Cross Scale Simulation On Heat And Mass Transfer Of Air-cooled Condenser In Power Plant

Air-cooled condensers with obvious water conservation benefit can be an important alternative for power plant near coal mines where water source is of shortage over the past few decades. The flow and heat transfer performance not only depends on heat transfer efficiency among fins, it is also restricted by finned tube bundles, air cooled condensers (ACC), air cooled island, main structures of power plant, and the meteorological and the geographic conditions. The smallest and largest length scale in this typical multi-scale system have bridged106-107m order of magnitude. The experiment and numerical simulation methods adopted by flow and heat transfer research of air cooling system in power plant always consume gigantic calculating time and resource. Moreover, considered simultaneously interacting mechanism among all length scale levels, the established models used multi-grid method in numerical simulation were easily restricted by the mesh interconnection on the interfaces between large and small scale regions. And the gigantic models were easy to exceed the calculating ability of the existing computer.Influenced by the natural environmental wind, the reduced order models based proper orthogonal decomposition (POD) method were established about air side velocity and temperature fields of two-dimensional air cooled condenser. In order to analyze the flow and heat transfer laws, the variable fields at new cases were predicted quickly and accurately. The weight coefficients for POD modes were obtained by cubic spline interpolation and flux matching procedure, and analyzed the respective possessing advantages and disadvantages. In order to obtain the robust reduced order models over the whole researching range of parameter, the improved complementary POD(PODc) approach was adopted in the present research.The calculating efficiencies of variable fields have been improved obviously in air cooled condenser, and the calculating time and resources were significantly saved through the reduced order models based POD method with similar precision to mutlti-grid CFD simulating results. The introduced POD method is very effective to deal with the complex flow and heat transfer problem in air cooled condenser of power plant under the comprehensive influence of ACC structure and ambient wind. The present investigation may provide a rapid and reliable approach for the research of flow-thermo rules, structure optimization, and real-time operation control of air cooling system in power generating unit.Due to the high dependence of flow and heat transfer performance of three-dimensional ACC onto the natural wind angle, combined procedure (PODs-c) of spare POD (PODs) with complementary POD (PODc) was reformulated to treat the high nonlinear issue with large variable gradients generating kinds of vortices in ACC at the relative small natural direction angle cases. And the calculating precisions have been obviously improved. The reformulated PODs-c effectively extends the researching parameter range of flow and heat transfer for ACC utilized reduced order models based POD.In order to deal with the multi-scale flow and heat transfer problem of air cooling system in power plant, a cross scale modeling methodology combined POD and CFD was proposed in the present paper. Reduced order models based proper orthogonal decomposition were established about variables in small-scale region, and the flow and heat transfer status were predicted quickly and accurately. On the cross scale interfaces between large and small scale regions, numerical simulation of flow and transport characteristics on large-scale region were realized, with the boundary condition of the reserving transport information from reduced order solution in small scale region.The proposed cross scale modeling methodology was adopted to research the flow and heat transfer characteristic of air cooling system crossing two neighbor characteristic lengths, including that of the air cooling island region containing2x30air cooled condensers with small length scale, and the large-scale one consisted of power plant buildings and the geomorphology. The hot plume recirculation of the air cooling island caused by environmental natural wind, as well as the heat transfer deterioration of downwind ACC cells were revealed.The cross scale relationship of air flow and heat transfer characteristic, as well as the interdependent relationship between kinematic and dynamic in air cooling system were realized adopted the present cross scale modeling methodology. And interacting mechanism among different length scale turbulent vortex were revealed. The calculating time and resources were significantly saved through the present cross scale modeling methodology with similar precision to multi-grid CFD simulating technique. The cross scale modeling methodology can be used to solve the existing multi-scale problem in other fields, and the researched achievement exerts positive contribution to the research of multi-scale science.