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首页> 外文期刊>International Journal of Heat and Mass Transfer >Heat and mass transfer in a cylindrical heat pipe with a circular-capillary wick under small imposed temperature differences
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Heat and mass transfer in a cylindrical heat pipe with a circular-capillary wick under small imposed temperature differences

机译：施加小的温差的带有圆形毛细管芯的圆柱形热管中的传热和传质

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Highlights•A simple heat pipe is used to study the heat transfer mechanism in heat pipes.•Heat pipes are driven by the vapor pressure difference between the hot and cold ends.•Heat pipes are characterized by two dimensionless numbers H and S when ΔT/T0 ≪ 1.•Under normal operation of heat pipes, H ≫ S ≫ 1 and the Nusselt number Nu = S.•Optimal pipe length and wick thickness are found for maximum evaporative heat transfer.AbstractHeat pipes are efficient in transferring heat and have been applied in various thermal systems. Previous models of heat pipes use the heat rate through the pipe as an input parameter, and therefore lack predictive capabilities. Here, we demonstrate, using a simple heat pipe, that if the evaporation and condensing kinetics are properly modeled, then the heat rate is predicted. We consider a cylindrical heat pipe with the inner wall lined with a circular-capillary wick. The capillaries are filled with a partially wetting liquid, and the center of the pipe is filled with its vapor. Initially, the heat pipe is at temperature T0and the system is under thermodynamic equilibrium. Then, one end of the pipe is heated to T0 + ΔT, while the other end cooled to T0 − ΔT, and the system reaches a steady state. The equilibrium vapor pressure at the hot end is higher than that at the cold end, and this pressure difference drives a vapor flow. As the vapor moves, the vapor pressure at the hot end drops below the equilibrium vapor pressure which induces continuous evaporation from circular pores on the wick surface. At the cold end, the vapor pressure exceeds the equilibrium vapor pressure so that the vapor condenses and releases the latent heat. The condensate moves back to the hot end through the capillaries in the wick to complete a cycle. We assume that the pore size is infinitesimal compared with the pipe dimensions. Thus, pore-level events can be treated separately from pipe-level events. The evaporation rate in each pore is solved in the limit the evaporation numberE→∞, and an analytic leading-order solution is obtained, assuming ΔT/T0 ≪ 1. The evaporation rate is incorporated into vapor-flow and energy-balance equations along the pipe. Two dimensionless numbers emerge from these equations: the heat pipe number, H, which is the ratio of heat transfer by vapor flow to conductive heat transfer in the liquid and wall, and the evaporation exponent, S, which controls the evaporation gradient along the pipe. We find that vapor-flow heat transfer dominates in heat pipes and H ≫ S ≫ 1. Under these conditions, the non-dimensionalized heat rate through the insulated pipe is found to be simply S. Analytic solutions are also obtained for the pipe temperature and all the other variables. For maximum evaporative heat transfer, we find an optimal pipe length for fixed pipe cross-sectional dimensions, and an optimal wick thickness for a fixed pipe length. These optimal pipe length and wick thickness can help to improve the design of heat pipes and are found for the first time.
机译： 突出显示 • 一个简单的热管用于研究热管中的传热机理。 • 加热管由蒸汽压驱动 • 当ΔT/ T 0 ≪ 1时，热管的特征是两个无量纲的数字H和S。 • 下方正常o •，热管的运转，H≫ S≫ 1和Nusselt数Nu =S。 找到了最佳的管道长度和灯芯厚度，以实现最大的蒸发热传递。 < / ce：list> 摘要 热管道有效地传递热量，并已应用于各种热力系统。以前的热管模型使用通过热管的热量作为输入参数，因此缺乏预测能力。在这里，我们使用简单的热管证明，如果对蒸发和冷凝动力学进行了正确建模，则可以预测出热量。我们考虑一个圆柱形热管，其内壁衬有一个圆形毛细管芯。毛细管中充满了部分润湿的液体，管子的中央充满了蒸汽。最初，热管的温度为T 0 ，系统处于热力学平衡状态。然后，将管道的一端加热到T 0 +ΔT，而另一端冷却到T 0 < / ce：inf> −ΔT，系统达到稳定状态。热端的平衡蒸气压高于冷端的平衡蒸气压，并且该压差驱动蒸气流动。随着蒸气的移动，热端的蒸气压下降到低于平衡蒸气压的水平，该平衡蒸气压引起灯芯表面上圆形孔的连续蒸发。在冷端，蒸气压超过平衡蒸气压，因此蒸气冷凝并释放潜热。冷凝水通过灯芯中的毛细管返回热端，完成一个循环。我们假设孔径与管道尺寸相比是无限小。因此，孔隙水平事件可以与管道水平事件分开处理。每个孔中的蒸发速率在极限蒸发量中得到解决。 E → ∞ ，并假设ΔT/ T 0 ≪ 1，得到解析的前导解，并结合了蒸发速率沿管道的蒸汽流量和能量平衡方程式。从这些方程式中得出两个无因次数：热管数H，即通过蒸汽流动的热传递与液体和壁中的传导性热传递的比率，以及蒸发指数S，其控制沿管的蒸发梯度。我们发现蒸汽流传热在热管和H≫ S vapor1中占主导地位，在这种情况下，通过隔热管的无量纲热率简单地为S。所有其他变量。为了获得最大的蒸发热传递，我们找到了固定管道横截面尺寸的最佳管道长度，以及固定管道长度的最佳灯芯厚度。这些最佳的管道长度和灯芯厚度可以帮助改进热管的设计，并且是首次发现。

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    Pramesh Regmi; Harris Wong;

  • 作者单位

    Department of Mechanical and Industrial Engineering, Louisiana State University;

    Department of Mechanical and Industrial Engineering, Louisiana State University;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);
  • 原文格式 PDF
  • 正文语种 eng
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