Thermodynamic and economic comparison of pressure shift freezing and isochoric pressurization without a hyperbaric pump

Abstract Pressure-assisted freezing produces frozen foods with finer ice crystals, less drip loss and longer microbiological shelf life than conventional freezing, but its adoption has been limited because the conventional implementation, pressure-shift freezing (PSF), requires a hyperbaric pump delivering 100–200 MPa whose capital cost and mechanical complexity are the principal barrier to industrial deployment. A rigid constant-volume chamber cooled in a standard industrial freezer reaches the same pressurized subzero state passively, because partial ice formation in a confined volume drives the pressure along the ice Ih liquidus; this eliminates the pump at the cost of freezing sacrificial water, an overhead that grows with subzero depth. This work compares the two routes thermodynamically on an equal-output basis, from the ambient inlet state to the common pressurized subzero state that both must reach, with all water and ice properties evaluated from the IAPWS formulations. The two paths differ in a way that is thermodynamically fundamental: the PSF vessel is a moving-boundary system held at constant pressure by its pump, so its cooling duty is an enthalpy change and the pump must also supply boundary work as the fluid contracts, whereas the isochoric chamber is rigid, so its duty is an internal-energy change and no external work is supplied at all. Per kilogram of product delivered to the common state, isochoric pressurization consumes 53–87 kJ kg⁻¹ less electrical energy than batch PSF between − 5 and − 20 °C, and is competitive with an aspirational continuous flow-through PSF architecture above approximately − 9.4 °C. The crossover between the two routes is governed by the ratio of pumping to refrigeration efficiency rather than by either efficiency individually. Because the analysis stops at the shared state, the comparison is independent of what is done downstream, and applies equally to isochoric preservation, in which the product is held unfrozen at that state, and to the hypothetical use of the isochoric chamber as a pressure generator for a subsequent decompression-nucleation step. The framework identifies batch operation, rather than the choice between mechanical and isochoric pressurization, as the dominant thermodynamic liability of conventional PSF.