Consider a refrigerator whose 40 watts light bulb remains on continuously as a result of a malfunction of the switch. If the refrigerator has a COP of 1.3 and the cost of electricity is 8 cents per kW-hr, determine the increase in the energy consumption of the refrigerator and its cost per year if the switch is not fixed.

A 75 hp motor that has an efficiency of 91% is worn out and is replaced by a high-efficiency motor that has an efficiency of 95.4%. Determine the reduction in heat gain of the room due to higher efficiency under full-load conditions.

A household refrigerator that has a power input of 450 watts and a COP of 2.5 is to cool five large watermelons, 10 kg each, to 8°C. If the watermelons are initially at 20°C, determine how long it will take for the refrigerator to cool them. The watermelons can be treated as water whose specific heat is 4.2 kJ/kg-K.

When a man returns to his wall-sealed house on a summer day, he finds that the house is at 32°C. He returns on the air conditioner which cools the entire house to 20°C in 15 minutes. If COP is 2.5, determine the power drawn by the air conditioner. Assume the entire mass within the house is 800 kg of air for which cv = 0.72 kJ/kg-K, cp = 1.0 kJ/kg-K.

A heat source at 800 K losses 2000 kJ of heat to a sink at 500 K. Determine the entropy generated during this process.

Helium gas is compressed in an adiabatic compressor from an initial state of 14 psia and 50°F to a final temperature of 320°F in a reversible manner. Determine the exit pressure of Helium.

Air passes thru a nozzle with efficiency of 90%. The velocity of air at the exit is 600 m/s. Find the actual velocity at the exit.

A 50 kg block of iron casting at 500 K is thrown into a large lake that is at a temperature of 285 K. The iron block eventually reaches thermal equilibrium with the lake water. Assuming average specific heat of 0.45 kJ/kg-K for the iron, determine the entropy generated during this process.

A windmill with a 12 m diameter rotor is to be installed at a location where the wind is blowing at an average velocity of 10 m/s. Using standard condition of air (1 atm, 25°C), determine the maximum power that can be generated by the windmill.

Consider a large furnace that can supply heat at a temperature of 2000°R at a steady rate of 3000 Btu/s. Determine the exergy of this energy. Assume an environment temperature of 77°F.

A heat engine receives heat from a source at 1200 K at a rate of 500 kJ/s and rejects the waste heat to a medium at 300 K. The power output of the engine is 180 kW. Determine the irreversibility rate for this process.

A dealer advertises that he has just received a shipment of electric resistance heaters for residential buildings that have an efficiency of 100 percent. Assuming an indoor temperature of 21°C and outdoor temperature of 10°C, determine the second law efficiency of these heaters.

A thermal power plant has a heat rate of 11,363 Btu/kW-hr. Find the thermal efficiency of the plant.

A rigid tank contains 2 kmol of N2 and 6 kmol of CO2 gases at 300 K and 115 MPa. Find the tank volume using the ideal gas equation.

A spherical balloon with a diameter of 6 m is filled with helium at 20°C and 200 kPa. Determine the mole number.

The air in an automobile tire with a volume of 0.53 ft3 is at 90°F and 20 psig. Determine the amount of air that must be added to raise the pressure to the recommended value of 30 psig. Assume the atmospheric pressure to be 14.7 psia and the temperature and the volume to remain constant.

A rigid tank contains 20 lbm of air at 20 psia and 70°F. More air is added to the tank until the pressure and temperature rise to 35 psia and 90°F, respectively. Determine the amount of air added to the tank.

A rigid tank contains 5 kg of an ideal gas at 4 atm and 40°C. Now a valve is opened, and half of mass of the gas is allowed to escape. If the final pressure in the tank is 1.5 atm, the final temperature in the tank is?

The pressure of an automobile tire is measured to be 200 kPa (gage) before the trip end 220 kPa (gage) after the trip at a location where the atmospheric pressure is 90 kPa. If the temperature of the air in the tire before the trip is 25°C, the air temperature after the trip is?

Water is boiling at 1 atm pressure in a stainless steel pan on an electric range. It is observed that 2 kg of liquid water evaporates in 30 min. The rate of heat transfer to the water is?

