A study on the characteristivs of heat transfer in an engine piston

The piston temperature distribution with varying engine torque and speeds for a real engine operation has been determined by a numerical model. The model is developed by the finite element conduction method combined with engine simulation. In this model, the two boundary temperature concept instead of one constant boundary temperature was presented to approximate the ambient temperatures along the piston skirt. The two temperatures were first estimated, then adjusted by the iterated proces, for predicting piston temperatures, according to the energy balance of the whole engine energy system. In order to verify the predicted values, input data for cycle simulation were obtained, the piston temperatures were also measured. In this way the good agreement between the model and experimental results could be checked.     

Non-absorbable gas effects on heat and mass transfer in falling film absorption

Film absorption involves simultaneous heat and mass transfer in the gas-liquid system. While the non-absorbable gas does not participate directly in the absorption process, its presence does affect the overall heat and mass transfer. An experimental study was performed to investigate the heat and mass transfer characteristics of LiBr-H₂O solution flowing over 6-row horizontal tubes with the water vapor absorption in the presence of non-absorbable gases. The volumetric concentration of non-absorbable gas. air, was varied from 0.17 to 10.0%. The combined effects of the solution flow rate and its concentration on the heat and mass transfer coefficients were also examined. The presence of 2% volumetric concentration of air resulted in a 25% reduction in the Nusselt number and 41% reduction in the Sherwood number. Optimum film Reynolds number was found to exist at which the heat and mass transfer reach their maximum value independent of air contents. Reduced Nusselt and Sherwood numbers, defined as the ratio of Nusselt and Sherwood numbers at given non-absorbable gas content to that with pure water vapor, were correlated to account for the reduction in the heat and mass transfer due to non-absorbable gases in a falling film absorption process.     

洁净压缩空气系统

对洁净压缩空气系统的主要组成部件进行了介绍，对低露点系统有关气动元件的组合特点作了说明，对低发尘系统气动元件的匹配技术作了阐述。并在此基础上介绍了能稳定的供给低露点和低发尘的洁净压缩空气的气动系统。     

A study on correlation between pressure variations and augmentation of heat transfer in acoustic fields

The present paper investigated the correlation between the acoustic pressure variations and the augmentation of heat transfer in the ultrasonic induced acoustic fields. The augmentation ratios of heat transfer coefficient were experimentally measured and were compared with the profile of the pressure distribution in the acoustic fields predicted by numerical analysis. For numerical analysis, a coupled finite element-boundary element method (coupled FE-BEM) was applied. The results of the present study reveal that the acoustic pressure is higher near two ultrasonic transducers than other points where no ultrasonic transducer was installed. The augmentation trend of heat transfer is similar with the profile of the acoustic pressure distribution. In other words, as the acoustic pressure increases, the higher augmentation ratio of heat transfer is obtained. Numerical and experimental studies clearly show that the acoustic pressure variations are closely related to the augmentation of heat transfer in the acoustic fields.     

The study on pressure oscillation and heat transfer characteristics of oscillating capillary tube heat pipe

In the present study, the characteristics of pressure oscillation and heat transfer performance in an oscillating capillary tube heat pipe were experimentally investigated with respect to the heat flux, the charging ratio of working fluid, and the inclination angle to the horizontal orientation. The experimental results showed that the frequency of pressure oscillation was between 0.1 Hz and 1.5 Hz at the charging ratio of 40 vol.%. The saturation pressure of working fluid in the oscillating capillary tube heat pipe increased as the heat flux was increased. Also, as the charging ratio of working fluid was increased, the amplitude of pressure oscillation increased. When the pressure waves were symmetric sinusoidal waves at the charging ratios of 40 vol.% and 60 vol.%, the heat transfer performance was improved. At the charging ratios of 20 vol.% and 80 vol.%, the waveforms of pressure oscillation were more complicated, and the heat transfer performance reduced. At the charging ratio of 40 vol.%, the heat transfer performance of the OCHP was at the best when the inclination angle was 90°. the pressure wave was a sinusoidal waveform, the pressure difference was at the least, the oscillation amplitude was at the least, and the frequency of pressure oscillation was the highest.     

A study on the heat transfer characteristics of a self-oscillating heat pipe

In this paper, the heat transfer characteristics of a self-oscillating heat pipe are experimentally investigated for the effect of various working fluid fill charge ratios and heat loads. The characteristics of temperature oscillations of the working fluid are also analysed based on chaotic dynamics. The heat pipe is composed of a heating section, a cooling section and an adiabatic section, and has a 0.002m internal diameter, a 0.34m length in each turn and consists of 19 turns. The heating and the cooling portion of each turn has a length of 70mm. A series of experiments was carried out to measure the temperature distributions and the pressure variations of the heat pipe. Furthermore, heat transfer performance, effective thermal conductivity, boiling heat transfer and condensation heat transfer coefficients are calculated for various operating conditions. Experimental results show the efficacy of this type of heat pipe.     

