蒸汽直埋管道保温层厚度的计算与影响因素分析

在不同保温层间温度、埋深、土壤导热系数的条件下,对“钢套钢”蒸汽直埋管道保温结构的厚度进行了计算,与实际工程中的数据进行比较,得出保温层间合理的控制温度及埋深,并讨论不同的土壤导热系数对保温结构厚度的影响。     

关于设备与管道保温热损失及经济厚度的计算与讨论

一、问题的提出国标GB4272－84设备与管道保温技术通则4．1．1条中规定：为减少保温结构散热损失的保温层厚度应按“经济厚度”的方法计算，并且其散热损失不得超过规定值。传统的“经济厚度”的定义是保温层的年散热损失费用与保温工程投资的年分摊费用之和为最小值，这个保温层厚度就叫做“经济厚度”。国标GB8175－87设备与管道保温设计导则5.3．1条中规定对于园筒面的保温层经济厚度计算公式为：式中：Do－保温层外径（m）；S－投资年分摊率；Di－保温层内径（m）；S＝fn－热单价（元／106KJ）；i－银行利率λ－保温材料导热系数KC…     

影响保温工程热损失的因素分析

本文对保温材料的导热系数、湿度、保温层厚度等影响保温工程热损失的一些因素作了简要分析。说明影响保温工程热损失的主要因素是材料的导热系数。     

基于MATLAB的电缆线临界绝缘厚度分析

电缆线包裹保温层主要为了加强热量散失，存在一个临界热绝缘直径使得散热量最大。分析了自然对流和强制对流条件下保温层材料导热系数分别为常数和随时间变化时电缆线传热模型一，给出了有关计算式，利用MATLAB对传热过程进行了数值模拟，获得了相应情况下的临界热绝缘直径、外表面温度和散热量。结果可用于电缆线设计参考。     

也谈保温层经济厚度的计算机计算程序

<正> 《节能》1986年第八期上刊登了吉林工业大学热能系张忠进、金文桂同志的《保温层经济厚度的计算机计算程序》,文章利用计算机计算保温层经济厚度,对节能工作是有积极意义的。但由于作者对经济厚度存在着一些错误的理解,导致了算机程序和计算结果的错误。为此,我们俩人也编制了保温层经济厚度的计算机程序,与张、金二同志讨论。并希望我们编制的程序能为保温层的厚度设计,保温材料的生产服务。 1.张、金二同志的文章前面指出:“所谓经济保温层厚度,就是指保温后每年热损失折合费用与投资的年分摊额之和为最小的保温层厚度”。在文章的后面又说:“选取适当的保温层厚度§=(r_2-r_1),使得保温设施投资     

供热管道保温材料的选择及经济保温层厚度计算

合理选择供热管道的保温材料及经济保温层厚度,对减少管道在输送热媒过程中的散热损失,降低工程造价尤为重要。本文根据国家现行标准和有关规定,对热网保温材料的选择、经济保温层厚度的简便计算方法进行了阐述。为工程实践中在管道保温方面,达到节能降耗,节约投资的目的提供参考。     

热网管道的保温厚度与工质温度、保温材料导热系数的关系计算

在国家规定的热网管道的每米热损失下,其保温层厚度随着保温材料的导热系数及工质温度的不同而不同。利用导出的计算公式,通过计算,将以上四个参数的关系用图表的形式表示出来,以供在热网管道的保温中予以应用。     

有空气保温层的蒸汽直埋管道保温厚度计算与分析

对不同介质温度条件下有空气保温层的"钢套钢"蒸汽直埋管保温结构厚度进行了数值计算,并将计算结果与无空气保温层的保温结构厚度进行了比较.计算结果若用于实际工程,可在确保保温效果的前提下,减小保温层厚度和外套钢管的使用量,以达到减少材料的使用、节约投资的目的.     

