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34 Chapter 1 Getting Started

(e) The composition of a closed system cannot change. (f) According to Archimedes’ principle, the magnitude of the buoyant force acting on a submerged body is equal to the weight of the body.

1.61 Answer the following true or false. Explain.

(a) A refrigerant at an absolute pressure of 0.8 atm is at a gage pressure of 0.2 atm. (b) Temperature is the property that is the same for each of two systems when they are in thermal equilibrium.

(c) The Rankine degree is a smaller temperature unit than the Kelvin degree. (d) A vessel holding 0.5 kmol of oxygen (O 2 ) contains 16 lb of O 2 . (e) A control volume is a special type of closed system that does not interact in any way with its surroundings. (f) The pressure unit psia indicates an absolute pressure expressed in pounds force per square inch.

c DESIGN & OPEN ENDED PROBLEMS: EXPLORING ENGINEERING PRACTICE

1.1D In the United States today, nearly all of our electricity is produced by fossil-fuel power plants burning coal or natural gas, nuclear power plants, and hydroelectric power plants. Using the Internet, determine the percent contributions of these types of electricity generation to the U.S. total. For each of the four types, determine at least three significant environmental considerations associated with it and how such environmental aspects affect the respective plant design, operation, and cost. Write a report with at least three references.

1.2D Mercury is recognized as a significant biohazard. This has led to the elimination of mercury-in-glass thermometers (see Energy & Environment in Sec.1.7.1) and increasing regulation of coal-fired power plants, emissions from which are the major source of U.S. soil and water mercury con- tamination. Investigate medical complications of mercury exposure and their economic impact. Report your findings in a well-documented PowerPoint presentation.

1.3D Ecological footprints measure humankind’s demands on nature. Using the Internet, estimate the amount of land and water needed annually to support your con- sumption of goods and services and to absorb your wastes. Prepare a memorandum reporting your estimates and listing at least three things you can do to reduce your footprint.

1.4D One type of prosthetic limb relies on suction to attach to an amputee’s residual limb. The engineer must consider the required difference between atmospheric pressure and the pressure inside the socket of the prosthetic limb to develop suction sufficient to maintain attachment. What other considerations are important as engineers design this type of prosthetic device? Write a report of your findings including at least three references.

1.5D Design a low-cost, compact, light-weight, hand-held, human-powered air pump capable of directing a stream of air for cleaning computer keyboards, circuit boards, and hard-to-reach locations in electronic devices. The pump cannot use electricity, including batteries, nor employ any chemical propellants. All materials must be recyclable. Owing to existing patent protections, the pump must be a distinct alternative to the familiar tube and plunger bicycle pump and to existing products aimed at accomplishing the specified computer and electronic cleaning tasks.

1.6D Magnetic resonance imaging (MRI) employs a strong magnetic field to produce detailed pictures of internal organs and tissues. As shown in Fig. P1.6D , the patient reclines on a table that slides into the cylindrical opening where the field is created. Considering a MRI scanner as a system, identify locations on the system boundary where the system interacts with its surroundings. Also describe significant occurrences within the system and the measures taken for patient comfort and safety. Write a report including at least three references.

MRI scanner

Fig. P1.6D

1.7D A major barrier to wider deployment of solar power systems by homeowners and small businesses is the initial cost to purchase and install rooftop components. Today some U.S. municipalities and utilities are developing plans to assist property owners to acquire such components through loans and leasing arrangements. Investigate and critically evaluate these and other options for fostering deployment of solar power systems discovered through design-group brainstorming and use of the Internet. Report your findings in a poster presentation.

1.8D The sphygmomanometer commonly used to measure blood pressure is shown in Fig. P1.8D . During testing, the cuff is placed around the patient’s arm and fully inflated by repeated squeez- ing of the inflation bulb. Then, as the cuff pressure is gradually reduced, arterial sounds known as Korotkoff sounds are monitored with a stethoscope. Using these sounds as cues, the systolic and diastolic pressures can be identified. These pressures are reported in terms of the mercury column length, in mmHg. Investigate the physical basis for the Korotkoff sounds, their role in identifying the systolic and diastolic pressures, and why these pressures are significant in medical practice. Write a report including at least three references.

