Additional Engine cooling

[Stephen Jeavons]

17 minutes ago, Boater Sam said:

Its not the VOLUME  that determines how it cools but the surface AREA in contact with the canal water. How many square feet? How many horses in the engine? Maximum 4 times the area.

Hi Sam,

Based on that, I'm woefully under-cooled as I have just 7 sq feet in contact with water (side and bottom). and a 72 horse engine.

I don't see the logic in not including volume.

For two tanks having the same area in contact with the water, A half inch thick tank where the water spends little time in the tank (as there isn't much of it) cannot provide as much cooling as a 6 inch wide tank where the water spends far more time being cooled as it passes through more slowly. What am I missing?

 

Stephen

 

[Boater Sam]

26 minutes ago, Stephen Jeavons said:

Hi Sam,

Based on that, I'm woefully under-cooled as I have just 7 sq feet in contact with water (side and bottom). and a 72 horse engine.

I don't see the logic in not including volume.

For two tanks having the same area in contact with the water, A half inch thick tank where the water spends little time in the tank (as there isn't much of it) cannot provide as much cooling as a 6 inch wide tank where the water spends far more time being cooled as it passes through more slowly. What am I missing?

 

Stephen

 

You are missing the fact that heat transfer is what is required not just heating lots of water. A large volume initially gives you a big heat dump but once up to temperature you have to still lose the same amount of heat into already hot water,  it just doesn't absorb any more heat ad infinitum!  

The other problem as I know to my cost is finding somewhere for the 4% expansion of a big volume of cooling water to go when its already pretty full at room temperature.

 

Your skin tank is woefully undersize, if you get on a river and open the engine up to anything approaching full power you will boil like a kettle after a while. That tank would just about cope with a BMC 1.5D or a small Beta/Isuzu.

Edited April 26, 2019 by Boater Sam
added more

[PeterF]

57 minutes ago, Stephen Jeavons said:

Hi Sam,

Based on that, I'm woefully under-cooled as I have just 7 sq feet in contact with water (side and bottom). and a 72 horse engine.

I don't see the logic in not including volume.

For two tanks having the same area in contact with the water, A half inch thick tank where the water spends little time in the tank (as there isn't much of it) cannot provide as much cooling as a 6 inch wide tank where the water spends far more time being cooled as it passes through more slowly. What am I missing?

 

Stephen

 

Heat transfer between a liquid and a metal surface occurs due to turbulence in the fluid continuously moving small volumes of hot fluid to the cooler steel and turbulence is generated by moving the fluid at high velocity. The best tank is one that is very thin with high velocity, but this would have a high pressure drop, so you come to a compromise, wide enough to pump fluid around but not too wide. With a very wide tank and slow flow without turbulence, the flow is laminar and only the thin layer of liquid next to the surface gets cooled down, the bulk of the fluid does not touch the surface and exits the unit uncooled. Before retirement I designed industrial heat transfer equipment.

Edited April 26, 2019 by PeterF

[Stephen Jeavons]

1 hour ago, ditchcrawler said:

I also suspect you have an oil cooler for the hydraulic oil 

It has a fairly large skin tank in the engine room for that. Most of it is below the water line

4 minutes ago, PeterF said:

Heat transfer between a liquid and a metal surface occurs due to turbulence in the fluid continuously moving small volumes of hot fluid to the cooler steel and turbulence is generated by moving the fluid at high velocity. The best tank is one that is very thin with high velocity, but this would have a high pressure drop, so you come to a compromise, wide enough to pump fluid around but not too wide. With a very wide tank and slow flow without turbulence, the flow is laminar and only the thin layer of liquid next to the surface gets cooled down, the bulk of the fluid does not touch the surface and exits the unit uncooled. Before retirement I designed industrial heat transfer equipment.

Would the baffles in the tank also aid turbulance?

[Boater Sam]

8 minutes ago, Stephen Jeavons said:

It has a fairly large skin tank in the engine room for that. Most of it is below the water line

Would the baffles in the tank also aid turbulance?

That's why they are there, to prevent a direct non turbulent flow between in and out, they lengthen the route the water has to take.

They are not perfectly sealed on both sides, they are welded to one side, boat or inner plate, so the other side of them may not even be touching anything but the effect they have is still very advantageous.

