工程热力学与传热学：2008-2009 期末A.doc

中国石油大学（北京）2008-2009学年度第1学期储运2006《工程热力学与传热学》期末试卷—A卷（闭卷）姓名： 班级： 学号： 工程热力学传热学总分题号一二三四五得分All the answers be written on the answer sheetThermodynamics一. PROBLEMS ( 30 points for total )1 Consider a well insulated rigid tank that is divided into two compartments by a partition. Initially, one side holds air, while the other side is evacuated. The partition Is now removed, and the air fills the entire tank. Analysis: (1) the change of internal energy of the air;(2) Is the work done by air? （6 points）2 Write the applicable conditions of the expressions.（8 points）.(1); (2); (3); (4) 3 Describe the change of enthalpy（焓）of ideal gas during a process from an initial state 1 to a final state 2 in T-s diagram.（4 points）4 A system undergoes a process between two fixed states first in a reversible manner and then in an irreversible manner. For which case is the entropy change greater? Why? （4 points）5 According to the T-s figure of an ideal regenerative rankle cycle（回热循环）, describe the thermal processes involved in the cycle. Write the expression of thermal efficiency. （8 points）二. CALCULATION（30 points for total）1 Consider a well insulated horizontal rigid cylinder that is divided into two compartments by a piston that is free to move but does not allow either gas to leak into the other side. Initially, one side holds 0.5kg of the ideal gas at 30C, and 0.4MPa, while the other side holds 0.5kg of the same ideal gas at 30C, and 0.12MPa. Now thermal equilibrium is established in the cylinder as a result of heat transfer through the piston.（1） Find expressions for the equilibrium temperature T and pressure P reached. （2） Calculate the entropy changes for A and B and the total entropy change of the cylinder. Assume that Cv,m is constant, Rg=0.287kJ/(kg.K). （15 points）2 An inventor claims to have devised a heat pump which exchanges heat with reservoirs at 393K and 300K, the work is provided by a heat engine which exchanges heat with two constant temperature reservoirs at 1200 K and 300 K. The heat engine absorbs heat QH=1100 kJ, produces work Wnet=742.5kJ Determine：(1) Can the heat engine work? reversible or irreversible?(2) If the heat pump rejects heat Q1=2400 kJ，can the heat pump work? reversible or irreversible?(3) The maximum amount of heat that heat pump produces Q1,max.（15 points）Heat Transfer三. PROBLEMS ( 24 points for total )1 Describe the expressions (1) Fourier’s law; (2) Fin efficiency;(3) The surface resistance to radiation（表面辐射热阻）;(4) The space resistance to radiation（空间辐射热阻）.（6 points）2 The nondimensionalized equation of laminar boundary layer on a flat plate of constant temperature is . Write the definitions and meanings of Nu, Re, Pr.（6 points）3 Describe the characteristics of the velocity and thermal boundary layer.（6 points）4 The figure shows a ideal gray diffuse surface.Try to write the radiation energy involved with the surface. Write the expressions of radiosity（有效辐射） and net radiation heat transfer（净辐射热流）of the surface. （6 points）四. CALCULATION（16 points for total）A Steam pipe with an outside radius of 4cm is covered with a layer of asbestos（石棉）insulation [λ=0.15W/(m.℃) ] 1cm thick, which is in turn covered with fiberglass（玻璃纤维）insulation [λ=0.05W/(m.℃) ] 3cm thick. The outside surface of the steam pipe is at a temperature of 330℃, and the outside surface of the fiberglass insulation is at 30℃.Determine (1) the heat transfer rate per meter length of the pipe and; (2) the interface temperature between the asbestos and the fiberglass insulation. 中国石油大学（北京）2006-2007学年度第一学期储运2004《工程热力学与传热学》期末试卷——A卷（闭卷）工程热力学部分五. 判断对错（每题1分，共计5分）1 气体被压缩时一定消耗外功；（ ）2 理想混合气体中，各组元的体积分数等于其摩尔分数；（ ）3 不可逆过程的熵变无法计算；（ ）4 当m公斤的河水与G公斤的沸水具有相同的热力学能时，它们的可用能一定相同；（ ）5 湿空气的含湿量d一定时，温度越高，其吸湿能力越强；（ ）六. 问答题（共计18分）1. 将满足以下要求的理想气体多变过程表示在同一个p-v图和T-s图上(1)理想气体的定温，定压，定容和定熵过程；(2)工质又膨胀，又降温，又放热的多变过程。

5分）2. 欲设计一台热机，使之能从温度为973K的高温热源吸热2000 kJ，并向温度为303K的低温热源放热800 kJ，问此循环能否实现？（4分）3. 解释湿空气的露点温度，说明将未饱和湿空气转变为饱和湿空气的方法4分）4. 如图为蒸汽一次回热循环的T-s图， 指出各相应过程的特点，并写出热效率的计算公式5分）七. 计算题（共计30分）1 有一汽缸和活塞组成的系统，汽缸壁和活塞均由绝热材料制成，活塞可在汽缸中无摩擦地自由移动初始时活塞位于汽缸中间，A，B两侧各有1 kg空气，两边的压力、温度都相同, 并有PA1= PB1 =0.45 MPa，TA1= TB1= 900K现对A侧冷却水管通水冷却，A侧压力逐渐降低，直至压力降低到PA2= PB2= 0.3 MPa时试计算：（1） A，B两侧的体积，温度是多少？（2） 冷却水从系统带走的热量是多少？（3） A，B腔内气体的熵变及整个气体组成的系统熵变是多少？按定值比热容计算且k=1.4, cV=0.717 kJ/(kgK) 15分）2 将1 kmol理想气体在400K下从0.1 MPa缓慢地定温压缩到1.0 MPa，试计算下列三种情况下此过程气体的熵变，热源的熵变和总熵变。

1） 过程无摩擦，热源温度为400K；（2） 过程无摩擦，热源温度为300K；（3） 过程有摩擦，比可逆压缩多消耗20%的功，热源温度为300K15分）传热学部分四. 回答问题（共计21分）5 一个具体导热问题的完整数学描述应包括哪些方面？写出直角坐标系，无内热源，常物性，非稳态三维导热的微分方程4分）6 写出如图角部边界节点温度的有限差分方程式2分）7 流体自然对流换热特征数关联式包括哪些准则，写出各准则的表达形式及物理意义6分）8 以流体外掠平板时流动边界层为例，分析说明边界层内热量交换的特点5分）9 如图，两表面组成一封闭系统，试确定角系数的值已知两表面面积A1，A24分）五. 计算题（共计26分）1 用热电偶测量气体的温度热电偶近似为球形，直径为0.5mm，初始温度。