TECHNOLOGY AREAS: Ground/Sea Vehicles

ACQUISITION PROGRAM: PMS 320 Electric Ships Office

OBJECTIVE: Develop and demonstrate durable, long-life heat exchangers suitable for recovering waste heat from highly transient exhaust combustion air ranging in temperature from 500 to 1200 °F.

DESCRIPTION: Typical gas turbine engines are less than 40% efficient at full power and significantly less at part power. Diesel engine efficiency is more uniform across its operating power range but top efficiency does not typically exceed 45%. The engine exhaust stream is the primary pathway of engine waste heat. Recovering useful energy from engine exhaust waste heat will directly reduce system fuel consumption and increase overall system efficiency. Previous U.S. Navy efforts have shown promise in recovering engine exhaust waste heat in the interest of saving fuel, but reliability issues with the heat exchanger design have prevented implementation. The heat exchanger is subjected to high thermo-mechanical stresses due to highly transient engine loading profiles, which results in large temperature variations and non-uniform heat distributions within the exhaust stream. Corrosion and fouling are common issues when extracting heat from combustion air exhaust stream. If waste heat recovery systems are to be transitioned into the current or future fleet, development of durable, long-life heat exchanger is a necessary prerequisite.

Innovative research is sought to produce the next generation of exhaust to fluid heat exchangers capable of extracting at least half of the waste heat leaving the engine: The hot exhaust combustion air shall flow on the exterior of the heat exchanger and transfer heat to a non-aqueous fluid (eg. refrigerant) assumed to be entering the heat exchanger between 60 and 130 °F. Pressure drop shall be minimized on both the combustion air and fluid side of the heat exchanger. Face velocities of the combustion air stream entering the heat exchanger shall be designed for 5000 fpm. Pressure drop across the combustion air side of the heat exchanger shall be less than 4 inches of water. The heat exchanger design shall be capable of withstanding a temperature change from ambient conditions to 1200 °F within one minute. The heat exchanger design shall also be capable of withstanding a thermal shock when a non-aqueous fluid at 60 degrees Fahrenheit enters a 1200 °F heat exchanger. Weight and volume of the heat exchanger design shall be minimized.

PHASE I: Design a durable, long-life heat exchanger for recovering waste heat meeting the characteristics described above. Quantify the heat exchanger efficiency and pressure drop to transfer heat analytic modeling and component validation. The ability of the heat exchanger to withstand highly transient temperature variation, corrosion and fouling shall be addressed.

PHASE II: Develop and demonstrate a reduced scale heat exchanger prototype sized to transfer at least 250 KW of heat. The ability to withstand extreme temperature cycles shall be demonstrated. Validate analytic models developed in Phase I and evaluate scalability of design to larger sizes.

PHASE III: Design and develop an improved heat exchanger using the knowledge gained during Phases I and II. This heat exchanger must meet military unique requirements such as shock and vibration. Develop a commercialization strategy for dual use.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: The heat exchangers developed under this topic could be used to increase the efficiency of any vehicle relying on fuel combustion engines. The developed technology can be applied to many waste heat applications to improve energy efficiency.

REFERENCES:
1. http://www.rolls-royce.com/Images/fs_501_tcm92-6730.pdf

2. MIL-PRF-16884, Performance Specification for Fuel, Naval Distillate, NATO Symbol F-76.

3. Marine Gas Oil, ASTM D-975 Grade No. 2-D.

4 Marron, H.D., Gas Turbine Waste Heat Recovery Propulsion for U.S. Navy Surface Combatants, 1980, uploaded in SITIS 12/02/10.

KEYWORDS: Thermal Management; Heat Exchanger; Waste Heat Recovery; Gas Turbine

** TOPIC AUTHOR (TPOC) **

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