Not being a thermodynamics expert,

Technically, this is Heat and Mass Transfer. Thermodynamics is a whole 'nother topic...

I have a question that someone may be able to answer. Peter is going to add two gallons of additional coolant to the reservoir. It seems to me that won't amount to a "hill of beans" to his cooling efforts. Can someone quantify that?

The very limited data shared to date does not give us much basis. A system that is at least approaching equilibrium will have the coolant dT/dt decreasing as temps go up. So far the data indicates one steady slope at full power and a lower slopes at lower power settings. That is how an insulated system looks - zero heat rejection. If it is rejecting some heat, it is a long ways (temperature wise) from steady state in the data I have been watching.

The insulated case can be considered the upper bound - Raptor already has several hundred pounds of metal and a couple gallons of coolant that warms up way too fast. Adding 50 more pounds of coolant will only slow things down a little. Coolant's job is to pick up heat at the engine, then give up that heat at the HX and do it several times a minute. Normally, the amount of coolant needed is just enough to fill the engine, the HX, and the lines. Everything beyond that reduces the dT/dt some, but does nothing for the steady state temperatures of the system, which is about flow rates of coolant, HX design, and ambient air flow through the HX.

Usually a climb to any cruise altitude will require a system that can go to steady state at coolant temps below boiling for coolant and at reasonable oil temps at climb power and airspeeds... At these power to weight ratios, must of us either climb at full power or at some high fraction.

All of this suggests a minimum of 3x current heat rejection to the air. Now maybe a lot of that could be obtained with good pressure recovery onto the various HX faces. Peter has not discussed duct design yet... Has anyone seen a pressure recovery duct to any of the HX?

Does anybody have any numbers on weight of aluminum, steel, and coolant in the base engine? We can then calculate thermal capacity before and after adding 50 pounds to the coolant load.

So far we have little basis for how much heat is being rejected... so that will be tough too.

Billski