CHF and dryout point in vertical narrow annuli

Experimental study associated with CHF and dryout point in narrow annuli is conducted with 1.5 mm and 1.0 mm gap, respectively. Distilled water is used as work fluid. The parameters examined were: pressure from 2.0 MPa to 4.0 MPa; mass flux from 26.0 kg/(m² s) to 69.0 kg/(m² s); heat flux from 10 kW/m² to 70 kW/m²; exit equilibrium mass quality from 0.52 to 1.08. It is found that CHF monotonously increases with mass flux in internally heated annuli and bilaterally heated annuli. However, the observed trends are not similar to that in externally heated annuli. The CHF is not affected significantly by mass flux. Critical qualities of dryout point (X_DO) decreases with mass flux and increases with inlet qualities. Under the same conditions X_DO in outer tube are always larger than that in inner tube. According to experimental data, a criterion for the appearance of dryout point for bilaterally heated has been presented. The comparison with the correlations [K{cyrillic}U{cyrillic}T{cyrillic}A{cyrillic}T{cyrillic}Ye{cyrillic}L{cyrillic}A{cyrillic}D{cyrillic}Z{cyrillic}Ye{cyrillic}, C.C., 1979. T{cyrillic}ye{cyrillic}d{cyrillic}p{cyrillic}l{cyrillic}o{cyrillic}e{cyrillic}n{cyrillic}ye{cyrillic}r{cyrillic}g{cyrillic}ye{cyrillic}t{cyrillic}i{cyrillic}k{cyrillic}a{cyrillic}, No. 6] and experimental data indicates that the existing correlations applied to tube cannot predict X_DO in narrow annuli well. Based on experimental data, a new correlation is developed.