Analysis of flow boiling heat transfer in narrow annular gaps applying the design of experiments method

Gunar Boye,Frank Beyrau,Jürgen Schmidt

doi:10.1177/1687814015584544

Gunar Boye, Frank Beyrau + Show 1 more

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https://doi.org/10.1177/1687814015584544

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Abstract

The axial heat transfer coefficient during flow boiling of n-hexane was measured using infrared thermography to determine the axial wall temperature in three geometrically similar annular gaps with different widths ( s = 1.5 mm, s = 1 mm, s = 0.5 mm). During the design and evaluation process, the methods of statistical experimental design were applied. The following factors/parameters were varied: the heat flux [Formula: see text], the mass flux [Formula: see text], the vapor quality [Formula: see text], and the subcooled inlet temperature [Formula: see text]. The test sections with gap widths of s = 1.5 mm and s = 1 mm had very similar heat transfer characteristics. The heat transfer coefficient increases significantly in the range of subcooled boiling, and after reaching a maximum at the transition to the saturated flow boiling, it drops almost monotonically with increasing vapor quality. With a gap width of 0.5 mm, however, the heat transfer coefficient in the range of saturated flow boiling first has a downward trend and then increases at higher vapor qualities. For each test section, two correlations between the heat transfer coefficient and the operating parameters have been created. The comparison also shows a clear trend of an increasing heat transfer coefficient with increasing heat flux for test sections s = 1.5 mm and s = 1.0 mm, but with increasing vapor quality, this trend is reversed for test section 0.5 mm.

Highlights

The requirements to realize high heat fluxes, to cool components at defined temperatures, and to minimize the use of hazardous or toxic media lead to simultaneous developments of increasingly smaller devices and an increased use of miniature evaporators
The Design of Experiments’’ (DoE) is employed as an experimental strategic planning method
It allows using a relatively small experimental effort to determine the effect of the factors on the heat transfer coefficient as system response, even if the effects’ proportional influence differs considerably

Summary

Introduction

The requirements to realize high heat fluxes, to cool components at defined temperatures, and to minimize the use of hazardous or toxic media lead to simultaneous developments of increasingly smaller devices and an increased use of miniature evaporators. The resulting economic importance leads to numerous scientific studies, in recent years since the work of Lazarek and Black.[1]. Knowledge of the heat transfer coefficients of such equipment is of fundamental importance for the constructing engineer. The reviews of Tibirixcaand Ribatski[2] show that—more than 30 years later—there are different and sometimes even conflicting evidence on the effect of the parameters on the heat transfer coefficient. The resulting need for research requires a large experimental effort to receive secured results at a maximum variation of all known factors.

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