工程熱力學(xué)與傳熱學(xué)習(xí)題(英文版)：第五章 水蒸氣與濕空氣

1、第五章 水蒸氣和濕空氣水蒸氣英文習(xí)題1. Volume and energy change during evaporation A mass of 200 g of saturated liquid water is completely vaporized at constant pressure of 100 kPa. Determine (a) the volume change and (b) the amount of energy added to the water.2. Pressure and volume of a mixture A rigid tank contain

2、s 10 kg of water at 90. If 8 kg of the water is in the liquid form and rest is in the vapor form. Determine (a) the pressure in the tank and (b) the volume of the tank.3. Properties of saturated liquid-vapor mixtureAn 80-L vessel contains 4 kg of refrigerant-134a at a pressure of 160 kPa. Determine

3、(a) the temperature of the refrigerant, (b) the quality, (c) the enthalpy of the refrigerant, and (d) the volume occupied by the vapor phase.4. Charging of a rigid tank by steam A rigid insulated tank that is initially evacuated is connected through a valve to a supply line that carries steam at 1 M

4、Pa and 300. Now the valve is opened, and steam is allowed to flow slowly into the tank until the pressure reaches 1 MPa, at which point the valve is closed. Determine the final temperature of the steam in the tank.濕空氣英文習(xí)題1. The amount of water vapor in room air A 5-m 5-m3-m room shown in Fig.5-1 con

5、tains air at 25 and 100 kPa at a relative humidity of 75 percent. Determine (a) the partial pressure of dry air, (b) the specific humidity, (c) the enthalpy per unit mass of the dry air, and (d) the masses of the dry air and water vapor in the room.2. Fogging of the windows in a house In cold weathe

6、r, condensation frequently occurs on the inner surfaces of the windows due to the lower air temperatures near the window surface. Consider a house, shown in Fig.5-6, that contains air at 20 and 75 percent relative humidity. At what window temperature will the moisture in the air start condensing on

7、the inner surfaces of the windows?3. The specific and relative humidity of airThe dry and the wet-bulb temperatures of atmospheric air at 1 atm (101.325 kPa) pressure are measured with a sing psychrometer and determined to be 25 and 15, respectively. Determine (a0 the specific humidity, (b0 the rela

8、tive humidity, and the enthalpy of the air.4. Heating and humidification of air An air-conditioning system is to take in outdoor air at 10 and 30 percent relative humidity at a steady rate of 45 m3/min and to condition it to 25 and 60 percent relative humidity. The outdoor air is first heated to 22

9、in the heating section and then humidified by the injection of hot steam in the humidifying section. Assuming the entire process takes place at a pressure of 100 kPa, determine (a) the rate of heat supply in the heating section and (b) the mass flow rate of the steam required in the humidifying sect

10、ion.5. Cooling and dehumidification of airAir enters a window air conditioner at 1 atm, 30, and 80 percent relative humidity at rate of 10 m2/min, and it leaves as saturated air at 14. Part of the moisture in the air that condenses during the process is also removed at 14. Determine the rates of hea

11、t and moisture removal from the air.工程熱力學(xué)與傳熱學(xué)第五章 水蒸氣與濕空氣 習(xí)題習(xí) 題1. 熱水泵必須安裝在熱水容器下面距容器有一定高度的地方，而不能安裝在熱水容器的上面，為什么？2. 鍋爐產(chǎn)生的水蒸氣在定溫過程中是否滿足q=w的關(guān)系？為什么？3. 有無0或低于0的蒸汽存在？有無高于400的水存在，為什么？4. 25MPa的水，是否也象1MPa的水那樣經(jīng)歷汽化過程？為什么？5. dh=cpdT適用于任何工質(zhì)的定壓過程，水蒸氣定壓汽化過程中dT=0，由此得出結(jié)論，水定壓汽化時(shí)dh=cpdT=0，此結(jié)論是否正確，為什么？6. 試解釋濕空氣，濕蒸汽，飽和濕空氣。

12、7. 在相同的溫度和壓力下，濕空氣與干空氣相比，哪個(gè)密度大？8. 同一地區(qū)，陰雨天的大氣壓力為什么比晴朗天的大氣壓力低？9. 兩種濕空氣的總壓力和相對(duì)濕度相同，問溫度高的濕空氣含濕量大，還是溫度低的濕空氣含濕量大？為什么？10. 早晨有霧，為什么往往是好天氣？11. 冬季，室內(nèi)玻璃窗內(nèi)側(cè)為什么會(huì)結(jié)霜？12. 為什么陰雨天晾衣服不宜干，而晴天宜干？13. 冬季室內(nèi)供暖，為何要加濕？14. 霉季時(shí)，為何冷水管的表面常有水滴出現(xiàn)？15. 試?yán)盟魵獗?，判斷下列各點(diǎn)的狀態(tài)，并確定各狀態(tài)的焓，熵，干度及比體積。（1）p=20MPa，t=300；（2）p=9MPa，v=0.017m3/kg；（3）p=4

