Badar Rashid

Modeling and Analysis of Thermal Damping in Heat Exchanger Tube Bundles

Most structures and equipment used in nuclear power plant and process plant, such as reactor internals, fuel rods, steam generator tubes bundles, and process heat exchanger tube bundles etc., are subjected to Flow Induced Vibrations (FIV). Costly plant shutdowns have been the source of motivation for continuing studies on cross-flow induced vibration in these structures. Damping has been the target of various research attempts related to FIV in tube bundles. A recent research attempt has shown the usefulness of a phenomenon termed as “thermal damping”. The current paper focuses on the modeling and analysis of thermal damping in tube bundles subjected to cross-flow. It is expected that the present attempt will help in establishing improved design guidelines with respect to damping in tube bundles.Copyright

A Comparative Study of Cross-Flow Induced Vibrations in Heat Exchanger Tube Bundles Using Bond Graph Approach

Flow-induced vibration (FIV) has been a major concern in the nuclear and process industries involving steam generator and heat exchanger tube bundle design. Various techniques and models have been developed and used for the analysis of cross-flow induced vibration of tube bundles. Bond Graph approach has been applied to existing FIV excitation models, followed by a comparative study. Results have been obtained using 20-SIM software. It is expected that the current approach will give a new dimension to the FIV analysis of tube bundles.© 2005 ASME

Modeling and Simulation of Elastohydrodynamic Lubrication of Piston Skirts Considering Elastic Deformation in the Initial Engine Start-Up

The presence of Elasto-hydrodynamic Lubrication (EHL) film between opposing piston and liner surfaces prevents possible solid-to-solid contact and wear. This enhances engine life manifold as compared to when the EHL film is non-existent in the initial engine startup or breaks down during normal engine operation. Forced dry sliding of piston during engine cranking followed by partial lubrication in the initial engine startup leads to adhesive wear. This research investigates the possibility of an EHL film on such an occasion by considering elastic deformation of opposing piston skirt and liner surfaces due to Elasto-hydrodynamic (EHD) pressures. The geometry of piston skirts is defined and governing equations are applied to determine hydrodynamic pressures. The EHL film thickness profile generated by inverse solution technique and its expression is defined by incorporating contact geometry and EHD pressures in the piezoviscous regime. A computer code is developed and used to simulate the performance parameters and their behavior during initial engine startup. Due to critical factors such as engine speed, redial clearance between piston skirts and liner and lubricant viscosity, a time dependent 2-D EHL film profile is generated. The simulated results indicate that, despite piston eccentricities due to secondary oscillatory motion, EHL film established between the opposing piston skirts and liner surfaces prevented possible solid-to-solid contact in the entire duration of 720-degree crankshaft rotation, which corresponds to four piston strokes.Copyright

Analysis of Swage Autofrettage in Metal Tube

Autofrettage (self-hooping) is used to induce advantageous residual stresses into pressure vessels to enhance their fatigue lifetime. The process is achieved by increasing elastic strength of a cylinder with various methods such as hydraulic pressurization, mechanical swaging, or by utilizing the pressure of a powder gas. This research work deals with the swage or mechanical autofrettage of metal tubes. The objective is to attain a bore size of 125mm. Normally such a bore size is achieved with hydraulic autofrettage. However, we have used two-stage mechanical autofrettage to achieve the desired bore size. At first stage the swage diameter achieved is 118mm, and in the second stage, the diameter achieved after machining is 125mm. The temperature variation for swage is 38°C to 50°C. The applied pressure varies from 85 to 180 bars inside the tube. The process was applied to a number of tubes selected randomly. The swage autofrettage process was also analyzed using numerical simulation based on finite element method. The results of numerical simulation are compared with design parameters.Copyright

Modeling and Simulation of Cross-Flow Induced Vibrations in Tube Bundles Using Bondgraph Approach

A considerable research has been carried out in the field of Cross-Flow Induced Vibrations (CFIV) in tube bundles of process exchangers and nuclear steam generators. Various excitation mechanisms such as vortex shedding, turbulent buffeting, fluid-elastic instability and acoustic resonance and other parameters like natural frequencies, damping, wear work rates at the loose tube supports and various geometric tube arrangements have been the focus in single and two-phase cross-flow. In the current research work, CFIV has been studied by using Bondgraph approach. The Bondgraph models have been subjected to simulation using the software (20-SIM). Results obtained have shown a strong usefulness of Bondgraph approach to complex CFIV systems.Copyright

A Review on Fluid Structure Interaction Modeling Using Bondgraph Method

Modeling of complex multi-dynamic systems is a formidable challenge. Extensive research has already been carried out focusing on modeling of fluid flow using conventional techniques. This research paper aims at carrying out review on fluid structure interaction specifically adopting bondgraph approach. A comprehensive review, on modeling of fluid dynamic systems, osmosis and hydraulics, rotary piston hydraulic motor, with the help of bondgraph method is carried out. This will facilitate to explore important areas of original research using bondgraph method.Copyright

