南昌大學(xué)材料熱力學(xué)答案

1、The problems of the first law1.1 a lead bullet is fired at a frigid surface. At what speed must it travel to melt on impact, if its initial temperature is 25 and heating of the rigid surface of the rigid surface is neglected? The melting point of lead is 327. The molar heat of fusion of the lead is

2、4.8kJ/mol. The molar heat capacity CP of lead may be taken as 29.3J/(mol K)鉛子彈射向一個寒冷的表面。在什么速度必須前往融化的影響,如果它的初始溫度是25,加熱的剛性表面剛性表面被忽視?鉛的熔點為327。的摩爾熔化熱鉛是4.8焦每摩爾。摩爾熱容CP的鉛可能作為29.3 j /(摩爾K)Solution: 1.2 what is the average power production in watts of a person who burns 2500 kcal of food in a day? Estimate t

3、he average additional powder production of 75Kg man who is climbing a mountain at the rate of 20 m/min什么是平均功率的生產(chǎn)在一個人誰燃燒2500千卡的食品在一天的瓦特？估計平均加粉生產(chǎn)75公斤人誰是登高山以20米/分的速度Solution 1.3 One cubic decimeter (1 dm3) of water is broken into droplets having a diameter of one micrometer (1 um) at 20.(a) what is the

4、 total area of the droplets?(b) Calculate the minimum work required to produce the droplets. Assume that the droplets are rest (have zero velocity)Water have a surface tension of 72.75 dyn/cm at 20 (NOTES: the term surface energy (ene/cm2) is also used for surface tension dyn/cm)水一立方分米（1立方分米）被分成20，直

5、徑一微米（1微米）的液滴。（一）什么是液滴的總面積？（b）計算需要產(chǎn)生的液滴的最小工作。假定液滴墊（具有零速度）水具有72.75達(dá)因/厘米的表面張力在20（注：術(shù)語表面能量（烯/厘米2）也可用于表面張力達(dá)因/厘米）Solution 1.4 Gaseous helium is to be used to quench a hot piece of metal. The helium is in storage in an insulated tank with a volume of 50 L and a temperature of 25, the pressure is 10 atm. As

6、sume that helium is an ideal gas.(a) when the valve is opened and the gas escapes into the quench chamber (pressure=1 atm), what will be the temperature of the first gas to hit the specimen?(b) As the helium flows, the pressure in the tank drops. What will be the temperature of the helium entering t

7、he quench chamber when the pressure in the tank has fallen to 1 atm?氣態(tài)氦被用于驟冷一熱的金屬片。氦是在存儲在隔熱的罐體積為50升和25的溫度下，壓力為10個大氣壓。假設(shè)氦是一種理想的氣體。（a）該閥打開，氣體逃逸到激冷室中（壓力=1atm）中，這將是第一氣體的打試樣的溫度時？（b）由于在氦氣流，在罐中的壓力下降。會是怎樣進(jìn)入驟冷室中的氦氣的溫度時，在罐中的壓力降低到1個大氣壓？Solution: 1.5 An evacuated (P=0), insulted tank is surrounded by a very lar

8、ge volume (assume infinite volume) of an ideal gas at a temperature T0. The valve on the tank is oened and the surrounding gas is allowed to flow suickly into t(e tank until the pressure insie the tank is equals the pressure outside. Assume that no heat flow takes place. What is the0final tempeture

9、kf te gaS in the tank? The heat cap!city mf the gas, Cp and Cv each ay be(assumed to be c/nsuantp and SvMhint: one way to approach the xroblem is to define the system as the gas ends up in the tank.抽成真空（P= 0），辱罵箱由在溫度T0的一個非常大的量的理想氣體的（假定無限量）包圍。水箱上的閥是oened和周圍的氣體被允許流動suickly成噸（例如罐，直到壓力insie罐是等于外界壓力。假定沒有

10、熱流發(fā)生。這是the0final tempeture kf的TEE氣？！在罐中的熱帽城市MF的氣體，Cp和CV每個IAY被（假定為c/ nsuantp和SvMhint：接近xroblem的一種方法是定義系統(tǒng)作為氣體結(jié)束了在罐中。solution 1.6 Calculate the heat of reaction of methane with oxygen at 298K, assuming that the products of reaction are CO2 and CH4 (gas)This heat of reaction is also called the low calor

