Research On The Impact Of The Fluctuant Fluid On The Heat Transfer Performance In Reverse-cycle Evaporators

Evaporators are widely used in various fields, which must be consumed a large amount of energy each year. In the process of the evaporative crystallization, the heating pipes within evaporator are very easily attached by a large number of crystal grains and fouling. These are the main factors that reduce the heat transfer coefficient of the Evaporators. For the reverse-cycle evaporators, the produce of crystallization and fouling in the heating pipes will affect the running of reverse-cycle steadily and chronically, and the productivity reduced severely. For the purpose of on-line cleaning in reverse-cycle evaporators, now combine the surge at the outlet of the circulation pipe with the reciprocating-spiral. In the reverse-cycle evaporators, as evaporation is mainly occur in the circulation pipe, steam bubbles polymeric constantly when the process of upward flow. Finally at the outlet of the circulation pipe, it become a surge.For the purpose of the optimization about the work-spiral’s wire diameter and pitch, a single-tube bench is established and an experiment is conducted in room-temperature. The result of the experiment is, the optimum parameters of the wire diameter of the work-spiral is1.8mm and the pitch of the work-spiral is 35 mm in the f′′3000238 mm tube.Base on the optimization about the work-spiral, single-tube high-temperature experiment and numerical simulation are conducted to research the origin of the surge in reverse-cycle evaporators. This research can help to use the energy of the surge to uniform cleaning by reciprocating-spiral, and prepare for the pilot scale experiment in the behind. The single-tube high-temperature experiment verify the existence of the surge in the reverse-cycle evaporators,and conduct a preliminary optimization of flexible spring, and the result shows that the preferable elastic coefficient of the flexible spring is 13~16 m N in the f′′3000238 mm tube.Use the water as the experiment medium, reverse-cycle evaporator pilot scale experiment is established to verify the reciprocating distance of the flexible spring and to explore the factors that affect the magnitude of the surge energy. The pilot scale experiment shows that the reciprocating distance of the flexible spring reach 1.2 times the work-spiral’s pitch, this means the requirement of uniform cleaning in reverse-cycle evaporator is satisfied. The main factors that affect the magnitude of the surge energy are the temperature of the heating steam and the insertion of a break bubble trap in the circulation pipe.In order to verify the descale effect and the heat transfer enhancement effect of thecombination between surge and reciprocating-spiral, manganese sulfate crystallization experiments are conducted. The result of the experiment show that the technology of the combination between surge and reciprocating-spiral has a strong cleaning ability, and the heat transfer coefficient of the reverse-cycle evaporators which has reciprocating-spiral is higher than the reverse-cycle evaporators which has no reciprocating-spiral 76% when the heating is stable. The optimization experiment about work-spiral is conducted on the pilot scale experiment bed. The result show that the work-spiral whose outer diameter is f 29 mm is better than those work-spiral whose outer diameter are f 27 mm and f 31 mm in thef′′3000238 mm tube.