Archive for January, 2009

When ice sublimates in a vacuum (that’s the process where by ice goes directly to water vapor without first melting), it requires heat (just like when you sweat and the sweat evaporates, the process of evaporation removes heat thereby cooling your body). This causes the ice to get colder and colder until it’s so much colder than the surrounding environment that the radiant heat being transferred to the ice equals the amount of heat being consumed by the sublimation process. I’ve seen this effect cause the ice in the freeze dryer to go from being about -5′C down to about -45′C. If you can add additional heat via the heating coils, then the ice stays warmer and sublimates faster. I was worried because the lowest setting for the heater thermostats on the freeze dryer is 60′F (about 15′C). I was afraid that the thermostats wouldn’t allow me to set the temp any lower, and that a temp this high would actually add so much heat that it would cause the ice to melt before it sublimated and thereby screw up the freeze drying process. As it turns out, even though 60′F is the first mark on the thermostats, if you don’t turn them all the way up to that first mark, they still work and they will allow you to set the temperature lower than that. They actually go all the way down to about 23′F (or -5′C). So, I set the thermostats to about 40-50′F (6-10′C), which is above freezing, but due to the laws of thermodynamics and heat transfer principles, the shelf can be slightly above freezing and still not transfer enough heat to the ice to cause it to melt. By being able to set the heat to this setting and then just leave the heat turned on all the time (versus going out once an hour to turn the heat on for 5 minutes or so just to rewarm the shelves from -25′C up to about 0′C), I should be able to speed the drying process. I’m hoping to get the total drying time down from roughly 48 hours to 24 hours. If I can, then I both half my costs per batch, and double my annual capacity (assuming the machine is kept running 24/7). This is important because I can only get somewhere around 2,000 to 8,000 pills worth of product per batch, and with a dosage of 3 to 4 pills per day per, that’s not a whole lot of production capacity should this business take off. So, the faster I can run stuff through, the longer we can make do with this freeze dryer before I have to build the custom freeze dryer I’ve been designing in my mind. BTW, when I’m done building that custom freeze dryer, I’m going to name the specific method of freeze drying that it uses the “Ledford Method” of freeze drying. I’m such an egomaniac