低温多效海水淡化用蒸汽喷射器的优化设计

提高蒸汽喷射器性能,能够降低低温多效海水淡化系统能耗,采用理论推导和数值模拟相结合的方法对喷射器性能进行研究。在喷射器索科洛夫设计方法的基础上,修正了喷射器最大可达喷射系数的计算模型。利用改进的喷射器设计模型对某低温多效海水淡化用蒸汽喷射器进行优化设计,喷射系数达到1.35,优于原方法计算结果 0.96。并对喷射器几何模型进行CFD数值模拟验证,结果表明喷射器的可达喷射系数及结构尺寸处于最优值,验证了改进的喷射器设计模型的可靠性。     

蒸喷制冷机最大喷射系数的计算(摘要)

索科洛夫和津格尔提出了一套喷射器计算理论,计算方法是:根据设计工况,求出各种动力函数值,然后进行最大喷射系数的计算,再按最大喷射系数下的各动力函数值进行喷射器各部最佳尺寸的设计。这种方法虽然较准确,但计算繁杂,要想得到高精度的结果,手工计算是不现实的。笔者根据其计算理论,编制出计算喷射系数的程序,用电子计算机找出在规定工况下的最大喷射系数和各动力函数值。     

蒸汽压缩/喷射制冷系统喷射器设计及节能分析

蒸汽压缩/喷射制冷系统是一种有效的节能系统,可以减少节流膨胀损失,降低压缩机压力比,提高制冷系统效率。选择5种计算工况对蒸汽压缩/喷射制冷系统进行计算,研究喷射器结构与蒸发温度和冷凝温度的变化规律,并与普通蒸汽压缩系统对比,从制冷量、压缩机耗功、性能系数三个角度分析新系统的节能效果。计算结果表明蒸汽压缩/喷射制冷系统在低温工况条件下节能效果最优,制冷量最大可提高29%,压缩机耗功最大可降低65%,COP值最大可提高63%。     

带回热两级喷射制冷循环的特性分析

为了提高喷射制冷系统的性能系数,建立了双热源驱动的带回热两级喷射制冷循环的理论计算模型。以纯工质R236fa为研究对象,讨论回热对单工质两级喷射制冷系统性能的影响,并与传统单级喷射系统性能进行比较。最后利用?分析比较传统单级系统和新型两级喷射系统的?损情况。研究结果表明,在相同工况下,当系统采用单工质时,加回热的系统性能更优,系统的性能系数可以提高约15%~20%,相对于传统的单级系统可以提高50%以上,其?效率相对传统单级喷射系统更具明显优势。     

燃油喷射汽油机NOx排放的计算研究

根据扩大的Zeldovich理论建立了计算燃油喷射汽油机NOx排放量的双区模型．介绍了NOx排放量的计算方法．分析了点火提前角、过量空气系数、进气压力、进气温度和气缸壁温度等因素对NOx排放量的影响．研究结果表明．双区模型是一种简便而有效的模型．     

燃煤粉电站锅炉效率在线监测模型研究

针对目前我国燃煤粉电站锅炉不能实时监测锅炉效率的不足,根据能量守恒原理提出了燃煤粉电站锅炉效率在线监测模型.通过电站DAS系统对电站锅炉效率计算模型所需的数据进行数据采集,把采集到的相关数据输入到模型中进行计算就可以实现电站锅炉运行效率的在线监测.对某台220t/h燃煤粉电站锅炉的实际测试表明,该模型可以实现对电站锅炉运行效率进行在线监测,在此基础上可以优化电站锅炉的运行或者进行针对性的技术改造,进而达到提高锅炉运行效率的目的.     

基于数值仿真的气动喷射阀回流间隙的优化

气动喷射阀是微电子封装中不可或缺的封装设备,但现有气动喷射阀在喷射高黏胶液时仍不能完全满足工业界对胶滴一致性的需求,原因在于其喷射高黏胶液时常出现因喷射速度太小而导致的挂胶漏喷现象.要减小上述现象的发生概率,就必须提高现有气动喷射阀的高黏流体喷射能力.回流间隙作为气动喷射阀的关键尺寸,直接影响着喷射阀的喷射能力.为了通过优化回流间隙来提高喷射能力,首先建立气动喷射阀的胶液喷射数值仿真模型并通过实验验证其可靠性,同时基于不同回流间隙的仿真数据建立了相应的高斯拟合模型.然后利用拟合模型以胶滴滴落速度为优化目标对回流间隙进行优化,通过优化前后的喷射对比验证了优化结果的可靠性,最后获得气动喷射阀的最优回流间隙.     

结霜工况下热泵空调器性能的数值模拟

本文对热泵空调器在结霜工况下的运行性能进行了理论模拟,建立了热泵空调器制冷系统稳态分布参数模型和结霜过程的动态分布参数模型.在系统模型建立中把结霜过程视为准稳态过程.计算结果表明在霜刚开始形成时,有助于增大管壁和空气之间的换热系数,当霜层达到一定厚度时热泵的制热能力,性能系数等讯速下降.经与其他已发表的文献比较计算结果合理.     

