变频技术在空调水系统中的应用与节能分析

根据空调水系统在不同工况下运行的性能与特点 ,分析了冬夏及部分负荷运行时空调水系统的流量和扬程的差异。提出了空调水系统在冬夏及部分负荷运行时 ,循环水泵应采用变频技术 ,合理配备。并举出工程实例分析比较循环水泵变频运行的特性与耗能情况。     

蓄冷空调控制策略的选择及运行优化

蓄冷技术在空调中的应用使得满足空调负荷有更多的灵活性和复杂性。蓄冷空调能否达到节能降耗的目的，不仅取决于进行系统的合理设计，也取决于系统运行控制策略的合理选择和优化。本文介绍了蓄冷空调系统运行策略的选择原则、影响优化运行的因素和实现优化运行的方法。     

一次泵变流量系统概述

暖通业界的设计师、设备运营者迫切希望获得节能、可靠、高效的中央空调水系统。下面介绍的就是这样一项革新成果：中央空调冷冻水系统中的一次泵变流量技术。国外大量一次泵变流量系统的成功安装及可靠运行,不但开拓了其在有关行业推广的市场,而且加深了有关行业对其的认识与了解。然而,由于一次泵变流量系统固有的复杂性使得许多建筑设备设计专家不愿意使用一次泵变流量系统。本文将通过介绍一次泵变流量系统设计特点及其主要运行设备的性能特性,消除这些暖通设计师的顾虑。更重要的是,本文所介绍的技术特点对于空调系统的安全高效运行十分关键。     

空气处理机组中的PLC控制设计

室外空气状态在1年中变化范围非常大,空调系统全年运行调节应按照空调工况划分几个阶段来进行,为了实现空调系统在运行过程中能够实现工况在各个相邻分区中的自动转换,应用PLC技术对空调系统进行自控设计。考虑到目前冷水机组及热泵机组均自带独立的控制系统,无须另外设计,本程序仅针对组合式空气处理机组控制系统进行设计。     

住宅空调方案选择研究

本文以上海某一高层建筑住宅为例,分析三种典型住宅空调方案的特点,采用BIN法计算了各方案的全年能耗,研究了各方案的初投资和运行费用。研究表明:变制冷剂流量热泵空调年耗电量在三个方案中最小,具有显著的节能效果;但在初投资上却是最高,与分体空调器和风冷热泵空调系统相比没有竞争优势;但是在运行费用上,变制冷剂流量热泵空调的年运行费用最低,与风冷热泵空调系统、分体空调器相比分别节省了10.9%、11.7%的电费。     

空调冷冻水泵变频能耗特性的研究

通过分析冷冻水管路特性随空调负荷变化的特点 ,得出了计算空调冷冻水泵变频调速运行总能耗的一般关系式。研究表明 ,在中央空调系统中 ,由于冷冻水管路特性曲线随空调负荷而变化 ,在确定水泵变频调速运行的能耗时已不能直接应用泵的相似定律 ;变频冷冻水泵的能耗并不与转速或流量的三次方成正比 ,而是与空调负荷、空调用户的流量分配及空调用户的位置等有关。     

基于建筑热惰性的空调系统动态调节优化研究

从运行方式的角度对地板辐射+地源热泵空调系统进行优化，以济南某办公建筑为例，利用Trnsys仿真模拟软件建立地板辐射+地源热泵空调系统模型，通过改变负荷侧水泵流量、机组功率、系统启停时间，比较不同方式运行的舒适性和经济性，探索地板辐射供冷系统建筑围护结构的蓄热特性。结果显示：在保证舒适性的前提下，可以减小负荷侧水泵流量和机组功率，确定最佳运行参数，减少系统能耗；墙体总蓄热时间为12.5 h，放热时间为11.5 h，由于墙体具有热惰性，温度变化具有明显的峰值延迟现象；系统在7:30～18:00运行能够缩短运行时间，降低空调系统运行能耗。     

空调水系统合理配置与节能研究

根据空调水系统在不同工况下运行的性能与特点,分析冬夏及部分负荷运行时,空调水系统的流量和扬程差异。提出了空调水系统冬夏及部分负荷运行时,循环水果应分别设置,合理配备。并举出工程实例分析比较循环水泵分设与不分设两种方案运行的特性与耗能情况。     