11、ific power of methane convert the answer into unites of Btu/1000 SCF of methane. SCF means standard cubic feet, taken at 298 and 1atm計算的甲烷與氧氣的反應(yīng)熱在298K，假定反應(yīng)的產(chǎn)物是二氧化碳和甲烷（天然氣）反應(yīng)的該熱也被稱為甲烷的低發(fā)熱量轉(zhuǎn)換的答案為英制熱量單位/ 1000的SCF聯(lián)信甲烷。 SCF是指標(biāo)準(zhǔn)立方英尺，在298和1大氣壓采取NOTE: this value is a good approximation for the low calorific

12、 powder of natural gasDATA: solution1.7 Methane is delivered at 298 K to a glass factory, which operates a melting furnace at 1600 K. The fuel is mixed with a quantity of air, also at 298 K, which is 10% in excess of the amount theoretically needed for complete combustion (air is approximately 21% O

13、2 and 79% N2)(a) Assuming complete combustion, what is the composition of the flue gas (the gas following combustion)?(b) What is the temperature of the gas, assuming no heat loss?(c) The furnace processes 2000kg of glass hourly, and its heat losses to the surroundings average kJ/h. calculate the fu

14、el consumption at STP (in m3/h) assuming that for gas H1600-H298=1200KJ/KG(d) A heat exchanger is installed to transfer some of the sensible heat of the flue gas to the combustion air. Calculate the decrease in fuel consumption if the combustion air is heated to 800K甲烷輸送在298K到玻璃工廠，而經(jīng)營一個熔化爐，在1600 K的燃

15、料與空氣的量在298 K，這是10的過量理論上所需要的完整的燃燒量（混合時，也空氣是約21的O 2和79N 2）（一）假設(shè)完全燃燒，什么是煙道氣（燃?xì)馊紵韵拢┑慕M成？（二）什么是氣體的溫度，假設(shè)沒有熱損失？（三）爐處理的玻璃2000公斤每小時，并且它的熱損失到周圍環(huán)境中的平均千焦耳/小時。在計算STP的燃油消耗（以m3/ h）的假設(shè)氣體H1600-H298=1200KJ/ KG（d）一個熱交換器安裝將一些煙道氣的顯熱的燃燒空氣。計算燃料消耗的降低，如果燃燒空氣被加熱到800KDATA STP means T=298K, P=1atm Solution1.8 In an investigati

16、on of the thermodynamic properties of a-manganese, the following heat contents were determined:H700-H298=12113 J/(g atom) H1000-H298=22803 J/(g atom)Find a suitable equation for HT-H298 and also for CP as a function of temperature in the form (a+bT) Assume that no structure transformation takes plac

17、e in the given tempeture rang.Solution 1.9 A fuel gas containing 40% CO, 10% CO2, and the rest N2 (by volume) is burnt completely with air in a furnace. The incoming and ongoing temperatures of the gases in the furnace are 773K and 1250K,respectively. Calculate (a) the maximum flame temperature and

18、(b) heat supplied to the furnace per cu. ft of exhaust gas Solution 1.10 (a) for the reaction ,what is the enthalpy of reaction () at 298 K ?(b) a fuel gas, with composition 50% CO, 50% N2 is burned using the stoichiometric amount of air. What is the composition of the flue gas?(c) If the fuel gas a

19、nd the air enter there burner at 298 K, what is the highest temperature the flame may attain (adiabatic flame temperature)?（a）在該反應(yīng)中，什么是在298K反應(yīng)（）的焓？（b）一種燃料氣體，以組合物中50的CO，50的N 2是利用空氣的化學(xué)計量量的燃燒。什么是煙道氣的組合物？（c）如果燃料氣體和空氣進(jìn)入燃燒器有在298K，什么是火焰可能達(dá)到的最高溫度（絕熱火焰溫度）？DATA :standard heats of formation at 298 KHeat capaci