Consider a person standing in a breezy room at 20°C. Determine the total rate of heat transfer from this person if the exposed surface area and the average outer surface temperature of the person are 1.6 m2 and 29°C, respectively, and the convection heat transfer coefficient is 6 W/m2 with emissivity factor of 0.95.

Water is boiler in a pan on a stove at sea level. During 10 minutes of boiling, it is observed that 200 grams of water has evaporated. Then the rate of heat transfer to the water is:

An aluminum pan whose thermal conductivity is 237 W/m-°C has a flat bottom whose diameter is 20 cm and thickness of 0.4 cm. Heat is transferred steadily to boiling water in the pan through its bottom at a rate of 500 watts. If the inner surface of the bottom of the pan is 105°C, determine the temperature of the surface of the bottom of the pan.

For heat transfer purposes, a standing man can be modeled as a 30 cm diameter, 170 cm long vertical cylinder with both the top and bottom surfaces insulated and with the side surface at an average temperature of 34°C. For a convection heat transfer coefficient of 15 W/m2 -°C, determine the rate of heat loss from this man by convection in an environment at 20°C.

A 5 cm diameter spherical ball whose surface is maintained at a temperature of 70°C is suspended in the middle of a room at 20°C. If the convection heat transfer coefficient is 15 W/m2 -°C and the emissivity of the surface is 0.8, determine the total heat transfer from the ball.

A frictionless piston-cylinder device and a rigid tank contain 1.2 kmol of an ideal gas at the same temperature, pressure and volume. Now heat is transferred, and the temperature of both systems is raised by 15°C. The amount of extra heat that must be supplied to the gas in the cylinder that is maintained at constant pressure is?

A supply of 50 kg of chicken at 6°C contained in a box is to be frozen to -18°C in a freezer. Determine the amount of heat that needs to be removed. The latent heat of the chicken is 247 kJ/kg, and its specific heat is 3.32 kJ/kg-°C above freezing and 1.77 kJ/kg-°C below freezing. Thecontainer box is 1.5 kg, and the specific heat of the box material is 1.4 kJ/kg-°C. Also the freezing temperature of chicken is -2.8°C.

Water is being heated in a closed pan on top of a range while being stirred by a paddle wheel. During the process, 30 kJ of heat is transferred to the water, and 5 kJ of heat is lost to the surrounding air. The paddle wheel work amounts to 500 N-m. Determine the final energy of the system if its initial energy is 10 kJ.

A classroom that normally contains 40 people is to be air-conditioned with window air- conditioning units of 5 kW cooling capacity. A person at rest may be assumed to dissipate heat at a rate about 360 kJ/hr. There are 10 light bulbs in the room, each with a rating of 100 watts. The rate of heat transfer to the classroom through the walls and the windows is estimated to be 15,000 kJ/hr. If the room is to be maintained at a constant temperature of 21°C, determine the number of window air-conditioning units required.

A 4 m x 5 m x 6 m room is to be heated by a baseboard resistance heater. It is desired that the resistance heater be able to raise the air temperature in the room from 7 to 23°C within 15 minutes. Assuming no heat losses from the room and an atmospheric pressure of 100 kPa, determine the required power of the resistance heater. Assume constant specific heats at room temperature.

A student living in a 4 m x 6 m x 6 m dormitory room turns on her 150 watts fan before she leaves the room on a summer day, hoping that the room will be cooler when she comes back in the evening. Assuming all the doors and windows are tightly closed and disregarding any heat transfer through the walls and the windows, determine the temperature in the room when she comes back 10 hours later. Use specific heat values at room temperature, and assume the room to be at 100 kPa and 15°C in the morning when she leaves.

A piston-cylinder device whose piston is resting on top of a set of stops initially contains 0.50 kg of helium gas at 100 kPa and 25°C. The mass of the piston is such that 500 kPa of pressure is required to raise it. How much heat must be transferred to the helium before the piston starts rising?

In order to cool 1 ton (1000 kg) of water at 20°C in an insulated tank, a person pours 80 kg of ice at -5°C into the water. Determine the final equilibrium temperature in the tank. The melting temperature and the heat of fusion of ice at atmospheric pressure are 0°C and 333.7 kJ/kg, respectively.

