Sock drying out on Nyle L53

[Dzag]

Hello folks,
I'm having trouble with the sock/wick drying out on my wet bulb and for the life of me can't figure out why. We're on our third load and every few days it drys out but yet there's still water in the reservoir. We've installed the wet bulb within about an inch of the water reservoir where you can barely remove the lid. Also have distilled water in the reservoir. Any ideas would be greatly appreciated. Everything else seems to be working as it should but I know the wick on the wet bulb drying out every couple days shouldn't be happening.

[Southside]

Is it getting too much air flow? Do you have a photo of it as installed? 

[Dzag]

Is it getting too much air flow? Do you have a photo of it as installed?

I don't think so. I was originally thinking maybe that was the case so I added a board on the bottom and front to break any air flow coming back and under the stack. I'll take a picture tomorrow and post it to get your thoughts. It definitely has me scratching my head at this point.

[Southside]

What's the moisture content of the load in there now?  Are you pulling moisture from the lumber or is it locked up and you have a very dry chamber - thus drying out the only moisture in there being on the wick?

[YellowHammer]

Is your sock higher or lower than the water in reservoir?  It needs to be level to lower.

Cut some off and try a new section, or reverse it.

Thread the wick through a piece of Tygon tubing from the bottle to the sensor to totally enclose it.

You must also have a very dry chamber.   

[Dzag]

Is it getting too much air flow? Do you have a photo of it as installed?

What's the moisture content of the load in there now?  Are you pulling moisture from the lumber or is it locked up and you have a very dry chamber - thus drying out the only moisture in there being on the wick?

Currently I'm at 11 percent my wet bulb is set at 95 and dry bulb set at 120 and I'm reading about 98 on the wet bulb and the dry at 119-120. I'm assuming I'm drying too fast as well as this load went in at 22 percent and in 14 days I'm at 11?

[Dzag]

Is your sock higher or lower than the water in reservoir?  It needs to be level to lower.

Cut some off and try a new section, or reverse it.

Thread the wick through a piece of Tygon tubing from the bottle to the sensor to totally enclose it.

You must also have a very dry chamber. 

I'm level with the cap. I do like the hose idea.

my wet bulb is set at 95 and dry bulb set at 120 and I'm reading about 98 on the wet bulb and the dry at 119-120. I'm assuming I'm drying too fast as well as this load went in at 22 percent and in 14 days I'm at 11?

For the record I'm in south east Texas.

[Dzag]

I'm obviously still learning here so I appreciate any feed back gentleman.

[Dzag]

Also my chamber is a 20' container with closed cell spray foam.

[YellowHammer]

No, 98/120 is about right, 1% EMC change in the wood is a little slow unless it is a white oak species.

Not level with the cap, level to the average height of the water in the reservoir.  It the water is not flowing fast enough due to the absorbency and the capillary effect of the muslim fibers to keep up, then try to reduce the head pressure by lowering the end of the sock. 

Also, how tight is the hole in cap?  Is it restricting water flow?  I drilled mine open a notch.  The wet fibers can swell and plug the flow. 

How old is the sock, how many times has it been used, (three)?  Is it crusty?

If you are reading wet bulb at 98% why do you say the wick is dry? It only needs to be slightly moist, at most, for evaporative cooling to achieve an accurate WB reading.  

[Dzag]

No, 98/120 is about right, 1% EMC change in the wood is a little slow unless it is a white oak species.

Not level with the cap, level to the average height of the water in the reservoir.  It the water is not flowing fast enough due to the absorbency and the capillary effect of the muslim fibers to keep up, then try to reduce the head pressure by lowering the end of the sock. 

Also, how tight is the hole in cap?  Is it restricting water flow?  I drilled mine open a notch.  The wet fibers can swell and plug the flow. 

How old is the sock, how many times has it been used, (three)?  Is it crusty?

If you are reading wet bulb at 98% why do you say the wick is dry? It only needs to be slightly moist, at most, for evaporative cooling to achieve an accurate WB reading. 


I actually just put a new sock on for this load. It drys out to the point where it does feel a bit crusty and then the wet bulb will sky rocket up to over 110.

