Thermodynamics

espectively. If the pressure rise of oil in the pump is measuredto be 400 kPa and the motor efficiency is 90 percent,determine the mechanical efficiency of the pump.Pump12 cm8 cmOil∆P = 400 kPa0.1 m 3 /sFIGURE P2–77Motor35 kW2–78E A 73-percent efficient pump with a power input of12 hp is pumping water from a lake to a nearby pool at a rateof 1.2 ft 3 /s through a constant-diameter pipe. The free surfaceof the pool is 35 ft above that of the lake. Determine themechanical power used to overcome frictional effects inpiping. Answer: 4.0 hpEnergy and Environment2–79C How does energy conversion affect the environment?What are the primary chemicals that pollute the air?What is the primary source of these pollutants?2–80C What is smog? What does it consist of? How doesground-level ozone form? What are the adverse effects ofozone on human health?2–81C What is acid rain? Why is it called a “rain”? Howdo the acids form in the atmosphere? What are the adverseeffects of acid rain on the environment?2–82C What is the greenhouse effect? How does the excessCO 2 gas in the atmosphere cause the greenhouse effect?What are the potential long-term consequences of greenhouseeffect? How can we combat this problem?2–83C Why is carbon monoxide a dangerous air pollutant?How does it affect human health at low and at high levels?2–84E A Ford Taurus driven 15,000 miles a year will useabout 715 gallons of gasoline compared to a Ford Explorerthat would use 940 gallons. About 19.7 lbm of CO 2 , whichcauses global warming, is released to the atmosphere when agallon of gasoline is burned. Determine the extra amount ofCO 2 production a man is responsible for during a 5-yearperiod if he trades his Taurus for an Explorer.2–85 When a hydrocarbon fuel is burned, almost all of thecarbon in the fuel burns completely to form CO 2 (carbondioxide), which is the principal gas causing the greenhouseChapter 2 | 103effect and thus global climate change. On average, 0.59 kg ofCO 2 is produced for each kWh of electricity generated from apower plant that burns natural gas. A typical new householdrefrigerator uses about 700 kWh of electricity per year.Determine the amount of CO 2 production that is due to therefrigerators in a city with 200,000 households.2–86 Repeat Prob. 2–85 assuming the electricity is producedby a power plant that burns coal. The average productionof CO 2 in this case is 1.1 kg per kWh.2–87E Consider a household that uses 11,000 kWh of electricityper year and 1500 gallons of fuel oil during a heatingseason. The average amount of CO 2 produced is 26.4lbm/gallon of fuel oil and 1.54 lbm/kWh of electricity. If thishousehold reduces its oil and electricity usage by 15 percentas a result of implementing some energy conservation measures,determine the reduction in the amount of CO 2 emissionsby that household per year.2–88 A typical car driven 12,000 miles a year emits to theatmosphere about 11 kg per year of NO x (nitrogen oxides),which cause smog in major population areas. Natural gasburned in the furnace emits about 4.3 g of NO x per therm, andthe electric power plants emit about 7.1 g of NO x per kWh ofelectricity produced. Consider a household that has two carsand consumes 9000 kWh of electricity and 1200 therms ofnatural gas. Determine the amount of NO x emission to theatmosphere per year for which this household is responsible.FIGURE P2–8811 kg NO xper yearSpecial Topic: Mechanisms of Heat Transfer2–89C What are the mechanisms of heat transfer?2–90C Does any of the energy of the sun reach the earth byconduction or convection?2–91C Which is a better heat conductor, diamond or silver?2–92C How does forced convection differ from naturalconvection?2–93C Define emissivity and absorptivity. What is Kirchhoff’slaw of radiation?2–94C What is blackbody? How do real bodies differ froma blackbody?