Pressure-retarded osmosis (PRO) uses a semipermeable membrane to produce renewable energy from salinity-gradient energy. A spiral-wound (SW) design is one module configuration of the PRO membrane. The SW PRO membrane module has two different flow paths, axial and spiral, and two different spacers, net and tricot, for draw- and feed-solution streams, respectively. This study used an experimental approach to investigate the relationship between two interacting flow streams in a prototype SW PRO membrane module, and the adverse impact of a tricot fabric spacer (as a feed spacer) on the PRO performance, including water flux and power density. The presence of the tricot spacer inside the membrane envelope caused a pressure drop due to flow resistance and reduced osmotic water permeation due to the shadow effect. The dilution of the draw solution by water permeation resulted in the reduction of the osmotic pressure difference along a pressure vessel. For a 0.6 M NaCl solution and tap water, the water flux and corresponding maximum power density were 3.7 L m(-2)h(-1) and 1.0 W/m(2) respectively at a hydraulic pressure difference of 9.8 bar. The thickness and porosity of the tricot spacer should be optimized to achieve high SW PRO module performance.

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Simulation of the heat pump cycle and the drying process has been carried out to obtain the design parameters of the dryer. The analysis indicates that a specific moisture extraction rate (SMER) greater than 3.4 kg/kWh can be obtained. A box-type heat pump dryer has been developed and investigated for the performance of drying of shredded radish. Heat pump drying took 1.0-1.5 times longer than hot air drying. However, the heat pump dryer showed considerable improvement in energy savings. The SMER of the heat pump dryer was about three times higher than that of the hot air dryer.