Moist Air Properties (MA)

Global moist air properties for attached circuit

• 

Libraries:
Simscape / Foundation Library / Moist Air / Utilities

Description

The Moist Air Properties (MA) block defines the moist air properties that act as global parameters for all the blocks connected to a circuit. The moist air mixture is composed of dry air, water vapor, and optional trace gas or water droplets. The default trace gas is carbon dioxide.

Dry air, water vapor, and trace gas are assumed to be semiperfect gas. Pressure, temperature, and density obey the ideal gas law. Other properties are functions of temperature. You specify them as one-dimensional arrays corresponding to the Temperature vector.

Each topologically distinct moist air circuit in a diagram can have a Moist Air Properties (MA) block connected to it. If no Moist Air Properties (MA) block is attached to a circuit, the blocks in this circuit use the properties corresponding to the default Moist Air Properties (MA) block parameter values.

Examples

Vehicle HVAC System

Models moist air flow in a vehicle heating, ventilation, and air conditioning (HVAC) system. The vehicle cabin is represented as a volume of moist air exchanging heat with the external environment. The moist air flows through a recirculation flap, a blower, an evaporator, a blend door, and a heater before returning to the cabin. The recirculation flap selects flow intake from the cabin or from the external environment. The blender door diverts flow around the heater to control the temperature.

• Open Model

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

Medical Ventilator with Lung Model

Models a positive-pressure medical ventilator system. A preset flow rate is supplied to the patient. The lungs are modeled with the Translational Mechanical Converter (MA), which converts moist air pressure into translational motion. By setting the Interface cross-sectional area to unity, displacement in the mechanical translational network becomes a proxy for volume, force becomes a proxy for pressure, spring constant becomes a proxy for respiratory elastance, and damping coefficient becomes a proxy for respiratory resistance.

• Open Model

Pneumatic Actuator with Humidity

How the Simscape™ Foundation Library moist air components can be used to model a pneumatic actuator operating in a humid environment. The Directional Valve is a subsystem composed of four Variable Local Restriction (MA) blocks, and the Double-Acting Actuator is a subsystem composed of two Translational Mechanical Converter (MA) blocks in opposite mechanical orientation.

• Open Model

Ports

Conserving

A — Connection port

moist air

Conserving port that connects the block to the moist air network. You can connect it to any point on a moist air connection line in a block diagram. When you connect the Moist Air Properties (MA) block to a connection line, the software automatically identifies the moist air blocks connected to the particular circuit and propagates the properties to all these blocks.

Parameters

Dry Air

Dry air specific gas constant — Universal gas constant divided by molar mass of dry air

287.047 J/kg/K (default)

Universal gas constant divided by molar mass of dry air.

Temperature vector — Vector of temperature values for table lookup

vector

Vector of temperature values, to be used for table lookup of other properties as a function of temperature. Dry air, water vapor, and trace gas properties share the same temperature vector.

The default value is [-56.55, -50 : 10 : -10, -5 : 1 : 5, 10 : 10 : 350]' degC.

Dry air specific enthalpy vector — Vector of specific enthalpy values for table lookup

vector

The vector of specific enthalpy values of dry air, to be used for one-dimensional table lookup based on the corresponding temperature value. The vector size must be the same as the temperature vector size.

The default value is [342.416126230579; 349.005511058471; 359.063577249119; 369.119948684177; 379.175469465129; 389.230944678417; 394.258910928084; 395.264534937366; 396.27017101329; 397.275819932805; 398.281482472874; 399.287159410541; 400.292851523015; 401.298559587728; 402.304284382408; 403.310026685143; 404.315787274435; 409.34489180313; 419.404921755863; 429.468036401264; 439.535033154839; 449.606720928652; 459.683919949603; 469.767460521911; 479.858181001348; 489.956925196484; 500.064539372946; 510.181869006204; 520.309755403634; 530.449032296018; 540.60052248087; 550.765034584465; 560.943359995745; 571.136270013102; 581.344513234296; 591.568813210327; 601.809866375885; 612.068340261954; 622.344871990218; 632.640067043998; 642.95449830646; 653.288705353699; 663.643193987949; 674.018435994423; 684.414869104228; 694.832897145098; 705.272890361557; 715.735185886199; 726.220088344236; 736.727870574087; 747.258774447567; 757.813011774199] kJ/kg.

