Near Bracebridge Ontario, which sits on the southwestern part of the Grenville province of the Canadian shield, at 45° north and 79.3° west of the prime meridian, summer has been cool and wet. I’m on a smallish lake, and lake water surface temperature is around 21° Celsius (70° Fahrenheit), much cooler than usual for late August. But if you are lucky enough to have a sauna, or some other kind of recreational/therapeutic heat bath, then your physical comfort is actually enhanced, not adversely affected, by inclement weather and temperature. No matter how cold or gloomy it gets, you can always have a good sweat and then plunge into a cold lake or river. If you have never tried that, well it’s something you should do at least once in your lifetime. It is a transcendent experience.
There are a few different kinds of heat baths, but my preference is for the Finnish sauna, which is a simple room built around some sort of radiant heater (mine is wood fired) with rocks on top of it. The heater raises the room’s, and the rocks’, temperature to well above 100° Celsius, and you just sit on a bench and sweat until you can’t take it any more, at which point you take a few steps to a nearby lake or river and plunge in. It is incredibly relaxing, and socially very enjoyable.
For those who are science-minded, the wood-fired Finnish sauna especially is a fascinating classroom and laboratory in which to study practical real-time thermodynamics and fluid dynamics; to feel their real-world meaning on your own hide. It is a simple low-tech design—as I mentioned above, a cedar-paneled room with cedar benches; one of the walls straddles an iron woodburning stove which you feed from outside. This allows you to play with both temperature and humidity. You control temperature with the type, size, and amount of wood you feed into the firebox from outside the sauna room; and humidity by pouring water on the hot rocks on top of the firebox inside the room.
The humidity part is especially fascinating for those like me who incessantly marvel at the physical properties of water. Sit in a dry sauna at, say, 110° C and it can be pretty intense. Then pour a couple of ladles of water on the rocks on top of the firebox. That’s intense. The liquid water flashes to steam relatively quickly—in 10 to 20 seconds, depending on how much you pour, its original temperature, and the temperature of the rocks. An invisible but palpable wave of fresh moist heat slow-motion ricochets around the room, enveloping you and causing fresh sweat to pop out of your pores. It totally transforms what is already a transformative experience.
Finns call this sauna rock steam löyly (crudely pronounced lulu), which translates to “spiritual steam.” It is truly powerful; again, I urge you to experience it at least once. Until you do, consider this. My personal preference is to pour two ladles of water onto the rocks. Each ladlefull of water is about one-tenth of a litre—one hundred grams. Today the lake surface temperature is around 21° C. To turn each of those 100 grams of liquid 21° water into steam, the following has to happen.
- The temperature of each gram of 21° liquid water has to increase to 100°. That means roughly 79 calories of heat energy has to go into it. (A calorie by definition is the amount of heat required to raise the temperature of a gram of liquid water at 15° by one degree Celsius.)
- Once the gram of liquid water has reached 100° C, another 542 calories of heat energy has to go into it. This is called the latent heat of evaporation.
Each gram of liquid 21° water must absorb 621 calories of energy before it becomes steam. So if you pour 100 grams of 21° water onto the sauna rocks, they will need 62,100 calories of energy to turn to steam.
I normally pour two ladlefuls, i.e., 200 grams, of water onto the rocks. So the energy required to turn all that liquid into vapour is 124,200 calories.
The vapourization takes roughly 10 to 20 seconds.
So, 124,200 calories, or 519,876 joules, to turn one-fifth of a liter—200 grams—of liquid water at 21° into löyly. Averaged over the 20 seconds it takes to turn liquid to steam, that works out to about 26 kilowatts.
Is that a lot of power? Well, a 1980 study of power production by Olympic weightlifters measured the jerk drive of a 110-kilogram (243-pound) weightlifter at 4,786 watts, or roughly 4.8 kilowatts. That was a study of a 1975 competition. The current world record for the clean and jerk in the 105+ class is 263 kilograms (about 580 pounds); we can safely bet that the 1975 lift was somewhat less than that.
So, a champion weightlifter outputs 4.8 kilowatts to jerk-drive a barbell weighing close to 263 kilograms, or 580 pounds, to a straight arm position over his head, in a move that lasts less than two seconds. It takes 5.4 times that amount of power, over a 10- to 20-second spurt, to turn a couple of ladles of water—200 grams, or 7 ounces—into steam.
This may be why the Finns call it löyly.
It is certainly why we use steam to do work for us. If a champion weightlifter has to train full time in order to muster up 4.8 kilowatts for two seconds as his crowning lifetime athletic achievement, then there is no way that I, an ordinary mortal, could on my own produce 26 kW, even for a microsecond, let alone for 10 or 20 seconds. If I want the transcendent effect of 200 grams of löyly sweeping through a cedar-paneled room in the middle of winter, I have to get the power to make it from somewhere else. In my case, I harness the physical force of electromagnetism: I burn wood.
Because of the 542 calories of energy that are required to turn a gram of liquid water at 100° C into steam, steam has a lot of power. This is why, on a societal scale, steam makes most of the electricity that is currently powering the world. In my province of Ontario, steam plants are making at least 65 percent of the electricity (see the bullet list just below Item A1). Heat from the fissioning of uranium is turning water to steam, and steam pressure is driving the turbines that turn generators to make electricity.