During the hydraulic system operation, the hydraulic oil generates a lot of heat. If this heat cannot be dissipated, it will reduce oil viscosity, accelerate component wear, and cause unstable system operation. If you are a machinery manufacturer or an engineer, this article about hydraulic heat exchangers will be helpful to you.
What is the Hydraulic Heat Exchanger？
The hydraulic heat exchanger is a cooling device used in the hydraulic system to regulate the oil temperature. It uses air or water as a cooling medium to remove excess heat from hydraulic oil through heat exchange, maintaining the oil temperature within the normal operating range.
Why use a Hydraulic Heat Exchanger？
Maintain Oil Viscosity and Make Sure Good Lubrication
Hydraulic oil is very sensitive to temperature changes. When the oil temperature rises, the oil viscosity decreases. The thinner hydraulic oil cannot form a good protective oil film between the hydraulic pump, motor, and valve, resulting in increased internal leakage.
The hydraulic heat exchanger controls the oil temperature to keep the hydraulic oil within the ideal viscosity range, making sure that all components receive good lubrication and reducing friction losses.
Extend the Hydraulic Components and Seals Service Life
Excessive oil temperature can accelerate the wear of hydraulic pumps, valves, and other components. At the same time, it can also cause metal components’ thermal expansion, resulting in changes to the clearance and causing jamming.
In addition, the seals and flexible hoses in the system are mostly made of rubber or synthetic elastomer materials. The continuous high temperature will accelerate these materials’ hardening, brittleness and deformation, and then cause leakage. The hydraulic heat exchanger reduces thermal stress and slows down material aging, thereby extending the hydraulic components and seals service life.
Delay the Oil Oxidation and Deterioration
Hydraulic oil will undergo chemical reactions with oxygen in the air at high temperatures, producing acidic substances, sludge, and paint film deposits. These substances can clog the control valve core, corrode hydraulic components, and reduce the hydraulic oil lifespan.
Hydraulic heat exchangers control the oil temperature, slow down the oxidation rate, and keep the oil clean. This can also extend the oil change cycle and reduce your operating costs.
Improve System Efficiency
When the oil temperature rises and causes an increase in internal leakage, the flow rate of the hydraulic pump decreases and the volumetric efficiency declines. The response speed of hydraulic actuators will slow down, and pressure fluctuations will increase, which will affect the operational accuracy.
Hydraulic heat exchangers can maintain the oil temperature stability and keep a stable hydraulic energy conversion. This will reduce power loss and improve system efficiency.
Make Sure Continuous Operation
Construction machinery, fixed hydraulic stations, and other equipment typically require long term continuous operation. If the heat dissipation is not smooth, it is easy to cause the system to overheat and shut down. System overheating can also easily lead to seal failure, internal leakage and component damage, thereby increasing the maintenance time.
The hydraulic heat exchanger can continuously exchange heat, keeping continuous production operations.
How does the Hydraulic Heat Exchanger Work?
The hot oil first enters the hydraulic heat exchanger from the hydraulic system. The interior of a hydraulic heat exchanger is usually composed of metal pipes, plates, or fin structures. These structures are usually made of materials with good thermal conductivity, such as aluminium alloy or stainless steel.
When the hot hydraulic oil flows through these structures, the heat is transferred from the metal surface to the cooling medium, such as air or water. This process typically involves various heat transfer methods such as conduction and convection, which gradually lower the oil temperature.
Then, the cooled hydraulic oil returns to the oil tank or reenters the system circulation, achieving continuous heat dissipation.
Hydraulic heat exchangers are usually installed in the return oil pipeline or in an independent cooling circuit. Some systems are equipped with temperature control valves or temperature sensors. When the oil temperature exceeds the set range, the oil will enter the heat exchanger for cooling to prevent excessive cooling.
Types of Hydraulic Heat Exchangers
Air-Cooled Hydraulic Heat Exchanger
The air-cooled hydraulic heat exchanger uses air as the cooling medium for heat dissipation. It is usually composed of an aluminum alloy heat dissipation core, a fin structure and a fan.
