How the refrigerator works: operating principle and device for 8th grade

The refrigerator is one of the most important household appliances, but few people think about how exactly it maintains a low temperature inside. If you are in 8th grade and studying physics, then you already know the basic laws of thermodynamics that underlie the operation of this device. In this article we will examine the principle of operation of a refrigerator using simple examples, without complex formulas, but with an explanation of key processes.

Have you ever wondered why a refrigerator does not “produce cold”, but vice versa? removes heat? Or why is the back wall of the device always warm? The answers lie in the cyclic operation of the refrigerant (special gas) and the main components: compressor, condenser and evaporator. Even if you do not plan to become an engineer, understanding these processes will help you operate the equipment correctly and avoid breakdowns.

The material was prepared taking into account the school physics curriculum for grade 8, but it will also be useful for those who simply want to understand the structure of the refrigerator. We will not go deep into the calculations, but we will explain in detail each stage of the work - from the compression of the refrigerant to the formation of ice in the freezer.

The main parts of the refrigerator and their functions

Any refrigerator, be it a modern model Samsung No Frost or Soviet ZIL-63, consists of four key elements. Each of them plays its role in the cooling process:

• 🔧 Compressor is the “heart” of the refrigerator, which compresses the refrigerant (gas) and forces it to circulate throughout the system. It works on the principle of a pump, creating a pressure difference.
• 🌀 The condenser is a coil on the back wall where hot gas gives off heat to the environment and turns into liquid. That is why the back of the refrigerator is always warm.
• ❄️ Evaporator is located inside the chamber. Here the liquid refrigerant boils, absorbing heat from the air and cooling the products.
• 🔄 Thermostatic valve (TRV) - doses the flow of refrigerant into the evaporator, maintaining the required pressure.

In modern models they can additional elements are added, for example, fans for uniform distribution of cold (technology No Frost) or electronic control units. But the basic scheme has remained unchanged for more than 100 years!

Interesting fact: the first household refrigerator General Electric was released in 1927 and ran on toxic gas ammonia. Today, safe refrigerants are used instead, for example R-134a or R-600a (isobutane).

Physics of the process: how the refrigerant “transfers” heat

The whole principle of operation of the refrigerator is based on two physical phenomena:

1. Evaporation of liquid absorbs heat. For example, if you drop alcohol on your hand, you will feel cold - this is because the alcohol evaporates, taking heat from your skin.
2. Compressing the gas increases its temperature. You can feel this if you quickly inflate a bicycle tire - the pump heats up.

The refrigerant in the refrigerator goes through these processes in a closed cycle:

1. Compressor compresses the gas, increasing its pressure and temperature (up to +70...+90°C).
2. Hot gas enters condenserwhere it is cooled by the air of the room and turns into liquid (gives off heat!).
3. Liquid refrigerant through TRV enters the evaporatorwhere the pressure drops sharply and it boils, absorbing heat from the chamber.
4. The cooled gas returns to the compressor, and the cycle repeats.

Key point: the refrigerator does not “create cold,” but moves heat from the inside to the outside. That is why during operation it heats the air in the kitchen. If you've ever noticed that a small kitchen gets hotter in the summer when the refrigerator is on, that's normal!

It is curious that in the freezers of industrial refrigerators (for example, in supermarkets) they use the same principle, but with other refrigerants capable of cooling down to -40°C. And in cryogenic installations, the temperature drops to -150°C!

Why does the refrigerator turn off periodically?

If you listen, you will notice that the compressor does not work constantly, but turns on and off at intervals. This is not a breakdown, but normal operationwhich ensures:

• ⚡ Saving electricity. Continuous operation of the compressor would lead to excessive consumption of electricity.
• 🛠️ Overheating protection. The compressor motor requires periodic cooling.
• 📉 Maintaining a stable temperature. After reaching a given level, the cold remains for some time thanks to thermal insulation.

