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When an electrohydrodynamic (EHD) pump is used as a power source to drive a refrigerant liquid, the temperature dependence of the EHD pump characteristics must be made clear; however, this topic has hardly been investigated. Therefore, this study measures the pump characteristics under different temperatures ranging from 3 to 45 °C using the fluorine solvents Vertrel XF (C5H2F10) and Novec 7100 (C4F9OC2H5) as the working fluids. The pressure developed by the EHD pump at zero flow rate increases with decreasing temperature. The slope of the pressure–flow rate characteristics is steeper with lower temperature. The numerical simulation results obtained under the assumption that the injected charge density increases with decreasing temperature agree relatively well with the experimental results and reveal the effect of the fluid temperature.

This paper experimentally and numerically investigates the effect of the meniscus on the heat-transfer of a loop heat pipe (LHP) evaporator as an aid in performance prediction. The meniscus on the three-phase contact line (TPCL) between the case, wick, and grooves was observed using a glass tube evaporator and a microscope. Acetone was used as the working fluid. The evaporator heat-transfer coefficient decreased as the heat flux increases at a low heat flux regime. Thereafter, it rapidly increased to a maximum at a certain heat flux and then decreased again. This trend is due to the change in the size of the meniscus and transition of the vapor-liquid phase state on the contact surface between the case and the wick. In the analysis, a one-dimensional heat transfer model of the meniscus is proposed based on thin liquid-film evaporation theory. The amount of evaporation from the meniscus was calculated by the one-dimensional model and then integrated with the macroscopic numerical model of the evaporator. Considering the meniscus, the amount of evaporation increased, and therefore, the heat-transfer coefficient increased. The predicted heat-transfer coefficient agrees well with the measured value.

Rotor behavior may affect the torque characteristics of gerotor pumps, but the measurement of the behavior has received little attention. Thus, in this study, we measure the rotor behavior of a gerotor pump used for automatic transmissions under various operating conditions. The experiments revealed that the inner rotor rotated near the middle of the cover wall and casing sidewall, slightly tilted with respect to them. The outer rotor rotated in the vicinity of the casing sidewall and came closer to the sidewall with decreases in the dimensionless parameter μN/ΔP (where μ [Pa·s] is the oil viscosity, N [s−1] is the rotational speed, and ΔP [Pa] is the pressure difference). In addition, the eccentricity of the outer rotor was observed to increase with decreases in μN/ΔP. The inclination of the inner rotor and the approximation of the outer rotor to the casing sidewall may increase the driving torque of the pump. Taking the measured results on rotor behavior into account, a clear physical meaning is given to an existing mathematical model of viscous friction torque.

Small axial fans are used for cooling electronic equipment and are often installed in a casing with various slits. Direct aeroacoustic simulations and experiments were performed with different casing opening ratios to clarify the effects of the flow through the casing slits on the flow field and acoustic radiation around a small axial fan. Both the predicted and measured results show that aerodynamic performance deteriorates at and near the design flow rate and is higher at low flow rates by completely closing the casing slits compared with the fan in the casing with slits. The predicted flow field shows that the vortical structures in the tip vortices are spread by the suppression of flow through the slits at the design flow rate, leading to the intensification of turbulence in the blade wake. Moreover, the pressure fluctuations on the blade surface are intensified, which increases the aerodynamic sound pressure level. The suppression of the outflow of pressurized air through the downstream part of the slits enhances the aerodynamic performance at low flow rates. Also, the predicted surface streamline at the design flow rate shows that air flows along the blade tip for the fan with slits, whereas the flow toward the blade tip appears for the fan without slits. As a result, the pressure distributions on the blade and the torque exerted on the fan blade are affected by the opening ratio of slits.

The liquid–vapor phase distribution and displacement in the capillary evaporator of a loop heat pipe (LHP) are key phenomena affecting the steady-state and transient operating behavior. This study conducts optical observation of liquid–vapor phase behavior in the evaporator using a transparent glass tube heated by far-infrared radiation during start-up of the LHP. A quartz wick-acetone LHP system is designed, fabricated, and operated successfully with a heat flux of 1 W/cm2 transported by the cylindrical evaporator. To investigate effect of the liquid–vapor phase distribution in the evaporator at the initial state, start-up experiments with eight phase patterns—which are either liquid-saturated or two-phase in each of the inlet of the vapor line, grooves, and compensation chamber (CC)—are performed. The phase distribution affects the temperature profile although it has no effect upon the steady-state characteristics, and nucleate boiling occurs in the wick or groove simultaneously with evaporator-temperature drop when both the grooves and the inlet of the vapor line are completely filled with liquid. Liquid–vapor displacements from start-up to the steady-state are classified into four transient behaviors, which include boiling in the CC and meniscus oscillation at the three phase contact line within the case, wick, and groove.

This paper reports a numerical investigation into the effects of interactions between two mechanisms of charge injection and dissociation on overall Electrohydrodynamic (EHD) pump characteristics. The following three types of electrode configurations are modeled: a plate and a bar, two plates on a channel wall, and embedded two-plate electrodes. The simulation results show that when the both mechanisms act in concert, the total developed pressure is augmented to be larger than the sum of the pressures developed by each mechanism separately. The degree to which the pressure is synergistically augmented depends on the configuration of electrodes.