Dry air dynamic viscosity vector — Vector of dynamic viscosity values for table lookup

vector

The vector of dynamic viscosity values of dry air, to be used for one-dimensional table lookup based on the corresponding temperature value. The vector size must be the same as the temperature vector size.

The default value is [14.2568883320012; 14.6140127728333; 15.1517277055779; 15.6806860159119; 16.2012351072083; 16.7137043125028; 16.9670071730589; 17.017438062815; 17.0677930842452; 17.1180725309876; 17.1682766951315; 17.2184058672268; 17.2684603362935; 17.3184403898301; 17.3683463138234; 17.4181783927569; 17.4679369096204; 17.7156358640698; 18.2056751785154; 18.68879035749; 19.1652344664982; 19.6352478927873; 20.099059103658; 20.5568853601578; 21.0089333871663; 21.4554000014051; 21.8964726992323; 22.3323302062775; 22.7631429910631; 23.1890737447833; 23.6102778293792; 24.0269036959922; 24.4390932757886; 24.8469823450548; 25.2507008663546; 25.6503733074314; 26.0461189394339; 26.4380521159325; 26.8262825340948; 27.2109154792923; 27.5920520543128; 27.969789394274; 28.3442208682439; 28.7154362685068; 29.0835219883356; 29.4485611890712; 29.8106339572472; 30.1698174524429; 30.5261860464955; 30.8798114546565; 31.2307628592324; 31.5791070262086] s*μPa.

Dry air thermal conductivity vector — Vector of thermal conductivity values for table lookup

vector

The vector of thermal conductivity values of dry air, to be used for one-dimensional table lookup based on the corresponding temperature value. The vector size must be the same as the temperature vector size.

The default value is [19.8808489374933; 20.4162454629695; 21.2248743590758; 22.0232452890903; 22.8117314495857; 23.5906913619588; 23.9767075412237; 24.053639990175; 24.1304826682191; 24.2072359051629; 24.2839000294007; 24.3604753679152; 24.4369622462801; 24.5133609886625; 24.5896719178249; 24.6658953551279; 24.7420316205333; 25.1214164701832; 25.8738283029331; 26.6180150229276; 27.3542674377332; 28.0828634735341; 28.8040686837224; 29.5181367785657; 30.2253101618423; 30.9258204644224; 31.6198890677835; 32.3077276126633; 32.9895384896798; 33.6655153099498; 34.33584335461; 35.0007000027879; 35.6602551380254; 36.3146715334901; 36.9641052165342; 37.6087058133173; 38.248616874307; 38.8839761815308; 39.5149160384798; 40.1415635435708; 40.7640408480637; 41.3824653993118; 41.9969501701893; 42.6076038755117; 43.2145311762238; 43.8178328720941; 44.4176060836121; 45.013944423749; 45.6069381602018; 46.1966743687041; 46.783237077953; 47.3667074066625] mW/m/K.

Minimum valid pressure — Lowest pressure allowed

1 kPa (default)

Lowest pressure allowed in the moist air network. The simulation issues an error when pressure is out of range.

Maximum valid pressure — Highest pressure allowed

inf MPa (default)

Highest pressure allowed in the moist air network. The simulation issues an error when pressure is out of range.

Minimum valid temperature — Lowest temperature allowed

-56.55 degC (default)

Lowest temperature allowed in the moist air network. The simulation issues an error when temperature is out of range.

Maximum valid temperature — Highest temperature allowed

350 degC (default)

Highest temperature allowed in the moist air network. The simulation issues an error when temperature is out of range.

Pressure and temperature outside valid range — Whether to notify when pressure or temperature are outside valid range

Error (default) | Warning | None

Select what happens if the moist air pressure or temperature go beyond the valid range during simulation:

• None ― The block does not return an error if the properties go out of range.

