Principle of operation of a gas refrigerator: design and cycle stages

Many owners of campers, summer cottages and lovers of long-term Road travelers often wonder how exactly a gas refrigerator is able to maintain a low temperature without the use of an electric compressor. Unlike the usual household models that can be found in any kitchen, there are no moving mechanical parts that create vibration and noise. Absorption system, which underlies the operation of such devices, uses heat from the combustion of gas or an electric heater to start physical and chemical processes.

Understanding how a gas refrigerator works helps not only to operate it correctly, but also to diagnose faults in a timely manner. The basis of the entire system is a closed circuit filled with a special mixture of substances that circulate under pressure. The key point is that ammonia in this system acts as a refrigerant, and water and hydrogen ensure its movement and absorption.

You don't need to be a chemical engineer to understand the basic principles, but knowing the main components will greatly simplify maintenance. Heat transfer occurs due to the temperature difference in different parts of the system, which creates a natural draft for the movement of gases. It is the absence of a compressor that makes such units virtually silent and extremely reliable in shaking off-road conditions.

Design of absorption cooling system

The heart of any absorption refrigerator is a complex system of tubes and chambers located in the rear of the case. This entire structure is sealed and filled with a working mixture under a certain pressure. The main components are the generator, condenser, evaporator and absorber, each of which performs its own unique function in the refrigeration cycle.

The generator, often called a reboiler, is a chamber where the working mixture is heated. In this unit, under the influence of heat from a gas burner or heating element, active boiling of the solution begins. Here ammonia water is divided into ammonia vapor and a weak solution, which then flows down.

At the top of the system there is a condenser, where hot ammonia vapor gives off heat to the environment and turns into a liquid state. Next, the liquid enters the evaporator, where it is mixed with hydrogen. It is in this place that a sharp drop in pressure occurs, which leads to intense evaporation and absorption of heat from the internal chamber of the refrigerator.

The absorber completes the cycle, in which the hydrogen-ammonia mixture meets the poor solution flowing from the generator. Water actively absorbs ammonia vapor, restoring the concentration of the solution, after which it is again supplied to the generator. This continuous process ensures a stable low temperature.

• 🔥 Generator - a zone for heating and separating the mixture into components.
• ❄️ Evaporator - the place where direct cooling of the products occurs.
• 💧 Absorber - a chamber for absorbing ammonia vapor with water.
• 🌡️ Condenser - a radiator for cooling and liquefying vapors.

All these elements are connected by thin tubes, the diameter of which is selected to ensure the correct movement of substances due to the difference in density and pressure. Violation of the tightness of any of the connections leads to complete inoperability of the device, since working fluid evaporates and the system becomes airy.

Physical and chemical processes inside the circuit

To understand why a gas refrigerator works this way, and not otherwise, it is necessary to consider the behavior of substances at different temperatures. It is based on the ability of water to absorb large volumes of ammonia at low temperatures and release it when heated. This process is called absorption, and it is radically different from the usual compressor circuit.

In the generator, the temperature reaches approximately 150-200 degrees Celsius. With this heating, ammonia actively boils away from the aqueous solution, creating high pressure in the upper part of the system. Ammonia vapors, being lighter than the solution, rush upward, passing through the separator, where they are separated from the remaining water.

⚠️ Attention: The temperature in the burner area can reach critical values, so under no circumstances touch the metal parts of the back wall while the device is operating.

Then the vapors enter the condenser, where cooled by air circulating along the radiator fins. Turning into liquid, ammonia loses energy and is ready for the next step. In the evaporator, it meets hydrogen, which does not dissolve in ammonia, but creates a pressure of the mixture equal to the pressure in the condenser.

Thanks to the law of partial pressures, ammonia begins to actively evaporate in the presence of hydrogen, even at relatively low temperatures. This process requires a large amount of heat, which it takes from the interior of the chamber. Thus, heat exchange occurs without mechanical compression of gases.

The role of the gas burner and ignition system

The energy source in autonomous mode is the gas burner, which heats the lower part of the generator. Modern models are equipped with piezo ignition systems or electronic ignition, which greatly simplifies starting. However, the principle of gas supply remains physical, based on pressure differences.

Gas from the cylinder through a reducer enters the mixer, where it is enriched with air. It is important that the mixture is correct, otherwise combustion will be incomplete, which will lead to the formation of soot on the heat exchanger. Soot significantly reduces the efficiency of heat transfer and can cause failure.