This paper focuses on investigating friction behavior in pre-sliding regime and developing a new mathematical model of friction for fluid power actuators. Using pneumatic cylinders with different sizes, an experimental setup is built to measure friction force-displacement characteristics in presliding regime under various conditions of pressures in the cylinder chambers. A new mathematical model of friction for the pneumatic cylinders is proposed by incorporating a hysteresis function into the new modified LuGre model. The experimental results show that when the pressures are varied, friction of the pneumatic cylinders in pre-sliding regime is represented by behavior of a nonlinear spring. In addition, hysteresis behavior with nonlocal memory is obtained in the friction forcedisplacement characteristics and that the size of the hysteresis loop is increased with increasing pressures in the cylinder chambers. The simulation results show that the new friction model can accurately simulate the friction behavior of the pneumatic cylinders in pre-sliding regime as well as sliding regime.

Simple, lightweight electrohydrodynamic pumps having no moving parts and producing no mechanical vibration or noise can enhance heat transfer, control fluid flows, and increase drying. This paper reports a numerical investigation of electrohydrodynamic (EHD) pumps having one centrally located emitter and two collector electrodes. Results show that optimum sizes exist in the length of and spacing between the collectors. Collector electrodes with triangular cross-sections can yield better performance than those having rectangular cross-sections. The magnitude and distribution of the charge density significantly influence pump performance.

The liquid–vapor phase distribution and displacement in the capillary evaporator of a loop heat pipe (LHP) are key phenomena affecting the steady state and transient operating characteristics. This study intends to analyze the liquid-vapor interface behavior in the capillary evaporator that causes operational instability and enhances the heat-transfer while performing optical observation in the transparent cylindrical evaporator during the LHP operation. A quartz wick-acetone LHP system was designed and fabricated, which operated successfully with a maximum heat flux of 5.9 W/cm2. Phase displacement in various operations, such as the start-up involving nucleate boiling, capillary limit, hysteresis, and step-up of the heat load were observed. Binarized image quantitatively processed revealed dynamic characteristics on the contact surface between the wick and case. Comparison of the phase displacements during the start-up involving nucleate boiling and nucleate boiling after normal start-up showed that the equilibrium vapor phase on the contact surface between the evaporator case and wick is formed by both imbibition and drainage. On the step-up-down test of the heat load, a visual evidence of hysteresis of the evaporator heat-transfer coefficient due to the phase distribution in the wick was noticed. The simulation results showed that the residual liquid phase along the three phase contact line within the case, wick and grooves, observed by the visualization experiment, is of low temperature. Therefore, the distribution of the residual liquid can enhance the evaporator heat-transfer coefficient. This characteristic is the key aspect of optimizing the porous structure of the wick.

This paper reports on an improvement of the filtration speed of charge injection type of electrostatic oil filter. Numerical simulations of the ion drag flow field and electric field are performed to compare the charge density distribution, ion drag flow pattern, and electric field strength distribution for different electrode and filter element shapes. Filtration experiments are conducted and the experimental results are discussed in relation to the simulation results. It is shown that the numerical simulations used in this study can contribute in predicting a better structure for electrostatic oil filters.

This paper deals with experimental investigation and modeling of dynamic friction behaviors in the sliding regime of pneumatic cylinders. Using three pneumatic cylinders, friction characteristics are investigated and modeled under various conditions of velocity variation and pressures. It is shown that a hysteretic behavior can be seen at low velocities in the friction force-velocity relation and the friction force varies nearly linearly with the velocity at high velocities. The hysteretic loop is expanded to higher velocities when the frequency of the velocity variation is increased, and its size is increased with increasing driving pressure and is decreased with increasing resistance pressure. It is shown that such behaviors can be relatively accurately simulated by the new modified LuGre model in which a few static parameters are varied with the frequency of velocity variation.

This paper deals with modeling of dynamic friction behaviors of hydraulic cylinders. Using hydraulic cylinders with different packing materials and sizes, friction characteristics are experimentally investigated under different magnitudes of external load. It is shown that the dynamic friction characteristics are affected by the packing material of the cylinder and by the pressures in the cylinder chambers. Comparisons between dynamic friction characteristics measured and those predicted by the modified LuGre model show that the model cannot simulate the real hysteretic behaviors of the friction force–velocity curve in the fluid lubrication regime. The modified LuGre model is improved by replacing the usual fluid friction term, which is proportional to velocity, with a first-order lead dynamics. It is shown that the proposed model can give accurate simulation results in the fluid lubrication regime.

This paper deals with the effects of the configurations of electrodes and filter elements on the filtration speed of a charge injection type of electrostatic oil filter, which has been proposed by Yanada et al. It has been demonstrated that the filtration speed can be increased by injecting charges into oils. However, investigation into the effects of the configurations of the electrode and filter element has been limited. In this paper, several types of filter model with different configurations are proposed and their performance is experimentally investigated. A better filter configuration is proposed.

