【正文】 enser surface, that the far left region was indeed cooler than the bulk of the condenser surface. Figure 12 shows the condenser surface temperature to be almost at a uniform 95–100176。C. In Fig. 11, the active condenser surface temperature is in the 100–105176。C range which is reasonable considering a portion of its condenser surface is cooler due to the presence of air. The horizontal figures show typical behavior for a large flat heat pipe with a large and small amount of air loading. This would be the case if air infiltrated a hermetically sealed heat pipe through cracks in the welds and leaks in the system valves. It should also be pointed out that after the tests of both cases, it was determined that more air appeared to have infiltrated the systems. This was confirmed by taking final pressure readings when the heat pipe cooled down. For the large air case, the initial pressure reading was 33 kPa at 25176。C, and the final pressure reading was near 60 kPa at 25176。C. For the small air case the initial pressure reading was kPa at 25176。C (almost free of air), and 10 kPa at 25176。C as the final reading, thus some air did infiltrate the small gas case. The reasons for the air infiltration were the Monel pins and welds. There were 45 pins that served as the internal support structure for this heat pipe, hence 90 welds. It was very hard to keep all welds intact, especially during the thermal cycling of the tests, ., on/off, etc. Figure 11. Figure 12. B.Vertical Orientation. The next series of infrared images, Figures 13,14,15,16,17,18, show the operation of the air infiltrated flat heat pipe in a vertical orientation. For this orientation, the evaporator section was located below the condenser section. The heat input range was again 200–800 W. Figure 13 depicts the large gas loaded case at a heat input of 200 W. As can be seen, the only active portion of the condenser region is in the lower left corner adjacent to the evaporator section (not seen because it was covered with thermal insulation hence the evaporator appears cooler than the condenser on the IR videotape). The heat pipe condenser was operating asymmetrically and the air appears to cover most of the condenser heat transfer area. Figure 14 shows the condenser surface to be more active at 200 W for the small gas loading case. In fact, two thirds of the condenser surface is believed to be actively condensing as indicated by the fairly uniform surface temperature on the order of 33176。C. Also seen are some thermocouple wires which are the yellow lines in the picture. The cool spots on both sides of the heat pipe are the PVC clamps. Figure 13. Figure 14. Figure 15. Figure 16. Figure 17. Figure 18. At a heat input of 400 W for the large gas loading, Fig. 15, the heat pipe condenser is operating in a highly asymmetric fashion. The active condenser region is believed to be the growing finger on the left. The air which is believed to be depicted by the lower temperature blue `color39。 is in the middle and along the right edge. The air inside the condenser section is almost 18176。C cooler than the water vapor (white/red). An estimation of the effect of the thermal resistance due to the condensate falling film thickness on outside surface temperature showed that for a range of condensate film thickness between to mm, the surface temperature variation should only be about 5176。C. What apparently is happening is that as the water vapor gets hotter due to the increase in heat input, it bees less dense that the cooler air, and since the air has no place to go, a buoyancy driven flow field is believed to be established. The cooler air is more dense than the water vapor and sinks. The asymmetrical flow could have been established by nonuniformities in the evaporator heat flux, which was established by eight cartridge heaters inside an aluminum block, and the entire block coated with heat sink pound on the side in contact with the evaporator. Any gaps in the heater block to the evaporator surface caused by surface warpage could create a nonuniform heating environment. The Monel surface of the heat pipe did exhibit some warpage after the welding processes. The green regions are indicative of a more diffused waterair mixture if one assumes the internal pressure of the heat pipe at any given operating heat input is fairly constant. Due to the relatively large cross sectional area of the vapor core, m2, the vapor velocities for the present heat input range are very low. Thus, the observed condenser surface temperature distributions are not believed to be caused by differences in pressure due to the vapor velocity from one part of the condenser to another. The 400 W input small air infiltration case is shown in Fig. 16. The condenser surface temperatures appear to be more symmetrical, but buoyancy effects are still present. As can be seen, the water vapor appears to rise up along both edges of the condenser section. The noncondensable air appears to sink slightly in the central portion. It is interesting to note that in the horizontal orientation, the air was more readily pressed towards the fill pipe. Buoyancy effects for the horizontal orientation were minimal. In the vertical orientation, airwater vapor buoyancy effects are more pronounced due to the influence of gravity. It would be interesting to conduct a future study of varying aspect ratios involving the width and depth of the vapor flow channel, with the heat pipe length. Also of interest would be to pare these results to cylindrical gas loaded/air infiltrated heat pipes with varying aspect ratios involving internal vapor flow diameter and heat pipe length. Figures 17 and 18 depict the 800 W heat input cases for the large and small air infiltrations, respectively. The large air case, Fig. 17 shows the same general trend as Fig. 15. Figure 18 depicts a buoyant effect much like a lava lamp. ConclusionsA large, flat heat pipe was fabricated from Monel metal sheets and Monel