What is the difference between a direct expansion and a flooded evaporator?

What is the difference between a direct expansion and a flooded evaporator?

What is the distinction between a direct expansion evaporator and a flooded evaporator? A flooded evaporator does not entirely evaporate and heat the refrigerant, whereas a direct expansion evaporator fully evaporates and heats the refrigerant at a high temperature. This difference in design affects how the two types of systems are maintained.

Direct expansion systems have one or more valves located in the refrigerant line between the compressor and the evaporator that open and close to allow refrigerant to be moved through the system. These valves may be electric, such as power-operated thermostats, or they may be spring-loaded devices used for control purposes. Direct expansion systems are easy to maintain because any part of the system can be inspected or replaced if necessary. For example, the evaporator core can be removed from the case and replaced if it becomes damaged. Flooded systems do not have valves located in the refrigerant line; instead, they use a liquid pump to force liquid refrigerant into the evaporator during operation. This liquid flows through the fins of the evaporator absorbing heat from outside air flowing over the unit. When the liquid returns to the tank, it is heated by the evaporated gas and becomes superheated vapor which is pushed back into the compressor for further compression and discharge into the environment. Flooded systems are less accessible than direct expansion systems because the tank and all other components inside the chassis must be removed to service or replace any parts that might need replacing.

What is a dry expansion evaporator?

Scheme for a Dry Expansion Evaporator The dry expansion, also known as direct expansion, is a method of limiting the mass flow of refrigerant supplied to the evaporator to the amount that can be totally evaporated on its journey to the far end of the evaporator, resulting in only steam reaching the compressor suction input. This is done by using a valve located in the supply line just before it reaches the evaporator, called a dry-expansion valve (DEV). As the name suggests, there is no liquid refrigerant flowing through this valve. Instead, only vapor enters the compressor. Since less fluid enters the compressor, it needs to run at a lower speed to achieve the same effect. This leads to better efficiency levels and reduced compressor noise.

Dry expanders were first developed in the early 1950s by the United States Navy. They are now used throughout the refrigeration industry. A dry expansion system consists of a DEV, a charge air cooler (CAC), and some sort of control circuit. The DEV limits the flow of refrigerant into the evaporator so that it can be completely evaporated. Any excess flow beyond that needed for complete evaporation will drain back out of the compressor in the form of gas. This leaves only the amount of fluid required to meet the demand of the closed-loop system.

What are the two types of evaporator flow control?

There are two techniques for controlling evaporator flow. There are two types of evaporators: (1) dry expansion evaporators, also known as direct expansion or D-X-evaporators, and (2) flooded evaporators. The type of evaporator you have determines how you control its flow.

With a dry expansion evaporator, water flows into the unit through a tube called the trimaural. As it passes over the heat exchanger, which is filled with antifreeze, it turns into vapor. This vapor enters another tube called the coreflow, where it is split into three parts: one goes to the heater, one to the compressor, and one is let out into the atmosphere through a pipe called the blowoff valve. As the compressor takes in air, it pulls in this refrigerant vapor from the trimaural and compresses it. When the compressor needs more refrigerant, it sends some out through its own system. This causes the compressor to run longer and save energy.

A flooded evaporator uses liquid refrigerant that flows through tubes inside the trimaural instead. It too gets split into three parts: one goes to the heater, one to the compressor, and one is let out into the atmosphere through a pipe called the blowoff valve. As the compressor takes in air, it pulls in this liquid refrigerant from the trimaural and compresses it.

When referring to evaporators, the terms "direct expansion" and "dry type" can be used interchangeably.?

The words "direct expansion" and "dry type" can be used interchangeably when referring to evaporators. Condensers in high-pressure chillers can be either air-cooled or water-cooled. In high-pressure chillers, the only metering devices are thermostatic expansion valves. These valves open under pressure from a compressor motor drive unit or electronic controller as needed to maintain set points for temperature and pressure. They close when heat is no longer being drawn from the fluid by the expander. The thermostatic valve closes automatically when the fluid reaches its target temperature, at which point any remaining fluid flow over the valve's closing set point is cut off.

In low-pressure chiller/heat pumps, metering devices include mechanical expansion valves and electropneumatic valves. Mechanical expansion valves use a biasing spring to force a ball or other object into contact with a small orifice in order to permit refrigerant to flow through the valve. Electropneumatic valves are controlled electronically using an electric signal from a controller to actuate a valve mechanism inside the device. This type of valve opens under the influence of an electrical signal and closes upon loss of this signal. There is no physical object such as a ball that must be moved by an electromagnet to control the flow of refrigerant. Instead, the entire valve mechanism itself is activated by an electric signal.

What are the different types of D-X evaporators?

D-X evaporators and flooded evaporators There are two techniques for controlling evaporator flow. Both types use a valve to control flow between coils.

In a dry expansion evaporator, also called a direct expansion evaporator, water is not used to control flow between coils. Instead, air is forced through small holes in the casing surrounding each coil. The increased temperature of the coil causes the refrigerant inside it to change phase from a liquid to a gas, which increases the volume of the coil and thus its resistance to flow. The greater the difference in pressure between the interior of the casing and the exterior, the more open the hole must be to avoid restricting flow.

In a flooded evaporator, also called an indirect expansion evaporator, water is used to control flow between coils. Water enters the casing at one end and flows out the other, turning off when it reaches the outlet port. The weight of the water inside the casing forces any liquid that might form against the direction of flow, preventing any possibility of restriction.

So flooded evaporators require less pressure to turn off the flow than dry expansion evaporators.

About Article Author

Chasity Neal

Chasity Neal is an interior designer who has been working in the industry for over 15 years. She started her career as an architect, but found that she loved designing interiors more than anything else. Her favorite part of the process is coming up with design solutions for clients and getting to see their reactions when they first see their new space.

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