保冷效果评价指标改进研究

保冷效果评价国标规定:保冷结构外表面温度应高于设计工况下的空气露点温度。然而,保冷结构外表面温度和空气露点温度均随环境参数的变化而波动,这给保冷结构外表面温度及设计工况下空气露点温度的确定带来不便。本文基于传热学和空气物理特性相关知识,分析了保冷结构的传热过程,拟合了保冷结构外表面温度与空气露点温度的差值(Δt_(w-l))和环境温湿度之间的函数关系,分析了空气温湿度对Δt_(w-l)的影响。并以哈尔滨地区空气参数为例,对分析结果进行了验证。在此基础上,对国标中的设计工况提出了改进建议。结果表明,Δt_(w-l)随室外空气干球温度及相对湿度的升高而近似一阶线性降低;现有国标规定的以夏季空调室外计算干球温度和最热月平均室外计算相对湿度作为设计工况不能代表实际运行的最不利工况;建议在进行保冷设计与保冷效果评价时,环境空气干球温度取当地室外空气干球温度较大值,相对湿度取最热月最大室外计算相对湿度。     

建筑环境与暖通空调节能设计分析

建筑环境与暖通空调对人们日常生活有十分紧密的联系,主要是由于人们的日常生活和工作一般都在建筑内,为了保障建筑物内空气环境的温湿度,常常采用暖通空调系统来实现这一目的。基于此,对建筑环境与暖通空调节能设计进行简要探讨。     

对全空气定风量系统“可调新风比”的探讨与建议

<正>在公共建筑的空调设计中,常用的空调形式为全空气系统、风机盘管+新风系统、温湿度独立控制系统。无论采用哪种空调系统,都要根据建筑内的人员密度以及空调房间内的人数,确定空调房间的新风量。对于风机盘管+新风系统、温湿度独立控制系统,新风系统完全可以根据计算的新风量设计,相应的每层的新风机房、新风竖井、排风竖井、集中的新风热回收机组都按此新风量进行设计。那么对于全空气系统,又是如何规定的呢?1相关规范对伞空气定风培系统的可调新风比要求     

绿色植被内空气温湿度计算的数学模型

绿色植被对改善建筑物室内外空气环境、降低建筑物能耗有益。求解绿色植被内空气温、湿度值是从理论上阐明绿色植被对建筑物室内外空气环境的具体影响程度的必要条件。该文以绿色植被中的空气小气候为研究对象，以传质传热理论为基础，结合生态学知识，针对绿色植被内空气的温湿度值建立封闭的微分方程组，并对该数学模型进行了论证。     

薄膜片基空调系统节能改造

针对车间原有的一次回风空调系统存在较大能耗损失问题的情况,通过将原设计的一次回风系统,改造成温湿分控系统的方法,对新风部分加装降温除湿设备,对新风进行深度除湿。用原有表冷器承担部分降温功能,另外增加新的表冷器对新风进行除湿和降温,将混合空气降温到20℃左右送到车间,满足生产使用。温室分控系统的使用可以确保在夏季停用空气再热系统,从而减少因温湿联控造成的热量损失。试验研究证明该方案可以大大降低机组运行费用,具有节能降耗的应用价值。     

考虑环境温湿度的空冷PEMFC最佳工作温度研究与控制

空冷型质子交换膜燃料电池(PEMFC)属于阴极开放式燃料电池,无外部增湿装置,因此空冷型PEMFC阴极入口处空气的温度和湿度必然对燃料电池工作性能有着不可忽视的影响。通过实验研究空冷型PEMFC最佳工作温度与环境温湿度及输出电流之间的关系,分析不同环境温湿度和输出电流对空冷型PEMFC最佳工作温度的影响。最后设计空冷型PEMFC控制系统,根据得到的不同环境温湿度下的空冷型PEMFC最佳工作温度曲线,采用PID控制方法实现不同温湿度环境条件下的最佳工作温度控制。     

