24.13 A microchannel reactor is being developed for the reforming of methane gas (CH4) to CO2 and H2 gas using steam (H2O vapor) at high temperature. Prior to entering the reforming reactor, CH4 (species A ) and H2O vapor (species B ) at a nonreactive temperature of 400C are mixed within a microchannel gas preheater zone with an inner diameter of only 50m(0.0050cm). The Peclet number, defined as Pe=DAend must be at least 2.0 before this gas stream is fed into the reforming reactor. It is also desired to keep the gas velocity (v) constant at 4.0cm/s. For purposes of calculation, it may be assumed that CH4 is diluted in H2O gas. a. What is the Knudsen diffusion coefficient for CH4 inside the microchannel? Is Knudsen diffusion important? b. At what total system pressure (P) should the process be operated at to meet the aforementioned design constraints of Pe=2.0 and n=4.0cm/s ? At this total system pressure. what is the gas-phase molecular diffusion coefficient of CH4 in H2O ? 24.14 The Stokes-Einstein equation is often used to estimate