CRITICAL HEAT-FLUX DURING NATURAL CONVECTIVE BOILING ON UNIFORMLY HEATED INNER TUBES IN VERTICAL ANNULAR TUBES SUBMERGED IN SATURATED LIQUID

An experimental study has been made of critical heat flux (CHF) of nat ural convective boiling on uniformly heated inner tubes in vertical an nular tubes. The experiment was performed at a pressure of P = 0.1 to 3.1 MPa for the clearance of 0.4 to 4.0 mm, the heated tube diameter o f 5 to 10.6 mm, the annular tube length of L = 58 to 840 mm and three kinds of liquids. The effects on the CHF are mainly discussed about th e pressure in which the density ratio of the test fluid rho(upsilon)/r ho(l) varies frgm 6.24 x 10(-4) to 0.16 and of the ratio of L/D(he) = 2 to 500, where an equivalent heated length, D(he), serves as a parame ter connecting the clearance with the heated tube diameter. The experi ment shows that the CHF obtained depends on the ratio of L/D(he) and t hen a generalized correlation can be derived predicting the CHF data w ell.