Mongkolwongrojn, Mongkol

Preferred name

Alternative Name

Mongkolwongrojn, M.

Main Affiliation

School of Engineering

mongkol.mo@kmitl.ac.th

Now showing 1 - 10 of 19

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Theoretical investigation of transient elastohydrodynamic lubrication with newtonian solid-liquid lubricants
(2006-10-01)
Mongkolwongrojn, M.
;
Thammakosol, K.
This paper reports a theoretical investigation of transient elastohydrodynamic lubrication of a line contact. A time-dependent Reynolds equation and elasticity equations for compressible solid-liquid lubricants were solved using finite volume and multigrid techniques. The lubricants used were mineral oils mixed with very small solid particles, MoS<inf>2</inf> and FIFE which can be treated as Newtonian fluids. The two surfaces were initially at rest and in contact. The transient oil film pressure and oil film thickness were calculated numerically. This simulation showed the significant effects of solid particles on the lubrication characteristics. Copyright © 2006 John Wiley & Sons, Ltd.
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Transient elastohydrodynamic lubrication in artificial knee joint with non-Newtonian fluids
(2010-05-01)
Mongkolwongrojn, Mongkol
;
Wongseedakaew, Khanittha
;
Kennedy, Francis E.
This paper presents the transient analysis of a human artificial knee joint under elastohydrodynamic lubrication (EHL) for point contact with non-Newtonian lubricants. The artificial knee joints use ultra high molecular weight polyethylene (UHMWPE) against metal with time-varying speed and load during walking. This numerical simulation employed a perturbation method, Newton Raphson method and multigrid method with full approximation technique to solve simultaneously both the time-dependent Reynolds equation, with non-Newtonian fluid based on a Carreau model, and the elasticity equation. The general numerical schemes are implemented to investigate the characteristics of elastohydrodynamic lubrication in human artificial knee joints; profiles of pressure and film thickness are determined, with varying material and lubricant properties, applied loads and speeds. The results show that the elastohydrodynamic fluid film thickness between the metallic component of the artificial knee joint and the soft polyethylene bearing becomes larger as the contact area increases and the fluid film pressure decreases. At the beginning of the first walking cycle, the film thickness is lower than in subsequent cycles because of the time required to develop the fluid film; after the first cycle, the fluid film is similar for every cycle and is dependent on transient applied load and speed during human movement. © 2009 Elsevier Ltd. All rights reserved.
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Elastohydrodynamic lubrication of rough surfaces under oscillatory line contact with non-newtonian lubricant
(2008-09-01)
Mongkolwongrojn, Mongkol
;
Wongseedakaew, Khanittha
;
Kennedy, Francis E.
This paper presents the results of a transient analysis of elastohydrodynamic lubrication (EHL) of two parallel cylinders in line contact with a non-Newtonian lubricant under oscillatory motion. Effects of the transverse harmonic surface roughness are also investigated in the numerical simulation. The time-dependent Reynolds equation uses a power law model for viscosity. The simultaneous system of modified Reynolds equation and elasticity equation with initial conditions was solved using the multigrid, multilevel method with full approximation technique. The film thickness and the pressure profiles were determined for smooth and rough surfaces in the oscillatory EHL conjunctions, and the film thickness predictions were verified experimentally. For an increase in the applied load on the cylinders or a decrease in the lubricant viscosity, there is a reduction in the minimum film thickness, as expected. The predicted film thickness for smooth surfaces is slightly higher than the film thickness obtained experimentally, owing primarily to cavitation that occurred in the experiments. The lubricant film under oscillatory motion becomes very thin near the ends of the contact when the velocity goes to zero as the motion direction changes, but a squeeze film effect keeps the fluid film thickness from decreasing to zero. This is especially true for surfaces of low elastic modulus. Harmonic surface roughness and the viscosity and power law index of the non-Newtonian lubricant all have significant effects on the film thickness and pressure profile between the cylinders under oscillatory motion.
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Theoretical characteristics of hydrodynamic journal bearings lubricated with soybean-based oil
(2002-01-01)
Mongkolwongrojn, M.
;
Arunmetta, P.