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group basis. The project might involve a device or technique for minimally invasive surgery, an implantable drug-delivery device, a biosensor, artificial blood, or something of special interest to you or your design group. Take several days to research your project idea and then prepare a brief written proposal, including several references, that provides a general statement of the core concept plus a list of objectives. During the project, observe good design practices such as discussed in Sec. 1.3 of Thermal Design and Optimization, John Wiley & Sons Inc., New York, 1996, by A. Bejan, G. Tsatsaronis, and M. J. Moran. Provide a well-documented final report, including several references.

1.11D Conduct a term-length design project involving the International Space Station pictured in Table 1.1 done on either an independent or a small-group basis. The project might involve an experiment that is best conducted in a low- gravity environment, a device for the comfort or use of the astronauts, or something of special interest to you or your design group. Take several days to research your project idea and then prepare a brief written proposal, including several references, that provides a general statement of the core concept plus a list of objectives. During the project, observe good design practices such as discussed in Sec. 1.3 of Thermal Design and Optimization, John Wiley & Sons Inc., New York, 1996, by A. Bejan, G. Tsatsaronis, and M. J. Moran. Provide a well-documented final report, including several references.

Air

One-way valve

Inflation bulb

Mercury column

Pressure release valve

patm

pc

Cuff pressure, pc L

Fig. P1.8D

1.9D Over the globe, unsafe levels of arsenic, which is a tasteless, odorless, and colorless poison, are present in underground wells providing drinking water to millions of people. The object of this project is to identify low-cost, easy-to-deploy, and easy- to-use treatment technologies for removing arsenic from drinking water. Technologies considered should include, but not be limited to, applications of smart materials and other nanotechnology approaches. Write a report critically evaluat- ing existing and proposed technologies. List at least three references.

1.10D Conduct a term-length design project in the realm of bioengineering done on either an independent or a small-

Design & Open Ended Problems: Exploring Engineering Practice 35

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(d) If a system undergoes a process involving heat transfer with its surroundings but no work, that process is said to be adiabatic. (e) Thermal radiation can occur in a vacuum.

2.97 Answer the following true or false. Explain.

(a) Work is done by a system on its surroundings if the sole effect on everything external to the system could have been the raising of a weight.

(b) Cooling of computer components achieved by a fan-induced flow of air falls in the realm of radiation heat transfer. (c) For every thermodynamic cycle, the net amounts of energy transfer by heat and work per cycle are equal. (d) A flywheel spinning owing to an input of electricity stores energy as internal energy. (e) Kinetic and potential energy are each extensive properties of a system.

c DESIGN & OPEN-ENDED PROBLEMS: EXPLORING ENGINEERING PRACTICE

2.1D Visit a local appliance store and collect data on energy requirements for different models within various classes of appliances, including but not limited to refrigerators with and without ice makers, dishwashers, and clothes washers and driers. Prepare a memorandum ranking the different models in each class on an energy-use basis together with an accompanying discussion considering retail cost and other pertinent issues.

2.2D Select an item that can be produced using recycled materials such as an aluminum can, a glass bottle, or a plastic or paper grocery bag. Research the materials, energy requirements, manufacturing methods, environmental impacts, and costs associated with producing the item from raw materials versus recycled materials. Write a report including at least three references.

2.3D Design a go-anywhere, use-anywhere wind screen for outdoor recreational and casual-living activities, including sunbathing, reading, cooking, and picnicking. The wind screen must be lightweight, portable, easy to deploy, and low cost. A key constraint is that the wind screen can be set up anywhere, including hard surfaces such as parking lots for tailgating, wood decks, brick and concrete patios, and at the beach. A cost analysis should accompany the design.

2.4D In living things, energy is stored in the molecule adenosine triphosphate, called ATP for short. ATP is said to act like a battery, storing energy when it is not needed and instantly releasing energy when it is required. Investigate how energy is stored and the role of ATP in biological processes. Write a report including at least three references.

2.5D The global reach of the Internet supports a rapid increase in consumer and business e-commerce. Some say e-commerce will result in net reductions in both energy use and global climate change. Using the Internet, interviews with experts, and design-group brainstorming, identify several major ways e-commerce can lead to such reductions. Report your findings in a memorandum having at least three references.

2.6D Develop a list of the most common residential cooling options in your locale. For these options and assuming a 2300-ft2 home, compare installation cost, carbon footprint, and annual electricity charges. Which option is the most

economical if a 12-year life is assumed? What if electricity costs twice its current cost? Prepare a poster presentation of your findings.

