the idea that a smaller hose does nothing to restrict flow is insane. i wanted to say ludicrous, but i wasnt sure how to spell it lol. yes the pressure builds up, and yes the water goes faster. BUT, the pressure builds up because less water is allowed to go through the restriction. more water from the pump is pushed behind it. since water doesnt compress, the remaining water that doesnt make it through the restriction has to be displaced to make room for the new water from the pump. if restrictions just made the water go faster, then a pin-sized hole in the end of an otherwise blocked tube would have the same flowrate as an open tube. not so.
microchannels do restrict flow. but one has to consider the idea of parallel channels. a heater core, for instance, has 1/2" inlet and outlet, lets say. instead of having 1/2" tubing go all through it, it splits the water flow into many different smaller channels whose cross-sectional area ads up to something like 1/2". each small opening, of course, applies some backward pressure, which is why there is always a bit of a flowrate drop going through any component except the pump lol.
the "two lengths of tubing, length A and length B" example i dont agree with. are you saying that the 1/2" tubing would let enough water through to fill up the 2"? no way. if that were true, then all the drainage pipes you see going into ponds and whatnot would always be spouting water. just like the CICO philosophy... trickle in=trickle out. the only flowrate difference between the two tubes would be because the 1/2" tubing provides less friction to the water because the contact surface area with the inside of the tubing is less. in the 1/2" 100ft, there would be very little space, if any, between the water and the sides of the tube, but with the 1/2" to 2" the water would flow along the bottom, leaving only the bottom of the water in contact with the tubing.
"That constant rate will increase when you remove a restrictive component and replace it with a less restrictive one." This only applies when you actually take the restrictive part out of the loop, i.e. replace 3/8" tubing with 1/2" tubing.
this all makes sense to me. *tink tink*
jungle