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Vapor Quality Sensor (2P)

Measure vapor fraction in two-phase fluids


Two-Phase Fluid/Sensors

  • Vapor Quality Sensor (2P) block


The Vapor Quality Sensor (2P) block measures the fraction of vapor in a two-phase fluid. That fraction can be expressed on a mass basis (the vapor quality of the fluid) or on a volume basis (the vapor void fraction). The choice of basis is given in the Vapor fraction specification block parameter.

The measurement is made at port A and reported, as a physical signal, at port X. Its value can range from 0 in pure liquid to 1 in pure vapor. Intermediate values correspond to two-phase mixtures. The sensor is ideal—neither mass nor energy exchanges take place, and the measurement is therefore undisturbed by them.

If pressure should rise above the critical point for the fluid, vapor and liquid cease to exist, and the measurement becomes undefined. The block then outputs -1, a dummy value that serves merely to indicate a critical or supercritical state.


Vapor fraction specification

Type of measurement to report at port X. Select Vapor quality for the mass fraction of vapor in a two-phase fluid. Select Vapor void fraction for the volume fraction instead. The measurement can range from 0 to 1 in both cases (save for critical and supercritical fluids, for which the output is always -1.


The block has two ports:

  • A — Two-phase fluid node at which to measure the proportion of vapor in a two-phase fluid mixture.

  • X — Proportion of vapor expressed as a mass fraction or as a volume fraction. The type of fraction depends on the Vapor fraction specification setting.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Introduced in R2018b