Abstract
Field synergy characteristics in condensation heat transfer with non-condensable gas (NCG) over a horizontal tube were numerically simulated. Consequently, synergy angles between velocity and pressure or temperature gradient fields, gas film layer thickness, and induced velocity and shear stress on gas–liquid interface were obtained. Results show that synergy angles between velocity and temperature gradient fields are within 73.2°–88.7° and ascend slightly with the increment in mainstream velocity and that the synergy is poor. However, the synergy angle between velocity and pressure gradient fields decreases intensively with the increase in mainstream velocity at θ ≤ 30°, thereby improving the pressure loss. As NCG mass fraction increases, the gas film layer thickness enlarges and the induced velocity and shear stress on gas–liquid interface decreases. The synergy angles between velocity and temperature gradient fields increase, and the synergy angles between velocity and pressure gradient fields change at θ = 70°, decrease at θ < 70°, and rise at θ > 70°. When the horizontal tube circumference angle increases, the synergy angles between velocity and temperature or pressure gradient fields decrease, the synergy between velocity and pressure fields enhances, and the synergy between velocity and temperature fields degrades.
Highlights
Heat transfer enhancement is an important research topic in the heat transfer field at home and abroad
The reason is that the gas film layer is formed by the accumulation of non-condensable gas (NCG) carried on the condensate surface by vapor that condenses over the horizontal tube
Given the circumferential angle of horizontal tube θ, synergy angles between velocity and temperature or pressure gradient fields decrease with the increase in mainstream velocity
Summary
Heat transfer enhancement is an important research topic in the heat transfer field at home and abroad. The heat transfer parameters of an oscillating flow heat pipe have been optimized based on field synergy theory.[5] An elliptical tube bundle replaced by a circular tube bundle can improve the synergy between velocity and temperature fields.[6] When the boundary condition of heat flux is provided in a helical baffle, the helical tube with low curvature presents high heat transfer coefficients.[7,8] A helical coil can effectively enhance the convective heat transfer of solar-energy thermal-collecting tube,[9] and increasing the overlapping of the same pitch baffle can improve the convective heat transfer property of the shell. Parameter distributions in the gas film layer are uniform, including temperature, velocity, and NCG concentration.[21] Zhang and Wang[22,23] experimentally analyzed the effect of air column on condensation in a non-vacuum gravity heat pipe and air accumulation on the gas-liquid interface in vapor condensation across the horizontal tube. The enhancement potential of condensation heat transfer and the variation laws of flow resistance and pressure drop were revealed
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