I will try lowering my wet bulb though to be even or lower than the water in the reservoir.

[jimF]

If you are not forming surface checks you are not drying too fast. The faster you dry, the more effective the conditioning process will be. Also, you cannot dry slow enough to make conditioning unnecessary, if you are going to resaw the lumber to make parts.
 I think the design/arrangement of your wick setup is part of the problem of a dry sock. The picture shows that is a long way from the water to the sensor. Typical commercial arrangement is the sensor about an inch directly above a trough of water and the "sock" is like a curtain draped over the sensor into the water.
As in a recent thread, I disagree with most comments here, you must have the full blast of the airflow over the wet-bulb to get an accurate reading. If the sensor/water setup if good, your sock will not dry out due to airflow; unless you have other problems like: the RH is too low or mineral build up.

[doc henderson]

what is the species.  in general, increasing exposure to dry air dehydrates things.  a human in the wind has increased fluid loss.  a human breathing faster or with high minute ventilation, loses more water.  It seems reasonable that direct air at 100 mph vs 2 mph would make a difference.  the drop in temp is due to pulling heat for the phase change of the water to vapor.  you do not want the sock to be in its own microenvironment like in an enclosure, but straight-line wind in your kiln would surely change the readings as you pull more water into the air.  larger air volume per minute at less than 100% RH hitting the sock.  based on general knowledge this makes sense to me.  I am however not a wood drying engineer. @jimF  

[jimF]

The sock will only dry out to a level specific to the RH it is exposed above an air velocity. Whether it is 200 ft/min or 800ft/min but will not reach that level in say 5ft/min. You want to get the velocity above the point where the drying will not change for a given RH. This is how the psychometric chart are calculated.

A wood drying research scientist I am, if you are interested.

[doc henderson]

yes, I read your profile.  I appreciate your input.  I feel there is a happy spot in the middle whereas the extremes may cause error.

[doc henderson]

I found the chart.

[Southside]

The picture shows that is a long way from the water to the senso

The bulb is quite close to the water in those photos, any closer and it would be in the water. The distance between the bulb and the water is pretty much the same as my kiln so I don't think that is the problem. 

[doc henderson]

copy from search follows.  it stated elsewhere that a min. Of 2 M/S was needed to overcome the layer of humidity around the wick on the wet bulb.

Air velocity plays a significant role in the phenomenon of wet bulb depression, which is the difference between the dry bulb temperature (the regular air temperature) and the wet bulb temperature (measured using a thermometer covered with a wet cloth). Let's explore how air velocity impacts this:

• Scrubbing Away Boundary Layer:
  
  
  
  • Higher air velocity tends to scrub away the thin boundary layer of saturated moist air that forms around the wet bulb surface.
  • This boundary layer affects the accuracy of wet bulb temperature measurements.
  • By increasing air velocity, we reduce the influence of this boundary layer, leading to more accurate wet bulb readings¹.
• Temperature Drop Across the Load:
  
  
  
  • When air flows across a wet bulb thermometer, it evaporates water from the wet cloth.
  • The rate of evaporation depends on the dryness of the air flowing over the wet bulb.
  • Higher air velocity results in faster evaporation, leading to a greater temperature drop across the wet bulb.
  • Consequently, the wet bulb temperature decreases more, resulting in a larger wet bulb depression².

In summary, increased air velocity enhances the accuracy of wet bulb measurements by minimizing the boundary layer effect and promoting efficient evaporation. Understanding these effects is crucial for applications such as climate control, meteorology, and industrial processes. 🌡�💨

[doc henderson]

i also found the following.  looking for information and an academic discussion.  thanks Jim.  Doc.

The numerical difference between the dry- and wet-bulb temperatures is known as the wet-bulb depression. Since the rate of moisture evaporation depends on the speed of the air over the wet-bulb, the wet-bulb temperature will also depend on the air speed. However, the wet-bulb becomes independent of the air velocity above 2 m/s.