13、.5MPa，t=450；（4）p=1MPa，x=0.9。16. 某汽輪機(jī)入口蒸汽的壓力p1=1.3MPa，t1=350，出口蒸汽壓力p2=0.005MPa。假設(shè)蒸汽在汽輪機(jī)內(nèi)進(jìn)行理想絕熱膨脹，忽略進(jìn)出口動(dòng)能差，求每千克蒸汽流過汽輪機(jī)所作的軸功及乏汽（排氣）的溫度和干度。17. 蒸汽在p=1.5MPa。x=0.95的狀態(tài)下進(jìn)入過熱器，被定壓加熱成為過熱蒸汽后進(jìn)入汽輪機(jī)，理想絕熱膨脹至p=0.005MPa，x=0.9的出口狀態(tài)，求每千克蒸汽在過熱器中吸收的熱量。習(xí) 題 解 答1. 答；避免熱水汽化。2. 答：不滿足，水蒸氣是實(shí)際氣體，其熱力學(xué)能是溫度和比體積的函數(shù)，定溫過程中熱力學(xué)能變化不為0，故

14、定溫過程中。3. 答：有0和低于0的蒸汽存在，無400的水，因?yàn)樗呐R界溫度為pcr=22.064MPa，tcr=373.99，當(dāng)蒸汽的溫度超過臨界溫度時(shí)，無論如何增加壓力，也不可能將汽態(tài)轉(zhuǎn)變?yōu)橐簯B(tài)。4. 答；不能，壓力超過臨界壓力，飽和液體和飽和蒸汽的差別完全消失，對(duì)水進(jìn)行加熱，會(huì)由飽和水馬上轉(zhuǎn)變?yōu)轱柡驼羝?. 答：不正確，水蒸氣定壓汽化階段，比定壓熱容趨于。6. 答；濕空氣是含有水蒸氣的空氣；濕蒸汽是飽和水和飽和水蒸汽共存時(shí)的狀態(tài)；飽和濕空氣是由干空氣和飽和水蒸氣組成的空氣。7. 答：在大氣壓力和溫度相同的情況下，濕空氣的密度將永遠(yuǎn)小于干空氣的密度。8. 答：在同一水平面上,如果氣壓分布

15、不均勻，如果某地區(qū)的氣壓低,周圍地區(qū)的空氣就在水平方向上向該地區(qū)流入，使該地區(qū)的空氣上升，上升的空氣因所受的壓強(qiáng)減小而膨脹，溫度降低，空氣中的水汽凝結(jié)。所以，低氣壓中心地區(qū)常常是陰雨天。.9. 答：根據(jù)；知濕空氣的總壓力和相對(duì)濕度相同時(shí)，溫度高的濕空氣含濕量大。10. 答：有時(shí)候早晨起來，只見迷迷蒙蒙一片大霧，打開門窗，它也會(huì)象輕煙一樣飄進(jìn)來?？墒遣灰嗑?，你可以依稀看見窗外的景物了，最后終于霧散氣朗，麗日當(dāng)空。俗話說：早晨地罩霧，盡管曬稻谷，正是這個(gè)意思。早晨有霧，大氣是潮濕的，白天太陽照射地面，地面積累了大量的熱，由于水分的蒸發(fā)，溫度較高的空氣也能夠容納較多的水汽，因此空氣中的水汽比較多。

16、太陽下山以后，熱量就開始向空中散發(fā)，接近地面的空氣的溫度也隨著降低，天氣越好，天空中的云越少，地面的熱不受任何阻礙，散發(fā)得越快，空氣濕度也降得越低。到了后半夜和早晨，地面空氣的溫度已經(jīng)降得很低了，這時(shí)候，就是在室內(nèi)，我們也很容易感覺到上半夜涼得多。接近地面的空氣溫度降低以后，空氣里的水汽超過了飽和狀態(tài)，多余的水汽就凝結(jié)成細(xì)小的水滴，分布在低空，這就是氣象學(xué)上所說的輻射霧，這種霧通常產(chǎn)生在高氣壓中心附近，而在高氣壓中心附近，常常是晴好天氣。所以出現(xiàn)這種霧的時(shí)候，盡管早晨濃霧彌漫，只要太陽一出，把霧氣蒸散，這一天就多半是晴天。11. 答：冬季，室內(nèi)外空氣溫差較大，靠近玻璃窗內(nèi)側(cè)的室內(nèi)空氣被定壓冷卻

17、，當(dāng)空氣溫度降低到水蒸氣分壓力對(duì)應(yīng)的飽和溫度時(shí)，此時(shí)空氣中的水蒸氣達(dá)到飽和狀態(tài)，并開始有水滴從空氣中戲出，若溫度降低并低于零度，這時(shí)析出的水滴便結(jié)霜。12. 答；陰雨天，空氣中相對(duì)濕度較大，既空氣中水蒸氣含量較多，此時(shí)空氣的吸濕能力較差，陰雨天晾衣服不宜干；晴天時(shí)，相對(duì)濕度較小，濕衣服中的水分容易被吸收，晾衣服宜干。13. 答：室內(nèi)供暖，隨著室內(nèi)空氣溫度不斷升高，室內(nèi)空氣的相對(duì)濕度降低，空氣變得干燥，使人感到不舒服。故要在供熱的同時(shí)，向空氣中加入一定的水分，保證室內(nèi)空氣具有一定的濕度。14. 答：霉季時(shí)，空氣中相對(duì)濕度較大，水蒸氣的分壓力較大，冷水管表面溫度較低，當(dāng)其溫度低于水蒸氣分壓力對(duì)應(yīng)的飽和溫度時(shí)（露點(diǎn)），空氣中的水蒸氣轉(zhuǎn)變?yōu)轱柡退魵?，并有蒸汽凝結(jié)為水，從空氣中析出。15. 答：（1）未飽和水狀態(tài)，h=1333.4 kJ/kg，s=3.2072 kJ/(kg.K)