Numerical analysis of photocatalytic CO2 reduction in optical fiber monolith reactor with optimized structures

• Two optimized structures of OFMR were proposed by adding reaction surfaces.
• Light power and production rate per input power were introduced.
• CH3OH concentration is linear with light power by the integration of light intensity.
• Outlet CH3OH concentration increases by 69.7% and 108.2% in two optimized structures.
• It is of benefit to the design of OFMR to achieve the optimized structure of reactor.

It is a promising way to mitigate CO2 and produce fuels by solar energy in the optical fiber monolith reactor (OFMR). Two optimized structures of OFMR were proposed by adding reaction surfaces in this paper. Light power reaching reaction surfaces and production rate per input power were introduced to better analyze the advantages of the present structures. The linear relation between the light power obtained by the integration of light intensity and CH3OH concentration was discovered, in the condition of the same velocity and fiber number. The inverse proportional relation between the CH3OH concentration and flow velocity was presented. Outlet CH3OH concentration reaches 3.004 × 10−5 mol m−3 and 3.685 × 10−5 mol m−3 in the two structures, increasing by 69.7% and 108.2% respectively, comparing with previous experimental results 1.770 × 10−5 mol m−3. The maximum transmission efficiency of the light power arrives at 2.297% for one optimized model, and the highest production rate reaches 3.018 × 10−12 mol s−1 W−1 in another optimized model. The optimal structure parameters are that the radius of the middle tube is 1.2 mm and reactor length is 50 mm by analyzing the concentration filed, average outlet concentration and light intensity for various radii and lengths. It is of benefit to the design of OFMR to achieve the optimized structure of reactor.