Introduction to Food Engineering

Home Syllabus

Components of a Refrigeration System and Pressure Enthalpy Diagram

Learning Outcomes

At the end of this module, you will be able to:

  1. draw a refrigeration cycle on a PH diagram
  2. identify various regions on a PH chart
  3. write mathematical expressions required to design a refrigeration sytem and evaluate its performance


In the previous module, you learned about various components of a refrigeration system and the role of a refrigerant in transferring heat from one location to another. We described the enthalpy content of the refrigerant under different state conditions (such as when it is a vapor or a liquid) on a Pressure-Enthalpy (PH) diagram. In the next video, we will draw a refrigeration cycle on a PH diagram. We will examine both the PH chart and the schematic diagram of the refrigeration components side-by-side. Then we will trace the flow of the refrigerant on the PH chart to observe changes in its state as the refrigerant flows through the system.

Now that we have seen the schematics of a refrigeration system and a PH diagram let us consider the PH chart of a real refrigerant, namely HFC-134a, one of the most widely used refrigerants around the world. In the next video, we will observe the critical regions and curves that help us to determine the enthalpy content of the refrigerant from the PH diagram. A good understanding of these regions and curves is essential for you to know so that you can later extract useful information from this chart for design purposes.

In the next video, we will write various expressions for calculations involving the design of a vapor compression refrigeration system. As you will note, these mathematical expressions are quite simple.


In this module, you learned how we could draw a vapor compression cycle on a pressure enthalpy diagram. Then you viewed a PH chart of refrigerant HFC-134a in more detail by identifying various regions and curves on the PH chart. Lastly, you considered mathematical expressions that are necessary for solving problems involving the design of refrigeration systems. To use these equations, you need values of enthalpy or heat content for a given refrigerant. In the next module, you will learn how to determine the required enthalpy values from a PH chart.