The article analyzes the changes in requirements for oxide emissions resulted from fuel combustion in accordance with the International Convention for the Prevention of Pollution from Ships MARPOL 73/78. The problem of improving the energy efficiency of large-capacity gas tankers is studied by using different types of marine fuel. An energy audit was carried out on board a gas carrier with deadweight of 54,354 tons and propulsion system power of 12,400 kW. The energy audit relied on data of six voyages of a gas-carrier from July 14, 2016 to January 19, 2017. The Energy Efficiency Operational Index defined as carbon dioxide emissions per ton-mile of cargo movement, was used as a tool for assessing the energy efficiency of the ship. The research included the methods of comparative analysis of fuel change during the voyages. The comparative analysis was applied to calculate changes of consuming fuels with different lower caloric value. There have been given general characteristics of heavy fuel RMG 380 and diesel fuel DMA. Values of all parameters for analysis of operational coefficient of power efficiency were taken from the engineer’s log, cargo record book and oil record book, as well as from energy efficiency operation indicator reports of the company after each voyage. Based on the results of the assessment, the conclusions were drawn and perspectives were developed concerning the use of marine fuels and modification of the ship power plant. It has been inferred that using liquefied natural gas as main fuel increases power and economic efficiency of a ship and meets new requirements of MARPOL 73/78 to 2020 on sulfur content in fuel. The conducted research and preliminary calculations make it possible to predict an increase in the economic efficiency of a large-tonnage fleet while maintaining a high environmental friendliness.

The article presents the comparison of the head losses under the boiling refrigerant flow in horizontal and vertical evaporators. The values of all the components of the hydraulic resistance, such as the friction losses, local resistance, flow acceleration and leveling head have been calculated, compared and analyzed. Graphic dependences of the pressure loss of the two-phase flow on the mixture density and the apparatus height, as well as the effect of hydraulic resistances on the changes in boiling temperature have been obtained. It has been stated that studying the effectiveness of vertical evaporators comprises two main components: defining heat transfer and hydraulic resistance in the course of working fluids boiling in the vertical pipes. The second part of the study is under consideration. Vertical evaporators are higher than horizontal ones, which leads to greater losses when overcoming the leveling head of a larger column of a two-phase flow. Other components of the hydraulic resistance in the horizontal and vertical apparatus are comparable, although the friction losses and local resistance losses in the vertical evaporators may be less. In a vertical apparatus the main losses appear due to overcoming the leveling head, the remaining losses are smaller than in the horizontal apparatus. Therefore, when designing vertical apparatuses, one must not use the ratio of the apparatus length to its diameter, which is recommended for the horizontal apparatuses (L/d ratio for horizontal and vertical is 6). The ratio for the vertical apparatus should be significantly less. The experiments performed on the air-water model proved that L/d ratio of vertical evaporators should be within 1.0 ÷ 2. More precise values of this parameter can be found after testing R410A refrigerant.

The paper describes small-capacity irrigation evaporators that improve the performance of a refrigeration unit, as they exclude the release of liquid freon into the compressor suction pipe under sharp increasing of heat load or during ship rolling. The relevance of studying heat transfer at freons boiling in a moving film has been proved. The results and analysis of experimental data on average heat transfer coefficients are presented. The graph shows the dependence of the average heat transfer coefficients on the heat flux density at various irrigation densities. There are presented the results of special experiments determining the effect of irrigation density on heat transfer. It has been stated that the effect of pressure or saturation temperature in the modes of evaporation and developed boiling manifests itself in different ways. With developed boiling, the beam pitch does not have a significant effect on heat transfer. The experiments were carried out on two stands: small-row and multi-row. The pipes were heated with an internal electric heater. It has been inferred that heat transfer in the film is more intense than in volume, therefore, smooth steel pipes can be used in irrigation evaporators instead of finned copper tubes, which are used in flooded devices. The boiling process in a film can be described by equations valid for a large volume, taking into account quantitative differences. The values of a constant coefficient and the criteria exponents are given; the similarity equation for the regime of developed bubble boiling of freons is derived. The calculated dependencies can be applied in evaluating the operation of irrigation evaporators of ship refrigeration units.

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The article represents the advantages and disadvantages of refrigeration machines operating on non-azeotropic refrigerant mixtures. There has been illustrated their specific feature in comparison with pure substances: they are non-isothermal during phase transitions. It can be effective when cooling or heating flows that significantly change the temperature, and ineffective when working with volumes, where it is necessary to maintain a constant temperature. In the first case there takes place a decrease in the internal irreversibility of heat transfer processes in evaporators and condensers; in the second case - an increase. When using mixed refrigerants, it is possible to simultaneously obtain several temperature levels in a single-stage machine at the same pressure in the evaporators, they can obtain low boiling points of the refrigerant without vacuum in the evaporator and regulate the refrigeration capacity of the machine by changing the composition of the mixture. The prospects of using mixtures of working bodies of refrigerating machines have been proved. The diagrams T-S, T-ξ, i-ξ are presented allowing to calculate the cycle of the machine, to determine its operating parameters and to calculate the technical and energy characteristics. The developed thermal diagrams make it possible to accurately examine the dynamics of the boiling and condensation processes of a binary mixture, show the change in the concentration of the mixture in the vapor and liquid phases and make it possible to construct and calculate the cycle of a refrigeration machine operating on a mixed refrigerant. Examples of constructing cycles of two schemes of refrigeration machines operating on a mixed refrigerant are considered: with separation of the working substance flow and without separation. Methods for calculating the cycle are provided