Due to large number of design parameters, numerical analysis is inevitable for heat exchanger design with wire-screen structures. This paper establishes a direct simulation method to study the laminar flow and heat transfer at the pore level. The experiment validation proves this analysis is reliable. For both the pressure drop and heat transfer characteristics, various configurations of wire-screen meshes are investigated, where water has been used as coolant. Material properties difference such as conductivity and heat capacity ratios of the two phases are evaluated. Structure porosity is also quantified and it is found that there exists an optimised porosity for the thermal performance. The properties of water at 20 degrees C are used for the fluid phase. (c) 2006 Elsevier Ltd. All rights reserved.