Seeking to maintain a steam condensation vacuum of about 0.06Bar

[sanka]

Just looking for a bit of advice on a problem I am currently having.

I am doing some research into the condensation characteristics of steam when under vacuum. However, I am having difficulty maintaing the desired level of vacuum of around 0.06Bar in my current system. Anytime I achieve the vacuum, the pressure begins to rise, as air is leaking into the system.

I believe it is an issue with my current set-up, which is a scaled - down version of a steam & condensate loop. This loop is 1/2" in diameter and consists of a seperator, a series of valves, condensate tank and instrumentation for measuring pressure & temperature. It is assembled using standard plumbing materials such a barell nipples, T-pieces, which are all threaded. I initially thought these fittings would be adequate be it seems they are prone to leakages when under vacuum.

In short, I need a steam & condensate loop that can provide steam to the heat exchanger at the desired pressure of 0.06Bar. I want to be able to maintain this pressure without the need for a vacuum pump to continually displace the air leaking in (So I need a system that will not leak under a vacumm of 0.06Bar). I would be grateful for any suggestions regarding my current set-up or if I need to look into an alternative design such as Swakelok, etc?

Thanks in advance!

 

[Mech_Engineer]

I think you're going to have to build a proper vacuum system with vacuum grade hardware. Take a look at companies like MDC to find vacuum hardware that can be bought for such a task, things like cleanliness and seals are very important for vacuum systems.

Also, what are you doing to control the temperature of your system?

 

[sanka]

Thanks for the advice. So it is possible to achieve and mantain a pressure of 0.06Bar as long as the system is adequately designed and built?

In my system, I have an air-cooled heat exchanger (basically a finned tube with a bank of fans). By varying the speed of these fans, the steam saturation temperature (and hence, pressure) will vary accordingly. By increasing the fan speed (thereby increasing air-side heat transfer coefficient), the saturation temperature of the steam decreases. By decreasing fan speed, the temperature increases. This allows me to control the tempeature and pressure in the system.

 

[Mech_Engineer]

Thanks for the advice. So it is possible to achieve and mantain a pressure of 0.06Bar as long as the system is adequately designed and built?

Systems can be built that maintain 10^-6 Torr for weeks or even months at a time, maintaining .06 Bar (45 torr) is definitely possible given the correct equipment. Remember though that in a closed system changes in temperature will also result in pressure changes; if you're looking for a constant-pressure system with variable temperature, you'll have to utilize some sort of active pressure control system.