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1、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
2、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 volum
3、e 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 m
4、oisture.（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 rise
5、s 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) therm
6、al 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 ，the kinematic viscosity (= / ), and the thermal diffusivity=( / cp). （这是可以预测的，这取决于引力加速度，g，热膨胀系数 ，运动粘度 (= / ) ，和热扩散系数= ( / cp) 。 ）These variables can be expressed
7、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
8、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 for
9、ced 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
10、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 tube
11、s.（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。）Local conditions influence the values of the convection coefficient in a mixed convection regime, but the references permit locating the pertinent regime and approximating the convection coefficient.（当地条件影响了在混合对流区域的对流系数的值，但是可引用当地区域相关允许值和近似得到对流换热系数。 ）6. Fundamentals
12、 of industrial Ventilation （工业通风的基础）In essence this boils down to heat transfer and mass transfer between the incoming air and air the already within the building.（从本质上讲，这归结于进入的空气和已经在建筑物内的空气的传热和传质。 ）If owing to excessive internal heat production the temperature of the air in the building tends to ex
13、ceed the specified norms, cooler air is introduced and mixed with the indoor air; the temperature of the air (owning to heat transfer) then remains at the norm. （这是由于建筑物内部产热过多导致空气的温度往往超过规定的指标，引入冷的空气引入与室内空气混合（由于传热），使空气温度保持不变。 ）If harmful gases or vapours are released, their concentration is heldwithi
14、n specified limits by dilution with the clean incoming air.（如果有害挥发性气体被释放掉，它的浓度将会被在一定范围内通过引入室外清洁空气来稀释。）7. Natural Ventilation Fields of Application （自然通风的应用领域）The time has long passed when it was necessary to demonstrate the benefits of natural ventilation and justify its application. The proofs were
15、 simple and very convincing.（时间已经过去很久了当它有必要去表明自然通风的好 处 和 证明 它 的 可用 性 。 ）They were based on comparisons of mechanical ventilation and natural ventilation. （这是基于自然通风和机械通风的比较。 ）In hot shops where all the emphasis was laid on mechanical ventilation, and natural air change, being regarded as unimportant,
16、 was not taken into account at all.（在热的车间里，所有的重点是机械通风， 自然通风被认为是无足轻重的，没有被重视到的。）It was found in all the tests that the volume of natural air change many times exceeded the volume of mechanical ventilation. （很多测试表明，自然通风的换气量几倍于机械通风的换气量。 ）This revealed the negligible role of general mechanical ventilation despite its heavy installation and running costs. （这表明，全面的机 械 通 风 是 不 会 估 计 到 它 的 很 大 的 装 备 和 运 行 花 费 。 ）Mechanical ventilation in these cases was best used as a corrective to na
