(完整版)建筑环境与设备工程专业英语段落翻译

2. Conduction（导热）

The best heat-insulating solids own their insulating properties to the air or to other gases contained in cells within the material.（最好的隔热材料在空气和材料细胞中拥有自己的绝热性能。）These cells cause the heat to flow through the solid material through a long tortuous passage. （这些细胞使热量需要通过一个漫长曲折的通道才能流过这个坚实的固体。）In addition, the available cross-sectional area of the solid material is much less than the projected area. （另外，见识的固体材料可用的横截面面积比投影面你少得多。）Experimental evidence shows that many small unicellular pockets of gas are much more effective than a series of connected cells having the same total volume in giving insulating value to a substance. （试验表明，一个物体在给定的总量上具有相同的绝热值上，许多小口袋气体单细胞比的一系列连通细胞更加有效）There may be considerable variation in the thermal conductivity of any given insulating material because the conductivity depends on its density, the size and number of its air cells, and its absorbed moisture.（在任何给定的绝热材料的导热系数方面有很大的差异，这是因为导热系数取决于它的密度，空气细胞的大小和数量，和它吸收的水蒸气。）

3. Natural Convection（自然对流）

Consider heat transfer by natural convection between a cold fluid and a hot surface.（考虑到冷流体和热表面之间的自然对流换热。）The fluid in immediate contact with the surface is heated by conduction, becomes lighter and rises because of the difference in density of the adjacent fluid. （流体在表面直接接触通过传导加热，将变的更轻，也会上升，这是由于相邻流体的密度差异。）The motion is resisted by the viscosity of the fluid. （这种运动会被流体的粘度所抵制）The heat transfer is influenced by（传热的影响）: (1) gravitational force due to thermal expansion, (2) viscous drag and (3) thermal diffusion.（由于热力膨胀的引力，粘性阻力和热扩散。）It may be expected to depend on the gravitational acceleration g, the coefficient of thermal expansion β，the kinematic viscosity ν(=μ/ρ), and the thermal diffusivityα= (κ/ρc p). （这是可以预测的，这取决于引力加速度，g，热膨胀系数β，运动粘度ν(=μ/ρ)，和热扩散系数α=(κ/ρc p)。）These variables can be expressed in terms of dimensionless number（这些热量可以早无量纲方面表示）: the Nusselt number, Nu, is a function of the product of the Prandtl number, Pr, and Grashof number, Gr, which, when combined, depend on the fluid properties, the temperature difference between

the surface and the fluid, ∆t, and the characteristic length of the surface, L. （努谢尔特数，Nu；普朗特数推导的函数，Pr，和格拉晓夫数；Gr，在混合条件下，取决于流动的特性，温差取决于流体和表面温度的不同，∆t；表面特征长度，L。）The constant c and exponent n depend on the physical configuration and nature of flow.（系数c和指数n取决于不同的物理构造和流动性质。）

Natural convection can affect the transfer coefficient in the of weak forced convection. （自然对流可以影响现存在的微弱的受迫对流的传导系数。）As the forced convection effect , i.e. , the Reynolds number, increases, the “mixed convection ”(superimposed forced-on-free convection) gives way to the pure forced convection regime.（对于受迫对流的影响，即雷诺数，增加，“混合对流”（加上自然对流影响的受迫对流）被单纯的受迫对流区域所替代。）Since the heat transfer coefficient in the mixed convection region is often larger than calculated based on the natural or forced convection heat transfer.（由于在混合对流区域的传热系数往往大雨基于自然对流或受迫对流的换热计算结果。）The reference given before summarizes natural, mixed, and forced convection regimes for vertical and horizontal tubes.（在作出参考之前总结了纵向和横向管段的自然、混合和受迫对流区域。）