太阳能空气集热及转轮除湿/加湿混合系统冬季供暖分析

针对一种太阳能空气集热及转轮除湿混合系统,在上海冬季典型低温干燥气候条件下对供暖运行进行研究,实验测试直接供暖,加湿供暖和热泵效应供暖3种不同供暖模式的供暖效果,分析冬季太阳辐射对空气集热温度的影响,不同环境温湿度下3种工作模式对供暖温湿度的影响以及加湿供暖与热泵效应供暖模式中回风对供暖温湿度的影响。实验结果表明,3种模式下送风温度随再生温度升高而升高,送风湿度取决于处理风入口湿度和再生温度的大小,系统在采用回风的加湿供暖模式下,平均送风湿度达到12 g/(kg干空气),送风温度为26~37℃,冬季全天大部分时间能有效满足室内送风的温湿度要求。     

生物质气化烤烟系统技术研究

针对目前烤烟设备存在的污染环境及热效率低等问题，提出以生物质能为能源，通过间接换热与直接换热相结合的方式进行烤烟的工艺。并详细介绍了基于这一思想所研究设计的由生物质燃气燃烧器、烟气净化器、温湿度控制系统、烤箱等主要部分组成的生物质气化烤烟系统。试验证明该系统能很好地满足烤烟所需的各种工艺条件，在温湿度的控制、能源利用效率方面都较传统土烤房有较大提高，热效率可达58.33％。     

基于物联网技术的热力站在线监测系统

为了贯彻城市集中供热热网质量并调的方针,响应环保与节能减排的号召,基于物联网与应用计算机控制技术,结合集散控制的思想,构建"物联网+热网控制"智能监控系统,设计了远程智能在线监测系统,使得远程监控中心可以与现场分散控制中心实现联合调控,可以依据换热站的现场采集现场变频调节、电能监测、大电流柜温湿度监测及控制、电机轴温、振动与噪音监测、环境温湿度监测、站内水浸、门禁系统、照明控制、视频监控等参数,实现了热网系统安全、稳定、节能地运行。     

高压电缆附件数字化工艺库系统

对高压电缆附件数字化工艺库系统模块进行了基本介绍.分析了高压电缆附件数字化工艺库系统的功能模块、设计逻辑.该系统可大幅降低技术人员图纸审查效率,有效避免人工审查时的不确定因素,为高压电缆安全稳定运行建立一道安全防线.     

Experimental study of free convection heat transfer and condensation of vapor of humid air over an inclined cold tube

In this study condensation heat transfer on a cold inclined circular cylinder due to natural convection for various conditions is investigated experimentally. The cylinder is placed in an isolated test room to permit pure natural circulation of ambient air. Ambient temperature and humidity of the test room are controlled by a refrigeration cycle and humidifying. The ambient relative air humidity changed in the range of 30 to 50% and temperature from 25 to 35 °C. The ethylene‐glycol/water solution is used as a refrigerant to control and keep the temperature of the test section at a constant value. The cold surface temperature is varied from 2 to 6 °C. The condensation rate and heat flux are found to depend mainly on time, temperature difference between ambient air and cold surface, ambient relative humidity, and tube inclination. Results are plotted for various conditions with respect to time. The experimental results are used to propose a correlation to predict the condensate mass flow rate for free convection heat transfer. © 2012 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21015     

Approximate analytic solution for performances of wet fins with a polynomial relationship between humidity ratio and temperature

It is well known from the psychrometric properties of humid air that a linear relationship between specific humidity and dry bulb temperature (DBT) never exists. However, to establish analytical models of the performance and optimization analysis of wet fins, a linear relationship instead of psychrometric variation has been adopted by many researchers. For betterment of results in comparison with the existing value, the present study establishes a new approximate analytical model with the selection of the cubic polynomial relationship between specific humidity and dry bulb temperature. In view of this, thermal analysis of wet fins of straight profile has been addressed. The temperature profile and performance parameters of fully wet fins have been evaluated by Adomian decomposition method (ADM). A new scheme is furnished to carryout the performance analysis of partially wet fins using ADM. A notable difference in results is found while the present result has been compared with that values obtained from the published linear models.     

