log ph diagram

The log ph diagram

The thermodynamic state of a fluid (e.g. the refrigerant R134a) can be represented in state diagrams as a single point. Complete processes such as refrigeration cycles are visualized by connecting points with lines. These connecting lines correspond to changes in the state of the fluid.

In refrigeration technology, the pressure-enthalpy diagram is by far the most frequently used state diagram. The pressure is mostly scaled logarithmically, hence the name log ph diagram.

Isolines and the vapor dome

The thermodynamic properties of a refrigerant are represented in the state diagram as lines of constant state variables - so-called isolines. For example, this can be the temperature. All Points at which the temperature is constant lie on a line called an isotherm. An overview of all common isolines is given in the by-standing table.

Isolines are characteristic of a certain refrigerant and its thermodynamic properties. The log ph diagram with all its isolines can be seen as something like the fingerprint of a refrigerant.
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The dark-colored area represents the wet steam region, also known as the two-phase region. Here the refrigerant's state has two phases: Liquid and gaseous. In practice, these two phases can be seen by the human eye as vapor bubbles in the liquid.

In our interactive diagram, all isolines and the two-phase region can be switched off. This allows you to create tidy diagrams that contain only the lines relevant to the specific question and are not overloaded with additional information.

Representation of a refrigeration cycle

In our interactive log ph diagram, refrigeration cycles can be parameterized in different ways. For a simple refrigeration cycle, we offer the possibility to specify either the evaporating and condensing pressure or the evaporating and condensing temperature.

A detailed description of a simple refrigeration circuit in the log ph diagram can be found here. The article explains all occurring state changes in detail and links them to the corresponding refrigeration components.

In the log ph diagram, not only heat pump and refrigeration processes can be represented, but any desired thermodynamic cycle process. Just select an evaporation pressure that is higher than the condensation pressure and you will get an Organic Rankine Cycle (ORC). This cycle runs clockwise instead of counterclockwise as the heat pump or refrigeration cycle.

Complicated processes can be entered with the free input of state points. This is of course a bit more tedious. You are welcome to contact, us if you are interested in additional features or need a custom version of the diagram for your website or software project.