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首页> 外文期刊>Memoirs of the Faculty of Engineering KYUSHU University >Boiling Heat Transfer in Rectangular Channels of Small Gaps
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Boiling Heat Transfer in Rectangular Channels of Small Gaps

机译：小间隙矩形通道中的沸腾传热

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An experimental investigation was conducted to elucidate boiling heat transfer and flow pattern in a narrow-flat rectangular channel of a 100 mm-heated length with K-113 as the test fluid. The cross section of the channel is 20 mm wide and its height (referred to the gap) is varied as 0.2, 0.5, 1.0 and 2.0 mm to form a narrow boiling space. It was found that heat transfer coefficient is a complex function of mass velocity, heat flux and vapor quality for a given value of the gap size. In the downstream of the onset point of nucleation there follows the bubbly flow region of nucleate boiling dominance. This region is localized rather shortly in the present narrow channels and replaced by the regions of successive slug and annular flows where convective evaporation becomes dominant. Heat transfer coefficient in the slug and the annular flow regions increases in the flow direction under some thermal and hydrodynamic conditions until dry-out quality is approached, while for another conditions heat transfer coefficient decreases steadily in the flow direction. This steady decrease is observed when the gap size is small, mass velocity low and heat flux is high. In the present narrow channels five flow patterns are identified: (a) bubbly flow of spherical bubbles, (b) bubbly flow of two-dimensionally flattened bubbles, (c) coexistence of slug and bubbly flows, (d) slug flow, and (e) annular flow. A smaller gap of the narrow channels gives higher heat transfer coefficients when heat fluxes are low, whereas heat transfer deterioration begins at lower quality as heat flux becomes higher.
机译：进行实验研究以阐明在加热长度为100 mm的狭窄扁平矩形通道中以K-113为测试流体的沸腾传热和流动模式。通道的横截面为20毫米宽，其高度（称为间隙）为0.2、0.5、1.0和2.0毫米，以形成狭窄的沸腾空间。已经发现，对于给定的间隙尺寸值，传热系数是质量速度，热通量和蒸汽质量的复杂函数。在成核起始点的下游，跟随着成核沸腾优势的气泡流动区域。该区域相当短地位于当前的狭窄通道中，并被对流蒸发占主导的连续的段塞和环形流区域取代。在某些热和流体动力条件下，块状和环形流动区域中的传热系数在流动方向上增加，直到达到干透质量为止；而在另一种情况下，传热系数在流动方向上稳定地减小。当间隙尺寸较小，质量速度较低且热通量较高时，可以观察到这种稳定的降低。在目前的狭窄通道中，确定了五个流动模式：（a）球形气泡的气泡流;（b）二维扁平气泡的气泡流;（c）团状和气泡状流并存;（d）团状流;以及（ e）环形流动。当热通量低时，窄通道的间隙越小，传热系数就越高，而当热通量变高时，传热劣化开始于较低的质量。

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