Abstract

A pronounced stratification of the temperature (density) of the fluid over the cross section of the heating zone occurs in a thermosyphon that is slightly inclined to the horizontal and has a high degree of water filling, which leads to the onset of natural circulation of the medium along the length of the thermosiphon. In this case, there is an upward flow of water or a steam–water mixture in the upper part of the thermosiphon and a downward flow in the lower part. In experiments with a full-scale thermosiphon, the natural circulation in question increased the axial heat transfer through nonboiling water along all thermosiphon zones by three to seven times as compared to the heat transfer in a vertical thermosiphon. The estimated mass flow rate of natural circulation along the heating zone ranged from 25 to 105 kg/(m² s). The heat-transfer coefficient and friction factor are estimated at the boundary of countercurrent water flows induced by natural circulation. The conditions of poorer cooling of the thermosiphon heating zone due to steam separation at its upper generatrix are examined. A decrease in the mass filling of the thermosiphon, i.e., an increase in the average void fraction of the medium in it, successively leads to the onset of bubbling steam condensation within the transport section and then in the cooling zone, with a decrease in the length of the upper section of nonboiling water. A transition to film condensation of steam occurs at the limit along the entire length of the cooling zone with a countercurrent steam flow and a near-wall film of its condensate above the level of the steam–water mixture in the thermosiphon.

中文翻译：

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水平方向略微倾斜的热虹吸管中流体的自然循环

摘要

在热虹吸管中，流体在加热区横截面上的温度（密度）明显分层，该热虹吸管相对于水平面略有倾斜，并且充水程度高，这导致水的自然循环开始。介质沿着热虹吸管的长度方向移动。在这种情况下，热虹吸管的上部有水或蒸汽-水混合物的向上流动，而下部则有向下的流动。在使用全尺寸热虹吸管的实验中，与垂直热虹吸管的热传递相比，所讨论的自然循环使沿所有热虹吸管的非沸腾水的轴向热传递增加了三到七倍。沿加热区自然循环的估计质量流量范围为25至105 kg /（m ²s）。在自然循环引起的逆流水流边界处估计了传热系数和摩擦系数。考察了由于热虹吸管上母线的蒸汽分离而使热虹吸管加热区冷却较差的条件。热虹吸管质量填充的减少，即其中介质的平均空隙率的增加，依次导致在输送段内然后在冷却区内发生鼓泡的蒸汽冷凝，而冷凝温度降低。非沸腾水上部的长度。沿着冷却区的整个长度，在极限温度下会发生蒸汽向薄膜冷凝的过渡，其中逆流蒸汽流及其冷凝物的近壁薄膜高于热虹吸管中蒸汽-水混合物的高度。