Research on pumped two-phase single-sided cold plate of IGBT for rail transit applications

ABSTRACT The use of pumped two-phase cooling to improve the thermal management of insulated gate bipolar transistor (IGBT) in rail transportation is a novel cooling technology. An experimental investigation on pumped two-phase cold plate of IGBT used in HXD1C locomotives was conducted at a mass flow rate of 0.1 kg/s–0.29 kg/s and a heat flux of 6.2 W/cm2, with R245fa as the working fluid. The experimental results showed that the base temperature nonuniformity can be controlled within 2.2 °C at flow rates of 0.14 kg/s and 0.19 kg/s, which is of great benefit to the reliability of IGBT. Based on well known correlations for saturated flow boiling in tubes, an analytical model was developed and compared with the experimental data. The model could predict the base temperature data within an error band of ±3 °C, as well as capture the trend of base temperature as a function of vapour quality and mass flow rate. The performance of the pumped two-phase cold plate of IGBT could be further improved with the aid of the developed model.

Investigation of mechanical properties and tribological performance of Al-LSP and Al-Al2O3 composite

Purpose This study aims to develop the Al-Si-Mg metal matrix composite, reinforced distinctly with lime stone powder (LSP; 12% by weight) and Al2O3 (12% by weight), and compare their mechanical properties and tribological performance. Design/methodology/approach The composites are fabricated through stir casting process. In view of the previous work, the Al-LSP composite with LSP reinforcement (12 Wt.%) shows enhanced mechanical properties and tribological performance, as compared with other weight percentages. Findings Though the Al-LSP composite is less expensive, it shows similar hardness, tensile strength and specific strength, when compared with Al- Al2O3 composite. However, the Al-LSP composite exhibits significant enhancement of above three properties, when compared with Al-Si-Mg metal. The systematic factorial design of experiments is obtained through Taguchi OA [L9]. The tribological performance is estimated through wear rate (WR-mm3/m) and coefficient of friction (CF) by varying the operating parameters of sliding distance (SD), load (L) and sliding velocity (SV). According to ANOVA results, the optimal condition of WR for all the tested materials is L1SD3SV1. Further, the optimal condition of CF is L1SD1SV3 for Al-LSP and Al-Si-Mg metal, while L2SD3SV2 is for Al-Al2O3 composite. The regression equation predicts the measured experimental values within error band of ± 8 percentage. Originality/value A comparison of two composite materials (Al-LSP and Al-Al2O3) with same weight fractions (12%) shows almost same trend in both the mechanical and tribological testing process. However, the developed Al-LSP composite exhibited better properties than the Al-Al2O3 and Al-base. Therefore, Al-LSP can be suggested for automotive applications (i.e., connecting rod, cylinder liners, camshaft) and structural applications (such as frames, over hanging supports), without compromising in desirable original with properties of constituents in the new material, which is achievable for looking to the end uses.

A Mathematical Model for Windmilling of a Turbojet Engine

The transient windmilling characteristic of a modern turbojet engine under different flight conditions and altitudes is obtained with numerous tests conducted at an Altitude Test Facility (ATF). A simple and practical mathematical model for predicting the transient and steady-state rotational speed of a simple turbojet engine in flight has been developed. The method is derived from Froude’s momentum theory or disk actuator theory and implemented to a turbojet engine. A correction factor is introduced to match with test results of KTJ-3200 being indigenously developed by Kale R&D Inc. The present model’s predictions are compared with the test data of Microturbo TRI 60 engine and KTJ-3200 engine. The estimation of the present windmilling model fits very well with test results of two different engines within an error band of ±1.2% for various atmosphere conditions depending on flight speed, altitudes and temperature. The present model is compared with loss modeling windmilling estimation methods described in literature which requires large amount of inputs as blade angle, blade pitch and component efficiencies. The comparison with the available windmilling model at literature shows that both models capture the terminal speed estimation very well. However, the model in literature is not able to capture the transient engine speed, which is important for missile applications as the missile can be fired before the engine reaches to terminal speed. The difference between the test data and the available model during transients is up to 50%. The present model matches perfectly with test data even at transients. It is more practical and much simpler than the available windmilling model in the literature to estimate the both transient and terminal windmilling speed of the turbojet engines. The agreement between the present model, KTJ 3200 test data, windmilling method available in the literature and test data of Microturbo TRI 60 is very good for most of the ranges investigated.

