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.