A fan is powered by 0.5 hp motor and delivers air at a rate of 85 m3/min. Determine the highest value for the average velocity of air mobilized by the fan. Take the density of air to be 1.18 kg/m3

An Ocean-Thermal Energy Conversion power plant generates 10,000 kW using a warm surface water inlet temperature of 26°C and cold deep-water temperature of 15°C. On the basis of a 3°C drop in the temperature of the warm water and a 3°C rise in the temperature of the cold water due to removal and addition of heat, calculate the power required in kW to pump the cold-deep water to the surface and through the system heat exchanger if the required pumping pressure increase is 12 kPa. Assume a Carnot cycle efficiency and density of cold water to be 100 kg/m3 .

A plate-type solar energy collector with an absorbing surface covered by a glass plate is to receive an incident radiation of 800 W/m2. The glass plate has a reflectivity of 0.12 and atransmissivity of 0.85. The absorbing surface has an absorptivity of 0.90. The area of the collector is 5 m2. How much solar energy in watts is absorbed by the collector?

A tank contains liquid nitrogen at -190°C is suspended in a vacuum shell by three stainless steel rods of 0.80 cm in diameter and 3 meters long with a thermal conductivity of 16.3 W/m2 - °C. If the ambient air outside the vacuum shell is 15°C, calculate the magnitude of the conductive heat flow in watts along the support rods.

A tank contains liquid nitrogen at -190°C is suspended in a vacuum shell by three stainless steel rods of 0.80 cm in diameter and 3 meters long with a thermal conductivity of 16.3 W/m2 - °C. If the ambient air outside the vacuum shell is 15°C, calculate the magnitude of the conductive heat flow in watts along the support rods.

An elastic sphere containing gas at 120 kPa has a diameter of 1.0 m. Heating the sphere causes it to expand to a diameter of 1.3 m. During the process the pressure is proportional to the sphere diameter. Calculate the work done by the gas in kJ

An ideal gas with a molecular weight of 7.1 kg/kg mol is compressed from 600 kPa and 280 K to a final specific volume of 0.5 m3/kg. During the process the pressure varies according to P = 620 + 150υ + 95 υ2 where p is in kPa and υ in m3/kg. Calculate the work of compression in kJ/kg

A one cubic meter container contains a mixture of gases composed of 0.02 kg-mol of oxygen and 0.04 kg-mol of helium at a pressure of 220 kPa. What is the temperature of this ideal gas mixture in Kelvin?

A 12 DC electrical motor draws a current of 15 amps. How much work in kJ does this motor produce over a 10-minute period of operation?

A 4 liter (2-liter per revolution at standard pressure and temperature) spark ignition engine has a compression ratio of 8 and 2200 kJ/kg heat addition by the fluid combustion. Considering a cold air-standard Otto cycle model, how much power will the engine produce when operating at 2500 rpm?

A simple Rankine cycle produces 40 MW of power, 50 MW of process heated and rejects 50 MW of heat to the surroundings. What is the utilization factor of this cogeneration cycle neglecting the pump work?

The rate of heat transfer to the surroundings from a person at rest is 400 kJ/hr. Suppose that the ventilation system fails in an auditorium containing 120 people and assuming that the energy goes into the air of volume 1500 m3 initially at 300 K and 101 kPa, calculate the rate in °C /min of air temperature change.

An insulated box containing helium gas falls from a balloon 4.5 km above the earth’s surface. Calculate the temperature rise in °C of the helium when box hits the ground.

Consider two Carnot heat engines operating in series. The first engine receives heat from the reservoir at 2400 K and rejects the waste heat to another reservoir at temperature T. The second engine receives heat by the first one, convert some of it to work, and rejects the rest toa reservoir at 300 K. If thermal efficiencies of both engines are the same, determine the temperature T.

An ideal gas mixture consists of 2 kmol of N2 and 6 kmol of CO2. The mass fraction of CO2 is?

. An ideal gas mixture consists of 2 kmol of N2 and 6 kmol of CO2. The apparent gas constant of mixture is?

A Carnot cycle operates between the temperature limits of 300 K and 1500 K, and produces 600 kW of net power. The rate of entropy change of the working fluid during heat addition process is?