热能英语第三版哈工大部分翻译 Heat transfer involving motion in a fluid caused by the difference in density and the action of gravity is called natural or free convection. Heat transfer coefficients for natural convection are generally much lower than for forced convection ,and it is therefore important not to ignore radiation in calculating the total heat loss or gain. Radiant transfer may be of the same order of magnitude as natural convection, even at room temperatures, since wall temperatures in a room can affect human comfort. 传热涉及流体中密度差异和重力的作用引起的流体运动称为自然或自由对流。自然对流传热系数通常要低于强制对流,因此,重要的是计算总热量损失或增加时不要忽略辐射。即使在室温条件下，辐射传热可能和自然对流是同一个数量级的,因为在一个房间里壁温度会影响人类生活的舒适度。 Water vapor is one of the products of combustion for all fuels which contain hydrogen. The heat content of a fuel depends on whether this water vapor is allowed to remain in the vapor state or is condensed to liquid. In the bomb calorimeter the products of combustion are cooled to the initial temperature and all of the water vapor formed during combustion is condensed to liquid. This gives the high, or gross, hest content of the fuel with the heat of vaporization included in the reported value. For the low, or net heat of combustion, it is assumed that all products of combustion remain in the gaseous state. 水蒸气是所有含有氢的燃料燃烧产物之一。燃料的热含量取决于水蒸气被允许留在蒸汽状态还是凝结成液体。在弹式量热计中燃烧产物被冷却到初始温度，所有在燃烧过程中形成的水蒸气凝结成液体。这给了高位发热量,或总发热量,热量包括燃料的报告值中的蒸发热。对于低发热量,或净燃烧热量,是假设所有燃烧产物是气态的情况下。 Fluid flow can be compressible or incompressible, Liquids can usually be considered as flowing in compressible. But even a highly compressible gas may sometimes undergo unimportant changes in density. Its flow is then practically incompressible. In flight at speed of sound in air(described by subsonic aerodynamics),the motion of the air relative to the wings is one of nearly incompressible flow. 流体有可压缩及不可压缩的,液体通常可以被认为是不可压缩的流体。但即使一个高度可压缩气体有时可能在密度上不发生显著的变化，它的流动几乎是不可压缩流动。以远低于空气中声速的速度飞行时(亚音速空气动力学),空气的运动相对机翼来说几乎是不可压缩流动。 Extensive experimental investigations have established the values of thermal conductivities of many substances and the effect of temperature on these conductivities. Note that the thermal conductivity of any metal is very high in comparison with that of any gas. The reported values thermal conductivities of metals are valid only for metals of a given degree of purity. Particularly for those metals with the highest values of thermal conductivity, the introduction of a slight amount of another metal will cause a significant change in the thermal conductivity. 广泛的实验研究已经确定了许多物质导热系数的值的和温度对这些传导系数的影响。请注意,任何金属的导热系数比任何气体高很多。金属导热系数实验值只对给定的纯度金属是对应有效的。特别是对于那些具有最高导热系数的金属,引入一个轻微的数量的另一个金属会导致热导系数的显著的变化。 The equipment diagram for the basic vapor compression cycle is illustrated in Fig.4.1.minimum components of this cycle include compressor , condenser , expansion valve and evaporator . the ideal cycle considers hest transfer in the condenser and evaporator without pressure losses , a reversible 本文来源：https://www.wddqw.com/doc/2c3ebad3cbd376eeaeaad1f34693daef5ef71368.html