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engineering
mechanical engineering

Questions and Answers of Mechanical Engineering

Describe the operation of an ocean thermal energy converter (OTEC). How is this system different from a solar pond system?
How is current density defined? What are light-induced recombination current and dark current or reverse saturation current?
How should a house be designed to receive solar heat for (a) Winter-dominated (b) Summer-dominated climates? Why?
What is a trombe wall? Why is it used?
What fraction of the solar energy is in the visible range(a) Outside the earth's atmosphere(b) At sea level on earth? Answer the same question for infrared radiation.
What is a shading device? Is an internal or external shading device more effective in reducing the solar heat gain through a window? How does the color of the surface of a shading device facing
Define the SHGC (solar heat gain coefficient), and explain how it differs from the SC (shading coefficient). What are the values of the SHGC and SC of a single-pane clear-glass window?
What does the SC (shading coefficient) of a device represent? How do the SCs of clear glass and heat-absorbing glass compare?
Describe the solar radiation properties of a window that is ideally suited for minimizing the air-conditioning load.
What is the effect of a low-e coating on the iner surface of a window glass on the (a) Heat loss in winter. (b) Heat gain in summer through the window?
Solar radiation is incident on a flat-plate collector at a rate of 930 W/m2. The glazing has a transmissivty of 0.82 and the absorptivity of absorber plate is 0.94. Determine the maximum efficiency
Solar radiation is incident on a flat-plate collector at a rate of 750 W/m2. The glazing has a transmissivity of 0.86 and the absorptivity of absorber plate is 0.95. The heat loss coefficient of the
Solar radiation is incident on a flat-plate collector at a rate of 260 Btu/h·ft2. The product of the transmissivty of glazing and the absorptivity of absorber plate is τα = 0.85 for this single
Solar radiation is incident on a flat-plate collector at a rate of 880 W/m2. The product of the transmissivty of glazing and the absorptivity of absorber plate is 0.82. The collector has a surface
The specifications of a flat-plate collector is as follows: τ = 0.88, α = 0.97, U = 1.3 Btu/h·ft2·oF. The heat removal factor for the collector is 0.92, the solar insolation is 210 Btu/h·ft2,
A concentrating collector has a concentration factor of CR = 15 and the optical efficiency of the aperture-to receiver process ηar = 0.93. The solar insolation is 520 W/m2, and the ambient air
A solar power plant utilizes parabolic trough collectors with a total collector area of 2500 m2. The solar irradiation is 700 W/m2. If the efficiency of this solar plant is 8 percent, what is the
In a solar pond, the water temperature is 30oC near the surface and 75oC near the bottom of the pond. If the thermal efficiency of this solar pond power plant is 3.6 percent, what is the second-law
A solar-power-tower plant is considered for Houston, Texas. Heliostats with a total area of 400,000 ft2 are to be used to reflect solar radiation into a receiver. When the solar irradiation is 250
A solar cell has an open circuit voltage value of 0.55 V with a reverse saturation current density of Jo = 1.9 × 109 A/m2. For a temperature of 25oC, determine (a) The current output density Js (b)
A solar cell has an open circuit voltage value of 0.60 V with a reverse saturation current density of Jo = 3.9 × 109 A/m2. The temperature of the cell is 27oC, the cell voltage is 0.52 V, and the
A solar cell has an open circuit voltage value of 0.60 V with a reverse saturation current density of Jo 5 4.11 3 1010 A/ft2. (a) For a temperature of 75oF, determine the load voltage at which the
Reconsider Prob. 18 - 40E. What is the maximum conversion efficiency of this solar cell? Prob. 18-40E A solar cell has an open circuit voltage value of 0.60 V with a reverse saturation current
The competition car developed by a group of engineering students use solar cells with a total area of 8 m2. The solar radiation is incident on the cells at a rate of 860 W/m2. The shaft power output
Consider a building located near 40o N latitude that has equal window areas on all four sides. The building owner is considering coating the south-facing windows with reflective film to reduce the
