WATER SPRAY SOURCE

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claudia
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Joined: Tue Jun 11, 2019 2:56 pm

WATER SPRAY SOURCE

Postby claudia » Wed Jul 24, 2019 3:31 pm

Good afternoon to all the ENVImet staff. I use the v4.4.3 Summer19 licensed version and I'm trying to understand how water sprays work. Once I created them in the database source directory, I tried to use them in the simulation, but some doubts came up. In my case I have 24 nozzles working simultaneously with "point" configuration and with a total flow rate of 1.5 liters / minutes. In the "emission profile user" item, the output is requested every hour: if the flow rate value is requested in µg / s, what should I write under the "hourly emission" item? A further question: is it possible to simulate a water spray with on / off operation? That is, if I had water sprays that work for 20 seconds and stop working every 10 seconds, what value should I write not only in the hourly emission, but also in the "adjust flow step"? Sorry for all these questions, but I really searched everywhere, not just on the forum, but I found little or nothing. For the moment I am doing various test simulations, but the doubts that this is correct are many. Thank you in advance.

Claudia

Tim
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Re: WATER SPRAY SOURCE

Postby Tim » Wed Jul 24, 2019 8:32 pm

Hi Claudia,

The user emission profile can only be defined for 1 hour, so the specified value will be contantly released during the hour in the simulation. You will have to calculate the value from your flow rate. On/Off operatiion cannot be simulated, you will have to take it into account when calculating the emission value.
Adjusting the flow step is about the calculation interval of wind flow and is not connected to the pollutant simulation.

Best regards,
Tim

claudia
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Joined: Tue Jun 11, 2019 2:56 pm

Re: WATER SPRAY SOURCE

Postby claudia » Thu Jul 25, 2019 9:59 am

Thank you very much Tim, you clarified my doubts. You are always very friendly and kind. Greetings and thanks again.
Claudia

claudia
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Re: WATER SPRAY SOURCE

Postby claudia » Tue Aug 20, 2019 11:41 am

Good morning to all the staff. I wanted to explain a problem to you: I did the same simulation with and without water spray respecting all the parameters and the initial settings, but the temperature does not change. I performed various simulations, but the results are always the same. I created my "user sources" called "water spray", I entered the hourly flow rates for each nozzle and verified that "multiple sources", "activechem" and "isoprene" are zero. Where can I go wrong? What is the value of the special ID in the database? Please help me understand how water sprays work.

Tim
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Re: WATER SPRAY SOURCE

Postby Tim » Tue Aug 20, 2019 12:23 pm

Hi Claudia,

I think in this topic (you probably already read), some details about water spray are answered, e.g. about the SpecialIDs: http://www.envi-hq.com/viewtopic.php?f=3&t=2716&p=8690&hilit=spray&sid=00d5ba553ec028586a82d7038ab6630f&sid=00d5ba553ec028586a82d7038ab6630f#p8690.

It should definitely have an effect on the output. If you are sure that you digitized the source in your model area and the values defined in the DBManager are large enough, you may zip the SIMX, INX and EDB file and upload the zip here. I will then have a look what could cause the issue.

Best regards,
Tim

claudia
Posts: 23
Joined: Tue Jun 11, 2019 2:56 pm

Re: WATER SPRAY SOURCE

Postby claudia » Thu Aug 22, 2019 10:30 am

Hi Tim. I followed the indications of what is written on the forum chat you indicated to me. The simulation stops after three hours creating a "Dump Panic": at the point where I have water sprays, an area is created with temperatures far below zero that send the simulation to crash. I tried and tried again, but the results are always the same. Before sending you what you asked, I wanted to ask you with a total flow rate of 1.5 liters / minute on 24 nozzles, each hourly flow rate requested during the simulation period is 1041666,667 μg / s. Is this calculation correct for you too? I ask because in the example of the fountain the value is 5 by far smaller. Am I wrong perhaps in the calculation and in the unit of measurement of the flow rate? Furthermore, when asking for the hourly flow rate at 0: 00h we mean the flow rate value at midnight or at the start of the simulation, which in my case occurs at 5 in the morning? I await a reply and thank you in advance.

Tim
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Re: WATER SPRAY SOURCE

Postby Tim » Thu Aug 22, 2019 2:57 pm

Hi Claudia,

I would say that the calculation is correct but the water amount is much too high. That amount of water can never be evaporated which caused the latent heat flux to get corrupted.
I'd try it with the default values.

0:00h is 0:00h and not the start of the simulation.