Vegetable-based oils are not only biodegradable but also environmentally advantageous, and the range of lubrication applications offered by them continues to grow. Recently, vegetable-based oils have been combined with synthetic esters to produce modified vegetable-based oils. This paper presents an investigation of the theoretical characteristics of hydrodynamic journal bearings lubricated with non-Newtonian soybean-based oil. The soybean-based oil was mixed with synthetic esters and silicone oil. The relationship between the shear stress and shear strain rate of the oil was obtained experimentally. The time-dependent modified Reynolds equation including non-Newtonian effects was formulated for short circular journal bearings. The perturbation technique was applied to the Reynolds equation to obtain zero- and first-order pressure equations. The finite difference method was used to calculate the pressure distribution numerically. The static and dynamic characteristics, such as pressure distribution, Sommerfeld number, attitude angle, and spring and damping coefficients, were obtained numerically. It was found that the nonlinear factors of the non-Newtonian soybean-based oil strongly affected the performance characteristics of the journal bearings.
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Lubrication and wear of artificial knee joint materials in a rolling/sliding tribotester
(2007-04-01)
Kennedy, Francis E.
;
Van Citters, Douglas W.
;
Wongseedakaew, Khanittha
;
Mongkolwongrojn, Mongkol
This paper describes the influence of lubrication on wear during testing of materials for artificial knee joints in a rolling/sliding tribotester built to simulate contact conditions in a total knee replacement. The test configuration consists of parallel cylinders (pucks) of ultrahigh molecular weight polyethylene (UHMWPE) and polished cobalt-chrome alloy in oscillatory rolling/sliding contact in a bath of dilute (25%) bovine serum. Wear tests of three different UHMWPE materials were run under constant load at 40% sliding for 1.5 million oscillation cycles at 1.5 cycles/s. Wear of the UHMWPE was determined by measuring the profile of the cylindrical contact surface of the puck before and after each test. Profile measurements were repeated after at least 53 days to eliminate the contribution from creep. Differences between initial and final profiles were attributed to wear of the UHMWPE. It was found that the largest wear depth in the lubricated tests occurred near the ends of the oscillatory contact area, while dry (unlubricated) tests of the same materials showed a peak wear depth near the center of the contact area. In the lubricated tests, the worn depth was lowest for the most heavily irradiated material. Analysis of the elastohydrodynamic lubrication in the rolling/sliding contact was carried out assuming a line-contact situation with smooth cylindrical surfaces. The time-dependent modified Reynolds equation and the elasticity equation with initial conditions were solved numerically using a multigrid technique with full approximation scheme, and using a Newton Raphson method to solve the highly nonlinear system of equations. The thickness of the lubricating film of bovine serum was determined for points along the length of the wear track. It was found that the smallest film thickness (h<inf>min</inf>) occurs very close to the location in the oscillating contact where the greatest wear occurs, owing to the very low entraining velocity near the ends of the oscillation cycle. The coefficient (K) for wear of the UHMWPE was found to be relatively constant over the central section of the oscillatory motion, but increased to a higher value where h<inf>min</inf> decreased to near zero. Thus, the important influence of lubrication on wear of artificial knee bearings was demonstrated. Copyright © 2007 by ASME.
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Static Characteristics of High-Speed Slider Bearings Lubricated with Non-Newtonian Fluids (In the Case of Infinitely Long Bearings)
(1995-01-01)
Hashimoto, Hiromu
;
Mongkolwongrojn, Mongkol
In this paper, the static characteristics of infinitely long slider bearings lubricated with non-Newtonian fluids are examined theoretically by considering the fluid inertia effects. In the derivation of the modified Reynolds equation, the fluid inertia terms in the momentum equation for the lubricant film are averaged over the film thickness, and the Rabinowitsch empirical model is used as a constitutive equation of non-Newtonian fluids. Applying the modified Reynolds equation to the infinitely long slider bearings, the film pressure, load carrying capacity, friction force and inlet flow rate are obtained under various values of the dimensionless nonlinear factor and film thickness ratio, and the effects of fluid inertia on these static characteristics are discussed. © 1995, The Japan Society of Mechanical Engineers. All rights reserved.
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Effect of bearing materials on journal bearings under TEHL with lubricant based on Carreau model
(2020-02-17)
Gunnuang, Waleephan
;
Aiumbhornsin, Chatchai
;
Wongsa-Ngam, Jittraporn
;
Mongkolwongrojn, Mongkol
