Modelling thermostatic expansion valves

• A general purpose theoretical model of a thermostatic expansion valve is described and evaluated.
• Results are in good agreement when the model is tested against current standards and manufacturer's data.
• The model can be applied easily to different types of thermostatic expansion valve.
• Examples are provided of the model's use in the study of refrigerator operating faults such as hunting.

This paper describes and evaluates the development of generalised steady state and transient mathematical models for thermostatic expansion valves (TEVs) of the types used in commercial refrigeration systems. The model is of a generalised nature, because it is not necessary to input performance or geometrical data for a particular valve to operate the model. However, if required, the models can provide an accurate correlation of valve manufacturer's data. Derivations are provided and validating data is presented. The mathematical models described in the paper form part of computer software that simulates the thermal operation of whole refrigeration systems. The software is titled Vapour Compression Refrigeration System (VCRS) simulator, and by way of example the paper presents results from the VCRS simulator which are used to aid a discussion of operating faults, such as hunting and under damping and their possible causes, where these can be attributed to the expansion valve.