IF a vacuum works, then positive pressure would work too. How? By releasing the positive pressure.
ie pressure up the vessel, (difficult apparatus) and then the drying occurs during the 'depressurizing phase'. Not easy, but plausible.
I think the major drying would occur (in the vacuum system) during the time when the pressure is equalizing, and carries the liquid water out. Yes, there would have been sublimation, but I think its effectiveness would be minimal.
I think you need to bone up a bit on the terms "vapor pressure" and "phases of water". When you pressurize the atmosphere over any water supply (liquid or solid phase), you lower the amount of evaporation from that body of water. Since you are seeking to increase the amount of water that evaporates, adding pressure will not help.
Here is a scenario in which adding pressure might accelerate the out-gassing of water from lumber.
1. Take a dried source of air with exceedingly low water content, and pressurize your tank.
2. Wait a long time for the water vapor to reach equilibrium.
3. Vent the pressurized air.
You should be aware that this pressurization will not probably be any faster than just cycling de-humidified air through your tank, without the equilibration cycle.
I think you do not quite understand what the vapor pressure of water is. Here is the my short-version of that concept:
Water will always leap into the air and establish a pressure inside any vessel. If you take a pressure tank with a water layer at the bottom at freezing temperature, vacuum ALL the air out, the pressure at which you reach equilibrium is the "vapor pressure" for water at freezing. If you increase the temperature, wait for equilibrium and re-measure the pressure inside, then you will have the vapor pressure at that temperature.
Regardless of the actual barometric pressure, the vapor pressure of water is determined
only by the temperature. It is a physical constant in water, just like the freezing point and the boiling point under standard conditions.
When the actual pressure around a body of water is lower than the vapor pressure of the water...you will get rapid evaporation. When you increase the actual pressure well above the vapor pressure of the water for any given temperature, you will reduce evaporation.
These are the physical properties of water, and they never change.
I think you can be assured that any method of kiln drying of wood that uses increased pressure will take way too much energy. The whole idea behind the vacuum process is not that it works magically better somehow than normal air drying, but that it will use less energy for rapid dehydration than heating the wood. You could dry the wood out rather rapidly by baking it at180°F, but look at all the energy you would be burning up. It also allows you to accelerate the drying process without heating the wood up so much that you do damage to it.
The vacuum kiln should be able to accomplish rapid drying of wood with less tendency to have uneven drying. It will be way more energy intensive than a plain solar kiln, or simply covering with a tarp and waiting for summer to do the drying for you. Generating a vacuum takes energy; just not as much energy as boiling off all the water. Even that equation will be subject to the efficiency of your vacuum pump.
Your pressurization method will use more energy than simply heating up the wood and drying with forced air.