变频技术与空调节能

分析了空调系统流量调节方式与能耗的关系,根据变频调速技术的节能原理,通过实例说明变频调速装置用于空调的变流量调节可显著节能,提高空调系统的经济性。     

空调系统的节能运行

随着空调应用的日益广泛,强调空调系统的节能运行,对降低空调运行能耗和运行费用,促进国民经济的可持续发展具有十分重要的意义。本文结合目前国内空调系统现状和工程实际,分析和提出了实现空调系统节能运行的某些措施和方法。     

150单缸机试验台冷却系统流动与传热计算分析

基于Flowmaster软件建立了150单缸柴油机试验台冷却系统流动与传热模型,并在某大功率发动机上进行了验证。在此基础上分析得到了冷却水温度和流量、气缸套和气缸盖温度变化对冷却水总传热流量的影响规律,以及管道尺寸、壁面粗糙度、冷却水流量对冷却水流动总阻力的影响规律。     

基于流固耦合的气缸盖温度场仿真研究

以某高速大功率柴油机气缸盖为研究对象,建立了由气缸盖、气缸体、气缸套以及气缸盖内冷却水道组成的流固耦合系统;通过合理施加流体域及固体域边界条件,利用CFX进行流动与传热计算,得到了冷却水速度场、温度场以及气缸盖温度场,为气缸盖热机耦合的进一步研究提供依据。     

Heat and Mass Transfer in Adsorption-chemical Cooling with Phase Transitions in a Sorbent

The complex model of heat and mass transfer during adsorption and chemical heat conversion is presented. It includes combined effect of physical and chemical adsorption and accompanying ammonia condensation/evaporation directly inside the sorber taking into account the conjugate heat transfer between the sorbent and the heat-transfer fluid. It was found that the specific cooling power and average cooling temperature are one-valued function of a ratio of the sorber length to the mass flow of heat-transfer fluid. The use of condensation/evaporation in a sorbent can increase the temperature effect more than twice.     

ORC直接接触式蒸发器传热性能研究

为分析低温余热发电ORC直接接触式蒸发器内分散相在连续相中的传热性能,分别选用新型环保有机工质R245fa和THERMINOL-R 66导热油作为分散相和连续相,进行ORC直接接触式蒸发器传热性能的研究,分析了初始传热温差、工质体积流量和导热油质量流量对ORC直接接触式蒸发器容积传热系数的影响．结果表明：容积传热系数随着传热时间的增加先呈增大趋势,然后逐渐减小并趋于平稳,但大于传热开始阶段的容积传热系数;在工质体积流量和初始传热温差为定值的情况下,为获得较大的容积传热系数,导热油质量流量应控制在较小的范围内．     

循环流化床锅炉燃烧系统动态特性分析

根据循环流化床锅炉(CFBB)的工作特点以及燃烧系统输入和输出过程变量间的耦合关系,讨论了CFBB的蒸汽压力和床温的动态特性。认为引起蒸汽压力变动的主要原因在于燃料量(内扰)和汽轮机调门的变化(外扰);而影响床温变化的主要因素是给煤量、风量、物料循环量的变动,并从传热和燃烧过程分析了这些因素间的相互耦合关系。这对CFBB燃烧自动控制系统的设计与调试,以及整个控制系统的可靠运行都至关重要。     

Effect of external recycle on the performances of flat-plate solar air heaters with internal fins attached

The influence of external recycle on the collector efficiency in solar air heaters with internal fins attached, has been investigated theoretically. The application of external recycle operation to solar air heaters actually has two conflict effects. One is the increase in fluid velocity to decrease the heat-transfer resistance, which is good for performance, while the other is lowering the driving force (temperature difference) of heat-transfer, due to the remixing at the inlet, which is bad for performance. It is found that considerable improvement in collector efficiency is obtainable if the operation is carried out with an external recycle, where the desirable effect overcomes the undesirable effect. The enhancement increases with increasing reflux ratio, especially for operating at lower air flow rate with higher inlet air temperature.     

