Comparative Study of Convective and Radiative Heat Transfer in Milliflow Reactors

Abstract

Nowadays, infrared emitters are mostly used in the food industry as drying method. However, there is also great potential for such heaters in flow chemistry. Flow reactors do not only require thermal efficiency but also accurate modulation of heat transfer. This can be achieved by the use of infrared emitters. In this research, the electrical efficiency of three different types of infrared emitters: short, medium and long wave, is determined. Next, these efficiencies are benchmarked against a convection oven which uses forced convection of hot air. In addition, the influence of surface absorptivity of the stainless steel is tested with and without a black coating. It was hypothesized that the black coating would enhance energy absorption. Similar trends in heat transfer were observed between the three different types of infrared emitters. When both convection and infrared heating used the same amount of electrical power and were both applied in the same convective setup, the net absorbed thermal power was 10 percentage points higher in the infrared setups than by convective heating. This indicates that the efficiency of transferring thermal energy to the liquid in a tubular reactor is higher for infrared heaters than for the convection oven. In addition, a black coating of the flow reactor improved the absorbed power with 6 percentage points. In conclusion, the infrared emitters are excellent for heating flow reactors with high absorptivity, and are more efficient than convection ovens.