The main objective of this paper is to evaluate the temperature drop and potential cooling effect due to cavitation of an arbitrary liquid. Cavitation results from a pressure decrease into the metastable liquid region, to the point where some of the liquid nucleates (boils). Under adiabatic conditions, the energy required to produce this phase change is pulled from the fluid itself, which results in a temperature drop.
The paper discusses the fundamental thermodynamics associated with the temperature drop in an effort to better understand the cooling process and to identify of the optimum fluid capable of developing significant cooling results.
The analysis presented here focuses on a general Equation of State (EOS), to represent an arbitrary fluid. At a given temperature, such an EOS yields a relationship between pressure and density (or specific volume). The van der Waals EOS was used initially to define the saturated liquid and saturated vapor lines, for water, R134a, R22 and R123. Work later focused on the Peng Robinson EOS, which better represents the properties of a wide variety of substances. The Peng Robinson EOS was used to investigate different fluids such as water, R134a, R22 and R123. The principle of corresponding states was introduced, to express the thermodynamic variables in terms of reduced (or relative) state variables. Coexistence curves and spinodal curves were determined numerically. This stems from the unique values of the acentric factor for each fluid.
A basic theory was then formulated using the Peng Robinson EOS to determine the maximum temperature reduction. ΔTmax, which will occur if the cavitation phase transition occurs adiabatically. Variables that affect this maximum temperature drop are identified are shown to include latent heat of vaporization, specific heat, and “equivalent quality” at the spinodal line limit.
Further analysis of the temperature drop as a function of reduced pressure was investigated for water, R134a, R123, and R22, and reveals that an apparent optimum (or maximum) temperature drop is achieved for a general fluid when the reduced pressure equals approximately 0.5.
