Mass-conserving dynamic organic Rankine cycle model to investigate the link between mass distribution and system state

This study presents a mass-conserving dynamic numerical model to capture dynamic response of ORCs (organic Rankine cycles) when the system experiences a change in expander's rotational speed, pump's capacity factor, and conditions of hot and cold heat transfer fluids. ORC's dynamic response is tracked specifically considering evaporator pressure, condenser pressure, degree of superheating at the evaporator exit, degree of sub-cooling at the condenser exit, and the mass distribution along evaporator, condenser and liquid receiver tank. The developed model is novel due to the way subcomponent models are integrated together. Specifically, this integration includes fully coupled tank and condenser models. The model is validated against an experimental benchmark study for various steady state conditions and further verified considering mass and energy conservation principles. A parametric study is carried out to identify parameters which can be used for devising a new autonomous control strategy for organic Rankine cycles. It is illustrated through simulations that the mass distribution over ORC sub-components are linked to the system's overall state; and both the liquid level in the tank and the degree of sub-cooling at the tank exit can be used to devise a control system by changing pump's capacity factor and expander's rotational speed