The Study On Numerical Simulation Of Heat Transfer And Flow Characteristics In The Waste Heat Boiler

Under the background of the energy reserves' shortages and serious environmental pollution, as an important equipment for recovering heat, the waste heat boilers become more and more popular in the industry of chemical, thermal and the system which waste heat is generated. Compared with the radiant heat boilers, the advantages of the fire tube waste heat boiler are simple structure, easier to clean, higher reliability, longer life, etc. There is an important significance about designing and optimizing its structure.Since it is difficult to test the complex flow field inside the waste heat boiler evaporator in the site, adopted the CFD numerical simulation methods, the paper simulates and analysis the internal flow field, which are some references for the design and optimization of the structure.Based on the data of the waste heat boiler provided by Tianhua institution, with the help of ICEM software, the geometry model and structured grids of the whole area inside and outside of the waste heat boiler evaporator are built using a 1:1 scale. The paper simulates the boiling heat transfer conditions outside the shell-tube and the smoke flow conditions inside the pipe by using Fluent software.For boiling phase variable condition in the shell-side, standard k-? turbulence model and Mixture model as the calculation model was adopted as the calculation model. The UDF is used to compute the source of mass and energy boiling phase change transfer phase. It established velocity inlet boundary, pressure outlet boundary and no-slipped solid wall boundary. The unsteady numerical simulation is used. Through the distribution of the vapor, temperature and pressure, the conclusions are that liquid water in the shell side of the tube would boil because it absorbs the heat from the smoke tube when the temperature is higher, and the water liquid will change into the water vapor, and the water vapor will flow slowly into the outlet boundary. Closer to the center of the smoke pipe, the water liquid will boil more easily. The volume fraction of the water vapor is significantly higher than that is close to the outer wall. The volume fraction of water vapor will be stable when the heat exchange is equal. And the number is about 0.3.The temperature of the mixed phase gradually decreases along the axis of the smoke tube to the outer wall, the number reduced from 573 K to 363 K. The pressure gradually decreases along positive direction of the Y-axis, the maximum pressure is 2.64×106Pa which is on the bottom section. Since the outlet is atmospheric boundary and the number level of operating pressure inside the boiler is up to 106 Pa large pressure, it results in uneven distribution of pressure. The results show that the outlet diameter has a significant impact on the volume rate of the water vapor, both the liquid water temperature on the inlet boundary and the diameter of the smoke pipe will affect the size of the heat transfer coefficient, thus affecting the amount of water to produce steam. From security and economic aspects, when the diameter of the steam outlet is 48 mm and the diameter of the steam outlet is 60 mm, the best inlet temperature of liquid water is settled as 373 K.For the flue gas flow tube, the standard k-? turbulence model and DOM radiation model are adopted as the calculation model. No-slipped solid wall boundary and standard wall function is set up on the wall. The temperature distribution is simulated by unsteady numerical simulation method. The paper simulates the variation of the temperature field, the results show that the convection heat transfer act as a dominant position of the total heat transfer, the max ratio of radiation heat transfer isn't more than 30%, the temperature drop more quickly when the diameter of smoke pipe is lager and the velocity of the smoke gas is greater. But the lager velocity of smoke gas will shorten the life of the waste heat boiler, so when setting up flue gas velocity, it is necessary to the critical value of flue gas velocity. From the simulation results, the election of gas flow rate is 10 m/s.