A manufacturing facility located at 32o N latitude has a glazing area of 60 m2 facing west that consists of doublepane windows made of clear glass (SHGC = 0.766). To reduce the solar heat gain in
A house located in Boulder, Colorado (40o N latitude), has ordinary double-pane windows with 6-mm-thick glasses and the total window areas are 8, 6, 6, and 4 m2 on the south, west, east, and north
Repeat Prob. 11-45 for double-pane windows that are gray-tinted. Prob. 11-45 A house located in Boulder, Colorado (40o N latitude), has ordinary double-pane windows with 6-mm-thick glasses and the
Consider a building in New York (40o N latitude) that has 76 m2 of window area on its south wall. The windows are double-pane heat-absorbing type, and are equipped with light-colored venetian blinds
A typical winter day in Reno, Nevada (39o N latitude), is cold but sunny, and thus the solar heat gain through the windows can be more than the heat loss through them during daytime. Consider a house
Repeat Prob. 18-48 for a south window.Prob. 18-48A typical winter day in Reno, Nevada (39o N latitude), is cold but sunny, and thus the solar heat gain through the windows can be more than the heat
Some consider electric cars as "zero emission" vehicles and an ultimate solution to the air pollution problem. Do you agree? Explain.
Determine the rate of net heat gain (or loss) through a 9-ft-high, 15-ft-wide, fixed 18 -in single-glass window with aluminum frames on the west wall at 3 PM solar time during a typical day in
What is the difference between a windmill and a wind turbine?
What are the three key locations on the wind-speed scale? Explain each one briefly.
Consider two locations both at the same altitude with the same wind speed but the air temperature at one location is higher than the other. Which location has more wind power potential? Why?
Consider two locations with the same wind speed and ambient air temperature but one location is at a higher altitude than the other. Which location has more wind power potential? Why?
There are three sites with the following average wind power densities: site A: 75 W/m2, site B: 500 W/m2, and site C: 800 W/m2. Do you recommend a wind turbine installation for all three sites?
How is the overall wind turbine efficiency defined? How is it related to the wind turbine efficiency?
What is the theoretical limit for wind turbine efficiency based on the second law of thermodynamics? Is this limit same as the Betz limit? Why? Explain.
Three different inventors come up with three wind turbine designs with these claimed efficiencies: Turbine A: 41 percent, Turbine B: 59 percent, Turbine C: 67 percent. How do you evaluate these
A wind turbine with a blade diameter of 50 m is to be installed in a location where average wind velocity is 7.5 m/s. The average temperature and pressure of ambient air in this location are 23oC and
Consider a location with an average wind power density of 200 W/m2. What is the corresponding average wind speed? Another location has a wind power density of 400 W/m2. What is the average wind speed
A wind turbine with a blade diameter of 25 m is to be installed in a location where average wind velocity is 6 m/s. If the overall efficiency of the turbine is 34 percent, determine (a) The average
The measurements over an entire week period indicates that a wind turbine with a blade diameter of 40 m has produced 11,000 kWh of electricity. If the overall efficiency of the wind turbine is
The wind velocity in a location varies between 16 ft/s and 24 ft/s. A wind turbine with a blade span diameter of 185 ft is to be installed. The wind turbine efficiency is 30 percent at a wind
The air velocity is 25 ft/s at the inlet of a wind turbine and 19.5 ft/s at the exit. What is the wind turbine efficiency if the frictional effects are neglected?
The pressures just upstream and downstream of a hydraulic turbine are measured to be P1 and P2, respectively. How do you determine the maximum work, in kJ/kg, that can be produced by this turbine?
Why are we usually more interested in the overall efficiency of turbine-generator combination rather than the turbine efficiency?
It is argued that hydraulic turbines cannot have an efficiency of 100 percent even in the absence of irreversible losses due to limitation by the second law of thermodynamics. Do you agree? Explain.
How is a solar cell different from a heliostat?
