Linear Stability Analysis of Turbo Heat Pumps Available to Purchase

A typical turbo heat pump system consists of a centrifugal compressor, expansion valve, and two heat exchangers or plenums — a condenser and evaporator. Compared to a gas turbine, a turbo heat pump introduces additional complexities because it is a two-phase, closed-loop system with heat exchange using a real gas/liquid (refrigerant) as working fluid. For such systems, a new linear stability model has been developed by applying a linearized small perturbation method to the nonlinear turbo heat pump surge model. When the new linear model is applied to a compressor in an open loop system (e.g. turbocharger), results identical to those of Greitzer’s model are obtained. When applied to an operating turbo heat pump, the new model accurately predicts the surge onset point. Finally, results from a parametric study on the influence of the B parameter on surge onset are presented. Thus, the new model can be applied to predict stability of various compression systems — either open or closed-loop systems running single or two-phase working fluids with or without heat exchange.