Design of an energy saving oil cooler system using hot gas

According to the development of machine tools to higher speed and multi axes, thermal error which is known to account for about 70% of the total error of machine tools is becoming a serious issue. To reduce thermal error, the heat generating parts of machine tools are cooled down by direct contact with a cooling medium. The medium in most cases is oil, thus, the cooling device is called oil cooler. In this study, an oil cooler system employing hot gas bypass method was developed to improve the performance including energy efficiency of the oil coolers used for ultra-precision machine tools. Through tests, the developed system exhibited high temperature control accuracy of ±0.1°C, and less energy consumption than conventional on/off type (equipped with heater for preventing excessive cooling) by about 45%. The proposed oil cooler system is applicable to semiconductor process, ultra-precision injection molds, as well as ultra-precision machine tools to improve product quality and energy efficiency of production facilities.     

电子设备热设计中高效导热垫的选型方法

文中针对电子设备热设计中高效导热垫选型缺乏理论计算的现状,提出了基于导热垫厚度和导热系数计算的导热垫选型方法。该方法以热源与散热板的间隙尺寸链为基础,通过尺寸链公差和导热垫压缩量的关系,推导出导热垫厚度计算方法;通过自然对流散热理论,计算散热板的温度,再以单层平壁导热理论给出的导热系数与温差公式为基础,提出导热系数的计算方法,进而确定导热垫的型号。最后用实例详细介绍了电子设备热设计中导热垫的选型方法,并通过仿真验证了该方法的合理性。     

Effects of gas flow on particulate deposition in EGR coolers

This paper presents the test approach to investigate the effects of gas flow rate on particulate deposition inside the exhaust gas recirculation (EGR) coolers. The tests were carried out on a diesel engine equipped with the EGR cooler that a given total gas flow rate passed through and that contained pluggable exchanger tubes to adjust the flow rate in the tubes. Test results show that under the given coolant temperature and EGR gas temperature, the lower flow rate in the exchanger tube is and the longer tubes are, the more particulate with D_p > 50 nm deposit in the cooler. With the given total gas flow rate passing through the cooler, the lower flow rate in the exchanger tube is and the longer tubes are, the larger deposit mass is inside the cooler. In the cases of longer tubes, the effects of gas flow rate on the deposit mass are depends on the effects of gas velocity on the particulate deposition, rather than the effects of flow rate on the particulate number passing through the heat exchanger tube per minute.

     

A non-destructive method to assess condition of gas turbine blades,based on the analysis of blade-surface images

There is a non-destructive method to assess condition of gas turbine blades in the article presented. The method is based on the processing of blade-surface images in visible band of the electromagnetic wave. Presented are also the results of research into the influence of high-temperature loads on blades of a gas turbine. The relations are shown between the temperature of heat treatment of the blades and a change in colour of blade surfaces as well as changes in the microstructure of the blade material. These relations are suitable for the assessment of changes in the microstructure, which result from the supercritical temperature of the working medium affecting the blade. The method can prove useful for the in-service assessment of the blade material’s overheating level.     

A method to calculate the reliability of the gas pipeline segment under axial compression

An algorithm is presented for probabilistic calculation of the gas pipeline strength reliability for the case when the ultimate strength of the pipe steel, compressing force, gas pressure, Young’s modulus, temperature drop, pipe thickness, and diameter are distributed normally.     

A new method to evaluate the influence coefficient matrix for gas path analysis

To create an online diagnostic system for a gas turbine, a well-formulated-influence coefficient matrix (ICM), a key component in a widely used existing theory, is essential. However, according to a recent research of the present authors, parameter deviations estimated by the traditional ICM contain unavoidable errors. These errors, called matching deviations, have been verified to be a consequence of the shifting operating point caused by component deterioration. Here we present a simple and accurate method which is still based on the widely accepted existing theory that accounts for component deterioration. Matching coefficients are introduced in this method to isolate and eliminate matching deviations. The ICM yielded by this method can improve the accuracy of both measurement prediction and parameter deviation estimations. By modeling a commercial power generation engine, a demonstration of the new method is presented and its limitation is discussed. This paper was recommended for publication in revised form by Associate Editor Tpmg Seop Kim Di Xia received a B.S. degree in Mechanical Engineering from Tongji University and is currently a Ph.D. candidator at the School of Mechanical Engineering at Jiaotong University in Shanghai, China. Dr. Xia’s research interests are in the area of gas turbine and gas path analysis.     