• Warning ― The block issues a warning, but continues the simulation.

• Error ― The block returns an error and stops the simulation.

Atmospheric pressure — Absolute pressure of the environment

0.101325 MPa (default)

Absolute pressure of the environment.

Atmospheric temperature — Absolute temperature of the environment

20 degC (default)

Absolute temperature of the environment.

Water Vapor

Enable entrained water droplets — Option to model water droplets

Off (default) | On

Select whether the block models entrained water droplets in the moist air mixture. If you clear this checkbox, the model ignores any nonzero values for water droplets in the parameters and inputs of blocks connected to the network. The block equations listed on the block reference pages replace the water droplet terms in calculations with 0.

For more information on modeling water droplets, see Modeling Moisture and Trace Gas Levels.

Water vapor specific gas constant — Universal gas constant divided by molar mass of water vapor

461.523 J/kg/K (default)

Universal gas constant divided by molar mass of water vapor.

Water vapor saturation pressure vector — Vector of vapor saturation values for table lookup

vector

Vector of vapor saturation values for water as a function of temperature, to be used for one-dimensional table lookup. Moist air becomes saturated when the partial pressure of water vapor is equal to the water vapor saturation pressure. Therefore, condensation may occur. The vector size must be the same as the temperature vector size. Dry air, water vapor, and trace gas properties share the same temperature vector.

The default value is [1.71168953425982e-06; 3.93770601979424e-06; 1.28411717710344e-05; 3.80051394873809e-05; .00010323902900209; .000259873810798063; .000401741022116384; .000437454836117844; .000476040820618202; .000517704666185737; .000562664883741207; .000611212677444345; .000657088049117899; .000705987905898279; .000758082381149132; .000813549384183233; .000872574861129522; .00122818386934022; .0023392147667769; .00424668834054807; .00738442748706953; .0123512704340234; .0199458019246787; .0312006356960619; .0474147199263783; .0701823607447713; .10141797792131; .143375967241115; .198665399739302; .270259606559999; .361500961984849; .476101381081492; .618139196722055; .792053183687694; 1.0026345688121; 1.25501792086105; 1.55467186826983; 1.90739066433297; 2.31928772772542; 2.79679245576864; 3.34665187151016; 3.97593907083533; 4.69207105435535; 5.5028394740883; 6.41645928168037; 7.4416425436169; 8.58770832955728; 9.86474556030261; 11.2838558865497; 12.8575218898034; 14.6001810568052; 16.5291642526045] MPa.

Water specific enthalpy of vaporization vector — Vector of specific enthalpy of vaporization values for table lookup

vector

Vector of the difference between the specific enthalpy of saturated water vapor and the specific enthalpy of saturated liquid water as a function of temperature, to be used for one-dimensional table lookup. The vector size must be the same as the temperature vector size. Dry air, water vapor, and trace gas properties share the same temperature vector.

The default value is [2836.88241275372; 2837.81392500514; 2838.63937175807; 2838.7309929628; 2838.06905313927; 2836.62597341095; 2835.60023952573; 2835.37006381376; 2835.13143158077; 2834.88429145066; 2834.62859062897; 2500.93420564316; 2498.55329907119; 2496.17495082036; 2493.79885912205; 2491.42474723191; 2489.05236104642; 2477.20875029194; 2453.54955988604; 2429.83856603313; 2406.00136954922; 2381.97406342174; 2357.69101156389; 2333.08088387814; 2308.06565480412; 2282.56034405021; 2256.47287422313; 2229.70428017508; 2202.14968030993; 2173.69998896199; 2144.24368406447; 2113.66758247452; 2081.85585110571; 2048.68725710494; 2014.03141249899; 1977.7449923284; 1939.66849592886; 1899.62342931686; 1857.40930169838; 1812.79975416601; 1765.53721731251; 1715.32525772152; 1661.81700477787; 1604.59703745016; 1543.1534616334; 1476.83692476464; 1404.80240352424; 1325.92091736114; 1238.61667822208; 1140.5102987018; 1027.62017777647; 892.733785613825] kJ/kg.

