- #1
halfgt2
- 3
- 1
Hi physicists!
I am scratching my head to remember the most basic laws of fluid flow while I try to irrigate things from a barrel. Not exactly rocket science, I know ;-) But very exciting for me ...
The situation is simply a pump (cheap submersible one) put into a barrel (sitting on the bottom) where the barrel is placed at the beginning of a row of plants. The plants need to be watered. A main hose rises vertically inside the barrel from the pump goes along the line of plants and abruptly ends in a stopper, just beyond the last plant in the line.
Each plant gets a little individual sprayer connected to the main hose (looking like a drinking straw piercing the hose with its opening suspended in the center of the diameter of the hose). The sprayer tubes permits a relatively minor flow rate, like a leak, compared to what the hose is capable of delivering. For arguments' sake let's say each sprayer takes 1% of the potential flow in the area of interest, so the pump is always generating some pressure.
Now, this is sort of a closed system if I read this amazing thread right:
https://www.physicsforums.com/threads/pump-head-requirement-closed-vs-open-loop.753612/
Except mine is "leaky" since the whole purpose is to release water very slowly. So the small pump is placed in the barrel of barrel height H, call it a meter if you like. The hose is actually about 0.5 inches Inside diameter and the sprayer connectors 0.125" inner diameter just to get a good idea, but the restriction is in the sprayer connected on the far end of it where it is tied on to the plant.
The sprayers deliver the leaks :) at say they are at height h in each pot around 1 foot high. For poor gardeners who would like to grow vegetables for less than $10/pound, pumps and barrels can be expensive for just a few pots ... so how to best design this? The pressure drop is negligible from beginning to end of the hose (it is short, say 5 meters), but the spray heads deliver a volume and quality --and I'm guessing-- ~linearly increasing vs. pressure if that makes sense from observation. A certain pressure is necessary for a good spray and it is always more than the pump I buy can make. Questions:
1) If the hose runs vertically from the pump on the bottom of the barrel to height H, over the edge, and then drops to the ground of height = 0 where it runs along the ground, from which the sprayer connectors rise up to heights h and deliver in n sprayers (6 in a small example), how could we describe the pressure loss from running the hose out of the top of the barrel vs. perforating the barrel on the bottom and basically pumping at h=0?
2) How beneficial in terms of decreasing pressure loss, if much at all, would it be to raise the entire main hose to h' by say putting it on a track running along the plants, like an elevated train?
3) Is there a relationship of sort that would be useful for designing this employing P=pressure, h0, h, H?
I realize most of this deals with understanding "suction pressure" and differential pressure like siphons generate, but I still don't have a confident grasp of it. Looking for some help! I'd rather not perforate the barrel, but at some point higher pressure pumps become very expensive for the garden budget.
Thanks!
halfgt2
I am scratching my head to remember the most basic laws of fluid flow while I try to irrigate things from a barrel. Not exactly rocket science, I know ;-) But very exciting for me ...
The situation is simply a pump (cheap submersible one) put into a barrel (sitting on the bottom) where the barrel is placed at the beginning of a row of plants. The plants need to be watered. A main hose rises vertically inside the barrel from the pump goes along the line of plants and abruptly ends in a stopper, just beyond the last plant in the line.
Each plant gets a little individual sprayer connected to the main hose (looking like a drinking straw piercing the hose with its opening suspended in the center of the diameter of the hose). The sprayer tubes permits a relatively minor flow rate, like a leak, compared to what the hose is capable of delivering. For arguments' sake let's say each sprayer takes 1% of the potential flow in the area of interest, so the pump is always generating some pressure.
Now, this is sort of a closed system if I read this amazing thread right:
https://www.physicsforums.com/threads/pump-head-requirement-closed-vs-open-loop.753612/
Except mine is "leaky" since the whole purpose is to release water very slowly. So the small pump is placed in the barrel of barrel height H, call it a meter if you like. The hose is actually about 0.5 inches Inside diameter and the sprayer connectors 0.125" inner diameter just to get a good idea, but the restriction is in the sprayer connected on the far end of it where it is tied on to the plant.
The sprayers deliver the leaks :) at say they are at height h in each pot around 1 foot high. For poor gardeners who would like to grow vegetables for less than $10/pound, pumps and barrels can be expensive for just a few pots ... so how to best design this? The pressure drop is negligible from beginning to end of the hose (it is short, say 5 meters), but the spray heads deliver a volume and quality --and I'm guessing-- ~linearly increasing vs. pressure if that makes sense from observation. A certain pressure is necessary for a good spray and it is always more than the pump I buy can make. Questions:
1) If the hose runs vertically from the pump on the bottom of the barrel to height H, over the edge, and then drops to the ground of height = 0 where it runs along the ground, from which the sprayer connectors rise up to heights h and deliver in n sprayers (6 in a small example), how could we describe the pressure loss from running the hose out of the top of the barrel vs. perforating the barrel on the bottom and basically pumping at h=0?
2) How beneficial in terms of decreasing pressure loss, if much at all, would it be to raise the entire main hose to h' by say putting it on a track running along the plants, like an elevated train?
3) Is there a relationship of sort that would be useful for designing this employing P=pressure, h0, h, H?
I realize most of this deals with understanding "suction pressure" and differential pressure like siphons generate, but I still don't have a confident grasp of it. Looking for some help! I'd rather not perforate the barrel, but at some point higher pressure pumps become very expensive for the garden budget.
Thanks!
halfgt2
Last edited: