Study On The Performance Of Graphite Heat Exchanger For Salinity Wastewater Treatment

Evaporation is an important method in salinity wastewater treatment. But the steel heat exchanger is ususlly badly corroded by the salinity wastewater. Graphite heat exchanger is an good substitute of steel heat exchanger for corrosion protection. The thermal performance of graphite heat exchanger is the sticking point to decide the feasibility to use graphite heat exchanger in salinity wastewater treatment. In this paper, the thermal performance of graphite block heat exchanger is studied by the method of numerical model and experiment. The objective of this paper is obtaining the heat transfer coefficient and heat transfer rate under different operation conditions.The main contents of the dissertation are as follows:1. Using the software FLUENT, a numerical model has been used to determine the wall resistance of graphite block heat exchangers with different sizes of holes. The results show that, the bigger the holes, the smaller the wall resistance.2. Using the sofeware FLUENT, a three-dimensiond numerical model has been used to determine the heat transfer coefficient under different operation conditions. The results show that heat transfer coefficient increases that with the increasing of flow rate and inlet temperature. The decrease of concentration is favorable for overall heat transfer coefficient.3. Using the software MATLAB, a number relational expression has been got under different Re and Pr conditions. The results show that, when Re is between 5594 and 17340, Pr is between 2.5 and 5.4, Nu is in direct ratio with Re08 and Pr0.2 when Re is between 11188 and 32513, Pr is between 2.5 and 5.4, Nu is in direct ratio with Re0.7 and Pr0.15, when Re is between 1600 and 3623, Pr is between 26.5 and 36.4, Nu is in direct ratio with Re0.7 and Pr0.15, when Re is between 2058 and 5981, Pr is between 26.5 and 36.4, Nu is in direct ratio with Re0.63 and Pr0.13.4. A test rig has been assembled to investigate the themodynamic performance of a rectangular graphite block heat exchanger. The results show that, the overall heat transfer coefficient is mainly influenced by flow rate, and the increase of flow rate is favorable for overall heat transfer coefficient. 5. The number relational expression for steam condensation in horizontal tube has been modified according to the experimental results to get a number relational expression fit to graphite block heat exchanger:6. Using the overall heat transfer coefficient and the heat transer coefficient in the side of steam condensation. The heat transfer coefficient in the side of salinity wastewater under different operating conditions has been determined. The experimental and simulation results has been compared, the discrepancy is under 16%, it indicates that the numerical model predict the thermal performance of the graphite block heat exchanger accuratelly, and provide the method and theoretical basis for industrail applications.