2.7D Homeowners concerned about interruption of electrical power from their local utility because of weather-related and utility system outages can acquire a standby generator that produces electricity using the home’s existing natural gas or liquid propane (LP) fuel source. For a single-family dwelling of your choice, identify a standby generator that would provide electricity during an outage to a set of essential devices and appliances you specify. Summarize your findings in a memorandum including installed-cost and operating-cost data.

2.8D Despite the promise of nanotechnology (see Horizons in Secs. 1.6 and 2.2), some say it involves risks requiring scrutiny. For instance, the tiny size of nanoparticles may allow them to evade the natural defenses of the human body, and manufacturing at the nanoscale may lead to environmental burdens and excessive energy resource use. Research the risks that accompany widespread production and deployment of nanotechnology. For each risk identified, develop policy recommendations on safeguards for consumers and the environment. Write a report with at least three references.

2.9D The object of this project is to create a preliminary design of an energy-efficient dwelling at a locale of your choice. Consider factors including, but not limited to, placement of the dwelling on the lot, means for heating and cooling the dwelling, means for providing hot water, appliances, and building materials. The total cost must be no more than the average of newly constructed dwellings in the locale selected. Prepare a PowerPoint presentation of your design, including at least three references.

2.10D An advertisement describes a portable heater claimed to cut home heating bills by up to 50%. The heater is said to be able to heat large rooms in minutes without having a high outer-surface temperature, reducing humidity and oxygen levels, or producing carbon monoxide. A typical deployment is shown in Fig. P2.10D. The heater is an enclosure containing electrically-powered quartz infrared lamps that shine on copper tubes. Air drawn into the enclosure by a fan flows over the tubes and then is directed back into the living space. According to the advertisement, a heater capable of heating a room with up to 300 ft2 of floor area costs about $400 while

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88 Chapter 2 Energy and the First Law of Thermodynamics

one for a room with up to 1000 ft2 of floor area costs about $500. Critically evaluate the technical and economic merit of such heaters. Write a report including at least three references.

the invention requires no net water from the mains, the inventor maintains that nothing should be paid for water usage. The inventor also maintains that this approach not only gives a coefficient of performance superior to those of air-source heat pumps but also avoids the installation costs associated with ground-source heat pumps. In all, significant cost savings result, the inventor says. Critically evaluate the inventor’s claims. Write a report including at least three references.

Fig. P2.10D

Hot body: interior of dwelling

Cold body: water storage tank

Basement

Heat pump

Water to mains

Water from mains

Qin

Qout

+ –

Fig. P2.11D

2.11D An inventor proposes borrowing water from municipal water mains and storing it temporarily in a tank on the premises of a dwelling equipped with a heat pump. As shown in Fig. P2.11D, the stored water serves as the cold body for the heat pump and the dwelling itself serves as the hot body. To maintain the cold body temperature within a proper operating range, water is drawn from the mains periodically and an equal amount of water is returned to the mains. As

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3.147 Answer the following true or false. Explain.

(a) If water, initially a superheated vapor at 30 MPa, is cooled at constant pressure, the water eventually will become saturated vapor, and then with sufficient additional cooling condensation to saturated liquid will occur. (b) A quasiequilibrium process for which the pressure– volume relation is described by p/Vn 5 constant, where n is a constant, is called a polytropic process. (c) For simple compressible systems, the state principle indicates that the number of independent intensive thermodynamic properties required to fix an intensive state is two. (d) For ammonia at 0.45 MPa and 50°C, the specific enthalpy is 1564.32 kJ/kg. (e) For gases modeled as ideal gases, the value of the specific heat ratio cyycp is greater than 1.

3.148 Answer the following true or false. Explain

(a) The change in specific volume from saturated liquid to saturated vapor, (yg 2 yf), at a specified saturation pressure increases as the pressure decreases. (b) A two-phase liquid–vapor mixture with equal volumes of saturated liquid and saturated vapor has a quality of 50%. (c) The following assumptions apply for a liquid modeled as incompressible: The specific volume (density) is constant and the specific internal energy is a function only of temperature. (d) Carbon dioxide (CO2) at 320 K and 55 bar can be modeled as an ideal gas. (e) When an ideal gas undergoes a polytropic process with n 5 1, the gas temperature remains constant.

c DESIGN & OPEN-ENDED PROBLEMS: EXPLORING ENGINEERING PRACTICE

3.1D Dermatologists remove skin blemishes from patients by applying sprays from canisters filled with liquid nitrogen (N2). Investigate how liquid nitrogen is produced and delivered to physicians, and how physicians manage liquid nitrogen in their practices. Also investigate the advantages and disadvantages of this approach for removing blemishes compared to alternative approaches used today. Write a report including at least three references.

