Drawing a log(P)-h Diagram

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CoolProp has built-in functionality to draw the log(P)-h diagram of a refrigerant, together with some means to draw a simple vapor compression cycle on this diagram. Based on CoolProp’s functionality a small wrapper class LogPhDiagram in package hvac.charts has been developed to draw the log(P)-h diagram of a refrigerant quickly.

from hvac import Quantity
from hvac.fluids import Fluid
from hvac.charts import StandardVaporCompressionCycle, LogPhDiagram

Q_ = Quantity

Drawing an Empty log(P)-h Diagram

First we need a refrigerant. Let’s take R410A for example:

R410A = Fluid('R410A')

To create the log(P)-h diagram for R410A and show it, the code below will do it:

R410A_diagram1 = LogPhDiagram(R410A, size=(8, 6), dpi=96)

# hide the header and footer of the figure
R410A_diagram1.figure.canvas.header_visible = False
R410A_diagram1.figure.canvas.footer_visible = False

R410A_diagram1.show()

Drawing a Standard Vapor Compression Cycle on the log(P)-h Diagram

A standard vapor compression cycle is described by:

• the refrigerant

• the evaporation temperature

• the condensation temperature

• the degree of superheat of the refrigerant vapor at the exit of the evaporator (useful superheat)

• any additional superheating of the refrigerant vapor in the suction line between the evaporator outlet and the compressor inlet

• the degree of subcooling of the refrigerant liquid at the exit of the condenser or the entrance of the expansion device

• the isentropic efficiency of the compressor

For example let’s consider the following standard vapor compression cycle:

• refrigerant: R410A

• evaporation temperature: 5 °C

• useful superheat: 10 K

• additional superheat: None

• condensation temperature: 50 °C

• subcooling: 10 K

• isentropic efficiency: 73.88 %

We need first to create an instance of class StandardVaporCompressionCycle with the data from above:

cycle_R410A_1 = StandardVaporCompressionCycle(
    Refrigerant=R410A,
    evaporationTemperature=Q_(5, 'degC'),
    condensationTemperature=Q_(50, 'degC'),
    evaporatorSuperheat=Q_(10, 'K'),
    subCooling=Q_(10, 'K'),
    suctionLineSuperheat=None,
    isentropicEfficiency=Q_(73.88, 'pct')
)

Next, we instantiate class LogPhDiagram passing in the cycle we’ve just created and call show() on the diagram:

R410A_diagram2 = LogPhDiagram(R410A, size=(8, 6), dpi=96)
R410A_diagram2.setCycle(cycle_R410A_1)
R410A_diagram2.show()