KR21: How to verify if the injected spray-mass is correct or not in FLUENT?
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In many spray related applications, it is important to ensure if the sprayed mass is consistent with that of the test conditions. Many of these applications involve evaporating sprays. In SCR systems, the spray is a mixture of urea and water (multicomponent). In many In-cylinder applications, the spray velocity (and hence mass flow rate) varies with time. In all these situations, there are high chances that the spray mass flow-rate is incorrectly specified. To ensure that the spray-mass is correct, do the following: Go to Report ->Discrete Phase->Summary, Select all the injections and click on Summary. This will report the summary of each injection on Fluent console. The end of this report will have "summary of all injections". Note the "Total Mass (kg)". This is the liquid mass present in the system. Now go to Report ->Volume Integrals, select "Mass Integral" under "Report Type", and select all the cell zones. In the Field Variable, select "Species" and "Mass fraction of evaporating species". Click on Compute and note down the vapor mass of the injected spray in the system. Take a sum of the liquid mass (from step 1) and vapor mass (from step 2) and this will give you the total injected mass. Confirm that the actual injected spray mass (from your tests) is the same as the injected mass you calculate from step-3 above. Example: There is a variable flow-rate injector that injects fuel into in-cylinder of a diesel engine. The flow rate varies with time. Therefore, to calculate the total flow rate, you need to find out area under the "Mass flow rate" vs. "Time" curve. Assume that this mass is 2.63653e-05 kg. Now you need to find out the injected mass from your Fluent setup. For this, you will have to run the case till you exceed past the "stop time" specified in the injections panel. Figure-1 below explains steps to calculate injected mass. Note the following: This procedure applies to a closed system. If your model has inlets and/or outlets, you'll have to also keep a note of the amount of liquid (and vapor) mass that has entered or left the domain. For multi-component sprays, in step-2, you will have to find mass integral of the mass fraction of each of the evaporating species separately and then sum it up. c. If you have wall-film model in your setup, the "Total mass (kg)" in step-1 will include the wall-film mass. |
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