Air Flow Meters for Kilns

      A discussion on the state of technology for monitoring airflow inside a kiln during drying, and about whether the data is useful in any case.June 13, 2014

Question
I am looking for a portable air velocity meter with data logging capability that would be suitable for measuring and logging air velocity inside my kilns. I would like to be able to place this meter inside the kiln for a given length of time and then be able to download the readings to a computer. Can anyone recommend a good meter for this?

Forum Responses
(Commercial Kiln Drying Forum)
From contributor W:
Do you have a computer running the kiln? If so, whoever supplied it can provide you a velometer and program. Simply measuring the temperature drop across the load is as helpful.



From contributor D:
This is more than you are asking for but we have an instrument that we developed for Penn State. It collects data on air velocity, temperature and humidity on both sides of the stack. Data is transmitted through a wireless connection to an office computer where software turns it into historical graphs, etc.


From Gene Wengert, forum technical advisor:
As air velocity changes little, if any, during a kiln run (except for heating up cycle when air density changes are large), you should be able to figure air flow based on current going to the motors and be very accurate and also be fairly inexpensive.


From contributor W:
Figuring the air flow inside a kiln is not so simple. Anyway it depends from the precision you need and from what you want to do with velocity data. If you want to study flow dynamic in stacks you should look for a little anemometer to influence the air flow as little as possible. Probably a hot wire anemometer is a good choice but it can't be left in a working kiln because it suffers much pollution.


From Gene Wengert, forum technical advisor:
Hot wire anemometers are not very good for kiln work unless they are 100% uni-flow. The problem is that the flow in the non-x direction causes an increase in the reading, but the flow of air is not increased.


From the original questioner:
In the past we have used simple handheld meters to measure airflow. They are easy to use, accurate enough for our purposes and work great for spot checks. However, these types of meters require our kiln operators to enter the kiln while the fans are running, and we feel that there can be potential safety issues in having a person taking measurements and working inside the kiln while itís in operation. I believe taking airflow readings on a regular basis important, and that's the main reason for the post, is to get some alternate ideas.


From Gene Wengert, forum technical advisor:
I am curious what you do after the readings are made. Do you use the readings for making any determinations that you will change the drying conditions? (For example, if the values in one spot are low for one particular run, do you have the lumber repositioned? I have seen many instances of measuring air flow, but very few where the values were used to make any decisions. Hence, knowing the air flow values from run to run is seldom of any value to most folks.


From contributor B:
All of those things can be determined by checking with a traditional anemometer while the kiln is running at various stages in the process. The only problem I see is the safety factor is at high temps, as alluded to above. I agree, unless you are going to make some sort of change in the load during the kiln schedule, which is not practical, I'm not sure that recording the info is necessary.


From contributor Y:
Measuring current flow to the fan motors is accurate to determine the fans velocity but not quite as accurate in measuring the air velocity. Lumber stacking can have a great effect on the air velocity.


From contributor K:
If a hotwire anemometer is the chosen method to measure the airflow, the best one given your application is made by Kurz Instruments. It is made for high temperatures and is the same type of unit designed for use in smoke stack emissions measurement. It is the hardiest portable out there.


From Gene Wengert, forum technical advisor:
To contributor K: In lumber drying, air flow affects drying especially above 40% MC and somewhat down to 20% MC, but not much under 20% MC. At these higher MCs, almost all kilns are 130 F or cooler. Hence, there is not any need for the high temperature unit you suggest.



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