Ejector loop reactors are appealing devices for two fluids mixing. The high interfacial area produced in such reactors gives them an advantage over the conventional contactors. Suction chamber where the two streams of the primary and secondary fluid meet is an important part of the overall ejector geometry. The present work deals with optimization of the geometry of the suction chamber using computational fluid dynamics (CFD). The effect of (i) projection ratio (L-TN/D-T), i.e., ratio of the distance between the nozzle tip and throat (LTN) to the throat diameter (DT), (ii) the diameter of the suction chamber (D-S) and (iii) the angle of the converging section (theta) on the entrainment rate of the secondary fluid have been studied. It was observed that for low values of projection ratio the entrainment rate was low. It increased with an increase in the projection ratio; however, became constant beyond a particular value of this ratio. The effect of D-S n the rate of entrainment was observed to be more complex. The entrainment rate showed a maximum value when D-S was varied over a wide range. The results obtained for different values of 0 suggest that the optimum lies in the range of 5 degrees-15 degrees. The results have been explained on the basis of flow patterns produced. (c) 2008 Elsevier Ltd. All rights reserved.