热工第二章习题课

p3=105 Pa , A3=0.3 m2, cf3= ?, t3= ?
8. 某燃气轮机装置，如图。已知压缩机进口处空气的比焓
h1=290 kJ/kg。经压缩后 , 空气升温使比始增为 h2 =580 kJ/kg。在截面2处空气和燃料的混合物以 c f 2 =20 m/s的速度进入燃烧室, 在定压下燃烧, 使工质 吸入热量 q = 670 kJ/kg。燃烧后燃气进入喷管绝热膨
Determine the net amount of heat added to the air in kJ/kg.
p1 100kPa
1
T1 20C
1 1.19kg / m3 1
c f 1 130m / s
A1 0.112m2
Q
Ws
2
p2 180kPa T2 150C
（1）压缩过程中对每公斤气体所作的功 ; （2）每生产 1 kg的压缩气体所需的功 ; （3）带动此压气机至少要多大功率的电动机 ？
习题
课 稳定流动能量方程式的应用
7. 现有两股温度不同的空气，稳定地流过如图所示
的设备进行绝热混合, 以形成第三股所需温度的空
气流。各股空气的已知参数如图中所示。
设空气可按理想气体计，其焓仅是温度的函数,
Tutorial
Energy Balance for Steady-Flow Systems
13. Consider a gas turbine power plant with air as the working fluid, Air enters at 100kPa, 20ºC (ρ=1.19kg/m3), with a velocity of 130m/s through an opening 0.112m2 cross-sectional area. After being compressed, heated and expanded through a turbine, the air leaves at 180kPa, 150ºC (ρ=1.48kg/m3), through an opening of 0.100m2 cross-sectional area. The power output of the plant is 375kW. The internal energy and enthalpy of the air are given in kJ/kg by U=0.717T and h=1.004T, where T is temperature on the Kelvin scale.
（1）B中气体的热力学能变化ΔUB； （2）A和B总的热力学能变化ΔUA+B。
Βιβλιοθήκη Baidu
Q=20kJ
A
B
习题
课 闭口系统能量方程式的应用
3. 由生物力学测定可知，一个人在静止时向环 境的散热率为400kJ/h。在一个容纳2000人 的礼堂里，由于空调系统发生故障，求：
（1）故障后20min内，礼堂中空气的热力学 能增加量；
Tutorial
Energy Balance for Steady-Flow Systems
12. Air passes through a gas turbine system at a rate of 4.5 m /s. It enters the turbine system with a velocity of 90 m /s and a specific volume of 0.85 m3/kg. It leaves the turbine system with a specific volume of 1.45 m3/kg. The exit area of the turbine system is 0.038 m2. In its passage through the turbine system, the specific enthalpy of the air is reduced by 200 kJ/kg and there is a heat transfer loss of 40 kJ/kg. Determine (a) the inlet area of the turbine in m2; (b) the exit velocity of the air in m /s; (c) the power developed by the turbine system in kilowatts.
（2）假定礼堂和环境无热量交换，将礼堂和 所有的人取为热力系，该系统热力学能 变化为多少？
习题
课 闭口系统能量方程式的应用
4. 一闭口系统从状态1沿1-2-3途径到状态3，传递给
外界的热量为47.5kJ，而系统对外作功为30kJ，
如图示，
（1）若沿1-4-3途径变化时，系统对外作功15kJ，
求过程中系统与外界传递的热量。
Tutorial
The first law of thermodynamics
11. An adiabatic tank similar to the one that Joule used in determining the mechanical-thermal energy equalities contains 10 kg of water. A 110 V, 0.1 A motor drives a paddle wheel and runs for 1 hr. Determine the change of specific and total internal energy of the water.
2 1.48kg / m3 2 A2 0.100m2
Tutorial
Energy Balance for Steady-Flow Systems
14. Air is compressed in a frictionless steady-flow process from 90kPa, 150ºC (v=0.918m3/kg), to 130kPa in such a manner that p(v+0.250)=constant, where v is in m3/kg, inlet velocity is negligible small, and discharge velocity is 110m/s. Calculate the work required per kilogram of air.