蒸汽喷射器引射系数及引射混合过程的动量效率分析

蒸汽喷射器因其简单可靠、费用低廉,应用越来越广泛.本文基于热力学方法,设计出一套适用于蒸汽喷射器的理论计算模型,从理想及实际蒸汽喷射引射压缩过程对蒸汽喷射器进行详细的热力学解析,提出一套蒸汽喷射器的计算方法,对引射系数以及引射混合过程的动量效率进行着重分析.     

7075-T651铝合金喷丸工艺的仿真与试验研究

为探究喷丸工艺参数对材料残余应力分布的影响,以7075-T651铝合金材料为研究对象,基于铝合金材料特性和试验条件,利用ANSYS/LS-DYNA建立喷丸有限元模型,获得了不同喷射距离、喷射压力和弹丸直径下残余应力的分布情况。结果表明：增大喷射压力和弹丸直径可以显著提高最大残余压应力和残余压应力影响深度,且喷射距离应保持在适当的范围内,最后将应力计算值和实测值进行对比,最大偏差为(10.0±12.5) MPa,偏差率不超过6.9%。分析认为通过有限元模型能够准确地获得残余应力的分布情况,有助于开展喷丸工艺参数对残余应力分布规律的影响研究。     

并联涡旋式压缩机油气平衡系统模拟分析及结构优化

采用两相流Eulerian模型对并联涡旋式压缩机油气平衡系统进行CFD模拟分析,得出引起2台压缩机油位差的原因是吸气管到各台压缩机分管路压差的不平衡。为减小2台压缩机的油位差,在其中1台压缩机吸气口端设置限流环,并进行模拟分析及试验验证。结果表明,在压缩机吸气口端设置直径为23 mm的限流环可以使2台压缩机的油位差不大于2 mm,满足并联涡旋式压缩机安全运行要求。     

A lumped-parameter thermal model for scroll compressors including the solution for the temperature distribution along the scroll wraps

A lumped-parameter thermal model is presented to predict the temperature in different chambers and components inside scroll compressors with particular attention to gas superheating in the suction process. Thermal resistances between the components are based on global heat transfer conductances, whereas conduction heat transfer through the scroll wraps is solved via a one-dimensional finite volume method. The thermal model was coupled to a thermodynamic model of the compression cycle and then applied to simulate the compressor performance under different conditions of speed and pressure ratio. The model was able to correctly predict the compressor temperature for operating conditions within the range of those adopted for its calibration. The results showed a strong coupling between the compressor thermal profile and the temperatures of the motor and lubricating oil. It has also been found that heat conduction through the scroll wraps reduces slightly the discharge temperature.     

Grenzbereiche von Seitenkanalverdichtern im Vakuumbetrieb

The kinematic viscosity of the gas rapidely rises with decreasing suction pressure in the vacuum region, which leads to a decrease of the reynolds number of the flow in the side channel and to a laminar flow structure which may cause a modification of the side-channel-compressor behavior during the energy transfer. By the reduced density of the gas in the vacuum region of the side channel compressor the mass flow and the transfered specific enthalpy are decreased with constant volume flow. Through that, the specific growth of enthalpy during the compression and during the expansion of the mass flow in the breaker decreases. This leads to a decrease in the growth of the temperature during the compression at the same pressure ratio and the thermal load of the compressor is reduced. The polytropic change of state of the gas during the compression approaches an adiabatic change of state for decreasing suction pressure in the vacuum region. The polytropic change of state of the expansion flow in the breaker approaches the theoretical expected isothermal change of state for decreasing suction pressure, whereby side channel compressors are relieved of thermal load and higher pressure ratios are within reach. So the breaker of the side channel compressor, which causes in pressure operation mode high specific dissipation losses and leads to high polytropic exponents effects in the higher vacuum region thermodynamic advantages of the pressure region.     

Numerical modeling of startup and shutdown transients in reciprocating compressors

Several phenomena that affect energy consumption, noise level and reliability of compressors are associated with transient effects that occur during the compressor startup and shutdown. This paper presents a simulation methodology, experimentally validated, developed to analyze the compressor in such transients. Because the time scale associated with the compressor thermal behavior is much larger than that related to the mechanical physics, a thermal equilibrium condition has been considered herein for convenience. Results for valve displacement, piston motion, pressure in the compression chamber and resistive torques are provided to illustrate the application of the methodology and to assist an understanding of the physical aspects that affect the compressor performance throughout the startup and shutdown. It is observed that the dynamics of suction and discharge valves are greatly affected. Moreover, the model is employed to estimate the minimum voltage required for the compressor startup as a function of the equalized pressure and the auxiliary coil actuation time.     

