Refrigeration and Heat Pump Systems

What is the primary objective of a heat pump system?

In a Carnot vapor refrigeration cycle, how is the coefficient of performance defined?

What is the maximum theoretical coefficient of performance for any refrigeration cycle operating between a cold region at 0 degrees Celsius (273 K) and a warm region at 26 degrees Celsius (299 K)?

In the context of departures from the Carnot cycle, what is meant by 'dry compression'?

Why is a simple throttling valve typically used in vapor-compression refrigeration systems instead of an expansion turbine?

A unit for refrigeration capacity is the 'ton of refrigeration'. What is this unit equal to?

In an ideal vapor-compression refrigeration cycle using Refrigerant 134a, saturated vapor enters the compressor at 0 degrees Celsius (h1 = 247.23 kJ/kg). It is compressed isentropically, exiting with an enthalpy of h2s = 264.7 kJ/kg. Saturated liquid leaves the condenser with an enthalpy of h3 = 85.75 kJ/kg. The throttling process means h4 = h3. What is the coefficient of performance for this cycle?

What environmental concern led to the development of HFC refrigerants like Refrigerant 134a as substitutes for CFCs like Refrigerant 12?

In a cascade refrigeration cycle, how are the individual vapor-compression cycles connected?

What is the primary function of the 'absorber' component in an absorption refrigeration system?

What is a significant advantage of multistage compression with intercooling in a refrigeration cycle?

In a vapor-compression heat pump system with refrigerant states designated as in Figure 10.11, which expression correctly represents the coefficient of performance?

What is the function of the reversing valve in an air-source heat pump?

How does the Brayton refrigeration cycle differ fundamentally from the vapor-compression refrigeration cycle?

In an ideal Brayton refrigeration cycle, air enters the compressor at 1 bar, 270 K (h1=270.11 kJ/kg). It is compressed isentropically to 3 bar, exiting at h2s=370.1 kJ/kg. The air is then cooled to 300 K (h3=300.19 kJ/kg) before expanding isentropically through a turbine, exiting at h4s=219.0 kJ/kg. What is the coefficient of performance?

What is the effect of irreversible heat transfer between the refrigerant and the cold/warm regions on the performance of a vapor-compression cycle?

In an absorption refrigeration system using lithium bromide and water, which substance is the refrigerant and which is the absorbent?

A vapor-compression cycle with an 80 percent efficient compressor has an isentropic work input of 38.8 kJ/kg. What is the actual work input per unit mass?

What is the function of the 'rectifier' component shown in the modified ammonia-water absorption system in Figure 10.10?

What is the primary purpose of the regenerative heat exchanger in the modified Brayton refrigeration cycle shown in Figure 10.14?

For a heat pump, the coefficient of performance is always...

In a multistage refrigeration cycle with a flash chamber as shown in Figure 10.8, what is the state of the refrigerant entering the flash chamber at state 6?

What is the key advantage of a cascade refrigeration system regarding refrigerant selection?

A vapor-compression cycle is modified to include an 80 percent efficient compressor and subcooling of the condenser exit liquid. The saturated vapor at the compressor inlet is at -10 C (h1=241.35 kJ/kg). The isentropic enthalpy at the exit is h2s=272.39 kJ/kg. The subcooled liquid exiting the condenser has an enthalpy of h3=91.49 kJ/kg. What is the coefficient of performance?

In a Brayton refrigeration cycle with irreversibilities, the compressor and turbine each have an isentropic efficiency of 80 percent. The isentropic work of compression is 99.99 kJ/kg and the isentropic work of the turbine is 81.19 kJ/kg. What is the net power input per unit mass?

What does the term 'subcooling' refer to in a vapor-compression refrigeration cycle?

In the simple absorption cycle shown in Figure 10.9, where ammonia is the refrigerant and water is the absorbent, what is the state of the solution leaving the absorber at point 'a' and entering the pump?

Why does the coefficient of performance of an air-source heat pump decrease as the outside ambient temperature drops?

An ideal vapor-compression cycle operates with Refrigerant 134a. Saturated vapor enters the compressor at -10 C (h1=241.35 kJ/kg) and saturated liquid leaves the condenser at 9 bar (h3=99.56 kJ/kg). Isentropic compression to 9 bar results in an exit enthalpy of h2s=272.39 kJ/kg. The mass flow rate is 0.08 kg/s. What is the refrigeration capacity in tons?

In a gas refrigeration system for aircraft cabin cooling, how is the cooling effect achieved?

What is the key difference in the compression process between a vapor-compression cycle and an absorption cycle?

What does a pressure-enthalpy (p-h) diagram, commonly used in the refrigeration field, show?

A Carnot heat pump operates between a cold region at -3 degrees Celsius (270 K) and a warm region at 27 degrees Celsius (300 K). What is its coefficient of performance?

In a vapor-compression cycle, what is the process that occurs in the condenser?

An ideal vapor-compression refrigeration cycle has a refrigeration capacity of 12.9 kW. The compressor requires a power input of 1.4 kW. What is the coefficient of performance?

Which component is present in a Brayton refrigeration cycle but not in a standard vapor-compression refrigeration cycle?

In Example 10.3, the rate of exergy destruction in the compressor is 0.58 kW and the rate of exergy destruction in the expansion valve is 0.39 kW. The compressor power input is 3.1 kW. What percentage of the power input is destroyed in the compressor?

What is the physical process that occurs in the evaporator of a vapor-compression refrigeration system?

The coefficient of performance of a heat pump is 5.0. If the work input to the compressor is 2 kW, what is the rate of heat delivered to the warm region?

What is the primary heat source for the generator in an absorption refrigeration system?

An actual vapor-compression cycle has a compressor work input of 2.48 kW and a refrigeration capacity of 3.23 tons. Given that 1 ton of refrigeration equals 3.517 kW, what is the coefficient of performance?

According to the discussion on refrigerant selection, which type of compressor is best suited for low evaporator pressures and refrigerants with large specific volumes?

In a multistage compression refrigeration cycle, how is intercooling typically accomplished?

A Carnot refrigeration cycle is made up of four processes. Which of the following is NOT one of those processes?

An ideal Brayton refrigeration cycle has a net power input of 33.97 kW and produces a refrigeration effect of 92.36 kW. What is the coefficient of performance?

Which of the following describes a key feature of an actual vapor-compression cycle that differs from the ideal vapor-compression cycle?

In a vapor-compression heat pump, what is the source of the heat transferred to the refrigerant in the evaporator?

A Brayton refrigeration cycle with irreversibilities has a net power input of 108.5 kW and a refrigeration capacity of 63.08 kW. What is its coefficient of performance?

What is the primary reason that absorption refrigeration systems have a much smaller work input compared to vapor-compression systems?

In the ideal vapor-compression cycle, what process is assumed to occur as the refrigerant passes through the expansion valve?