Viewing a single comment thread. View all comments

Awkward-Motor3287 t1_j8h2yyp wrote

Reply to comment by NameUnavail in Is there a formula to know the temperature of fluids after mixing ? by malahchi

Why does it have to be this complex? Can't it just be calculated like averages are? If mix 1 part 100 degree water and 2 parts 200 degree water, can't I just do the following? (100 + 200 + 200)÷3=166 degrees. Assuming both waters came from the same source of course.

0

jbhelfrich t1_j8h3h1p wrote

If the two liquids are the same (C_Liquid1 = C_Liquid2) that's exactly what you do get. But the OP asked for a generalized answer for any two fluids.

17

Cheetahs_never_win t1_j8jhbz3 wrote

No - it's generally a good approximation if at the two states, the fluid's properties are approximately the same.

That's not always true for huge differences in temperature and/or pressure.

1

NameUnavail t1_j8ha5wt wrote

As I said, so long as it's the same type of liquid you absolutely can. The weighted average for equal portions simply would be the average

But if you have different liquids that doesn't work because different liquids can store different amounts of heat

6

Scrapheaper t1_j8hn4nh wrote

Only if the heat capacities of the two liquids are identical.

This is actually a very simplistic case since many liquids heat up or cooldown when mixed together due to thermodynamics.

1

Cheetahs_never_win t1_j8jgch7 wrote

Temperature is only one facet of the total energy state and is simply insufficient on its own to get the job done. I know, we thought the same thing and burned the crap out of ourselves in the shower.

We can't alter the universe's laws for our convenience - we tried, doesn't work. :)

And from the universe's perspective, a temperature scale that's built off a particular kind of matter within a certain range that's convenient for weird ape-people on a specific planet on a specific star is no way to run an entire universe.

1