The Viscosity of Water Increases as Temperature Drops

This week we had a drop in temperatures from a range of 70 high/50 low oF to a range of 60/40 oF. I didn’t think much of it other than worrying about how my new cucumber, pepper, winter squash, and okra seedlings would fare in the cold weather. Much to my dismay, yesterday morning when I went out to see how my plants fared, the water level was really low. I had no idea what had happened, but I quickly filled my rain barrel and added the de-chlorinating agent to make it safer for the fish, and then drained all 50 gallons into the Aquaponics sump.   whew!

That evening when I got home, I checked it again – the water level was even lower than it was that morning!   Again I frantically added 50 gallons, and while doing so, found that the cause was not a terrible leak, but the new strawberry tubes!  They were overflowing; the drain tube was not draining the tubes very fast and there was an inch of freestanding water over the standpipe.  What in the world?   I quickly lowered the standpipe and it drained again somewhat.

This morning I checked it again – the water had not overflowed, but was fairly high and near the overflowing limit, so I took the standpipe out completely, which should leave the strawberry tubes only about half full of water.   This should still be fine, as I think all of my plants still have roots in the water, and the shale tends to wick up water anyway.

Thinking about it some more, I went online today and googled the viscosity of water and its changes at various temperatures – as this was the only explanation of why the water was not draining well now when it did just fine previously.   Viscosity is pretty much the measurement of internal resistance in a liquid.  The higher the viscosity, the slower it flows.  For example, honey has a higher viscosity than water, and flows much more slowly.   For water at various temperatures, I found the following data:

Temperature
t –
(oF)
Dynamic Viscosity
µ –
(lb s/ft2) x 10-5
Kinematic Viscosity
ν –
(ft2/s) x 10-5
32 3.732 1.924
40 3.228 1.664
50 2.730 1.407
60 2.344 1.210
70 2.034 1.052
80 1.791 0.926
90 1.580 0.823
100 1.423 0.738
120 1.164 0.607
140 0.974 0.511
160 0.832 0.439
180 0.721 0.383
200 0.634 0.339
212 0.589 0.317

The above is fairly apparent – water gets more viscous as temperature drops.   Hence it makes sense that the strawberry tubes require a greater head to drain out the 5/8 inch tube to the sump, and resulted in overflowing.  The change in Dynamic Viscosity from 50 oF to 40 oF is fairly significant: 2.73 to 3.22.

The lesson learned here is that I’ll need to either keep the standpipe off all the time, or at least remove/lower it when temperatures get low. When it gets warmer, I should be able to have a fairly high standpipe with good flow, which is better for new seedlings that don’t have roots long enough to reach the lower half of the strawberry tube.

NFT Tubes Added!

NFT stands for “Nutrient Film Technique,” which I think traditionally involves styrofoam rafts holding netpots and floating on water in a hydroponics operation.   In this case, I have 3″ netpots filled with shale that was too small for the growbeds, but still large enough to stay in the netpots (great use of what I thought was useless except as soil amendment).    I have 20 feet of 4″ PVC pipe going out away from the growbeds, then a U-turn and 20 feet back, with holes every 10 inches.   This gives me about 45 usable holes for plants, plus one over the drain standpipe.  

Here’s the building process: cutting, painting, bolting, gluing…

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I’ve gone ahead and planted 26 Chandler strawberry plants that came in the mail from Nourse Farms the other day, as well as moved the single garlic chive I have in growbed 2 to the first hole.

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Here is a view of the water input (back, hose from GB 2 drain) and drain (front, hose to GB 2 sump tank):

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Strawberry plants in place:

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Nat Jr inspects the drain standpipe, watching it burp and splash.

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Nat helped me fill in the empty holes with neoprene-capped netpots, which should help prevent evaporation on holes that are not in use.  The garlic chive plant is in the hole closest to the water input.

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At first I had issues with the drain – leaked around the brass fitting into the PVC when I did a water test. I drained it all and sealed it with silicone. After that, I had issues with the drain hose not draining fast enough, and had to play with the height of the drain standpipe to get a decent siphon, but now I don’t think it’s in danger of overflowing out the netpot holes anymore. Now the single biggest risk to this system:  a 3 year old boy.

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Finally, a video:

Seedlings Started

Last fall I did not have a very good success rate with starting from seed, so this season I was determined to improve upon that. I read several books on growing from seed, and while there are lots of things to try, the basics involve:

  1. Soak the seeds in water (or sometimes a seed stimulant) for an hour or so before you start them in the seed pellet. This should speed the germination rate.
  2. Get a seed germination heat mat – these raise the temp 10 – 20 deg F, and seeds germinate really well around 80 degrees or so. This was probably the biggest downfall last fall.
  3. Once started, have a decent light source, better than south-facing window. Best if a flourescent bulb is 1-2 inches from the top of the plants.

So here’s my makeshift germination station – some people pay $96 for a shelf with a light, I figured I’d just use a sawhorse and shop light that I had in the garage, and I strung it up:

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I put the seeds in and on the heat mat (on top of glass from a dismantled TV stand – don’t want a heat mat doing who knows what to the rug) on Saturday and left the light off until Sunday – veggies don’t really need light for germination, I read. I also added Roma and Cherry Tomatoes on Sunday evening. Then I turned the light on Monday morning at 6 AM. Here’s what they looked like Monday night when I came home:

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That was a shocker! Most seeds have a 7 day germination time at best, some 14 or 20 days. I simply did not expect so much so soon. Tuesday (tonight) when I came home, I was floored:

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Wow, some of them are growing like weeds! I am no longer able to keep the seed tray cover on, which means that the pellets will dry out a little faster.

Okra and thyme:

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Basil (yeah, I put way too many seeds in each, overcompensating for my bad luck last time):

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Winter squash and cucumbers, my giants. Notice the roots have busted out the sides of the pellets – I am worried they will dry out:

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At this point, I should transplant those last two to bigger containers and move them off of the heat mat. That would allow me to keep the lid on the rest, preventing the heat mat from drying them out… but some things I’ve read say people don’t even use a top… so maybe I’ll go a day or two without it and see what happens. Tomorrow we are supposed to get a lot of rain, so I am not going to put them into Aquaponics just yet, but maybe Thursday. In a normal garden, you should transplant and keep inside and fertilize for a month until they get strong, but when I have a nice fertilizing grow-bed outside, I wonder if it makes more sense to just gamble and put the seedlings in their gravel and let them run.

Aquaponics Current State

We’re at the end of the cold season, and the cold season crops are pretty much played out. We also had some pretty strong wind last week, which laid waste to GB #1, but there’s not much work keeping anyway… The Kale is still good, and the artichoke (perennial, which I should probably move out of AP) and the grapevine I put in the other week, of course. Broccoli, Arugula, and Romaine Lettuce all going to seed.

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Growbed 2 is still an overflow-holding from #1, and the red peppers I planted died off (though I forgot, the two or three in GB #1 look like they are going to make it). Growbed 3 is shallower since I ran out of gravel, and only just now has radishes popping up. I put some carrot seeds in there the other week, but in retrospect, they would have been better in a deeper growbed, no? Perhaps I did that because the package said they are good when small, perhaps up to 5 inches.

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In other news, I have started new seeds indoors, using a seedling heat mat that should help more seeds start. Tomatoes, winter squash (veggie spaghetti), cucumbers, two types of basil, red, orange and jalapeno peppers, garlic and regular chives, thyme, and even some red okra. We’ll see what happens!