Heat Exchanger Design in Combined Cycle Engines Helen Webber and Simon Feast Reaction Engines Ltd., D5 Culham Science Centre, Abingdon, Oxon, OX14 3DB, UK
- Paper number
IAC-08.C4.5.1
- Author
Ms. Helen Webber, Reaction Engines Ltd., United Kingdom
- Year
2008
- Abstract
Combined cycle engines which employ a pre-cooled turbo-compressor for the airbreathing ascent phase and rocket propulsion for the later phase of the ascent are potentially the most promising propulsion system for achieving single stage to orbit vehicles. These engines have several major heat exchangers performing different roles; extracting heat from incoming air in the precooler, topping up cycle flow temperatures to maintain constant turbine operating conditions and extracting rejected heat from the power cycle via regenerator loops for thermal capacity matching. However, these engines are sensitive to component efficiencies and the heat exchangers must be closely matched thermally both in capacity rate and in temperature difference across the heat transfer surface. As the engine becomes more fuel efficient the capacity ratio of air to fuel increases and the cycle becomes more complex due to the highly parallel configuration needed to keep capacity rate matching between the cycle intermediate working fluid and the hydrogen fuel. Temperature limitations in the high temperature section of the intake precooler make this situation worse by having a very high coolant capacity relative to the air flow in the hot section. This high coolant flow must transfer the rejected heat to the hydrogen in a capacity rate matched rejection system, resulting in multiple parallel cooling flows. Cycle analysis is presented which shows the effect of these factors and the level of precooler enhancement and regenerator compactness. The precooler and the regenerators are especially critical components with characteristics which need to be met through advances in the technology of heat exchangers. The cycle intermediate working fluid is at high pressure, typically 200 bar. The hydrogen is also at similar pressures. This makes the achievement of high heat transfer with low pressure drops in the regenerators relatively easy but dictates a compact design with extremely small cooling channels. On the other hand, the precooler has the air at relatively low pressure on one side and coolant at 200 bar on the other. This means that the low pressure flow must have large flow area as well as a large heat transfer surface to be efficient. This dictates that the walls must be efficient containment structures and results in a tubular surface which is in effect a miniature shell and tube configuration.
- Abstract document
- Manuscript document
IAC-08.C4.5.1.pdf (🔒 authorized access only).
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