Search

The vertical condensers have advantages of small occupation area, convenient in assemble or dismantle tube bundle and simple structure etc. However, the low heat transfer performance limits their applications. To enhance the heat transfer, a novel type of vertical condensers was designed by introducing trisection helical baffles with liquid dams and gaps for facilitating condensate drainage. Four configurations of vertical condensers with trisection helical baffle are experimentally studied and compared to a traditional segment baffle condenser. The enhancement ratio of trisection helical baffle schemes is about 1.5–2.5 and the heat transfer coefficient of the dual-thread trisection helical baffle scheme is superior to that of the single-thread one by about 19%. Assistant by the theoretical study, the experimental data is simulated and the condensation enhancement mechanisms by applying trisection helical baffle in vertical condenser are summarized as condensate drainage, short tube construct and reduce steam dead zone functions of the helical baffles. [ABSTRACT FROM AUTHOR]

Abstract: A visualization study is conducted to investigate condensation flow in wide rectangular silicon microchannels with the hydraulic diameter of 90.6 μm and width/depth ratio of 9.668. Droplet-annular compound flow, injection flow, and vapor slug-bubbly flow are observed along the channel, which differ from that in other cross-sectional shape microchannels. In the droplet-annular compound flow region, the vertical walls (short side) of the channel are completely covered by the condensate, while droplet condensation still exists on the horizontal wall (long side) of the channel. The location of the injection flow will be postponed with the increasing inlet vapor Reynolds number. The injection frequency will increase with the increasing inlet vapor Reynolds number and condensate Weber number. More specifically, the frequency in the wide rectangular microchannels is lower than that in triangular microchannels having the same hydraulic diameter. It is confirmed that the cross-sectional shape of the microchannel plays a significant role on the instability of condensation flow. In addition, the correlation of Nusselt number is also presented. [Copyright &y& Elsevier]

Abstract: A visualization experiment is conducted to investigate the condensation of steam in a series of triangular silicon microchannels. The results indicate that droplet, annular, injection and slug-bubbly flow are the dominant flow patterns in these triangular silicon microchannels. With increased mass flow rate, or an increase in the hydraulic diameter under the same Reynolds number, the location at which the injection occurred is observed to move towards the channel outlet. The frequency of the injection increases, i.e. the flow of condensation instability is higher with increased inlet vapor Reynolds number, condensate Weber number and the prolongation of the injection location, or with a decrease in the hydraulic diameter of the channel. In addition, the wall temperature of the channel decreases along the condensation stream. The total pressure drop, the average condensation heat transfer coefficient and the average Nusselt number are observed to be larger with increased inlet vapor Reynolds number. Moreover, it is found that the condensation heat transfer is enhanced by a reduction in the channel scale. [Copyright &y& Elsevier]