防止管道表面结露的保温层厚度估算

当管道或容器的表面温度低于周围空气的露点时,空气中的水蒸汽就会冷凝,使管道表面结露。为防止管道外表面结露,管道外应包扎足够厚的保温层。所需保温层的最佳厚度可以用计算方法确定,但用诺模图求取更为方便。下图为估算保温层厚度的诺模图,现将用法举例如下: 已知条件:公称管径d=4英寸,管内流体温度t_0=10℉,周围静止空气于球温度t_a=90℉,相对湿度RH=90％,保温层的平均导热系数K=0.30Btu·h/(英尺~2·℉·英寸)。步骤     

高温蒸汽管道保温层厚度计算影响因素的研究

通过对高温蒸汽管道保温层厚度计算进行研究,从技术性和经济性两方面分析了影响保温层厚度的主要因素,并对计算中如何正确选取保温原始计算数据进行了探讨。所得结论对实现经济计算、节约能源、提高电厂经济效益具有重要参考意义。     

含二氧化硅气凝胶和相变材料三层玻璃窗热性能分析

为了研究含二氧化硅气凝胶和相变材料三层玻璃窗对严寒地区建筑能耗的影响,建立了相变材料层与其他透明壁层结合发生的传热数值模型。分析了含二氧化硅气凝胶和相变材料三层玻璃窗在不同二氧化硅气凝胶厚度、导热系数和不同保温材料下的动态热调节性能,得到了含二氧化硅气凝胶和相变材料三层玻璃窗内表面热流密度和液相率随时间的变化规律。结果表明:随着二氧化硅气凝胶厚度增加,总传热量降低和液相率增加,当二氧化硅气凝胶厚度为20～30 mm时,可以实现有效的利用太阳能;随着二氧化硅气凝胶导热系数增加,总传热量升高和液相率降低;当二氧化硅气凝胶的导热系数从0.022降低到0.014 W/(m·K)时,最大液相率从0.83增加到1.00。二氧化硅作为保温层比相变材料作为保温层具有更好的保温隔热作用。     

Determination of the economical insulation thickness of building envelopes simultaneously in energy-saving renovation of existing residential buildings

When the energy saving rate of existing residential buildings renovation is determined, the thermal performances of external walls, windows, and roof interact with each other. Therefore, it is necessary to study the determination of economical insulation thickness of building envelopes considering the interaction among building envelope performances. The objective function and its bound of envelope thermal performance optimization in the energy-saving renovation of existing residential buildings in severe cold and cold zones in China were established. It is the conditional extremum problem and can be solved through Lagrange’s method of multipliers to determine the economical insulation thickness of external walls and roofs simultaneously. The method is proved to be feasible by an existing residential building in Beijing. When the same window types are selected, the energy-saving renovation program of the building envelope determined by the Lagrangian optimization method can produce the minimum investment in insulation, minimum investment payback period, and the largest net present value (NPV) of the life cycle.     

Economic and environmental impacts of insulation in district heating pipelines

The determination of optimum thickness of insulation is often applied to energy technologies and building projects. In this study, the energy, economic and environmental evaluations of thermal insulation in district heating pipeline are discussed. The optimum insulation thickness, energy saving over a lifetime of 10 years, payback period and emissions of CO₂, CO and SO₂ are calculated for nominal pipe sizes and fuel types based on heating loads in Afyonkarahisar/Turkey. The life cycle cost analysis is used to determine the optimum thickness of the pipeline material in order to take into account the change in inflation that directly affect both the cost of pipeline material and fuels depending on fuel type. The results show that the highest value of optimum insulation thickness, energy savings, emissions and the lowest payback period are reached for a nominal pipe size of 200 mm. About three times more energy saving results by making 200 mm nominal pipe instead of 50 mm. Considering the economical and environmental advantages, the geothermal energy is a better choice and then fuel-oil. When thermal insulation is done in a district heating pipeline, there will be a significant reduction of 21% in the amount of CO₂ emitted to the atmosphere.     

Effective thermal conductivity analysis of xonotlite-aerogel composite insulation material

A 3-dimensional unit cell model is developed for analyzing effective thermal conductivity of xonotlite-aerogel composite insulation material based on its microstructure features. Effective thermal conductivity comparisons between xonotlite-type calcium silicate and aerogel as well as xonotlite-aerogel composite insulation material are presented. It is shown that the density of xonotlite-type calcium silicate is the key factor affecting the effective thermal conductivity of xonotlite-aerogel composite insulation material, and the density of aerogel has little influence. The effective thermal conductivity can be lowered greatly by composite of the two materials at an elevated temperature.     