Turbulent heat transfer of supercritical carbon dioxide in square cross-sectional duct flow

Numerical simulations are performed to develop a new heat transfer coefficient correlation applicable to the gas cooler design of a trans-critical carbon dioxide air-conditioner. Thermodynamic and transport properties of the supercritical gas cooling process change dramatically and significantly vary heat transfer coefficients to be much different from those of single or two phase flows. In the present study, the elliptic blending second moment turbulent closure precisely reflecting the effects of these thermo-physical property variations on the turbulent heat transfer is employed to model the Reynolds stresses and turbulent heat fluxes in the momentum and energy equations. Computational results related to the development of turbulent heat transfer during in-duct cooling of supercritical carbon dioxide were used to establish a new heat transfer coefficient correlation that would be widely applicable to a gas cooler design involving turbulent heat transfer of supercritical carbon dioxide in square cross-sectional duct flows. This paper was recommended for publication in revised form by Associate Editor Kyung-Soo Yang Seong Ho, Han received a B.S. degree in Mechanical Engineering from Kookmin University in 2003. He then went on to receive his M.S. degree from Korea University in 2005. He is currently in a Ph. D. course at Mechanical Engineering at Korea University in Seoul, Korea. His research interests are in the area of hydrogen energy, polymer electrolyte membrane fuel cell.     

Thermoelastohydrodynamic Analysis of Spur Gears with Consideration of Surface Roughness

Thermoelastohydrodynamic lubrication (TEHL) analysis for spur gears with consideration of surface roughness is presented. The model is based on Johnson’s load sharing concept where a portion of load is carried by fluid film and the rest by asperities. The solution algorithm consists of two parts. In the first part, the scaling factors and film thickness with consideration of thermal effect are determined. Then, simplified energy equation is solved to predict the surfaces and film temperature. Once the film temperature is known, the viscosity of the lubricant and therefore friction coefficient are calculated. The predicted results for the friction coefficient based on this algorithm are in agreement with published experimental data as well as those of EHL simulations for rough line contact. First point of contact is the point where the asperities carry a large portion of load and the lubricant has the highest temperature and the lowest thickness. Also, according to experimental investigations, the largest amount of wear in spur gears happens in the first point of contact. Effect of speed on film temperature and friction coefficient has been studied. As speed increases, more heat is generated and therefore film temperature will rise. Film temperature rise will result in reduction of lubricant viscosity and consequently decrease in friction coefficient. Surface roughness effect on friction coefficient is also studied. An increase in surface roughness will increase the asperities interaction and therefore friction coefficient will rise.     

The theoretical study of the measuring thermal diffusivity of semi-infinite solid using the photothermal displacement

A method of measuring the thermal diffusivity of semi-infinite solid material at room temperature using photothermal displacement is proposed. In previous works, within the constant thickness of material, the thermal diffusivity was determined by the magnitude and phase of deformation gradient as the relative position between the pump and probe beams. In this study, however, a complete theoretical treatment of the photothermal displacement technique has been performed for thermal diffusivity measurement in semi-infinite solid materials. The influence of parameters, such as, radius and modulation frequency of the pump beam and the thermal diffusivity, was studied. We propose a simple analysis method based on the zero-crossing position of real part of deformation gradient and the minimum position of phase as the relative position between two beams. It is independent of parameters such as power of pump beam, absorption coefficient, reflectivity, Poisson’s ratio, and thermal expansion coefficient.     

Conjugate heat transfer study on a ventilated disc of high-speed trains during braking

The heat dissipation of a ventilated disc on high-speed trains during emergency braking is studied to improve heat dissipation performance. The conjugate heat transfer method is employed to understand the distribution and variation of convective heat transfer coefficients on the disc surfaces during braking. Finite element models of the ventilated disc and the complicated air flow field under the train are built. Boundary conditions are derived based on real working conditions. Heat transfer simulation is carried out using the FLUENT computer code. Simulation results, including temperature rise of the disc, convective heat transfer coefficient distribution, and heat transfer rate, are presented and analyzed. Using materials with high thermal conductivity coefficients and reducing the heat transfer wall thickness of the disc are proposed to improve the heat dissipation performance of the disc based on the simulation results. Both methods are effective in improving the heat transfer rate of the disc with a 10% improvement in the improved thermal conductivity case and a 30% improvement in the reduced wall thickness case.     

