Tham khảo tài liệu 'advanced gas turbine cycles episode 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 58 Advanced gas turbine cycles . Cycle with two step cooling CHT iC2 For two step cooling now with iưeversible compression and expansion Fig. shows that the turbine entry temperature is reduced from T2 to J s by mixing with the cooling air ệịị taken from the compressor exit at state 2 pressure p2 temperature T2 Fig. . After expansion to temperature Tg the turbine gas flow 1 ự H is mixed with compressor air at state 7 mass flow abstracted at the same pressure p7 with temperature T- . to give a cooled gas flow 1 ự H ipC at temperature Tn. This gas is then expanded to temperature ll . It may be shown 5 that T IC2 t iu - - 1 V - - x where L 1 t7tT7C xl - T7 f jV . It has been assumed here that X XH so that the efficiencies 7 c and TjT are the same over the isentropic temperature ratios X and XL. For the a s example quoted earlier with this form of two stage cooling with X xh ựrH t L the thermal efficiency is reduced from uncooled to . by still not a significant reduction. If the second step of cooling uses compressor delivery air rather than air taken at the appropriate pressure along the compressor then the analysis proceeds as before except that the expansion work for the processes 7 11 in Fig. is replaced by that coưesponding to 7 11 in Fig. . It may be shown 5 that the efficiency may then be written as 1 IC2 T 1U - pe x - 1 - ự - L - ViAUh - l 3 - x . The second term in the curly brackets is very small indeed and may be ignored the last term in these brackets effectively represents the throttling loss in this iưeversible cycle. For the numerical example the cooled efficiency becomes a reduction of from tj ru . The extra loss in efficiency for throttling the cooling air from compressor discharge to the appropriate pressure at the LP turbine entry is thus for the numerical example which is again quite small. Fig. . Temperature-entropy diagram for two .
