第三章 理想气体的性质和理想气体的热力过程
英文习题
1. Mass of air in a room
Determine the mass of the air in a room whose dimensions are 4 m×5 m×6 m at 100 kPa and 25℃
2. State equation of an ideal gas
A cylinder with a capacity of 2.0 m contained oxygen gas at a pressure of 500 kPa and 25℃ initially. Then a leak developed and was not discovered until the pressure dropped to 300 kPa while the temperature stayed the same. Assuming ideal-gas behavior, determine how much oxygen had leaked out of the cylinder by the time the leak was discovered.
3
3. Two tanks are connected by a valve. One tank contains 2 kg of carbon monoxide gas at 77oC and
0.7 bar. The other tank holds 8 kg of the same gas at 27oC and 1.2 bar. The valve is opened and the gases are allowed to mix while receiving by heat transfer from the surrounding. The equilibrium temperature is 42℃ Using the model, determine (a) the final equilibrium in bar, and (b) the heat transfer for the in kJ.
Carbon Monoxide2kg, 77oC0.7barTank 1valveFIGURE 3-1Carbon Monoxide8kg, 27oC1.2barTank 2energy final ideal gas pressure, process,
4. Electric heating of air in a house
The electric heating systems used in many houses consist of a simple duct with resistance wires. Air is heated as it flows over resistance wires. Consider a 15-kW electric system. Air enters heating section at 100 kPa and 17oC with a volume flow rate of m/min. If heat is lost from the air in the duct to the surroundings at a rate of 200 W, determine the exit temperature CP=1.005 kJ/(kg. K).
FIGURE 3-23
the 150 of air.
5. Evaluation of the Δu of an ideal gas
Air at 300 K and 200 kPa is heated at constant pressure to 600 K. Determine the change in internal energy of air per unit mass, using (a) data from the air table, (b) the functional form of the specific heat, and (c) the average specific heat value.
6. Properties of an ideal gas
A gas has a density of 1.875 kg/m at a pressure of 1 bar and with a temperature of 15oC. A mass of 0.9 kg of the gas requires a heat transfer of 175 kJ to raise its temperature from 15oC to 250oC while the pressure of the gas remains constant. Determine (1) the characteristic gas constant of the gas, (2) the specific heat capacity of the gas at constant pressure, (3) the specific heat capacity of the gas at constant volume, (4) the change of internal energy, (5) the work transfer.
FIGURE 3-33
7. Freezing of chicken in a box
A supply of 50 kg of chicken at 6℃ contained in a box is to be frozen to -18℃ in a freezer. Determine the amount of heat that needs to be removed. The latent heat of the chicken is 247 kJ/kg, and its specific heat is 3.32 kJ/kg.℃ above freezing and 1.77 kJ/kg.℃ below freezing. The container box is 1.5 kg, and the specific heat of the box material is 1.4 kJ/kg.℃. Also, the freezing temperature of chicken is -2.8℃.
8. Closed- system energy balance
A rigid tank which acts as a perfect heat insulator and which has a negligible heat capacity is divided into two unequal parts A and B by a partition. Different amounts of the same ideal gas are contained in the two parts of the tank. The initial conditions of temperature T, pressure p, and total volume V are known for both parts of the tank. Find expressions for the equilibrium temperature T and pressure P reached after of the partition. Calculate the entropy change for A and B and entropy change of the tank. Assume that Cv,m is constant,
0.2MPa300K0.01m3A0.1MPa300K0.01m3Bremoval the total
9. Thermal processes of an ideal gas
3
3
FIGURE 3-4An air receiver has a capacity of 0.85 m and contains air at a temperature of 15℃ and a pressure of 275 kN/m. An additional mass of 1.7 kg is pumped into the receiver. It is then left until the temperature becomes 15℃ once again. Determine (1) the new pressure of the air in the receiver, (2) the specific enthalpy of the air at 15℃ if it is assumed that the specific enthalpy of the air is zero at 0℃. Take cp=1.005 kJ/kg.K, cc=0.715 kJ/kg.K.
10. Air is compressed steadily by a reversible compressor from an inlet state of 100KPa and 300K to
an exit pressure of 900 kPa. Determine the compressor work per unit mass for isentropic compression with k=1.4, (1) isentropic compression with k=1.4, (2) polytropic compression with n=1.3, (3) isothermal compression, and (4) ideal two-stage compression with intercooling with a polytropic exponent of 1.3.
