SCYC51090 57617276-C 58053899 SCYC 51090 硬盘控制板 ABB
出于暖通空调目的，空气被视为不可压缩流体。
对于不可压缩流体，封闭系统中的流体量为
常数任何流出都必须被等价的流入抵消，或者
系统中保持的流体量必须发生变化。这是
质量守恒定律允许我们考虑流体在
就像我们在银行里数钱一样。详见参考文献3
讨论这个主题。
*另见16章。
暖通空调工程基础：1部分
下载自数字工程图书馆@McGraw-Hill（www.digitalengineeringlibrary.com）
版权所有©2004麦格劳-希尔公司。版权所有。
任何使用均受网站上给出的使用条款的约束。
暖通空调工程基础：1部分7
1.6热力学*
热力学与物质的热特性有关
与宇宙的自然亲和力，从更高到更高
低能量状态。热力学研究物质的能力
接受能量水平的变化（将比热作为一种特性）
并将焓作为能量水平的测量尺度）。为此
在提醒段落中，请记住：
物质的能量接受能力称为比热
英制单位为Btu每磅每华氏度。水
比热为1.0 Btu/（lb F）是佳的受热介质之一。
相位变化中的能量接受能力称为
从液体到气体（即水到蒸汽）的蒸发潜热
以及从液体到固体（即水到冰）的熔化潜热。
同样，水的蒸发潜热约为
1000 Btu/lb和144 Btu/lb的熔化潜热非常好
在恒定温度下涉及大量能量的
相变。
热力学可用于检查制冷循环
使用数学工具和技术分析
设备和系统。
热力学一定律说“能量守恒”对于
就金钱而言，我们可以考虑能源投入、产出和
存储热力学与流体力学的结合使我们
计算背负在流体流上的能量流
信心。
热力学二定律说，能量留给自己
总是从高到低，从快到慢，从暖到冷。
要使事情向上发展，否则，我们必须消耗能量。
没有永动机这样的东西。
湿度测量学是热力学的一个专业，涉及湿空气（空气和水蒸气的混合物）的物理。参见参考文献4
本主题的进一步讨论。
1.7传热†
在研究热传递时，我们研究通过质量运动的能量
通过传导，通过对流从固体到移动液体，或
通过辐射从一个物体到另一个物体。记得：
SCYC51090 57617276-C 58053899 SCYC 51090 硬盘控制板 ABB
SCYC51090 57617276-C 58053899 SCYC 51090 硬盘控制板 ABB
For HVAC purposes, air is considered to be an incompressible fluid.
For incompressible fluids, the amount of fluid in a closed system is
constant. Any outflows must be offset by equivalent inflows, or there
must be a change in the amount of fluid held in the system. This is
the Law of Conservation of Mass and allows us to account for fluid in
a process just as we count money in the bank. See Ref. 3 for further
discussion of this topic.
*See also Chap. 16.
HVAC Engineering Fundamentals: Part 1
Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com)
Copyright © 2004 The McGraw-Hill Companies. All rights reserved.
Any use is subject to the Terms of Use as given at the website.
HVAC Engineering Fundamentals: Part 1 7
1.6 Thermodynamics*
Thermodynamics has to do with the thermal characteristics of matter
and with the natural affinity of the universe to go from a higher to a
lower energy state. Thermodynamics deals with the ability of matter
to accept changes in energy level (relates to specific heat as a property
and to enthalpy as a scale of measurement of energy level). For this
reminder paragraph, remember:
The energy acceptance capacity of a substance is called specific heat
with English units of Btu per pound per degree Fahrenheit. Water
with a specific heat of 1.0 Btu/ (lb F) is one of the best heataccepting media.
The energy acceptance capacity in a change of phase is called the
latent heat of vaporization from liquid to gas (i.e., water to steam)
and latent heat of fusion from liquid to solid (i.e., water to ice).
Again, water with a latent heat of vaporization of approximately
1000 Btu/ lb and a latent heat of fusion of 144 Btu/ lb is very good
at involving large quantities of energy at constant temperature in
the phase change.
Thermodynamics can be used to examine the refrigeration cycles
with mathematical tools and techniques to analyze performance of
equipment and systems.
The first law of thermodynamics says that ‘‘energy is conserved.’’ For
matter as for money, we can account for energy inputs, outputs, and
storage. Combining thermodynamics with fluid mechanics allows us
to calculate energy flows piggybacked onto fluid flows with accuracy
and confidence.
The second law of thermodynamics says that energy left to itself
always goes from high to low, from fast to slow, from warm to cold.
To make things go uphill, to go otherwise, we must expend energy.
There is no such thing as a perpetual-motion machine.
Psychrometrics is a specialty of thermodynamics involving the physics of moist air, a mixture of air and water vapor. See Ref. 4 for
further discussion of this topic.
1.7 Heat Transfer†
In studying heat transfer, we study energy in motion—through a mass
by conduction, from a solid to a moving liquid by convection, or from
one body to another through space by radiation. Remember:
SCYC51090 57617276-C 58053899 SCYC 51090 硬盘控制板 ABB
