Boiling heat transfer of Freon-113 flowing normal to a tube Effect of tube diameter

The effect of heater diameter on the pool and flow boiling heat transfer of saturated Freon-113 was studied. The heaters were horizontal copper tubes of diameter 1.59 to 7.94 mm (pool) and 3.18 to 12.7 mm (flow), heated internally by condensing steam. The test fluid at atmospheric pressure flowed upward, normal to the heaters, at approach velocities of 2.4, 4.0, and 6.0 m/s. For flow boiling, at a fixed velocity and wall temperature, smaller tubes resulted in higher heat flux values, except at low wall temperatures. The maximum heat flux was proportional to the 0.44 power of velocity and inversely proportional to the 0.28 power of diameter. In pool boiling, the critical diameter was different for each regime of boiling, and depended on the characteristic bubble size.