tube data and limited annulus evaporation data, addressing concerns about small annular gaps. The equations achieve a mean deviation of 14% across 780 data points from 19 studies, are applicable to both horizontal and vertical tubes with quantified orientation differences, and have been validated against extensive annulus data.

Abstract

In 1976, the author presented in graphical form a general correlation named CHAPT for the estimation of heat transfer coefficients during saturated boiling at subcritical heat flux in tubes and annuli. It was compared to 780 data points from 19 independent experimental studies and found to have a mean deviation of 14% using data that included eight fluids and a wide range of parameters. The correlation was shown to be applicable to both horizontal and vertical tubes and the difference between the two orientations was clearly quantified. Because of its applicability to a wide range of fluids and conditions, including horizontal and vertical orientations, this correlation has drawn considerable attention from the scientific and engineering community. However, the use of the CHART correlation in computer calculations has been difficult because of its graphical form. After receiving several inquiries about availability of equations expressing this correlation, the author has developed and presents in this paper equations that represent the CHART correlation accurately. Since its publication in 1976, this correlation has been tested against a large amount of additional data for tubes by the author and other researchers, with the results summarized here. Furthermore, the correlation was compared with only a fewmore » data points for evaporation in annuli and there were questions regarding application to small annular gaps. A large amount of additional data for annuli have now been analyzed, and the results of this analysis are presented in this paper.« less