Responsible for turning on/off thermostat (or an electronic control unit in modern models). It measures the temperature in the chamber and sends a signal to the compressor. For example, if you set +5°C, then:

1. The compressor runs until the temperature drops to +3...+4°C.
2. Then it turns off and the refrigerator “rests” until the temperature rises to +6...+7°C.
3. The cycle is repeated.

In new refrigerators with inverter compressors (for example, LG GA-B489) the motor operates almost continuously, but with variable power. This allows you to save up to 30% of electricity and reduce noise.

⚠️ Attention: If the refrigerator turns on too often (every 5-10 minutes) or, conversely, does not turn off for hours, this may indicate thermostat malfunction, refrigerant leak or problems with the door seal. In such cases, diagnostics are required.

What is No Frost and how does it differ from a regular refrigerator?

In old refrigerators (and many budget models today) it is used drip defrosting system. The principle is simple: frost forms on the back wall, which periodically thaws and flows into the pan. But in refrigerators with technology No Frost (for example, Bosch KAN92VI30R) everything is arranged differently:

• 🌀 The fan evenly distributes cold air throughout the chamber.
• ❄️ Frost does not form on the walls, but on a hidden evaporator.
• 🔥 The heater is periodically turned on, which melts the ice, and the moisture is removed outside.

Advantages No Frost:

• ✅ No need defrost the refrigerator manually (1-2 times a year is enough for hygienic cleaning).
• ✅ Quick temperature restoration after opening the door.
• ✅ Uniform cooling of all shelves.

Disadvantages:

• ❌ Higher price.
• ❌ Takes up more space due to the fan and air ducts.
• ❌ May dry out the food a little (solved by sealed packaging).

Important: No Frost only available in freezer compartment or both chambers (full No Frost). Carefully read the characteristics when purchasing!

Uneven cooling|Continuous fan operation|Ice on the back wall|Unpleasant odor due to moisture accumulation-->

How is the temperature regulated in different areas of the refrigerator?

Even if you set the thermostat to +5°C, the temperature will be different in different parts of the refrigerator. This is due to natural air circulation:

• 🥶 The coldest zone - the top shelf next to the back wall (usually +2...+3°C there). Ideal for perishable products: meat, fish, milk.
• 🍎 Middle zone is the central shelves (+4...+5°C). Suitable for ready-made dishes, cheeses, sausages.
• 🥬 The lower shelves and drawers —it is warmer here (+6...+8°C), but higher humidity. Optimal for vegetables, fruits, herbs.
• 🥛 Door are the warmest part (+8...+10°C), since when opened they come into contact with room air. It is better to store only stable products here: drinks, sauces, oil.

In the freezer, the temperature is usually -18°C (standard for long-term storage), but in some models (for example, Liebherr GP 1476there is a zone superfreezing down to -24°C for quick freezing.

Modern refrigerators are often equipped several freshness zones with separate adjustment. For example:

• Zone "0°C" —for meat and fish (slows down the growth of bacteria, but does not freeze).
• High humidity zone —for herbs and vegetables (prevents wilting).

⚠️ Attention: If unpleasant odorappears in the refrigerator, this does not always mean that the food has spoiled. Often the reason is dirty drainage hole (where water flows during defrosting) or mold on the door seal. Regular cleaning will help avoid the problem.

Refrigerator energy consumption: how to save electricity?

The refrigerator operates around the clock, so its share in the total energy consumption of the house can reach 20–30%. However, there are ways to reduce costs:

• 🔌 Energy efficiency class. Modern models of the class A+++ (for example, Siemens KI86SAF30) consume 2 times less electricity than old refrigerators of the class C.
• 🌡️ Optimal temperature. Setting +4...+5°C in the refrigerator and -18°C in the freezer is enough for food safety and savings.
• 🚪 Minimize door opening. Each time you open the refrigerator, it loses up to 30% of the cold and spends energy restoring the temperature.
• 🧊 Do not place hot dishes. This causes the compressor to work harder. Cool food to room temperature before placing.
• 📍 Correct location. The refrigerator should not be placed next to a stove, radiator, or in direct sunlight. Optimally - in the coolest corner of the kitchen.

