Thermodynamic Properties Sensor (MA)

Measure specific enthalpy, density, specific heat at constant pressure, and specific entropy of air mixture

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Libraries:
Simscape / Foundation Library / Moist Air / Sensors

Description

The Thermodynamic Properties Sensor (MA) block represents an ideal sensor that measures specific enthalpy, density, specific heat at constant pressure, and specific entropy of the air mixture in a moist air network. There is no mass or energy flow through the sensor.

The block measures these thermodynamic properties at the node connected to port A.

You have a choice of outputting these measurements normalized by the mass of the whole air mixture, or by the mass of dry air and trace gas only. The second option is consistent with the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) standards.

The specific entropy reference value, used for sensor calibration, is 0 for each constituent of the moist mixture at atmospheric pressure and atmospheric temperature. Atmospheric pressure and atmospheric temperature are defined by the parameters of the Moist Air Properties (MA) block connected to the circuit.

Examples

Aircraft Environmental Control System

Models an aircraft environmental control system (ECS) that regulates pressure, temperature, humidity, and ozone (O3) to maintain a comfortable and safe cabin environment. Cooling and dehumidification are provided by the air cycle machine (ACM), which operates as an inverse Brayton cycle to remove heat from pressurized hot engine bleed air. Some hot bleed air is mixed directly with the output of the ACM to adjust the temperature. Pressurization is maintained by the outflow valve in the cabin. This model simulates the ECS operating from a hot ground condition to a cold cruise condition and back to a cold ground condition.

• Open Model

Ports

Output

h — Specific enthalpy measurement, J/kg

physical signal

Physical signal output port for measuring the specific enthalpy of the air mixture.

Dependencies

To enable this port, select the Enthalpy check box.

ρ — Density measurement, kg/m^3

physical signal

Physical signal output port for measuring the density of the air mixture.

Dependencies

To enable this port, select the Density check box.

cp — Specific heat at constant pressure measurement, J/(kg*K)

physical signal

Physical signal output port for measuring the specific heat of the air mixture at constant pressure.

Dependencies

To enable this port, select the Specific heat check box.

s — Specific entropy measurement, J/(kg*K)

physical signal

Physical signal output port for measuring the specific entropy of the air mixture.

Dependencies

To enable this port, select the Entropy check box.

Conserving

A — Sensor inlet

moist air

Moist air conserving port. Connect this port to the node in the moist air network where you want to measure the thermodynamic properties.

Parameters

Measurements based on — Select measurement convention for sensor output

Unit mass of moist air mixture (default) | Unit mass of dry air and trace gas

Select whether measurements are normalized by the mass of the whole air mixture, or by the mass of dry air and trace gas only:

• Unit mass of moist air mixture — For each thermodynamic property, the measured mass of that property in a moist air volume is divided by the mass of the most air mixture.

• Unit mass of dry air and trace gas — For each thermodynamic property, the measured mass of that property in a moist air volume is divided by the mass of dry air and trace gas (leaving out the mass of the water vapor). Use this option when you need to compare your measurements with ASHRAE figures and charts.

Enthalpy — Control output port visibility for measuring specific enthalpy

Off (default) | On

Selecting this check box exposes the output port h, which lets you measure the specific enthalpy of the air mixture.

Enthalpy reference state — Select reference state for specific enthalpy output

As provided in Moist Air Properties (MA) block (default) | 0 degC with water as vapor | 0 degC with water as liquid

Select the reference state for specific enthalpy output:

• As provided in Moist Air Properties (MA) block — The sensor outputs mixture enthalpy based directly on the enthalpy vectors provided in the Moist Air Properties (MA) block, with no adjustments. This option is for informational purposes only because the library blocks use adjusted values.

• 0 degC with water as vapor — The sensor outputs mixture enthalpy adjusted to reference state of 0 kJ/kg at 0 degC. These are the values used in the library blocks and shown in the simulation data log.

• 0 degC with water as liquid — The sensor outputs mixture enthalpy adjusted so that liquid water has the reference state of 0 kJ/kg at 0 degC. In this case, enthalpy of water vapor includes the enthalpy of vaporization, or latent heat, at the reference state. These are the values used in the wall condensation calculations.

Dependencies

To enable this parameter, select the Enthalpy check box.

Density — Control output port visibility for measuring density

On (default) | Off

Selecting this check box exposes the output port ρ, which lets you measure the density of the air mixture.

Specific heat — Control output port visibility for measuring specific heat

Off (default) | On

Selecting this check box exposes the output port cp, which lets you measure the specific heat of the air mixture.

Entropy — Control output port visibility for measuring specific entropy

Off (default) | On

Selecting this check box exposes the output port s, which lets you measure the specific entropy of the air mixture.

Extended Capabilities

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

Version History

Introduced in R2018a

R2023b: Consistent reference state for specific enthalpy in moist air domain

To ensure consistency in a moist air mixture, all the specific enthalpies must have the same reference temperature. Therefore, starting in R2023b, the moist air domain uses a consistent reference temperature of 0 degC. When you enter specific enthalpy vectors in the Moist Air Properties (MA) block, the block internally shifts these vectors to be 0 kJ/kg at 0 degC. The library blocks then use these adjusted values in the internal calculations. The simulation data log also displays the adjusted specific enthalpy values.

The new Enthalpy reference state parameter in the Thermodynamic Properties Sensor (MA) block lets you view the specific enthalpy values adjusted with respect to different reference states. The As provided in Moist Air Properties (MA) block option outputs the same values as in previous releases.

R2023a: Usability enhancement for moist air sensors

Moist air sensor blocks with multiple output ports now have conditional port visibility on the block icon. You can use the block parameters to expose only the ports that you need for measurements in a particular model.

There is no compatibility impact when you use the Thermodynamic Properties Sensor (MA) block in your models. However, if you use this block in your custom composite components, you need to update the composite component code.

Old Syntax	New Syntax
sensor = foundation.moist_air.sensors.thermodynamic_sensor;	sensor = foundation.moist_air.sensors.thermodynamic_sensor(enthalpy=true, specific_heat=true, entropy=true);