Barkan M. Kavlicoglu

A comparative study of thermal behavior of iron and copper nanofluids

Nanofluids consist of nanoparticles dispersed in heat transfer carrier fluid and are typically used for enhancing thermal conductivity in devices and systems. This study investigated the synthesis of iron and copper nanoparticle-based thermal fluids prepared using a two-step process. Chemical precipitation was used for the synthesis of the powders, and ultrasonic irradiation was used to disperse the nanoparticles in the carrier fluid (ethylene glycol). The size distributions of the nanopowders in the carrier fluid were determined using dynamic light scattering resulting in average particle sizes of around 500 nm. The crystallite sizes of the powders were below 20 nm. Thus, both types of nanofluids are comparable with regard to crystallite size, particle size, and morphology resulting in a direct comparison of material properties and their effect on thermal conductivity of the nanofluids. A guarded hot parallel-plate method and dynamic tests were used to compare the thermal conductivities of the nanofluids. It was shown that thermal conductivity can be enhanced by up to 70% for copper nanofluids. It was also demonstrated that for a given particle concentration, copper nanofluids are superior in thermal conductivity compared to iron nanofluids.Nanofluids consist of nanoparticles dispersed in heat transfer carrier fluid and are typically used for enhancing thermal conductivity in devices and systems. This study investigated the synthesis of iron and copper nanoparticle-based thermal fluids prepared using a two-step process. Chemical precipitation was used for the synthesis of the powders, and ultrasonic irradiation was used to disperse the nanoparticles in the carrier fluid (ethylene glycol). The size distributions of the nanopowders in the carrier fluid were determined using dynamic light scattering resulting in average particle sizes of around 500 nm. The crystallite sizes of the powders were below 20 nm. Thus, both types of nanofluids are comparable with regard to crystallite size, particle size, and morphology resulting in a direct comparison of material properties and their effect on thermal conductivity of the nanofluids. A guarded hot parallel-plate method and dynamic tests were used to compare the thermal conductivities of the nanofluids...

Particle size effects in the thermal conductivity enhancement of copper-based nanofluids

We present an analysis of the dispersion characteristics and thermal conductivity performance of copper-based nanofluids. The copper nanoparticles were prepared using a chemical reduction methodology in the presence of a stabilizing surfactant, oleic acid or cetyl trimethylammonium bromide (CTAB). Nanofluids were prepared using water as the base fluid with copper nanoparticle concentrations of 0.55 and 1.0 vol.%. A dispersing agent, sodium dodecylbenzene sulfonate (SDBS), and subsequent ultrasonication was used to ensure homogenous dispersion of the copper nanopowders in water. Particle size distribution of the copper nanoparticles in the base fluid was determined by dynamic light scattering. We found that the 0.55 vol.% Cu nanofluids exhibited excellent dispersion in the presence of SDBS. In addition, a dynamic thermal conductivity setup was developed and used to measure the thermal conductivity performance of the nanofluids. The 0.55 vol.% Cu nanofluids exhibited a thermal conductivity enhancement of approximately 22%. In the case of the nanofluids prepared from the powders synthesized in the presence of CTAB, the enhancement was approximately 48% over the base fluid for the 1.0 vol.% Cu nanofluids, which is higher than the enhancement values found in the literature. These results can be directly related to the particle/agglomerate size of the copper nanoparticles in water, as determined from dynamic light scattering.

A Semi-Active, High-Torque, Magnetorheological Fluid Limited Slip Differential Clutch

The design, development, and performance characterization of a magnetorheological (MR) fluid clutch for automotive limited slip differential (LSD) applications is presented in this study. The controllability of MR fluids provides an adjustable torque transmission and slippage for the LSD application. Three-dimensional electromagnetic finite element analysis (FEA) is performed to optimize the magnetic circuit and clutch design. Based on the results obtained from the FEA, the theoretical torque transfer capacity of the clutch is predicted utilizing Bingham-Plastic constitutive model. The clutch is characterized at different velocities and electromagnet electric input currents. Both the torque transfer capacity and the response time of the clutch were examined. It was demonstrated that the proposed MR fluid LSD clutch is capable of transferring controllable high torques with a fast response time. DOI: 10.1115/1.2203308

Heating of a High-torque Magnetorheological Fluid Limited Slip Differential Clutch

Theoretical and experimental studies on heating of a high-torque, multi-plate magnetorheological (MR) fluid limited slip differential (LSD) clutch are presented. A lumped parameter system approach is assumed for theoretical heating analysis. The experimental study is conducted to examine the temperature rise of the clutch. Electric power input and slippage effects are investigated both theoretically and experimentally. The effect of temperature increase on the torque performance of the clutch is also examined. The results show that the transferred torque is insensitive to clutch temperature increase. For all cases, theoretical and experimental results are in good agreement.

