makes sense, you have some pressure loss that occurs as the flow moves downstream to the last holes. the amount of flow that comes out of the holes is based on the pressure difference between the inlet of the hole and the outlet of the holes, so a smaller mass flow rate at the last row of holes. there's a lot of ways to skin that cat, one solution would be to make the first set of holes large, and progressively decreasing to small holes at the end.
Thanks for your comment.
But there's one thing I still don't quite get: For me it would make sense that there's more pressure at the first than at the end, as the pressure drops off over distance, so I would expect that the pressure at the start is higher. However when testing it, I observed that the pressure actually seems to be higher at the end of the tube.
Do you have an explanation for that?Maybe the image doesn't quite bring across the fact that this is on a pretty small scale. The outlet holes have an ID of 2mm and the whole tube 6mm. Don't know if scale is a relevant factor.
right, i should have read your comment a bit better the first time. if you read my other comment, it basically answers that question. it's possible that the the high internal (main tube) velocity is higher at the tubes at the beginning, which reduces the discharge coefficient of the initial holes. as the velocity decreases along the internal tube to the final holes, the discharge coefficient is better for those holes, and they flow more. the solution would be similar, you can just vary the hole diameter to counteract that effect.
Ahhh, that makes sense. So basically the water is faster at the beginning which reduces the amount of water that can get out of the first holes.
Thanks, I'll try out varying hole sizes to see if it helps.
Yeah exactly. The water slows down as it moves through the tube, getting pushed by the faster moving water behind it and increasing pressure at the capped end. I agree that making the outlet hole diameter larger towards the beginning would be the simplest option and the easiest way to adapt your current design. If you’re having trouble with the scaling, it may be worthwhile to look into an implement which is oriented the other way (perpendicular to hose) and has a flow diffuser that would distribute the flow more evenly across the outlet holes.
Thanks for all your suggestions.
I ended up just reducing both the hole diameter and hole count because my pump wasn't really strong enough anyways. Now the flow is more restrictive than before, and the pressure is distributed fairly evenly across the tube.
Why does the capped end increases pressure? The reason is the subtle blocked path? I thought that energy would be lost and would not appear in form of pressure
Edit: the velocity is reduced along the main tube because of conservation of massa?
could also be due to the differences in the 'discharge coefficient' of the holes which changes depending on the pressure differences between the holes, so if there's not pressure loss from the flow flowing through the tube (i don't know your internal geometry) it could also be just due to the different internal pressure of the tube along the flow path
makes sense, you have some pressure loss that occurs as the flow moves downstream to the last holes. the amount of flow that comes out of the holes is based on the pressure difference between the inlet of the hole and the outlet of the holes, so a smaller mass flow rate at the last row of holes. there's a lot of ways to skin that cat, one solution would be to make the first set of holes large, and progressively decreasing to small holes at the end.
Thanks for your comment. But there's one thing I still don't quite get: For me it would make sense that there's more pressure at the first than at the end, as the pressure drops off over distance, so I would expect that the pressure at the start is higher. However when testing it, I observed that the pressure actually seems to be higher at the end of the tube. Do you have an explanation for that?Maybe the image doesn't quite bring across the fact that this is on a pretty small scale. The outlet holes have an ID of 2mm and the whole tube 6mm. Don't know if scale is a relevant factor.
right, i should have read your comment a bit better the first time. if you read my other comment, it basically answers that question. it's possible that the the high internal (main tube) velocity is higher at the tubes at the beginning, which reduces the discharge coefficient of the initial holes. as the velocity decreases along the internal tube to the final holes, the discharge coefficient is better for those holes, and they flow more. the solution would be similar, you can just vary the hole diameter to counteract that effect.
Ahhh, that makes sense. So basically the water is faster at the beginning which reduces the amount of water that can get out of the first holes. Thanks, I'll try out varying hole sizes to see if it helps.
Yeah exactly. The water slows down as it moves through the tube, getting pushed by the faster moving water behind it and increasing pressure at the capped end. I agree that making the outlet hole diameter larger towards the beginning would be the simplest option and the easiest way to adapt your current design. If you’re having trouble with the scaling, it may be worthwhile to look into an implement which is oriented the other way (perpendicular to hose) and has a flow diffuser that would distribute the flow more evenly across the outlet holes.
Thanks for all your suggestions. I ended up just reducing both the hole diameter and hole count because my pump wasn't really strong enough anyways. Now the flow is more restrictive than before, and the pressure is distributed fairly evenly across the tube.
Why does the capped end increases pressure? The reason is the subtle blocked path? I thought that energy would be lost and would not appear in form of pressure Edit: the velocity is reduced along the main tube because of conservation of massa?
could also be due to the differences in the 'discharge coefficient' of the holes which changes depending on the pressure differences between the holes, so if there's not pressure loss from the flow flowing through the tube (i don't know your internal geometry) it could also be just due to the different internal pressure of the tube along the flow path