Hydraulic oil flows through the internal pipes of the heat dissipation core or finned tubes. The fan drives the cold air to pass through the heat exchange surface. Air carries away heat from the oil during the flow process, thereby reducing the oil temperature.
The air-cooled hydraulic heat exchanger does not require an external water source. It only needs to be connected to a power source or driven by a hydraulic motor to operate the fan. Its installation is flexible and convenient. It is very suitable for mobile devices or outdoor environments.
In addition, the air-cooled hydraulic heat exchangers have a simple structure and do not require complex piping systems. It will not be affected by water quality or have leakage problems. Therefore, it is widely used in construction machinery and mobile hydraulic equipment.
However, the heat dissipation capacity of the air-cooled hydraulic heat exchanger is easily affected by the environmental temperature. The fan operation will also generate some noise. For high power systems, air-cooled heat exchangers may require a larger heat dissipation area to meet your cooling requirements.
Water-Cooled Hydraulic Heat Exchanger
The water-cooled hydraulic heat exchanger conducts heat exchange by using circulating water as the cooling medium. Its interior includes independent oil and water circuits. Hydraulic oil and cooling water flow in different channels and transfer heat through metal walls.
Due to the high heat capacity of water, water-cooled hydraulic heat exchangers typically have higher heat dissipation efficiency than air-cooled hydraulic heat exchangers. And the heat dissipation performance is less affected by the environmental temperature. It is more suitable for hydraulic systems with high loads or continuous operation.
Water-cooled hydraulic heat exchangers can be divided into shell and tube type and plate type according to their structure.
Shell and Tube Hydraulic Heat Exchanger
The shell and tube hydraulic heat exchanger is composed of a shell and the internal tubes. The cooling water flows through the tubes, while the hot oil flows between the tubes inside the shell. The two fluids exchange heat through the tube walls.
In order to enhance the heat exchange efficiency, baffles will be installed inside the shell. The baffle will cause the oil to change its flow direction inside the shell and pass horizontally through the tubes. This can increase the length of the oil flow path and the degree of turbulence, thereby improving heat transfer efficiency.
The shell and tube hydraulic heat exchanger has a large heat transfer area and strong pressure bearing capacity. Its structure is sturdy and capable of handling high flow hydraulic oil. It is suitable for equipment that operates continuously for a long time, such as metallurgical equipment, ship systems, and large hydraulic power units.
However, the shell and tube heat exchangers have a large volume and require a stable water source system. In addition, if the water quality is poor, scaling and blockage may occur inside the tubes. You need to perform regular maintenance.
Plate Hydraulic Heat Exchanger
The interior of the plate hydraulic heat exchanger is composed of a series of thin metal plates with specific wave shapes stacked together. Between the plates, there are extremely narrow fluid channels formed through brazing or sealing gaskets.
The hydraulic oil and the cooling water flow in opposite directions in the different channels. The wave structure makes the fluid generate strong turbulence even at low flow rates, improving heat exchange efficiency.
The plate hydraulic heat exchanger has a higher heat exchange efficiency. Its structure is compact and it is lightweight, making it suitable for devices with limited space. At the same time, you can also adjust the heat exchange capacity by increasing or decreasing the number of plates.
However, the pressure bearing capacity of plate hydraulic heat exchangers is relatively low. Due to the very narrow fluid channels between the plates, it requires high cleanliness of oil and water. Small impurities may cause blockages in the flow channel.
Under high pressure fluctuations, the stability of plate hydraulic heat exchangers is usually not as good as that of shell and tube hydraulic heat exchangers. It is usually used in applications that require high heat transfer efficiency and limited installation space, such as injection molding machines, CNC machines, and automation equipment.
The Application of Hydraulic Heat Exchangers
Construction Machinery
Construction machinery is one of the most typical application fields of hydraulic heat exchangers. Excavators, loaders, bulldozers and cranes and other equipment usually operate under high load and for long periods of continuous work.
