Let's say we have a long cylinder and two pistons inside the cylinder, and some vapour between the pistons. Now we make the pistons accelerate with some coordinate acceleration, along the cylinder axis, same coordinate acceleration for both pistons. Cylinder is static. Going to the frame of the pistons, we can see that vapour will cool and then turn to liquid, as the vapour is doing work, as distance between the pistons increases, in the pistons frame. Now let's go to inertial frame and observe our vapour condenser. We see entropic vapour turning into less entropic liquid. So the question is: Were does the entropy go, in the inertial frame?