 possibl ga mixtur aerodynam possibl ga mixtur aerodynam studi advantag realiz compress-flow emploi substitut heavi ga place air heavi gase consid previou investig toxic chemic activ case freon ratio specif heat greatli air report base idea properli mix heavi monatom ga suitabl heavi polyatom ga heavi ga mixtur correct ratio specif heat nontox nonflamm thermal stabl chemic inert compris commerci compon calcul wind-tunnel characterist 63 ga pair compris 21 polyatom gase properli mix three monatom gase argon krypton xenon mach number reynold number tunnel pressur ga-mixtur wind tunnel specif-heat ratio air appreci smaller requir power correspond air wind tunnel analog advantag realiz compressor fire-rang applic select proport ga mixtur ordinari wind-tunnel temperatur dimensionless characterist air flight temperatur possess air ordinari wind-tunnel temperatur possess characterist involv relax time bulk viscos variat viscos temperatur variat specif heat temperatur fall categori applic heat-transfer ga mixtur concoct prandtl number rang 0 2 0 8 