Dynamic Analysis of Fluid Flowing Through Micro Porous Filters Using Bondgraph Approach

Delivery of optimized fuel injection pressure to combustion chamber of an engine assembly leads to optimum torque and horsepower. Contaminant free supply of fuel without compromising on volume flow rate is the most important design requirement. Incorporation of very fine fuel filters having less than 10 micron rating reduces volume flow rate at the injection nozzles whereas fuel filter with larger pore size stabilize the injection pressure but may result into failure of fuel injection pump assembly due to scuffing produced by the fuel contaminant between the plunger and sleeve of hydraulic head of fuel injection pump. The fuel flows from fuel tank through low-pressure injection line, primary and secondary fuel filters, fuel transfer pump, fuel injection pump, and high-pressure injection line and injector nozzles. Modeling and simulation of volume flow rate vis-a-vis fuel injection pressure together with micro-porous fuel filter poses a formidable challenge. Bondgraph method (BGM) is ideally suited for the modeling and simulation of such a multi-domain dynamic system. The aim of this research is to apply BGM to model and simulate the optimized fuel injection pressure and analysis of filters with different micro-porosity and their effect on volume flow rate. Fuel filter porosity, inlet and outlet pressures of transfer pump, fuel injection pump and low/high pressure injection line pressure have been determined experimentally. These experimentally determined parameters are then used as input in our Bondgraph model for the dynamic analysis of fuel injection pressure incorporating micro-porous filters.© 2006 ASME

SCUFFING FAILURE ANALYSIS DUE TO AN ABRASIVE CONTAMINANT IN HIGH PRESSURE INJECTION FUEL SYSTEM

The presence of rigid abrasive contaminant between the plunger and sleeve of high-pressure injection fuel system causes scuffing failure. The abrasive contaminant is modeled as a spherically shaped rigid particle. The contaminant is envisioned to penetrate into the sleeve while positioning itself in rubbing contact with the plunger. Excessive temperature rise known as flash temperature between the particle-plunger interface is used as an indication of whether scuffing would take place. The model uses flash temperature in conjunction with the material properties to determine the critical particle size that may result in scuffing failure. The range of critical particle size initiating significant abrasive wear is determined and validated with the experimental results available in literature. Our predicted model can be used as a guide for selecting an appropriate filter size for high-pressure injection fuel system.Copyright

Scuffing Failure Due to an Abrasive Contaminant and Filter Suitability in High Pressure Injection Fuel System

The field studies have revealed that there is an unprecedented high failure rate of rotary diesel fuel injection pump (RDFIP). The presence of rigid abrasive contaminant between the plunger and sleeve of hydraulic head assembly of RDFIP causes scuffing failure. The abrasive contaminant is modeled as a spherically shaped rigid particle. The contaminant is envisioned to penetrate into the sleeve while positioning itself in rubbing contact with the plunger. Excessive temperature rise known as flash temperature between the particle-plunger interface is used as an indication of whether scuffing would take place. Flash temperature is determined by incorporating operating speed of pump, particle size, minimum film thickness, fuel properties, thermomechanical and surface properties of plunger and sleeve. Thermomechanical properties are determined through material composition of plunger and sleeve by spectroscopic techniques. Coordinate measuring machine is used to determine the radial clearance between the plunger and sleeve. Three high-pressure injection pumps are taken as case study for obtaining experimental data. This experimental data is used as an input in our theoretical model for the determination of flash temperature duly analyzing partial and diametric penetration of the abrasive contaminant. The model uses flash temperature in conjunction with the material properties to determine the critical particle size that may result in scuffing failure. The exact rating of fuel filter based on the critical particle size of the contaminant producing scuffing failure in the plunger and sleeve of hydraulic head assembly of RDFIP is also determined. The range of critical particle size initiating significant abrasive wear is determined and validated with the experimental results available in literature.Copyright

Modeling and Simulation of Residual Stresses in Mechanical Autofrettage

The autofrettage process is used to induce advantageous residual hoop stresses into pressure vessels to enhance their fatigue lifetime. Such pre-stressed pressure vessels are routinely used in power, nuclear, process, armament, and food industries. The autofrettage process can be accomplished by applying hydraulic or mechanical pressure or by the pressure of powder gas to the bore of a thick cylinder to induce residual stresses. The two processes are referred to as hydraulic and mechanical autofrettage respectively. The objective of this research is to analyze mechanical or swage autofrettage, which is achieved by ramming an oversized conical mandrel into the bore, thus driving it into the plastic regime. When the mandrel is removed, the outer elastic portion compresses onto the inner plastic regime, thus causing compressive residual stresses. The percentage of material that undergoes plastic deformation determines the level of autofrettage. A computer code based on finite element method is developed to analyze residual stresses including Bauschinger effect duly incorporating failure criteria such as von Mises and Tresca conditions. The computer code developed is benchmarked using analytical solutions based on Lame’s equations. Using this code, parametric studies are carried out to optimize the depth of penetration of the plastic regime into the material thickness of the bore. The results based on modeling and simulations are validated by using other available computer codes and experimental data.Copyright