Airside pressure drop characteristics of three analogous serpentine tube heat exchangers considering heat transfer for aero-engine cooling

This study explores the design,analysis,and air pressure drop assessment of three analogous air–fuel heat exchangers consisting of thin serpentine tube bundles intended for use in high Mach number aero-engines.In high speed flight,the compressor bleed air used to cool high temperature turbine blades and other hot components is too hot.Hence,aviation kerosene is applied to precool the compressor bleed air by means of novel air–fuel heat exchangers.Three light and compact heat exchangers including dozens of in-line thin serpentine tube bundles were designed and manufactured,with little difference existing in aspects of tube pitches and outer diameters among three heat exchangers.The fuel flows inside a series of parallel stainless serpentine tubes(outer diameter:2.2,1.8,1.4 mm with 0.2 mm thickness),while the air externally flows normal to tube bundles and countercurrent with fuel.Experimental studies were carried out to investigate the airside pressure drop characteristics on isothermal states with the variation of air mass flow rates and inlet temperatures.Non-isothermal measurements have also been performed to research the effect of heat transfer on pressure drops.The experimental results show that inlet temperatures have significant influence on pressure drops,and higher temperatures lead to higher pressure drops at the same mass flow rate.The hydraulic resistance coefficient decreases quickly with Reynolds number,and the descent rate slows down when Re>6000 for all three heat exchangers.Additionally,the pressure drop on heat transfer states is less than that on isothermal states for the same average temperatures.Moreover,the pressure drop through heat exchangers is greatly affected by attack angles and transverse pitches,and an asymmetric M-shaped velocity profile is generated in the crosssection of sector channels.

Local resistance characteristics of elbows for supercritical pressure RP-3 flowing in serpentine micro-tubes

Based on the demands of compact heat exchangers and micro cooling channels applied for aviation thermal protection on aero-engines,the elbow localflow resistance charac-teristics for supercritical pressure aviation fuel RP-3flowing in adiabatic horizontal serpentine tubes with the inner diameter of 1.8 mm and the massflux of 1179 kg/(m^(2)·s)were experimen-tally studied.The long-short-tube method was used to obtain the elbow pressure drop from the total serpentine tube pressure drop,and the effects of system pressures(P/Pc=1.72-2.58)and geometry parameters including bend numbers(n=5-11),bend diameters(D/d=16.7-27.8),and bend distances(L/d=20-60)on elbow pressure drops and local resistance co-efficients are analyzed on the basis of the thermal physical property variation.The results show that both the increase in the elbow pressure drop and the decrease in the local resistance coef-ficient with temperatures speed up at the near pseudo-critical temperature region of T>0.85Tpc.And the growth of the elbow local pressure drop could be inhibited by the increase of system pressures,while the local resistance coefficient is slightly affected by pressures.The influence of bend diameters on the local resistance coefficient is mild when D/d is larger than 22.2 in the premise of fully developedflow in straight tubes.Furthermore,a piecewise empir-ical correlation considering the bend diameter and physical property ratio is developed to pre-dict the elbow pressure drop of the serpentine tube and optimize the layout of the cooling tube system on aero-engines.