Lab Module Depressurization Using the Vent/Relief Valve 1999-01-2194

This paper updates the analytical rationale and the computed results from those presented in the initial paper delivered on this subject (see the first reference listed below). The operational scheme is the same in this paper as in the earlier paper. The ACS Ventilation and Relief Valve (VRV) in the depressurizing Lab Module is wide open due to the need to suppress a large fire in the Lab or to remove the contaminated Lab atmosphere. All crew-men have evacuated the Lab Module and all previously open hatches in the Lab Module have been closed. In the reference paper analytical efforts were made to investigate: 1.) partial blockage of the screen due to ice accumulation 2.) performance of a thermostatically controlled heater attached to the screen, requiring 300 to 400 watts during depressurization and 3.) performance when allowing the Temperature and Humidity Control system fan to run during depressurization and to thereby cause significant heat transfer increases between cabin air and cabin aisle way walls. None of these efforts proved successful.

In this paper significant increases in heat transfer between cabin air and the Space Station’s structure and installed equipment have been added to the modeling. These come from: 1.) a re-evaluation of the air flow path from the cabin to the VRV (with a much greater heat transfer area for the parallel flows in the equipment packed stand-offs compared to the lesser heat transfer area for flow down the aisle way) and the 2,) radiant heat transfer from structural panels, wiring, tubing, etc. to the foggy atmosphere composed of air and water droplets (earlier), and/or ice particles (later), assumed in the cabin’s atmosphere. These added heat transfer terms do not prevent ice formation, but they do significantly reduce the amount of ice formed. And the revised air flow path is significantly complex that the unknown amount of ice that will be separated out on surfaces, en route, will be larger that originally envisioned. The upshot of these analyses is that the decision has been made to use the present existing screen.