Abstract: Metallic tubes (10,10') for boiling have an outer surface (12) for contacting a refrigerant and an inner surface (14) for contacting a liquid heat transfer medium to be chilled. The outer surface (12) has a plurality of radially outwardly extending helical fins (18); the tube inner surface (14) has a plurality of helical ridges (16). The fins (18) of the outer surface are notched to provide nucleate boiling cavities having pores (30). The fins (18) and notches (N) are so spaced that the pores (30) have an average area less than 0.00009 square inches and a pore density of at least 2000 per square inch on the tube outer surface. The helical ridges (16) on the inner surface have a predetermined ridge height and pitch and are positioned at a predetermined helix angle, the inner surface having a severity factor .PHI. in the range of 0.006 to 0.008.

Abstract: A heat transfer tube for use in a refrigeration evaporator. This tube includes an outer surface with axially spaced bent fins which form and enclose annular tunnels. The bent fins have top edge portions which have peripherally spaced sets of notches of different sizes on the same fin convolution and refill gaps for fluid flow to the tunnels for heat transfer through the annular wall. The concept of placing different pore sizes next to each other on the same fin allows a more efficient use of the tube's surface area for evaporative heat transfer.