基于元体能量平衡法的垂直U型埋管换热特性的研究

基于元体能量平衡法建立了垂直U型埋管的传热模型,模型考虑了流体温度的沿程变化,并通过引入热干扰角与等效传热间距反映两管脚间的热干扰问题,使之更符合实际的传热情况。通过所建模型对U型埋管的换热特性进行了数值模拟,结果表明:增加土壤与回填物导热系数、管脚间距、管内流体流量及减小管脚热干扰角与进口流体温度(供热工况下)均可以增强埋管的换热效果,其中土壤导热性影响最为显著。但回填物导热系数不可无限制增大,其大小还要考虑对增强管脚间热干扰的影响及其与管脚间距的相互关联性。同时,流量的增加要考虑对流动阻力增加的限制,可以采用变流量设计来进行调节与优化。此外,为了充分发挥地源热泵的能效,实际设计应该考虑埋管、热泵及负荷三者间的相互匹配性。     

Optimization principles for convective heat transfer

Optimization for convective heat transfer plays a significant role in energy saving and high-efficiency utilizing. We compared two optimization principles for convective heat transfer, the minimum entropy generation principle and the entransy dissipation extremum principle, and analyzed their physical implications and applicability. We derived the optimization equation for each optimization principle. The theoretical analysis indicates that both principles can be used to optimize convective heat-transfer process, subject to different objectives of optimization. The minimum entropy generation principle, originally derived from the heat engine cycle process, optimizes the convective heat-transfer process with minimum usable energy dissipation focusing on the heat–work conversion. The entransy dissipation extremum principle however, originally for pure heat conduction process, optimizes the heat-transfer process with minimum heat-transfer ability dissipation, and therefore is more suitable for optimization of the processes not involving heat–work conversion. To validate the theoretical results, we simulated the convective heat-transfer process in a two-dimensional foursquare cavity with a uniform heat source and different temperature boundaries. Under the same constraints, the results indicate that the minimum entropy production principle leads to the highest heat–work conversion while the entransy dissipation extremum principle yields the maximum convective heat-transfer efficiency.     

Conjugated heat transfer in double-pass laminar counterflow concentric-tube heat exchangers with sinusoidal wall fluxes

An analytical method is proposed to predict the temperature distribution and local Nusselt number for laminar flow in a double-pass countercurrent heat exchanger with sinusoidal heat flux distribution. A design of inserting in parallel an impermeable barrier to divide an open conduit into two subchannels for conducting double-pass operations, resulting in substantially improved the heat transfer rate, has been evaluated theoretically in the fully developed region. Comparison with the theoretical results shows that the heat-transfer efficiency improvement for double-pass concentric circular heat exchangers is generally higher than those in the single-pass operations without an impermeable barrier inserted. The influences of the impermeable-barrier location on the heat-transfer efficiency improvement and power consumption increment, as indicated from theoretical predictions, can be used to determine the economical feasibility in operating double-pass devices.     

Condensation from gas–vapour mixtures in small non-circular tubes

Careful measurements have been made during condensation of steam from steam–air mixtures flowing in a small, flattened, horizontal tube. The ranges of the relevant variables covered (inlet temperature, pressure, air mole fraction and mixture mass flow rate) were chosen to simulate those occurring in an exhaust heat-exchanger tube of a proposed fuel-cell engine. The experimental tube was cooled by water in laminar counter flow to simulate the external heat-transfer coefficient (air flowing over fins) in the application. The total heat-transfer rate was found from the mass flow rate and temperature rise of the coolant. The tube wall temperature was measured by thermocouples attached in grooves along its length. Special arrangements were made to ensure good mixing of the coolant (in laminar flow) prior to measuring the inlet and outlet temperatures. The condensate was separated using a cyclone at exit from the tube. A simple model was developed to predict local and total heat-transfer and condensation rates and local bulk vapour composition, temperature and pressure along the tube in terms of the inlet parameters and the wall temperature distribution. The measured heat-transfer and condensation rates for the tube were found to be in good agreement with the calculated values without having recourse to empirical adjustment.