Heat Leaks – Value Vs Cost

Heat Leaks – Value Vs Cost

Value vs. Cost of Heat Leak

Due  to  the  extreme  temperature  difference  between  liquid  nitrogen  and ambient  air,  a  large  amount  of  heat will  transfer  even  through  a  very  short section  of  uninsulated or  poorly-insulated pipe  component  very  quickly. This can have a substantial impact on the entire system.

Even though the loss is not immediately visible nor is it significant for one day, but over time that loss can add up to thousands of dollars. Increased heat leak at any point in the system can cause two-phase fluid that increases pressure drop, causing irregular flow of liquid, which reduces the overall flow rate. Two- phase  flow  will  create  significantly higher  pressure  drops  through  the  pipe system,  irregular  liquid  delivery,  results  in  warmer  liquid  at  the  cryogen use point  and  shortens  the  life  of  valve  seats  and  other  components  within  the system.

Case Study 1:

Consider a food production company that utilizes a 30-meter (100-foot) run of vacuum jacketed pipe (VJP), along with a 0.5-meter (2-foot) connection of foam-insulated pipe. 

For the VJP with a diameter of 1.0 inch, the typical heat transfer rate is approximately 0.5W/m (0.52 BTU/hr/ft). Thus, the total heat leak for the 30-meter run of VJP can be calculated as 30 x 0.5 = 15W (52 BTU/hr). 

On the other hand, for the foam-insulated copper pipe, the typical heat transfer rate is around 20W/m (20 BTU/hr/ft). Consequently, the heat leak for the 2-foot section of foam-insulated copper pipe can be determined as 0.5 x 20 = 10W (40 BTU/hr).


The 0.5m(2-foot) section of foam insulated copper pipe is responsible for 40% of the total heat transferred into the pipe.

Total heat leak for the 30m run of fully vacuum insulated pipe is 15W. 

The heat leak for the 30m VJP system plus the 0.5m foam insulated copper pipe is 25W, which translated to 0.56L per hour of liquid nitrogen loss.

Case study 2:

A semiconductor plant is currently undertaking a project involving a 100meters (300ft) of 1.5″NB piping system to supply liquid nitrogen to six units of HALT/HASS equipment. They have received two quotations: one for a copper piping system with 3″ PU insulation priced at $40,000.00, and another for an SS304L vacuum insulated piping system priced at $160,000.00.

To conduct a ROI (Return on Investment) analysis, the project engineer needs to estimate the heat leaks and LN2 loss for both systems. The analysis is based on the assumption that the cost of LN2 will average $0.50 per Liter over the next ten years. The results of the analysis are presented below.