Consider the common situation in which a researcher is trying to match the reynolds number of a large prototype vehicle with that of a small-scale model in a wind tunnel. compare the wind tunnel air at 10°c and at 45°c, all else being equal. for air at atmospheric pressure and at t = 10oc, rho = 1.246 kg/m3 and μ = 1.778×10-5 kg/m·s. at t = 45oc, rho = 1.109 kg/m3 and μ = 1.941×10-5 kg/m·s.