Abstract
This paper presents the experimental results on flow boiling heat transfer of ammonia inside a horizontal internally spirally grooved steel tube with 12mm in averaged inner diameter. Experimental conditions are 40 to 80kg/(m2s) in mass velocity, about 0.7MPa in pressure, and 0 to 20 kW/m2 in heat flux. Measured values on frictional pressure drop in adiabatic condition were correlated by Higashiiue's correlation, which was developed based on the experimental results with fluorocarbon refrigerants. On the measured heat transfer coefficients, very little significant effect of heat flux was found even in the small mass velocity condition, and also smaller influence of mass flux was observed than expected from the forced convection heat transfer theory. The measured heat transfer coefficients were compared with the predicted values by the author's previously developed correlation for fluorocarbon refrigerants,and this equation could not predict heat transfer coefficients of ammonia well. The trends of circumferential distribution of wall temperature in high quality region were different from those observed in the case of fluorocarbon refrigerants. In high quality region, annular mist flow regime appears instead of ordinary annular flow regime.
