| Fresh air load is one of the most important loads in building energy consumption,and the use of heat recovery between fresh air and return air is an effective means to reduce the fresh air load.Considering the enhancing heat and mass transfer properties of nanofluid,the gas-liquid heat and mass transfer performance of Ti O2-Ag nanofluid was investigated,converting the traditional"gas-solid-gas"heat transfer between fresh air and return air into"gas-nanofluid-gas"heat transfer,enhancing the gas-liquid contact area by spraying and bubbling,and synergistically utilizing the photocatalytic degradation ability of Ag-doped Ti O2 nanoparticles to purify the air.This study can provide some reference for nanofluid-based total heat recovery air purification equipment,and the specific research work and results are as follows:The nanofluid was prepared by two-step method,the PEG 1000 was selected as the best dispersant for the nanofluid,and the optimal ratio of nanoparticles to dispersant was determined to be 10:1.The stability of the nanofluid prepared by this method was evaluated,and it was found that the nanofluid with longer oscillation time and shorter storage time had better stability within a certain range.The nanofluid with a volume fraction of 0.05%had the best stability,and the nanofluid prepared by this method was tentatively judged to meet the experimental requirements.The overall performance of the system was tested experimentally,and the effects of the system parameters and nanofluid parameters on the experimental effects were investigated.The experimental results showed that the system had a good effect of enhancing heat transfer and air purification.The bubbling condition had a better gas-liquid heat transfer effect compared to the spray condition,and the setting of gas flow rate should consider both nanofluid stability and gas-liquid contact time to obtain the best heat and mass transfer effect.With the increase of liquid level height,the contact time between bubble and fluid was longer,and the effect of heat and mass transfer were enhanced.The effect of nanofluid stability and volume fraction on enhancing heat transfer was investigated by optimizing the Ti O2-Ag nanofluid preparation method and re-examining the heat transfer experiments.The results showed that the ability of the nanofluid enhancing heat transfer increased with the increase of volume fraction,as shown by the temperature change of both nanofluid and gas.The flow field and temperature of the nanofluid under bubble conditions was simulated,the change of velocity field can be divided into two stages in which bubble column velocity decayed to a minimum value and then slowly grown to equilibrium,where the gas inlet flow was the key factor,the larger the flow rate,the greater the initial kinetic energy obtained but the faster the velocity decayed,so the inlet gas flow rate suitable for this size should take into account the initial kinetic energy of the gas,the velocity decay trend and the system operating time.The simulation results showed that the temperature distribution of the flow field basically corresponded to the velocity distribution.When the volume fraction of nanofluid increased,the density and viscosity increased,which led to a decrease in the velocity of gas diffusion,making the gas retention time became longer,the temperature of the exit gas decreased,and the heat and mass transfer effect was thus enhanced. |
