| Ground source heat pump has a wide application in our country because of its low cost, high efficiency, environmentally friendly, etc., which is mainly divided into soil source heat pump and the underground water source heat pump. The soil source heat pump using closed buried tube, extracts heat from soil through the heat exchanger, while the underground water source heat pump extracts heat from groundwater directly, through the heat exchanger. The high salinity of underground salt water in coastal areas could destruct the heat exchanger seriously, resulting in perforation failure of heat exchange plate. Therefore, metal corrosion and protection in ground source heat pump system is becoming research hotspot in recent years. HA177-2 brass and TA1 titanium are corrosion resistant alloys metal commonly used in ground source heat pump. Different concentrations of NaCl, Na2SO4, NaHC03 were added into distilled water to simulate the underground saltwater in coastal areas. Weight-loss measurements, electrochemical tests and chemical analysis were applied to analyze the effects of different anions on the two alloys. And use the methods of adding inhibitors and self-assembled monolayers to improve the corrosion resistance of the two alloys. So we can provide theoretical reference for corrosion protection of metal material in heat pump system. The main conclusion are as follows:(1) The corrosion laws of the main anions of the underground salt water on metalsAccording to the characteristics of the coastal underground salt water of high salinity, taking Cl- as the center, in combination with SO42-,HCO3- to test the interactive effects of different anions in groundwater on the two alloys. The results showed that the corrosion current density, the weight loss and dezincification increased with the increasing of Cl- concentration, and corrosion resistance declined. Low concentration of SO42- with less than 1 g/L inhibited the damage of Cl-, improving the corrosion resistance of HA177-2 brass, but high concentration of SO42- had a damaging effect on it; the rule of TA1 titanium was on the contrary. When the concentration of HCO3- was less than 0.5 g/L, the increase of HCO3- concentration promoted the damage of Cl- on HA177-2 brass. The corrosion resistance of TA1 titanium is so good that there was no inflection point within the scope of the studied concentration of HCO3-. The coexistence of these three kinds of anion accelerated the corrosion of TA1 titanium, while inhibited that of HA177-2 brass. In addition, the current density of HA177-2 brass and the TA1 titanium both increased with the increase of temperature, explaining that the rise of temperature reduced the corrosion reaction activation energy and decreased the corrosion resistance of the metal.(2) The corrosion inhibition of BTA on the metalsFor closed soil source heat pump system, adding BTA to reach the purpose of anticorrosion. The inhibition of benzotriazole (BTA) and compound corrosion inhibitor on corrosion behaviors of HA177-2 brass were studied by weight-loss measurements, electrochemical tests and chemical analysis. With the increasing concentration of BTA, the current density of HA177-2 brass decreased rapidly, and the weight loss and dezincification reduced effectively. When the concentration of BTA was 200mg/L, the inhibition efficiency reached maximum, which decreased with the increase of temperature. After adding ethylene glycol antifreeze, the synergistic effect of BTA inhibitors and ethylene glycol enhances the inhibition efficiency further. The results showed that the inhibition effect of the common air condittoning corrosion inhibitors on HA177-2 brass than that of BTA, indicating the common air conditioning corrosion inhibitors also applied to complex groundwater environment.(3) The corrosion inhibition of phytic acid self-assembled monolayersFor the open underground water source heat pump system, using self-assembled membrane technology to achieve the purpose of the anticorrosion. The inhibition efficiency of the self-assembled monolayers varying with phytic acid concentration and self-assembly time was systematically studied in this paper. The results showed that, the inhibition efficiency of self-assembled monolayer of the two alloys increased firstly and then decreased with the concentration of phytic acid and self-assembled time increased. The inhibition efficiency of HA177-2 brass was improved further after adding sodium molybdate, and the optimum concentration of sodium molybdate was 250 mg/L. The combination of phytic acid and sodium molybdate has no inhibition on TA1 titanium. |
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