In order to control humidity in air conditioning system, various desiccants are used to dehumidify air in air conditioners. One of simple methods, which can be used to coat desiccant materials on surface of heat exchanger in air conditioners, is dip coating. Typical, desiccants used in dehumidifying system is silica gel in a form of solid-state powder. This powder has low adhesion with the heat exchanger surface. To improve adhesion of the silica gel powder, some glue is generally applied on the surface of heat exchanger. The dehumidification properties of silica gel, however, will be remarkably reduced because of less surface area of silica gel powder. Instead of silica powder, this work aims to synthesize silica gel using sol-gel method, which the sol-state material can be suitably used in dip coating. In experimental study, silica gel was synthesized by sol-gel method of precursors with 1 M sulfuric acid (H2SO4). The pH was adjusted using sodium silicate solution (Na2O(SiO2)x.xH2O) and rinsing with DI water. Surface area, pore volume and size, phase composition, morphology, and percentage of moisture adsorption of the synthesized silica gel were characterized. Silica gel fabricated with pH 5 showed the highest percentage of moisture adsorption compared with other samples. In addition to the highest percentage, silica gel with pH 5 could adsorb water up to 28 times of its own weight. X-ray diffraction (XRD) results showed that Na2SO4 impurity were successfully eliminated after rinsing with DI water more than 4 times. Finally, adhesive property of silica gel on aluminium-fin samples was tested with scalloped tape-test method. It was observed that, to improve the adhesion property of silica gel on the aluminium fins, prior to dipping of silica gel, the fins should be etched with sulfuric acid. The acid can adjust the surface of fines to be much rougher.