11. A rigid cylinder contains a “floating” piston, free to move within the cylinder without friction. Initially,
it divided the cylinder in half, and on each side of the piston the cylinder holds 1 kg of the same ideal gas at 20oC, and 0.2 MPa . An electrical resistance heater is installed on side A of the cylinder, and it is energized slowly to PA2=PB2=0.4 MPa. If the tank and the piston are perfect heat insulators and are of negligible heat capacity, cv=0.72 kJ/(kg·K). Calculate（1）the final temperatures, volumes of A,B sides, （2）the amount of heat added to the system by the resistor. (3）the entropy changes of A,B sides, （4）the total entropy change of the cylinder.
工程热力学与传热学
第三章 理想气体的性质和热力过程 习题
习 题
1 理想气体的cp和cV之差及cp和cV之比是否在任何温度下都等于一个常数？
2
如果比热容是温度t的单调增函数，当t2 >t1时平均比热容c0,c0,ct中哪一个最大？哪一个
1t1t2t2最小？ 3
如果某种工质的状态方程式遵循pv?RgT，这种物质的比热容一定是常数吗？这种物质的比
热容仅是温度的函数吗？ 4
在p-v图上画出定比热容理想气体的可逆定容加热过程，可逆定压加热过程，可逆定温加热过
程和可逆绝热膨胀过程。 5
将满足空气下列要求的多变过程表示在p-v图和T-s图上：
（1）空气升压，升温，又放热； （2）空气膨胀，升温，又吸热；
（3）n=1.6的膨胀过程，并判断q，w，?u的正负： （4）n=1.3的压缩过程，并判断q，w，?u的正负。 6 7 8 9
在T-s图上，如何将理想气体任意两状态间的热力学能和焓的变化表示出来。 凡质量分数较大的组元气体，其摩尔分数是否也一定较大？试举例说明之。 理想混合气体的比热力学能是否是温度的单值函数？其cp-cV是否仍遵循迈耶公式？
有人认为，由理想气体组成的封闭系统吸热后，其温度必定增加，这是否完全正确？你认为哪
一种状态参数必定增加？
10 一绝热刚性汽缸，被一导热的无摩擦的活塞分成两部分，最初活塞被固定在某一位置，汽缸的一侧储有0.4MPa，30℃的理想气体0.5kg，而另一侧储有0.12MPa，30℃，0.5kg的同样气体。然后放开活塞任其自由移动，最后两侧达到平衡。设比热容为定值。试求：（1）平衡时的温度(℃)；（2）平衡时的压力（MPa）。
11 如图所示的两室（图中跑面线代表绝热），由绝热且与汽缸间无摩擦的活塞隔开。开始时。两室的体积均为0.1m3，分别储有空气和氢气，压力各为0.9807×105Pa，温度各为15℃。若对空气侧加热，直到两室内气体压力升高到1.9614×105Pa 为止。求空气的终温及外界加入的热量。已知空气的cV=715.94J/（kg.K），kH2=1.41。
12 6kg的空气，由初态p1=0.3MPa，t1=30℃经下列不同过程膨胀到同一终压p2=0.1MPa；（1）定温过程；（2）定熵过程；（3）n=1.2。试比较不同过程中空气对外所做的膨胀功，交换的热量和终温。 13 2kg的某种理想气体按可逆多变过程膨胀到原有体积的3倍，温度从300℃降为60℃，膨胀期间作膨胀功418.68kJ，吸热83.736kJ，求cp和cV。
14 某气体的摩尔质量为29×10-3kg/mol，由t1=320℃定容加热到t2=940℃，若过程中热力学能变化量?u=700kJ/kg，试按理想气体计算其焓和熵的变化量。
15 空气进入活塞式压气机的状态为p1=0.1MPa，t1=27℃，经可逆绝热过程压缩到t2=207℃，求压缩过程终了空气的压力，热力学能的变化量及过程中空气与外界交换的功量。（1）按定值比热容计算；（2）按空气热力性质表的数据计算。
16 某理想气体在定压过程中吸收了3349kJ的热量，设cV=0.741kJ/(kg.K)，Rg=0.297kJ/（kg..K）。
求其对外所作的功及热力学能的变化。
