Quick identification of gases for enhancing heat transfer in turbulent pipe flows using standard correlation equations for the convective coefficient and the friction factor

This paper addresses a simple algebraic procedure for the quick identification of gases (different than air) that are capable of enhancing heat transfer in turbulent pipe flows while causing small-to-moderate accretions in pressure drops. Relying on standard correlation equations for the convective coefficient and the friction factor, the algebraic procedure is centered on the existing competition between the four intervening thermophysical properties: density ρ, viscosity η, specific heat capacity at constant pressure cp and thermal conductivity λ. To judge the ability of a candidate gas, a figure-of-merit articulating the convective coefficient h and the pressure drop Δp is chosen. Fixing the length-to-diameter ratio L/D of the pipe along with the average fluid velocity uave, it turns out that the hΔp ratio is directly proportional to λcp and inversely proportional to η approximately. In this way, the units of the hΔp ratio are closely equivalent to the units of the specific heat capacity cp. A case study involves twenty five gases (pressure of 1 atm and temperature of 300 K) commonly used in turbulent forced convection pipe flows for industrial applications. It is demonstrated that the three better gases are helium, hydrogen and methane. Qualitatively, helium is superior to air by a factor of 5.22, hydrogen is superior to air by a factor of 3.58 and methane is superior by a factor of 2.24.