工程热力学与传热学
工程热力学 第二章 热力学第一定律
习题
习题
课 闭口系统能量方程式的应用
1. 一活塞汽缸设备内装有5kg的水蒸气，由初态
的热力学能 u1=2709.0kJ/kg 膨胀到 u2=2659.6kJ/kg，过程中加给水蒸气的热量 为80kJ，通过搅拌器的轴输入系统18.5kJ的
轴功。若系统无动能，位能的变化，试求通过
（1）单位质量蒸汽流经汽轮机对外输出的功； （2）不计进出口动能的变化，对输出功的影响； （3）不计进出口位能差，对输出功的影响； （4）不计散热损失，对输出功的影响； （5）若蒸汽流量为220t/h，汽轮机功率有多大。
6. 空气在某压气机中被压缩。压缩前空气的参数是 p1 =0.1MPa, v1 = 0.845m3/kg, 压缩后的参数是 p2 =0.8 MPa, v2= 0.175 m3/kg。假定在压缩过 程中, 1 kg 空气的热力学能增加146 kJ, 同时向 外放出热量 50 kJ, 压气机每分钟生产压缩空气 10 kg。 求 :
胀到状态3’, h 3' = 800 kJ/kg, 流速增加到 cf 3' , 此燃气进入动叶片, 推动转轮回转作功。若燃气在动叶
片中的热力状态不变 , 最后离开燃气轮机的速度
c f 4 = 100 m/s o
求:
（1）若空气流量为100 kg/s, 压气机消耗的功率为多大?
（2）若燃气的发热值 qB=43 960 kJ/kg , 燃料的耗量为 多少?
（3）燃气在喷管出口处的流速 c f 3' 是多少? （4）燃气轮机的功率为多大?
（5）燃气轮机装置的总功率为多少?
Tutorial
Expansion work, useful work
9. Consider the expansion of air inside a cylinder. Let the initial volume be 0.025 m3 and the initial pressure be 10MPa. Let the expansion process be quasi-static and let the path be given by pV1.4 =constant. If the final volume of the gas is 0.20 m3, determine (a) the total amount of work done by the gas; (b) the amount of work done by the gas against the spring.
活塞所作的功。
u1=2709.0kJ/kg
u2=2659.6kJ/kg
5 kg
W peddle= -18.5kJ
Q=80 kJ
W piston= ?
习题
课 闭口系统能量方程式的应用
2. 如图所示，一刚性汽缸，一端受热，其他部分 绝热，内有一不透热的活塞，活塞与缸壁间无 摩擦。现自容器一端传热，Q=20kJ，由于活塞 移动对B作功10kJ。求：
Tutorial
The first law of thermodynamics
10. An inventor claims to have developed a workproducing cycle which receives 1000 kJ of heat from a heat source, rejects 200 kJ of heat to a heat sink, and produces a net work of 700 kJ . How do we evaluate this claim?
p1 90kPa
v1 0.918m3 / kg 1 cf1 0
1
Win
2
2 p2 130kPa c f 2 110m / s
Tutorial
Energy Balance for Steady-Flow Systems
15. A mixture of air and water vapor with an enthalpy of 120kJ/kg enters the dehumidifying section of an air-conditioning system at a rate of 320kg/hr, liquid water drains out of the dehumidifier with an enthalpy of 42 kJ/kg at a rate of 7.0kg/hr. An air vapor mixture leaves with an enthalpy of 47kJ/kg. Determine the rate of heat removal from the fluids passing through the dehumidifier.
按 |h|kJ/kg = 1. 004 |T|K计算， 理想气体的状态方 程为 pv= RgT, Rg=287 J/(kg. K) 。若进出口截面 处的动、位能变化可忽略,
试求出口截面的空气温度和流速。
绝热 cf1=10 m/s, A1=0.1 m2, t1=5 ℃, p1=105 Pa cf2=15 m/s, A2=0.15 m2, t2=37 ℃, p2=105 Pa
（2）若系统从状态3沿图示曲线途径到达状态1，
外界对系统作功6kJ，求该过程中系统与外界
传递的热量。
p
（3）若U2=175kJ，U3=87.5kJ，
1
2
求过程2-3传递的热量及
状态1的热力学能。
4
3
0 V
习题
课 稳定流动能量方程式的应用
5. 某一蒸汽轮机，进口蒸汽参数为p1=9.0MPa， t1=500℃，h1= 3386.8 kJ/kg，cf1=50m/s， 出口蒸汽参数为p2=4.0kPa，h2= 2226.9 kJ/kg， cf2=140m/s，进出口高度差为12m， 每kg蒸汽经汽轮机散热损失为15kJ. 试求：