Hot water as it relates to cleaning

Interesting article on water temperature as it relates to cleaning and how hot the water really is at the tip of a wand on a truck mount.
http://www.cleanfax.com/article.asp?IndexID=6636117

If you hit the related links near the top of the article, you will find the below little nugget of info as well (FYI, their water is hot, but not as hot as they like to brag about, especially during certain seasons):

The temperature test

To test how much the temperature will drop during hot water extraction cleaning, I did a simple nonscientific test on a hot summer (90 degrees Fahrenheit) day. The carpet was placed near the truckmount and I used a short hose to minimize heat losses. I used a non-contact calibrated thermometer to measure the temperature (any other type of thermometer would have given a lower and erroneous reading as it would take away heat from carpet to get a reading).

The hot water coming from the truckmount under pressure was at 230 degrees Fahrenheit. Guess what the temperature was at the cleaning wand? You may be surprised to know that at the inside area of the cleaning wand the temperature measured 124 degrees Fahrenheit and outside the wand it was only 114 degrees Fahrenheit; such was the drop in temperature. One can surmise that on a colder day with a longer hose, the temperature at the cleaning point would be even lower.

Before everyone gets excited and thinks the machine is at fault, consider this question:

Why does the temperature drop so dramatically at the wand?
When a gas or liquid flows from high pressure to low pressure, it expands and, on expansion, loses a tremendous amount of heat. It loses so much that you can solidify carbon dioxide gas to a solid dry ice when you open up a pressurized cylinder at room temperature (the dry ice has a temperature of -109 degrees Fahrenheit).

This is based on what is known in science as the Joule-Thomson effect. When hot water under pressure flows from the heat exchanger or burner and goes through the wand, it loses heat as a result. The further the wand is from the heat source, the more it will lose heat, especially in colder weather. In addition, the hot water coming out as an atomized fan spray from the nozzle loses heat and cools down further. The carpet also acts like a heat sink, dropping the temperature down further.