A New Approach to Modeling Slip and Work Input for Centrifugal Compressors

A new method of modeling slip factor and work input for centrifugal compressor impellers is presented. Rather than using geometry to predict the behavior of the flow at the impeller exit, the new method leverages governing relationships to predict the work input delivered by the impeller with dimensionless design parameters. The approach incorporates both impeller geometry and flow conditions and, therefore, is inherently able to predict the slip factor both at design and off-design conditions. Five impeller cases are used to demonstrate the efficacy of the method, four of which are well documented in the open literature. Multiple implementations of the model are introduced to enable users to customize the model to specific applications. Significant improvement in the accuracy of the prediction of slip factor and work input is obtained at both design and off-design conditions relative to Wiesner's slip model. While Wiesner's model predicts the slip factor of 52% of the data within ±0.05 absolute error, the most accurate implementation of the new model predicts 99% of the data within the same error band. The effects of external losses on the model are considered, and the new model is fairly insensitive to the effects of external losses. Finally, detailed procedures to incorporate the new model into a meanline analysis tool are provided in the appendices.

A New Approach to Modeling Slip and Work Input for Centrifugal Compressors

A new method of modeling slip factor and work input for centrifugal compressor impellers is presented. Rather than using geometry to predict the behavior of the flow at the impeller exit, the new method leverages governing relationships to predict the work input delivered by the impeller with dimensionless design parameters. The approach incorporates both impeller geometry and flow conditions and, therefore, is inherently able to predict the slip factor both at design and off-design conditions. Five impeller cases are used to demonstrate the efficacy of the method, four of which are well documented in the open literature. Multiple implementations of the model are introduced to enable users to customize the model to specific applications. Significant improvement in the accuracy of the prediction of slip factor and work input is obtained at both design and off-design conditions relative to Wiesner’s slip model. While Wiesner’s model predicts the slip factor of 52% of the data within ±0.05 absolute error, the most accurate implementation of the new model predicts 99% of the data within the same error band. The effects of external losses on the model are considered, and the new model is fairly insensitive to the effects of external losses. Finally, detailed procedures to incorporate the new model into a meanline analysis tool are provided in the appendices.

Heat Transfer Characteristics of High Heat Generating Integrated Circuit Chips Cooled Using Liquid Cold Plate—A Combined Numerical and Experimental Study

This paper deals with the experimental and numerical investigations of seven integrated circuit (IC) chips cooled using the water flowing inside the cold plate at different flowrates. The study includes the supply of three different heat input cases under four different flowrates (0.063 kg/s, 0.125 kg/s, 0.25 kg/s, and 0.5 kg/s) to cool the high heat-generating IC chips mounted on the SMPS board at various positions. The optimal configuration (71-11-74-76-65-24-15) for the arrangement of the 7 IC chips is considered for the analysis. The numerical simulations are carried out using the commercial software ansys fluent (R-16) to support the experiments. Both the results (IC chips temperature) agree with each other in the error band of 8–14%. The smallest chip U6 attains the maximum temperature, as its heat attenuation rate is very high. The water flowing inside the cold plate absorbs the heat from the IC chips; by increasing the flowrate (Reynolds number increases), there is an increase in the convective heat transfer coefficient of the chips (Nusselt number increases) and ultimately cools these faster. A correlation is proposed for the Nusselt number of the chips with the Reynolds number of the flow. The results suggest that the liquid cold plate plays a vital role in the cooling of the IC chips and leads to better thermal management.

