No 1 (2017)

The paper presents the results of the overview of literature data on the presence of calculation dependences that allow determining average heat transfer coefficients along the surface and local heat transfer coefficients at refrigerants boiling inside tubes. The calculation dependences to determine heat transfer coefficients at boiling inside tubes for different conditions of flow are cited. The calculations carried out and the comparison of calculated and experimental data resulted in the choice of the formulae for calculation of a heat transfer coefficient when a singlephase liquid flows inside tubes as well as for calculation of a heat transfer coefficient in the zone of a developed bubble boiling of a refrigerant in a large volume. The formulae allow calculating thermal characteristics of evaporators at refrigerants boiling inside tubes more accurately. The use of calculation dependences cited gives the possibility to reduce the time for searching and actualization of formulae that suit more for calculation of thermal characteristics of evaporators at refrigerants boiling inside tubes.

The paper examines an economic appropriateness of using systems of a heat pump hot water supply under Russian economic conditions. Also cost effectiveness of hot water generation using a boiling plant on natural gas was specified. A comparative analysis of technologies of hot water supply systems examined is given. It was defined in a calculated manner that full production costs of hot water generation (US dol./year) are equal for both technologies. A cost price of 1 gram calorie of heat for heating water using a heat pump is a little lower than using a boiling plant. But the payback time of a heat pump hot water supply system under Russian conditions is longer. It is shown that the system of hot water supply using a boiling plant provides a quick repayment and so is economically an effective trend.

The process of freezing influences deeply the product elements formation and their dispersibility at ice cream production. The shape and dimension of ice cream structural elements that are ice crystals and air bubbles depend greatly on freezing speed and mechanical impact on the product. The freezing speed increases significantly at the product freezing in a liquid nitrogen medium. The paper cites the results of experimental studies with respect to the estimation of the impact of the process of the quick freezing of liquids in a liquid nitrogen medium on dispersibility of structural elements and organoleptic indices of ice cream. Also a comparative estimation of qualitative indices of ice cream produced at mixtures freezing in the liquid nitrogen medium and in the freezer was carried out. It was defined that the freezing of the mixture for ice cream led to the formation of small ice crystals that couldn’t be felt by sense organs. The possibility to produce frozen desserts in the liquid nitrogen medium as well as using mixtures for fullcream ice without food additives - stabilizers of structure and consistence was justified.