Advances in Air Conditioning Technologies by Chua Kian Jon & Md Raisul Islam & Ng Kim Choon & Muhammad Wakil Shahzad

Author:Chua Kian Jon & Md Raisul Islam & Ng Kim Choon & Muhammad Wakil Shahzad
Language: eng
Format: epub
ISBN: 9789811584770
Publisher: Springer Singapore

4.5.3 Direct Synthesis

The direct synthesis of zeolites on the finned tube heat exchangers and various metal substrates such as aluminium and copper foams have been extensively investigated. The synthesis process involved hydrothermal zeolitization in a closed system with varying temperature, pressure, and time depending on the types of zeolites. The required synthesis time could be a few hours to several days. The hydrothermal experiments established that the zeolite phase laumontite is formed in the temperature interval between 30 and 450 °C at 1 kbar H2O pressure and an experiment duration of 6 weeks. Bonaccorsi et al. [35] reported that direct synthesis coating of zeolite 4A and zeolite Y on aluminium form good adhesive strength, coating thickness, and other properties. The industrial application of direct synthesis coating is limited as the synthesis yields a coating thickness of about 10–50 μm. Among all types of coating processes, dip-coating and electrostatic spray coating requires impeller operating steps and can be easily implemented in industries for mass production compared with the direct synthesis method. Dip coating has an advantage over the electrostatic spraying coating as the use of sensitive devise and gun for spraying raises the investment, operating and maintenance costs. Moreover, heat exchangers of complex geometries can be coated uniformly using the dip coating. The adhesive strength of dip coating can be enhanced by employing appropriate synthesis methods. A comparison of the three types of coating processes is summarized in Table 4.4.Table 4.4Comparison of dip, electrostatic spray, and direct synthesis coating processes

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