Numerical Investigation Of Flow And Heat Transfer In Primary Surface Recuperators For Micro Gas Turbines

An exhaust heat recovery recuperator is the key point to achieve thermal efficiency of 30% or higher for a micro gas turbine. A recuperator is using extra energy from the exhaust gas to heat the inlet compressed air. The efficiency of a simple cycle micro turbine is only 17%~20%, while a recuperated cycle micro turbine can reach a 30% or higher efficiency. The characteristics of a micro turbine request a heat exchanger with good reliability, high performance potential, compact size, lightweight, structural integrity and adaptability to automated production. A primary surface recuperator (PSR) of cross-corrugated surface has more acceptable property to meet the demanding requirements for micro turbines.3-D numerical simulation models have been set up for different corrugation angle PSR units. Data of simulation show that average Nusselt number increases with Reynolds number increasing;in the range of 0° ≤θ≤75°, Nusselt number increases with corrugation angle increasing, during 75° <θ≤90° , decreases with corrugation angle increasing;when P/H <2, Nusselt number increases with pitch-to-high ratio increasing, when P/H>2, decreases with pitch-to-high ratio increasing;Friction coefficient decreases with Reynolds number and pitch-to-high ratio increasing, increases with corrugation angle increasing. The best surface for heat transfer is P/H = 2.2, θ = 60° surface.Considering of temperature variation, 3-D simulations for entire channel of PSR have also been studied. The results of numerical predictions were obtained and compared with those data by empirical calculations. Among some special Reynolds number range, the heat transfer and pressure drop from simulation and those data by empirical calculations are almost the same. The heat transfer is slightly enhanced as increasing Reynolds number, while the pressure drop is obviously enlarged when increasing the Reynolds number. Moreover, the efficiency of a recuperator is improved with flux decreasing.A special surface of PSR for a micro gas turbine has been studied. The heat transfer and pressure drop of θ = 60° PSR can be calculated by modifying those data reached from θ = 0° PSR simulation.