The paper presents the results of experimental work aimed at studying the effect of porous layer parameters on the thermal performance of water evaporators. The results show that there are optimum particle sizes that are associated with maximum boiling heat rates and heat transfer coefficients. The results also show that the layer thickness has monotonic effect on the evaporators' performance but its impact is less pronounced compared to that of the particle size. The trends are explained in terms of the contradicting effects that exist within the layer. The research also showed that the effect of the heat load, represented by temperature and velocity of the load air, was negligible. Boiling heat transfer coefficients of up to 5 kW/m(2) degrees C were achieved. (c) 2007 Elsevier B.V. All rights reserved.