| The direct absorption of solar energy has the advantages of simple structure and high heat collection efficiency,is widely used in anaerobic reactors and other areas of normal temperature heat collection.During the operation of anaerobic reactor,it is necessary to maintain a medium temperature environment(about thirty-five °C)all year round to maintain the high efficiency of microbial metabolism.The application of direct solar energy absorption technology in the heating of anaerobic reactor can effectively reduce its electric energy consumption.It is the key to improve the power saving rate of the solar anaerobic reactor to study the photothermal conversion characteristics and analyze its effect on the anaerobic reaction.In this paper,the photothermal conversion characteristics and anaerobic fermentation characteristics of push-flowing direct absorption solar anaerobic reactor were studied.Firstly,the photothermal properties of alumina-water nanofluid,which is like that of oilfield wastewater,were selected as the internal fluid of the reactor.Then,a two-dimensional photothermal and biochemical model was established to analyze the effects of baffle number,inlet flow rate,baffle height and reactor length on the temperature field and anaerobic fermentation process in the reactor.Finally,an experimental platform for photothermal transformation of the reactor was built to verify the accuracy of the simulation results and give some suggestions for improvement.The specific research results are as follows:(1)Based on the "two-step method",the nano-fluid samples with different volume concentrations of alumina-water were prepared.The optical parameters were measured by ultraviolet visible spectrophotometer and thermal parameters were measured by Hot Disk analyzer.It was found that the nano-fluid had high light absorption and thermal conductivity when the volume concentration was 0.005%.(2)A two-dimensional photothermal and biochemical model of the reactor was established by using the finite volume method and the improved ADM1 model.The results show that increasing the number of baffles can improve the heat collection efficiency of the reactor,but the friction loss between the fluid and the baffles also increases,with the maximum increase of194.46%.The inlet flow rate has a great influence on the heat collection of the reactor.The inlet flow rate and the external radiation intensity have a functional relationship on the optimal gas production of the reactor.The height of the baffle has a great influence on the temperature uniformity of the reactor.With the increase of the height,the variance of the temperature of the monitoring line decreases by 0.14.The longer the reactor,the higher the overall temperature behind it,the better the uniformity of temperature.(3)An experimental platform for photothermal conversion of the reactor was built,and the influence of factors on the temperature field inside the reactor was analyzed by measuring the temperature values of the inlet and outlet of the reactor and the location of the internal monitoring line.The results show that the overall error rate is very low,and the maximum error rate is 0.5%,indicating that the simulation value is relatively accurate.The experimental values of outlet temperature under different conditions are lower than the simulated values,which may be caused by:(1)Thermal insulation material is not added to the nanofluid pipeline in the experimental equipment;(2)The air layer between the top of the reactor and the nanofluid increases the thermal conductivity resistance,which hinders the heat conduction. |
