This study deals with a transient laminar flow, which is started from rest, in the entrance region of a porous pipe. This flow analysis is applied to transpiration cooling systems and research equipment for production of tidal current. In this report, the problem is analyzed by a modified momentum integral method using the integral form of the equations of continuity, momentum and energy. The following conclusions were obtained; (1) Dynamic distributions of velocity profiles, wall frictions and pressures are obtained numerically. (2) The relation between the flow rate of injection or suction and inlet length of the entrance region is made clear. (3) Each dynamic state in the pipe is found with changeable inlet velocities and with variable suctions or injections. (4) It is confirmed that the modified momentum integral method is valid for the slip velocity on the porous wall which makes the inlet length short.
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