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Date: | Fri, 4 Dec 2020 19:22:28 -0500 |
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Found an interesting relationship today.
Tambient vs the difference between the T at center of bottom board (T ent) and the ambient.
The slope of this line is directly related to convective heat transfer. The steeper the slope the higher the convective heat loss or air movement (natural convection).
The difference between the Single 2019 and Single 2020 is around how my bases are setup. 2019 has 2" of styrofoam and 3/4" plywood below the open screened BB. 2020 has an open gap into a 8' x 2' cavity (now completely protected by snow).
It would be interesting to see the slope (this relationship) for an insulated hive with a top entrance, with and without a slatted rack as well as an un-insulated hive with a top entrance. I see evidence of this every morning during the summers nectar flow (soaking wet landing board). This also explains why early morning (coldest part of the day) likely has the highest nectar drying rate.
We haven't had any <-40C yet this winter, last year we had tons. The Single 2019 scatter chart seems wonky below -40. This is due to my weather station's lower limit of -40C. The delta (Tent-Tambient) will not be correct. We dropped to -50C last winter.
Application: In an insulated hive without a top entrance, this effect drives the air exchange in the hive (CO2, Humidity, O2, etc...). Therefore the velocity of the natural convection is driven by the R-Value or lack of, the size of the cluster (waste heat generation value) both of which are controllable by the beekeeper. T ambient is what it is, but can be predicted based on historical data. With the correct data would it be possible to setup the hive just right for the geographical location. An un-insulated wooden hive will not have this natural convection (buoyancy effect) in either winter or summer, therefore the bees must drive air movement via fanning (energy input). An insulated hive with a top entrance will likely have a some of the buoyancy effect but not as much. Insulated hives without a top entrances gets the full benefit of the heat escaping the cluster.
It is actually really easy to setup this temperature measurement. If you have a sensor (i.e. T2 Broodminder), use an elastic to fasten it to the center of a flat stick (1/4"x1" x ~17" long). You then insert this through your lower entrance so that the censor will be ~ centered front/back on your bottom board.
If you are a Uni professor and you have access to Mechanical Engineering students (3 or 4th year) or masters who are looking for a project, this could be one. Calculating this can get quite complex and requires simulations (CFD) to calculate a few special empirical values.
https://drive.google.com/file/d/1gVHnttyelPEC12Owxe0AkOZrpXoLinPg/view?usp=sharing
Refer to ABJ August 2017 Honey Bee Engineering: Top Ventilation and Top Entrances by Derek Mitchell if you want to better understand this concept.
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