[jimF]

for those of us that relate better to miles/hour; 2m/s equals 4.5mi/hr.
If your readings are effected by diverting some of the airflow, it would indicate the airflow over your sock is  less than 4.5mi/hr.

As for the arrangement of the water/sock, the sensor may not be much above the water but that horizontal distance might cause the water to evaporate before it reaches the sensor. therefore not providing the amount of water needed at the sensor to provide accurate readings.

[doc henderson]

wouldn't low airflow be less likely to dry out the wick, as it is buffered by a humid local microenvironment, that is not being moved by adequate airflow greater than 4.5 mph? 
that would increase saturation and decrease evaporation and decrease the WB depression estimating a higher RH kicking on the compressor.?
sounds like the capillary action on the sock cannot keep up with evaporation, so maybe the RH is too low for the system as is.

[jimF]

It is possible, it would need a comparison testing or specific data input: airflow. water consumption etc for detailed calculations.  Why not just use the conditions the calculations assumed that were used for the psychometric chart, they use stable conditions that don't vary for setup to setup?

[doc henderson]

And that is the issue.  what is going on here that does not meet the standard setup?  Is it a very dry kiln or is the mechanism not set up right?  some feel it is plenty close and others feel it is too far.  I think we are both trying to help.  you have education, training and experience.  Is it faulty equipment?  what I am getting is there is a for sure low limit air speed that will make the WB not accurate and poss. and extreme high speed.  I guess he could measure and see if he has at least the 2 M/S.  But prob. not a need for a huge amount over that.  I am trying to ask questions, and hopefully you can continue to help with answers and information.  thanks Jim.

[doc henderson]

@Dzag are you able to measure your airflow?  Does your wood continue to dry?

[YellowHammer]

Cut some off and try a new section, or reverse it.

You must also have a very dry chamber. 

2 m/s is 393 fpm.  It looks like he is using a Nyle kiln, with a Nyle supplied water bottle.  In my discussions with Don Lewis, owner of Nyle kilns, many years ago, he would design the kilns for a very conservative hardwood air flow rate, at 150 fpm, which is below the optimum for many species but he felt it would prevent most kiln operators from harming hardwood.  He knew it was slow, but he had his reasons, he considered it a safe airflow for his systems, and so designed and supplied kiln hardware for it.  

So, in most of these kilns, there is not enough fan flow to reach optimal psychometric air velocity along the walls of the kiln where the bottle is mounted, unless additional fans are installed to get the overall airflow and velocity up, which I have done in all my kilns.  Therefore, given the potential design con(restraints) of the kiln, it is essential to put the wick in a region in as much airflow as possible, and the general instructions with with the kiln are "put the wicks in a high airflow area zone" or something like that.  I had not noticed it before but the cradle the bottle is in has a piece of wood potentially blocking the airflow over the probe.  

I would convert the cedar bracket to a shelf, with an open side, to increase airflow.  I would make sure the probes are in a "high airflow" area and since there already is excessive drying of the wick, would probably go ahead and move it to another location, in leu of having an anemometer and doing an air velocity survey.

I would cut off a new section of wick.

You must have a very dry chamber that is drying the sock before the moisture gets to the portion of the sock over the probe, which is actually mounted about as close as possible given the constraints of the Nyle water bottle system allows for that setup.  The cap is about 2" diameter, and the RTD probe about that as well n length, so the the total sock exposed is about 3" give or take, just enough to clear the cap for removal, and enough to fully cover the probe.

Most kiln recreational operators do not have an anemometer to measure air velocity.

So I would double check:
Put the WB and DB probes in a region in the kiln where there is high(er) airflow, given the design of the kiln and the fan placement.

Make sure the water has adequate pressure head to flow down the wick to the area of the probe.  I personably like to drill a hole and come out the side of the water reservoir, not out of the lid, as this makes the run to the RTD probe shorter, more closely aligns the wick to the height of the average water level, and also makes removing the cap and refilling easier.  As a general rule, if the wick is close mounted (it looks like it is given the water bottle configuration) and the height of the sock is correct, if it has been trimmed back and fresh, and the water level correct, then water should be freely wetting the wick.