Edited April 26, 2019 by Boater Sam
smellings & Added

[ditchcrawler]

13 minutes ago, Stephen Jeavons said:

It has a fairly large skin tank in the engine room for that. Most of it is below the water line

Would the baffles in the tank also aid turbulance?

If you require more cooling could you perhaps combine the two skin tanks?

 

[PeterF]

12 minutes ago, Stephen Jeavons said:

It has a fairly large skin tank in the engine room for that. Most of it is below the water line

Would the baffles in the tank also aid turbulance?

Yes the baffles help as Boater Sam says to avoid a direct bypass route, but they also increase the velocity by making the flow path of lower cross sectional area, industrial heat exchangers use them extensively. Therefore, you could make your tank 4 times wider and put lots of baffles in to compensate and have a large coolant volume for no reason and a more expensive tank to boot. Keep it narrow with few baffles.

[Stephen Jeavons]

For the time being then, I'm going to change the thermostat as Tony suggests, pipe in the calorifier and avoid rivers. (other than the Colne where I'm resident :D)

 

Hope to swap the engine for a more suitable 2 or 3 cylinder Lister in a year or two and probably ditch the hydraulic drive as well. The boat deserves better.

 

Thanks for all the advice everyone.

 

Stephen

12 minutes ago, ditchcrawler said:

If you require more cooling could you perhaps combine the two skin tanks?

 

Can't do that. The hydraulic system uses the one in the engine room and I only have a single skin tank for the engine.

[ditchcrawler]

28 minutes ago, Stephen Jeavons said:

 

Can't do that. The hydraulic system uses the one in the engine room and I only have a single skin tank for the engine.

I only have a single skin tank, a good size one, the water flows from the engine to the skin tank and then back to the engine via the hydraulic oil cooler.  Or do you pass your oil through the skin tank?

 

[Stephen Jeavons]

35 minutes ago, ditchcrawler said:

I only have a single skin tank, a good size one, the water flows from the engine to the skin tank and then back to the engine via the hydraulic oil cooler.  Or do you pass your oil through the skin tank?

 

My hydraulic system is totally independent with its own skin tank/reservoir with oil filter attached. The engine coolant uses the skin tank in the back cabin. Your system seems to be integrated. The hydraulic pump and motor on my boat was an afterthought.

[PeterG]

On 01/08/2018 at 21:08, nicknorman said:

No. Ours has the normal skin tank on the swim. The fuel tank is under the engine, integral with the baseplate however. Maybe Hudsons with mid-engines have skin tank in the baseplate? They have to be pretty thin so than the hot water doesn’t just flow over (under) the upper surface though. Perhaps that and them being the low point in the system, might lead to a risk of sludging up?

No Hudsons with Engine rooms have skin tanks on the swim as well.  Perhaps this is one of the very early builds?

[WotEver]

3 hours ago, PeterG said:

No Hudsons with Engine rooms have skin tanks on the swim as well.  Perhaps this is one of the very early builds?

Nick’s Hudson doesn’t have an engine room. 

[cuthound]

16 minutes ago, WotEver said:

Nick’s Hudson doesn’t have an engine room. 

 

Indeed, like most modern trads, the engine is in the basement, (along with the butler). ?

Edited April 26, 2019 by cuthound
Clarification

[PeterG]

On 26/04/2019 at 19:07, WotEver said:

Nick’s Hudson doesn’t have an engine room. 

Yes that is why I was clarifying his question on Hudsons with an engine room as he did not know, or perhaps only his butler is allowed to look?

[blackrose]

On 25/04/2019 at 17:50, Boater Sam said:

If its unpressurised and doesn't boil, its OK.

 

 

It's ok on the GU between Ricky and Uxbridge, but if it's getting to 90C on a canal it could well boil on a river. If you're not intending to take it on any rivers I'm sure it will be fine, but the Thames isn't far away so who knows.

On 26/04/2019 at 15:52, Boater Sam said:

Your skin tank is woefully undersize, if you get on a river and open the engine up to anything approaching full power you will boil like a kettle after a while. That tank would just about cope with a BMC 1.5D or a small Beta/Isuzu.

 

Yes indeed