Analysis of thermal performance and optimization of concentric circular fins under dehumidifying conditions

The analysis of wet fins was carried out by many investigators with the variation of a linear relationship between specific humidity and the corresponding saturation temperature of air adjacent to the fin surface. For determination of the fin surface temperature under this scheme, fin-tip temperature is essentially known a priori which can be employed to calculate the psychrometric parameters associated with the dehumidification process. On the other hand, the tip temperature is only known after the salving the governing equation and it is also a function of the psychrometric properties of air. Thus for the simplicity, dew point temperature is considered as the tip temperature for calculating only the psychrometric parameters of fully wet fins in a recent publication. Nevertheless, in the actual situation this dew point temperature never satisfies at the tip and therefore psychrometric parameters calculated with the assumption of the dew point temperature at the tip may be incorrect. In the present work, an iterative scheme is demonstrated for determination of the actual tip temperature and local fin surface temperature. With considering this aspect, thermal analysis of a new geometric fin, namely, annular step fin (ASF) is proposed for the more effective utilization of fin material in comparison with the annular disc fin. An optimization study has also been made by using the modified thermal analysis of fully wet fins and the analysis of partially wet fins, separately. A remarkable change in results has been noticed when they are compared with that of the published result. Finally, it is worthy to mention that the maximum heat transfer rate per unit volume for an ASF is always higher than that of the annular disc fin for the identical design condition.     

Formulation and validation of a mathematical model of the microclimate of a greenhouse

A mathematical model MICroclimate of GREENhouse (MICGREEN), consisting of set of algebraic equations, was developed. The equations were written for four components of the greenhouse viz. cover, inside air, canopy surface and bare soil surface. It was assumed that the greenhouse air is well mixed, thermal properties of materials of construction do not change with time and solar radiations pass through cover without absorption. The values of dimensions and material properties of the greenhouse constructed at the Research Farm of Department of Soil and Water Engineering, Punjab Agricultural University, Ludhiana were put in these equations. The inputs to the model are ambient air temperature, solar radiations on normal surface, solar radiations on earth's surface, temperature of the soil under canopy and temperature of the soil at a depth of 6 cm. A computer program was written in C++ language. The equations were solved using Gauss–Seidal Iteration method. The outputs of the model are greenhouse cover temperature, inside air temperature, canopy temperature and bare soil temperature. The relative humidity of the inside air is predicted from the predicted inside air temperature with the help of psychrometric chart. To validate this model, experiments were conducted on greenhouse to obtain data during winter as tomato crop was being grown. The results of computer model were compared with the experimental results and agreement was found between the measured and predicted values.     

Thermal Performance Investigation of Mechanical Draft Cooling Tower Using Psychrometric Gun Technique

This paper presents an experimental work that studies the performance of a counterflow cooling tower with expanded wire mesh packing. Due to complicated configuration of the expanded wire mesh packing surface, it is not possible to measure the temperature of the air in the intermediate section of the cooling tower, but only that of the exit air and water temperature. In the experimental study a new concept of psychrometric gun technique is used to measure dry/wet bulb temperature of air at intermediate points of tower packing. First, the paper elaborates on the effect of atmospheric conditions, water mass flow rate and inlet temperature on the variation of the thermodynamics properties of moist air inside the cooling tower and thermal performance characteristics. Second, exergy analysis is applied to study the cooling tower potential of performance using the psychrometric gun technique. An analytical model was compared with experimental data.     

