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During ground testing and micro-g operation of Capillary Pumped Loops (CPLs), oscillations of the system pressure drop have been observed. In some cases, it is highly probable that they contributed to deprimes of the system when the magnitude of the pressure oscillations exceeded the capillary limit of the wick. A hydrodynamic stability theory was proposed in 1994 to explain the oscillatory behavior of the CPL systems. The theory has given insight to the cause of pressure oscillations in CPL systems and their effect on system operation. The theory indicates that the pressure oscillations are a function of the system design parameters and the operational conditions. One of the system parameters which affects the pressure oscillations is the wick spring constant of the porous wick structure in the evaporator. The wick spring constant is determined from porosity, pore size and permeability of the wick.

The the past, the design of a Capillary Pumped Loop involved mainly on the thermodynamics and heat transfer aspects of the system. The fluid flow dynamics of the working fluid were deemed benign to the system performance. Recently theoretical and experimental studies have revealed several mechanisms that led to the deprime of the capillary pumps. These mechanisms were all related to the dynamics of the fluid movement inside the loop.

A capillary pumped loop (CPL) with a single starter pump in its evaporator section has been demonstrated to have very reliable start-ups and robust operation. In order to service payloads with large thermal footprints or to service multiple payloads, a CPL with multiple starter pumps seems a logical approach. However, questions were raised concerning its reliability for successful start-ups. In order to verify the feasibility of such a concept, a test program was conducted at NASA Goddard Space Flight Center, using four starter pumps plumbed in parallel. The main purpose of this experimental investigation was to verify the system's ability to provide a successful start-up and to retain performance characteristics demonstrated by a CPL with multiple evaporators of the traditional two-port pump design. Tests were conducted progressively by installing one, two and four pumps in the test loop.