TECHNOLOGY AREA(S): Ground/Sea Vehicles

ACQUISITION PROGRAM: Next Generation Electronics Cooling System FNC (proposed)

OBJECTIVE: Develop a compact and efficient refrigerant liquid-vapor phase separation system capable of operating under dynamic platform motion with minimal system impact.

DESCRIPTION: Two-phase cooling systems are being explored to extract large heat loads from future shipboard high-energy sensors and weapons due to their decreased size, weight, and power consumption. One such system, a two-phase pumped refrigerant loop, circulates refrigerant between the cold plate (evaporator) and the condenser, but the durability of the circulation pump and, thus, the reliability of the cooling system require that the refrigerant be a single-phase liquid at the pump inlet. Ensuring that no entrained vapor enters the pump can be accomplished by sub-cooling the refrigerant, but this adds system complexity, increases pumping power, and requires a larger condenser. Physically separating the vapor from the liquid is an attractive alternative, but traditional liquid-vapor separators can’t be used in shipboard applications because they rely on the buoyant vapor rising out of a static pool of refrigerant. Recently, a number of phase separators have been developed for microgravity environments. However, the dynamic motion of a sea vessel will affect the two-phase flow regimes within the separator differently than microgravity. In addition, these separators have been designed to output a single-phase vapor for use in vapor compression cooling systems, instead of the single-phase liquid required for pumped refrigerant loops.

The goal of this topic is to design and fabricate a liquid-vapor phase separator for a refrigerant that delivers single-phase liquid under dynamic platform motion. The separator must comply with DOD-STD-1399/301a, which defines the criteria for the magnitude, period, and acceleration of various platform motions, e.g. the static design limit for ship roll is 45° from horizontal, and accept vapor qualities as high as 0.8, a refrigerant mass flow of several kilograms per second, and a saturation temperature near ambient. Separators should minimize their electrical consumption and pressure drop, as these impact the overall performance of the cooling system.

PHASE I: Develop concepts for compact, high efficiency liquid-vapor phase separator. Validate design performance through analytical modeling and subscale demonstration with vapor qualities up to 0.50 and orientation independence of +/- 30°.

PHASE II: Based on Phase I effort, build and demonstrate a prototype for the operation of a liquid-vapor phase separator capable of delivering 1 kg/s of R134a in a pumped refrigerant loop with inlet vapor qualities up to 0.8. The separator should maintain proper operation when subjected to the ship motion dynamics discussed in DOD-STD-1399/301a.

PHASE III DUAL USE APPLICATIONS: Finalize design and manufacturing plans for a liquid-vapor phase separator using the knowledge gained during Phases I and II. The separator is intended to be installed as part of a two-phase pumped refrigerant loop thermal management system aboard a future surface combatant. Private Sector Commercial Potential: The development of refrigerant phase separators capable of operating under the orientation and dynamic motion associated with shipboard installation has commercial applications that include cooling of electric vehicles and commercial vessels.

REFERENCES:

• Department of the Navy, Naval Sea Systems Command, DOD-STD-1399/301a, “Ship Motion and Attitude,” (1986).
• S. Kuravi, B. Glassman, et al, “Design of a Two-Phase Separator for Variable Gravity Applications,” Proceedings of the 37th AIAA Thermophysics Conference, AIAA 2004-2288 (2004).
• M. Ellis, F. Best, and C. Kurwitz, "Development of a Unique, Passive, Microgravity Vortex Separator," Proceedings of the 2005 ASME International Mechanical Engineering Congress and Exposition, IMECE2005-81616, (2005).

KEYWORDS: Electronics Cooling; Two-Phase Cooling System; Pumped Refrigerant; Liquid-Vapor Phase Separator; Thermal Management

** TOPIC AUTHOR (TPOC) **

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