Water vapor specific enthalpy vector — Vector of specific enthalpy values for table lookup

vector

The vector of specific enthalpy values of water vapor, to be used for one-dimensional table lookup based on the corresponding temperature value. The vector size must be the same as the temperature vector size. Dry air, water vapor, and trace gas properties share the same temperature vector.

The default value is [2396.55944251649; 2408.68643343608; 2427.1988031141; 2445.702165897; 2464.18429108356; 2482.62529466839; 2491.82135326629; 2493.6580151792; 2495.49372578218; 2497.32843835745; 2499.16210446923; 2500.99462758899; 2502.83092214066; 2504.6665223621; 2506.50140563013; 2508.335548891; 2510.16892865793; 2519.32352241995; 2537.56068088674; 2555.67742615292; 2573.6403223998; 2591.4109179101; 2608.9455037701; 2626.19492016262; 2643.10444358428; 2659.61377634497; 2675.58278696023; 2696.1846256545; 2716.49989553741; 2736.6235210957; 2756.61216047011; 2776.50561773853; 2796.33378922508; 2816.11979583049; 2835.88181423877; 2855.63430574511; 2875.38889327595; 2895.15500577172; 2914.94035964689; 2934.75132290228; 2954.59319330244; 2974.47041285505; 2994.38673458964; 3014.34535328009; 3034.34900867103; 3054.40006755764; 3074.50058946898; 3094.65237953784; 3114.85703128106; 3135.11596137801; 3155.43043805905; 3175.80160435813] kJ/kg.

Water vapor dynamic viscosity vector — Vector of dynamic viscosity values for table lookup

vector

The vector of dynamic viscosity values of water vapor, to be used for one-dimensional table lookup based on the corresponding temperature value. The vector size must be the same as the temperature vector size. Dry air, water vapor, and trace gas properties share the same temperature vector.

The default value is [6.81365662228272; 7.04953750742707; 7.40970098298307; 7.76991278093907; 8.13017290129507; 8.49048134405107; 8.67065368632907; 8.70668960445667; 8.74272600580827; 8.77876289038387; 8.81480025818347; 8.85083810920707; 8.88687644345467; 8.92291526092627; 8.95895456162187; 8.99499434554147; 9.03103461268507; 9.21124319676307; 9.57169660671907; 9.93219833907507; 10.2927483938311; 10.6533467709871; 11.0139934705431; 11.3746884924991; 11.7354318368551; 12.0962235036111; 12.4570634927671; 12.8179518043231; 13.1788884382791; 13.5398733946351; 13.9009066733911; 14.2619882745471; 14.6231181981031; 14.9842964440591; 15.3455230124151; 15.7067979031711; 16.0681211163271; 16.4294926518831; 16.7909125098391; 17.1523806901951; 17.5138971929511; 17.8754620181071; 18.2370751656631; 18.5987366356191; 18.9604464279751; 19.3222045427311; 19.6840109798871; 20.0458657394431; 20.4077688213991; 20.7697202257551; 21.1317199525111; 21.4937680016671] s*μPa.

Water vapor thermal conductivity vector — Vector of thermal conductivity values for table lookup

vector

The vector of thermal conductivity values of water vapor, to be used for one-dimensional table lookup based on the corresponding temperature value. The vector size must be the same as the temperature vector size. Dry air, water vapor, and trace gas properties share the same temperature vector.