20、ties J/(mol K) to be used for this problem N2=33, O2=33, CO=34, CO2=57Solution 1.11 a particular blast furnace gas has the following composition by (volume): N2=60%, H2=4, CO=12%, CO2=24% (a) if the gas at 298K is burned with the stochiometric amount of dry air at 298 K, what is the composition of t

21、he flue gas? What is the adiabatic flame temperature?(b) repeat the calculation for 30% excess combustion air at 298K(C)what is the adiabatic flame temperature when the blast furnace gas is preheated to 700K (the dry air is at 298K)(d) suppose the combustion air is not dry ( has partial pressure of

22、water 15 mm Hg and a total pressure of 760 mm Hg) how will thE dlaMe temperature be affected?DaTA(k J?mol) EMBED Equation.3 EMBED Equation.3 5 Solution EMBED Equation.3 (b)repeat the calculation for 30% excess0combustion air at 298K EMBED Equation.3 (C)what is the adiabatic flame temperature when th

23、e blasp furnace gas is preheated to 700K (the dry air is at 298K) (d) suppose the combustion air is not dry ( has partial pressure of water 15 mm Hg and a total pressure of 760 mm Hg) how will the flame temperature be affected? 1.12 A bath of molten copper is super cooled to 5 below its true melting

24、 point. Nucleation of solid copper then takes place, and the solidification proceeds under adiabatic conditions. What percentage of the bath solidifies?DATA: Heat of fusion for copper is 3100 cal/mol at 1803(the melting point of copper)CP,L=7.5(cal/mol), CP,S=5.41+(1.5*10-3T )(cal/mol)Solution1.13 C

25、uprous oxide (Cu2O) is being reduced by hydrogen in a furnace at 1000K,(a)write the chemical reaction for the reduced one mole of Cu2O(b)how much heat is release or absorbed per mole reacted? Given the quantity of heat and state whether heat is evolved (exothermic reaction) or absorbed (endothermic

26、reaction)氧化亞銅（氧化亞銅）正被在一爐中于1000K降低氫，（一）寫為氧化亞銅的減少一摩爾化學(xué)反應(yīng)（二）有多少熱量釋放或每摩爾吸收反應(yīng)的？鑒于熱量和狀態(tài)量的熱量是否演變（放熱反應(yīng)）或吸收（吸熱反應(yīng)）DATA: heat of formation of 1000K in cal/mol Cu2O=-41900 H2O=-59210solution,exothermic reaction1.14(a) what is the enthalpy of pure, liquid aluminum at 1000K?(b) an electric resistance furnace is u

27、sed to melt pure aluminum at the rate of 100kg/h. the furnace is fed with solid aluminum at 298K. The liquid aluminum leaves the furnace at 1000K. what is the minimum electric powder rating (kW) of furnace.DATA : For aluminum : atomic weight=27g/mol, Cp,s=26(J/molK), Cp,L=29(J/molK), Melting point=9

28、32K, Heat of fusion=10700J/molSolution1.15 A waste material (dross from the melting of aluminum) is found to contain 1 wt% metallic aluminum. The rest may be assumed to aluminum oxide. The aluminum is finely divided and dispersed in the aluminum oxide; that is the two material are thermally connecte

29、d.If the waster material is stored at 298K. what is the maximum temperature to which it may rise if all the metallic aluminum is oxidized by air/ the entire mass may be assumed to rise to the same temperature. Data : atomic weight Al=27g/mol, O=16g/mol, Cp,s,Al=26(J/molK), Cp,s, Al2O3=104J/mol, heat

30、 formation of Al2O3=-J/molSolution;1.16 Metals exhibit some interesting properties when they are rapidly solidified from the liquid state. An apparatus for the rapid solidification of copper is cooled by water. In the apparatus, liquid copper at its melting point (1356K) is sprayed on a cooling surf

31、ace, where it solidified and cools to 400K. The copper is supplied to the apparatus at the rate of one kilogram per minute. Cooling water is available at 20, and is not allowed to raise above 80. What is the minimum flow rate of water in the apparatus, in cubic meters per minute?DATA; for water: Cp=

32、4.184J/g k, Density=1g/cm3; for copper: molecular weight=63.54g/molCp=7cal/mol k, heat of fusion=3120 cal/molSolution:1.17 water flowing through an insulated pipe at the rate of 5L/min is to be heated from 20 to 60 b an electrical resistance heater. Calculate the minimum power rating of the resistan