R32变频滚动转子压缩机变工况模型及运行特性

本文研究了R32变频滚动转子式制冷系统,实验分析了压缩机运行频率、吸排气压比、蒸发温度对不同吸气状态下压缩机电效率变化规律的影响,并以此建立了适用于吸气过热和吸气带液的压缩机电效率模型。结果表明:1)在相同压比、相同蒸发温度下,压缩机电效率均随电子膨胀阀开度的变大呈线性下降趋势,且吸气带液段斜率大于吸气过热段,即压缩机吸气带液时,压缩机电效率下降程度更大;2)相同压比下,蒸发温度越高,电效率越小;相同蒸发温度下,压缩机压比越高,电效率越小。同时,压缩机压比越高,蒸发温度对压缩机电效率的影响越大;3)验证工况下模型计算值与实际值最大相对误差为1.83%,最小相对误差为0.03%,具有较好的可靠性;4)压缩机在低频率下运行时性能会恶化,此时模型的准确性会降低,因此模型适用于压缩机频率高于额定频率、吸气干度大于0.88的工况。     

A new structure and theoretical analysis on leakage and performance of an oil-free R290 rolling piston compressor

Lubricating oil improves the reliability of compressors and systems, whereas increases the system complexity. Compared with other types of compressors that have oil-free models, a rolling piston compressor has more leakage paths and bigger leakage loss. Therefore, the leakage is an important problem to be solved in order to develop an oil-free rolling piston compressor. The paper put forward a new structure of rotary compressor adopting a low pressure shell, connecting the cavities within piston and behind vane to the cavity at suction pressure and using radial compliance mechanisms. Then the leakage models were developed to calculate the mass flow rates within both the present rolling piston compressor without any oil as sealant and the new structure of oil free compressor. Results showed that by the new structure, the influences of leakage on the performance of a R290 oil free rolling piston compressor can be largely decreased.     

A Simulation Study on the Transient Motion of a Reciprocating Compressor Suction Valve Under Complicated Conditions

Stepless capacity control technology for reciprocating compressors is a key contributor to energy saving for the petroleum and petrochemical industries. Devices called “unloaders” are utilized to control the capacity of the compressor by forcibly holding the suction valves open during a variable portion of the compression stroke to control the compressor output. This approach can also lead to various faults of the suction valve. This paper describes the simulation and experimental studies of the transient motion of suction valves under stepless capacity control. Beginning with mathematical models for the normal cycle, improved models of a reciprocating compressor under stepless capacity control have been built. A simulation study of the working process of a double-acting reciprocating compressor has been completed. Theoretical formulas for the transient motion of the valve plate under complicated conditions and the dynamic pressure in the cylinder are compared with the experimental results. Based on the above simulations, a finite element analysis of the valve plate and valve seat has been completed. The experiment results showed that the vibration of the compressor cylinder under complicated conditions was consistent with numerical simulation results. Research presented in this paper is significant in providing tools for diagnosing faults in order to optimize the design of reciprocating compressors that utilize a stepless capacity control system.     

Strömungstechnisches und thermodynamisches Verhalten von Seitenkanalverdichtern im Vakuumbereich

Because of the lower gas density side channel compressors perform in vacuum operation better fluidic performace than in pressure operation for generating overpressure. The thermal load of the compressors is reduced by the lower final compression temperature. The polytropic expansion of the lower mass flow in the breaker, which removes thermal energy both from the expanding gas and from the housing and therefore causing a cooling of the compressor, contributes especially to the varied thermodynamic performance in vacuum operation. This inner thermodynamic performance of the compressor in the breaker area and the suction area provides together with the lower power absorption an advantageous performance of side channel compressors in vacuum operation at absolute pressures p _S=10 to 40 kPa. These advantages in operation and thermodynamic advantages are as bigger as higher the vacuum and as lower the gas density get. From this a promising development of side channel compressors as vacuum pumps also in a higher vacuum region can be deduced.     

Efficiency analysis of power consumption in small hermetic refrigerant rotary compressorsAnalyse,du point de vue du rendement,de la consommation d'énergie dans les petits compresseurs frigorifiques rotatifs hermétiques

Theoretical and experimental studies of small hermetic rotary compressors for room air conditioners are reported. Comparing rotary and reciprocating compressors from the viewpoint of efficiency, the rotary compressor has a disadvantage of higher friction loss because the sliding surfaces in the compression chamber increase in number, however it has the following three significant features: volumetric efficiency is high; valve loss is low; since suction, compression and discharge are performed simultaneously, suction velocity and discharge velocity become approximately one half. Therefore the efficiency of the rotary compressor is higher than that of the reciprocating compressor.     

Efficiency analysis of power consumption in small hermetic refrigerant rotary compressors

Theoretical and experimental studies of small hermetic rotary compressors for room air conditioners are reported. Comparing rotary and reciprocating compressors from the viewpoint of efficiency, the rotary compressor has a disadvantage of higher friction loss because the sliding surfaces in the compression chamber increase in number, however it has the following three significant features: volumetric efficiency is high; valve loss is low; since suction, compression and discharge are performed simultaneously, suction velocity and discharge velocity become approximately one half. Therefore the efficiency of the rotary compressor is higher than that of the reciprocating compressor.