Why is the vapor absorption refrigeration cycle called a heat operated cycle? Discuss the working principle of vapor absorption refrigeration.

How does heat exchanger help to improve performance of vapor absorption cycle.

A refrigeration system working on Bell-Coleman cycle receives air from cold chamber at 5°C and compresses it from 1 bar to 4.5 bar. The compressed air is cooled to a temperature of 37°C before it is expanded in the expander. Calculate the COP of the system when compression and expansion are i) isentropic and ii) $PV^{1.25} = \text{Constant}$.

What are the basic differences between refrigeration and air con-conditioning?

Draw and label the P-V and T-S diagrams of Bell-Coleman air refrigeration cycle and hence prove the COP of the cycle for isentropic compression and expansion is
$$COP = \frac{1}{(r_p)^{\frac{\gamma-1}{\gamma}} - 1}$$
Where $r_p$ is the compression or expansion ratio.

In a refrigeration plant working on Bell-Coleman cycle, air is compressed to 5 bar from 1 bar. Its initial temperature is 10° C. After compression, the air is cooled upto 20° C in a cooler before expanding back to a pressure of 1 bar. Determine the theoretical COP of the plant and net refrigerating effect. Take $C_p = 1.005$ kJ/kgK.

Define heat engine, heat pump and refrigerating machine. Make a comparison among them by schematic diagram and relevant mathematical expressions.

Draw the schematic, $P-v$ and $T-s$ diagram and label all the components and process of air refrigerator working on Bell-Colemon cycle.

A simple air cooled system used for an aeroplane having a load of 10 tonnes. The atmospheric pressure and temperature are 0.9 bar and 10°C respectively. The pressure increases to 1.013 bar due to ramming. The temperature of the air is reduced by 50°C in the heat exchanger. The pressure in the cabin is 1.01 bar and the temperature of air leaving the cabin is 25°C. Determine (i) Power required to take the load of cooling in the cabin; and (ii) COP of the system. Assume that all the expansions and compressions are isentropic. The pressure of the compressed air is 3.5 bar.

What are the main disadvantages of refrigeration cycle with air as working substance?

Why aircraft cooling is needed? If an airplane is moving at 1500 km/hr, how much temperature will rise?

In a Bell-Coleman refrigeration plant, the air is drawn from cold chamber at 1.0 bar and 12°C and compressed to 6 bar. The same is then cold to 15°C and the cooler depending in the expander to cold chamber pressure of 1.0 bar. Determine the theoretical COP of the plant and the net refrigeration effect per kg of air if the compression and expansion is followed by $PV^{1.4} = \text{constant}$.

Draw and level the P-V and T-S diagram of Bell Coleman air refrigeration cycle and hence prove the COP of the cycle for isentropic compression and expansion.

$$COP = \frac{1}{(r_p)^{\frac{\gamma-1}{\gamma}} - 1}$$

The atmospheric air at pressure 1 bar and temperature -5°C is drawn in the cylinder of the compressor of Bell-Coleman refrigerating machine. It is compressed isentropically to a pressure of 5 bar. In the cooler, the compressed air is cooled to 15°C, pressure remaining the same. It is then expended to a pressure of 1 bar in an expansion cylinder, from where it is passed to the cold chamber. Find (i) the work done per kg of air and (ii) COP of the plant.
(Assume for air expansion law, $pv^{1.2} = \text{constant}$; compression law $pv^{1.4} = \text{constant}$ and specific heat of air at constant pressure = 1 KJ/kg°K.