Trickle beds (TBRs) can be problematic because of the presence to two fluid phases. The liquid phase trickles down through a bed of catalyst particles helped along by a co-current gas phase. Typically, a trickle bed is made up of porous catalyst particles in an unordered, random packing. Open channels through which the fluid can flow are irregular in shape and cross section, tortuous and of wide variability in length. Channels can separate and also intersect. Wetting of the particles and entrapment of the liquid phase between particles affects channel shape. Environments within these fluid filled spaces can be quite dissimilar when one or more reaction occurs because of diffusion into surface wetted particles, liquid filled particles or particles devoid of liquid. Both gas and liquid compositions as well as temperature can differ significantly among nearby channels. As a result of this situation, rates of a catalytic reaction may be enhanced in some regions of the packing and reduced in others. Some regions of the bed may have temperatures well above the average. These may be designated ashot spots. Other regions may suffer from so little liquid they may be viewed as dry zones. In addition, flow distribution becomes poorer over the bed cross section with time as preferred flow channels develop due to temperature changes at different points within the bed. These changes can cause bed hot spots or dry regions to fade and reappear, and even wander with time.