Question

The expansion device used in domestic refrigerator working on vapour compression cycle is

• A. Electrically operated throttle valve
• B. Manually operated valve
• C. Thermostatic valve
• D. Capillary tube

Hint:

\textbf{Expansion Device} in refrigeration: Reduces pressure and regulates flow of refrigerant to evaporator.
\textbf{Capillary Tube:} A long, thin tube providing a fixed restriction. Simple, cheap, no moving parts.
Widely used in small, hermetically sealed refrigeration systems with relatively constant loads, such as \textbf{domestic refrigerators}, freezers, and window air conditioners.
\textbf{Thermostatic Expansion Valves (TEVs)} are more common in larger systems or those with varying loads, offering better control.

Answer 1

The Correct Option is D

In a vapor compression refrigeration cycle (used in domestic refrigerators, air conditioners, etc.), the expansion device (also called a throttling device or metering device) has two main functions: 1. To reduce the pressure of the high-pressure liquid refrigerant coming from the condenser down to the low pressure of the evaporator. 2. To regulate the flow of refrigerant into the evaporator. This pressure reduction causes the refrigerant to cool significantly due to the Joule-Thomson effect, allowing it to absorb heat in the evaporator. Common types of expansion devices:
Capillary Tube: A long, narrow tube of fixed diameter. The pressure drop occurs due to friction and acceleration of the refrigerant as it flows through the tube. Capillary tubes are simple, inexpensive, and have no moving parts, making them very common in small refrigeration systems like domestic refrigerators, freezers, and small air conditioners where the load is relatively constant.
Thermostatic Expansion Valve (TEV or TXV): A more sophisticated device that regulates refrigerant flow into the evaporator based on the superheat of the refrigerant vapor leaving the evaporator. It can adjust to varying load conditions. Used in larger or more complex systems. (Option c is a type of expansion valve).
Automatic Expansion Valve (AEV): Maintains a constant pressure in the evaporator. Less common now.
Float Valves (High-side, Low-side): Maintain a constant liquid level in a float chamber or evaporator. Used in some larger systems.
Orifice plates / Short tube restrictors: Simpler fixed restriction devices. Options provided:
(a) Electrically operated throttle valve: Electronic expansion valves (EEVs) exist, offering precise control, but are more common in larger/advanced systems, not typically "domestic refrigerators" where cost and simplicity are key. "Throttle valve" is a general term.
(b) Manually operated valve: Not used as the primary expansion device in an automatic refrigeration cycle like a domestic refrigerator.
(c) Thermostatic valve (Thermostatic Expansion Valve - TEV): As described, this is a modulating valve used for varying loads, common in commercial refrigeration and larger AC systems, but less so in typical domestic refrigerators which usually have a simpler device.
(d) Capillary tube: This is the most common expansion device used in domestic refrigerators and small hermetic refrigeration systems due to its simplicity, low cost, and reliability (no moving parts). Therefore, the expansion device predominantly used in domestic refrigerators is the Capillary tube. \[ \boxed{\text{Capillary tube}} \]