Monsak Pimsarn

Efficient evaluation of spur gear tooth mesh load using pseudo-interference stiffness estimation method

This paper presents a new method, pseudo-interference stiffness estimation (PISE), for evaluating the equivalent mesh stiffness and the mesh load in gear system. The PISE method is based on evaluation of the geometric overlap of two assumedly rigid bodies and estimation of the contact force based on this artificial overlap area (or volume) and the singular stiffness (at the point of contact) of the bodies. Computationally, this procedure is orders of magnitude about 2000 times (in our numerical simulation) faster than finite element analysis of contacting bodies. This significant gain in computational efficiency leads itself to practical dynamic simulation of complex gear systems. In this paper, examples of two cylinders contact problem were solved by PISE method and finite element contact model. The results from both methods show reasonable agreement. PISE is then applied to gear teeth contact problem to estimate the equivalent mesh stiffness. The estimated results were compared with the finite element contact results. The comparison from PISE and finite element contact analysis also shows good agreement.

Pseudo-interference stiffness estimation, a highly efficient numerical method for force evaluation in contact problems

This paper presents a novel method, Pseudo-Interference Stiffness Estimation (PISE), for evaluating the contact compliance and the contact load in the contacting elastic solids. The PISE method is based on the evaluation of the geometric overlap of two assumedly rigid bodies and estimation of the contact force based on this artificial overlap area (or volume). In this paper, an example of the dynamic simulation of two disk collision problem is solved both by PISE method and finite element contact model. The contact force and velocity changes during impact from both methods are shown to be in good agreement. However, PISE method is, computationally, orders of magnitude (about 3000 times in our numerical simulations) faster than finite element contact analysis. The proposed method will be of practical use in contact force approximation of contacting bodies, such as meshing of spur gear teeth, cam analysis and synthesis, robotic grabbing, and numerous other applications.

Augmented heat transfer in rectangular duct with angled Z-shaped ribs

An experiment is focused on the design of the suitable ribs used for enhancing heat transfer in a rectangular duct heat exchanger by using wall heat transfer (Nusselt number), friction loss (friction factor) and thermal performance (thermal enhancement factor) data. The Z-shaped ribs were set on the rectangular duct at 30°, 45° and 60° and flat rib was set at 90° relative to the air flow direction. Reynolds numbers studied ranging from 5000 to 25,000 in the test section. The rectangular duct has aspect ratio, AR = 10 and height, H = 30 mm with the Z-rib height (e), e/H = 0.2 and the rib pitch (P), P/H = 3. The ribs were fitted in Z-shape (Z-rib) aligned in series on the whole area of the upper plate. The results of the Z-ribs show the significant increase in heat transfer rate and friction loss over the smooth channel. The 45° Z-rib provides the highest increase in the heat transfer rate and the best thermal performance

Design of the Experimental Procedures for Analysis of Thermal and Electrical Properties of a Prismatic LiFeYPO4 Battery in a Modified Electric Car

As being the most important part in the energy supply system, the battery must be carefully monitored in order to optimize the performance and to prolong its life. The most affected parameter to the battery is the operating temperature as the higher operating temperature increase the performance but shorten the life and with lower operating temperature can ensure longer life but reduce the performance. With this, the battery thermal management system is created in order to keep the operating temperature at the suitable range. In order to achieve this, thermal behaviour in loaded condition must be analysed beforehand. A series of experimental procedures is designed for the selected lithium iron phosphate battery to determine the thermal properties such as heat capacity, heat generation, and cell temperature according to the electrical load applied. Derived thermal model of lithium ion battery was utilized for this purpose as it shows the relationship between the thermal, electrical properties and other parameters such as voltage, current and cell temperature. When the battery is applied with electrical load, the data of voltage, current, and surface cell temperature can be used to determine the thermal properties and at the same time, electrical properties such as open circuit voltage, state of charge and internal resistance are also obtained for the performance evaluation.

Performance Assessment in a Heat Exchanger Tube with Opposite/Parallel Wing Twisted Tapes

The thermohydraulic performance in a tube containing a modified twisted tape with alternate-axes and wing arrangements is reported. This work aims to investigate the effects of wing arrangements (opposite (O) and parallel (P) wings) at different wing shapes (triangle (Tri), rectangular (Rec), and trapezoidal (Tra) wings) and on the thermohydraulic performance characteristics. The obtained results show that wing twisted tapes with all wing shape arrangements (O-Tri/O-Rec/O-Tra/P-Tri/P-Rec/P-Tra) give superior thermohydraulic performance and heat transfer rate to the typical twisted tape. In addition, the tapes with opposite wing arrangement of O-Tra, O-Rec, and O-Tri give superior thermohydraulic performances to those with parallel wing arrangement of P-Tra, P-Rec, and P-Tri around 2.7%, 3.5%, and 3.2%, respectively.

