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Excessive impact pressures can develop when an evacuated system is filled with liquid. Such a process is usually highly chaotic, especially when the system geometry is complex. Available computational methods by themselves cannot provide the necessary answers. The International Space Station (ISS) heat exchanger has a complex flow system, and a synthesis of computational and experimental methods was necessary to design the system. The FLOW-NET two-phase flow program was used to determine the range of loss coefficients and the liquid-vapor interface mass and energy transfer that would fit the measured impact pressures. These loss coefficients could then be used to compute the impact pressures for a design configuration similar to the one tested at a range of operating conditions.

The International Space Station thermal control system is a one-phase ammonia loop. However, under some operating conditions two-phase flow is introduced into the system. Safe equipment operating envelopes during the two-phase flow periods, which usually are transient in nature, must be established either experimentally or computationally. The computational methodology has been developed to a point to make the computational approach feasible and can be used to establish such operational envelopes. Two-phase flow analysis of the active thermal control system (ATCS) ammonia pump was conducted to determine the safe operating envelopes. Analysis was conducted to determine the pump dynamic environment under two operating conditions: (1) fill of the entire ammonia loop during the initial on-orbit system fill; (2) fill of a radiator Orbital Replacement Unit (ORU).

The discharge characteristics of a typical CO2 fire extinguisher system under consideration for the US space station have been analyzed using the FLOW-NET computer program. The discharge time, mass, and ultimate pressurization are determined by calculating the transient until a resting state is achieved. Accuracy of the numerical solution procedure is demonstrated using different nodalizations and by comparing calculated results for an ideal gas against analytic results. Because the length of the supply tank can be several orders of magnitude smaller than the length of the transfer line, transient calculations may require a very small time step and considerable computer time. A procedure is described to modify the geometric model, which reduces required computer time by an order of magnitude without loss of accuracy. Sensitivity of the results to the equation of state model is discussed.