Experimental and numerical investigation of fractal-tree-like heat exchanger manufactured by 3D printing

© 2018 Elsevier Ltd The manufacturing difficulties of complex fractal-tree-like heat exchangers have limited their industrial applications, although many evidences have shown that they have significant advantages in heat transfer. Nevertheless, the emerging 3D printing technology has brought great opportunity for the development of complex structured device. In the present study, three-dimensional (3D) fractal-tree-like heat exchangers were designed and manufactured using 3D printing technology. Their performance was evaluated from both thermal and hydrodynamic perspectives, the flow characteristics were investigated in detail. The results show that a fractal-tree-like heat exchanger can improve hydrodynamic performance, reduce pressure drops and has great heat transfer ability. In general, the fractal-tree-like heat exchanger has a comprehensive advantage over the traditional spiral-tube exchangers as it has a higher value of coefficient of performance (COP). Furthermore, the 3D printing provides a visual, efficient, and precise approach in the present research

Descriptive statistics for the variables used in the spatial panel-data model.

Descriptive statistics for the variables used in the spatial panel-data model.</p

Synoptic meteorological conditions during the high-PM_2.5 episode.

Synoptic meteorological conditions during the high-PM2.5 episode.</p

Moran’s I statistics for residuals, LM, and robust LM test results.

Moran’s I statistics for residuals, LM, and robust LM test results.</p

Weekly average PM_2.5 concentrations observed in Chinese cities in the pathways of backward trajectories by the distance to the receptor cities in Korea.

Weekly average PM2.5 concentrations observed in Chinese cities in the pathways of backward trajectories by the distance to the receptor cities in Korea.</p

Average effects of LRTT from China on local PM_2.5 concentration.

Average effects of LRTT from China on local PM2.5 concentration.</p

Observed PM_2.5 concentrations from monitoring data and backward trajectory pathways.

Observed PM2.5 concentrations from monitoring data and backward trajectory pathways.</p

Sample maps for aerosol optical depth and copernicus atmosphere monitoring service PM_2.5 concentration with wind direction.

Sample maps for aerosol optical depth and copernicus atmosphere monitoring service PM2.5 concentration with wind direction.</p

Spatial panel-data FE model results.

This study identifies causal links between a high-PM2.5 episode in Korea and air pollutants originating from China during a high-PM2.5 episode that occurred in Korea between February 23 and March 12, 2019. Datasets on ground-based PM2.5 levels in Korea and China, airflows from the back-trajectory models, and satellite images were investigated, and long-range transboundary transport (LRTT) effects were statistically analyzed using spatial panel-data models. The findings are: 1) visual presentations of the observed PM2.5 concentration in China and Korea, back-trajectory air flows, and satellite images from the Moderate Resolution Imaging Spectroradiometer Aerosol Optical Depth and the Copernicus Atmosphere Monitoring Service clearly show that transboundary air pollutants from China affect PM2.5 concentration in Korea; 2) the effect of LRTT from China is likely to intensify under certain meteorological conditions, such as westerly winds from China to Korea, the formation of high pressure in China and low pressure in Korea, relatively high temperature, and stagnant air flow in Korea; 3) the results from the spatial panel-data models provide statistical evidence of the positive effect of LRTT from China on increasing local PM2.5 concentration in Korea. The nationwide average LRTT contributions to PM2.5 concentration in Korea are 38.4%, while regional contributions are 41.3% for the Seoul Metropolitan Area, 38.6% for the northwest region, and 27.5% for the southeast regions in Korea, indicating the greatest impact on the Seoul Metropolitan Area.</div

Air pollution ground monitoring stations in Korea and China together with the nine Korean cities considered for back-trajectory models.

Air pollution ground monitoring stations in Korea and China together with the nine Korean cities considered for back-trajectory models.</p