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All-glass solar collector exhaust heat treatment process using composite molecular pump pumping high vacuum
The composite molecular pump instead of the oil diffusion pump for all-glass vacuum tube solar vacuum exhaust exhaust pumping high vacuum test. Selected three types of molecular pump, the collector tube automatically continuous baking exhaust line experiment. After about one year longer production run test, the molecular pump suffered more than 190 times the heat pipe nozzle rupture caused by atmospheric impact, there is no damage, no significant changes in vacuum performance. The collector tube prepared by molecular pump baking exhaust technology, according to the national standard at a temperature of 350 ℃, 48 h high temperature aging test, the getter speculum disappearance rate of about 5%, only 10% of the national standard value. All-glass vacuum tube solar water heater is the core component, the quality of a direct impact on the water heater's thermal performance. The vacuum performance between the collector sandwich is one of the key indicators, affecting the heat loss of the collector, thus affecting the thermal efficiency. Solar water heater collector tube life is usually 20 years, during the operation of the collector tube temperature of about 50 ℃ ~ 80 ℃, collector tube itself deflated, so that the inner and outer glass tube between the vacuum gradually decreased. In the course of 20 years of use, the heat conduction loss of the gas in the heat pipe sandwich is much less than the heat radiation loss, for example, the heat conduction heat loss is less than 10% of the total heat loss. Using high-temperature baking vacuum method, to obtain a long-term heat pipe to maintain high vacuum performance [1]. Collector bake exhaust device is one of the key equipment for the production of heat pipes in the device inside and outside the glass tube and the sun solar collector selective absorption coating heating exhaust heat at high temperatures through the tail pipe pumping sandwich Vacuum, vacuum tube to obtain the required high degree of vacuum tube, making the collector tube deflation in use less. In addition, the final process of the collector tube is high-frequency evaporation activated getter. The getter coating activated at the closed end of the collector tube absorbs the trace gases released during the high temperature operation of the collector tube, mainly water vapor, so that the collector tube sandwich maintains a good degree of vacuum for 20 years of operation. This work in the company's production of automatic collector tube continuous baking exhaust line. Domestic heat pipe baking exhaust production process are used oil diffusion pump pumping high vacuum, the experiment uses a composite molecular pump to replace the vent line on the crude oil diffusion pump pumped high vacuum. Compared with the oil diffusion pump, the molecular pump itself has no oil, the water molecule pumping speed long time stability, energy saving and so on. In addition, the molecular pump runs reliably and requires little maintenance for a long period of time, such as two years of production. However, the molecular pump by the atmospheric impact of poor performance, the price is more expensive. 1, experiment In this experiment, a composite molecular pump instead of the oil diffusion pump pumping high vacuum, continuous automatic exhaust pipe in the heat pipe. The exhaust line is equipped with 42 trolleys loaded with roasted exhaust manifolds and 40 collector tubes per trolley. The exhaust air line operates at a transmission speed of about 0.80 m / min. Each trolley runs 12 furnaces a day, Exhaust air line operation day baking exhaust manifold 20000. Baking exhaust process temperature 450 ℃, baking time 40 min. Venting trolley schematic diagram shown in Figure 1 [2]. The trolley's vacuum system consists of a pre-rotary vane pump, a composite molecular pump and a high-vacuum piping system. High molecular vacuum pump above the cylinder side of the open four holes, leads to four connected to the vacuum pipe. Each connecting vacuum tube and a vacuum tube collector tube connection. Four installed heat pipe vacuum tube blind flange sealed at both ends, composed of two parallel pipes. Two vacuum heat pipes installed in each group are connected with the head and the tail of the vacuum pipe, and the gaps between two adjacent ends are as small as possible. Each installed heat pipe vacuum pipe through the tail pipe seat can be installed 10 to be baked exhaust manifold. Connect the vacuum pipe and heat pipe installed Vacuum pipe diameter of about 70 mm, the inner surface of the polished. Each connecting vacuum pipe is equipped with an isolation valve. High vacuum valve with its own design of the valve, valve height and stem stroke without affecting the conductance as short as possible, the height of about 110 mm. Figure 2 shows the collector tube exhaust line equipped with a composite molecular pump photo. Two rows of heat collectors are mounted on the table of the trolley, the following is the high vacuum pipeline system next to the table top, and the composite molecular pump under the high vacuum valve replaces the original oil diffusion pump. 1. Seal the tail pipe 2. Install the collector tube high vacuum pipe 3. Blind flange 4. Connect the high vacuum pipe 5. High valve 6. Isolation valve 7. Composite molecular pump 8. Rotary vane pump 9. Trolley control system Figure 1 Exhaust line trolley schematic Figure 2 collector exhaust line with a composite molecular pump trolley photos 3, the conclusion we use three composite molecular pump, pumping speed of 600 L / s, 1200 L / s of water cooling, 1200 L / s air-cooled molecular pump, respectively, installed in the exhaust line of the three trolleys, about a year collector tube exhaust test baked. The pumping speed of 600 L / s molecular pump with 400 Hz operating frequency, the remaining two pumping speed of 1200 L / s using 350 Hz operating frequency. During the one-year production and operation of three molecular pumps, Taiwan's molecular pump produced more than 90,000 heat-collecting tubes, subjected to more than 190 times of atmospheric rupture of the heat-collecting tube nozzle, and did not cause any damage to the molecular pump blades and disks. No change in performance, still able to meet the requirements of continued production and operation. During the process of exhausting at 450 ℃ for 40 min, the early pressure was about 5 × 10-2 Pa with three molecular vacuum pumping trolleys, and gradually decreased to 1 × 10 -3 Pa with the heating process About, collector pressure when the seal is about 7.0 × 10- 4 Pa. The pumping speed is 600 L / s. The early pressure of the molecular pump is higher than the other two molecular pumps. The heat pump tube made by molecular pump baking and exhausting process was heated at 350 ℃ for 48 h, and the disappearance rate of getter was about 5%, which was about 10% of the national standard, indicating that the composite molecular pumping High vacuum vacuum tube collector prepared excellent performance.