| On the road of achieving emission peak,carbon neutrality and pursuing high quality economic development,people’s requirements for indoor air qualities are increasing on the one hand,and the government is actively advocating energy saving and emission reduction on the other hand,which has created a contradiction between improving indoor air quality and energy saving.As one of ideal equipment to solve this contradiction,Fresh air handle unit with full heat exchanger has a broad application prospect and has attracted the widespread attention both at home and abroad.Compared with the general duct flow field,Fresh air handle unit with full heat exchanger has a complex internal flow field flow condition due to the presence of total heat exchanger core and centrifugal fan.This paper mainly adopts the method of numerical simulation to visualize the internal flow field,and combines the experimental and theoretical analysis conclusions to study the duct flow field and noise characteristics of Fresh air handle unit with full heat exchanger.The main research contents of this paper are as follows:(1)In this paper,the flow field of Fresh air handle unit with full heat exchanger was simplified,and the three-dimensional steady-state numerical simulation of the flow field of the single fresh air basin was analyzed,and the pressure field,velocity field and streamline distribution at the flow field section inside the unit,as well as the velocity vector distribution inside the unit as a whole and the centrifugal fan box were analyzed in detail,which provided a reference for the in-depth study of the three-dimensional flow in the air duct space of Fresh air handle unit with full heat exchanger.This provided a reference for an in-depth study of the three-dimensional flow in the duct space of Fresh air handle unit with full heat exchanger.The accuracy of the flow field model was verified by experimental measurements of the outlet flow rate of the unit.(2)Based on the steady-state flow field information,a structural optimization scheme to change the axial position of the centrifugal fan in the box was proposed and simulated.The simulation results showed that the centrifugal fan was shifted 20 mm in the negative direction of the y-axis in the box was the optimal scheme,and the largest increased of the flow rate at the speed of 2472 r/min under three speeds of the unit,which was 16 m~3/h,increased of 10.5%.The flow field of the optimized solution was compared with the prototype flow field,and the reasons for the increased flow rate of the unit were analyzed:the optimized solution reduced the high static pressure area near the impeller worm tongue and reduced the flow separation in the flow channel near the worm tongue,while the pressure in the low pressure area at the impeller inlet was relatively lower,which made it easier for the airflow to be sucked into the inside of the impeller flow channel;balancing the airflow at the inlet of the two impellers of the fan made the airflow speed more uniformly distributed along the axial direction,and the area of the low speed area in the central area was reduced;the overall vortex range in the box was effectively controlled,and the vortex at the left side of the box inlet was basically eliminated,reducing the vortex loss.(3)This paper proposes to add deflectors to improve the uniformity of inlet airflow of centrifugal fans on the basis of the structural optimization scheme of deflecting the centrifugal fans in the negative direction of the y-axis by 20 mm in the box,and designed four different deflectors with different deflection directions.The largest increased in flow rate was 5 m~3/h,which was 2.8%higher than which of the unit without deflector.Analyzing the flow field of the unit without deflector and the unit with four types of deflectors respectively,it was found that the airflow at the inlet surface of the centrifugal fan box with mixed deflectors had the largest velocity component along the positive direction of x-axis,which was favorable for the airflow to enter the box,while the uniformity at the inlet of the centrifugal fan box was also improved compared with the unit without the addition of deflectors.(4)Theoretical analysis of the aerodynamic noise source of the fresh air unit with full heat exchanger,and the dipole sound source as the main pneumatic sound source.The noise experimental test was conducted on the unit,and the noise at the measurement point had a large sound pressure level in the middle and low frequency band.Broadband noise model in Fluent was used to derive the distribution of dipole sound sources on the surface of the unit.The maximum surface sound power level inside the unit at three speeds appeared on the surface of the impeller of the centrifugal fan,and the maximum surface sound power level of the unit after taking two optimization measures was smaller than which of the unit prototype.Taking the impeller surface as the noise source,the noise spectrum and noise pressure level at the measurement point were calculated by opening the sound comparison model of FW-H equation,and the value of sound pressure level was close to the experiment,and the noise pressure level at the measurement point of the optimized unit was lower than that of the prototype unit. |
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