6.Hl2 returning air is expected to be at lower temperature than the air in the hull. Also since there is a tradeoff between the temperature difference and the mass flow rate. To keep the heat pump equipment small requires a small;, which suggests that T 4 be as low as possible. If the materials for the radiator come from the Moon, the metals available are limited to aluminum and iron. T 2 is thus upper-limited to 1700°K, since 1789°K melts low carbon steel. T 2 also has lower limit 295°K; this happens if the compressor does no work on the air, and corresponds to the passive external radiator case. T 3 has lower limit 273°K, to avoid formation of ice crystals within the radiator. Bringing T 3 close to 273°K condenses water from the air, a desirable feature for humidity control. ~owever, the water should be trapped out between the radiator and the turbine, to avoid liquid and ice problems in the turbine. From and the other restrictions mentioned above, an envelope for T 4 and T 2 can be defined. This is shown in Figure 6.H4. VI.H.5: NUMBERS Pinputsunlight p inputlifestyle Poutputhull+shield 2.79xl0 7 watts (see VI. 8 . 2 l 2.0xl0 6 watts (see VI.El 3.6xl0 6 watts (see VI.El 8.6xl0 6 watts (see VI. 8. 3l
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