Detailed multiphysics modeling and validation of thermocouple readings in fires

Abstract

Detailed CFD models of mineral-insulated metal-sheathed (MIMS) thermocouples are discussed and thermocouple readings in fire environment are validated against experimental thermocouple data for a Hencken burner flame. Thermocouple readings are presented as functions of equivalence ratio, thermocouple diameter, thermocouple orientation, position of the junction, depth of insertion into fire, and sheath surface emissivity. Effects of surface oxidation, sheath diameter, and insertion depth on thermocouple response time are analyzed in detail. Computational results are compared with published experimental data. Overall, predictions showed excellent agreement with experimental data. Small deviations occurred in the case of insertion depths due to axial heat losses.

A CFD study on the reacting flow of partially combusting hot coke oven gas in a bench-scale reformer

“…To compensate for this effect, radiative heat transfer towards the thermowell was also included in the CFD model. During the HCOG reforming by partial oxidation, carbon species may be deposited on the surface of the thermowell [47,48]. This may lead to a difference in the predicted and measured temperatures due to radiation effects.…”

Evaluation of a new device for simultaneous measurement of heat flux and gas velocity in a diffusion flame

“…This relationship is based on measurements for similar alloys, at similar states of surface oxidation. 6,7 Inlet temperature was fixed at 1100 K (thermocouple measured free-stream temperature) and k-epsilon turbulence model was used. Turbulent kinetic energy and turbulent dissipation were changed based on the inlet velocity which was varied until experimental pressure data were in reasonable agreement with computational results.…”

Effect of thermocouple insertion depth in multiple directions on temperature measurements

“…As shown in Table 2, surface emissivity changes as a function of temperature, due to surface oxidation. 5 The model uses k-epsilon turbulence, two-layer all y + wall treatment, and Reynolds-Averaged Navier-Stokes (RANS) in the gas phase and includes thermal radiation and convection at the sheath surface and conduction through solids. It is assumed that air and methane are perfectly mixed before entering the computational domain.…”

“…The virtual thermocouple model in Vulcan and experimental validation based on well-established flame experiments, using a Hencken burner, various sizes of thermocouples, and Coherent Anti-Stokes Raman Spectroscopy (CARS), are discussed in detail for MIMS thermocouples. 3,4 To supplement these earlier research investigations, detailed multiphysics modeling 5 was performed using a commercial code STAR-CCM + . 6 Although Vulcan and STAR-CCM + have similar physical modeling capabilities, the commercial code has more versatile meshing capabilities, which is an advantage when complex, multiregion grids are needed.…”

“…As discussed in the study in Ref. 5,5 thermocouple readings are presented as a function of equivalence ratio, thermocouple diameter, thermocouple orientation, position of the junction, depth of insertion into fire, and sheath surface emissivity. Effects of surface oxidation, sheath diameter, and insertion depth on thermocouple response time are analyzed in detail.…”