DETERMINING THE HEAT-TRANSFER COEFFICIENTS OF THE FRAMES OF ELECTRICAL MACHINES SELF-COOLED IN PARTIAL VACUUM,
Abstract
The results are reported of an experimental investigation of heat transfer from horizontally and vertically oriented electric machines in a large vacuum chamber under all possible conditions (viscosity, molecular viscosity, and molecular) of free motion of air. Pressures from 10 minus super 5 to 760 torr were created in a vacuum chamber whose relative size permitted simulating infinite space heat exchange conditions. Four electric machine frame simulators having diameters of 40,80,100, and 140 mm were tested. The relations found from the above experiments generally corroborate the well known theory of heat exchange in vacuum. Thus, a serious reduction in the heat transfer within the 0.6 to 760 torr range can be explained by the decreasing convection; a constant heat transfer in the 0.1 to 0.7 torr range is due to the approaching of thermal conduction conditions. A heat transfer reduction at pressures under 0.1 torr can be explained by a boundary layer effect, viz., a temperature step that characterizes molecular viscosity conditions. In the molecular range the heat conductance was proportional to the pressure; no such relation was observed in the experiments because of the blackness of the machine simulators. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Feb 26, 1970
- Accession Number
- AD0704003
Entities
People
- M. N. Ulyanitskii
Organizations
- National Air and Space Intelligence Center