Heat Exchanger

When the sistema idraulico is working, the temperature of the hydraulic oil should be kept between 15～65℃. If the oil temperature is too high, the oil will deteriorate rapidly. At the same time, the viscosity of the oil will decrease, and the efficiency of the system will decrease. The fluidity becomes worse, the system pressure loss increases, and the pump’s self-priming ability decreases. Therefore, maintaining a stable oil temperature is a necessary condition for the normal operation of the sistema idraulico. Due to the limitation of load and other factors, sometimes the oil temperature cannot be met by the natural adjustment of the oil tank itself, and external facilities are needed to meet the oil temperature requirements of the equipment. The heat exchanger is the most commonly used temperature control facility. The heat exchanger is divided into two types: cooler and heater.

Coolers can be divided into water-cooled, air-cooled, and ammonia-cooled according to the cooling form. Among them, water-cooled and air-cooled are commonly used cooling forms. There are mainly three types of water coolers: serpentine tube type, shell and tube type, and fin type.

In hydraulic systems, multi-tube coolers are generally used. Water is the cooling medium and passes through the tubes, and oil flows between the tubes in the tube. The flow of water in the pipe is mostly designed as a two-program. Water pipes are made of brass pipes instead of steel pipes. Because steel pipes are difficult to clean and easy to rust, the thickness of the pipe wall is generally 1~1.5mm. Since the temperature of the cylinder and the tube are different, thermal compensation measures should be considered when designing.

For oil cooling, air-cooled coolers are also used in places where water is scarce or equipment is inconvenient for water use. Air-cooled coolers have a poor effect and higher equipment costs, but cheap electricity can be used instead of water. Sometimes a car radiator is used instead.

1. The Installation Position of The Cooler

• The cooler is generally installed on the return line of the hydraulic system or the overflow line of the overflow valve. The heating of the oil is due to a large amount of high-pressure oil flowing out of the overflow valve. At this time, the cooler should be installed on the drain line of the overflow valve. In this way, the temperature of the overheated oil decreases before it returns to the oil tank. After the cooler is installed, the pressure loss is generally 0.01 to 0.1MPa. The picture shows an example of the installation position of the cooler. The pressure oil output by the hydraulic pump directly enters the heat-generating oil return of the system and the oil overflowed by the overflow valve is cooled by cooler 1 and then returns to the oil tank. The one-way valve 2 is used to protect the cooler and open the shut-off valve 3 when the cooler is not needed to provide a passage.
• The cooler should not be placed in front of the return oil filter. As shown in the figure, as the oil temperature decreases and the viscosity increases after passing through the cooler, the flow capacity of the filter will be weakened. The cooler should be placed in the return oil filter as much as possible. Later, if necessary, a separate cooling circuit can be used.

The cooler is installed on the overflow valve drain pipeline and the system’s oil return pipeline. In this way, the temperature of the overheated oil is reduced before returning to the tank. After the cooler is installed, the pressure loss is generally 0.01 to 0.1 MPa.

2. The Flow Capacity of The Cooler

The cooler is generally located in the oil return line of the hydraulic system, and its heat dissipation effect is directly related to the speed of the liquid flow in the cooler.

The heat dissipation of the cooling device is proportional to the flow of the cooling medium passing through. The cooling power of the Tathagata is low, and the cooling effect is low. The pressure change in the flow may harm the operation of the system. If the pressure difference flowing through the cooler is too high, it may lead to the structure of the cooler. destroy.

3. The Problem of Determining The Cooling Area

• The cooling area of the cooler should be sufficient. During the working process of the hydraulic system, part of the energy will be consumed by the overflow valve and the flow loss of the system, and this part of the energy will be converted into heat energy, which will increase the oil temperature. When the oil temperature rises, it will increase the leakage on the one hand, and shorten the service life of the oil on the other hand. The use of a cooler is one of the main means to control the oil temperature. The heat dissipation surface is the key parameter of the cooling device, and its value should be obtained through careful analysis and calculation of the system. When selecting heat dissipation specifications, if Han has set a heat dissipation area corresponding to the appreciation value, a specification with a slightly larger heat dissipation area should be selected.
• When selecting the cooling area of the cooler, the conditions of the cooling medium provided on-site should be considered. Water is widely used as a cooling medium. When the cooling area and coefficient of the cooler remain unchanged, the condition of the cooling water becomes very important. Due to the different seasons and regions, the temperature of the cooling water that can be provided is different. When the cooling water temperature is low, the cooling effect is good, and vice versa.
• When the cooling water pipe is thicker and the pressure difference between the inlet and return water is large, the water flow per unit time is large, and the cooling effect is good. Otherwise, it is poor. Therefore, when choosing a cooler, you should understand the cooling water conditions on-site.

4. Condensation on The Surface of The Cooling Water Pipe

Due to the presence of moist gas in the air, it will condense into the water after being in contact with a colder water pipe, which will cause corrosion of metals and even affect the safety of the electrical system. Heat insulation measures should be used to prevent condensation.

5. Prevent Scaling Problems

• Increase the inlet water flow rate and open the inlet and return water valves to discharge the air in the cooler. To prevent the formation of scale, the cooling water temperature is required to be as low as possible. It is best to use a softened water source.
• Except for civil tap water, other water sources (such as groundwater, industrial circulating water, etc.) should be equipped with a water filter on the cooler inlet pipe according to the actual situation to prevent the gradual formation of dirt or local blockage in the cooler and reduce the heat exchange effect. as the picture shows.