The default value is [11.46288215976; 11.941997488935; 12.676358586935; 13.414208884935; 14.155548382935; 14.900377080935; 15.274099879935; 15.348949115735; 15.423833243535; 15.498752263335; 15.573706175135; 15.648694978935; 15.723718674735; 15.798777262535; 15.873870742335; 15.948999114135; 16.024162377935; 16.400502076935; 17.155798374935; 17.914583872935; 18.676858570935; 19.442622468935; 20.211875566935; 20.984617864935; 21.760849362935; 22.540570060935; 23.323779958935; 24.110479056935; 24.900667354935; 25.694344852935; 26.491511550935; 27.292167448935; 28.096312546935; 28.903946844935; 29.715070342935; 30.529683040935; 31.347784938935; 32.169376036935; 32.994456334935; 33.823025832935; 34.655084530935; 35.490632428935; 36.329669526935; 37.172195824935; 38.018211322935; 38.867716020935; 39.720709918935; 40.577193016935; 41.437165314935; 42.300626812935; 43.167577510935; 44.038017408935] mW/m/K.

Water vapor diffusivity in air — Smoothing coefficient for flow reversals

25 mm^2/s (default)

Coefficient for the diffusive flux of water vapor in the moist air mixture due to the difference in concentration of water vapor. During mixture flow reversal, the water vapor mass flow rate at the ports smoothly transitions between the upstream and downstream value based on the diffusivity.

Trace Gas

Trace gas model — Select how to model trace gas in the air mixture

None (default) | Track mass fraction only | Track mass fraction and gas properties

Select how the block models the amount of trace gas in the air mixture:

• None — No trace gas is present. The moist air mixture consists of only dry air and water vapor. Any nonzero values of trace gas level in parameters and variable targets of the blocks connected to the circuit are ignored. All connections to the trace gas source blocks in the model are also ignored. Therefore, you do not need to modify your model based on the trace gas modeling selection.

• Track mass fraction only — The trace gas level can be nonzero and vary during simulation. However, the amount of trace gas is assumed to be small enough to have a negligible impact on the fluid properties of the moist air mixture.

• Track mass fraction and gas properties — The trace gas level can be nonzero and vary during simulation. The fluid properties of the moist air mixture depend on the amount of trace gas in the mixture.

For more information on the impact of these options on block and system equations, see Trace Gas Modeling Options.

Trace gas specific gas constant — Universal gas constant divided by molar mass of trace gas

188.923 J/kg/K (default)

Universal gas constant divided by molar mass of trace gas.

Dependencies

Enabled when the Trace gas model parameter is set to Track mass fraction only or Track mass fraction and gas properties.

Trace gas specific enthalpy vector — Vector of specific enthalpy values for table lookup

vector

The vector of specific enthalpy values of trace gas, to be used for one-dimensional table lookup based on the corresponding temperature value. The vector size must be the same as the temperature vector size. Dry air, water vapor, and trace gas properties share the same temperature vector.

The default value is [439.555216260064; 444.670268200251; 452.538618847003; 460.487124258496; 468.522588768941; 476.649415958793; 480.74798538725; 481.57054318762; 482.394052398751; 483.218514288831; 484.043930029015; 484.870300696555; 485.697627277859; 486.525910671489; 487.355151691079; 488.185351068185; 489.016509455051; 493.186704139431; 501.599194953048; 510.107689961685; 518.711611080182; 527.410026793075; 536.201764778798; 545.085474203452; 554.059675505208; 563.122805485367; 572.27325096919; 581.509373027928; 590.829525105886; 600.232066705818; 609.715373581392; 619.277845178105; 628.917909922924; 638.634028838794; 648.424697859328; 658.288449140109; 668.223851601449; 678.229510889093; 688.304068901113; 698.44620299875; 708.654624994591; 718.928079991818; 729.265345132425; 739.665228299475; 750.126566808087; 760.648226111439; 771.229098541268; 781.868102096908; 792.564179292476; 803.316296068366; 814.123440770426; 824.984623198037] kJ/kg.

Dependencies

Enabled when the Trace gas model parameter is set to Track mass fraction and gas properties.

Trace gas dynamic viscosity vector — Vector of dynamic viscosity values for table lookup

vector

The vector of dynamic viscosity values of trace gas, to be used for one-dimensional table lookup based on the corresponding temperature value. The vector size must be the same as the temperature vector size. Dry air, water vapor, and trace gas properties share the same temperature vector.

