Talking about the selection of oil cooler / air cooler of hydraulic system (1)
Air-cooled oil cooler (referred to as air cooler or oil cooler ) is an aluminum alloy plate-fin heat exchanger that uses air as a cooling source. Its characteristics are that the oil channel and the air channel of the heat exchanger core are replaced. The heat fin has a large heat exchange area with the same volume ratio and high heat transfer efficiency. It uses air as a medium for heat exchange. Compared with water-cooled radiators, it is not only easy to install and maintain, but also avoids oil-water mixing caused by copper pipe bursts, which causes severe damage to the system. Secondly, for the equipment (such as construction machinery) that needs to change the work place, there is no need to consider the supply of water, and there is no disassembly and reconstruction of the water circulation system, which is an increasingly widely used environmental protection product.
At present, there are many manufacturers of air coolers in China, and the models are not the same. The performance parameters and installation dimensions are quite different, which will cause some problems for the user's selection and use. Here, in combination with the experience of our factory's development and production and customer use, talk about a few points that should be paid attention to in the selection of air coolers for your reference and hope to correct.
When designing any product, the first consideration is to achieve its functionality, or that functionality is the first priority. This is the most basic element of design. The same is true for air coolers, which provide oil for hydraulic systems of commonly used equipment. The requirements of temperature and heat dissipation are mainly reflected in three major aspects: first, applicable pressure; second, applicable flow rate; third, heat transfer efficiency. When choosing an air cooler, these three aspects must be met at the same time, so as to basically meet your requirements. Let ’s talk about these three aspects.
I. Applicable pressure
Usually refers to the maximum allowable working pressure, or design pressure. The air cooler is a pressure vessel. In the hydraulic system, it is only suitable for the return oil cooling of the circuit, so the air cooler should be selected according to the maximum pressure of the circuit. Why is it only used for oil cooling? Regardless of the cause of the rise in oil temperature, as far as the air cooler itself is concerned, the pressure resistance of the heat dissipation body (heat exchange core) is limited. Plate-fin aluminum alloy heat exchange The core's pressure resistance depends on its material physical properties, structure, and processing technology. For example, the structure and processing technology are the same, the material is the same, the thickness of the oil channel material is different, the pressure resistance is also different, the thicker the higher the pressure resistance. The design pressure of the plate-fin aluminum alloy air cooler is generally less than 3.5Mpa, based on cost and practicability, it is usually less than 2.0Mpa. The design pressure of foreign counterparts is mostly 1.6Mpa, which are far less than the maximum working pressure of the oil circuit. Obviously, too high pressure will cause burst damage of the heat exchange core. The design pressure of air cooler products circulating in the market is generally divided into three levels: 1, 1.0Mpa (such as AF series); 2, 2.0Mpa (such as AH series); 3, 3.5Mpa. The design pressure of 1.0Mpa is only suitable for drain cooling of variable vane pumps.
Considering the instability of the hydraulic system circuit pressure and the high-pressure pulse that may occur at the moment of oil return, in order to ensure the service life of the air cooler, the manufacturer strongly recommends that the independent circulation cooling method be given priority. Independent circulation is that the air cooler is no longer connected to the circuit of the working hydraulic system, but a separate cooling circuit is set up, that is, a cooling pump is installed to directly suck high-temperature hydraulic oil from the fuel tank, and then sent directly after cooling by the air cooler Return oil tank, so as to avoid damage to the air cooler due to excessive return pressure. The flow rate of the independent circulation cooling pump is usually selected to be less than one third of the hydraulic oil volume.
When the return oil cooling of the fixed pump is needed, the designer should consider the instability of the return pressure in the hydraulic system, connect the air cooler to the oil return port of the relief valve, and connect the air cooler to the inlet and outlet of the air cooler. A back pressure valve with an opening pressure of 0.5Mpa is connected in parallel between the oil outlets. This is the correct method (see the figure below). When used for variable displacement pump cooling, since its pressure is usually less than 1Mpa, as long as the flow is appropriate, it can be directly connected to the variable pump drain port. The author encountered such a case: a customer connected a model of AH0608TL (applicable pressure 2.0M0pa, flow rate 50L / min) to a fast-forward-industrial-fast-reverse working machine, and the result was during the process of mechanical debugging In the middle, it was found that the heat exchange core leaked oil, and the oil passage burst. The customer originally used a water cooler and switched to an air cooler at the request of the user. Since the air cooler is directly connected to the oil return path, there is no back pressure valve installed, and the system has a fast oil return speed. The pulse pressure was too high and the air cooler was knocked out instantly.
The design pressure of AH series air cooler produced by Foshan Nanhai Heyida Heat Exchange Equipment Factory is 2.0Mpa, oil channel hydraulic test pressure 3.0Mpa, holding pressure for 10 minutes, air tightness test pressure 2.2Mpa, holding pressure 30 There must be no leakage in the bell. This is a pressure inspection requirement before leaving the factory. The burst pressure of the heat exchange core is above 7.5Mpa.
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