Performance study of enhanced and smooth surface tubes in a system condenser of a multistage flash desalination unit

Fouling of the multistage flash (MSF) system condenser tubes used for water desalination reduces the system overall heat transfer coefficient very rapidly. Consequently, hearts the system efficiency and increases the cost of distillate water. In this study, a comparison between enhanced and plain tube performance characteristics is investigated experimentally in the MSF system. The study is performed for aluminium-brass tubes with inside diameters of 19.05, 23, and 29.5 mm. A three different flow velocity of 0.1, 0.1645, and 0.2398 m/s are examined with these three tubes. The study is carried over for two different coolants fresh and brine water. In this paper, the results for fresh water are presented. The results indicated that the overall heat transfer coefficient (U) varies with both coolant flow velocity and tube diameter. For both smooth and enhanced tubes, the higher the coolant speed or/and pipe diameter the larger the overall heat transfer coefficient. However, the effect of these two parameters is more significant with enhanced tubes. A gain in overall heat transfer coefficient by factor of 2.13 over smooth tubes can be achieved. Results also, showed that for certain tube diameter there is an optimum flow speed for maximum value of U. For a certain flow speed there is an optimum pipe diameter size. The results proved that the heat transfer coefficients of corrugated tubes are superior to plain tubes for most flow speeds and diameters investigated in the present study.

A test rig simulates the condenser of the multistage flash system (MSF) used for water distillation in real life is designed. A heat performance study for smooth and enhanced aluminium-brass tubes is investigated. To gain familiarity with enhanced tubes, fresh water is used as coolant medium. Three different tubes inside diameters of 19.05, 23, and 29.5 mm are considered. For each tube size a three coolant flow speeds of 0.1, 0.1645, and 0.2398 m/s are examined. In this study, the two tubes (enhanced and smooth) are tested simultaneously. The control valves on each tube is adjusted sequentially to fix the same flow speed in both tubes. The current study indicates that both tube size and coolant flow speed parameters influence the overall heat transfer coefficient for smooth and enhanced tubes. The higher flow speed or/and pipe diameters the larger the overall heat transfer coefficient. However, the effect of these two parameters is more significant in enhanced tubes than smooth tubes. For most test cases studied and parameters used the enhanced tubes results are superior to smooth tubes. A gain in overall heat transfer coefficient by factor of 2.13 over smooth tubes can be achieved. The experience gained in this study provides a base for the tests performed for MSF system condenser using real brine water as coolant medium, which simulates actual environment in real life.