3-D Numerical Study of the Effect of Thermocouple Normal Distance Location on the Steady State Surface Temperature of a Cylindrical Test Section

A 3-D thermal finite element analysis (FEA) was performed through ANSYS on a cylindrical test section. The model included 4 holes parallel to the top flat surface of the cylinder, each at different radial depths. The holes represented thermocouple locations that can be used to measure the radial surface temperature distribution of the test section.

The top of the test section was modeled with a constant convective boundary condition of 6000 W/m²-K while the bottom surface had a uniform heat flux boundary condition of 100 W/cm² . All other surfaces were insulated. Other Dimensions: D= 27.64 mm, DT =1.6 mm, H=32 mm

The objective was to find the minimum distance from the surface to the thermocouple holes (L) that would eliminate the effect of the thermocouple presence on the top surface temperature distribution. To ensure that top surface temperature variations are not caused by the thermocouples, the thermocouples should be located at a distance below the surface (L) that results in top surface isothermal conditions when exposed to a constant convective heat transfer coefficient.

Results show that for stainless steal, the thermocouples should be located at a distance greater than L=12DT for the thermocouples not to significantly interfere with the top surface temperature distribution

One way of keeping the thermocouples closer to the surface without interfering with the surface temperature distribution is to make the test section out of a higher thermal conductivity material. Results show that as the thermal conductivity of the material increases,the surface temperature distribution is less affected by the presence of the thermocouples.