The default value is [10.8921054191698; 11.2215357085649; 11.7233300740382; 12.2234238147811; 12.7215124453467; 13.2173328890673; 13.4643203184773; 13.5136406274989; 13.562934752385; 13.6122025024997; 13.6614436900741; 13.7106581301692; 13.7598456406398; 13.8090060420983; 13.8581391578796; 13.9072448140062; 13.9563228391538; 14.2012926853717; 14.6890687376044; 15.1738428124161; 15.6554929043332; 16.1339159800463; 16.6090257998657; 17.0807510097148; 17.5490334645512; 18.0138267508952; 18.4750948814453; 18.9328111390399; 19.3869570507278; 19.8375214755778; 20.2844997922255; 20.7278931741254; 21.1677079421287; 21.6039549853963; 22.036649242835; 22.4658092382469; 22.8914566632375; 23.3136160026627; 23.7323141980278; 24.1475803447965; 24.5594454200432; 24.9679420372927; 25.3731042257492; 25.774967231431; 26.1735673380029; 26.5689417053362; 26.9611282240413; 27.350165384404; 27.73609215832; 28.118947892972; 28.4987722151178; 28.8756049449796] s*μPa.

Dependencies

Enabled when the Trace gas model parameter is set to Track mass fraction and gas properties.

Trace gas thermal conductivity vector — Vector of thermal conductivity values for table lookup

vector

The vector of thermal conductivity values of trace gas, to be used for one-dimensional table lookup based on the corresponding temperature value. The vector size must be the same as the temperature vector size. Dry air, water vapor, and trace gas properties share the same temperature vector.

The default value is [10.489430678843; 10.9507672150864; 11.666197960308; 12.392559739764; 13.1299519771612; 13.8778409888416; 14.2554325416312; 14.3312274189707; 14.4071122346908; 14.4830860227061; 14.5591478179508; 14.6352966574703; 14.7115315815553; 14.787851634907; 14.8642558678259; 14.9407433374142; 15.0173131087819; 15.401364480906; 16.1751373988038; 16.9558134611595; 17.7432208682398; 18.5366976599676; 19.3360988502003; 20.1412225692689; 20.9517507672929; 21.7672310558863; 22.5871115634685; 23.4107980865695; 24.2377021890869; 25.0672663781241; 25.8989689893876; 26.732318357514; 27.5668446164644; 28.4020933015927; 29.2376215872816; 30.0729965057542; 30.9077942826816; 31.7416001931033; 32.5740086297993; 33.4046232539953; 34.2330571812868; 35.0589331874899; 35.8818839295189; 36.701552179391; 37.5175910702657; 38.3296643536716; 39.1374466671854; 39.9406238119064; 40.7388930391313; 41.5319633456945; 42.3195557774861; 43.1014037407076] mW/m/K.

Dependencies

Enabled when the Trace gas model parameter is set to Track mass fraction and gas properties.

Trace gas diffusivity in air — Smoothing coefficient for flow reversals

16 mm^2/s (default)

Coefficient for the diffusive flux of trace gas in the moist air mixture due to the difference in concentration of trace gas. During mixture flow reversal, the trace gas mass flow rate at the ports smoothly transitions between the upstream and downstream value based on the diffusivity.

Dependencies

Enabled when the Trace gas model parameter is set to Track mass fraction only or Track mass fraction and gas properties.

Extended Capabilities

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

Version History

Introduced in R2018a

R2024b: Model water droplets suspended in moist air flow

Blocks in the moist air domain can now model water droplets suspended in a moist air flow. To model water droplets, select Enable entrained water droplets in the Moist Air Properties (MA) block connected to your moist air network.

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.

Use the Enthalpy reference state parameter of the Thermodynamic Properties Sensor (MA) block to 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: Control block behavior when moist air properties go out of range during simulation

Previously, if moist air properties went beyond the valid range during simulation, the block would return an error. You can now use the new Pressure and temperature outside valid range parameter to control the block behavior if moist air properties go out of range during simulation.