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The effect of waste-heat-boiler weight and volume on the performance of an LM2500-based combined gas and steam turbine system (COGAS) is examined. The boiler is a once-through type which is controlled to extract the maximum heat from the gas turbine exhaust and still maintain acceptable minimum wall temperature. At a gas turbine power of 12,000 hp (8.95 MW), the boiler without feed-water heating can produce sufficient steam to generate 2840 hp (2120 kW) at a turbine efficiency of 80%. This boiler, including diffuser, weighs 19,300 lbs (8770 kg) and has a gas side pressure drop of 9 in. H2O (2.2 kPa). With feed-water heating, the steam power can be increased to 4000 hp (2980 kW) with a boiler weight of 38,3000 lbs. (17,400 kg). The 24 and 33% respective increases in power for these two systems at cruise are translated to 15 and 20% improvement in fuel consumption over the LM2500 gas turbine at the higher power levels of the COGAS system. At the lower power levels, both COGAS systems yield a 20% improvement in fuel consumption over the basic gas turbine. Keywords: Waste-heat recovery, Waste-heat-boiler sizing, Gas turbine, Heat Transfer, and Steam bottoming cycle.

A design study determined the weight and volume benefits of heat-transfer augmentation in large steam-condenser cooling systems. By using an advanced Navy computer model and the observed dependence of system performance on coolant flow rate, flow-optimized designs for minimum system size or weight could be found for any given enhancement. The analysis, conducted for a given steam flow, assesses the effects of tube geometry, overall condenser length, and design constraints relating to waterbox diameter and condenser vacuum. The systems incorporate new high-strength, lightweight materials (titanium and Inconel) and include a main condenser consisting of titanium tubes having a 5/8-in. (1.59 cm) o.d. and 0.035-in. (0.089 cm) wall. General coolant-pumping-power correlations are developed for the spirally enhanced geometries examined. Results for two enhanced-tube geometries indicate that condenser-tube enhancement can provide system weight reductions ranging from 20 to 5 percent for short and long condensers, respectively. Keywords: Heat-transfer enhancement; Spirally grooved titanium tubes; Computer modeling of cooling systems; and Flow optimization.