Heat engine and heat to electricity systems and methods with working fluid mass management control

A heat engine system for converting thermal energy into mechanical energy, comprising:

• a working fluid circuit configured to circulate a working fluid through a high pressure side and a low pressure side of the working fluid circuit, the working fluid circuit further comprises:
• a heat exchanger configured to be coupled to and in thermal communication with a heat source and to transfer thermal energy from the heat source to the working fluid within the high pressure side;
• an expander in fluid communication with the heat exchanger and fluidly arranged between the high and low pressure sides;
• a recuperator fluidly coupled to the expander and configured to transfer thermal energy between the high and low pressure sides;
• a cooler in fluid communication with the recuperator and configured to control a temperature of the working fluid in the low pressure side;
• and
• a pump fluidly coupled to the cooler and configured to circulate the working fluid through the working fluid circuit;
• and
• a mass management system fluidly coupled to the working fluid circuit and configured to regulate a pressure and an amount of the working fluid within the working fluid circuit, the mass management system further comprises:
• a mass control tank fluidly coupled to the high pressure side at a first tie-in point located upstream of the expander and to the low pressure side at a second tie-in point located upstream of an inlet of the pump;
• and
• a control system communicably coupled to the working fluid circuit at a first sensor disposed upstream to the inlet of the pump and at a second sensor disposed downstream from an outlet of the pump, and communicably coupled to the mass control tank at a third sensor arranged either within or adjacent the mass control tank.