Creating an effective cooling system for an engine is a task that requires accurate engineering calculations and an understanding of the principles of heat transfer. Liquid cooling allows you to remove significantly more heat than air, which is critical for forced engines or extreme load conditions. In this article we will analyze the process of designing and assembling our own heat exchange circuit, which in everyday life is often called a “refrigerator” for a motor.
The main difficulty lies not so much in connecting the tubes, but in the correct calculation of the heat transfer area and the volume of circulating liquid. Improperly designed system can lead to local overheating of the cylinders or, conversely, to underheating, which is equally harmful to the life of the internal combustion engine. You have to choose between a passive radiator and an active system with forced circulation.
Before you begin welding or soldering elements, you must determine the type of refrigerant and operating temperatures. Modern materials make it possible to create compact and efficient units, but Thermal conductivity coefficient of copper remains the benchmark to which you should strive when choosing materials for a heat exchanger.
Principles of liquid engine cooling
The fundamental task of any exhaust system heat is a continuous cycle of energy transfer from the hot parts of the engine to the environment. Coolantflowing through the channels in the cylinder block and head, it heats up and is then sent to the radiator. There, intensive heat exchange with air occurs, and the already cooled liquid is returned to the engine.
The efficiency of this process directly depends on the flow rate and the area of contact of the liquid with the cooling surfaces. If the speed is too low, a “steam jacket” effect will occur when the liquid boils at the walls, forming an insulating layer of steam. Turbulent flow inside the pipes and channels helps to destroy this layer and ensures uniform heating and cooling.
It is important to understand the difference between open and closed contour. Most automotive and stationary systems use a closed cycle under pressure, which increases the boiling point of water. System pressure created by a specially designed expansion tank or radiator cap.
⚠️ Warning: Working with hot liquids under pressure is dangerous. Never open the radiator or expansion tank cap until the engine has completely cooled down to avoid steam burns.
The key element here is the thermostat - a device that regulates the flow of fluid around the radiator on a cold engine. Without it, the engine will take a long time to reach operating temperature, increasing wear and tear and fuel consumption.
Calculation of power and selection of materials
In order for the engine “refrigerator” to work effectively, it is necessary to calculate the required radiation area. The power that needs to be removed depends on the type of engine, its efficiency and operating mode. Typically, about 30-40% of the energy of burned fuel is converted into heat, which must be utilized.
When choosing materials for a heat exchanger, preference is given to copper and aluminum. Copper tubes they have excellent thermal conductivity, but they are heavier and more expensive. Aluminum alloys are lighter and cheaper, which makes them the standard for most modern automotive systems.
A water-glycol mixture (antifreeze) is most often used as a working fluid, which not only does not freeze in winter, but also contains anti-corrosion additive packages. The use of clean water is permissible only in emergency cases or in special closed circuits with distillate.
The thickness of the tube walls also plays a role: too thin ones may not withstand pressure, too thick ones will create additional thermal resistance. The balance between strength and thermal conductivity is considered optimal.
Design of a homemade radiator
Independent production of a radiator is the most labor-intensive part of the project. The simplest design is a set of parallel tubes connected by collectors, with soldered or pressed fin plates. Fin area should be as large as possible for effective contact with air.
Assembly will require hard soldering or argon soldering welding if you are working with aluminum. It is important to ensure the tightness of all connections, since even a microscopic leak under pressure will turn into a serious problem when heated.
- 🔧 Collectors: are made of larger diameter pipes into which the ends of the heat exchange tubes are welded.
- 🌬️ Finning: you can use ready-made corrugated tapes made of copper or aluminum, which are soldered between the tubes.
- 💧 Tanks: The inlet and outlet pipes must be located so as to ensure flow across the entire radiator area.
There are also plate heat exchangers that can be adapted, but they create high hydraulic resistance. For a homemade system, the classic tubular-plate scheme is better suited.
⚠️ Attention: When soldering, use fluxes that do not require subsequent rinsing with acid, or carefully neutralize acid residues, otherwise corrosion will eat away the radiator from the inside in one season.
Selection of a circulation pump
Natural circulation (thermosiphon) is possible only in very simple systems with a vertical radiator position above the engine. For most tasks, especially if the “refrigerator” is located at a distance, a centrifugal pump is required.