This paper deals with the effect of filter element on the filtration speed of a charge injection type of electrostatic oil filter proposed by Yanada and his coworkers. The effect of the filter elements that are inserted between the emitter and collector electrodes on the filtration speed is examined using several types of oil. In order to discuss the effect of the filter elements on the filtration speed, numerical simulations of electrostatic field are conducted and ion drag flow patterns are measured using two-dimensional filter models. An optimal filter configuration is proposed.

This paper deals with the measurement and numerical simulation of the characteristics of ion drag pumps. The pressure-flow rate characteristics and the flow fields of ion drag pumps with different configurations are measured and are numerically simulated. Measured and simulated results are compared with each other. The value of the ionic mobility and the relation between the electric field strength and the injected charge density are determined so that the numerical simulation results agree well with measured results for a certain standard configuration of ion drag pump. It is shown that the pump characteristics can be simulated with a relatively good accuracy by the numerical simulation and that an appropriate selection of the value of the ionic mobility is essential to the success in numerical simulation. It is also shown that the accuracy of the numerical simulations for the pumps with configurations different from the standard one is lowered when the relation between the electric field strength and the injected charge density for the standard pump is used.

This paper deals with the identification of dynamic parameters included in the modified LuGre model and the identification method is applied to a hydraulic actuator. In order to simulate dynamic behaviors of friction of a hydraulic actuator well, Yanada and Sekikawa have modified the LuGre model by incorporating lubricant film dynamics into the LuGre model and have shown that the dynamic friction behaviors of a hydraulic actuator can be simulated by the modified LuGre model with a relatively good accuracy10). However, no method to identify the dynamic parameters included in the modified LuGre model has been proposed yet. In this paper, a method to identify the dynamic parameters, i.e., the time constant of lubricating film dynamics and the bristle stiffness is proposed. Using a single rod hydraulic cylinder, friction characteristics are experimentally investigated under various conditions of velocity variation under different supply pressures. The friction force of the hydraulic cylinder is measured based on the equation of motion using measured values of the pressures in the cylinder chambers and the acceleration of the hydraulic piston. Measured friction characteristics are compared with simulated ones by the modified LuGre model. It is shown that the dynamic behaviors of friction simulated using the parameters identified by the proposed method agree relatively well with those obtained by experiments and that the proposed identification method is appropriate. It is also shown that the time constant becomes longer under higher pressures and that the bristle stiffness does not depend on the pressure.

This paper deals with modeling of dynamic behaviors of friction in the sliding regime. Using a hydraulic cylinder, friction characteristics are experimentally investigated under various conditions of velocity variation. The friction force of the hydraulic cylinder is measured based on the equation of motion using measured values of the pressures in the cylinder chambers and the acceleration of the hydraulic piston. Comparison between measured unsteady-state friction characteristics and those predicted by the LuGre model shows that the LuGre model cannot simulate the real friction characteristics of hydraulic actuators. In this paper, the LuGre model is modified taking the dynamics of lubricant film formation into consideration. The lubricant film dynamics is approximated by a first-order lag element and its time constant is varied among the acceleration, deceleration and dwell periods. Experiments make clear the dynamic behaviors of the friction of the hydraulic cylinder. It is shown that the modified LuGre model can simulate the real dynamic behaviors of the friction of the hydraulic actuator with a relatively good accuracy.

This paper presents experimental and numerical simulation results of the electric and flow fields in a charge injection type of electrostatic oil filter. A previous work has shown that flow is generated from the tips of the projections of the emitter electrode towards the smooth electrodes because of ion drag phenomenon and that the flow may detach part of the contaminant particles captured on the smooth electrodes and may be the principal cause of the saturation of the filtration speed at higher applied voltages and oil temperatures. In order to minimize the bad influence of the ion drag flow on the filter performance, it is important to be able to predict the flow in filters of various configurations by numerical simulation. Experimental results of the flow field are compared to numerical simulation results. In addition, electric potential distribution is measured and is compared between experiment and simulation. It is shown that the magnitude of the ion drag flow is increased with increasing applied voltage, is decreased with decreasing electrode spacing and is larger for negative charge injection than for positive charge injection. Similar results can be obtained by numerical simulations but the improvement of simulation accuracy is necessary.

This paper deals with unsteady-state friction characteristics of a hydraulic actuator. Using a single rod hydraulic cylinder, friction characteristics are experimentally investigated under various conditions of velocity variation at different supply pressures. The friction force of the hydraulic cylinder is measured based on the equation of motion using measured values of the pressures in the cylinder chambers and the acceleration of the hydraulic piston. A method to identify dynamic parameters included in the modified LuGre model, which has been proposed by Yanada and Sekikawa, is proposed. Comparison between measured unsteady-state friction characteristics and those simulated by the modified LuGre model is conducted. It is shown that the unsteady-state friction characteristics simulated using the parameters identified agree with those obtained by experiments with a relatively good accuracy and that the proposed method to identify the dynamic parameters is appropriate. The effect of the supply pressure on the friction characteristics and the dynamic parameters are shown.