International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395 -0056
Volume: 04 Issue: 02 | Feb -2017
p-ISSN: 2395-0072
www.irjet.net
Performance Optimization of Steam Jet Ejector Using CFD A Review Darshan R. Vadalia ME scholar, Mechanical Department, LDRP-ITR, Gandhinagar, India ---------------------------------------------------------------------***---------------------------------------------------------------------
Abstract - Jet ejectors are popularly used in the chemical process industries because of their simplicity and high reliability. They are widely used to generate vacuums with capacity ranges from very small to enormous. Due to their simplicity, constant-pressure jet ejectors those are properly designed for a given situation are very forgiving of errors in estimated quantities and of operational upsets. The purpose of this project is to optimize the geometry of steam jet ejector used for refrigeration application in chemical plant. Exhaustive survey has been conducted on the influence of geometrical parameters on the efficiency of the ejector as well as critical flow parameters to improve the overall performance. The use of computational dynamics has been widely accepted by researchers to improve the performance of jet ejector. CFD gives detail insights on the flow characteristics, which allows accurately optimizing the ejector geometry. Since the ejector requires single point design for specific applications, using computer simulations early in the design process will significantly reduce the requirement of prototyping trials. The results obtained through CFD analysis will be used to optimize the geometry of the ejector, to achieve better efficiency by reducing pressure drop across the ejector geometry. Key Words : Steam Jet Ejector, Geometrical Parameters, Computational Fluid Dynamics(CFD)
1. INTRODUCTION Jet ejectors provide numerous advantages, like : They require little maintenance because there are no moving parts to break or wear. They have lower capital cost compared to mechanical devices because of their simple design. Their design is very straightforward. They are easily installed and require little supervision. On the other hand, the major disadvantages of jet ejectors are : They are designed to perform at a particular optimum point. Deviation from this optimum point can dramatically reduce efficiency. They have a low thermal efficiency at high compression ratios. 1.1 Operating Principle : As shown in Figure 1, the conventional jet ejector design has four major sections: 1. nozzle 2. suction chamber 3. Throat 4. diffuser
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Fig – 1: Conventional Jet Ejector Design[7] The operating principle of jet ejectors is described below: (1) Subsonic motive stream enters the nozzle at Point 1. It flows to the converging section of the nozzle, its velocity increases, and its pressure decreases. At the nozzle throat, the stream reaches sonic velocity. In the diverging section of the nozzle, the velocity increases to supersonic. (2) The entrained propelled fluid enters the ejector, flowing to Point 2. Its velocity increases and its pressure decreases. (3) The motive stream and entrained propelled stream begin to mix within the suction chamber; mixing is completed in the throat. (4) Inside the throat, a shock wave forms when the mixture velocity reduces to a subsonic condition. The back-pressure resistance can cause condensation at Point 3. (5) The mixture flows into the diverging section of the diffuser where the kinetic energy of the mixture is transformed into pressure energy. At Point 5, the pressure of the emerging fluid is slightly higher than at Point 3.
2. LITREATURE REVIEW 1. Natthawut Ruangtrakoon et al (2013) [1] in their study used CFD technique to investigate the effect of the primary nozzle geometries on the performance of an ejector used in the steam jet refrigeration cycle. In all cases, only one fixed geometry mixing chamber together with eight different primary nozzles was investigated numerically using the CFD package. The optimum condition was the primary nozzle with the throat diameter of 2.3 mm and exit Mach number of 4 operating with the boiler temperature of 120 ˚C at the evaporator temperature of 7.5 ˚C. From this study, it can be concluded that the CFD technique can be used as an efficient tool to predict the performance of a steam ejector. It can also be used to explain the mixing process which cannot be explained experimentally. The results show that geometries of the primary nozzles used and operating conditions have very strong effects on the ejector performance and therefore the system COP. ISO 9001:2008 Certified Journal
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