Critical Heat Flux (CHF) in a non-uniformly heated tube is a very important factor in designing boiling two-phase system, especially, a small capacity boiler with tube-nested combustor operated under low-pressure and low-mass-flux condition. However, the influence of the non-uniformly heat flux on the CHF has not been clearly understood so far. In this series of investigation, the non-uniform heat flux distribution was realized by using the Joule heating of eccentric tube. The experimental investigation on the CHF was conducted by using a forced convective boiling system with a test tube of dimensions of 20 mm I.D., 24 mm O.D. and 1800 mm in heated length, and the results were compared with the previous results of 900 mm in heated length. On the basis of these experimental results, the correlation of spreading coefficient was proposed. The new calculation model with this correlation and the treatment of the droplet has been confirmed with the experimental results.
