The efficiency of two cold supply systems (CSS) of a shop is compared: one operating on single stage cycle and the other with economizer. The comparison was done by the degree of the thermodynamic efficiency of refrigerating systems using the entropy and statistical method of the thermodynamic analysis. The dependences of the system operating parameters depending on time were used as the initial data. The dependences were obtained from the standard monitoring systems then averaged. The cycles corresponding to the operation of refrigerating systems compared and the formulae to calculate the minimal needed work to compensate the entropy generation in the elements of a refrigeration machine are cited. The results of the analysis showed that the degree of the thermodynamic efficiency of the system with economizer was higher than that of the system with single stage cycle. The use of a scroll compressor with economizer in the CSS saves the energy in comparison with the piston compressor; also the use of new generation scroll compressors with economizer will allow decreasing the capital costs of an aggregate. Keywords: entropy and statistical method of the thermodynamic analysis; singl stage refrigeration cycle; refrigeration cycle with economizer; cold supply system for a shop.
The urgency of the problem is linked with the increase of the world need in fresh water and plants for its production. The most widespread are membrane (reverseosmotic) and distillation methods of desalination. The authors examined the last cited method based on the water phase transformation. A mathematical model of a nonstationary heat and mass exchange process of a singlestage vacuum distillation plant that allows analyzing in detail the factors influencing the operation of such systems as well as optimizing the regimes and operation parameters and calculating the time of acceleration is offered in the paper. A diagram of a singlestage evaporator desalination installation operating according to a flow chart with mechanical vapour compression based on the fast roots vacuum pump is offered. The heat transfer regimes are estimated and the coefficients of heat transfer under water vapor evacuation are calculated. The authors examined the question concerning the necessity to confirm experimentally the mathematical model offered. Keywords: desalination, distillation, heat pump, vacuum heat pump water distillers, mechanical vapour compression, roots vacuum pump.
The paper cites the results of analytical and experimental studies relating to the estimation of the impact of the fat phase in ice cream on its consistence directly as a dispersed phase as well as a structurizing barrier on air bubbles in the agglomerated form after freezing that defines stability and dispersion of these structural elements. It is shown that the increase of the homogenization pressure by 25% contributes to the consistence improving due to the increase of the mixture viscosity 1,5 times and the 40% increase of the number of air bubbles sized less than 50 mm. When conducting microscopic studies of the ice cream air phase dispersion a direct participation of fat particles in stabilization of the air phase was confirmed by the presence of the accumulation of agglomerated fat particles in the air bubbles zone and fat particles aggregates after the air phase diffusion from the product. When choosing fats for ice cream it is recommended to take into account their qualitative and quantitative composition defining the capability of fats to transit to a solid state at the mixture maturation and to be adsorbed on the air bubbles surface when freezing the mixture in an agglomerated state. The interconnection of the agglomerated fat quantity in ice cream and its thermo and shape stability is justified. Keywords: fat phase dispersion; consistence; agglomerated fat particles; thermo and shape stability of ice cream.