1) Air flows through in the pipe of tubular exchanger at 60 m3/h. The dimension of pipe is 573.5 mm and its length is 3 m long. If the viscosity of air is 0.019 mPas, thermal conductivity is 0.028 W/mK, specific heat is 1 kJ/kgK and the density is 2.188 kg/m3 . The Re=( ).