3.2D The EPA (Environmental Protection Agency) has developed an online Personal Emissions Calculator that helps individuals and families reduce greenhouse emissions. Use the EPA calculator to estimate, in the home and on the road, your personal greenhouse emissions or your family’s greenhouse emissions. Also use the calculator to explore steps you as an individual or your family can take to cut emissions by at least 20%. In a memorandum, summarize your findings and present your program for lowering emissions.

3.3D Methane-laden gas generated by the decomposition of landfill trash has economic value. Research literature on the possible uses of landfill gas. Contact the manager of a large landfill in your locale concerning the capture and use, if any, of landfill gas generated by the facility. Write a report including at least three references.

3.4D Use of the constant-volume calorimeter to measure the calorie value of foods and other substances, as illustrated in Example 3.6, is one of three general types of biological calorimetry. Two others are differential scanning calorimetry and isothermal titration calorimetry. For these two, investigate the objectives and instrumentation of each. Present your findings in a memorandum, including sketches of the respective instrumentation together with summaries of how the instrumentation is used in the laboratory.

3.5D A newspaper article reports that on a day when an airline cancelled eleven flights from Las Vegas because the local

temperature was approaching the 117°F operating limit for its jets, another airline canceled seven flights from Denver because the local temperature there was above the 104°F operating level for its propeller planes. Prepare a 30-min. presentation suitable for a middle school science class explaining the technical considerations behind these cancellations.

3.6D Due to their zero ozone depletion and low global warming potential natural refrigerants are actively under consideration for commercial refrigeration applications (see box in Sec. 3.4). Investigate the viability of natural refrigerants in systems to improve human comfort and safeguard food. Consider performance benefits, safety, and cost. On the basis of your study, recommend especially promising natural refrigerants and areas of application where each is particularly well suited. Report your findings in a PowerPoint presentation.

3.7D According to the New York City Transit Authority, the operation of subways raises tunnel and station temperatures as much as 14 to 20°F above ambient temperature. Principal contributors to the temperature rise include train motor operation, lighting, and energy from the passengers themselves. Passenger discomfort can increase significantly in hot- weather periods if air conditioning is not provided. Still, because on-board air-conditioning units discharge energy by heat transfer to their surroundings, such units contribute to the overall tunnel and station energy management problem. Investigate the application to subways of alternative cooling strategies that provide substantial cooling with a minimal power requirement, including but not limited to thermal storage and nighttime ventilation. Write a report with at least three references.

3.8D Some oil and gas companies use hydraulic fracturing to access oil and natural gas trapped in deep rock formations. Investigate the process of hydraulic fracturing, its benefits, and environmental impacts. On this basis, write a three-page brief for submission to a congressional committee considering

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160 Chapter 3 Evaluating Properties

whether hydraulic fracturing should continue to be exempt from regulation under the Safe Drinking Water Act. The brief can provide either objective technical background to inform committee members or take a position in favor of, or against, continuing the exemption.

3.9D Water is one of our most important resources, yet one of the most poorly managed—it is too often wasted and polluted. Investigate ways we can improve water use as a society in industry, businesses, and households. Record your daily water use for at least three days and compare it to that of those living in the poorest parts of the globe: about one gallon per day. Write a report including at least three references.

3.10D Passive solar heating may become more effective in coming years through incorporating phase-change materials (PCMs) into building materials. Investigate incorporation of phase-change materials into products used by the building industry to enhance passive solar heating. For each product, determine the PCM type, melting point, and accompanying phase-change enthalpy. Discuss how the PCM affects per- formance of the building material and how this benefits space heating. Prepare a 25-minute PowerPoint presentation suitable for a high school chemistry class based on your findings. Include at least two instructional aides to enhance your presentation.

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230 Chapter 4 Control Volume Analysis Using Energy

effects, and using the ideal gas model with constant specific heats for the air, plot the temperature, in 8F, and the pressure, in lbf/in.2, of the air in the chamber versus time for m# 5 1, 2, and 5 lb/min.

