12/8/2023 0 Comments Scroll compressor![]() ![]() Leakage losses have a significant negative impact on the volumetric efficiency of scroll machines. However, the lack of oil results in a poorer volumetric performance. The use of an oil-free design has other benefits, such as reduced mechanical losses, increased life, and a cleaner compression process (no presence of oil). ![]() The presence of some oil in the scroll machine means that an oil film will partially fill the leakage gaps, resulting in significantly improved volumetric efficiency. With an oil-free machine, a specified clearance is set between the scrolls, with the intent of preventing any contact during operation. The decision to use an oil-free or oil-lubricated scroll machine has a significant impact on the leakage losses. The scroll wraps are locally heated and cooled, which means they expand or contract locally, which results in larger leakage gaps in some cases and smaller leakage gaps in others. Heat transfer also has a complex relationship with leakage losses. Leakage losses contribute to a reduction in both isentropic efficiency and volumetric efficiency. In general, as the pressure ratio of the machine increases, the impact of leakage losses also increase. As a result, internal leakage is an unfortunate side effect. In a real scroll machine, manufacturing concerns dictate that the scroll wraps cannot be in perfect contact at all times. In an idealized scroll machine, the orbiting and fixed scrolls are manufactured perfectly and are in perfect contact throughout the compression process, which results in no area for leakage of gas from higher to lower pressure during the compression process. Since the scrolls do not contact and all loads are taken through ball bearings, the second largest source for mechanical losses are the bearings, which take both the radial and axial loads. Other sources of mechanical losses in an oil-lubricated compressor include frictional losses caused by rubbing of the orbiting and fixed scrolls, the thrust bearings required to carry the axial load, and any mechanical losses incurred by auxiliary systems, such as cooling fans, cooling water pumps, and so on.įor an oil-free design, the dominant source of mechanical losses is the rubbing between the tip-seal and the base of the scroll components. In a scroll machine, the bearings are also used to overcome the orbiting scroll’s desire to rotate and force it instead to take on an orbiting trajectory. For an oil-lubricated design, by far the dominant source is the radial bearings that are required to support the mechanical loads generated by the compression process. There are a number of sources of mechanical losses in scroll machines, and these losses vary according to whether the unit is oil-free or oil-lubricated. ![]() Two surfaces that have a low applied load but a high contact speed will still experience significant mechanical losses. The amount of mechanical loss is proportional to the product of the applied load on the contact point and the velocity of the contact. Mechanical losses are caused by friction between two surfaces that are passing by each other at some speed. Optimization of scroll machine performance must take all of these interactions into account. A reduction in the discharge pressure drop can increase the leakage losses. For instance, mechanical losses contribute to a decrease in volumetric efficiency by heating the gas in the suction chamber. ![]() The different loss mechanisms are linked. In general, the losses in scroll machines fall into one of the following categories: mechanical losses, leakage losses, heat transfer, pressure drop, and over- or under-compression losses. To understand the amount of electrical power required for the machine, we must understand the factors that contribute to a non-ideal compression process. Figure 1: Energy Flows in a Scroll Machine Based on Efficiency Estimates In addition, losses like leakage and heat transfer tend to decrease the amount of fluid that can be pumped by the machine, thereby decreasing the volumetric efficiency. Like other types of compressors, scroll machines (compressors and vacuum pumps) do not carry out ideal compression processes, and the required power input is always higher due to inefficiencies. Even if the compression process is ideal, thermodynamics dictates that mechanical power is required to carry out this compression process. When a scroll compressor or vacuum pump is selected for an application, the ultimate goal is to compress a low-pressure gas at the inlet of the machine and turn it into a compressed gas at the outlet. An introduction to scroll technology efficiencies and associated losses. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |