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“The inner grooves stir the refrigerant as it passes through the tubes,” said Wenson Zheng, deputy director of technology for ICA. “Such stirring is crucial to efficient heat transfer.” According to Zheng, the effects of inside-tube surface enhancements are well understood from fluid mechanics theory. Nonetheless, hard experimental data on small-diameter copper tubes is essential to the design of advanced coils for air conditioning and refrigeration products with high energy efficiency.
The laboratory experiments were performed at the Institute of Refrigeration and Cryogenics at Shanghai Jiaotong University (SJTU) in Shanghai, China. The research was co-sponsored by the International Copper Association. The tube sizes that were selected and tested were the small diameters of special interest to OEMs. “They are at the sweet spot in coil design,” said Zheng. “Heat-transfer coefficients are high yet pressure drops are still manageable.”
R-410A was the refrigerant tested in the copper tubes of various small diameters, with and without enhanced inner surfaces. Other parameters such as refrigerant flow rate, vapor quality, and oil concentration were carefully controlled. The data on tubes with smooth surfaces provided a baseline for comparison. “With all other factors being equal, very pronounced increases in the local heat transfer coefficient are plainly evident for the tubes with micro-grooving compared to smooth tubes,” said Zheng.
ICA said these data along with proposed models that fit the data can be used to simulate heat exchanger performance and bring new products to market. OEM members of the research consortium have already designed consumer products, such as room air conditioners, using small-diameter copper tubes with microgrooves, and these products are being introduced into global markets.
Experimental results and other technical materials are available online at www.microgroove.net.
For more information about heat exchanger coils made with small-diameter copper tubes, visit www.microgroove.net.
Publication date: 11/08/2010