AcuSolve Humid Air Model - Condensation And Evaporation Models

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AcuSolve Humid Air Model - Condensation and Evaporation models

28-05-2020 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.Humid Air Modelling- Condensation and Evaporation Modelling- Introduction Basic feature of Humid Air Model is already released in 2018 version of AcuSolve. This version is capable of predicting the relative humidity and dewpoint temperature. With 2020 version, Acusolve shall be capable of quantifying condensation andevaporation using humidity film thickness.Industrial Application includes refrigeration, headlamp, drying unit, HVAC

28-05-2020 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.Humid Air Modelling- Condensation- TheoryCondensation in AcuSolve is a surfacephenomenon and is triggered whensurface temperature is less than dewpoint temperatureEvaporation in AcuSolve is a surfacephenomenon and is triggered whensurface has water layer on it andtemperature of surface is greater thandew point temperature

28-05-2020 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.Humid Air Modelling- Condensation and Evaporation - Theory From Fick’s Law for binary system in stationary coordinate system, mass fluxes of vapour and airdefined as:Rearranging the the above two equation:Under the assumption that air does not dissolve inwater deposited, above equation becomes : Based on Latent heat, Heat Source or Sink: Humidity Film Thickness:CondensationEvaporation

28-05-2020 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.Humid Air Modelling- Condensation and Evaporation-TheoryHumidity film thickness Condensation and Evaporation areimportant phase change phenomenaassociated with Humid Air. These phenomena account for change ofphase - from water vapour to water forcondensation or from water to watervapour for evaporation on the surface.Condensation,Evaporationcheck Condensation releases latent heat storedin the vapor into system whileEvaporation process takes that heataway from the systemLatent HeatReleased/consumedRelative humidity,Dewpoint temperatureVelocity,pressuretemperatureWater vapour,dry air

28-05-2020 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.Condensation and Evaporation Problem Setup Humditiy Film thickness represent Condensation or evaporation phenomenon in aproblem. This needs to be modelled under Humid air model category. Humidity Film Thickness calculation is dependent on inital value hence this needs tobe modelled under transient simulation category. Humdiity film thickness variable value is assigned using the nodal initial condition. In addition to above, relative humidity or dew point temeprature value needs to beassinged at inlet boundary and in nodal initial condition.

28-05-2020 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.Condensation and Evaporation Model- Validation -Pool Evaporation Pool evaporation rate is a function of wind velocity andvapour pressure difference between the pool surface andambient vapour pressure which is defined as: where Pw is saturation vapour pressure at the pool surfaceand Pa is ambient vapour pressure which dependent onRelative humdity of the air. Pool Evaporation due to forced convection is studied atdifferent wind velocity (parallel to pool surface) of 2, 3 and4 m/s and pressure difference of 2,4,6 and 8 Kpa Pool Surface is maintained at 30 C and ambient air at 20 CExperimental Set-up

28-05-2020 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.Condensation and Evaporation Model- Validation -Pool EvaporationDifferent Plots from the case of wind velocity 2m/s and delta P 2Kpa

28-05-2020 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.Condensation and Evaporation Model- Validation -Pool Evaporation-ResultRef: Al-Shammiri, M. (2002). Evaporation rate as a function of water salinity. Desalination, 150(2), 943-8

28-05-2020 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.Condensation and Evaporation Model- Validation 2 – Evaporation fromPlate in a Box Initial Condition outletPlate Temperature is 63 Cand humidity film thicknessof 2e-5 m.Fluid in box with relativehumidity is 77 % and 25 CtemperatureBox wall is at 20 C and nowater deposition on itOne outlet at top of boxPlate at 63 C

28-05-2020 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.Condensation and Evaporation Model- Validation 2 – Evaporation fromPlate in a BoxMean Evaporation Mass Flux at PlateAcuSolve13.2 gm/minElectrolux and BonnUniversity15.6 gm/minVapour mass fraction

28-05-2020 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.Humid Air Modelling- Evaporation in a tumbler GlassA tumbler kept in room filled with hot water Initial Condition – Tumbler and roomtemeprature is of 27 degree C and waterat 90 degree CComparison with and without evaporationprocess Phase change due to Evaporation creates aheat sink These changes are often significant.

28-05-2020 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.Condensation and Evaporation Model- HeadLamp Condensation A car headlamp is switched on when thetrapped air is at Relative humdity of 100%. The Lens of the headlamp is exposed toambient condition of 27 C Below is the Humidity Film thickness at time172 SecThis simulation can help in detection of condensation at headlamp lens surface

28-05-2020 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.Condensation and Evaporation Model- Charge Air Cooler Condensation Single Tube of CAC was considered forstudy with the following Tube Inlet BoundaryCondition: Velocity 12 m/s,Temp 55 deg C, andRelative Humidity 50% Tube casing is made of Aluminium with thedimesnion of 680 mm x 64 mm x 7 mm. Appropriate heat transfer coeffient isimposed on tube external surface to reproduce the cooling fins effect The desired outlet temperature from CAC is26 CCac TubeCooling Fins

28-05-2020 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.Condensation and Evaporation Model- Charge Air Cooler CondensationThis simulation can help in quatifying the amount of water (gm/hr) that is beingdeposited on CAC tube on hourly basis

28-05-2020 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.Condensation and Evaporation Model- Dishwasher Aim – Time taken to dry up the utensilskept in dishwasher Initial Condition cupsDishes Temperature is 60 C, cupstemperature is 59 C and humidity filmthickness of 2e-5 m on both surfaces.Fluid in box with relative humidity is 82% and 60 C temperaturePlate and bowlsBox wall is at 55 C and no waterdeposition on itOne outlet at top of boxoutlet

28-05-2020 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.Condensation and Evaporation Model- DishwasherThis simulation can help in quantifying the efficieny of dishwasherVapour mass fraction

28-05-2020 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.Condensation and Evaporation Model- RefrigeratorFan Fluid Initial Condition temperature set to20 C, Relative humidity 95 %. Glass door is exposed to ambienttemperature condition of 20 C Evaporator when turned on is at -25 CEvaporator Coil

Basic feature of Humid Air Model is already released in 2018 version of AcuSolve. This version is capable of predicting the relative humidity and dewpoint temperature. With 2020 version, Acusolve shall be capable of quantifying condensation and evaporation using humidity film thickness.