33、ce heater in watts. Specify the system and basis for you calculation. DATA; For water Cp=4.184J/g k, Density=1g/cm3Solution: 1.18 The heat of evaporation of water at 100 and 1 atm is 2261J/mol(a) what percentage of that energy is used as work done by the vapor?(b)if the density of water vapor at 100

34、 and 1 atm is 0.597kg/m3 what is the internal energy change for the evaporation of water?Solution: 1.19 water is the minimum amount of steam (at 100 and 1 atm pressure) required to melt a kilogram of ice (at 0)? Use data for problem 1.20Solution 1.20 in certain parts of the world pressurized water f

35、rom beneath the surface of the earth is available as a source of thermal energy. To make steam, the geothermal water at 180 is passed through a flash evaporator that operates at 1atm pressure. Two streams come out of the evaporator, liquid water and water vapor. How much water vapor is formed per ki

36、logram of geothermal water? Is the process reversible? Assume that water is incompressible. The vapor pressure of water at 180 is 1.0021 Mpa( about 10 atm) Data: CP,L=4.18J/(g k), CP,v=2.00J/(g k), HV=2261J/g, Hm=334 J/gSolution:The problems of the second law2.1 The solar energy flux is about 4J cm2

37、/min. in no focusing collector the surface temperature can reach a value of about 900. If we operate a heat engine using the collector as the heat source and a low temperature reservoir at 25, calculate the area of collector needed if the heat engine is to produce 1 horse power. Assume the engine op

38、erates at maximum efficiency. 太陽能通量為約4J平方厘米/分鐘。在沒有聚焦集電極的表面溫度可達(dá)到約900的值。如果操作使用集電極作為熱源和低溫貯存器的熱機(jī)，在25，計算所需集電極的面積如果與熱機(jī)是產(chǎn)生1馬力。假設(shè)在發(fā)動機(jī)工作在最大效率。Solution2.2 A refrigerator is operated by 0.25 hp motor. If the interior of the box is to be maintained at -20 ganister a maximum exterior temperature of 35, what the

39、maximum heat leak (in watts) into the box that can be tolerated if the motor runs continuously? Assume the coefficient of performance is 75% of the value for a reversible engine.一臺冰箱由0.25馬力電機(jī)。如果該箱的內(nèi)部被保持在-20ganister的35的最高表面溫度，什么最大熱泄漏（以瓦特為單位）到可容忍的盒子，如果馬達(dá)連續(xù)運(yùn)行？假定的性能系數(shù)為一可逆發(fā)動機(jī)的值的75。Solution:2.3 suppose an

40、 electrical motor supplies the work to operate a Carnot refrigerator. The interior of the refrigerator is at 0. Liquid water is taken in at 0 and converted to ice at 0. To convert 1 g of ice to 1 g liquid. H=334J/g is required. If the temperature outside the box is 20, what mass of ice can be produc

41、ed in one minute by a 0.25 hp motor running continuously? Assume that the refrigerator is perfectly insulated and that the efficiencies involved have their largest possible value.Solution: 2.4 under 1 atm pressure, helium boils at 4.126K. The heat of vaporization is 84 J/mol what size motor (in hp)

42、is needed to run a refrigerator that must condense 2 mol of gaseous helium at 4.126k to liquid at the same temperature in one minute? Assume that the ambient temperature is 300K and that the coefficient of performance of the refrigerator is 50% of the maximum possible.Solution: 2.5 if a fossil fuel

43、power plant operating between 540 and 50 provides the electrical power to run a heat pump that works between 25 and 5, what is the amount of heat pumped into the house per unit amount of heat extracted from the power plant boiler.(a) assume that the efficiencies are equal to the theoretical maximum

44、values(b) assume the power plant efficiency is 70% of maximum and that coefficient of performance of the heat pump is 10% of maximum(c) if a furnace can use 80% of the energy in fossil foe to heat the house would it be more economical in terms of overall fissile fuel consumption to use a heat pump o

