Compressed Air/Water in Pressure Vessel

1. Generally you can expect water to condense in the vessel. There are too many variables to work out specific amounts. Like the humidity of the air that's compressed which changes from day to day. The temperature of the air that day as it's felt on the walls of the tank. The rate of air flow thru the tank.

2. Some of those same variables would determine the condensate temperature.

3. The air dew point is continuously dropping until the heat of compression is dissipated. So the dew point in the tank would be less. That is unless there is a refrigerated dryer used and where its placed in the system.

As "ozzb" stated, the amount of water entering the system will depend on the temperature and humidity of the intake air. However, in the reciever, the air and condensed water will be in equilibrium. As long as there is any amount of condensate in the tank, the air and water will be at the same temperature and the air will be saturated, 100% RH. If the air tank is cooled, more water will condense, if the tank becomes warmer, more condensate will evaporate, but the air will remain saturated.

That is how a refrigated air dryer works. The air is cooled to just above the freezing point of water, and the condensate is seperated from the air. The air will be saturated at the chiller temperature, but because the condensate has been removed, the dewpoint of the air will remain at the chiller temperature as the air warm up to room temperature. As long as the air temperature remains above this dew point, no water can condense.

I apologise for any misspellings, the spell check funcction dosn't seem to be working today.

1- Water will always condense inside an air receiver tank as long as the inlet air relative humidity is high enough. To work out this level, you need to know how to use a psychometric chart or at least follow a course on air and gas behaviour...

In short: Air can absorbe water from the environment up to a saturation point which is 100% relative humidity (RH 100%). That is if enough water is available to allow it to reach that point(in g/m3 of water in the air). If the air is cooled at the same temperature, this RH100% point will change in terms of how much water in weight (g/m3) is required to saturate the air. Therefore, the excess water in term of g/m3 will need to be shed and will condense in droplet etc.

in your case, the answer will need a lot of data at the different points you mentioned and to give a formula will be complicated. The best way is to define the status of the air at each stage, in terms of temperature, pressure and RH%. Referring back to the Psychometric chart will the help you answer the different questions you put.

A1: it depends upon the temperature and humidity of the air coming in and the temperature and pressure to which it is compressed.

A2. At equilibrium, yes, they will be the same.

A3. The dewpoint after a cooler will be the same as the cooled air temperature, assuming 100% RH.

.-If you agree I will try to make some explanations

a) In the exit of the compressor the air go by an intercooler of heat and it cools down to a temperature that depends on the cooler type, and it can be of around 20 to 35 centigrade Grades
b) In entering the air to the Tank or accumulator of air, the conditions of the air will be absolutely of 100% of humidity and when entering in area of low speed or it calm down and of low temperature, you to precipitate the water surplus
b) to Remember that the air will be to 100% in the whole pipe and in all moment, it will be considered a slope after the Tank and drainage the water, except if a dryer exists
c) they Remember that humidity in the suction can be from 40 to 90% and it can have a quantity of water from 15 to 28 g/m3, but when it is to compress it to 7 bar the conditions the Dowpoit they change it is another for what will condense the surplus of water

Greetings to all

Alberto

Air leaving a compressor with after-cooler will likely be about 45-50C, saturated.

Assuming that the storage tank is cooler than that, water will condense. You can calculate approx. how much with a Psych chart- looking at water content at 45C saturated and at tank temp, saturated.

As stated earlier, condensate and air in tank will be same temp (which also means that air is still saturated (100% RH) but at lower temp and with less water.

Dew point after cooler is about 45C, dew point in tank is tank temp.

Although not asked- assuming that temperatures of distribution pipes is at least same or cooler than tank, water will still come out. Even if pipe temps are higher, as soon as the air pressure is released, the air-borne moisture will start to be released due to air cooling from expansion and released pressure on water vapor.

To avoid this, either a refrigerated dryer OR a desiccant dryer should be located after the storage tank.

Dear powerengine, Is this the same system as in an earlier thread of yours.... You want to start a diesel engine with compressed air? Consider the tank as a good collection point to drain the condensate (oily water is a slip trip hazard) there are many different types of automated drain systems, some with timers or mechanical means. You might want to include a manual drain connection too. Utilize a inline filter drier as the last point to keep the system dry and protect the starter. I suppose freezing pipe wont come in to play in your application. If i'm understanding your situation "sizing drainage" it will be determined by standard pipe and capacity will be satisfied by the valve selection. if this needs to be a reliable system include it in a daily check list for operating personal. below is a good link for more information. http://www1.eere.energy.gov/industry/bestpractices/pdfs/compressed_air_sourcebook.pdf Hope this helps