Abstract
An experiment was carried out to obtain data on critical heat flux (CHF) in vertical internally heated annuli cooled with Refrigerant (R-134a) at high-pressure subcooled and low-quality conditions (outlet pressure:1.78–2.72 MPa, mass flux: 587–2135kg/m2s, critical quality: −0.64–0.12). The test section has two forms, concentric, eccentric (ε = 0.435, 0.783). At inlet conditions, parametric trends of the CHF data in concentric annuli have been shown consistent with those obtained in experiments in tubes. At local conditions, the reversed trend of CHF with increasing mass flux occurs a lower critical quality. The effect of eccentricity on CHF depends mainly on local flow conditions. At high subcooled conditions, eccentricity causes punishment to CHF and CHF decreases with the increase of eccentricity. The eccentricity effect appears to be diminished at low subcooled conditions. An interesting phenomenon occurs in high pressure and high flow (HPHF) conditions, where CHF with eccentricity of 0.783 is higher than CHF with eccentricity of 0.435. This is because the larger cross flow causes bubbles to be more easily leave away from the narrow gap in annuli with high void migration. The effect of eccentricity on CHF was studied from the mechanism of two different types of CHF (DNB and Dryout) in vertical eccentric internally heated annuli.
