Using a T type probe, the effect of the interstitial material (interposer) on the thermal contact resistance of a junction has been estimated by measuring an individual carbon fiber with different interposers, including the solidified metallic powder, lubricant grease, and dry contact as a comparison. For the metallic powder, the thermal contact conductance was obtained to be 3.0 M W m−2 K−1 by changing the fiber length when the same contact between the fiber and the hot wire was maintained. However, this method can only be applicable to the solidified contact, and the stability of the operating temperature is a must in each length measurement. To estimate the thermal contact resistance of the lubricant Apiezon N grease, even a dry contact, an improved T type probe was employed, by applying an alternative current to the hot wire. This method was verified by measuring the same type of carbon fiber in the frequency range of 0.1 to 1Hz based on a Labview-based virtual lock-in measurement system. The same value of the thermal effusivity of the test fiber was obtained with different interposers, and the thermal contact conductances for the dry contact and high vacuum grease were found to be 0.10 M W m−2 K−1 and 0.26 M W m−2 K−1, respectively.
Study of metallic powder flow in discrete coaxial nozzles