The safety system usually includes a thermocouple, which is heated by the pilot burner flame. While the thermocouple is hot, it produces a current that keeps the gas valve open. If the flame goes out, the thermocouple cools, the current disappears, and the valve shuts off the gas supply, preventing leakage.

Adjusting the gas pressure is carried out by replacing the nozzle or adjusting the reducer on the cylinder. To operate on liquefied propane-butane and natural gas, different settings are required, since their calorific value and pressure are different.

Refrigerant circulation and hydrogen environment

One ​​of the most surprising features of absorption refrigerators is the absence of pumps for pumping the refrigerant. The movement of liquids and gases occurs exclusively due to gravity and gas lift technology. In the lifting tube, ammonia vapor bubbles carry the liquid with them, causing it to rise upward.

Hydrogen in this system plays the role of a buffer. It circulates only between the evaporator and the absorber, without changing its state of aggregation. Since hydrogen is lighter than air, but heavier than ammonia vapor under certain conditions, its movement is strictly regulated by the design of the tubes.

In the evaporator, which is usually located in the upper part of the chamber, intense boiling of ammonia occurs. Ammonia vapor, saturated with hydrogen, falls down the tube into the absorber. There, ammonia dissolves in water, and pure hydrogen, which has become lighter than the mixture, rises again.

If the balance of hydrogen in the system is disturbed (for example, there is a leak), the refrigerator stops cooling as it disappears the driving force for the evaporation of ammonia. It is impossible to restore the amount of hydrogen at home; specialized equipment for evacuation and refilling is required.

Energy efficiency and the influence of external conditions

Gas refrigerators are significantly inferior to their compressor counterparts in energy efficiency. Most of the energy is spent not on cooling, but on maintaining the process of separating the mixture. However, their main advantage is the ability to operate from any heat source, including gas, diesel or even solid fuel.

Operating efficiency directly depends on the ambient temperature. The hotter it is outside, the worse the condenser works, and the more difficult it is for the system to remove heat. In very hot weather, the gas burner may work to the limit, consuming more fuel.

To improve heat transfer, the back wall of the refrigerator should have free air access. Often, additional fans are installed in camper niches, which are turned on by a temperature sensor in order to force air through the radiator fins.

Gas consumption depends on the volume of the chamber and the quality of thermal insulation. On average, one standard 50-liter cylinder is enough for 2-3 weeks of continuous operation in a moderate climate. In winter, at low temperatures, efficiency may decrease due to gas condensation in the lines.

Typical faults and diagnostics

Despite the simplicity of the design, gas refrigerators can fail. The most common problem is clogging of the system, when solid corrosion products or scale block the thin tubes. In this case, the circulation stops and the cold ceases to be produced.

Another common problem is hydrogen leakage. Because hydrogen molecules are very small, they are able to leak through microscopic pores in the metal over time. You can check the tightness using a soap solution, but special gas analyzers are often required to detect hydrogen leaks.

If the refrigerator has stopped cooling on gas, but is running on electricity, the problem is most likely in the ignition or gas supply system. It is necessary to check:

• 🔍 The presence of gas in the cylinder and the position of the valve.
• 🔥 The cleanliness of the burner nozzle (jet).
• ⚙️ The operation of the thermocouple and solenoid valve.

⚠️ Attention: Self-disassembly of the sealed circuit of an absorption refrigerator is prohibited without special equipment and knowledge, since there may be toxic substances under pressure inside.

Cleaning the heat exchanger from soot is a procedure that can and should be carried out regularly. The soot acts as a heat insulator, preventing the flame from effectively heating the generator. For cleaning, use special brushes or blow with compressed air after removing the burner.

Rules for safe operation

Safety when using gas equipment comes first. Since the system uses open flames and flammable gas, ventilation regulations must be strictly observed. When installing the refrigerator in a niche, be sure to have ventilation holes at the bottom and top.

Before the start of the season, always check the integrity of the gas hoses and connections. A soap solution will help you quickly detect leaks by the bubbles that appear. It is not allowed to use an open flame to check for leaks!

When transporting the refrigerator, especially if there is ammonia left in the system, the tilt angle must be observed. Although they do not contain oil, as in compressor ones, damage to the geometries of the tubes can lead to solids entering the wrong zones after switching on.

If you If you smell gas, immediately turn off the valve on the cylinder, open all windows and do not turn on electrical appliances. Only after complete ventilation can you begin to search for the cause.