A naphthalene sublimation study on heat/mass transfer for flow over a flat plate

It is important to completely understand heat/mass transfer from a flat plate because it is a basic element of heat/mass transfer. In the present study, local heat/mass transfer coefficient is obtained for two flow conditions to investigate the effect of boundary layer using the naphthalene sublimation technique. Obtained local heat/mass transfer coefficient is converted to dimensionless parameters such as Sherwood number, Stanton number and Colburnj-factor. These also are compared with correlations of laminar and turbulent heat/mass transfer from a flat plate. According to experimental results, local Sherwood number and local Stanton number are in much better agreement with the correlation of turbulent region rather than laminar region, which means analogy between heat/mass transfer and momentum transfer is more suitable for turbulent boundary layer. But average Sherwood number and average Colburnj-factor representing analogy between heat/mass transfer and momentum transfer are consistent with the correlation of laminar boundary layer as well as turbulent boundary layer.     

A study on the pressure loss,heat transfer enhancement and fouling control in a vertical particulate flow

In this study, the pressure loss, the heat transfer rate and the fouling characteristics of a particulate flow were investigated. Particles used were the glass beads of 3.0 mm diameter with 2.54 specific gravity. The particles augmented the heat transfer at the flow velocities lower than 1.0 m/s. In this range, the heat transfer coefficient slighly increased as the particle volume fraction increased, and was almost independent of the flow velocity. The particles also increased the pressure loss at the flow velocities lower than 1.0 m/s. Above 1.0 m/s, however, the heat transfer coefficient and the pressure loss were essentially the same as those of flow with pure water. Through the flow visualization study, the collision frequency on the wall by particles is shown to be closely related with the heat transfer enhancement. The particles effectively controlled fouling. Fouling tests using ferric oxide revealed that the particles effectively removed the pre-exsisting deposit as well as they prevented the deposit buildup.     

基于PLC的空冷器恒温控制系统的设计

针对当前空冷器运行中存在的温度不稳定、控制精度低、工作强度大、能源浪费严重等问题,该文设计了一种空冷器变频恒温控制系统。在该系统中,通过应用将模糊控制和PID控制相结合的方法实现对空冷器风机的变频调速,不仅可以提高控制精度,并能保证空冷器管束温度的稳定性;同时,该系统还运用MCGS组态软件建立上位机操作界面和通过建立PLC主从站实现对运行过程的实时监控和远程操作,从而达到空冷器管束温度控制系统的自动化和智能化。     

逆流冷凝塔热泵系统热质交换过程数值模拟研究

冷凝塔作为冷凝式热泵系统的重要组成部分,其热质交换过程对于降低能耗及热泵系统设计具有重要意义.以逆流冷凝塔热泵系统形式为基础,通过建立冷凝塔内热质交换过程的数学模型,推导出热质交换过程的通用计算方程组,并以贵阳地区的气象参数为参考,对不同工况下塔内热质交换情况进行模拟计算及具体分析.研究结果表明,不同入口空气参数对溶液...     

Numerical study on flow and heat transfer characteristics of air-jet cooling system

Journal of Mechanical Science and Technology - The present study aims to numerically analyze the cooling characteristics of the air-jet array in designing more efficient air-cooling system. Heat...     

A study on the behavior and heat transfer characteristics of impinging sprays

The spray/wall interaction is considered as an important phenomenon influencing air-fuel mixing in the internal combustion engines. In order to adequately represent the spray/wall interaction process, impingement regimes and post-impingement behavior have been modeled using experimental data and conservation constraints. The modeled regimes were stick, rebound, spread and splash. The tangential velocities of splashing droplets were obtained using a theoretical relationship. The continuous phase was modeled using the Eulerian conservation equations, and the dispersed phase was calculated using a discrete droplet model. The numerical simulations were compared to experimental results for spray impingement normal to the wall. The predictions for the secondary droplet velocities and droplet sizes were in good agreement with the experimental data.     

An experimental study on the flow and heat transfer characteristics of an impinging jet

The flow and heat transfer characteristics of an impinging jet is investigated in two major stages. The first stage is about the investigation of the three dimensional mean flow and the turbulent flow quantities in free jet, stagnation and wall jet region. After a complete documentation of the flow field, the convective heat transfer coefficient distributions on the impingement plate are presented, during the second stage of the study. Heat transfer experiments using the new hue-capturing technique result in high resolution wall heating rate distributions. The technique is fully automated using a true color image processing system. The present heat transfer results are discussed in detail in terms of the flow characteristics. The measurements from the new method are compared with conventional heat flux sensors located on the same model. These heat transfer distributions are also compared with other studies available from the literature. The new non-intrusive heat transfer method is highly effective in obtaining high resolution heat transfer maps with good accuracy.     

