Experimental investigation on heat transfer characteristics of upward flow boiling in a vertical narrow rectangular channel

ABSTRACTHeat transfer experiment on water flow boiling was carried out in the upward direction under atmospheric pressure through a narrow rectangular channel heated on one-side by vapor having a gap of 2.75 mm, a width of 250 mm, and length of 1400 mm. The heat transfer coefficient and thermal hydraulic thresholds of the flow boiling in forced convective flow, such as the onset of nucleate boiling (ONB) and onset of fully developed nucleate boiling (OFDB) were investigated. The experiment was performed over a wide range of inlet temperature (75–95°C), mass flow rate (2–9 g/m), and heat fluxes (5–16 kW/m2). The effects of the parameters on the heat transfer coefficients have been discussed in detail. A series of ONB, FDB and heat transfer correlations were evaluated using the experimental data, and most of the correlations did not adequately fit the experimental results. A modified Hong et al. correlation and modified Zhu et al. correlation were used to predict the wall superheat at ONB and FDB respectively. The average errors (AEs) of the two correlations were 2.36% and −0.68%, and the root mean square errors (RMSEs) of them were both 14.00%. A modified Li and Wu correlation was used to predict heat transfer coefficients with the average error (AE) of 1.46% and the root mean square errors (RMSE) of 11.88%.KEYWORDS: flow boilingnarrow rectangular channelONBFDBheat transfer AcknowledgmentsThis research was supported by Shanghai Key Laboratory of Multiphase Flow and Heat Transfer in Power and Engineering Research Project (2019KJFZ201).Disclosure statementNo potential conflict of interest was reported by the author(s).Nomenclature A=area (m2)AE=average errorBo=boiling number, q/(Ghfg)Bd=Bond number, g(ρl-ρv)Dh2/σcp=constant-pressure specific heat of liquid (J/kg K)Dh=channel hydraulic diameter (m)E=convective boiling enhancement factorG=mass flux (kg/m2 s)g=gravitational acceleration (m/s2)h=heat transfer coefficient (W/m2 ℃)hfg=latent heat of vaporization (J/kg)k=thermal conductivity (W/m ℃)L=length (m)M=relative molecular massMAE=mean absolute errorm=mass flow rate (g/s)N=number of data pointsP=Pressure (MPa)Pr=critical pressurePr=Prandtl numberQ=quantity of heat exchange (W)q=heat flux (kW/m2)Rel=liquid Reynolds number, G(1-x)Dh/μlRMSE=root mean square errorS=nucleate boiling suppression factort=temperature (℃)We=Weber number (G2Dh/(ρlσ))x=vapor qualityXtt=Martinelli parameterGreek symbols=μ=dynamic viscosity (kg/m s)σ=surface tension (N/m)ρ=density (kg/m3)Subscripts=cal=calculatedcool=coolantcon=condensereff=effectiveeva=evaporatorexp=experimentalfdb/FDB=fully developed boilingin=inletl=liquidout=outletONB=onset of nucleated boilingOFDB=onset of fully developed nucleate boilingsat=saturationsp/SP=single phasesub=subcoolingtp=two phasev=vaporAdditional informationFundingThis work was supported by the Shanghai Key Laboratory of Multiphase Flow and Heat Transfer in Power and Engineering Research Project [2019KJFZ201].