The hydraulic system generates a large amount of heat. At the same time, these machines have limited space and the environmental temperature is high, making heat dissipation more difficult.
These machines often use air-cooled hydraulic heat exchangers, which use hydraulic motors or independent motors to drive fans for forced cooling. It can exchange heat without a stable water source.
Agricultural Machinery
Agricultural machinery such as tractors, harvesters, packers, and other equipment also uses hydraulic systems. These machines typically operate in environments with high levels of dust, vibration, and temperature fluctuations. They require high stability for the hydraulic system.
The hydraulic heat exchanger is used in agricultural equipment to control the oil temperature, making sure that the hydraulic actuators can maintain a stable output during long-term operation.
These machines run continuously for a long time during the harvesting season. If the oil temperature continues to rise, it will cause the action to slow down or stop. Hydraulic heat exchangers can improve the continuous operation capability of agricultural equipment.
Industrial Manufacturing Equipment
In the industrial manufacturing field, hydraulic heat exchangers are widely used in hydraulic presses, injection molding machines, die-casting machines, and metal forming equipment. These devices usually operate continuously within the factory. Temperature changes will directly affect the processing accuracy and product quality.
For example, the hydraulic system in injection molding equipment needs to drive the locking mechanism, injection system, and auxiliary devices. Continuous operation will result in a large heat load. It usually uses water-cooled hydraulic heat exchangers to provide higher heat dissipation efficiency and make sure long-term stable operation.
Mining and Heavy Industrial Equipment
Hydraulic crushers, conveying equipment, drilling machines and other equipment usually operate under high loads and in harsh environments, such as open-pit mines, underground mines and large material handling systems.
In these operating conditions, the hydraulic system is in a high-pressure state for a long time, generating a lot of heat. Hydraulic heat exchangers continuously remove heat from the system, making sure stable operation of equipment in extreme environments and improving production efficiency.
Ships and Marine Equipment
Equipment such as ship steering gears, deck machinery, hydraulic winches and offshore cranes usually operate in high humidity and high salt environments.
These applications typically employ water-cooled hydraulic heat exchangers and use seawater for heat dissipation. Its heat dissipation efficiency is high, making it suitable for ship systems with limited space but heavy loads.
How to Choose a Hydraulic Heat Exchanger?
Calculate the Thermal Load of the System
First, you need to determine how much heat the system needs to dissipate. Normally, the heat loss of hydraulic systems is about 25% to 30% of the input power. These energies need to be dissipated through hydraulic heat exchangers.
Consider the Hydraulic Oil Flow Rate and Pressure
The flow rate and pressure of hydraulic oil will affect the selection of the hydraulic heat exchanger size and structure. The larger the flow rate, the more oil passes through the hydraulic heat exchanger per unit time. Then you need to choose a hydraulic heat exchanger with a larger heat exchange area or higher heat exchange efficiency.
The system pressure must also match the pressure resistance of the hydraulic heat exchanger. In high-pressure hydraulic systems, you should choose hydraulic heat exchangers with higher strength shells and pressure resistant structures.
Furthermore, the flow channels inside the hydraulic heat exchanger will cause some pressure losses. If the pressure drop is too large, it will increase the burden on the hydraulic pump and reduce the system efficiency.
You also need to confirm the pressure drop parameters of the hydraulic heat exchanger and make sure that they are within the allowable range of the system.
Determine the Working Temperature Range
The heat dissipation capacity of hydraulic heat exchangers is closely related to the difference between oil temperature and cooling medium temperature. You need to determine the temperature difference between the target oil temperature and the environmental temperature.
The larger the temperature difference, the higher the heat exchange efficiency. At this time, you can choose a hydraulic heat exchanger with a small capacity.