It is argued that hydraulic turbines cannot have a maximum efficiency of 100 percent and there must be a lower upper limit for the turbine efficiency similar to Betz limit of wind turbines. Do you
How do you express the efficiency of a hydroelectric vpower plant when turbine, generator, and piping efficiencies are given? Show that this equation reduces to electric power output divided by the
What are the basic types of dynamic turbines? How do you compare them in terms of head and volume flow rate?
River water is collected into a large dam whose height is 65 m. How much power can be produced by an ideal hydraulic turbine if water is run through the turbine at a rate of 1500 L/min?
The pressures just upstream and downstream of a hydraulic turbine are measured to be 1325 kPa and 100 kPa, respectively. What is the maximum work, in kJ/kg, that can be produced by this turbine? If
Water is run through a hydraulic turbine at a rate of 11,500 L/min from a 160-m-high reservoir and produces 250 kW of shaft power. What is the efficiency of this turbine?
A hydraulic turbine-generator unit placed at the bottom of a 75-m-high dam accepts water at a rate of 1020 L/s and produces 630 kW of electricity. Determine(a) The overall efficiency of the
The pressures just upstream and downstream of a hydraulic turbine are measured to be 95 psia and 15 psia, respectively, and the water flow through the turbine is 280 lbm/s. The turbine accepts water
The irreversible losses in the penstock and its inlet and those after the exit of the draft tube are estimated to be 7 m. The elevation difference between the reservoir surface upstream of the dam
The piping efficiency of a hydroelectric power plant is estimated to be 98 percent while the turbine efficiency based on the net head is 87 percent and the generator efficiency is 97 percent. If the
A hydroelectric power plant consists of 18 identical turbine-generator units with an overall plant efficiency of 90 percent. The gross head of the dam is 150 m and the flow rate through each turbine
Classify geothermal resources based on temperature.
List the utilization of geothermal energy. Which use is most common?
Consider a liquid geothermal resource at a temperature of 110oC. An investor is considering a power plant construction on this site, and the investor is asking for your opinion whether this is an
What are typical geothermal resource temperature requirements for electricity production, cooling, and heating?
What is the difference between a ground-source heat pump and a geothermal heat pump? Explain. Why do geothermal heat pumps have higher COPs than air-source haet pumps?
What is the purpose of flashing process in geothermal power plants? Which property remains constant during a flashing process? What happens to pressure and temperature during a flashing process?
A geothermal site contains geothermal water available at wellhead at a rate of 100 lbm/s. The geothermal water is at 300oF with a vapor fraction of 35 percent. Determine the maximum thermal
A residential district is to be heated by geothermal water in winter. On an average winter day, geothermal water enters the main heat exchanger network of the district at 90oC at arate of 70 kg/s and
Geothermal liquid water from a well is available at 210oF at a rate of 86,000 lbm/h and is to be used for space cooling using an absorption refrigeration system. Geothermal water leaves the generator
The schematic of a single-flash geothermal power plant with state numbers is given in Fig. P18-91. Geothermal resource exists as saturated liquid at 230oC. The geothermal liquid is withdrawn from the
Reconsider Prob. 18-91. Now, it is proposed that the liquid water coming out of the separator be routed through another flash chamber maintained at 150 kPa, and the steam produced be directed to a
Reconsider Prob. 18-91. Now, it is proposed that the liquid water coming out of the separator be used as the heat source in a binary cycle with isobutane as the working fluid (Fig. P18-93).
Consider a binary geothermal cogeneration plant like that in Fig. P18-94 using geothermal water at 165oC with isobutane as the working fluid. The mass flow rate of geothermal water is 175 kg/s and
Reconsider Prob. 18-94. The space heating provided by this cogeneration plant will replace natural gas heating. How much money does this plant make by selling geothermal heat at a discount rate of
What are the sources of biomass energy? Why is it a renewable energy source? Explain.
How do the renewability and cleanliness of biomass compare with other renewables such as solar, geothermal, or wind?