Accurate Motion Control of a Pneumatic Linear Peristaltic Actuator

Pneumatic linear peristaltic actuators can offer some potential advantages when compared with conventional ones. The low cost, virtually unlimited stroke and easy implementation of curved motion profiles are among those benefits. On the downside, these actuators suffer high mechanical stress that can lead to short service life and increased leakage among chambers during the actuator lifetime. One way to cope with this problem is to impose the force—instead of the displacement—between rollers, as this has been shown to improve the endurance of the hose while reducing leakage during the actuator lifetime. This paper presents closed control loop results using such a setup. Previous studies with linear peristaltic actuators have revealed that, although it is possible to reach zero steady state error to constant references with closed loop control, the dynamic response obtained is very slow. This paper is mainly focused on this topic, namely on the development of several control laws to improve the dynamic performance of the system while avoiding limit cycles. The new developed control law leads to an average time of 1.67 s to reach a 0.1 mm error band in an experiment consisting of a series of 16 steps ranging from 0.02 to 0.32 m in amplitude.

Effects of Material on the Heat Transfer of R410A During Condensation and Evaporation

An Experimental investigation was conducted to demonstrate the effect of material on the heat transfer characteristics of R410A during evaporation inside two horizontal plain tubes with the same inner diameter of 6mm, and they are made of aluminum and stainless, respectively. The variation of vapor quality for test section were kept at 0.2–0.9, and mass velocities varied from 100 kg m−2s−1 to 400 kg m−2s−1. A series of single-phase and repetitive experiments was conducted to verify the accuracy and reliability of the test rig firstly. Various flow patterns including stratified, slug, and annular flow even dry-out may exist during the flow boiling experiments, while both ΔT-dependent and ΔT-independent flow are included for the test conditions of condensation. The results for evaporation have shown that the plain aluminum tube performs the best for all tested mass velocities. Several different correlations were employed to predict the present data and their predictive ability were compared. The results indicate that the Liu and Winterton can predict all the data points in an acceptable error band, and the slightly worse thermal performance of the stainless-steel tube may be attributed to the relatively low thermal conductivity. For condensation, little difference was found between two tested tubes, which means that the material and roughness may have little effect on the heat transfer performance during condensation.

Development and application of Pandemic Projection Measures (PPM) for forecasting the COVID-19 outbreak

This study aims to provide an accessible and dynamic estimate method to project the Covid-19 trend and hopefully it will help inform policymakers to allocate the needed medical equipment and supplies for saving more lives. A set of newly developed Pandemic Projection Measures (PPM) had been successfully applied to project daily new cases across countries. During the development, numerous trial and error iterations had been performed and then improved with live data. The procedures and computations for the PPM including Uphill Index (UHI), Downhill Indices (DHI), and Error Band Projection (EBP) estimates were explained and discussed along with graphical projections. The PPM was computed with daily live data for the USA, four U.S. states (Illinois, Massachusetts, New Jersey, and New York), France, Italy, Spain, Germany, and China. The results indicated that with the PPM estimations, the daily projections for the future trend were robust to reflect the most plausibility, since the PPM can be updated frequently. With the most up-to-date predictions, governments should be able to monitor the values of UHI and DHI for making a better decision for “flattening the curve”. Based on the empirical data, policymakers should pay more attentions for the following two scenarios: a) When expecting an apex of the outbreak, the UHI is higher than 1.20; and b) After passing a peak day, the DHI is still larger than 0.925. The applications of the PPM estimates are not designed for a one-time projection rather than updated frequently to improve the prediction precisions. With the same concepts from the PPM computations, the peak day and the number of new deaths could be predictable if more data are collected. Like many country leaders saying, “We will win the battle of coronavirus pandemic”, the author hopes to use this easily applicable estimate method to save more lives and to win. The results, currently presented with the data on April 16 and 17, 2020, were only used to explain how to apply the PPM estimates for predictions. The outdated results should not be used to compared with today’s outbreak trend.