The investigation of saturated boiling heat transfer was performed from porous surfaces in narrow space formed by two concelitric tubes with two open ends at atmospheric pressure. Experimental results show that for the grooved tubes with inserted tubes the boiling heat transfer coefficiellts increase with the decrease of gap size. The boiling critical heat flux decreases with the decrease of gap size. The grooved surfaces can also augment the critical heat flux. Sintered porous surfaces, in pool boiling, can enhance boiling heat transfer, but the boiling heat transfer from these surfaces is affected little by gap size of narrow spaces.