Numerical study of heat and mass transfer analogy for a simulated turbine endwall

Journal of Mechanical Science and Technology - In the present work, numerical investigation of heat and mass transfer analogy on a simulated turbine blade endwall is conducted. For similar...     

空气密度对高等级砝码量值传递工作的影响研究

高等级砝码在量值传递过程中,由于受到空气浮力的因素,对砝码的折算质量值造成影响,为了尽可能减少空气浮力对其的影响,需要对空气密度进行测量计算和修正,潮湿空气密度跟空气的压力、温度、湿度、空气中二氧化碳含量密切相关,精确测量潮湿空气中的温湿度、气压、二氧化碳含量是测定空气密度的基础,本文利用空气密度测量装置对实验室的空气密度进行连续测量,获得实验室条件下的空气密度变化情况,并从空气密度的变化情况定量分析研究高等级砝码质量值在传递过程中的影响值并加以修正,减少测量不确定度的影响,提高高等级砝码在量值传递过程的测量准确度。     

A study of signal noise reduction of the mass air flow sensor using the flow conditioner on the air induction system of heavy-duty truck

The mass air flow meter is a critical sensor that works based on thermal hot wire technology, used to determine the fuel to be injected into the cylinder and calculate the fuel-air ratio. In order to measure the airflow rate accurately, the flow should be uniform and smooth upstream of the sensor. The flow disturbance with a short straight length upstream of the flow meter results in the noise of the sensor signal. This noise causes unstable mass flow measurement on the system. Flow conditioners can be used to smooth the velocity profile of the flow. In this study, experimental and numerical methods were used to characterize the performance and operating accuracy of the mass flow meter used in heavy-duty truck applications. The flow conditioners were implemented to smooth the velocity profile around the mass flow meter that was disrupted by bends. The flow structures with and without flow conditioner were examined using Particle Image Velocimetry (PIV) to measure the time-averaged velocity. As well as the validated computational fluid dynamics (CFD) model provides data to understand the flow uniformity effect of the conditioner on the mass airflow (MAF) sensor. The optimization study was performed using a full factorial design of experiment (DOE) for flow conditioner design. A robust methodology was developed for the flow conditioner characteristics and mass airflow sensor implementation on the air induction system.     

An experimental study on the pressure drop and heat transfer through straight and curved small diameter tubes

A tube type heat exchanger is often the only solution when minimum pressure loss is a requirement. In addition, small diameter tubes are preferable because of an increased heat transfer area within an acceptable pressure loss limit. The present work reports on both an analytic model and experimental results with regards to the pressure drop and heat transfer characteristics of compact straight, C-curved, and U-curved tubes. The inner diameter of the tube (D) for our selected heat exchanger type was 1.26 mm with a thickness of 0.12 mm and a total length of 150.8 D. For the experiment, pressurized nitrogen gas bottles were used rather than an air compressor system in order to simplify the test facility. Hence the pressure conditions were easily set at 10, 30, and 50 bar corresponding to a range of Reynolds numbers from 10000 to 50000. To elevate the air temperature outside the tube (from 100°C to 400°C), an electric furnace was installed around the “test tube”. An analytic model to determine the pressure loss through curved tubes-referred to as the modified friction factor- is proposed. Good agreement was found between the modified friction factor and existing correlations, thus confirming the suitability of this model for determining pressure losses for different shape of tubes. The average measured Nusselt numbers were within 10- 15% of the Dittus-Boelter and Gnielinski correlations.     

An experimental study on the heat transfer and pressure drop characteristics of electronics cooling heat sinks with FC-72 flow boiling

Journal of Mechanical Science and Technology - An experimental study was performed to measure FC-72(C6F14) flow boiling heat transfer and pressure drop in heat sinks for electronics cooling. The...     

坐姿体压分布测量系统的研究

介绍了一套坐姿压力分布测量系统,该系统由硬件和软件两大部分组成,系统硬件包括压力传感器平板矩阵、信号切换电路、信号采集卡及计算机系统;系统软件主要由实时数据采集模块、数据存贮模块、数据计算分析和显示模块等组成。该系统能够对人体与座椅之间的压力分布进行测量,经计算机采集后的数据通过自行开发的软件处理直接以可视化方式显示结果。     

某天然气压缩机空冷器变频调速系统设计

针对某油田天然气压缩机空冷器电机不能调速造成的不利影响,以ACS510变频器为控制核心,设计了压缩机空冷器变频控制系统。文章重点阐述了系统结构和控制功能的实现方法。实践证明整个系统动态响应快,稳态精度高。节能效果明显。