Figure 2. Methanol molar fraction contour plots in the combined parallel plate heat exchanger-reactor for hydrogen production by steam-methanol reforming.
The effect of wall thermal conductivity on the average Nusselt number are illustrated in Figure 3 in the exothermic process of the combined parallel plate heat exchanger-reactor. The channeled, manifolded honeycomb, also referred to as the combined heat exchanger-reactor, may be used without any catalytic material, coated on the walls, purely as a heat exchanger or homogeneous reactor-heat exchanger. By proper choice of materials of construction, the heat exchanger can be designed to transmit both sensible heat by conduction and radiation heat. In this way, many and different reactions can be performed using the manifolded honeycomb system. The arrangement can either be used as a heat exchanger, where energy is transferred from one stream to another via conduction through the wall or it is suitable as a chemical reactor where the second set of channels allow the introduction of a heat transfer fluid. The energy required or generated through the reaction is removed via a heat transfer fluid in the second channel. The reaction can be a catalytic process and the catalytically active material can be coated onto the monolith passage walls to minimize pressure drop. In this arrangement, the heat transfer from the process catalyst to the dividing wall will be highly efficient, however, the uptake of the energy by the heat transfer fluid will suffer from all of the limitations of traditional heat transfer operations. In this case, the boundary layer will provide a significant resistance to heat transfer and will severely limit the rate of the process. Also, for this arrangement to successfully supply or remove heat and maintain a near isothermal longitudinal profile, considerable heat transfer fluid velocities must be utilized for the combined parallel plate heat exchanger-reactor. The high velocities will reduce the characteristic thickness of the boundary layer and ensure that a sufficient mass of heat transfer fluid is available to absorb the heat of reaction without significantly changing temperature. These requirements will lead to excessive pressure drop through the coolant channels. Therefore, a reactor design which minimizes the heat transfer fluid side pressure drop is required.