# Creating and implementing UDF for DPM droplet evaporation rate

 Register Blogs Members List Search Today's Posts Mark Forums Read September 10, 2023, 06:39 Creating and implementing UDF for DPM droplet evaporation rate #1 New Member   Join Date: Aug 2023 Posts: 5 Rep Power: 2 Hi, I am trying to simulate a flash atomizing water spray. I've read that the 'pressure boiling' and 'temperature dependent latent heat' models do not calculate an appropriately fast evaporation rate and I will need to use a UDF. I am currently doing a steady sim with interaction with continuous phase turned on. I have never used UDF's (or have programming experience beyond matlab) and don't know where/how to start. This is the calculation process (see below) I essentially need to follow (the code is written in Matlab, and I have all the parameters except for each droplet diameter, which I need to take from ansys at each iteration to get the new mass transfer rate (which is the mass removed from the droplet and added as a eulerian vapor phase). Any help as to how I would turn this into a UDF would be much appreciated. Thanks %% flashing mdot component % get surface area of particle using diameter provided by ansys D = D_p; % FROM ANSYS A_p = 4*pi*(D/2)^2; % using thermo constants and calculated alpha, along with surface % area calculate mass transfer from flashing mdot_flash = alpha * A_p * (TSH_act) / liq.hv; %% condensing mdot component % calculate Re with that D Re_star = liq.rho*u_rel_initial*D/mu_ref; % calculate Pr with known values Pr_star = mu_ref*cp_ref/k_ref; % calculate Nu* using Frossling correlation Nu_star = 2 + 0.552 * Re_star^0.5 * Pr_star^(1/3); % solve via netwon raphson % error tolerance err = 1e-20; % initial guess mdot_cond = 1; % initial diff diff = 1; % loop until converged mdot_cond while diff > err % coefficient for equation using fluent droplet diameter c1 = 2*pi*k_ref / cp_ref * D/2; % set old flow rate for difference calc m_old = mdot_cond; % set ratio for evaporation ratio_fc = mdot_flash/m_old; % calculate new mdot_cond mdot_cond = abs(c1 * (Nu_star / (1 + ratio_fc)) * log(1+(1+ratio_fc)*... ((h_ref-liq.h) / liq.hv))); % check difference from previous guess diff = abs(m_old-mdot_cond); i = i+1;end %% total mRES = mdot_cond + mdot_flash;  Tags dpm, evaporation, flashing flow, udf Thread Tools Search this Thread Show Printable Version Email this Page Search this Thread: Advanced Search Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are Off Pingbacks are On Refbacks are On Forum Rules Similar Threads Thread Thread Starter Forum Replies Last Post Schmitt pierre-Louis FLUENT 26 September 1, 2016 11:29

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