What is the main difference between fixed-orifice and thermostatic expansion valve (TXV) in regulating refrigerant flow?

What is the main difference between fixed-orifice and thermostatic expansion valve (TXV) in regulating refrigerant flow?

• A. Fixed-orifice modulates flow to match load; TXV provides constant flow.
• B. Fixed-orifice provides constant flow regardless of conditions; TXV modulates flow to maintain a target superheat.
• C. Fixed-orifice provides constant flow regardless of conditions; TXV modulates flow to maintain a target superheat over varying load.
• D. TXV eliminates need for superheat management.

Answer: (C)

The key idea is how flow regulation adapts to changing cooling or heating load. A fixed-orifice simply meters refrigerant by the size of the hole and the pressure difference; there’s no feedback to adjust flow as conditions change, so the flow rate stays essentially constant and the evaporator may become either overloaded with liquid or starved for refrigerant as load varies. A thermostatic expansion valve, on the other hand, uses a sensing bulb (often at the evaporator outlet) to monitor the actual superheat and then modulates the valve opening to hold a setpoint. When the load increases, the valve opens more to supply more refrigerant; when the load decreases, it closes some to reduce flow. This maintains the target superheat across varying conditions, improving efficiency and preventing liquid return to the compressor. The correct statement captures that fixed-orifice provides constant flow regardless of conditions, while the TXV modulates flow to maintain a target superheat over varying load.

The key idea is how flow regulation adapts to changing cooling or heating load. A fixed-orifice simply meters refrigerant by the size of the hole and the pressure difference; there’s no feedback to adjust flow as conditions change, so the flow rate stays essentially constant and the evaporator may become either overloaded with liquid or starved for refrigerant as load varies. A thermostatic expansion valve, on the other hand, uses a sensing bulb (often at the evaporator outlet) to monitor the actual superheat and then modulates the valve opening to hold a setpoint. When the load increases, the valve opens more to supply more refrigerant; when the load decreases, it closes some to reduce flow. This maintains the target superheat across varying conditions, improving efficiency and preventing liquid return to the compressor. The correct statement captures that fixed-orifice provides constant flow regardless of conditions, while the TXV modulates flow to maintain a target superheat over varying load.