Regenerator Effectiveness
Calculate the effectiveness of a regenerator (heat recuperator), ε = (T_out − T_in) ÷ (T_hot − T_in), comparing the actual heating of the cold fluid with the maximum possible (if it reached the hot exhaust gas temperature). The result (between 0 and 1, or ×100%) measures heat-exchange effectiveness: a regenerator uses a gas turbine's exhaust heat to preheat the air before the combustor, cutting fuel use and raising the regenerative Brayton cycle efficiency. Typical effectiveness is 0.7–0.9. Enter the inlet, outlet and hot-gas temperatures.
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Efetividade do regenerador
Numa turbina a gás, os gases de exaustão saem muito quentes — e o ar comprimido entra na câmara de combustão relativamente frio. O regenerador (ou recuperador) é um trocador de calor que aproveita essa diferença: usa o calor dos gases de escape para pré-aquecer o ar antes da combustão, de modo que menos combustível é necessário para atingir a temperatura de queima — elevando a eficiência do ciclo Brayton regenerativo. A efetividade mede quão bem o regenerador faz esse trabalho: ε = (T_saída − T_entrada) ÷ (T_quente − T_entrada). O numerador é o aquecimento real do ar (quanto ele de fato esquentou); o denominador é o aquecimento máximo possível, que ocorreria se o ar saísse tão quente quanto o gás de exaustão na entrada do regenerador. A razão fica entre 0 e 1: ε = 1 seria um trocador ideal (ar pré-aquecido até a temperatura do gás), impossível na prática. Regeneradores reais atingem 0,7 a 0,9; valores maiores exigem trocadores enormes, com mais perda de carga e custo. A regeneração só compensa quando a razão de pressão do compressor é moderada, caso contrário o ar comprimido já sai quente demais. Informe as temperaturas de entrada, saída e do gás quente.
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Back Work Ratio (BWR)
Calculate the back work ratio (BWR) of a power cycle, BWR = w_compressor ÷ w_turbine, dividing the work consumed by the compressor (or pump) by the gross work produced by the turbine. The dimensionless result shows what fraction of turbine work is reinvested to compress the fluid. In gas turbines (Brayton cycle) the BWR is high (0.4–0.6), since compressing gas is costly; in steam Rankine cycles it is tiny (~0.01), since pumping liquid is cheap. A high BWR makes the cycle sensitive to component efficiencies. Enter the compressor work and the turbine work.
Combined Cycle Efficiency
Calculate the efficiency of a gas-steam combined cycle, η_cc = η_gas + η_steam − (η_gas × η_steam ÷ 100), combining the gas turbine efficiency (Brayton, topping) with the steam cycle (Rankine, bottoming) that recovers heat from the exhaust gases. The result, in %, exceeds either cycle alone because the heat rejected by the gas turbine, instead of being wasted, raises steam for a second turbine. This is why modern combined-cycle plants top 60% efficiency, the highest in thermal generation. Enter the gas-cycle and steam-cycle efficiencies (in %).
Welding Preheat Temperature
Estimate the preheat temperature for welding, Tp = 350·√(CE − 0.25), as a function of the steel's carbon equivalent (CE). Preheating reduces the cooling rate, giving hydrogen time to escape and preventing the formation of brittle martensite and cold cracks in the heat-affected zone. Steels with a high CE require more preheating. Enter the steel's carbon equivalent.
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