Compare the mole of atoms in the unit of kmol in a 1 in block of copper with that in an identical block of aluminum.
10 kg of water (ρ = 1000 kg/m3) and 5 kg of ice (ρ = 916 kg/m3) are at equilibrium at 0oC. Determine the specific volume of the mixture.
If equal volumes of iron and copper (look up Table A-1 for densities) are melted together, determine (a) The specific volume. (b) Density of the alloy. Assume no change in the final volume. (c)
What is the atmospheric pressure in kPa if a mercury barometer reads 750 mm? Assume ρ = 13,600 kg/m3.
Determine the height of a mountain if the absolute pressure measured at the bottom and top are 760 mm and 720 mm of mercury, respectively. Assume ρHg = 13,600 kg/m3 and ρair = 1.1 kg/m3.
A Bourdon gage measures the pressure of water vapor at the top of a cylindrical tank with a height of 6 m to be 300 kPa. Determine (a) The absolute pressure at the bottom of the tank if 50% of the
An unknown mass is placed on the piston of a vertical piston-cylinder device containing nitrogen. The piston is weightless and has an area of 1 m2. The outside pressure is 100 kPa and the pressure
Determine the readings of the two Bourdon gages (outer first) if the inner tank (see figure) has a pressure of 500 kPa, the outer tank a pressure of 50 kPa and the atmosphere a pressure of 100 kPa.
(a) Determine the absolute pressure in kPa of the gas trapped in the piston cylinder device if the piston is weightless and the depth of the piston from the free surface is 20 m. Assume the outside
A piston separates two chambers in a horizontal cylinder as shown in the accompanying figure. Each chamber has a volume of 1 m3 and the pressure of the gas is 50 kPa. The piston has a diameter of 50
Two closed chambers A and B are connected by a water manometer. If the gage pressure of chamber A is 10 mm of mercury vacuum and the height difference of the water columns is 10 cm: Determine the
Determine the mass of one molecule of water (H2O). Assume the density to be 1000 kg/m3.
Air flows through a Venturi meter as shown in the accompanying figure. Determine the difference in pressure between point A and B if the height difference of the water columns is 3 cm. Assume ρair =
The maximum blood pressure of a patient requiring blood transfer is found to be 110 mmHg. What should be the minimum height of the ivy to prevent a back flow? Assume blood = 1050 kg/m3.
The temperature assigned for the ice and steam points are 0 and 100 on the Celsius scale and 32 and 212 on the Fahrenheit scale. Both scales use a linear division. (a) Show that the two scales are
The temperature T on a thermometric scale is defined in terms of property x by the function T = a.ln(xb) , where a and b are constants. The values of x are found to be 1.8 and 6.8 at the ice point
Two liquid-in-glass thermometers are made of identical materials and are accurately calibrated at 0oC and 100oC. While the first tube is cylindrical, the second tube has a conical bore, 15% greater
The signal (e.m.f.) produced by a thermocouple with its test junction at ToC is given by ε = aT + bT2 [mV], where a = 0.2 mV/oC and b = 5.1 x 10-4 mV/oC2.(a) Draw a graph of ε against T within the
A projectile of mass 0.1 kg is fired upward with a velocity of 300 m/s. (a) Determine the specific kinetic energy (ke). If the sum of KE and PE is to remain constant. (b) Determine the maximum
A truck of mass 10 tonnes (metric) is traveling at a velocity of 65 miles per hour. Determine (a) Kinetic energy (KE). (b) How high a ramp is necessary to bring it to a stop if the mechanical energy
A projectile of mass 0.1 kg is moving with a velocity of 250 m/s. If the stored energy (E) in the solid is 1.5625 kJ. (a) Determine the specific internal energy (u). Neglect potential energy and
A rigid chamber contains 100 kg of water at 500 kPa, 100oC. A paddle wheel stirs the water at 1000 rpm with a torque of 100 N-m while an internal electrical resistance heater heats the water,

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