China
Africa
Explore chapters and articles related to this topic
Convective Vaporization
Published in Ralph L. Webb, Nae-Hyun Kim, Principles of Enhanced Heat Transfer, 2004
The combination of total flow rate and local vapor velocity establishes a flow pattern, which changes with vapor quality. Horizontal tubes may behave differently from vertical tubes, because gravity force acts to stratify the liquid. Hence, enhancement requirements for horizontal tubes may be different from those for vertical tubes. Circular tubes are not the only “channel flow” geometry of interest. Brazed aluminum heat exchangers may use flat, extruded aluminum tubes having rectangular flow passages, or they may be of the plate-and-fin construction. Another channel flow geometry of interest is the annulus. Boiling on the outside of tubes in a bundle also involves convective effects. These geometries are also addressed.
Prediction of Pressure Drop for Flow Boiling in Rectangular Multi-Microchannel Heat Sinks
Published in Heat Transfer Engineering, 2019
Burak Markal, Orhan Aydin, Mete Avci
Figure 4 shows the comparison of the experimental findings with those predicted using the previous correlations considered. Unfortunately, all the correlations considered overpredict the experimental data. The correlation of Lockhart and Martinelli [26] shows the highest MAE of 1094.8%, and the percentage of the data points predicted within ±50% error band is zero (in Table 4). The other group correlations of [8], [13], [14], [27] show similar performance, while Huang and Thome's [5] correlation is between these two group correlations. However, the correlation of Lee and Garimella [8] makes relatively good predictions among them with a MAE of 493.6% and 4.1% of the data falls within for all error bands. Though the MAE of Huang and Thome's [5] correlation is 585.7%, this correlation captures 5.2% of the experimental data within ± 50% error band. From Figures 5a and b, it is seen that all the correlations capture the same trend with the experimental results. Two phase pressure drop increases with increasing heat flux and vapor quality. However, the curves of selected correlations (especially of [5]) are steeper. There are several reasons for these obvious deviations: (1) Channel sizes vary significantly from macro to micro. When the hydraulic diameter is reduced to microscale, the hydrodynamic and thermal behaviors significantly change. (2) Assumptions made and the experimental conditions change from study to study. There is even no consensus on the concept of microchannel. Some authors [29]–[31] have proposed physical classifications for the transition from conventional to small scales, while the others [32]–[34] have presented different criteria related to the bubble confinement based on the thermophysical properties. (3) The physical conditions are different for boiling and non-boiling flows (adiabatic and condensing). Some correlations are based on non-boiling flow data.
Experimental study on two-phase pressure drop and flow boiling heat transfer in a micro pin fin channel heat sink under constant heat flux
Published in Experimental Heat Transfer, 2021
Ki Moon Jung, Ajith Krishnan R, Udaya Kumar G, Hee Joon Lee
The experimental boiling heat transfer coefficient values for different mass fluxes at different vapor quality are shown in Figure 8. The heat transfer coefficient was observed to decrease rapidly with increasing quality in the region of vapor quality of less than 0.01. The heat transfer coefficient tends to decrease more smoothly in the vapor quality range of 0.01 to 0.043.