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Originally Posted by brucepick
Prius has some kind of vacuum lined tank to store the heated coolant for faster warmup. So I've heard.
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Yep
In a thermos type bottle.
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Anyway, put this inline with the coolant hose and waste coolant heat would be stored for a faster warm-up. Taking advantage of the heat of fusion (phase change) of paraffin should yield a pretty inexpensive heat storage device.
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Unfortunately, it will work both ways... If you've got hot liquid paraffin - it will stay around it's freezing point of ~56C for a long time as it slowly freezes due to a high latent heat (heat required for a phase change). BUT, if it's allowed to completely cool - all of that heat for the phase change will be lost to the paraffin heat sink. Taking
that much longer to warm up....
Autospeed had an article awhile back about using a paraffin thermal heat sink on an inter cooler. But they cautioned that it was only suitable if you didn't go beyond 56C for long periods of time.
From the angle: How to make this work.... You need some logic, and some control. Place the paraffin heat sink on a bypass line with a valve. If the engine is cold, and the heat sink is <56C - close the valve. If the engine is cold and the heat sink is >=56C - open the valve. If the engine is at operating temperature and running - open the valve. If the engine is off - close the valve (to prevent thermal siphoning - also depends on physical location).
Okay, I know it's more complicated - but it resolves the issue of longer warm ups on complete cold starts... You can likely store a lot more heat in a smaller volume compared to the Prius thermos system too