A setup for measuring the temperature dependence of the refractive indices of solids

A setup for measuring the temperature dependences of refractive indices n(T) of semiconductors and dielectrics in the temperature range 300–700 K at the wavelengths of a He—Ne laser λ=0.63, 1.15, and 3.39 μm is described. Samples in the form of plane—parallel plates serve as Fabry—Perot etalons the optical thickness of which depends on the temperature. Upon heating and subsequent cooling of a sample, interference oscillations of the refiected-light intensity are recorded and used to determine the dependence n(T). The values of the refractive index at room temperature and the thermal expansion coefficient used in calculations are taken from the literature. Comparing the interferograms obtained for a heated and cooled sample allows evaluation of the temperature difference between the sample’s probed area and a measuring thermocouple. The relative error in determining thermooptical coefficient dn/dT in the range 300–700 K is within 1%.     

Optimization of conformal cooling channels with array of baffles for plastic injection mold

Cooling system has an important role in the injection molding process in terms of not only productivity and quality, but also mold-making cost. In this paper, a conformal cooling channel with an array of baffles is proposed for obtaining uniform cooling over the entire free-form surface of molded parts. A new algorithm for calculating temperature distribution through molding thickness, mold surface temperature and cooling time was presented. The relation among cooling channels’ configuration, process parameters, mold material, molding thickness and temperature distribution in the mold for a given polymer is expressed by a system of approximate equations. This relation was established by the design of experiment and response surface methodology based on an adequate physical-mathematical model, finite difference method and numerical simulation. By applying this approximate mathematical relation, the optimization process for obtaining target mold temperature, uniform temperature distribution and minimizing the cooling time becomes more effective. Two case studies were carried out to test and validate the proposed method. The results show that present approach improves the cooling performance and facilitates the mold design process in comparison to the trial-and-error simulation-based method.     

A New Approach to the Calculation of Flash Temperatures in Dry, Sliding Contacts

The work done in overcoming frictional resistance between sliding surfaces is transformed into heat at the separate, very small and very highly loaded asperity contacts that make up the real area of contact. The temperatures at these initial asperity contacts (the ‘flash temperatures’) are usually much higher than the bulk temperatures and, although of very short duration, can cause potentially major local changes at the surfaces, such as softening, chemical transformations, and local melting. A new approach to calculating these flash temperatures is presented, which relies on the solution, by finite-element analysis, of the three-dimensional equation for transient heat flow in an hemispherical asperity. A Design of Experiments (DoE) exercise showed that the major influential factors on flash temperature were the thermal conductivity, the product of friction coefficient and hardness, the velocity of sliding, and the radius and degree of wear/flattening of the hemisphere. The DoE analysis also produced predictions for the flash temperature, which agreed extremely well with the FE calculations. Response surfaces of flash temperatures are presented, which facilitate the determination of flash temperatures without resorting to FE analysis.     

Microstructural model of ceramic cutting plate

A microstructural model of a ceramic cutting plate is developed. It permits the derivation of a calculation scheme for a mathematical model that includes the density, the elastic modulus, the thermal conductivity, the specific heat, the linear expansion coefficient, and Poisson’s ratio.     

Influence of tube wall longitudinal heat conduction on temperature measurement of cryogenic gas with low mass flow rates

Longitudinal heat conduction is an important parameter in the cryogenic field, especially in cryogenic heat exchangers. In the present study, the parasitic effect of tube wall longitudinal heat conduction on temperature measurement within the tube has been studied for cryogenic gas with low mass flow rates by finite element method and experimental tests. The effects of various parameters such as tube outlet temperature, tube wall thermal conductivity, mass flow rate, and tube wall thickness have been investigated. Axial positioning errors of temperature sensor due to tube wall longitudinal heat conduction were higher for lower gas flow rates. The results showed that the tube wall thermal conductivity leads to axial heat conduction within the tube wall, but the higher tube wall thermal conductivity does not lead to bigger axial positioning error of temperature sensor at tube outlet. According to data obtained from simulations and experiments, sensor with distance of 5 mm from tube outlet had 14.92% and 8.51% temperature measurement error (with respect to gas flow temperature at tube outlet) for tube wall thermal conductivities of 16 and 400 W m⁻¹ K⁻¹, respectively.     