Thermal Conductivity of Low-Density Polyethylene Foams Part Ⅱ: Deep Investigation using Response Surface Methodology

Here,we conducted a deep study on the thermal insulation performance of polymeric foams using response surface methodology(RSM).Cell size,foam density,and cell wall thickness were considered as variable parameters.Analysis of variance(ANOVA)tool was utilized to recognize the effective parameters on the different mechanisms of heat transfer.Regression models were presented to forecast the different mechanisms of heat transfer and their validities were checked using ANOVA tool as well as compared to the thermal conductivity results.Surface plots were used to study the interaction effect of significant parameters.The optimization procedure was performed using RSM.Foam density and cell wall thickness are effective parameters on the solid thermal conductivity whereas cell size and foam density were significant parameters on the thermal radiation.By decreasing foam density,gaseous thermal conductivity and thermal radiation were increased and solid thermal conductivity was reduced.The regression model predicted the overall thermal conductivity with an average error smaller than 3%.The results illuminated that the overall thermal conductivity in the optimum conditions was as small as 29 mW/mK.     

保温管道经济评估的优化设计模型

本文介绍了保温管道经济评估优化设计方案和三个优化设计模型。包括保温管道的单双层结构和最佳保温材料的优化选取,最佳保温层厚度的设计计算。优化设计模型中的传热模型采用管道分段求解方式,管道散热损失的计算分成水平管和竖直管两种,并考虑了支架的散热损失。保温管道的经济模型分为单层结构和双层结构两种。     

Measurements of thermal properties of insulation materials by using transient plane source technique

The paper reports on the measuring technique and values of the measured thermal properties of some commonly used insulation materials produced by local manufacturers in Saudi Arabia. Among the thermal properties of insulation materials, the thermal conductivity (k) is regarded to be the most important since it affects directly the resistance to transmission of heat (R-value) that the insulation material must offer. Other thermal properties, like the specific heat capacity (c) and density (ρ), are also important only under transient conditions. A well-suited and accurate method for measuring the thermal conductivity and diffusivity of materials is the transient plane source (TPS) technique, which is also called the hot disk (HD). This new technique is used in the present study to measure the thermal conductivity of some insulation materials at room temperature as well as at different elevated temperature levels expected to be reached in practice when these insulations are used in air-conditioned buildings in hot climates. Besides, thermal conductivity values of the same type of insulation material are measured for samples with different densities; generally, higher density insulations are used in building roofs than in walls. The results show that the thermal conductivity increases with increasing temperature and decreases with increasing density over the temperature and density ranges considered in the present investigation.     

A simple correlation for estimation of economic thickness of thermal insulation for process piping and equipment

Where the sole object of applying insulation to a portion of plant is to achieve the minimum total cost during a specific period (evaluation period), the appropriate thickness is usually termed as the economic thickness. The principle is to find at what thickness further expenditure on insulation would not be justified by the additional financial saving on heat to be anticipated during the evaluation period. Although an increase in the amount of insulation applied will raise the initial installed cost, but it will reduce the rate of heat loss through the insulation. Therefore it is necessary to reduce the total cost during the evaluation period. In this work, simple-to-use correlation, employing basic algebraic equations which are simpler than current available models involving a large number of parameters, requiring more complicated and longer computations, is formulated to arrive at the economic thickness of thermal insulation suitable for process piping and equipment. The correlation is as a function of steel pipe diameter and thermal conductivity of insulation for surface temperatures at 100 °C, 300 °C, 500 °C and 700 °C. A simple interpolation formula generalizes this correlation for wide range of surface temperatures. The proposed correlation covers pipeline diameter and surface temperature up to 0.5 m and 700 °C, respectively. The average absolute deviation percent of proposed correlation for estimating the economic thickness of the thermal insulator is 2% demonstrating the excellent performance of proposed simple correlation.