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replyMy understanding is that wax motors are based on actuation - they are intentionally and deliberately either heated to extend or cooled to retract, and if ambient temperature is used as one endpoint, the other will not be ambient (i.e. a heating element or cooling peltier).
replyThermostatic valves are ambient at both sides - they expand and contract naturally with the existing temperature, so they are not motors per se, because there's no actuation beyond the temperature.
Why does there need to be a thermal gradient? It seems like the action driving the actuator is the expansion of the wax due to temperature. You don't need a persistent heat flux to get that, the wax just needs enough heat warm up and change phase.
replyEdit: also, the actuation from the wax motor only happens while it is absorbing (or losing) heat, even if it later ends up in a steady state with no heat flux.
There needs to be a gradient or the wax won't move due to temperature. The motion is the change in state, as you say, but it won't change state if you don't heat or cool it.
replyThat's why it's a motor, like in dishwashers, not a thermostat like in e.g. greenhouse windows or radiators.
It doesn't need to be persistent, but without some way to create a state that is different than ambient, it's not a motor.
I disagree, I think motor in this case only means “creating movement”. The motor is the thing creating movement depending on the ambient temperature.
replyAlso you seem to have a miscommunication with the person replying to where they are talking about a special thermal gradient and you mean it in a temporal sense.
The wax expands due to ambient (even uniform) temperature. It's a linear actuator, so warm -> expanded and cool -> retracted.
replyI think by thermal gradient they mean a change in temperature over time, not space.
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