How Does a Refrigerator Work? Understanding Your Walk-in Cooler

Have you ever wondered, “How does a refrigerator work?” While rocket science and quantum physics can be incredibly complex, understanding refrigerator mechanics is straightforward. To grasp how a refrigerator operates, familiarize yourself with the following concepts:

Ideal Gas Law: The relationship between pressure, volume, and temperature of gasses.

Phase Transitions: The process of liquid turning into gas and vice versa.

Four-Step Refrigeration Cycle: The sequence that a refrigerator goes through to cool effectively.

Key Components: Understanding the main parts of your fridge and their functions.By learning these basics, you can diagnose issues early and save on repair and maintenance costs.

refrigeration cycle diagram

Understanding the Ideal Gas Law

PV = nRT. Does that sound familiar from your high school science classes? This is the Ideal Gas Law, where:

  • P = Pressure
  • V = Volume
  • T = Temperature
  • n = Amount of gas
  • R = Constant

For our understanding of the refrigeration cycle, we can focus on P, V, and T, as we don’t need to delve into n and R.

The key takeaway is that as pressure (P) increases, temperature (T) also increases. Conversely, if pressure decreases, temperature decreases as well. In refrigeration systems, pressure is manipulated by changing the volume:

  • Decreasing Volume: Increases both pressure and temperature.
  • Increasing Volume: Decreases both pressure and temperature.

This relationship is crucial for the refrigeration process, where managing pressure and temperature effectively is essential for cooling.

Example: Pumping Up a Bike Tire

Consider the process of pumping up a bike tire. As you push down on the pump, the volume of air decreases, leading to an increase in air pressure. This heightened pressure forces the air into the bike tire tube.

After several pumps, you may notice that the pump’s base becomes warm. This warmth occurs because the pressure of the air inside the pump is rising, which, according to the Ideal Gas Law, also increases the temperature. This example illustrates how the relationship between pressure and temperature operates in real-world scenarios.

Phase Transitions

At the heart of every refrigeration system lie some essential chemistry: phase transitions. In chemistry, a “phase” refers to a state of matter. While there are four states, we only need to focus on three to understand refrigeration: solid, liquid, and gas.

Because this process is cyclical, we could theoretically start at any step, so don’t worry if you need to read this a few times!

  1. Liquid Refrigerant Enters: The refrigerant, in its liquid phase, enters the fridge and freezer.
  2. Heat Absorption: As the refrigerant circulates, it absorbs heat energy from the interior, cooling the space.
  3. Phase Transition: Eventually, the liquid absorbs enough heat to transition into a gas. (This is a simplified explanation to aid your understanding.)
  4. Compression: The unit’s compressor raises the pressure of the gaseous refrigerant.
  5. Condensation: The hot gas then flows through the condenser coils outside the fridge. Here, it cools down and the phase changes back into a liquid as it comes into contact with the cooler exterior air.

This cycle is vital for the effective operation of your refrigerator.

How the Refrigeration Cycle Works

Refrigerators operate on a closed-loop system. At the core of this system is the refrigerant, which is often a blend of hydrofluorocarbons (HFCs) or isobutane. This refrigerant plays a crucial role in removing heat from the cooler interior and rejecting it into the air outside the fridge.

To understand the refrigeration cycle, we’ll begin with the main power-drawing component: the compressor.

Compressor – The Pressure Increaser

The compressor is the heart of your refrigerator and the component that consumes the most power. Think of it as a large vapor pump. Just as your heart pumps blood to your body, the compressor circulates refrigerant throughout the system. If the compressor fails, the entire refrigerator stops functioning.

The compressor’s primary role is to increase the pressure of the refrigerant. According to the Ideal Gas Law, this increased pressure also raises the refrigerant’s temperature. Cool vapor enters through the suction line, while hot vapor exits via the condensing line.

Condenser – The Heat Ejector

The condenser is the next step in the refrigeration cycle and is always located outside the fridge. It typically resembles a radiator, featuring tubes that run back and forth. These hollow tubes carry the refrigerant, and if laid out in a straight line, they would extend quite long.

The primary function of the condenser is to cool the refrigerant passively. Its high surface area allows for extensive heat exchange with the surrounding ambient air. If you touch the lines of a functioning condenser, they will feel warm to the touch.

As the refrigerant travels from the compressor toward the throttling device (which we’ll cover next), it gradually cools down. At a certain point in the condenser, most refrigerants undergo a phase change from a gas (higher energy) to a liquid (lower energy). This transformation is why the condenser is aptly named; the term condensation refers to the process of a gas turning into a liquid.

By the end of the condenser, the refrigerant is at a moderately warm temperature but under very high pressure.

Liquid line

The liquid line transports the liquid refrigerant from the condenser to the throttling device. Its primary function is to ensure that all refrigerants are in its liquid phase.

Occasionally, some refrigerants may reach the end of the condenser without fully transitioning from gas to liquid. For the metering device to function effectively, the refrigerant must be entirely in liquid form.

