How to accurately measure mass flow through server vents using an anemometer
How to accurately measure mass flow through server vents using an anemometer
(OP)
I have to work out the air mass flow coming out each vent on a server and have proposed to use a hot wire anemometer to measure the air velocity at each vent by placing it slightly inside one outlets of the vent (it is a grid pattern), then multiply that by the vented area and air density to find mass flow.
My concern is that I am instructing technicians to do it on site, and I am worried that the measurements may vary significantly depending on where on the vent they are taken from i.e. if they take it from the corner or side of the vent it may be different from the centre.
This is my first time trying to measure something like this and was wondering how others in the industry do it. Is there a better way of doing this?
My concern is that I am instructing technicians to do it on site, and I am worried that the measurements may vary significantly depending on where on the vent they are taken from i.e. if they take it from the corner or side of the vent it may be different from the centre.
This is my first time trying to measure something like this and was wondering how others in the industry do it. Is there a better way of doing this?





RE: How to accurately measure mass flow through server vents using an anemometer
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm
RE: How to accurately measure mass flow through server vents using an anemometer
Look at this: http://www.tsi.com/uploadedFiles/_Site_Root/Produc... and also scroll down this rather rambling thread
http://www.eng-tips.com/viewthread.cfm?qid=424482
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: How to accurately measure mass flow through server vents using an anemometer
Keith Cress
kcress - http://www.flaminsystems.com
RE: How to accurately measure mass flow through server vents using an anemometer
I could get the technician to take several measurements across each vent, but there are a total of 14 vents and he has to place the anemometer in place then shut the rack doors for each measurement, which will be quite tedious.
I was thinking about getting the tech to take a measurement from the middle of each vent to find the maximum velocity. We have a similar server here at head office that I could then take some measurements from to develop a rough velocity distribution across each vent, then scale that up or down with the maximum velocity the tech found.
Does anyone have a better idea on how we could do this?
RE: How to accurately measure mass flow through server vents using an anemometer
Hire a TAB contractor. Why invent the wheel? An independent will give you data with certs on the tester and instrument.
RE: How to accurately measure mass flow through server vents using an anemometer
(a photo would help) and/or a drawing of the "vent"
So you have a fan driven entry for cooling air and this exhausts through a series of metal holes?
I think the variance will be too difficult to average and will vary too much depending on what is in the cabinet and nd how it is fixed, type of tray inside, how well the door seals etc etc
Why don't you measure air in? would seem much easier?
Why are you doing this?, maybe there's a better way.
The flow rate and velocity of these things must be pretty low - you will get a large error trying it your way. IMHO.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: How to accurately measure mass flow through server vents using an anemometer
A TAB contractor will have a hood which will give you much better information.
RE: How to accurately measure mass flow through server vents using an anemometer
RE: How to accurately measure mass flow through server vents using an anemometer
Keith Cress
kcress - http://www.flaminsystems.com
RE: How to accurately measure mass flow through server vents using an anemometer
The photo below is a photo I've pulled off Google to show similar server venting.
The server that is having issues is not at my site so I am instructing a technician to take the readings. We do have an identical server configuration in our office, but a different server rack setup (which means different mass flows going through each server). My plan is to measure the velocity of each individual square of each vent we have in our office (yes, hundreds of them) and then place the readings in Excel. I have a TSI 9535 and a low velocity pitot tube to take the readings. From there I can build a velocity profile for each vent, which means the technician will only have to take one reading from a certain square and I can scale that value according to the velocity profile that I have for that vent. The reason for doing it this way is because the technician will not have enough time to take hundreds of readings in the field. The velocities will obviously be different values, but the relative velocity profiles of the vents should be the same.
RE: How to accurately measure mass flow through server vents using an anemometer
Wouldn't measuring air flow of the two fans provide a decent measure of combined air flow?
I'd think that thermal convection is minimal compared to the forced draft from the fans.
RE: How to accurately measure mass flow through server vents using an anemometer
I need to measure the airflow going in each server and coming out of each server vent, along with the temperature at each in order to calculate the heat produced by each card. Only then can we decide what needs more airflow and how we can achieve it.
RE: How to accurately measure mass flow through server vents using an anemometer
I would have thought what you need to do is create a grid of thermocouples all over the server cabinet and monitor temperature gain over time. Then you will find the literal "hot spots" and can do something about it.
An admirable attempt to do this from first principles, but I can't see it providing you with the real life information you need.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: How to accurately measure mass flow through server vents using an anemometer
That server in the photo is not the server I am measuring off - it is a generic image from Google. Yes those fans are small, I don't see why that is relevant though. There are many more fans in the system.
The servers we have in the office are the same as the servers in the field. The rack setup is different, yes. This means different magnitude airflows through each server. However I would have thought that the relative velocity profile would be approximately the same on each server i.e. if you record a single velocity reading from a specific spot on the field server, we can compare it to the same measurement taken on the office server to see how they differ. See below.
Then it is should just be a matter of calculating the average velocity, calculating the mass flow and then calculating the heat flow.
We have already setup temperature loggers at each air outlet. Originally the technicians just recorded temperature, however temperature alone won't tell us how much heat is being produced by the cards. To find this we need the mass flow, hence the velocity meter readings. Again, the reason for doing this is to understand exactly how much airflow is going through each partition in the server, how much heat is being produced in each partition, and how much airflow there actually should be. This will govern how we make changes to the current setup and how we also design future servers and racks.
RE: How to accurately measure mass flow through server vents using an anemometer
RE: How to accurately measure mass flow through server vents using an anemometer
I think DrRTU is correct - what you're interested in is heat , so go find the heat / temperature. You can worry about the air flow later when you're trying to solve the heat / temperature issue. So instead of just measuring the heat at the outlet, measure many more locations within the cabinet.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: How to accurately measure mass flow through server vents using an anemometer
rejection you use a wattmeter(s) to give you the precise heat load. There is no
other heat being dumped in the box than the heat brought in by the electrical
power. If this was some huge room with burners and electrical loads and heat
conveyance piping you'd need the complicated air flow volume and temperature to
get your heat rejection number but not with a server.
Keith Cress
kcress - http://www.flaminsystems.com