Refrigerant Ph Diagram (Part 2)

The pressure-enthalpy diagram is the most common graphical tool for analysis and calculation of the heat and work transfer and performance of a refrigeration cycle. The change in pressure can be clearly illustrated on the p-h diagram. Also, both heat and work transfer of various processes can be calculated as the change of enthalpy and at easily shown on the p-h diagram.

P-h enthalpy diagram consist of following lines:

  1. Constant pressure lines
  2. Constant enthalpy lines
  3. Saturation line
  4. Isothermal lines
  5. Isentropic lines
  6. Constant volume lines

Enthalpy “h” is along x-axis and absolute pressure “p” is along the y-axis, both expressed in logarithmic scale. The saturated liquid line separates the sub-cooled liquid from the two-phase region in which vapor and liquid refrigerants coexist. The saturated vapor line separates this two-phase region from the superheated vapor. In the two-phase region, the constant-dryness-fraction quality line subdivides the mixture of vapor and liquid. The constant-temperature lines are nearly vertical in the sub-cooled liquid region. At higher temperatures, they are curves near the saturated liquid line. In two-phase region, the constant temperature lines are horizontal. Also in the superheated region, the constant-entropy lines incline sharply upward, and constant volume lines are flatter. Both are slightly curved.

This article is a continuation of our older article, which was well received by users, so we decided to update the P-H Diagram list and provide you with a more complete list of the world's commercial refrigerants.
You can easily access the high quality refrigerant chart by clicking on the refrigerants listed in the table.


What is the significance of constant pressure lines on a P-H diagram?
Constant pressure lines on a P-H diagram represent the variation of enthalpy with temperature at a specific pressure. These lines are crucial in refrigeration cycle analysis as they enable the calculation of heat transfer and work done during various processes, such as compression, expansion, and evaporation. By analyzing the slope and curvature of these lines, engineers can determine the thermodynamic properties of refrigerants and optimize system design and operation.
How do isothermal lines differ from isentropic lines on a P-H diagram?

Isothermal lines on a P-H diagram represent constant temperature, whereas isentropic lines represent constant entropy. Isothermal lines are horizontal and indicate no change in temperature, whereas isentropic lines are curved and indicate a reversible adiabatic process. Understanding the difference between these lines is essential for analyzing refrigeration cycles, as isentropic processes are idealized and isothermal processes are more realistic.

What is the role of saturation lines on a P-H diagram?

Saturation lines on a P-H diagram separate the liquid and vapor regions of a refrigerant. These lines indicate the boundary between the saturated liquid and saturated vapor states. By analyzing the saturation lines, engineers can determine the thermodynamic properties of refrigerants at specific temperatures and pressures, which is critical for designing and optimizing refrigeration systems.

How can a P-H diagram be used to analyze a vapor-compression refrigeration cycle?

A P-H diagram can be used to analyze a vapor-compression refrigeration cycle by plotting the various processes, such as compression, condensation, expansion, and evaporation, on the diagram. By analyzing the enthalpy changes and pressure variations during each process, engineers can calculate the coefficient of performance (COP), refrigeration capacity, and energy efficiency of the system. This enables the optimization of system design and operation for improved performance and energy savings.

What are some common applications of P-H diagrams in HVAC and refrigeration systems?

P-H diagrams have numerous applications in HVAC and refrigeration systems, including system design, performance analysis, and optimization. They are used to select refrigerants, determine system capacity, and optimize operating conditions. P-H diagrams are also essential for troubleshooting and diagnosing system malfunctions, such as refrigerant leaks or compressor failures. Additionally, they are used in research and development to improve system efficiency and reduce environmental impact.

How can P-H diagrams be used to compare the performance of different refrigerants?

P-H diagrams can be used to compare the performance of different refrigerants by analyzing their thermodynamic properties, such as enthalpy, entropy, and pressure. By plotting the P-H diagrams for different refrigerants, engineers can compare their performance characteristics, such as refrigeration capacity, energy efficiency, and operating pressures. This enables the selection of the most suitable refrigerant for a specific application, taking into account factors such as environmental impact, safety, and cost.