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Rate of Zinc Consumption during Sacrificial Cathodic Protection of a Double Tube Copper Heat Exchanger Handling Saline Water

Darwish MF, El-Gayar DA and Farag HA

The inner copper tube of a double tube heat exchanger was fitted with zinc rings transverse to the flow of saline water to protect the inner tube against corrosion by sacrificial cathodic protection. Rate of Zn consumption during cathodic protection of copper in NaCl solution was determined under different operating conditions. The rate of dissolution of Zn rings surrounding the inner copper tube was found to increase with increasing solution flow rate, temperature and NaCl concentration. Activation energy Ea was found to be 3.864 kCal/mol, this value shows that Zn consumption takes place through a diffusion controlled mechanism. The rate of zinc consumption was found to decrease with increasing ring thickness. The rate passes through a maximum with increasing ring spacing.

The importance of the present study in assessing the cost of sacrificial cathodic protection in comparison with the competing impressed current cathodic protection was highlighted. Also, the possible rate of zinc rings as turbulence parameters to enhance the rate of heat transfer and increase the efficiency of the heat exchanger was pointed out.