R-452A P-h Diagram — Interactive Pressure–Enthalpy Chart

Loading P-h Chart...

About the R-452A P-h Diagram Ready to design the whole cycle? Open the Refrigerant Cycle Designer

R-452A quick facts

Type	Refrigerant blend
Critical temperature	75 °C (166.9 °F)
Critical pressure	40.06 bar (581 psia)
Typical applications	Low-GWP A1 replacement for R-404A (transport & commercial refrigeration)

R-452A FAQ

What is the R-452A p-h diagram?

A pressure–enthalpy chart for R-452A with pressure on a log scale: it shows the vapor dome, isolines, and the state points and process lines of a vapor-compression cycle. R-452A's critical point is 75 °C (166.9 °F) at 40.06 bar (581 psia); above it no two-phase region exists.

What are R-452A's key properties and designations?

R-452A is a refrigerant blend with a critical temperature of 75 °C (166.9 °F).

Is the R-452A p-h chart free to use?

Yes. The chart loads with R-452A preselected and is free to use: plot state points and cycles, overlay other refrigerants to compare, switch SI/IP units, and export to SVG or PNG.

Tutorials & how-to videos

Step-by-step tutorials and how-to videos for the p-h diagram are coming soon.

A free, interactive pressure-enthalpy diagram for more than 60 refrigerants. Plot state points, read the isolines and vapor dome, sketch a complete refrigeration cycle, overlay refrigerants to compare them, and export the result to SVG or PNG.

What is a pressure-enthalpy diagram?

A pressure-enthalpy diagram — usually drawn as a log p-h diagram — maps a refrigerant's specific enthalpy (horizontal axis) against its pressure on a logarithmic vertical axis. Because pressure spans several orders of magnitude over a working cycle, the log scale keeps the whole operating range readable on one chart. It is the standard way to visualize vapor-compression refrigeration and heat-pump cycles, size components, and reason about efficiency.

The vapor dome and the three regions

The bell-shaped vapor dome is the heart of the chart. Its left edge is the saturated-liquid line and its right edge is the saturated-vapor line; the two meet at the critical point at the top. The dome divides the diagram into three regions:

Subcooled liquid — left of the dome, fully liquid.
Two-phase mixture — inside the dome, a coexisting blend of liquid and vapor described by its quality (vapor mass fraction).
Superheated vapor — right of the dome, fully gas.

Reading the isolines

The families of curves on a p-h diagram each hold one property constant:

Isobars (constant pressure) — horizontal lines.
Isenthalps (constant enthalpy) — vertical lines.
Isotherms (constant temperature) — nearly vertical in the subcooled liquid, flat and horizontal inside the dome, then curving down into the superheated region.
Isentropes (constant entropy) — steep curves used to model ideal compression.
Isochores (constant specific volume or density) — shallow curves through the vapor region.
Quality lines (constant vapor fraction) — fan across the inside of the dome from 0 at the liquid line to 1 at the vapor line.

Drawing a refrigeration cycle

A basic vapor-compression cycle traces four processes around the chart. To size one rather than sketch it, the refrigerant cycle designer solves the same cycle against real compressor and heat-exchanger data.

Compression (1→2): the compressor raises the low-pressure vapor up an isentrope into the superheated region.
Condensation (2→3): heat rejection at constant pressure — a horizontal line left, desuperheating, condensing across the dome, often with some subcooling.
Expansion (3→4): the expansion valve drops the pressure at constant enthalpy — a vertical line straight down into the two-phase region.
Evaporation (4→1): heat absorption at constant pressure — a horizontal line right, back to the suction state, usually with some superheat.

The horizontal spans tell you the energy flows per unit mass: the refrigerating effect is the enthalpy rise across the evaporator (h₁ − h₄), the compressor work is the rise across compression (h₂ − h₁), and the coefficient of performance (COP) is their ratio, (h₁ − h₄) / (h₂ − h₁).

What this tool does

60+ refrigerants — including R134a, R410A, R32, R1234yf, R1234ze, R290 (propane), R744 (CO₂, with transcritical states), and R717 (ammonia).
State points and process lines drawn directly on the chart.
Compare refrigerants — overlay multiple vapor domes to evaluate alternatives side by side.
SI and IP units with a single toggle.
Export to SVG or PNG for reports and presentations.

Using the chart controls

The sidebar lets you build an analysis directly on the chart:

Conditions — a named group that sets the color of the state points and process lines you plot. Each condition is one operating scenario (for example "Baseline" and "High Ambient"): create several and switch between them to overlay and compare multiple scenarios on the same p-h chart, each in its own color.
State points — click the chart, or type any two properties (pressure, enthalpy, temperature, entropy, quality), to pin a point and read its full thermodynamic state.
Process lines — connect two state points to draw a process (compression, condensation, expansion, evaporation) and read the enthalpy change across it.
Compare refrigerants — overlay the saturation domes of other refrigerants to evaluate alternatives side by side.

Properties are computed with PreciseFluids.

P-h diagrams by refrigerant

Open the chart preloaded for a specific refrigerant — each page includes that fluid's critical point, boiling point, GWP, and safety class:

Interactive R-452A P-h Diagram (Log Pressure–Enthalpy Chart)