We use liquid nitrogen at our power station to freeze light and heavy water in piping. The ice plug formed within the piping acts as a “valve” and allows us to work on a section of the piping system that otherwise cannot be isolated. The liquid nitrogen enters a jacket that surrounds the piping. The LN2 arrives at atmospheric pressure and boils off in the vented jacket.

I have a tanker supplying LN2 at approximately 70 psig. It is sent through 200 feet of 1-1/2″ diameter hoses that are insulated with 1 inch of foam insulation. The second leg is 150ft of 1/2″ hoses which are similarly insulated. We are finding that only gaseous nitrogen arrives at the end of the 350 ft journey. Separately, i.e. in 150 ft of 1/2″ hose or 200 ft of 1-1/2″ hose, we are successful in sending LN2 to end of hose.

We suspect too much heat leak over the distance traversed. Which leg of hose should be replaced with vacuum jacketed hoses to minimize the heat leakage, the 200ft length or the 150 ft length? Hints as to how to calculate this would be appreciated.

Thanks for your assistance,
Jean Salopek P. Eng., Ontario Power Generation