RP-800 -- Heat Transfer and Pressure Drop in the Dry-Out Region of In-Tube Evaporation With Refrigerant/Lubricant Mixtures ✓ Most Recent

A summary of some of the objectives and conclusions reached in this project are:

• A literature search on post dryout heat transfer for pure refrigerants and for refrigerant-oil mixtures was performed and a comprehensive review written (Chapters 9,10 and 11);

• The correct thermodynamic definition of the heat transfer coefficient for evaporation of refrigerant-oil mixtures was presented and men used in the project, i.e. defining the heat transfer coefficient using the local bubble point temperature T_bub of the refrigerant-oil mixture rather than with the saturation temperature of the pure refrigerant T_sat incorrectly used in prior studies (Chapter 3);

• A new generalized approach, that is simple to implement, was developed for predicting bubble point temperatures of refrigerant-oil mixtures for miscible oils mat can be applied to any refrigerant-oil combination and is accurate over the local oil concentration range from 0-50 wt.% oil range confronted in direct-expansion evaporators with 0-5 wt.% oil in their refrigerant charge (Chapter 4);

• A new thermodynamic method for preparation of temperature-enthalpy-vapor quality (T-h-x) curves for refrigerant-oil mixtures for general application was developed and validated against test data (Chapters 5 and 6), including a simple expression for calculating local oil concentrations as a function of vapor quality;

• New, accurate thermodynamic methods for preparation of temperature-enthalpy-vapor quality (T-h-x) curves for the refrigerant blend R-407C and R-407C/oil mixtures were developed developed for thermal design of evaporators and for the present experimental tests, and was validated against measured test data (Chapter 12).