New burner trials

[Dan]

A way's back I had to sell all my brew stuff. I'm rebuilding and with the knowledge I have now about equipment I'm buying good stuff that doesn't cost an arm and leg. I'm not going all out crazy spending thousands of dollars. I just bought a new burner. It is a Bayou Classic SQ-14. Had a lot of great reviews, mostly from homebrewers! I got it new from Amazon for 52 bucks and a few cents. FREE SHIPPING. It arrived last night and I put my 15gallon keggle on it with five gallons of water, brought it up to a boil and let if go for an hour. Shut it down, let the keggle cool overnight and measured the boil off/evaporation rate after I got home from work today. Two gallons boiled off! I'm doing the same thing tonight, it's about 30 minutes into the boil (again water) and evaporating quickly. I figure two tries in similar enviormental conditions and I'll have my evap rate for at least the next month or so. I'll try it again once the temp drops and the air dries out even more. Will also give it a shot in the spring when there is more moisture in the air and another during the Central California valley hot summer.. 100-110 degrees mid-day. I have no idea if moisture in the air makes a difference. I'm not really a science type but to me it seems to make sense. The drier the air the more it sucks up moisture. I spent a good amount of time in Antarctica, cold as heck and easy to get dehydrated in. I don't believe it is the temp as much as the dry air that contributes to evap rates.

 

[GrittyGrizzler]

Boiling and evaporation are not the same, even though they both result in the vaporization of liquid. Evaporation occurs only from the surface of a liquid at a rate determined by the amount of thermal energy in the liquid and the vapor pressure deficit, or the relative "dryness" of the air. In contrast, boiling is the spontaneous vaporization of liquid throughout the entire volume due to the vapor pressure being raised to the atmospheric pressure, which is why you'll boil at different temps at different altitudes.

Both processes are happening when you're brewing your beer, but the amount of liquid vaporized due to boiling is many, many times larger than the amount due to evaporation. So, the relative humidity will not appreciably change your boil-off volume, and your volume lost due to vaporization would be the same in Miami as it would be in Death Valley (within measurable amounts, and for normal brewing times). The most important factor affecting the volume is the vigor of the boil (the rate of vaporization), and, to a lesser degree, the surface area through which this vapor can escape the liquid.

Taken altogether, you're not going to see a change in boil-off amount due to the ambient temperature or relative humidity, so there's no need to test your system at different times of the year for that. Of course, the ambient temp is going to change how long it takes to get your boil started, and how much energy you need to maintain it.

 

[OneHoppyGuy]

Damn Grizzly, that's great info! Where did you learn all this stuff? This should be a 'sticky' post.

 

[GrittyGrizzler]

Damn Grizzly, that's great info! Where did you learn all this stuff? This should be a 'sticky' post.

Hahaha, vaporization of liquid water by evaporation and transpiration (biological evaporation occurring from leaves) is sort of my wheel house (I model ecosystem water and carbon fluxes). Glad it was helpful info.

 

[Dan]

Holy cow. Thanks GrittyGrizzler! So no need to check again at different times of year that is nice to know. I did the experiment again last night, before I read your post and this time lost only 1.25 vice 2+ gallons, however as you stated "The most important factor affecting the volume is the vigor of the boil..." The first night when I lost a little over two gallons I boiled very vigorously and last night I maintained more of a gentle boil.

GG here’s a question for you. I was telling a co-worker about my experiment and he said the water on the bottom of the kettle would be hotter than on the top because it is closer to the heat. Is this right? I thought the temp throughout the kettle is the same temp, once it gets to 212 degrees it gets no hotter. I understand (very basically) that if the pot is a closed vessel or semi-closed (pressure cooker) the boil temp increases and I'm guessing that is because the atmospheric pressure inside the closed system increases with the pressure of the steam build up therefore increasing the boil temp. Or maybe I'm way off.

 

[GrittyGrizzler]

GG here’s a question for you. I was telling a co-worker about my experiment and he said the water on the bottom of the kettle would be hotter than on the top because it is closer to the heat. Is this right? I thought the temp throughout the kettle is the same temp, once it gets to 212 degrees it gets no hotter. I understand (very basically) that if the pot is a closed vessel or semi-closed (pressure cooker) the boil temp increases and I'm guessing that is because the atmospheric pressure inside the closed system increases with the pressure of the steam build up therefore increasing the boil temp. Or maybe I'm way off.

Temperature of liquids cannot be increased past their boiling point because at this point they're no longer liquids. However, the boiling point of a material depends on the atmospheric pressure. This is why water boils at a lower temperature at higher elevations. In a pressure cooker, the local atmospheric pressure is much higher than the ambient pressure and so the boiling point is elevated. So, a pressure cooker does not allow you to heat water above its boiling point, it just elevates the boiling point by increasing pressure.

Before you reach a vigorous boil in your kettle, there is probably some thermal stratification, and the water at the very bottom of the kettle is hotter. You can prove this to yourself either by measuring the temperature profile with a long probe, or my measuring before and after thorough mixing. Some mixing is occurring because as conduction heats the water in contact with the bottom of the kettle it becomes less dense and is displaced by cooler, more dense water from above. Watch your kettle as you approach a boil, you're likely to notice bubbles forming at the very bottom of the kettle before the water really gets boiling. However, during a vigorous boil the water becomes less thermally stratified because it's such a turbulent environment with all of the spontaneous vaporization and the liquid gets very well mixed.

I'm no engineer, so this is a bit outside of my comfort zone, and I'm positive there's some more interesting and complex physics going on (especially related to the mixing), but I think it's good enough for brewing.