The pump capacity must correspond to the volume of the cooling system. A pump that is too powerful will create cavitation and noise, and can also destroy the thin honeycomb of the radiator. Too weak will not provide the required fluid flow.
Usually for engines with a capacity of up to 2 liters, a pump with a capacity of 30-50 liters per minute is sufficient. It is important to pay attention to the pressure characteristic: the pump must overcome the resistance of the entire system, including the radiator, thermostat and narrow channels in the block.
| Pump type | Capacity (l/min) | Pressure (m) | Application |
|---|---|---|---|
| Low-power (12V) | 10-20 | 1-2 | Motorcycles, mopeds |
| Medium (automotive) | 40-60 | 5-8 | Passenger cars, generators |
| High-performance | 80-120 | 10-15 | Trucks with boosted internal combustion engines |
| Industrial magnetic | 20-100 | 3-6 | Systems with a sealed circuit |
The power supply to the pump must be protected by a fuse. Ideally, pump control should depend on temperature: turning on only after the engine has warmed up to a certain temperature.
Assembling the circuit and installing components
Installation of the system begins with placing the radiator in the zone of best airflow. If the natural air flow is not enough (for example, when idling), it is necessary to install an electric fan in front of the radiator.
The connection of all elements is carried out with heat-resistant hoses. Rubber hoses must withstand temperatures of at least 120-130°C. For fastening, use clamps with a screw clamp, which ensure uniform pressure around the circumference.
☑️ System assembly checklist
The expansion tank is installed at the top point of the system. It compensates for the thermal expansion of the liquid and allows air pockets to be removed when filling. The volume of the tank should be about 10-15% of the total volume of the system.
When laying hoses, avoid sharp bends that may block the flow of liquid. Also make sure that the hoses do not touch hot parts of the exhaust manifold or sharp edges of the body.
⚠️ Attention: Specifications of hoses and pipes may vary from manufacturer to manufacturer. Before purchasing, check the label on the product to make sure it is suitable for use with antifreeze at high temperatures.
How to remove an air lock?
Fill the system not completely, start the engine and let it idle. As it warms up, open the radiator cap (carefully!) or the special air release valve, adding fluid as the bubbles disappear.
Testing and first start
Before starting the engine for the first time, the system must be filled with liquid and pressure tested. This can be done using a compressor, applying a pressure of 1.5-2 atmospheres, and checking all joints for leaks with a soap solution.
When starting the engine for the first time, carefully monitor the temperature. Operating temperature should stabilize in the range of 85-95°C. If the arrow creeps higher, there may be air pockets in the system or the radiator performance is insufficient.
Check the operation of the thermostat: the lower radiator pipe should become hot only after the engine warms up. If it warms up immediately, the thermostat is stuck open or missing.
- 🌡️ Temperature control: use an external infrared thermometer to check that the radiator is heating evenly.
- 🔍 Visual inspection: look for drops of liquid or white traces of dried antifreeze on the connections.
- 🔊 Acoustic control: listen to the pump for howling bearings or cavitation noise.
After several heating and cooling cycles, be sure to recheck the tightness of the clamps, as the materials may shrink.
Frequently asked questions (FAQ)
Is it possible to use ordinary water instead of antifreeze?
Short-term - yes, but this is not recommended for continuous use. Water is corrosive to metal parts, has a lower boiling point and can freeze, causing the engine block to rupture. Use distilled water only in a mixture with antifreeze concentrate.
What size radiator to choose for a 1.5 liter engine?
For a 1.5 liter engine operating in moderate mode, a radiator with a cooling area of about 0.3-0.5 square meters is usually sufficient. However, the exact calculation depends on the engine power and operating conditions (city or highway).
Why does the cooling system become airy?
The main reasons: leaks in the connections through which air is sucked in when cooling; valve malfunction in the radiator cap; or an incorrect filling procedure, when the liquid blocks the exit of air from high points.
Is it necessary to flush the system before filling in new antifreeze?
Yes, definitely. Residues of old antifreeze, rust and scale can react chemically with the new fluid or clog the thin radiator channels. It is better to do flushing with distilled water with the addition of a special cleaner.
How often do you need to change the fluid in a homemade system?
It is recommended to change the coolant every 2-3 years or after 60,000 km. Over time, additives lose their properties, and the liquid becomes aggressive towards metals and rubber seals.