Numerical simulations of the piston effect for near-critical fluids in spherical cells under small thermal disturbance

•The piston effect for eight near-critical fluids is studied.•The indicative function of the specific heat ratio in piston effect is revealed.•The influences of the characteristic length and boundary condition are studied.•An impulse-momentum theorem analogy in piston effect is proposed.

Near the liquid–vapor critical point, strong anomalies in thermodynamic and transport properties induce the piston effect. In the present study, the piston effect is investigated in spherical cells filled with near-critical fluids under zero gravity and small thermal disturbance conditions by numerically solving the thermodynamic model. The results show typical fast-responding bulk temperature, together with high and stable temperature efficiency, which is determined by the particular nature of near-critical fluids. Particularly, a nondimensionalization method is developed to study the influences of the specific heat ratio on the piston effect by simulations for eight near-critical fluids. Results show the specific heat ratio is an efficient indicator, which is negatively correlated with the nondimensional bulk temperature change. The influences of the characteristic length and the boundary conditions on the piston effect are also studied for near-critical carbon dioxide. In addition, some rules concerning the boundary heat flux and the overall heat transfer are also discussed and concluded.