【正文】 At any point in a fluid, Pressure is the same in all directions. ? Pressure in a fluid increases linearly with depth. （液體中的壓力隨液體的深度線性增加） ? Pressure is the same at all points on a horizontal plane in a given continuous fluid at rest. （帕斯卡定律） . zgPPP ?????? ?12④ 壓力 p的測量 Pressure Measuring 絕對壓力與環(huán)境壓力的 相對值 —— 相對壓力 注意： 只有絕對壓力 p 才 是狀態(tài)參數(shù) 示意圖 Utube manometer Bourdon Tube 環(huán)境壓力與大氣壓力 指壓力表所處環(huán)境 注意： 環(huán)境壓力 一般為 大氣壓 ，但不一定。 Gage pressure（表壓力） is denoted as Pg 真空度表示絕對壓力低于大氣壓力的量值 Vacuum pressure （真空度）： Pressures below atmosphere pressure. It is the pressure difference between atmospheric and system pressure when system pressure is lower than atmospheric And it is denoted as PVAC or H. ④ 表壓與真空度 Gage Pressure and Vacuum Pressure 表壓力 =絕對壓力 大氣壓力 真空度 =大氣壓力 絕對壓力 絕對壓力與相對壓力 當(dāng) p pb 表壓力 pg gbp p p??當(dāng) p pb 真空度 pv bvp p p??pb pe p pv p relative pressure absolute pressure Gage pressure Vacuum pressure Attentions ? 如果大氣壓力發(fā)生變化，即使工質(zhì)的絕對壓力不變，測壓計的對數(shù)也會變，所以只有絕對壓力才是狀態(tài)參數(shù)。 Absolute pressure is the actual pressure at a given position P . 相對壓力反映絕對壓力與當(dāng)?shù)卮髿鈮毫Φ牟钪怠? Specific volume is the reciprocal of density and is defined as volume per unit mass. ?1??mVv kgm /3比體積是表示物質(zhì)內(nèi)部分子疏密程度的狀態(tài)參數(shù)。 2. Property （狀態(tài)參數(shù)） （ 2）狀態(tài)參數(shù)的特征 Characteristics of State Properties A. 狀態(tài)確定，則狀態(tài)參數(shù)也確定，反之亦然 Properties of a state are determined by the state. If the state is specified, its properties are fixed, or vise versa. B. 狀態(tài)參數(shù)的積分特征 ： 狀態(tài)參數(shù)的變化量與路徑無關(guān)，只與初終態(tài)有關(guān) The magnitude of the change in property is independent of the path (route), but just depend on the initial and final states. 1221xxdxxx??? ? ? 0dzC. 狀態(tài)參數(shù)的微分特征 ：全微分 Properties are functions of state, there exist differential for properties t h e n),( if yxfz ?dyyzdxxzdz ?????????After a series of change, the state returns to the original one, then the changes in its properties are ‘0’ 狀態(tài)參數(shù)的微分特征 設(shè) z =z (x , y) dz是全微分 y xzzd z d x d yxy???????? ???????? ??充要條件： 22zzx y y x???? ? ? ?可判斷是否是狀態(tài)參數(shù) Total differentials 壓力 p、溫度 T、比容 v （容易測量） (1)密度和比容 Density and Specific Volume 密度指單位體積所含物質(zhì)的多少。 （ A quantity of matter or a region in space chosen for study.） For example: 氣缸 活塞裝置 Cylinderpiston equipment 汽輪機(jī) Steam turbine (1) 外界（ Surroundings） The mass or region outside the system （ 2） 邊界（ Boundary） The real or imaginary surface that separates the system from its surroundings. (3) 系統(tǒng)與外界之間的質(zhì)量及能量交換都必須穿越邊界 The mass or energy exchange between system and its surroundings must cross the boundaries. 2. 系統(tǒng)，外界和邊界 System, Surroundings and boundary (4) Characteristics of Boundary ? 邊界是人為選定的 Boundaries are selected subjectively. ? 邊界可以是固定的，也可以是可移動的Boundaries can be fixed or movable. ? 邊界可以是真實的，也可以是假想的Boundaries can be real or imaginary. 熱力系統(tǒng)選取的人為性 鍋 爐boiler 汽輪機(jī) (turbine) 發(fā)電機(jī) (generator) 給水泵 (pump) 凝汽器(condenser) 過熱器(reheater) 只交換功 只交換熱 既交換功 也交換熱 真實、虛構(gòu) 固定、活動 fixed 、 movable real 、 imaginary 熱力系 外界 物質(zhì)交換 能量交換 物質(zhì)流進(jìn)和流出熱力系統(tǒng) 傳熱和作功兩種形式 Types of systems Energy can cross the boundary, in the form of heat and work. (1) 以系統(tǒng)與外界關(guān)系劃分： 有 無 是否傳質(zhì) 開口系 閉口系 是否傳熱 非絕熱系 絕熱系 是否傳功 非絕功系 絕功系 是否傳熱、功、質(zhì) 非孤立系 孤立系 閉口系與外界無物質(zhì)交換 A Closed system (a control mass 控制質(zhì)量 ) consists of a fixed amount of mass, and no mass can cross its boundary. That is, no mass enters or leave a closed system. such as, Pistoncylinder device (汽缸 活塞裝置 ） A. 閉口系統(tǒng)和開口系統(tǒng) Closed system and Open system An Open system (or a control volume 控制體積 ） is a properly selected region in space. Both mass and energy can cross the boundary of a control volume. such as, A Water heater, a turbine and a pressor, etc 開口系與外界有物質(zhì)交換 絕熱系統(tǒng)與外界之間無熱量交換 Adiabatic system is that no heat cross the boundary or heat is negligible pared with work cross the boundary 孤立系統(tǒng)與外界之間無任何物質(zhì)和能量交換 Isolated system is a special case that no mass and energy cross the boundary. B. 絕熱系統(tǒng)和孤立系統(tǒng) Adiabatic system and Isolated system 1 2 3 4 m Q W 1 ? 開口系 非孤立系＋相關(guān)外界 ＝ 孤立系 1+2 ? 閉口系 1+2+3 ? 絕熱閉口系 1+2+3+4 ? 孤立系 （ 2）其它分類方式 其它分類方式 物理化學(xué)性質(zhì) 均勻系（ Even System) 非均勻系 (Uneven System) 工質(zhì)種類 多元系 (multi substance system) 單元系 (Single substance system) 相態(tài) 多相 (Multiple Phase) 單相 (Single Phase) 最重要的系統(tǒng) 只交換熱量和一種準(zhǔn)靜態(tài)的容積變化功 容積變化功 壓縮功膨脹功 簡單可壓縮系統(tǒng) Simple pressible system Moving Boundary Work Compression Work Expansion Work 167。第一章 基本概念 Chapter 1. Basic Concepts ? 熱力系統(tǒng)（ Thermodyn