Best regards,
Tim

claudia
Posts: 23
Joined: Tue Jun 11, 2019 2:56 pm

Re: WATER SPRAY SOURCE

Postby claudia » Fri Aug 23, 2019 11:29 am

Hi Tim, thanks for the advice. I performed a test with 5μg / s value and the simulation turned, but reduced the temperature to a maximum of 0.3 ° C. I have verified flow rates in some scientific articles that treat water spray and actually the flow rates are much higher than the default ones. Furthermore, the one I mentioned in previous posts is the flow rate value suggested by the manufacturer: my work consists of a validation of experimental data and unfortunately I cannot change the flow rate of 1.5 liters / minute. I wanted to ask you if there is a max flow rate value beyond which the program crashes and if the title is actually correct, that is if the flow rate of each nozzle point is required in μg / s or in reality the etlice is not correct. Excuse me again for the trouble, but the flow values ​​to me seem really low. I await your clarifications and thanks again.

Tim
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Joined: Mon May 15, 2017 3:46 pm

Re: WATER SPRAY SOURCE

Postby Tim » Fri Aug 23, 2019 4:00 pm

Hi,

What I can say in general is that the flow rate of the nozzles being 1.5 l/min are probably not the values which should be used in ENVI-met. Of course, this amount of water will be sprayed by the nozzles but it is rather a mist of thick water droplets which do not evaporate instantly. They may be transported or they settle down on surfaces. What we simulate in ENVI-met is rather a fine spray of water droplets which are too small to be seen, e.g. emitted by a water fountain. These droplets evaporate more or less instantely causing the transformation of sensible to latent heat. Even if it is that huge amount of water to be sprayed by the nozzles, only a very small part of it will be considered as this water spray which ENVI-met wants to simulate. I think that may be the reason why the input values need to be that low.

We will definitely look into the source code once more within the next week and hope to understand why that values are considered as too low or why they are correct as they are. I will reply again, if I know whether that assumption above is correct or false.


Best regards,
Tim

claudia
Posts: 23
Joined: Tue Jun 11, 2019 2:56 pm

Re: WATER SPRAY SOURCE

Postby claudia » Fri Aug 23, 2019 4:19 pm

Thanks Tim for your concern. I will be waiting for your feedback. To next week.
Claudia

claudia
Posts: 23
Joined: Tue Jun 11, 2019 2:56 pm

Re: WATER SPRAY SOURCE

Postby claudia » Mon Aug 26, 2019 5:21 pm

Sorry again, I wanted to know if there are any new developments in the use of water sprays. In the online manual I read that the unit of measurement could be in mg / s and the manufacturer is unable to establish the emission of the final water powders. The only thing I know is that the flow rate written above evaporates completely for a height of nozzles of about 3 meters and the particles have a diameter of 10µm experimentally making a reduction of room temperature of about 2-3 ° C. Furthermore, by opening the 5µg / s test file taken from the pollutant folder in Leonardo, the water spray entries are completely void, although there is a minimal reduction in temperature. Why does this happen? What does it depend on? Is it not possible to have more information or a manual given that the version I use is licensed? I would like to reach a conclusion, as the search times are limited. Trusting in a swift response, I thank those who can help me.

enviadmin
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Re: WATER SPRAY SOURCE

Postby enviadmin » Wed Aug 28, 2019 5:58 am

Just to clearity: you do not enter the emissions summed up over an hour but the emission RATE for the different hours of the day per second.
That should lead to much lower values than your aggregation over 3600 seconds. Also your 1.5 l needs to be distributed over the 24 nozzles as you give the rate for each nozzle.
If you see a temperature effect then your setting should basically be ok and you should see data in the different fields of the pollutant file.
Do not use Multi-Pollutants if you work with water spray.
For the moment there us no publishable doc on the water spray but I will see what we can do

Michael

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Re: WATER SPRAY SOURCE

Postby enviadmin » Wed Aug 28, 2019 2:52 pm

I also think that you have mixed up the pump flow rate of the system and the output of a nozzlle. I have compared to some system I had on my disc, and it has a pump flow rate of 1.89 L/min (compareable to your figure), but the output (source) at a nozzle of 0.15 mm at a pressure of 70 Bar would be 4.01 l per HOUR..
You might want to check this...

Michael

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Re: WATER SPRAY SOURCE

Postby enviadmin » Wed Aug 28, 2019 3:07 pm

Also the emission rate for the spray is in g/s (compare to output data)

Michael

claudia
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Joined: Tue Jun 11, 2019 2:56 pm

Re: WATER SPRAY SOURCE

Postby claudia » Wed Aug 28, 2019 3:50 pm

Thanks Michael for your answers. I checked the data: each nozzle delivers a flow rate of 3.75 liters / hour. The pump has a pressure of 70 bar, a nominal water flow of 3litr / minute and the nozzle outlet diameter is 0.20 mm. For the nozzles I used a point source and one of my doubts is whether to take into account the volume of the cell in which the device is located and what was the unit of measurement to be adopted ("Particle filtering capacity of urban vegetation: A microscale numerical approach "). Knowing only the flow rate of the nozzles, how can I derive or refer to the emission rate value? Sorry again for the disturbance and if I have uncertainties in the use of the program, but I'm trying to deepen his knowledge.
Claudia


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