Achieving Uniform Temp of 600F on a Metal Chamber w/ 3 Thermocouples

[anolan23]

A flanged immersion heater is used to heat sand blast beads contained in a 400in^3 skinny cylindrical vessel (D=4"NPT, L=0.82m). My goal is to achieve a uniform temperature of 600F on the outside of the metal chamber. We used three thermocouples. One near the top portion on the outside of the chamber, one in the middle, and one on the bottom. Testing with this setup yielded the following results. The top thermocouple was hooked up to a temperature control that was set to 600F.

Top Thermocouple- 600F
Middle Thermocouple- 856F
Bottom Thermocouple- 497F

How can I make these temperatures more evenly distributed to 600F? Any suggestions?

NOTE: The immersion heater elements are a little shorter than the vessel that surrounds it.

 

[anolan23]

I'm thinking I can set the temperature control on the bottom thermocouple and then insulate the top and middle portions of the heating element. I am assuming the temperatures aren't uniform due to the heating element. Ya think?