Heat Transfer Enhancement in a Channel with Rib‐Groove Turbulators

This paper presents the effects of the rib‐groove turbulators on the heat transfer and friction characteristics in a rectangular channel. The experiments encompass the Reynolds number range from 1800 to 10,000; pitch ratios (PR = P/e) 6.6–13.3 by using air as the working fluid. The obtained results demonstrate that heat transfer rate in term of Nusselt number (Nu) increases with the increase of Reynolds number, whereas friction factor (f) shows the opposite trend. Both Nusselt number and friction factor increase with decreasing pitch ratio. It is also observed that heat transfer rate and friction factor for the channels with rib‐groove turbulators are higher than those for the smooth channel under similar test conditions. In addition, the correlations for heat transfer rate in term of Nusselt number (Nu) and friction factor (f) for channel with rib‐groove turbulators are also presented.

Thermal Performance Assessment of Turbulent Flow Through Dimpled Tubes

This paper presents the heat transfer augmentation and friction factor characteristics by means of dimpled tubes. The experiments were conducted using the dimpled tubes with two different dimpled-surface patterns including aligned arrangement (A-A) and staggered arrangement (S-A), each with two pitch ratios (PR = p/Di = 0.6 and 1.0), for Reynolds number ranging from 9800 to 67,000. The experimental results achieved from the dimpled tubes are compared with those obtained from the plain tube. Evidently, the dimpled tubes with both arrangements offer higher heat transfer rates compared to the plain tube and the dimpled tube with staggered arrangement shows an advantage on the basis of heat transfer enhancement over the dimpled tube with aligned arrangement. The increase in heat transfer rate with reducing pitch ratio is due to the higher turbulent intensity imparted to the flow between the dimple surfaces. The mean heat transfer rate offered by the dimpled tube with staggered arrangement (S-A) at the lowest pitch ratio (PR = 0.6), is higher than those provided by the plain tube and the dimpled tube with aligned arrangement (A-A) at the same PR by around 127% and 8%, respectively. The empirical correlations developed in terms of pitch ratio (PR), Prandtl number (Pr) and Reynolds number, are fitted the experimental data within ±8% and ±2% for Nusselt number (Nu) and friction factor (f), respectively. In addition, the thermal performance factors under an equal pumping power constraint of the dimple tubes for both dimpled-surface arrangements are also determined.Copyright

Thermal Enhancement in Tubes with Dual Twisted Tapes

Influence of the dual twisted tapes (DTs) on the heat transfer enhancement in a circular tube is reported. The effects of twist ratio (y/w = 2.0, 3.0 and 4.0) on the heat transfer rate, friction factor, and thermal performance factor in a tube under constant wall heat flux were investigated in turbulent regions. Computations, based on a finite volume method, and the SIMPLE algorithm, were carried out by QUICK schemes. From the numerical results, heat transfer rate and pressure loss increased as twist ratio of tape (y/w) decreased. Based on the same pumping power consumption, the optimum thermal performance was achieved by the use of the tapes with twist ratio of 3.0. In addition, the predictions of flow-thermal phenomena (streamline, velocity vector, TKE and local Nusselt number) are also described.

Experimental Study on Flow Friction and Heat Transfer in a Square-Duct Heat Exchanger with Winglet Turbulators

The paper presents an experimental study on airflow friction and heat transfer behaviors in a heat exchanger square-duct fitted with winglet turbulators. The experiments are carried out by varying the airflow rate in terms of Reynolds number from 4000 to 25,000. The winglets were mounted in tandem with three attack angles (α=30o, 45o and 60o), two winglet-pitch to duct-height ratios, (called pitch ratio, PR=P/H=1.0 and 1.5) and a single winglet-to duct-height ratio, (called blockage ratio, BR=e/H=0.2). Effects of the winglet parameters on heat transfer and pressure loss in terms of Nusselt number and friction factor are investigated. The experimental result reveals that the application of the winglets provides considerably higher heat transfer and pressure loss values than the smooth duct alone. The winglet at α=60o and PR=1 gives the maximum heat transfer and pressure loss but the one at α = 30o and PR=1.5 yields the highest thermal enhancement factor of about 1.49 at the lowest Reynolds number.

Tooth Profile Modifications for Optimum Dynamic Load in Spur Gears Based on Pseudo-Interference Stiffness Estimation Method

A systematic methodology combining optimization, three dimensional analytical rigid body dynamics and a novel method, namely, Pseudo-Interference Stiffness Estimation method (PISE) [1]- [2], is proposed to dramatically reduce gear design time and improve the spur gear system dynamic performance. The main aim of this methodology is to search for the pro les of tooth crowning and shaving that eventually lead to the optimum dynamic tooth load in the gear mesh. An example of the detailed design study is numerically investigated. The results show that the dynamic tooth load can be reduced to up to 50 percent of its original value. However, this reduction is only valid at the operating ranges of the design load and design speed. It is also found that the effect of pro le modi cation on the dynamic response of the gear system was mostly observed to be a reduction in the peak dynamic tooth load at the resonance speed. Later, the investigation of gear tooth durability was conducted to validate an improvement of gear life. The rating factors given in AGMA publication, Hertzian contact stress, bending fatigue stress, ash temperature and PV index are employed in gear durability determination. The results show that, with the reduction of 50 percent in dynamic tooth load, the reductions in PV index, bending fatigue, Hertzian contact stress, and ash temperature can be achieved up to 64, 58, 28 and 39 percent, respectively.Copyright