Influence of compression-expansion effect on oscillating-flow heat transfer in a finned heat exchanger

Compression and expansion of a working gas due to the pressure oscillation of an oscillating flow can lead to a temperature variation of the working gas, which will affect the heat transfer in the oscillating flow. This study focuses on the impact of the compression-expansion effect, indicated by the pressure ratio, on the heat transfer in a finned heat exchanger under practical operating conditions of the ambient-temperature heat exchangers in Stirling-type pulse tube refrigerators. The experimental results summarized as the Nusselt number are presented for analysis. An increase in the pressure ratio can result in a marked rise in the Nusselt number, which indicates that the compression-expansion effect should be considered in characterizing the heat transfer of the oscillating flow, especially in the cases with a higher Valensi number and a lower maximum Reynolds number.     

Optimization of cross angle based on the pumping dynamics model

The single cylinder and multi-cylinder pumping dynamics model of a swash plate piston pump were improved.Particular attention has been paid to the design influences of key parts of the valve plate such as relief groove,pre-compression/ expansion and fluid inertia effect of the unsteady flow.Some important parameters,such as the discharge area,discharge coefficient,fluid bulk modulus,were especially analyzed using numerical methods or by experiment-based estimation.Consequently,the mathematical results of pressure pulsation and flow ripple agree well with experimental results from the test-rig of the flow ripple.Therefore,the cross angle and the pre-compression angle of the valve plate was optimized,based on the pumping dynamics model.Considering both the flow ripple and the cylinder pressure of the pump,the cross angle is set to be 2.2° to 2.7° with a pre-compression angle of 1.7° to 2.2°,so the pumping dynamics character can obtain the best result.     

地方性传媒面临的挑战与突围

随着传媒技术的迅猛发展,媒体间的竞争日趋激烈.地方性媒体受各路强势媒体挤占发展空间,面临生存的窘境.传媒结构的不合理,全球化、数字化、商业化的影响和体制机制的制约,使得地方性传媒更加难以从技术革新和市场化产业运作等方面获得应有的活力.因此,以创新为首要途径,搭建地方媒体的文化骨架,突出地方特色,强化媒体服务,提升经营管理水平,已经成为地方媒体分割市场、适应生存、谋求发展的必然选择     

液压传动压力损失分析与研究

在汽车等各种机械加工设备中广泛使用液压传动,而液压在动力传动中都要产生压力损失。本文就液体在油管内流动时的压力损失计算方法进行了分析和研究,提出了正确计算公式,以免在液压传动系统设计与计算时产生错误。     

基于CAN总线的压装机控制器通信系统的设计

介绍了压装机的功能和特点,给出了一种基于双单片机的压装机智能控制器的设计方案,重点介绍了基于CAN总线的通信模块的硬件、软件设计,实践证明该设计切实可行.     

缓解考生高考压力的对策与建议

高考在为国家选拔人才,提供公平竞争的平台等方面发挥了积极功能,但它同时也带来了一定的负面影响：高考给考生、家长、教师和学校带来了巨大压力。以缓解考生压力这一心理问题立论,从四个方面分析了形成高考压力的深层原因及其所带来的消极影响,并提出相关的对策与建议。     

学习辅导类报刊的分版思考

学习辅导类报刊有着天然的分版土壤和市场驱动.分版的实质是产品细化.分版的目的是创造新的市场机会,提供更加个性化的优质服务.分版是一把双刃剑,在实践探索中,决策层务必要有理性,既要充分认识其优势,又要清醒认识其风险,尤其是要做好市场调研,把握好分版的时机.     

EAP研究述评

员工援助计划是近年来研究的热点之一,许多发达国家已经形成比较完整的体系并在实际应用中取得了预期的效果。对于处于社会主义初级阶段的中国的大多数企业来说,员工援助计划还是一个比较陌生的概念。关注员工,了解员工援助计划是企业和个人必然选择。     

大型高压釜设备安装技术

高压釜设备属于体积和重量都超大的整体设备,常规的施工方法和通用的起重机械无法进行安装。本文详细叙述了巴布亚新几内亚瑞木镍钴冶炼工程项目大型高压釜设备安装施工技术,可推广在矿山、冶金、化工和电力等领域用于超大型设备安装。     

Pressure observer based adaptive robust trajectory tracking control of a parallel manipulator driven by pneumatic muscles

This paper presents a pressure observer based adaptive robust controller (POARC) for posture trajectory tracking of a parallel manipulator driven by three pneumatic muscles without pressure sensors. Due to model errors of the static forces and friction forces of pneumatic muscles, simplified average flow rate characteristics of valves, unknown disturbances of entire system, and unmeasured pressures, there exist rather severe parametric uncertainties, nonlinear uncertainties and dynamic uncertainties in modeling of the parallel manipulator. A nonlinear pressure observer is constructed to estimate unknown pressures on the basis of a single-input-single-output (SISO) decoupling model that is simplified from the actual multiple-input-multiple-output (MIMO) coupling model of the parallel manipulator. Then, an adaptive robust controller integrated with the pressure observer is developed to accomplish high precision posture trajectory tracking of the parallel manipulator. The experimental results indicate that the system with the proposed POARC not only achieves good control accuracy and smooth movement but also maintains robustness to disturbances.