Diesel Heater Outlet Size Planning - 4 x Spaces To Heat

[pvb]

The unit has proven reliable, hence my reason for keeping it.

Yes, Mikuni heaters seem to have a good reputation.

 

[lpdsn]

Seriously, you're confused by that? It's basic A-level Physics. I'm disappointed.

 

[pvb]

When I was installing on Play d'eau, the engineer said the duct diameter must increase the further it has to go to decrease the drag and allow the hot air to flow more easily. Otherwise the air slows down and becomes ineffective.

Surely increasing the duct diameter will slow down the airflow?

Exactly, so it'll come out of the vent faster. Whereas if it was more constrained in the ducting and flowed faster it'd come out of the vent slower. Simple when you think about it.

There's essentially a fixed volume of air flowing through the duct, the volume will change according to fan speed. With a larger duct, the speed of the air will reduce, because the volume flowing stays the same. However, the amount coming out of the outlet will be the same.

 

[lpdsn]

There's essentially a fixed volume of air flowing through the duct, the volume will change according to fan speed. With a larger duct, the speed of the air will reduce, because the volume flowing stays the same. However, the amount coming out of the outlet will be the same.

For that to be true you're making two assumptions. Firstly, and the most obviously untrue, is that there is only one outlet. Secondly, that higher back pressure at the fan will not reduce the volume flowing.

Remember that the OP is talking about getting hot air to the forecabin and the advice given to him was that a larger diameter duct would help the air flow. The more resistance there is to the air flow to the forecabin the less air will go that way as there are other outlets (two existing plus a second new one in the OP's scheme).

 

[pvb]

For that to be true you're making two assumptions. Firstly, and the most obviously untrue, is that there is only one outlet. Secondly, that higher back pressure at the fan will not reduce the volume flowing.

Remember that the OP is talking about getting hot air to the forecabin and the advice given to him was that a larger diameter duct would help the air flow. The more resistance there is to the air flow to the forecabin the less air will go that way as there are other outlets (two existing plus a second new one in the OP's scheme).

I really can't be bothered, but I'll try to explain again. Piers posted that unless a larger duct is fitted, the air will slow down. I suggested that the air will slow down in a larger duct. You appeared to agree, but then went on to say that if the air flowed faster it'd come out of the vent slower. You may know what you think you mean, but it's not very clear.

 

[lpdsn]

I really can't be bothered, but I'll try to explain again. Piers posted that unless a larger duct is fitted, the air will slow down. I suggested that the air will slow down in a larger duct. You appeared to agree, but then went on to say that if the air flowed faster it'd come out of the vent slower. You may know what you think you mean, but it's not very clear.

Yes, I did agree and still do. The air flowing in the larger duct will flow slower and there will be a smaller pressure drop, hence greater residual pressure to force the air through the vent itself, whereas the faster flowing air in the smaller diameter duct would lead to a greater pressure drop and less residual pressure to force the air through the vent.

I never meant to start an argument. It was meant as a light-hearted comment that I thought you had the background to understand. I'm happy if we call it quits now as there's no real reason to continue discussing it.

 

[Piers]

I really can't be bothered, but I'll try to explain again. Piers posted that unless a larger duct is fitted, the air will slow down. I suggested that the air will slow down in a larger duct. You appeared to agree, but then went on to say that if the air flowed faster it'd come out of the vent slower. You may know what you think you mean, but it's not very clear.

If the duct decreases in diameter, the air will find it harder to pass through so will take the easy option and escape through the previous cabin outlets. By increasing the diameter the further the air has to travel, the less drag, the more the air will flow.