Design of U-shape milled groove conformal cooling channels for plastic injection mold

Besides the solid free-form fabrication technology, milling operation is an alternative applicable method to make complex cooling channels conform to the surface of the mold cavity. This paper presents the U-shape milled groove conformal cooling channels and proposes the design optimization process in order to obtain an optimal cooling channels’ configuration and target mold temperature. The relation between the cycle averaged thermal behavior of the mold cavity and the two-dimensional configuration of cooling channels was first investigated thoroughly by an analytical method. Design of experiment and 2D simulation were done to obtain the mold wall temperature and to check the feasibility of the analytical method. The optimization process of the free-form conformal cooling channels is based on the combination of both analytical method and 3D CAE simulation. The analytical step relies on explicit mathematic formulas, so it can approach the neighboring optimal solution quickly. Subsequently, the three-dimensional heat transfer simulation is applied to fine-tune the optimization results. A case study for a plastic car fender was investigated to verify the feasibility of the proposed method. The results show that conformal cooling channel gives a uniform cooling, reducing the cooling time and increasing the molded part’s quality with less effort of plastic designers and high computational efficiency.     

双金属复合滑动轴承的衬层厚度与温升的关系

根据Fourier定律导出了双金属轴承工作过程的温升计算模型和衬层厚度设计公式。温升是载荷功率和摩擦系数的线性增函数,其比例系数反映了双金属轴承结构和材料热特性对轴承温升的综合影响作用,它是衬层导热系数λ1的非线性减函数,是衬层厚度δ1的双面函数:当λ1>λ2时为非线性减函数;当λ1<λ2时为非线性增函数。衬层厚度存在临界值,当λ1>λ2时衬层厚度越大越好,但是当λ1<λ2时衬层厚度越小越好。     

An automated measurement setup for studying the dependences of the thermal conductivity and rheological characteristics of non-Newtonian fluids on the shear rate

An experimental setup designed for studying the rheological characteristics and thermal conductivity of liquid materials is described. The presented measurement and experimental-data-processing technique allows determination of the thermal conductivity of liquids as a function of the shear rate with allowance for the heat released in the studied material layer due to dissipation of the mechanical energy during a shearing motion and helps to find the consistence factor and the flow index for liquids that obey the power rheological law. The results of experiments on the determination of the thermal conductivity as a function of the shear rate of a 10% aqueous solution of polyoxyethylene and synthetic caoutchouc doped with nanostructural elements (carbon nanotubes and nanofibers) at different temperatures are presented. The thermal-conductivity measurement error is ≤10%, while the measurement errors for the consistence factor and the flow index are <7%.     

A thermal porosimetry method to estimate pore size distribution in highly porous insulating materials

Standard pore size determination methods such as mercury porosimetry, nitrogen sorption, microscopy, or x-ray tomography are not always applicable to highly porous, low density, and thus very fragile materials. For this kind of materials, a method based on thermal characterization is proposed. Indeed, the thermal conductivity of a highly porous and insulating medium is significantly dependent on the thermal conductivity of the interstitial gas that depends on both gas pressure and size of the considered pore (Knudsen effect). It is also possible to link the pore size with the thermal conductivity of the medium. Thermal conductivity measurements are realized on specimens placed in an enclosure where the air pressure is successively set to different values varying from 10(-1) to 10(5) Pa. Knowing the global porosity ratio, an effective thermal conductivity model for a two-phase air-solid material based on a combined serial-parallel model is established. Pore size distribution can be identified by minimizing the sum of the quadratic differences between measured values and modeled ones. The results of the estimation process are the volume fractions of the chosen ranges of pore size. In order to validate the method, measurements done on insulating materials are presented. The results are discussed and show that pore size distribution estimated by the proposed method is coherent.     

Method of calculating the reliability of a gas pipeline segment under transverse-longitudinal bending

A mathematical model for estimating the reliability of an underground gas pipeline segment, which is described as a flexible rod element subjected to axial compression and transversal bending, is developed. The mathematical expectation of the pipeline’s wall thickness according to the required reliability, when the initial parameters are distributed according to the Gaussian law, is found. The results of the investigation are intended for design bureaus and enterprises for long-distance gas transfer.