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

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.