Modern Evaporator Piping: Two-phase Riser & Gravity-Feed Sys
Modern Evaporator Piping: Two-phase Riser & Gravity-Feed System Design (2005)-Modern industry safety practices have, for the most part, moved the installation of vessels and valves outside of occupied spaces in order to reduce employee risk of accidental exposure to ammonia as well as to facilitate maintenance operations. The preferred location has been the roof, a location that in many cases is 15?35 feet above the evaporator. These higher elevations have resulted in dramatic changes to the velocities and pressure differences in both recirculated and flooded evaporator systems and the standard piping practices have not been updated to account for the liquid supply static head pressures and return riser flow issues. Historically, flooded evaporators had a liquid level usually no more than one or two feet above the evaporator outlet connection and the pipe sizes were relatively large for the mass flow. The large pipe diameters insured proper refrigerant flow in low head installations and allowed for oil separation and collection before the evaporator inlet. The return riser did not have turbulent flow by design. This paper presents a theoretical method for designing flooded systems that achieve proper flow conditions in the return riser and correctly predict the liquid line flow characteristics. The result is smaller sizes for lines and hand expansion valves, and evaporators with very similar saturated temperature conditions to the surge vessel many feet above it.
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