Calorimeter measurements of a heat pump dehumidifier: Influence of evaporator air flow

The performance characteristics of a Rankine cycle heat pump dehumidifier have been measured in a psychrometric calorimeter which provides close control of the air state. The quality of the measurements was monitored by applying energy and mass balance test criteria. The results show that the influence of the evaporator air flowrate on the moisture extraction rate, and on the energy efficiency of the drier, depends on the relative humidity of the evaporator inlet air stream. When the relative humidity is high the dehumidification efficiency is maximized when the evaporator air flow is maximized, within the range of air flowrates investigated. Below 50% relative humidity the specific moisture extraction rate exhibits an increasingly peaked maximum as a function of the evaporator air flowrate. This maximum moves to lower air flows when the relative humidity is lower.     

空调房间温湿度控制模拟分析

控制空调房间的设定温、湿度且使能耗最少是研究者关注的重要问题。文中以某一空调房间的变水量自动控制为例,分析了变水量空调系统的动态特性,研究了水流量变化、加湿量变化对房间温湿度的影响,分析模拟了PI控制参数的选取对控制过程影响进行。模拟结果显示合理的控制参数能实现较好的控制精度。     

Dynamic defrosting characteristics of air source heat pump and effects of outdoor air parameters on defrost cycle performance

The reverse-cycle defrosting characteristics of a 11.2 kW split-type air source heat pump (ASHP) were experimentally investigated under the defrosting conditions. Based on the experimental results, the effects of outdoor air parameters on defrosting cycle performance as well as the dynamic defrosting characteristics of the ASHP unit were analyzed. The experimental results indicate that with the increase of the outdoor air relative humidity at a constant air temperature and velocity, the total power consumption, defrosting time and endotherm from indoor room during defrosting period decreased linearly, and they also decreased as the outdoor air temperature increased, but the trends of the curves presented the concave-up. The duration of the defrosting period mainly depends on the wall temperature of outdoor heat exchanger, which is corresponding to the condensing pressure during the defrosting cycle. In this paper, the concept of total coefficient of performance (COP) is used to evaluate the performance of ASHP unit, and as the air temperature increased under the conditions of a fixed air relative humidity and air velocity, the total COP increased linearly, but it decreased linearly as the air relative humidity increased.     

基于CFD技术的太阳能污泥干燥室内热湿环境研究

基于传热传质理论,建立一种太阳能污泥干燥室内热湿耦合传递的数学模型。综合考虑空气流动以及对流和辐射传热,利用CFD软件Fluent的k~ε湍流模型、组分输运模型及辐射模型,初步分析了在太阳辐射条件下不同干燥室结构、排风形式以及通风量对太阳能污泥干燥室内干燥区域的温度、相对湿度以及速度分布的影响。模拟结果表明:干燥室内温、湿度模拟值与实测值吻合较好,平均相对误差分别为3.55%和5.39%。对比分析不同结构下干燥室内的流场分布,两出口排风形式的太阳能污泥干燥室可以形成良好的干燥微环境。当两出口排风风速≥5 m/s时,室内干燥区域温度高于室外环境温度,同时相对湿度低于室外环境相对湿度,且增大出流风速,在干燥区域内空气扰流强度增强,有利于干燥室内污泥水分的蒸发。     

Use of liquid desiccant cooling to improve the performance of vapor compression air conditioning

A hybrid air conditioning system, which consists of sections of desiccant dehumidification, evaporative cooling and vapor compression air conditioning, has been established in this paper. Experimental investigation demonstrates that cooling production and COP of the new hybrid system can be increased significantly, if they are compared with those of vapor compression system (VCS) alone. Assuming that the outlet temperature and humidity of the system are constant, psychrometric analysis at ARI conditions has been conducted under three different cases. The benefits are represented by lower electricity consumption of the compressor, higher COP of the system, less flow rate of condensation air, and reduced size of VCS, etc. The reason that the hybrid system is superior in performance to conventional systems lies in that desiccant dehumidification and evaporative cooling changes the inlet states of the air entering into VCS. Furthermore, the effects of dehumidification and evaporative cooling are analyzed in the paper.