Air (k equals 0.032 space W divided by m K comma space P r equals 0.7 ) at 320 oC flows across 4.5-cm-diameter tubes whose surface temperature is 55 oC with a Reynolds number of 8000. The Churchill and Bernstein convective heat transfer correlation for the average Nusselt number in this situation is N u equals fraction numerator 0.62 R e to the power of 0.5 end exponent P r to the power of 0.33 end exponent over denominator open square brackets 1 plus open parentheses 0.4 divided by P r close parentheses to the power of 0.67 end exponent close square brackets to the power of 0.25 end exponent end fraction The average heat flux in kW/m^2 in this case is