Numerical Simulation On Flow And Heat Transfer Characteristics In Coil Type Organic Heat Transfer Material Heaters

Coil type organic heat material heaters are widely used in industry because of its working characteristics of the high temperature and low pressure, but furnace tube overheating explosion often occur because heat transfer fluids are easily degraded in high temperature operation.In order to effectively prevent the happening of the accident on organic heat material heaters, it is necessary to study the flow and heat transfer characteristics in coil type organic heat transfer material heaters.The flow and heat transfer characteristics in pre 10 ring tubes located in the inner layer coil tube of coil type organic heat transfer material heaters were simulated by ANSYS CFX under condition of the change of hot oils physical properties and the input of tube wall heat. At the same time, the influence factors(spiral diameter D, wall roughness K,hot oils inlet velocity u, coil arrangement and furnace tube diameter d)were analyzed. Numerical simulation results show that the speed and intensity on the external surface of spiral furnace tube are also more than the inner surface,which is caused by centrifugal force and secondary flow; The secondary flow and pipe roughness effectively strengthen the heat exchange of organic heat transfer material; When the flow velocity is more than 3.5m/s, Screw diameter has more influence on flow and heat transfer characteristics for heat transfer fluids then flow velocity, While the flow velocity is less then 3.0m/s,the influence to the both is contrary;Heat transfer effectiveness for heat transfer fluids flowing in vertical typeSpiral Coil is stronger than flowing in vertical type Spiral Coil. Inlet velocity of thermal oil is more than 3 m/s, the influence of furnace tube diameter is small, but when the inlet velocity is less than 3 m/s, the influence of furnace tube diameter and flow velocity is obvious to the flow and heat exchange characteristics. Therefore, the inlet velocity of thermal oil on the radiant heating surface should be controlled during 3m/s to 4 m/s.At the same time, the ‘t' test way is applied to analyze the influence factors degree on the flow and heat exchange characteristics, the result as follow : spiral diameter D> furnace tube diameter d > dw > inlet velocity of thermal oil u > furnace pipe roughness K.Finally, flow resistance coefficient and heat exchange criterion association types are fitted according to the simulated data. which can provide reference for optimization design of Organic Heat Transfer Material Heaters.