SIMPLE MATHEMATICAL-MODEL FOR PREDICTING THE TRANSIENT-BEHAVIOR OF ANICE-BANK SYSTEM

The time-variable performance of a Refrigerant 22 ice-bank system was simulated by a dynamic model which was derived by assuming that heat t ransfer was always the limiting process, and which thus ignored hydrod ynamic processes. The model comprised four ordinary differential equat ions describing the position of the ice front, the water temperature, and the refrigerant evaporation and condensation temperatures, each of which was derived by energy balance, plus a number of algebraic equat ions. Measured plant performance was accurately predicted except immed iately after start-up, and in circumstances in which the assumption th at the dynamics of refrigerant flow did not exert any controlling infl uence on the overall process dynamics was inadequate (for example, whe n the thermostastic expansion valve operation becomes unstable). The m odel requires only data that should be readily available or can be eas ily estimated, and thus it is suitable for analyses in the design of i ce bank systems to handle time-varying conditions. Simple dynamic mode ls ignoring hydrodynamics can be adequate in circumstances where the m ain source of variation arises beyond the refrigeration circuit itself .