Metering/Throttling Device – The Pressure Dropper

The metering device, also known as the throttling device, is where the magic of refrigeration occurs. This component restricts the flow of refrigerant, and the most common types are capillary tubes and expansion valves (TXVs).

In capillary tubes, for example, this restricted flow is achieved by forcing the refrigerant through a long, narrow tube. Once the refrigerant passes through the throttling device, it enters a significantly larger space. As a result, the volume of the refrigerant increases substantially to fill this larger area.

Referring back to PV = nRT, we can understand that when the volume increases rapidly, both pressure and temperature will decrease significantly. This concept can be challenging to grasp, so let’s explore an imperfect analogy to clarify it.

The Dance Club Analogy

Imagine you are at a crowded club where everyone is dancing. As you can imagine, the room gets pretty hot! Now, let’s say you try to leave, but a whole bunch of people are also trying to exit through the only door. After waiting, it’s finally your turn to go through. As you step outside, you enter a large room with few people and plenty of space. This new room is much cooler because there’s less body heat, and you have ample room to move around and dance freely.

In this analogy:

  • The door represents the throttling device.
  • The crowded, hot room symbolizes the condenser.
  • The cool room signifies the evaporator.

On the condenser side of the metering device, the high pressure and temperature are akin to the crowd of dancers trying to exit. Conversely, on the evaporator side, there are far fewer people, representing lower pressure and temperature. Each dancer has more space to move around in the cool room.

While this analogy isn’t perfect, it should help you visualize how a throttling device operates in refrigeration.

Flashing

The concept of flashing is simple yet crucial. It describes the change in the state of the refrigerant after it passes through the throttling device and enters the evaporator. Refrigerants have the remarkable ability to flash (boil) at very low temperatures when exposed to low pressures. This characteristic allows the coil to cool down (become frosty) and effectively exchange heat with the air inside the room.

Evaporator – The Heat Absorber

After the metering device, the refrigerant enters the fridge through the evaporator. While similar to the condenser, the evaporator operates oppositely. It consists of a long, coiled, hollow tube that loops back on itself, but unlike the condenser, it runs through the interior of the refrigerator and freezer.

At the start of the evaporator, thanks to the throttling device, the refrigerant is extremely cold. As warm air from the room is pushed through the coil by the evaporator’s fans, the refrigerant absorbs heat and transitions back into a gas as it exits the evaporator coil. This process effectively cools the air inside the fridge.

The evaporator’s role is to remove heat from the air inside the refrigerator. This is why a fridge (or any cooling space) must be sealed; it allows for air recycling, enabling the evaporator to efficiently extract heat from the enclosed area.

Unlike the condenser, which transitions from hot to cool, the evaporator changes from cool to warm. In this phase change, the refrigerant converts from a liquid back to a gas, a process known as evaporation, which is the origin of the evaporator’s name.

The evaporator is a common component that can cause issues in coolers. If your refrigerator or freezer isn’t functioning properly, check the evaporator for any ice buildup.

The Suction Line

The suction line connects the evaporator to the compressor, running from inside the fridge to the outside. It is named the suction line because the compressor “sucks” the refrigerant from the evaporator and pushes it into the condenser.

Other Components That Make A Refrigerator Work

While the refrigeration cycle is essential, understanding the additional components of a refrigerator or freezer unit is equally important. At its core, the thermostat serves as the main control device in these systems. However, depending on the specific application, there may be various other components, such as pressure controls, fan delays, heaters, defrost timers, and solenoid valves.

The Thermostat

The thermostat in a fridge or freezer is the primary control device and one we are all familiar with. It functions as an automatic on/off switch that regulates the refrigerator’s operation. When the temperature inside the fridge rises above the set level, the thermostat activates the compressor to initiate the cooling cycle. The compressor continues to run until the thermostat indicates that the desired temperature has been reached.

When you lower the thermostat setting, the compressor operates more frequently to remove additional heat from inside the fridge. Conversely, increasing the thermostat setting reduces the compressor’s runtime.

Finding the ideal temperature for your cooler or freezer can help save on energy bills and extend the unit’s lifespan. Typically, a commercial walk-in cooler is designed to operate at 35°F, while a freezer should be set at -10°F.

Insulation and Structure

The structure of a fridge or freezer is crucial for its efficient operation. Proper insulation is essential; without it, a refrigerator or freezer would struggle to maintain its internal temperature. The layers of insulation create a barrier that separates the cold environment inside from the ambient air outside, effectively isolating the space.

More effective insulation reduces heat transfer, allowing the unit to use less energy while maintaining optimal cooling.

When considering a new cooler or freezer, it’s important to evaluate various structural aspects, including:

  • Size
  • Door type
  • Interior and exterior finish
  • Location of the condensing unit

These factors can significantly influence the performance and efficiency of your refrigeration unit.

Final Thoughts on How Refrigeration Works

Hopefully, you can now answer the question that brought you here: “How does a refrigerator work?” With a solid understanding of the refrigeration cycle and the key components of a refrigerator, it’s also important to familiarize yourself with common maintenance issues related to coolers and freezers.

By recognizing a few simple cues, you can save money, and time, and protect your products from spoilage! Contact Arctic to request more info.