• When the cooler is put into operation, the water valve should be opened slowly according to the procedure, and it should not be opened quickly, to avoid the formation of a “super-cooling layer” with poor thermal conductivity on the surface of the cooling pipe and affecting the cooling effect.

6. Cooling Medium Problem

Ordinary coolers should not use seawater as the cooling medium. The service life of the cooler mainly depends on the corrosion rate of the cooling medium to the heat exchanger material, and the factors that affect the corrosion rate are the materials used and the type of cooling medium. Ordinary cooler products are only suitable for fresh water as a cooling medium, not for seawater. If seawater is used, it should be specified. The manufacturer will use stainless steel materials to ensure its normal use and life.

7. Problems That Should Be Paid Attention to When Using Tube Cooler

• There should be a filter before the dirty medium passes through the cooler.
• It is best to install in a separate oil circulation circuit.
• During the test run, both circulation circuits need to be exhausted to achieve the purpose of high efficiency and no rust.
• First add the cold medium, and then gradually add the hot medium.
• The pressure of the cooling medium should be greater than the pressure of the cooling medium.
• The cooling medium is usually freshwater.
• Exhaust and clean regularly.

8. Problems That Should Be Paid Attention to When Using Plate Cooler

• Before use, check whether the compression bolt is loose and whether the compression size meets the specified size in the manual. If it does not meet the requirements, tighten the bolts evenly to make it reach the specified size.
• Hydraulic test should be carried out on the equipment before use. Test the pressure on both sides of the cold and hot separately. The test pressure is 1.25 times the operating pressure, the pressure holding time is 30min, and there is no leakage in each sealing part before it can be put into use.
• When the plate cooler is used in the food industry or the pharmaceutical industry with high hygiene requirements, it should be cleaned and disinfected before use to eliminate internal oil and debris.
• When the operating medium contains a large amount of sand or other debris, a filter device should be placed in front of it.
• The cold and hot medium inlet and outlet pipes should be connected by pressing the signs on the tight plate, otherwise, its performance will be affected.
• During operation, slowly inject the low-pressure side liquid, and then inject the high-pressure side liquid; when stopping, slowly cut off the high-pressure side fluid, and then cut off the low-pressure side fluid.
• After a long-term operation, different degrees of scale or dirt will be generated on the surface of the plate, which will reduce the heat transfer efficiency and increase the flow resistance. Therefore, it should be checked regularly to remove the dirt. When cleaning the plate, metal brushes should not be used to avoid scratching. Damage the plate and reduce the corrosion resistance.
• The damaged plate should be replaced in time. If there is no spare plate, two adjacent plates can be removed if the operating permits. (Note: The removed plate should not be a reversing plate, but Plate with four holes), while reducing the compact size accordingly.
• During maintenance, the aging gasket should be replaced, and the missing gasket should be re-bonded. Clear when bonding.
• Wash the gasket tank, apply adhesive, and align the gasket firmly.

9. The Operating Voltage of The Solenoid Water Valve Should be Consistent With The System Control Voltage

The solenoid water valve is included in the hydraulic accessories as a control valve for controlling the water inlet of the cooler. When selecting and purchasing, only the rated pressure and diameter of the valve are often paid attention to, and the control voltage is ignored, which often results in inconsistency with the system control voltage. And the accident of damaged device, so you need to pay special attention, as shown in the figure.

10. Heater Problem

• The heater should not be installed in the pipeline

The heater should not be installed in the pipeline. As shown in the figure, due to the limited length of the pipeline, the volume of oil contained in it is small. When the flow rate of the oil in the pipe is too low or the heater is turned on due to a malfunction, it may cause the local oil temperature to be too high and even cause fires and other accidents. A heater should be installed in the oil tank, and measures to ensure a reasonable temperature of the oil should be taken, such as adding a temperature relay and corresponding control circuits to limit the maximum oil temperature.

• The heater installation position should not be too high

Because the heat is conducted upwards and the heater position is too high, the oil below is not easy to be heated, which affects the heating effect; second, when the system is working, the oil level fluctuates, which may expose the heater to the oil surface, damage the heating element or cause an accident. Place the heater at the bottom of the oil tank and keep a certain distance from the bottom of the tank, as shown in the figure.

• The heater installation surface should not be sealed with rubber materials

The working fluid in the fuel tank is heated by the heater installed on the fuel tank. The temperature of the heater is very high during the heating process, and it will be transferred to the mounting flange through the heating tube. The higher temperature will cause the sealing rubber to quickly age, Loss of elasticity, causing oil leakage in the sealing part, should be made of heat-resistant oil-resistant rubber asbestos sheet gasket, as shown in the figure.

• The position of the temperature sensor bulb should not be too high

The working temperature of the hydraulic medium is one of the important indicators for the normal operation of the hydraulic system, and the test of the oil temperature is mostly done with a temperature sensor. If the position of the temperature bulb is too high, the temperature bulb may be above the liquid level due to the change of the liquid level during the working process. At this time, the temperature sensor cannot accurately measure the oil temperature, which will cause the oil temperature to be too high. Should be avoided as much as possible.

• The temperature bulb of the temperature measuring element in the fuel tank should be far away from the heater and the oil return and cooling oil pipes

Accurate and reliable detection and control of the oil temperature in the fuel tank are the prerequisites for ensuring the normal operation of the system. If the temperature measuring element temperature bulb is close to the heating pipe or the oil return pipe of the cooler, the error between the detected oil temperature and the actual oil tank temperature is relatively large, which is not conducive to the control of the system oil temperature, as shown in the figure.