tkunke
Mechanical
- Jul 9, 2012
- 4
Hello all,
I'm attempting to experimentally calculate the evaporative heat transfer from a series of parallel microchannels machined into a piece of copper. The test section is supplied heat by means of four cartridge heaters installed into the base, and thermocouples are instrumented along the height up to the microchannel surface. Using LabView, I am acquiring data and exporting to an excel template which automatically calculates the heat flux based on an energy balance of a control volume consisting of the top surface of the microchannels.
This heat transfer calculation takes into account the heat flux supplied to the bottom of the control volume, as well as the change in internal energy over Δt, or 0.001s. I am using 20 gauge wire type thermocouples which are inserted directly into the holes drilled into the side of the test section, bonded using Omegabond 101 thermal epoxy. These thermocouples have an associated uncertainty of ±0.5°C.
For the most part, the thermocouple sets display constant temperature readings within 0.5°C horizontally (i.e., I use 5 thermocouples at a location below the set of thermocouples directly placed under the microchannels), with one exception. One of the thermocouples reads appx. 1.2°C lower of temperature (64°C vs. 65.2°C) at steady state temperature.
My question is, is it possible that this is due to an air bubble surrounding the thermocouple in the epoxy, causing poor thermal conductivity and thus a nominally lower temperature readout? Or would such a scenario not result in this temperature differential, in which case I would likely point to the general uncertainty as the problem. I am dealing with single droplet evaporation, and as such this large differential among temperature readings is problematic. Any advice or discourse is greatly appreciated. I would be happy to supply whatever resources y'all might need in order to get a better understanding of the problem. Thank you!
Taylor
I'm attempting to experimentally calculate the evaporative heat transfer from a series of parallel microchannels machined into a piece of copper. The test section is supplied heat by means of four cartridge heaters installed into the base, and thermocouples are instrumented along the height up to the microchannel surface. Using LabView, I am acquiring data and exporting to an excel template which automatically calculates the heat flux based on an energy balance of a control volume consisting of the top surface of the microchannels.
This heat transfer calculation takes into account the heat flux supplied to the bottom of the control volume, as well as the change in internal energy over Δt, or 0.001s. I am using 20 gauge wire type thermocouples which are inserted directly into the holes drilled into the side of the test section, bonded using Omegabond 101 thermal epoxy. These thermocouples have an associated uncertainty of ±0.5°C.
For the most part, the thermocouple sets display constant temperature readings within 0.5°C horizontally (i.e., I use 5 thermocouples at a location below the set of thermocouples directly placed under the microchannels), with one exception. One of the thermocouples reads appx. 1.2°C lower of temperature (64°C vs. 65.2°C) at steady state temperature.
My question is, is it possible that this is due to an air bubble surrounding the thermocouple in the epoxy, causing poor thermal conductivity and thus a nominally lower temperature readout? Or would such a scenario not result in this temperature differential, in which case I would likely point to the general uncertainty as the problem. I am dealing with single droplet evaporation, and as such this large differential among temperature readings is problematic. Any advice or discourse is greatly appreciated. I would be happy to supply whatever resources y'all might need in order to get a better understanding of the problem. Thank you!
Taylor