Experimental Comparison of Water Fouling Characteristics on Copper Tubes and Stainless Steel Tubes Applied in Central Air-Conditioning

The application of stainless steel tubes instead of copper tubes in shell-and-tube heat exchangers for central airconditioning can significantly reduce the price of heat exchangers, but it may bring in the risk of water fouling increase during long-term operation, and thus a comparative investigation on the water fouling characteristics of copper tubes and stainless steel tubes is needed. In this study, an accelerated fouling experimental method is presented to speed up the fouling process on tubes, and the fouling masses, the fouling layer thicknesses as well as the fouling crystal patterns are comparatively analyzed to evaluate the fouling risk of these tubes. In the experiments, the test tube materials include copper and two types of stainless steels (i.e., SUS 304 and SUS 304Cu), water temperatures include 10 degrees C and 60 degrees C to respectively represent refrigeration and heating modes in central air-conditioning, and water flow velocities include 0.5 m/s and 1.6 m/s to respectively represent low and high load modes. The experimental results show that the fouling masses of stainless steel tubes are 23.8%-68.3% lower than those of copper tubes, the fouling layer thicknesses of stainless steel tubes are 23.2%-28.8% lower than those of copper tubes, and the fouling crystal patterns of stainless steel tubes are more unstable than those of copper tubes, which means that stainless steel tubes are less prone to fouling than copper tubes.