Response time and performance of a high-torque magneto-rheological fluid limited slip differential clutch

In this study, the response time and system characterization analyses of a high-torque magneto-rheological (MR) fluid limited slip differential (LSD) clutch are presented. The response time of the clutch is examined based on the objective of keeping the relative velocity difference of the shafts of the clutch less than a predetermined threshold value. The experimental setup allows the application of an external disturbance to the system, so that the relative velocity difference exceeds the threshold value. A velocity-based, closed-loop control system is designed and tested. Additionally, system identification experiments are performed to determine system parameters such as bearing friction coefficients, dry and viscous torque coefficients. These parameters are utilized in the theoretical response time analyses of the MR fluid LSD clutch. It is demonstrated that the overall response time of the system varies between 20 and 65 ms as a function of operating velocity and electromagnet current, including the response times of the controller, solenoid inductance and MR fluid and inertia effects. The response time reduces by increasing solenoid current and increasing the operating velocity.

High-torque magnetorheological fluid clutch

This study focuses on the design and characterization of a radial double-plate magneto-rheological fluid (MRF) clutch. The clutchs torque output can be controlled by adjusting the applied magnetic field. Electromagnetic finite element analysis (FEA) is performed to design and optimize the clutch. The shear stress distribution in MRF between the plates is theoretically predicted using the magnetic flux density distribution evaluated from the FEA. The output torque of the clutch is derived by using the Bingham plastic constitutive model. The output torque values are recorded for different input velocities and applied magnetic fields, and they are compared with the theoretical results. It was demonstrated that the clutch is capable of producing high controllable torques.

Study of a magnetorheological grease clutch

In high-speed viscous clutch applications that require low drag (viscous) torque, magnetorheological (MR) fluids are problematic due to their plastic viscosity. As the clutch speed increases the drag torque might exceed the allowable drag torque limit, because the viscous torque is proportional to the speed. To eliminate this problem, various MR greases are utilized in a clutch and their performance is examined. In the experimental study, the torque transfer capacity of a double-plate clutch for operating speeds up to 1200 rpm is conducted. Six different MR greases with various particle loadings and particle sizes are evaluated in the clutch. The rheological properties of MR grease with 90% particle loading in weight are compared with a commercially available MR fluid. The torque performance of the MR grease clutch is also compared with that of the clutch using MR fluid. It is demonstrated that the off-state (no applied magnetic field) torque output of the MR grease clutch is constant in the tested range of the operating speed. In contrast, the torque capacity of the clutch with MR fluid shows a strong dependence on the operating speed. Moreover, it is shown that the iron particle size of the MR grease does not affect the torque output. The MR greases demonstrated an up to 75% increase in the torque capacity compared to the commercial MR fluid. (Some figures may appear in colour only in the online journal)

Magnetorheological elastomer mount for shock and vibration isolation

A novel magnetorheological elastomer (MRE) mount is designed, fabricated, and tested to provide a wide controllable compression static stiffness range for protecting a system with variable payload from external shock and vibration. The shear static stiffness and compression dynamic stiffness were also studied. MRE is a field-controllable material in which the stiffness properties can be altered by changing the applied magnetic field. A MRE mount is developed by using 0.5-inch thick MRE layers and built-in electromagnets. The performance of the 2-layer MRE mount is characterized by compression, shear, vibration, and shock tests. The tests demonstrate that the variable-stiffness MRE mount can be used for shock and vibration isolation applications.

Study of a magneto-rheological grease (MRG) clutch

In this study the performance of various magneto-rheological (MR) greases in a clutch is examined. An experimental study is conducted to determine the torque transfer capacity of a double-plate clutch for operating speeds up to 1,200 rpm. Six different MR greases with various particle loadings and particle sizes are evaluated in the clutch. The rheological properties of MR grease with 90% particle loading in weight are compared with a commercially available MR fluid. The torque performance of the MR grease clutch is also compared with that of the clutch using MR fluid . It is demonstrated that, the off-state (no applied magnetic field) torque output of the MR grease clutch is constant regardless of the operating speed. In contrast, the torque capacity of the clutch with MR fluid shows a great dependence on the operating speed. Moreover, it is shown that the iron particle size of the MR grease does not affect the torque output. The MR greases demonstrated up to 75% increase in the torque capacity compared to the commercial MR fluid.

Multiplate magnetorheological fluid limited slip differential clutch

This study focuses on the design and characterization of a multi-plate magneto-rheological fluid (MRF) limited slip differential (LSD) clutch. Three-dimensional electromagnetic finite element analyzes are performed to optimize the MRF LSD clutch design. The torque transfer capacity of the clutch is predicted utilizing Bingham-Plastic constitutive model of the MRF. The MRF LSD clutch is tested at different velocities and applied magnetic fields. The clutch heating is also examined under different operating conditions to determine the thermal effects on the torque transfer performance of the multi-plate clutch.