Design of vacuum pumps for vacuum flash evaporation
Thread Content
I need to build a vacuum flash evaporation system. According to the information I found, when calculating the capacity of the vacuum pump, the condensable gases that are produced during the flash evaporation process must be included in the volume of gas to be pumped out. In this case: if the evaporation rate is 1 ton of water per hour, the vacuum level is 70 mm Hg, which equals 70/760*1.013*10^5 = 9330 Pa, and the temperature is 60 degrees Celsius, then the amount of condensable gas generated is given by V=nRT/p = (1000*1000/18)*8.31*(273+60)/9330 = 16477 cubic meters per hour, or 274 cubic meters per minute. This value is extremely high; no vacuum pump capable of handling such a volume exists. Therefore, as long as the condensable gas is connected to a condenser, there’s no need to use the calculations above (though condensable gas that cannot be condensed by the condenser still needs to be taken into account). I would appreciate any suggestions from everyone.
This requires adding a cooler at the outlet; otherwise, the negative pressure cannot be maintained.
The question is, if a cooler is added, how should the exhaust volume for the condensable gases be calculated?
First, condensation occurs; the condenser is involved in a phase change process. Then separation takes place, with the gas phase being in a saturated state. Of course, this is an ideal situation – in reality, a condenser cannot achieve complete condensation. Therefore, the vacuum pump needs to be sized to be larger, based on the calculated values.
The original poster’s analysis is correct – air is drawn out directly, and the amount of air drawn out is significant. Moreover, the poster failed to take into account the amount of non-condensable gases, as all vacuum containers have leaks; the amount of dry air that leaks out needs to be estimated based on the size of the container； When choosing to directly extract a large amount of potential gas, a liquid ejector or a two-stage steam ejector can be selected. Alternatively, a pre-cooler can be added; if a shell-and-tube condenser is used, to maintain a pressure of 9330 Pa, the inlet temperature of the cooling water must not exceed 30 degrees Celsius. The exhaust volume can be calculated based on the amount of dry air and the temperature and pressure of the cooled exhaust gas!
Thank you to everyone who replied above; I’ve basically figured out this issue now.
Are there any more detailed learning materials available?
Just starting out in the vacuum pump industry, learning *learning*: lol