Wall to Bed Heat Transfer Coefficient
 

I am trying to monitor the transient wall to bed heat transfer coefficient in a fluidized bed using a formula defined in the custom field calculator as
h= (gas volume fraction*gas thermal conductivity* gas temp gradient+ solid volume fraction*solid thermal conductivity* solid temp gradient)/( Wall temp-Bed temp)
However my problem is accessing the temperature gradients in the custom field calculator. I have tried using the /solve/set/expert function and answering yes to the keep temporary solver memory from being freed as suggested in some of the posts on the forum. However I get the following error


Error:
FLUENT received fatal signal (ACCESS_VIOLATION)
1. Note exact events leading to error.
2. Save case/data under new name.
3. Exit program and restart to continue.
4. Report error to your distributor.
Error Object: #f
when I try to access the temperature gradients. How do I overcome this problem?