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PH Diagram R12 PDF Download - A Guide to the Thermodynamic Properties of Refrigerant 12

Refrigerant 12, also known as R12 or dichlorodifluoromethane, is a chlorofluorocarbon (CFC) that was widely used as a refrigerant and propellant in the past. However, due to its ozone-depleting potential and high global warming potential, it has been phased out under the Montreal Protocol and replaced by alternative refrigerants such as R134a and R404A. R12 is still used in some applications, such as in older refrigeration and air conditioning systems, or as a reference fluid for thermodynamic calculations.

One of the most useful tools for understanding the thermodynamic behavior of refrigerants is the pressure-enthalpy (P-h) diagram, which shows the relationship between pressure and enthalpy for different phases and states of the refrigerant. The P-h diagram can be used to visualize various thermodynamic processes, such as compression, expansion, evaporation, and condensation, and to calculate important parameters, such as specific volume, entropy, temperature, quality, and coefficient of performance (COP).


A P-h diagram for R12 can be obtained from various sources, such as textbooks, handbooks, software programs, or online databases. However, some of these sources may have limited accuracy, accessibility, or compatibility. Therefore, it may be useful to have a PDF file that contains a high-quality P-h diagram for R12 that can be easily downloaded, printed, or shared. Such a PDF file can be found at [this link], which is a document from SWEP, a leading supplier of brazed plate heat exchangers. The document contains P-h diagrams for several refrigerants, including R12.

The P-h diagram for R12 in the PDF file is based on the Coolpack program, which is a software package developed by the Department of Mechanical Engineering at the Technical University of Denmark. The Coolpack program can be downloaded for free from [this website], and it can be used to generate P-h diagrams for various refrigerants, as well as to perform other thermodynamic calculations and simulations.

The P-h diagram for R12 in the PDF file shows the saturation curve, which separates the liquid and vapor regions, and the critical point, which is the highest temperature and pressure at which liquid and vapor can coexist. The diagram also shows several constant temperature (isotherm), constant entropy (isentrope), and constant quality (dryness fraction) lines. The diagram covers a pressure range from 0.01 to 100 bar and an enthalpy range from 0 to 500 kJ/kg.

The P-h diagram for R12 can be used to analyze various refrigeration cycles, such as the vapor-compression cycle or the absorption cycle. For example, consider a simple vapor-compression cycle that consists of four processes: 1-2: isentropic compression; 2-3: constant pressure heat rejection; 3-4: isenthalpic expansion; 4-1: constant pressure heat absorption. The cycle can be represented on the P-h diagram as shown below:

The following table summarizes some of the thermodynamic properties of R12 at each state point of the cycle:

StatePressure (bar)Enthalpy (kJ/kg)Entropy (kJ/kgK)Temperature (C)Quality


2103770.8272.6Superheated vapor

3103420.7638.4Saturated liquid

41.53420.76-9.7Saturated liquid

Using the P-h diagram and the table, we can calculate the COP of the cycle as follows:

COP = Q L / W in = (h 1 - h 4 ) / (h 2 - h 1 ) = (231 - 342) / (377 - 231) = 0.64

This means that for every 1 kJ of work input, the cycle can transfer 0.64 kJ of heat from the low-temperature reservoir to the high-temperature reservoir.

The P-h diagram for R12 can also be used to compare the performance of different refrigerants, or to evaluate the effect of changing the operating conditions, such as the evaporator and condenser pressures, on the cycle performance. For example, increasing the evaporator pressure or decreasing the condenser pressure would increase the COP of the cycle, but it would also increase the compressor work and the refrigerant mass flow rate.

In conclusion, the P-h diagram for R12 is a valuable tool for understanding and analyzing the thermodynamic properties and processes of refrigerant 12. A PDF file that contains a high-quality P-h diagram for R12 can be downloaded from [this link], which is a document from SWEP that also includes P-h diagrams for other refrigerants. The PDF file is based on the Coolpack program, which is a free software package that can be used to generate P-h diagrams and perform other thermodynamic calculations and simulations.


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