Hydrodynamic Studies Of An Airlift External-loop Reactor For Silicone Oil Light And Heat Aging

In order to ensure the high conversion efficiency of the solar cell applied at highlight illumination in concentrating photovoltaic (CPV) system, dimethyl has beenused as immersion liquid to cool solar cells. Long-term suitability of the immersionliquid such as dimethyl oil is essential for extension engineering application ofimmersion CPV system. However, aiming at eliminating the shortages ofconventional liquid aging test, an airlift external-loop photochemical annular reactor(AELPAR) was developed for temperature and UV-light aging test of dimethylsilicone oil. Hydrodynamics of reactor have been studied mainly. Also, heat transferperformance and light intensity distribution have been studied preliminarily in thispaper.The pressure difference method and tracer particle method have been used tostudy effect of superficial gas velocity, liquid viscosity, solid holdup and temperatureon flow parameters such as gas holdup and liquid circulation velocity. Theexperimental results show that gas holdup increased with superficial gas velocity,liquid viscosity and temperature increasing, and gas holdup in riser reached a maximalvalue when solid holdup was0.75%. Liquid circulation velocity increased with bothsuperficial gas velocity and temperature increasing, while decreases with liquidviscosity increasing. Liquid circulation velocity could reach a maximum value whensolid holdup kept variety among0.5%and0.75%. When superficial gas velocity was0.06m/s, temperature was raised fastest. In general, reactor axial temperature waswere-distributed.Light intensity distribution has been obtained based on optical theory. Based ontheory of two-phase flow, a correlation equation was established to calculate gasholdup in AELPAR. Flow pattern was divided into bubble flow pattern anddeveloping slug flow pattern two parts under whole operation parameter. A theoreticalmodel was developed to predict the liquid circulation velocity under quasihomogeneous flow hypothesis in bubble flow and modified split phase flowhypothesis in developing slug flow patterns. The comparison between simulation andexperiment results show that the predictions of the proposed model were in goodagreement with the experimental results with average error4.3%of gas holdup,4.43%of liquid circulation velocity under bubble flow and3.52%of liquid circulationvelocity under developing flow, respectively. 3-D numerical simulations of the reactor were carried out by Fluent software withRNG k-epsilon turbulent model and Euler-Eulerian two-phase model. Effect ofreactor structure parameters, operation parameters and physical parameters of siliconeoil on the gas-liquid two phase flow has been simulated and analyzed. The detaileddistribution of internal circulation liquid velocity and gas holdup were obtained andthe reactor structure was optimized as well by the simulation. The numericalsimulation results and experimental results were in good agreement. The simulationresults show that circulation liquid velocity increases and gas holdup decreases withliquid viscosity decreasing, the suitable superficial gas velocity is between0.02m/sand0.04m/s, and the optimum reactor height to diameter ratio and annular area ratiois47.6and0.31-0.41, respectively.