Many techniques have been developed in recent years to enhance boiling heat transfer. Bergles (1988), Thome (1990), and Web (1994) have reviewed most of these enhancement techniques for both pool boiling and flow boiling. Abhat and Seban (1974) studied the effect of copper mesh around a cylinder in water. Hasegawa et al. (1995) studied various woven meshes for boiling water on a plate. Asakavicius et al. (1979) examines surfaces with several layers of copper screen for boiling water, R-113 and ethanol. Typical enhancements were not very large, about 100 percent at low heat fluxes and much less at high heat fluxes. A recent experimental study on pool boiling by Shimada et al. (1991) showed that an interference plate (a plate with small holes located on a given ptich) placed with a small clearance over a copper heating surface traps the vapor bubbles stably. These holes in the interference plate facilitiates smooth the exchange of vapor-liquid and thereby higher heat fluxes at lower wall superheats between the heating surface and the liquid are achieved. Rao and Balakrishnan (1997) studied subcooled flow boiling over a horizontal heated tube (flow in the axial direction) covered with an interference sleeve having holes in a trinagular pitch. The sleeves were made of aluminium. The liquid boiled was distilled water at atmospheric pressures. They found that the various parameters which influence the boiling heat transfer performance are sleeve geometry (hole geometry and the clearance between the heating cylinder and the interference sleeve), mass velocity of the boiling liquid and the liquid inlet subcooling. Furthermore, it was found that the heat transfer enhancement factor is greatly reduced with higher subcoolings. In the present study, experiments have been carried out at saturated conditions. The details of the experimental setup, the test section, and the arrangement of the sleeve on the heating cylinder have been presented elsewhere (Rao and Balakrishnan, 1997). In the experiments, the applied heat flux was varied and the temperatures of the heating cyclinder and the liquid were measured. Since the vapor qualities encountered in the present study are small (up to a maximum value of 0.01), the results are presented in a format similar to those used in subcooled boiling and in pool boiling. Eight perforated sleeves were used to examine the sleeve geometries. The geometrical details of these sleeves are given in Table 1.The perforated interference sleeve technique is employed to enhance saturated flow boiling heat transfer on cylinders. The technique gives larger enhancement factors at saturated flow conditions compared to subcooled flow conditions. High enhancement factors were encountered with large hole pitch sleeves but with the disadvantage of an early transition to film boiling conditions. This transition heat flux is not influenced by the liquid mass velocity. Sleeves with large gap clearance of 2.3 mm gave poor performance at 577 kg/m2s mass velocities. The best boiling curve with high enhancement factors and with high film transition fluxes at low heat flux levels, was obtained with the sleeves with 2 mm holes.