Fig. 1

NIFTE fluid pump schematic, adapted from Reference [25]. Configuration. A NIFTE consists of four major elements: the displacer cylinder ➇ that contains the hot ➃ and cold ➄ heat-exchangers; the adiabatic vapor region ➈; the power cylinder ➆ that is connected to the load ➁; and the feedback connection tube ➅. The white area denotes the vapor phase, while the grey area denotes the liquid phase of the working fluid. Operational cycle. Low-grade heat from an external source is supplied to the system via the hot heat-exchanger (HHX) ➃ to vaporize the working fluid. The pressure in the adiabatic vapor region ➈ thus increases, causing the liquid level ➀ in the power cylinder ➆ to fall below the equilibrium level. The liquid level ➂ in the displacer cylinder ➇ drops as a result of the hydrostatic pressure via the feedback connection ➅. The vapor comes into contact with the cold heat-exchanger (CHX) ➄, where heat is removed from the system, causing the vapor to condense and the liquid height to rise back above the equilibrium position. Sustained oscillations in the load ➁ are thereby created by the cyclic condensation and evaporation of the working fluid in the cylinders