Interesting fact: in Europe, new energy efficiency standards have been in force since 2019, and many old classes (A+, A++) have been revised. Now the most economical class is A (without pluses), but with more stringent requirements.

*Calculation is based on an average tariff of 4 rubles/kWh (may vary depending on the region).

What happens if the refrigerator stops working?

Imagine: you open the refrigerator, but it does not cool. What to do? First of all, check:

1. Connecting to the network. Perhaps the lights were turned off or the circuit breaker in the control panel was triggered.
2. Thermostat. Try setting a lower temperature - if the compressor starts working, the problem is in the adjustment.
3. Door seal. Place a sheet of paper between the door and the body - if it falls out easily, the seal is worn and warm air is leaking.
4. Back wall. If the condenser (coil) is heavily contaminated with dust, it needs to be cleaned with a vacuum cleaner.

If simple measures did not help, possible reasons:

• 🔧 Breakage compressor - the most expensive repair (sometimes it is cheaper to buy a new refrigerator).
• ❄️ Refrigerant leakage —requires recharging the system (costs 3–5 thousand rubles).
• 📱 Malfunction of the electronic unit is a common problem in models with a display.
• 🔌 Failure in the power circuit —checked with a multimeter.

The average service life of the refrigerator is 10–15 years. If your model is older, repairs may not be practical. For example, replacing a compressor in a refrigerator Atlant 2005 will cost 8–12 thousand rubles, which is comparable to the cost of a new budget appliance.

How to check if the compressor is working?

If the refrigerator is not working It cools, but the light inside is on, listen: the compressor should make a slight hum. You can also touch the condenser (rear grill) - if it is cold, the refrigerant is not circulating. In modern models, a malfunction may be indicated by an error on the display (for example, E1 or F2).

FAQ: Frequently asked questions about the operation of the refrigerator

Why does the refrigerator hum when operating?

The hum comes from the compressor and fan (in models No Frost). This is normal, but if the noise has become stronger than usual, there may be reasons:

• The refrigerator is not level (adjust the legs).
• The compressor is worn out (needs replacement).
• The fan is touching ice or wires (needs to be defrosted and check).

Modern inverter compressors are quieter than traditional ones.

Is it possible to place a refrigerator on the balcony in winter?

No, if the temperature on the balcony drops below +10°C At low temperatures:

• Oil in the compressor. thickens, which can lead to breakdown.
• The thermostat may not operate correctly.
• The door seal loses elasticity.

An exception is models with climate class SN-T (designed to operate at +10…+43°C).

How long can the refrigerator operate without shutting down?

In normal mode, the compressor operates in cycles: on for 10–20 minutes, then off for 20–40 minutes. If the refrigerator does not turn off for more than that. 2–3 hours, this is a sign of a malfunction:

• The thermostat has failed.
• Refrigerant leak.
• Clog in the capillary tube.

In this case, you need to urgently call a technician, otherwise the compressor will overheat.

Why does ice form on the back wall of the refrigerator?

In refrigerators with a drip system (not No Frost), frost on the back wall is normal. It periodically thaws and water flows into the drainage hole. But if ice accumulates too quickly, there may be reasons. such:

• Frequent opening of the door.
• Loose closure (worn seal).
• High humidity inside (for example, if you place hot pots).
• Malfunction of the thermostat or heating element defrost.

Solution: defrost the refrigerator, check the seal and do not place liquid dishes without a lid.

Is it possible to turn on the refrigerator immediately after transportation?

No! After transportation (especially in a horizontal position), you need to wait:

• 2–4 hours if the refrigerator was transported vertically.
• 6–12 hours if it was lying on its side.

This is necessary so that the oil from the compressor flows back, otherwise when turned on, it may occur water hammer (compressor breakdown).