Circumferentially grooved heat pipes have been studied as capillary pumps to be used in two-phase heat transfer loops. Experimental results up to 1.7 W/cm2 were found for Freon 11 as the working fluid. To improve the knowledge of the performance of these capillary pumps, some design parameters are now studied. The heat transport capability and the capillary pumping pressure are analyzed for different values of the groove width, groove opening angle and inner radius of the capillary pump. Theoretical results indicates somewhat better performance for capillary pumps with rectangular grooves than with trapezoidal grooves. Fine groove widths and small values of inner radius are also desirable.