explain that energy transfers and transformations in mechanical systems always result in some heat loss to the environment. Like why is it necessary for a heat loss?
Answer
This is a hard topic but I'll try to give a brief reply.
"Heat" consists of random motion of atoms vibrating about in all directions at a variety of speeds. A heat engine strives to catch that random motion and turn it into a moving piston or a spinning turbine wheel. A simple measure of how much heat we have in (for example) a sample of hot gas is its temperature, and a perfect capture of heat energy from hot gas by an engine would mean the exhaust of that engine would be at zero temperature.
But the environment surrounding that engine is not at "zero temperature", it is at 270 degrees celsius above zero, which means that the exhaust of the engine will leave it with heat that the engine could not capture. This is one reason why heat engines cannot in principle extract all the heat energy out of a sample of hot gas.
Another reason is that no engine is perfect is that all its bearings and sliding and spinning parts have friction trying to slow them down as they move, and that friction steals work from the engine and turns it into heat which leaves the engine while it is running.
Yet another reason no heat engine is perfect is that it is impossible to completely prevent heat from leaking out through the walls of the engine while it is running. That leakage also contains heat energy that the engine obviously cannot use to do work for us.
No comments:
Post a Comment