Concept explainers
A hair dryer may be idealized as a circular duct through which a small fan draws ambient air and within whichthe air is heated as it flows over a coiled electric resistance wire.
(a) If a dryer is designed to operate with an electricpower consumption of
(b) Consider a dryer duct length of
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Fundamentals of Heat and Mass Transfer
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- A pump steadily draws water from a pond at a volumetric flow rate of 180 gal/min through a pipe having a 5 in. diameter inlet.The water is delivered through a hose terminated by a converging nozzle. The nozzle exit has a diameter of 2.6 in. and is located35 ft above the pipe inlet. Water enters at 58°F, 14.7 psi and exits with no significant change in temperature or pressure. Themagnitude of the rate of heat transfer from the pump to the surroundings is 5% of the power input. The acceleration of gravity is32.2 ft/s2. Determine the the power required by the pump, in hp.Select one:a. -7.16 hpb. -9.4 hpc. -1.76 hpd. -4.33 hparrow_forwardA pump steadily draws water from a pond at a volumetric flow rate of 180 gal/min through a pipe having a 5 in. diameter inlet. The water is delivered through a hose terminated by a converging nozzle. The nozzle exit has a diameter of 2.6 in. and is located 35 ft above the pipe inlet. Water enters at 58°F, 14.7 psi and exits with no significant change in temperature or pressure. The magnitude of the rate of heat transfer from the pump to the surroundings is 5% of the power input. The acceleration of gravity is 32.2 ft/s2. Determine the velocity of the water at the exit in ft/s. Select one: a. 10.88 ft/s b. 89.87 ft/s c. 3.59 ft/s d. 67.92 ft/sarrow_forwardWater at 60 deg. F is pumped from a reservoir to the top of a mountain through a 6-in SCH 120 pipe at an average velocity of 12 ft/s. The pipe discharges into the atmosphere at a level 3000 ft above the level in the reservoir. The pipeline itself is 4500 ft. long. If the overall efficiency of the pump and the motor driving it is 70% and the cost of electric energy to the motor is 4 cents per kilowatt-hour,1. what is the hourly energy cost for pumping this water? $3.21$ 18.32$12.83$81.23$ 32.18$23.81none of the givenarrow_forward
- The maximum flow rate of standard shower heads is about 3.5 gpm (13.3 L/min) and can be reduced to 2.75 gpm (10.5 L/min) by switching to low-flow shower heads that are equipped with flow controllers. Consider a family of four, with each person taking a 5-min shower every morning. City water at 15°C is heated to 55°C in an electric water heater and tempered to 42°C by cold water at the T-elbow of the shower before being routed to the shower heads. Assuming a constant specific heat of 4.18 kJ/kg·°C for water, determine the amount of electricity that will be saved per year, in kWh, by replacing the standard shower heads with the low-flow ones.arrow_forwardThe maximum flow rate of standard shower heads is about 3.5 gpm (13.3 L/min) and can be reduced to 2.75 gpm (10.5 L/min) by switching to low-flow shower heads that are equipped with flow controllers. Consider a family of four, with each person taking a 5-min shower every morning. City water at 15°C is heated to 55°C in an electric water heater and tempered to 42°C by cold water at the T-elbow of the shower before being routed to the shower heads. Assuming a constant specific heat of 4.18 kJ/kg·°C for water, determine the ratio of the flow rates of the hot and cold water as they enter the T-elbow.arrow_forwardcompare how heat transfer(conduction and convection and radiation) efficiency will affect the lifetime of the turbine. Note: The effect of each type of heat transfer separately and accuratelyarrow_forward
- A desktop computer is to be cooled by a fan. The electronic components of the computer consume 80 W of power under full-load conditions. The computer is to operate in environments at temperatures up to 50°C and at elevations up to 3000 m where the atmospheric pressure is 70.12 kPa. The exit temperature of air is not to exceed 60°C to meet the reliability requirements. Also, the average velocity of air is not to exceed 120 m/min at the exit of the computer case, where the fan is installed to keep the noise level down. Specify the flow rate of the fan that needs to be installed and the diameter of the casing of the fan.arrow_forwardWater at 60 deg. F is pumped from a reservoir to the top of a mountain through a 6-in SCH 120 pipe at an average velocity of 12 ft/s. The pipe discharges into the atmosphere at a level 3000 ft above the level in the reservoir. The pipeline itself is 4500 ft. long. If the overall efficiency of the pump and the motor driving it is 70% and the cost of electric energy to the motor is 4 cents per kilowatt-hour, 5. what is the volumetric flow rate in cubic feet / sec? 2.348.193.241.989.81none of the given4.32arrow_forwardToluene at 35 degrees Celsius is pumped from an open reservoir to a tank kept at a gauge pressure of 150 kPa. The pump itself is 3m below the reservoir, while the discharge tank is 10m above the reservoir. Assuming friction in the suction line is negligible, while in the discharge line the friction head amounts to 7.5 m, determine the net positive suction head available for the pump. If the pump has an efficiency of 65%, determine the total power input. At the given temperature, the density and vapor pressure of toluene are 862 kg/m3 and 40 mmHgarrow_forward
- In climates with low night-time temperatures, an energy-efficient way of cooling a house is to install a fan in the ceiling that draws air from the interior of the house and discharges it to a ventilated attic space. Consider a house whose interior air volume is 720 m3 If air in the house is to be exchanged once every 20 minutes, determine (a) the required flow rate of the fan and (b) the average discharge speed of air if the fan diameter is 0.5 m..arrow_forwardWater at 20°C is pumped at a constant rate of 9 m3/h from a large reservoir resting on the floor to the open top of an experimental absorption tower. The point of discharge is 5 m above the floor, and friction losses in the 50-mm pipe from the reservoir to the tower amount to 2.5 J/kg. At what height in the reservoir must the water level be kept if the pump can deliver only 0.1 kW? i.At what height should the liquid level in the reservoir be? ii.Determine the velocity of the water as it enters the top of the absorption tower. iii.Determine the mass flow rate of the flowing water (in kg/s)arrow_forwardWater enters the pump of a steam power plant at 15 kPa and 50°C at a rate of 0.15 m3 /s. The diameter of the pipe at the pump inlet is 0.25 m. What is the net positive suction head (NPSH) at the pump inlet? (a) 1.70 m (b) 1.49 m (c) 1.26 m (d) 0.893 m (e) 0.746 marrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning