21.Why are throttling devices commonly used in refrigeration and air-conditioning
applications?

Answer is given below

Explanation:

we know that some common types of throttling devices are

Hard -throttling devices Capillary valve Constant pressure throttling devicesThermostatic expansion valve Float expansion valve

so here throttling devices commonly used in refrigeration and air-conditioning because

To reduce the coolant pressure, the high pressure of the refrigerant from the condenser is necessary to reduce the evaporation to obtain evaporation at the right temperature  To meet the refrigerated load, the throttling valve flows through the coolant to cool the load at high temperatures.