The Numerical Simulation On New Heat Transfer Enhancement Technology And Enhancement Mechanism

Internationally the main method of heat transfer enhancement is affecting the flow field to achieve heat transfer enhancement by means of surface reshaping of heat transfer components, swirl generator and vibration. But the heat transfer enhancement is always accompany the universal existence of flow resistance increasing, making the system overall performance is difficult to improved significantly. Based on rheology, viscoelastic fluid with the characteristics of the secondary flow vertical to the main flow direction was found, so low viscosity viscoelastic highly effective heat transfer function fluid can be prepared through adding polymer solvent in heat transfer medium, through its unique the secondary flow characteristics which vertical to the heat transfer surfaces, the heat transfer enhancement was achieved on the premise of no increasing the flow resistance. The heat transfer enhancement technology of viscoelastic function fluid has great potential for development with low flow resistance characteristics, low cost and easy to promote the application and many incomparable advantages. So far, the literature report about the mechanism of heat transfer enhancement theory is rarely at home and abroad. Based on the characteristics of heat transfer enhancement, the full three dimension non-isothermal viscoelastic model of describing the heat transfer enhancement of viscoelastic function fluid and the corresponding efficient steady-state finite element numerical algorithm were established. On this basis, the influencing laws of the process parameters and viscoelasticity rheological properties parameters on the process of heat transfer enhancement were studied by means of numerical simulation. The heat transfer enhancement mechanism of viscoelastic function coupled with the pulsating flow was discussed. And through multi-field coordination mechanism, heat transfer enhancement mechanism was revealed, and the scientific theories foundation of the engineering application of this heat transfer enhancement technology was laid.The following main achievements were yielded:(1) Based on the theories of rheology and hydrokinetics and the characteristics of the heat transfer enhancement flow process of viscoelastic function fluid, the full three dimension non-isothermal viscoelastic theoretical model was established to describe the heat transfer enhancement process of viscoelastic function fluid by means of reasonable assumption. And on the basis of Mini-Element method, penalty function method, Galerkin method and EVSS/SUPG method and etc. stable finite element mixed, the efficient steady-state finite element numerical algorithm which suit to the theoretical model was established.(2) Viscoelastic highly effective heat transfer function fluid can be prepared through adding polymer solvent in heat transfer medium, the research indicated that under the same flow resistance and heat transfer characteristics parameters, viscoelastic function fluid has a significant heat transfer enhancement function compared to pure viscous fluid. The maximum heat transfer enhancement effect is up to 40%.(3) Viscoelastic highly effective heat transfer function fluid achieve heat transfer enhancement through the unique secondary flow characteristics which vertical to the heat transfer surfaces, the heat transfer enhancement was achieved. The heat transfer enhancement effect depends on the secondary flow intensity which vertical to the heat transfer surface, the stronger the secondary flow, then the better heat transfer enhancement, the secondary flow intensity is proportional to the second normal stress difference of heat flow.(4) The effect of heat transfer enhancement of viscoelastic highly effective heat transfer function fluid increased with the increase of relaxation time and the fluid flow rate.(5) The viscoelasticity function fluid and the pulsating flow have the obvious coupling heat transfer enhancement function, which make the heat transfer enhancement effect of viscoelastic function fluid further improved, the strengthened effect up to 8%. When the pulsating flow frequency is in the 0.1～20HZ range, the effect of coupling heat transfer enhancement increased with the reduction of pulsating flow frequency or the increase of pulsating flow amplitude. But when the pulsating flow frequency was reduced to 0.05HZ, the heat transfer emerged weakened phenomenon.