Fluids

Fluids

Why my droplet is experiencing drop in temperature during injection in DPM

    • RajasekarK123
      Subscriber
    • DrAmine
      Ansys Employee
      Are you injecting enough particles? What about your computational grid? Which sub-models are activated? What is the definition of your particles in terms of composition?n
    • RajasekarK123
      Subscriber
      I am injecting single particle(0.2 NaCl and 0.8 water) water is set to evaporate and NaCl not. Energy is ON, Turbulance model is Realizable K- epsilon, Species transport ON, DPM is ON and set to 10 interactions with continuous phase after established continuous flow field. n
    • RajasekarK123
      Subscriber
      I did face mesing for an axisymmetric domain. the domain size is 0.6 m in length and 0.125m in height. i meshed with 1mm mesh size.n
    • Rob
      Ansys Employee
      Please can you post images of the fluid temperature. How big is the droplet? n
    • DrAmine
      Ansys Employee
      as well as the multicomponent droplet properties.n
    • RajasekarK123
      Subscriber
      (Nacl (fluid droplet-particle)ntt(chemical-formula . Nacl)ntt(density (constant . 2160))ntt(specific-heat (constant . 88))ntt(thermal-conductivity (constant . 0.574))ntt(viscosity (constant . 0.001))ntt(dpm-surften (constant . 0.063))ntt(molecular-weight (constant . 58.44))ntt(reference-temperature (constant . 298.15))ntt(volatile-fraction (constant . 0.01))ntt(binary-diffusivity (constant . 1.57e-9))nt)nnt(Nacl-water (particle-mixture)ntt(species (names h2o Nacl))n
    • RajasekarK123
      Subscriber
      the droplet diameter is 1.8mm n
    • RajasekarK123
      Subscriber
      n
    • DrAmine
      Ansys Employee
      Not enough: screenshot from the panel of multicomponent particles to check what is set there. Is the case two-way coupled? If node based averaging is enabled please disable it. Just use Linearize Source Terms instead.n
    • RajasekarK123
      Subscriber
      when i keep higher temperature difference between the droplet and ambient the solution looks good but having low temperature difference causes the drop in temperaturen
    • RajasekarK123
      Subscriber
      n
    • RajasekarK123
      Subscriber
      The case is two way couplednn
    • RajasekarK123
      Subscriber
      AFTER LINEARIZING SOURCE TERM SAME RESULTS OBTAINEDn
    • RajasekarK123
      Subscriber
      hi I tried with the multicomponent droplet evaporation case file given in the customer portal, i changed the fluid temperature 301 and droplet temperature 300. other parameters are same as in the case file. in this case also droplet temperature is reducing, i attached the plot for the simulationnn
    • RajasekarK123
      Subscriber
      Sir, I am expecting your kind help for finishing the work, please help me.n
    • DrAmine
      Ansys Employee
      Which case on the customer portal? I will need to check it.n
    • DrAmine
      Ansys Employee
      Let me describe what can be realistic: droplet will heated till it reaches the vaporization temperature stars the law 2 then law 3. The latent heat is provided from continuous phase, temperature is reduced of the gas phase which might affect the droplet too if caught in re-circulation region or has a large stokes numbers. Same might happen with MM particle. But the change should not be dramatic for that reason: if you have seeing the behavior on a case from the customer portal please share with us the case / solution number.nnWorth testing though with update source terms every iteration / transient particle tracking.n
    • RajasekarK123
      Subscriber
      I wil provide the link of that case file here sirn
    • RajasekarK123
      Subscriber
      n
    • RajasekarK123
      Subscriber
      the solution number is 2046025n
    • RajasekarK123
      Subscriber
      I found a reason for the temperature reduction from a journal https://journals.ametsoc.org/jas/article/8/2/71/37827/THE-EVAPORATION-TEMPERATURE-AND-THERMAL-RELAXATION which says the droplet will reach the wet bulb temperature of the air to evaporate.nI am not confirm about the results, but the justification is somewhat acceptable.nKindly help me whether its correct or notn
    • DrAmine
      Ansys Employee
      Are you a commercial customer? Have you read my explanation? I will look in the files. Please be patient. n
    • RajasekarK123
      Subscriber
      Yes sir, now reading your previous explanation. n
    • DrAmine
      Ansys Employee
      Files are looking good and are in line with my explanation.n
    • RajasekarK123
      Subscriber
      sir did you check that with temperature modification like particle temperature 300 and air temperature 301. did you observe temperature reduction of particle?n
    • Rob
      Ansys Employee
      How big is the cell the droplet is injected into? Remember the droplet is tracked as a point mass but dumps all of it's evaporated mass & removes ALL of the energy needed to do this into one cell. If the droplet is bigger than the cell interesting things happen to the results. n
    • RajasekarK123
      Subscriber
      Dear Rob, The droplet size is 1.5 mm, cell size is 1 mmn
    • RajasekarK123
      Subscriber
      Any way I checked with the case file given by ansys and all the parameters are same in the case file but changing only the temperature makes these reduction in drop temperaturen
    • Rob
      Ansys Employee
      Decrease the droplet diameter to 0.01mm and see what happens. n
    • RajasekarK123
      Subscriber
      same reduction in temperature is observed. no change in the patternn
    • DrAmine
      Ansys Employee
      Still willing to know what do you expect? The gas is cooled as we are evaporating, now the cooled gas is in the contact with the non volatile part of the particle, heat exchange-> droplet is cooled. Also check the change of heat sing in the dpm summary: A positive Change of Heat denotes that heat is expelled from the continuous phase and absorbed by the particle, while a negative Change of Heat denotes heat is released by the particle to the continuous phase.nnDouble check if the sum of the DPM Enthalpy Source is in the same magnitude range as the one from the DPM summary (with negative sign)n
    • RajasekarK123
      Subscriber
      Thank you Amine sir for your kind explanation for all my queries. n
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