Q: Hot water system question

[architect23]

Thanks!

[Coach]

Generally, the faster water can be heated, less storage is needed because it can heat fast enough to deal with demand. The extreme example of this is a tankless heater.

[architect23]

Thanks Coach! So in this case, a larger heater with a smaller tank refers to a heater that heats quickly? Sorry if this is a basic question.

[architect23]

1) Another question- in my notes it states "the smaller the diameter of a pipe, the greater the friction at a constant flow rate. The greater the flow rate, the greater the friction at a given diameter." i don't understand this concept. Can anyone explain why this relationship is?

[architect23]

1) Another question- in my notes it states "the smaller the diameter of a pipe, the greater the friction at a constant flow rate. The greater the flow rate, the greater the friction at a given diameter." i don't understand this concept. Can anyone explain why this relationship is?

Can anyone clarify why a small pipe has a greater friction?

[nickedemus]

Well, I'm no expert, but think I can intuitively take a stab at it.

Visualize this:

Pipe 1
6" inside diameter
circumference 18.85"
area 28.27 sq in

Pipe 2
3" inside diameter
circumference 9.42"
area 7.07 sq in

Assume water is flowing through both pipes, without any room for air spaces.
The next assumption is that laminar flow is slower at the outside of the flow than at the center of the flow, due to friction.

Right off the bat, you can see that when diameter doubles, circumference also doubles. But area quadruples. So, the proportion of water that touches the circumference (and experiences friction) decreases in relation to the area of water that flows more freely through the pipe.

Does that help?

[architect23]

. So, the proportion of water that touches the circumference (and experiences friction) decreases in relation to the area of water that flows more freely through the pipe.

Does that help?

Nickedemus, thanks for your detailed reply! I am following you up until this last part there... can you explain this part?

[nickedemus]

Picture both pipes in section and compare the proportion of water that touches the inside surface of the pipe to the proportion that flows through without touching that surface.

But seriously, don't get caught up on little details like this. You don't have to understand every minute point. You may just have to memorize some things.