| Research Abstract |
1.Subcooled Flow Boiling Critical Heat Flux in a Vertical Copper Tube Controlled Dissolved Gas Concentration
The subcooled flow boiling CHF for the flow velocities (u=4.0 to 13.3 m/s), the outlet subcooling (ΔT_<sub,out> =46 to 119 K), the inlet subcooling (ΔT_<sub,in>=68 to 148 K) and the outlet pressure (P_<out>-800 kPa) are systematically measured by the experimental water loop installed the pressurizer. The Cupro-Nickel (Cu-Ni30%) tube of d=6 mm and L=60 mm (L/d=10) are mainly used in this work. It measures 0.15 μm in the inner surface roughness (Ra). The CHF, q_<cr,sub>, (35 points) are shown versus the outlet and inlet subcoolings measured, ΔT_<sub,out> and ΔT_<sub,in>, with the flow velocity as a parameter. The CHF become higher with an increase in flow velocity at a fixed ΔT_<sub,out> andΔT_<sub,in>. These illustrate the trends in the variation of CHF with increasing outlet and inlet subcoolings. The CHF for the ΔT_<sub,out> and ΔT_<sub,in> greater than around 30 K and 40 K incr
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ease with an increase in ΔT_<sub,out> and ΔT_<sub,in> respectively. The increasing rate becomes lower for higher ΔT_<sub,out> and ΔT_<sub,in>. The curves given by Eqs. (1) and (2) at each flow velocity are compared.
Bo=0.082{d/√<σ/g(ρ_l-ρ_g)>}^<-0.1> We^<-0.3>(L/d)^<-0.1> Sc^<0.7>(1)、Bo=C_1{d/√<σ/g(ρ_l-ρ_g)>}^<-0.1> We-^<0.3>(L/d)^<-0.1>e^<-(L/d)/C_2Re^<0.4>> Sc^<*C_3>>(2)
where, C_1=0.082, C_2=0.53 and C_3=0.7 for L/d 【less than or equal】 around 40 and C_1=0.092, C_2=0.85 and C_3=0.9 for L/d>around 40. The CHF data for ΔT_<sub,out>【greater than or equal】30 K and ΔT_<sub,in>【greater than or equal】40 K are in good agreement with the values given by the correlation against outlet and inlet subcooling, Eqs. (1) and (2). Little effect of tube material on CHF can be seen for low and high heat flow velocities, although the thermal conductivity, λ, of the Cupro-Nickel (Cu-Ni30%) becomes 2.1 times as large as that of SUS304 one. It is assumed from this fact that the correlations against outlet and inlet subcooling, Eqs. (1) and (2) would not be affected by the difference in tube material. Less
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