17 某理想气体由初态p1=0.5171MPa，V1=0.142m3，经一热力过程至p2=0.172MPa，V2=0.274m3，过程中气体的焓变?H=-65.4kJ。已知其比定容热容为cV=1.4kJ/(kg.K)，求（1）气体热力学能的变化?U；（2）气体的比定压热容cp。
习题课
理想气体状态方程的应用
18 启动柴油机用的空气瓶, 体积 V=0.3 m, 内装有p1=8 MPa，Tl=303 K 的压缩空气。启动后, 瓶中空气压力降低为 p2=4.6 MPa, 这时 T2=303 K。求用去空气的量 (mol) 及相当的质量 (kg)。
19 某活塞式压气机向容积为 9.5m 的储气箱中充入空气。压气机每分钟从压力为 po=750 mmHg, 温度为t0=15 ℃的大气中吸入 0.2m 的空气。若充气前储气箱压力表读数为0.5 bar, 温度为 t1 = 17 ℃。问经过多少分钟后压气机才能使储气箱内气体的压力提高到p2 =7bar,温度升为t2=50 ℃。
20 某电厂有三台锅炉合用一个烟囱, 每台锅炉每秒产生烟气 73 m(已折算成标准状态下的体积 ), 烟囱出口处的烟气温度为 100 ℃, 压力近似为 101.33 kP啊, 烟气流速为30 m/s。 求烟囱的出口直径。
理想气体的性质和计算
21 为了提高进人空气预热器的冷空气温度, 采用再循环管, 如图所示。己知冷空气的初始温度为 t1=20 ℃, 空气容积流量 为 VOl = 90000m/h(标准状态下)。从再循环管引来的热空气温 度t3=350 ℃。
(1) 若将冷空气温度提升至 t2=40 ℃, 求引出的热空气量。 设过程进行时的压力不变。
(2) 又若热空气再循环管内空气表压力为 150 mmH20, 流速为20 m/s， 当地的大气压为Pb=750 mmHg, 求再循环管的直径。
22 一绝热刚性气缸, 被一导热的无摩擦活塞分成两部分。最初活塞 被固定在某一位置上, 气缸的一侧储有压力为 0.2MPa，温度为 300K 的 0.01m 的空气，另一侧储有同容积，同温度的空气，其压力为 0.1MPa。去除销钉,放松活塞任其自由移动, 最后两侧达到平衡。设空 气的比热容为定值。试计算：
3
3
3
33
3
热空气350 ℃ 烟气 再循环管 40℃ 冷空气20 ℃ 空气预热器 A 0.2 MPa 300K 30.01m B 0.1 MPa 300K 30.01m （1） 平衡时的温度为多少？ （2） 平衡时的压力为多少？
（3） 两侧空气的熵变值及整个气体的熵变值为多少？
23 某绝热的刚性容器，若用一隔板将其分为A和B两个不相等的部 分，其内各装有不同数量的同一种理想气体，如图所示。气体状态参数 初始值是已知的。试推导隔板抽出后气体的平衡温度和平衡压力表达式。
理想气体的热力过程
24 在一个承受一定重量的活塞下有 27 ℃ 的空气 0.4 kg , 占据容积 0.25 m 。 试问（1）当加入25 kJ 热量后, 其温度上升到多少 ? 并作了多少功 ?
（2）若活塞到达最后位置后予以固定, 此后再继续加入 25 kJ 热量, 则其压力上至多少 ?
25 2kg 空气分别经过定温膨胀和绝热膨胀的可逆过程, 如图所示。从初态 PI = 9.807bar，t I = 300℃ 膨胀到终态容积为初态容积的 5 倍。 试计算（1）不同过程中空气的终态参数；
（2）对外界所作的功和交换的热量； （3）过程中热力学能，焓，熵的变化量。 设空气cp0 = 1.004kJ/(kg·K), R=O.287kJ/(kg·K), p 1 T T 1 2 2’ 3
A PATA VA B PBTB VB v 2 2’ s 0 K = 1.4 。
v 0 s 26 1kg 空气在多变过程中吸取 41.87kJ的热量时, 将使其容积增大 10 倍, 压力降低 8 倍。 求 : (1) 过程中空气的热力学能变化量；
(2) 空气对外所作的膨胀功及技术功。设空气 cvo=O.716kJ/(kg·K), K=1.4 。
27 在一具有可移动活塞的封闭气缸中, 储有温度 t1= 45 ℃, 表压力为pgl=10 kPa 的氧气0.3m。在定压下对氧气加热, 加热量为 40 kJ；再经过多变过程膨胀到初温 45 ℃, 压力为 18 kPa。设环境大气压力为 0.1 MPa, 氧气的比热容为定值。 求 : (1) 两过程的焓变量及所作的功；
(2) 多变膨胀过程中气体与外界交换的热量。
28 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, 压力均为0.45 MPa，温度同为900K。现对A侧冷却水管通水冷却，A侧压力逐渐降低。
求：（1）压力降低到0.3 MPa时，A，B两侧的体积是多少？ （2）冷却水从系统带走的热量是多少？
Q3
AB
百度搜索“77cn”或“免费范文网”即可找到本站免费阅读全部范文。收藏本站方便下次阅读，免费范文网，提供经典小说综合文库第三章 理想气体的性质与热力过程在线全文阅读。
相关推荐：