Vol 105, No 5 (2016)

The processes in the world around involve losses, and the task of any engineer is to take them into account at the stage of a machine design. But the losses may be concealed coming into being in one process and showing quite in another one. Such losses are the losses in the compressors owing to a nonequilibrium regenerative heat exchange. In some constructions they may be completely absent but in the others they may occur and lead to reducing the compressor output or showing in a different way. Today the methods of the thermodynamic calculation of a compressor don’t include a direct calculation of losses due to a nonequilibrium regenerative heat exchange. The paper analyses the mechanism of losses that appear due to regenerative heat exchange during the process of a cyclic gas compression in the compressor; the method to calculate such losses is cited. It is based on the analytic solution of the problem of the nonstationary heat conductivity in a semibounded body at harmonic boundary conditions. As an example to use the method were calculated the losses due to nonequilibrium regenerative heat exchange in the PB100 refrigeration compressor, the losses share of the compressor consumed power was defined. Keywords: compressors; work losses from nonequilibrium regenerative heat exchange in the compressor; thermodynamic calculation of a compressor; entropy analysis

The results of studies of the effect of cyclical temperature fluctuations of the cooling medium -18, -12, -18 °C (mode A) and -18, -4, -18 °C (mode B) with the frequency of cycles 1, 3 and 7 on the dispersion of ice crystals during storage of ice cream, ranked in terms as of «highest dimensions» (Crystal Dimension CD) and the rate of drop dispersion. It is established that the CD for 6 months of storage increased after 1, 3 and 7 cycles of fluctuations of temperature in the mode A compared to the CD of the control samples of ice cream for the same storage period (47 µm), respectively, 15 µm (31%), 16 µm (33%) and 22 µm (46%), in the mode B - 30 µm (63%), 42 µm (88%) and 59 µm (124%). The data obtained indicate that in all samples of ice cream after cyclical fluctuations and subsequent storage for 6 months CD exceeded the threshold of sensory sensitivity (50 µm). The results correlate with the data that characterize the rate of reduction of dispersion in terms of “tangent of inclination angle of trend line”, determining a graphical relationship of the average CD of ice crystals and the duration of storage. Keywords: ice cream, ice crystals, the temperature of the cooling medium, the range and amplitude of the temperature fluctuations, the dispersion of the ice phase, recrystallization, shelf life