Chapter 5, Problem 5.74P

If the container is placed in a colder environment, how will it affect the actual heat transfer and the irreversibility of the system?

John decides to make ice using a Carnot refrigerator that takes heat from water at 0°C to a room at 30°C. Suppose 200 g of water at 0°C are converted to ice at 0°C by the refrigerator. Calculate the mechanical energy that must be applied to the refrigerator in J. The latent heat of fusion of water is Lf-3.34x105 J/kg. Remember the definition of the coefficient of performance K and first calculate K.

Consider a conventional piston-cylinder system. Compute the work required to compress air to 0.2 m3 initially contained under atmospheric pressure and in a volume of 0.5 m3. Consider three cases:  a) the processes is isobaric: b) the process is adiabatic:   c) the process is isothermal:

b. An electric heater supplies (R+ 2.5) kW of power in the form of heat to water. If in 5.5 hours, 350 kg of water is heated from –10°C to 60 °C, find the work done (w) of heater. Also calculate the amount of heat energy (Q) transferred to the water. Consider the specific heat of water is 4184 J/kg K. R=30

A large heat pump should upgrade 4 MW of heat at 65 C to be delivered as heat at 145 C. What is the minimum amount of work input that will drive this?

Complete Solutions

A heat pump used for heating shown is essentially an air conditioner installed backward. It extracts energy from colder air outside and deposits it in a warmer room. Suppose the ratio of the actual energy entering the room to the work done by the device’s motor is 10.0% of the theoretical maximum ratio. Determine the energy entering the room per joule of work done by the motor given that the inside temperature is 20.0°C and the outside temperature is -5.00°C.

Suppose 400 kW of power potential is wasted during the process as a result of irreversibility. Let say the heat pump received heat at a rate of 1000 kJ/s from a heat source. The reversible power of the present process is found to be 800 kW. Find unavailable heat, which is rejected to the sink.

A vertical piston-cylinder assembly containing water is being heated on a stove. During this process, 140kJ of heat is transferred to the water’s expansion process (because of the heat addition), -20 kJ of work is done. Also, there is 50 kJ heat loss from the assembly. What is the water’s change of internal energy because of the heat addition process? Draw the diagram.