Transient one-dimensional conservation equations have been developed to analyze the heat and mass transfer within direct-contact evaporators and condensers. The conservation equations are solved numerically to predict water, air/vapor mixture and packed bed temperatures and humidity ratio within the evaporator and the condenser. The heat and mass transport models account for the transient variations within the packed-bed due to time varying inlet air and water temperatures and humidity. Direct contact evaporator and condenser experimental facilities have been configured. The measured water and air/vapor mixture temperature differences agree well with those predicted using the transient model. The measured humidity difference is slightly greater than that predicted, and the maximum deviation is on the order of 20%. (C) 2011 Elsevier Ltd. All rights reserved.