The flow condensation heat transfer (FCHT) in plain channels has a variety of applications in many industrial sectors, and thus it is important to predict FCHT coefficients accurately. This paper compiled a large compound FCHT database containing 5607 data points and 30 fluids and presented a strategy for developing a new correlation of FCHT coefficients. The parameter range of the database is the hydraulic diameter D = 0.493–20 mm, vapor quality x = 0.003–0.992, mass flux G = 24–1533 kg/m2 s, heat flux q = 2.9–422 kW/m2, reduced pressure pr = 0.04–0.95, liquid Prandtl number Prl = 1.7–8.5, liquid Reynolds number Rel = 11.6–5.3 × 104, and gas Reynolds number Reg = 75.1–9.1 × 105. Based on the database and strategy, a new general correlation with substantially better accuracy was developed, which is applicable to plain channels of various sizes and a broad operational parameter range. It predicts the database with a mean absolute deviation (MAD) of 14.1%, while the best existing Δ T-independent correlation predicts the database with an MAD of 20.2%. The applicability of the new and 38 existing correlations to individual fluids was assessed. The new correlation performs best for 8 of the 14 fluids that have more than 50 data points in the entire database, while the most accurate existing one performs best only for 2 of them. The Fang number Fa plays an important role in the new correlation, implying that it relates to the fundamental mechanisms of both boiling and condensation heat transfer.
The pool boiling heat transfer coefficient (HTC) and critical heat flux (CHF) of sodium dodecyl sulfate (SDS) surfactant solution under different concentrations and subcooling conditions were experimentally studied. The concentration of SDS was from 0 to 3000 ppm, and the subcooling degree was from 2 to 10 ℃. The heat transfer coefficient under different subcooling conditions was theoretically analyzed, and the real-time fluctuation of wall temperature was discussed in detail. It is found that the subcooling has little effect on the natural convection of pool boiling but significantly impacts the nucleate boiling, and that the phenomenon of temperature overshoot (TOS) is stronger in the SDS solution than in deionized water. Furtherly, the origin and development process of TOS were deeply analyzed by showing the development process diagram. Meanwhile, the CHF phenomena were visualized and traced experimentally. The influence of different subcooling degrees and SDS concentrations on the CHF was deeply explored, and the development process diagram of the vapor film under CHF conditions was plotted. The results provide detailed theoretical support for the HTC and CHF of SDS solution under subcooling conditions.
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