Thermodynamics?

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Graham
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I know very little in this field but if anyone else does I would appreciate a little advice.

I'm doing a simple project just now, more out of curiosity and fun but if it works then it's a bonus. I'm converting an 8 litre coolbox from the measly 12V Peltier system to having my car a/c cool the box instead.

It's nothing fancy, just ducting from a rear vent into the box and an outlet hole which will also have a flap so I can seal it if using the box without any active cooling.

My question is to do with the outlet hole. I'll be making it on the opposite side of the inlet and it will be at the top so as for optimum airflow. But thinking thermodynamics, will there be an ideal size of outlet hole and is it related to the inlet? (60x60mm)

Thanks
 
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I know very little in this field but if anyone else does I would appreciate a little advice.

I'm doing a simple project just now, more out of curiosity and fun but if it works then it's a bonus. I'm converting an 8 litre coolbox from the measly 12V Peltier system to having my car a/c cool the box instead.

It's nothing fancy, just ducting from a rear vent into the box and an outlet hole which will also have a flap so I can seal it if using the box without any active cooling.

My question is to do with the outlet hole. I'll be making it on the opposite side of the inlet and it will be at the top so as for optimum airflow. But thinking thermodynamics, will there be an ideal size of outlet hole and is it related to the inlet? (60x60mm)

Thanks

I can't help you with your problem but although you are interested in the dynamics of heat transfer, it has nothing to do with thermodynamics.
 
I know very little in this field but if anyone else does I would appreciate a little advice.

I'm doing a simple project just now, more out of curiosity and fun but if it works then it's a bonus. I'm converting an 8 litre coolbox from the measly 12V Peltier system to having my car a/c cool the box instead.

It's nothing fancy, just ducting from a rear vent into the box and an outlet hole which will also have a flap so I can seal it if using the box without any active cooling.

My question is to do with the outlet hole. I'll be making it on the opposite side of the inlet and it will be at the top so as for optimum airflow. But thinking thermodynamics, will there be an ideal size of outlet hole and is it related to the inlet? (60x60mm)

Thanks


I would imagine the outlet would be the same diameter as the inlet, though you could make it a bit smaller to bottleneck the cool air in the box a bit before it exits.
Is this the calc you are looking for ?
If its just a bit of fun I'd half the hole and see how I got on.
Or use a vent with variable baffles.
 
Though the cool air from the a/c will be 'pushing' in to the box.................as cold air is heavier than warm air I agree with the above that is the exit vent is smaller than the input one that might/should ensure that the cooler air is "held" longer in the box than is it was just(?) blowing straight through!
 
I expect for your purposes any advantages that could be gained from a properly designed outlet would be fairly small. I would suggest not making the outlet too large otherwise it could let warm air back in, on the other hand, given that a car ventilation system has multiple outlets, making it too small might just push more air out of the other vents rather than it going through the cold box. Avoid sharp edges on the outlet as these might reduce the rate of airflow.
 
Blim
I know very little in this field but if anyone else does I would appreciate a little advice.

I'm doing a simple project just now, more out of curiosity and fun but if it works then it's a bonus. I'm converting an 8 litre coolbox from the measly 12V Peltier system to having my car a/c cool the box instead.

It's nothing fancy, just ducting from a rear vent into the box and an outlet hole which will also have a flap so I can seal it if using the box without any active cooling.

My question is to do with the outlet hole. I'll be making it on the opposite side of the inlet and it will be at the top so as for optimum airflow. But thinking thermodynamics, will there be an ideal size of outlet hole and is it related to the inlet? (60x60mm)

Thanks

Blimey! How cold do you want your beer? :beer:
 
Thanks, I ended up using a spade bit just under 1/2 size of the inlet and this seems to be doing a good job.

I'm getting the temp of the coolbox down to 5 degrees C which allows a 500mm bottle of water to drop from 20 degrees C to 13 degrees C in twenty minutes. I'm happy with that but I've got a lot more testing to do because this was full blast at lowest temp setting.

My target is really just to have the water at room temperature, I'm not bothered about it being chilled, that's just a bonus, just so long as it's not that horrible hot temperature.
 
I can't help you with your problem but although you are interested in the dynamics of heat transfer, it has nothing to do with thermodynamics.

Heat/thermal conduction and the second law of thermodynamics come to mind with what I'm doing.
 
Clever old Saab air conditioned the glove box.
 
Clever old Saab air conditioned the glove box.

Love SAAB, great cars, my dad had a classic 900 n/a. Got a mate who has a 9-3 with the fantastic 2.8 V6 turbocharged engine which has been remapped. Off the mark isn't great as it's FWD and it can't get traction, but from about 30mph upwards the in-gear acceleration is insane and relentless; left my F30 330d X-Drive for dust. The interior is cheap though, which I suspect is due to GM interference.
 
We owned 5 Saabs over 25 years. The 99 was superb for its time, the 900 very good, the 9000 not worth the money and the 9-3 very nice but not built to the standard you'd expect for the price.

Saab 9-3 front CL7594.JPG
 
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