Air discharge

Well-insulated chamber

Air supply 30 lbf/in.2 200°F

pi = 14.7 lbf/in.2 Ti = 100°F

V = 1 ft3

Control valve Control valve

Fig. P4.130

c DESIGN & OPEN-ENDED PROBLEMS: EXPLORING ENGINEERING PRACTICE

4.1D Using the Internet, identify at least five medical applications of MEMS technology. In each case, explain the scientific and technological basis for the application, discuss the state of current research, and determine how close the technology is in terms of commercialization. Write a report of your findings, including at least three references.

4.2D A group of cells called the sinus node is the natural pacemaker of the heart and controls the heartbeat. Sinus node dysfunction is one source of the medical condition known as heart arrhythmia: irregular heartbeat. Significant arrhythmias are treated in several ways, including the use of an artificial pacemaker, which is an electrical device that sends the signals needed to make the heart beat properly. Research how both natural and artificial pacemakers operate to achieve their goal of maintaining a regular heartbeat. Place your findings in a memorandum that includes annotated sketches of each type of pacemaker.

4.3D Conduct a term-length project centered on using a low- wind turbine to meet the electricity needs of a small business, farm, or neighborhood selected by, or assigned to, your project group. Take several days to research the project and then prepare a brief written plan having a statement of purpose, a list of objectives, and several references. As part of your plan, schedule on-site wind- speed measurements for at least three different days to achieve a good match between the requirements of candidate low-wind turbines and local conditions. Your plan also should recognize the need for compliance with applicable zoning codes. During the project, observe good

practices such as discussed in Sec. 1.3 of Thermal Design and Optimization, John Wiley & Sons Inc., New York, 1996, by A. Bejan, G. Tsatsaronis, and M.J. Moran. Provide a well- documented report, including an assessment of the economic viability of the selected turbine for the application considered.

4.4D Generation of electricity by harnessing currents, waves, and tides is being studied across the globe. Electricity can be generated from currents using underwater turbines, as illustrated in Fig. P4.4D. Electricity also can be generated from the undulating motion of waves using tethered buoys. Like means can be used to generate power from tidal movements. Although currents and waves have long been used to meet relatively modest power needs, many observers today are thinking of large-scale power generation systems. Some see the oceans as providing a nearly unlimited renewable source of power. For a site in U.S. coastal waters, estuaries, or rivers, critically evaluate the viability of currents and/or waves for large-scale power generation by 2025. Consider technical and economic factors and effects on the ecosystem. Write a report including at least three references.

4.5D Owing to their relatively compact size, simple construction, and modest power requirement, centrifugal-type blood pumps are under consideration for several medical applications. Still, centrifugal pumps have met with limited success thus far for blood flow because they can cause damage to blood cells and are subject to mechanical failure. The goal of current development efforts is a device having sufficient long-term biocompatibility, performance, and reliability for widespread deployment. Investigate the status of centrifugal blood pump

allowing air to flow with a mass flow rate m# through each valve. The air within the chamber is well mixed, so the temperature and pressure at any time can be taken as uniform throughout. Neglecting kinetic and potential energy

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development, including identifying key technical challenges and prospects for overcoming them. Summarize your findings in a report, including at least three references.

4.6D Identify sites in your state where wind turbines for utility-scale electrical generation are feasible but do not yet exist. Prepare a memorandum to an appropriate governing or corporate entity with your recommendations as to whether wind-turbine electrical generation should be developed at the most promising sites. Consider engineering, economic, and societal aspects.

4.7D Recent disasters, including major oil spills, floods, hurricanes, and tsunamis have revealed the vulnerability of municipal water distribution systems to water-borne contamination. For the water distribution system of a municipality selected by, or assigned to, your project group, study the existing procedure for restoring the system to safe use after contamination. If no suitable decontamination procedure exists, make recommendations. Suggest easy-to- implement, cost-effective, environmentally-responsible measures. Document your findings in a memorandum.

4.8D The technical literature contains discussions of ways for using tethered kite-mounted wind turbine systems to harvest power from high-altitude winds, including jet streams at elevations from 6 to 15 kilometers (4 to 9 miles). Analysts estimate that if such systems were deployed in sufficient numbers, they could meet a significant share of total U.S. demand for electricity. Critically evaluate the feasibility of such a kite system, selected from the existing literature, to be fully operational by 2025. Consider means for deploying the system to the proper altitude, how the

power developed is transferred to earth, infrastructure requirements, environmental impact, cost, and other pertinent issues. Write a report including at least three references.

4.9D Forced-air warming systems involving inflatable thermal blankets …