How Does Refrigeration Valve Suppliers Work?

In a refrigeration circuit, the evaporator coil plays a critical role. Part of its responsibility is creating the controlled pressure drop necessary for the refrigerant to change phase, the bulk of which occurs via the system’s metering device, such as a thermostatic expansion valve (TXV).

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What is a distributor?

In evaporators with multiple refrigerant circuits, the next piece of equipment in the process after the TXV is the distributor. The term distributor describes the fixture – typically brass, but not always – that serves as a hub for a variable number of tubes, known as leads or circuit tubes, each of which connects to a corresponding refrigerant circuit in a given coil. As its name implies, the distributor’s function is to evenly distribute refrigerant throughout the evaporator’s circuiting.

Once the larger nozzle of the expansion valve opens, the distributor helps maintain consistent flow velocity through the evaporator after the pressure drops. Think of the expansion valve as the coarse focus on a microscope and the distributor as the fine focus – it’s a tag team of sorts. The expansion valve takes care of most of the pressure drop, and the distributor precisely completes the remainder.

Distributors also facilitate saturated, or two-phase flow – a more effective heat transfer medium than just liquid or vapor. As the refrigerant’s pressure drops as it enters the evaporator, the flow rate remains the same. This will cause some refrigerant to start boiling off, meaning that when it enters the coil’s circuitry, the refrigerant is a mixture of liquid and vapor. Liquid goes in, two-phase flow comes out.

Without a distributor, i.e. with just a standard header, two-phase flow is much more difficult to obtain in a multi-circuit evaporator, resulting in uneven distribution and inadequate, if any, saturation.

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Common distributor types and installation orientations

Orifice distributors

There are a few different shapes and types of distributors, but orifice distributors are common, resembling a showerhead, like the one pictured below.

However, where a showerhead controls and directs the flow of water, distributors do so for refrigerants. As its name implies, an orifice distributor works by controlling refrigerant flow via a small hole. In the cutaway below you can see the internal structure of the distributor. The groove near the bottom is where the disk with the nozzle is inserted, which is sized according to the desired flow velocity of the refrigerant as it enters the distributor leads.

Venturi distributors

The second type of distributor is what’s known as Venturi distributors, named after Giovanni Venturi, discoverer of the Venturi effect, which describes the pressure reduction that occurs as a fluid flows through a narrower section of a tube, illustrated below.

Courtesy of Thierry Dugnolle - Own work, CC0, https://commons.wikimedia.org/w/index.php?curid=

Rather than operating via pressure drop, Venturi distributors function based on – you guessed it – the Venturi effect. Instead of a sharp-edged orifice, Venturis have a tapered throat, the size of which is determined based on the number of circuits in the coil. These nozzles must be sized correctly at the time of fabrication, and cannot be adjusted after the fact.

Courtesy of Sporlan Division - Parker Hannifin Coporation

Installation orientation

There are several possible installation positions for distributors, and the decision of where to put the connections depends on things like the amount of space available as well application-specific performance considerations.

One positioning is vertical, as shown in the first photo below. The vertical positioning has the added benefit of gravity, which contributes to some improvement in efficiency, but many applications dictate alternative connection locations, like the subsequent photos.

Sizing

Nozzle selection is one of the most critical elements of designing a distributor. The nozzle controls flow rate, and a properly sized nozzle is vital for accurately meeting the pressure drop requirements of the evaporator assembly.

If your nozzle creates a hole that’s too large, the result is insufficient velocity, and two-phase flow will not be achieved. An undersized nozzle will result in excessive pressure drop through the distributor, which will reduce system capacity and efficiency.

Proper nozzle selection is a vital – and sometimes overlooked – part of any good system, and a number of resources exist to help make sure you choose the right one, such as this PDF from Sporlan, a leading distributor manufacturer.

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We’ve all been there. You step inside on a hot day and are mercifully greeted with a wall of cool air. Well, you have the refrigeration cycle to thank for that relief. While there are dozens of methods of heating and cooling, the basic function is still the same and is used in some form across countless industries and processes. But how does it work? This post will answer that question by outlining the main components of a standard refrigeration loop and the functions of each.

In simple terms, a refrigeration cycle's mission is heat absorption and heat rejection. As any HVAC instructor will tell you (emphatically), you can't make cold, you can just remove heat. The refrigeration cycle, sometimes called a heat pump cycle, is a means of routing heat away from the area you want to cool. This is accomplished by manipulating the pressure of the working refrigerant (air, water, synthetic refrigerants, etc.) through a cycle of compression and expansion.  

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That’s not the full picture, of course, but that’s the basic idea. Now, let’s get into the equipment that helps execute that job. There are certainly other components in most loops, but most would agree the four fundamental elements of a basic cycle are as follows:

• The compressor
• The condenser
• The expansion device
• The evaporator

The compressor

Compression is the first step in the refrigeration cycle, and a compressor is the piece of equipment that increases the pressure of the working gas. Refrigerant enters the compressor as low-pressure, low-temperature gas, and leaves the compressor as a high-pressure, high-temperature gas.

Types of compressors

Compression can be achieved through a number of different mechanical processes, and because of that, several compressor designs are used in HVAC and refrigeration today. Other examples exist, but some popular choices are: 

1. Reciprocating compressors

2. Scroll compressors

3. Rotary compressors

The condenser

The condenser, or condenser coil, is one of two types of heat exchangers used in a basic refrigeration loop. This component is supplied with high-temperature high-pressure, vaporized refrigerant coming off the compressor. The condenser removes heat from the hot refrigerant vapor gas vapor until it condenses into a saturated liquid state, a.k.a. condensation.

After condensing, the refrigerant is a high-pressure, low-temperature liquid, at which point it’s routed to the loop’s expansion device.

The expansion device

These components come in a few different designs. Popular configurations include fixed orifices, thermostatic expansion valves (TXV) or thermal expansion valves (pictured above), and the more advanced electronic expansion valves (EEVs). But regardless of configuration, the job of a system’s expansion device is the same - create a drop in pressure after the refrigerant leaves the condenser. This pressure drop will cause some of that refrigerant to quickly boil, creating a two-phase mixture.  

This rapid phase change is called flashing, and it helps tee up the next piece of equipment in the circuit, the evaporator, to perform its intended function.

The evaporator

The evaporator is the second heat exchanger in a standard refrigeration circuit, and like the condenser, it’s named for its basic function. It serves as the “business end” of a refrigeration cycle, given that it does what we expect air conditioning to do – absorb heat.

This happens when refrigerant enters the evaporator as a low temperature liquid at low pressure, and a fan forces air across the evaporator’s fins, cooling the air by absorbing the heat from the space in question into the refrigerant.

After doing so, the refrigerant is sent back to the compressor, where the process restarts. And that, in a nutshell, is how a refrigeration loop works. If you have any questions about the refrigeration cycle or its components and how they work, give us a call. We've been helping customers get the most out of their HVAC and refrigeration equipment for nearly 100 years.

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