Papers by Author: G. Polupan

Abstract: Experimental research results of the operational parameter effect on Thermal Contact Resistance (TCR) in a copper-aluminum L-type finned tube are presented. The investigated operational parameters were the maximum operational temperature and the number of repeated heating-cooling cycles. The TCR was experimentally determined by measuring the total heat supply, core tube wall and inner fin surface temperatures for steady-state and natural-convection conditions. In addition, the specimen was tested through up to 200 heating-cooling cycles. The experimental results showed a TCR increase of 81% at the same time as the average temperature difference between the hot inner flow and cooling air increased from 30°C to 130°C; over the maximum operational temperature (120°C), the TCR increased faster than before; and, after the heating-cooling cycle testing the TCR presented an increase of 31% in respect with the initial value. Such findings may be useful as a reference for preliminary thermal design and as recommendations for optimal operation of heat exchangers based on copper-aluminum L-type finned tubes.

Abstract: This paper presents the results of PL spectrum studies for Si nano-crystallites embedded in amorphous silicon matrix. Investigated layers were deposited by the hot-wire CVD method on glass substrates at the wafer temperature 300°C and different filament temperatures from the range 1650-1950°C. It was shown that variation of temperatures of filament (hot-wire) allows to produce the films with desirable parameters. Using of X-ray diffraction and photoluminescence methods the correlation between some photoluminescence bands and the sizes of Si nano-crystallites as well as the amorphous phase volume was shown. The nature of light emission is discussed.