Select the Cooling Method
The different application environments determine whether you should choose air-cooled or water-cooled hydraulic heat exchangers. If your device is mobile or located in remote areas with scarce water sources, you need to choose air-cooled hydraulic heat exchangers.
Fixed industrial equipment usually has a circulating cooling water system. You can choose water-cooled hydraulic heat exchangers to achieve higher heat dissipation efficiency.
Selecting Materials
In ordinary industrial indoor environments, you can choose hydraulic heat exchangers made of aluminum alloy materials with high thermal conductivity and light weight.
If it is a marine environment or a chemical plant, you must choose corrosion-resistant materials such as stainless steel or materials with special anti-corrosion coatings. This can prevent the salt fog or chemical media from eroding and shortening the lifespan of the hydraulic heat exchanger.
Consider the Installation Space and Location
The air-cooled hydraulic heat exchanger requires sufficient space for air intake and exhaust to prevent the return of hot air. For water-cooled hydraulic heat exchangers, you need to reserve space for the water pipe connections and maintenance.
FAQs
What are the Functions of the Temperature Control Valve in the Hydraulic Heat Exchanger?
The temperature control valve controls the oil circuit based on the oil temperature. When the oil temperature is lower than the set value, the temperature control valve switches the oil circuit, allowing the oil to return directly to the oil tank without passing through the hydraulic heat exchanger.
When the oil temperature rises to the set value, the temperature control valve switches the oil circuit, allowing the oil to flow through the hydraulic heat exchanger for heat dissipation.
What are the Functions of the Bypass Valve in the Hydraulic Heat Exchanger?
The bypass valve controls the oil circuit based on the system pressure. When the oil is too thick or the hydraulic heat exchanger is blocked, causing excessive pressure, the bypass valve will automatically open. This allows the oil to bypass the hydraulic heat exchanger, preventing it from being damaged due to overpressure.
Why is it Easy for Hydraulic Systems to Damage Hydraulic Heat Exchangers during Cold Start?
In low temperature environments, the hydraulic oil viscosity will increase. When oil flows through the small channels inside the hydraulic heat exchanger, it generates large flow resistance, leading to a rapid increase in back pressure.
This may exceed the pressure limit of the hydraulic heat exchanger, causing the heat dissipation core or flow channel to rupture.
What could be the Possible Reasons for the Decrease in Heat Exchange Efficiency of Hydraulic Heat Exchangers?
The thermal load of the hydraulic system exceeding the heat exchange capacity of the hydraulic heat exchanger can lead to a decrease in heat exchange efficiency.
Water-cooled hydraulic heat exchangers are easy to scaling or sludge deposition due to water quality. These sediments will adhere to the flow channel surface, reducing heat transfer efficiency.
The narrow flow channels of plate hydraulic heat exchangers make them easier to blockage. If the surface of the fins in an air-cooled hydraulic heat exchanger is clogged with dust or oil stains, it will also affect the heat dissipation performance.
How to Determine if Scaling or Blockage has Occurred inside a Hydraulic Heat Exchanger?
You can detect the temperature difference between the inlet and outlet of the hydraulic heat exchanger. Under normal operating conditions, the temperature of the oil should decrease after cooling.
If the temperature difference between the inlet and outlet is very small, it indicates that the heat exchange efficiency has decreased. And there might be blockages or deposits inside.
You can also observe the changes in pressure. If the pressure drop at both ends of the hydraulic heat exchanger exceeds the allowable value, this usually indicates that there is a blockage inside the flow channel.
How to Solve the Problem of Excessive Fan Noise in Air-Cooled Hydraulic Heat Exchangers?
You can install a variable frequency drive. It can adjust the fan rotation frequency by sensing the oil temperature. This can reduce operating noise and energy consumption. You can also choose to use low-noise blades with special structures or install shock-absorbing pads on the mounting base.
Final Thoughts
A suitable hydraulic heat exchanger can help your hydraulic system operate stably for a long time and improve work efficiency. If you need to purchase hydraulic heat exchangers, please feel free to contact us.
