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暖通專業(yè)英語論文(編輯修改稿)

2024-09-05 11:05 本頁面
 

【文章內(nèi)容簡介】 on the heat pipe and calibrating the infrared camera with these data. Later, during operational tests, the surface emissivity was measured at at 100176。C. Figure 4. A heated plate, m m, was fabricated from m thick aluminum stock. Eight equally spaced holes mm in diameter were centered and drilled through the aluminum cross section. Eight 1 KW Watlow firerod cartridge heaters, coated with heat sink pound, were inserted into the holes. The aluminum heater block was coated on one side with the heat sink pound on the side to be in contact with the heat pipe. A m m block of wood was then placed on the back side of the aluminum heater block and the wood/aluminum heater assembly was clamped to one side of the evaporator section. The entire heated evaporator section was then covered with thermal insulation. The thermocouples and cartridge heaters were then connected to a data acquisition system. Measurement uncertainty was +/–176。C per thermocouple channel and the heater input could be recorded +/–5W. A stand was fabricated so that the heat pipe could be operated at various angles of inclination. Experimental InvestigationData was taken for two types of heat pipe orientation and two different noncondensable gas loadings. Two gas loadings were selected in order to discern the effects caused by minor and major air leaks into the heat pipe. The first heat pipe orientation was horizontal. In this orientation the flat side of the heat pipe was parallel to the ground. In addition, the evaporator heater was on the side facing the ground, thus, the evaporator section was heated from below while the top portion of the evaporator section was adiabatic (thermal insulation was wrapped around the entire evaporator section). The second heat pipe orientation was vertical with the evaporator section placed below the condenser section. At 25176。C room temperature, the internal pressure of the heat pipe without gas loading would be the saturation pressure of the working fluid at 25176。C, or approximately kPa for water. Since this pressure represents a partial vacuum, it was very easy to bleed a little air into the heat pipe for the initial gas loading. For the first case, air was bled in until the pressure gage read 33 kPa. Assuming that the air would initially occupy the entire inside volume ( m3, approximately) at a partial pressure of kPa and temperature of 25176。C would mean that the air mass was approximately kg. The water fill was approximately 400 cc. In addition to the thermocouple measurements for the evaporator and condenser sections, the condenser temperature was also monitored on the side adjacent to the heater by infrared videography. Thus, the entire condenser surface temperature could be monitored and the results would be indicative of what was happening internally with respect to the vapor and gas (air) interfaces. In other words, in a typical heat pipe with no air infiltration, the inside temperature difference between the evaporator and condenser can be very close to an isothermal condition. When a noncondensable gas is introduced, there can be significant temperature differences between where the gas is located in the condenser, and where the vapor is located. These temperature differences would affect the condenser surface temperature distribution and would easily show up on the infrared camera video tape. Hence, one could get a real time thermal image of what was physically happening inside the condenser end of the flat plate heat pipe should air infiltrate the system. The infrared camera video system was calibrated by using the thermocouple data. The heaters were turned on, and the internal temperature of the heat pipe, before air was added, was set at 100176。C (internal pressure conditions equal to atmospheric conditions with water as the working fluid). The emissivity of the infrared camera was then dialed in until the IR camera was depicting a near isothermal condenser region at a temperature of 100176。C. This emissivity was . The IR camera system was now calibrated. Periodically, the emissivity would be checked by paring thermocouple data to IR data. There was a fluctuation in surface emissivity between and . Care was taken so as not to operate the flat heat pipe above 101 kPa internal conditions in order to prevent any puffing out along the heat pipe flat surfaces which might result in an emissivity calibration error, ., partial hemispherical surfaces. It was decided to only report the temperatures in this particular study using the IR camera since the IR camera data was within +/–1176。C of the thermocouple data. With the heat pipe charged with water and air, the apparatus was set in the horizontal orientation and the heat input was set at 200 W. After stabilization of the heat pipe, which took approximately three hours due to the large thermal mass of the heat pipe, temperatures stabilized and IR video data was taken. The heat input was then changed to 400 W and IR data was taken again when the heat pipe temperatures appeared to stabilize. This procedure was followed up to a heat input value of 800 W. The heaters were then shut down and the heat pipe allowed to cool overnight. The next day, it was noticed that the heat pipe temperature was at 24176。C, but its internal pressure was at 65 kPa instead of the original 33 kPa, so apparently some leaks had developed. Whether these leaks developed overnight or during the data runs is not clear. The heat pipe was placed in the vertical orientation, and with approximately the same amount of initial air inserted the process was repeated. An effort was made to seal the heat pipe from leaks and attempt a run with no air, but this turned out to be very difficult to achieve with the welded pin fabrication scheme presently employed. However, many of the leaks were sealed and the horizontal and vertical heat pipe results for very little added air show a marked contrast to the larger added air results. It should also be pointed out that as the
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