This work presents a transient analysis of journal bearings under thermal elastohydrodynamic lubrication (TEHL) based on the Carreau model. The effects of the elastic modulus of the bearing liner have been investigated using numerical simulations. A time-dependent modified Reynolds equation and an adiabatic energy equation based on the Carreau model have been formulated and numerically solved to examine the performance of the journal bearings. The results show that the minimum film thickness and the friction coefficient both increase with decreasing bearing liner elastic modulus. In contrast, the dimensionless load carrying capacity, dimensionless maximum film temperature, and dimensionless maximum film pressure all decrease with decreasing bearing liner elastic modulus. The stability regions tend to decrease in size for journal bearings under TEHL, especially for journal bearings composed of soft materials.
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Analysis of Indoor PM2.5 Contaminants Based on Outdoor Wind Velocity Through Different Infiltration Types
(2025-01-01)
Oo, Ghaim Man
;
Kotmool, Komsilp
;
Mongkolwongrojn, Mongkol
Nowadays, indoor PM2.5 concentrations have become a significant factor affecting indoor air quality (IAQ) and a major public concern, particularly with the rise of haze in Thailand and globally, as PM2.5 can penetrate human lungs. This research analyzes the dispersion of PM2.5 from outdoors to indoors using a fluid dynamics simulation framework that combines the Eulerian approach for continuous flow, the Lagrangian approach for particulate matter dispersion, and the RNG k-ε turbulent model for airflow. The study is aimed at protecting indoor environments from harmful exposure to PM2.5 from outdoor contaminants and improving IAQ. Primarily, three different infiltration types and shapes are studied to determine the minimum optimal positive room pressure, based on the impact of ambient wind velocity on indoor PM2.5 concentrations from outdoor pollutants. A minimum optimal pressure of 3.6 Pa and 27 air changes per hour (ACH) is sufficient to achieve a PM2.5-free indoor environment for all infiltration models. Furthermore, higher wind speeds can reduce indoor PM2.5 concentrations due to the increased momentum of particles. This research technique is implemented in the practical field study conducted within the laboratory room of the 55-Year Chalermprakiat Building. As a result, the investigated room, with an infiltration area of 0.06 m<sup>2</sup> and a rate of 0.0036 m<sup>3</sup>/s, will be certified as a clean room by achieving an optimal minimum pressure of approximately 0.01 Pa. This research will help achieve cleaner and safer indoor environments for any building by leveraging the optimal minimum pressure of cleanroom technology, provided that the infiltration rate and ambient wind velocity are accurately determined.
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Influence of indium addition on characteristics of Sn-0.3Ag-0.7Cu solder alloy
(2009-10-19)
Kanlayasiri, Kannachai
;
Mongkolwongrojn, Mongkol
;
Ariga, Tadashi
Effects of indium (In) addition on solidus and liquidus temperatures, wetting time, wetting force, tensile strength, and microhardness of Sn-0.3Ag-0.7Cu lead-free solder alloy were investigated in this paper. Indium was added and varied from 0 to 3 wt%. It is found that solidus and liquidus temperatures of the solder alloy are lowered as the In content is increased. However, In also increases the melting range between solidus and liquidus temperatures. Wetting time of the solder alloy is reduced by the addition of In while the wetting force is increased with the increase of In content. With the addition of In, the Sn-rich phase is smaller in size, and the intermetallic compounds are more uniformly distributed. As a result, tensile strength and microhardness of Sn-0.3Ag-0.7Cu are increased when In is added into the solder alloy. © 2009 Elsevier B.V. All rights reserved.
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Theoretical investigation in thermoelastohydrodynamic lubrication with non-Newtonian lubricants under sudden load change
(2006-10-01)
Mongkolwongrojn, M.
;
Aiumpornsin, C.
;
Thammakosol, K.
The time-dependent thermal compressible elastohydrodynamic lubrication of a sliding line contact has been developed to investigate the effect of a sudden load change. The time-dependent modified Reynolds equation with non-Newtonian fluids has been formulated using a power law model. Properties of non-Newtonian dilatant fluids for solid-liquid lubricants have been studied experimentally using two common solid particles; namely, molybdenum disulfide and polytetrafluoroethylene. The simultaneous systems of modified Reynolds, elasticity, and energy equations with initial conditions were solved numerically using a multigrid multilevel technique. The performance characteristics of the thermoelastohydrodynamic line contact were presented with varying dimensionless time for the pressure distribution, temperature distribution, and oil film thickness. The transient response of the line contact between two infinitely long cylindrical surfaces was simulated under a heavy step load function. The coefficients of friction were also presented in this work at steady condition with varying particle concentration. This simulation showed a significant effect of solid particles on thermoelastohydrodynamic lubrication under heavy load conditions. Copyright © 2006 by ASME.

Mongkolwongrojn, Mongkol

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