Cost-efficient desalination technology was developed successfully by integrating a countercurrent cascade of the novel cross-flow direct contact membrane distillation (DCMD) devices and solid polymeric hollow fiber-based heat exchange devices. Simulations have been carried out for the whole DCMD cascade to project values of gained output ratio (GOR) as a function of the number of DCMD stages as well as other important factors in the cascade vis-a-vis the temperatures and flow rates of the incoming hot brine and cold distillate streams. The simulation results were verified with experimental results from cascades consisting of two to eight stages. The numerical simulator predicts a GOR of 12 when unequal flow rates of the incoming brine and distillate streams are used. An artificial sea water was concentrated eight times successfully when a countercurrent cascade composed of four stages of the DCMD modules and a heat exchanger was used during the DCMD process. (C) 2010 American Institute of Chemical Engineers AIChE J, 57: 1780-1795, 2011