You put a lot on the plate for discussion, some very debatable.  Starting at the bottom (from memory), honey.  Honey's thermal resistance increases with decreasing honey temperature; viscosity also drops which has a big affect when honey is not crystallized.  I just checked honey stored in my 5F Freezer.  It is still a liquid albeit very viscous - I can leave a finger print in it.  Admittedly my honey does not crystallize quickly.  I would maintain, without test data, that leaving frames in place with honey and without honey provides thermal resistance of significanct value.  The effect on natural ventilation is likely a pressure drop increase over the height with two portal effects.  The idea of bottom slats besides being a nice volume for bees  (I use a medium) likely acts as a flow dampener, increases the pressure drop but also act as flow straightener device which should help establish laminar flow.  
In many discussions on ventilation I never see a discussion on vapor pressure differentials which is a driving force causing flow out of a hive. I would believe numbers show the internal hive vapro pressure is more often higher than outside the hive.   Also remember water vapor mixing with "air" is buoyant and rises.  I also agree temperature differentials causes convection currents with very low Reynolds number characteristics.
I have recently bought a thermal book, Heat and Mass Transfer, 700 pages, to replace my old book, lost over time.  I intend to relearn some stuff but I have hit a road block .  Current cheap weather stations measuring temperature and Relative Humidity (RH) do not have a wide enough sensing range with accuracy and deteriorate with time and high humidity - polymer based; temperature sensing seems acceptable.  As I think RH is intwined with temperature regulation by bees, measuring the variable is critical to understanding the internal dynamics. Measuring CO2 would likely be added on soon thereafter. I am going to look at high cost ceramic sensors and the idea of using thermal couples to determine RH inside a hive.  All a lot of work when I also like my gardening and construction projects. 
Without question external wind is a player - mostly negative I guess but a player in gas exchange in winter time as wind creates significant pressure differentials too.
I use to have an associate, a working friend, with a Phd in gas dynamics.  I may have to look him up if he is still alive and around.  When I have something repeatable I'll let you know.  In my balmy climate I do believe insulating heavily, eliminating top vents, controlling the bottom entrance has  a very positive effects on survival, supportive of early Spring brood rearing and capping honey.   

Good luck in your efforts,Bob

-----Original Message-----
From: Etienne Tardif <[log in to unmask]>
To: [log in to unmask]
Sent: Fri, Jan 15, 2021 4:35 pm
Subject: Re: [BEE-L] Ventilation in the beehive: Previous work review

I have been reviewing the science behind natural ventilation and how it works. A lot of these concepts could be tested in a beehive with the right equipment.

I have included my references. 

Some highlights and a few hypotheses
> convection is all about temperature differences (cluster surface temperature to internal temperature and average internal temperature to outside temperatures). Changes in air density is the main driver based on temperature differences. Forced or mixed convection occurs when natural convection is not enough (bee fanning) to maintain desired limits.

>the larger the cluster vs the hive volume, the less convection will occur outside the cluster inside the hive (good)
>small clusters or very tight clusters during cold periods will experience increased convection around the cluster surface area (hence the reason cluster is required to contract to reduce this heat loss), there is more open area for convective flows move through.
>the higher the enclosure R-value, the looser the cluster, convection is controlled by bee positioning, heating is likely driven by bees in the lower mantle (bees exposed to cooler temperatures). If the cluster is self organizing (bee behaviour based on local temperatures) then this makes complete sense. Upper bees are warm, therefore no heating required by them. If heater bees are in the lower section of the cluster, they will have easier access to "fresh air" vs those heater bees inside a tight cluster trying to maintain temperature and balance air (CO2, Moisture).
> Natural Convection can provide adequate air change inside the hive even through a small lower entrance (1 to 2 hours to change out internal air volumes based on theory). This number is higher in hives with double entrances. 
> The relationship between the area of the top and lower entrance determines potential flow (or limit due to throttling effects). A 3/4" top entrance (0.5sqin) will have an additional ~30% increase in flow (effective area) as the lower entrance is increased from 3/4" (0.5sqin) to 2sqin. When you have a 1" top entrance, this same increase to 2sqin in lower entrance area causes a ~125% increase in effective area.
> Wind will likely have an effect on air flow and direction of flow when using 2 entrances. This will likely be worse in hives with small clusters in large volumes. The wind effect (pressure change) is larger than the buoyance forces. The buoyancy forces are small in low R-value hives.
>when broodrearing starts, the enclosure average temperature rises significantly thus increasing the potential for natural ventilation to occur (delta T - temperature difference In - Out increases). This will further increase the energy for heat generation.
>a drop on the inside of the hive will cause turbulent flow (cold heavy air going in and warm air coming out (single entrance setup). This will cause mixing of both air streams. Incoming air (cold) will receive heat from outgoing air thus reducing heat losses.
>my slatted rack is likely having a similar effect. It is actually halving the area below the cluster where incoming air is pulled in, the rack bars will slow flow and also increase mixing of air streams.
> Honey frames, space between them are all critical, better to remove empty frames in a hive then to try to overwinter with them. Open space equals natural convection.

Again not trying to prove anybody right or wrong, just trying to understand the why. If you know of other theories driving ventilation and heat flow in the hive please let me know. 

I will get more IR footage of my clusters, as well as use some copper wires at the entrance to try observe dual air flows through one entrance. I am also looking at latent heat of both moisture in the air (energy release as condensation occurs) as well as that of honey at sub-zero temperatures, does it behave like water when it goes from liquid to solid?
https://drive.google.com/file/d/1nbCOq0hCh1J2DUl7OAkqOcmryTqCpQ2U/view?usp=sharing

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