METHODOLOGY OF MODEL SUBSTANTIATION FOR ANALYSIS OF OPERATION OF A TWO-STAGE SHIP REFRIGERATION UNIT IN NON-STATIONARY MODES

Abstract

The aim of the work is to develop a methodology for justifying the choice of a model for analyzing the operation of a two-stage ship refrigeration unit in non-stationary modes. This goal is  achieved by determining the equations for the cooling capacity at non-stationary modes, namely theequations of energy and material balances for heat exchangers. The expression for the enthalpy of the entire mass of refrigerant is considered. An expression for the formal representation of heat removed in or supplied to the apparatus of a two-stage ship refrigeration unit is proposed. The most important result of the research is a methodology for justifying the choice of a model for analyzing the operation of a two-stage ship refrigeration unit in non-stationary modes. Structurally, the proposed methodology consists of five stages. At the first stage, the mass of liquid and vaporous refrigerant in the condenser is determined by the thickness of the film and the density of the condensate according to the Nusselt formula. In the second step, the amount of heat dissipated from the condenser is determined by the heat balance of the cooling water. At the third stage, based on the results of determining the flow rate of the refrigerant at the outlet of the condenser, the mass of the vapor is calculated based on the ratios based on the calculation of the characteristics of the intermediate capacitance. In the fourth step, the refrigerant flow calculations are converted by determining the flow rate of the tanks entering the compressor from the two evaporation systems. At the final fifth stage, the cooling capacity of the two evaporation systems in a non-stationary mode is directly determined. Thus, the proposed methodology makes it possible to determine the possibility of using a particular model to analyze the operation of a ship refrigeration unit by considering the work processes of a ship refrigeration unit in non-stationary modes. It is determined that the combined use of a static model to determine the field of stationary or quasi-stationary modes and a linearized dynamic model allows obtaining a method for calculating the dynamic characteristics of components that is accessible for engineering calculations and gives results with a sufficiently high accuracy.