45、r a furnace ? do the calculations for cases a and b如果化石燃料電廠的540和50運(yùn)行提供了電力運(yùn)行的熱泵是25和5之間工作，什么是熱抽的熱量進(jìn)入屋內(nèi)每單位量的電廠中提取的金額鍋爐。（一）假設(shè)效率是等于最大理論值（二）假設(shè)的電廠效率達(dá)到最大的70，而熱泵的性能系數(shù)是最大值的10（c）若一爐可以使用能量的化石敵人80，以加熱房子會是更經(jīng)濟(jì)的整體裂變?nèi)剂舷氖褂脽岜没蛉蹱t的條件？做計算的情況下，A和Bsolution: 2.6 calculate U and S when 0.5 mole of liquid water at 273 K is m

46、ixed with 0.5 mol of liquid water at 373 K and the system is allowed to reach equilibrium in an adiabatic enclosure. Assume that Cp is 77J /(mol K) from 273K to 373KSolution: 2.7 A modern coal burning power plant operates with a steam out let from the boiler at 540 and a condensate temperature of 30

47、.(a) what is the maximum electrical work that can be produced by the plant per joule of heat provided to the boiler?(b) How many metric tons (1000kg) of coal per hour is required if the plant out put is to be 500MW (megawatts). Assume the maximum efficiency for the plant. The heat of combustion of c

48、oal is 29.0 MJ/k g(c) Electricity is used to heat a home at 25 when the out door temperature is 10 by passing a current through resistors. What is the maximum amount of heat that can be added to the home per kilowatt-hour of electrical energy supplied?Solution: 2.8 an electrical resistor is immersed

49、 in water at the boiling temperature of water (100) the electrical energy input into the resistor is at the rate of one kilowatt(a) calculate the rate of evaporation of the water in grams per second if the water container is insulated that is no heat is allowed to flow to or from the water except fo

50、r that provided by the resistor(b) at what rate could water could be evaporated if electrical energy were supplied at the rate of 1 kw to a heat pump operating between 25 and 100data for water enthalpy of evaporation is 40000 J/mol at 100; molecular weight is 18g/mol; density is 1g/cm3solution:2.9 s

51、ome aluminum parts are being quenched (cooled rapidly ) from 480 to -20 by immersing them in a brine , which is maintained at -20 by a refrigerator. The aluminum is being fed into the brine at a rate of one kilogram per minute. The refrigerator operates in an environment at 30; that is the refrigera

52、tor may reject heat at 30. what is them minus power rating in kilowatts, of motor required to operate the refrigerator?Data for aluminum heat capacity is 28J/mol K; Molecular weight 27g/molSolution:2.10 an electric power generating plant has a rated output of 100MW. The boiler of the plant operates

53、at 300. The condenser operates at 40(a) at what rate (joules per hour) must heat be supplied to the boiler?(b) The condenser is cooled by water, which may under go a temperature rise of no more than 10. What volume of cooling water in cubic meters per hour, is require to operate the plant?(c) The bo

54、iler tempeture is to be raised to 540,but the condensed temperature and electric output will remain the same. Will the cooling water requirement be increased, decreased, or remain the same? Data heat capacity 4.184, density 1g/cm3Solution: 2.11 (a) Heat engines convert heat that is available at diff

55、erent temperature to work. They have been several proposals to generate electricity y using a heat engine that operate on the temperature differences available at different depths in the oceans. Assume that surface water is at 20, that water at a great depth is at 4, and that both may be considered

56、to be infinite in extent. How many joules of electrical energy may be generated for each joule of energy absorbed from surface water? (b) the hydroelectric generation of electricity use the drop height of water as the energy source. in a particular region the level of river drops from 100m above sea

57、 level to 70m above the sea level . what fraction of the potential energy change between those two levels may be converted into electrical energy? how much electrical energy ,in kilowatt-hours, may be generated per cubic meter of water that undergoes such a drop?Solution: 2.12 a sports facility has

58、both an ice rink and a swimming pool. to keep the ice frozen during the summer requires the removal form the rink of 105 KJ of thermal energy per hour. It has been suggested that this task be performed by a thermodynamic machine, which would be use the swimming pool as the high temperature reservoir. The ice in the rink is to be maintain at a temperature of 15, and