Engine room ventilation system

Gokul43201

The OP seems to suggest this is the engine room of some small marine vessel. Don't they typically use water cooling in such cases, or would that be too risky (sea water) ?

russ_watters

Yes, they do use seawater and no, it isn't all that risky.

kkkasturi

russ-watters, our design is for a security craft.
Since we are allowing the deltaT to go higher( once the engines are turned off it wont take long to blow the air out), we came up with reltively small numbers 12800cfm.

Artman

If one or both engines are off for an extended period during the course of an hour, the heat gain isn't as high so the delta T won't necessarily be any higher. The air will change in the room in approximately 15 seconds. In my opinion, that should be plenty of air.

kkkasturi

How to calculate the time required to get the temperature of a room from 140F to 120F?
The case here is (marine), the delta T is 40F while the engines are running once the engines are shutdown, i need to calculate the time needed to bring down the temperature of the room to 120F

Artman

You can cool the air in the room quickly enough, about 7 or 8 seconds with 100 deg F incoming air, but this does not necessarily cool the contents of the room to 120 deg that fast. That amount of air will cool approximately 65,692 btuh in that time with a 40 deg delta T. How long it will take to cool the room depends on the room's contents, construction weight, color, windows, doors and other heat contributing factors.

For example, your engines will be hot (they will probably rise well above the 140 degrees F of the air) and giving off heat (until their casing cools). How long will it take to actually cool them? When they first shut off they will give off almost as much heat as when they were firing. This number will decrease until the case is cool, how fast this happens depends largely on the mass of the object, how well it conducts heat and surrounding air temperature. (Did I forget anything physicists?)

But the air in the room will cool to 120 deg F in about 1/8 of a minute with 100 deg F incoming air (although the engines, walls, furniture, etc. will still be hot).

Sorry it took so long to reply.

Gokul43201

...and the heat capacity of the object. The time constant for thermal response goes like ~C/K (heat capcity over conductivity).

kkkasturi

Thanks Artman

kleinjahr

kkkasturi. These are marine diesels? With no water jacket? Air cooled? Generally marine engines are water cooled, in my experience. The ocean makes a really big heat sink and it's convenient too.

suheri

if we give large air opening area (for ventilation), how it effect with noise???
thx everybody!!!!!

brewnog

Wow, a 2 year old post revived; well done.

Obviously a large opening in the walls of an engine room will allow engine noise to escape. That's why you put attenuators on ventilation louvres.