Experimental Study of Capillary-Fed Enhanced-Surface Tubular Evaporators - With Applications to Low Grade Energy Conversion

Abstract

A novel capillary feed concept was developed for deployment on an enhanced tubular evaporator intended for low grade thermal energy applications. The concept was applied to both vertical and horizontal evaporator orientations. Empirical testing initially focused on capillary feed development, but the bulk of research was conducted on closed single tube testing using anhydrous ammonia. A 2" one foot long proof of concept evaporator was tested along with two different ¾" five foot long (half-length) aluminum tubes. The target test LMTD was around 2 [K]. Results varied with test conditions, enhancement geometry, refrigerant flow rate, and evaporator orientation. Heat transfer performance of the evaporator, as well as water and refrigerant flow rates and pressure drops are assessed. Test operational constraints and uncertainty limitations are investigated. The capillary feed mechanism advantages and limitations are surveyed, and future works are recommended along with discussions about relevant operational considerations.