A Measurement of Mixing-Cup Temperature

Abstract

The accuracy of measurement of mixing-cup temperature is discussed for a cylindrical mixing chamber in which specially designed baffle plates are inserted. The temperatures measured by the chambers at the inlet and outlet of an electrically heated vertical tube are compared with those predicted by heat balance. The flow pattern in the mixing chamber is observed by the hydrogen bubble method. Pressure loss is also measured. For the accurate measurement, two baffle plates are sufficient in the laminar flow region when the distance between them is relatively large, while no baffle plate is necessary in the turbulent flow region. In the laminar-turbulent transition region (R_e=2 000∼3 000), temperature fluctuations at the heated tube wall as well as at the outlet of the mixing chamber are outstanding in comparison with those in laminar and turbulent regions. It is clarified, by simple analysis using a lumped-heat-capacity model, that the temperature fluctuations at the transition region are due to a combined effect of both laminar-turbulent flow intermittency and heat capacity of the heated tube.