The effect of a thermal mass on the performance of a T3.0 system

Thursday, May 14 2020

How an 87 pound aluminum load affected the ramp rates and liquid nitrogen usage in a T3.0 system

It is not unusual for the Customer Solutions Group to field questions from customers or prospective customers concerning the effect of a thermal mass on the performance of the Qualmark systems. Recently I was asked to demonstrate the thermal ramp rate of the Qualmark T3.0 system with an 87 pound aluminum load, using a specific thermal profile. I thought that the results, along with a comparison of liquid nitrogen usage with and without the load, would be of interest so I am presenting them here.

The thermal profile consisted of three cycles from -50°C to +175°C, with a programmed ramp rate of 60°C per minute and 5.75 minute dwells at each extreme. After logging data while running the desired profile in an empty chamber, I went through my fixturing and collected 87 pounds of aluminum sheets and extrusions, which I placed in the chamber so there was good air circulation through the load. The photo above shows the setup. After running the same profile with the load I was able to nicely compare the cold and hot thermal ramp rates as well as the liquid nitrogen usage with and with the load.

The graph below shows the product response, as measured on a plate near the center of the table, with and without the thermal load. As you can see, the cold ramp rate matched the programmed rate of 60°C/minute regardless of the load. Liquid nitrogen is an aggressive coolant! On the hot ramps, the load made a difference. Calculations show that the 87 pound load reduced the maximum ramp rate to about 38°C/minute.

The effect of the load on liquid nitrogen usage was not significant. This was what I expected. The thermal mass of the chamber interior and the vibration table has the most effect on utility usage. For the profile described above, an empty chamber used 41.35 gallons, while the chamber with the load used 49.12 gallons – about a 16% increase. Given that this load is much greater than the typical product load in a HALT, the mass of the product won’t have much effect on the utility usage of the system.

If you are wondering how the mass of your product might affect your HALT work, the snapshot of data given here can help. If you need more information, please don’t hesitate to contact the ESPEC Customer Solutions Group.

And remember – if it isn’t broken, you’re not done yet!

Neill Doertenbach

ESPEC Customer Solutions Engineer