析蜡潜热对架空管道停输介质温度分布影响研究

研究热油管道的停输介质的径向温度场分布,对确定安全停输时间具有重要的指导作用.由于考虑析蜡潜热的影响能更准确的描述热油管道停输介质的温度分布,建立了架空热油管道停输径向传热物理模型和数学模型,并用FLUENT软件模拟了架空管道停输温降过程中径向温度场分布.该方法能够准确模拟原油凝固过程中固液相界面的位置,模拟结果更符合...     

回填土质对埋地热油管道传热影响的研究

针对不同导热系数的土样回填管沟,忽略管道轴向温降建立二维非稳态传热模型,环境温度采用周期性边界条件。利用有限容积法,对方程进行离散,数值模拟了管道投产第一年内正常运行非稳态传热过程,同时应用"焓-多孔度"技术,并考虑原油凝固潜热对温降的影响,数值模拟了管道停输非稳态温降过程。结果表明:采用导热系数相对较小的土质回填管沟,管壁及保温层外壁热流密度明显减小,而且回填区温度较高散热较慢,由计算的安全停输时间可知,回填土质导热系数越小安全停输时间越长,模拟结果符合实际。     

海底含蜡原油管道停输降温过程的数值模拟

研究海底含蜡原油管道的停输降温过程,对避免＂凝管＂事故的发生起着重要的作用。针对海底含蜡原油管道运行环境的特点,建立海底管道停输时的非稳态传热模型,利用CFD软件模拟海底管道停输过程中温度随时间的变化规律,分析管径、管道周围海泥温度等因素对停输温降的影响,从而确定最佳停输时间,为海底含蜡原油管道制定再启动方案提供理论依据。     

原油管输不可逆过程火用的传递和转换规律研究

基于不可逆过程热力学的基本理论,探讨了原油管输过程各不可逆过程的强度量势场梯度驱动力作用下的火用流传递现象,结合原油管道输送过程的基本场平衡方程组和普遍化热力学体系的火用平衡动力学方程,推导了管输过程的热火用和压火用传递和转换方程,进一步建立管输过程的总火用传递方程。以某原油管道为例,对管道输送过程进行数值分析得到管输过程中热火用和压火用的传递和转换火用流分布规律,为将火用的传递转换规律应用到管道节能体系中提供理论基础和合理依据。     

原油管道伴热工艺热力分析

根据原油管道伴热方式,建立原油管道伴热系统能量平衡模型,对管道伴热系统进行数值模拟,计算原油和伴热水的沿程温度变化,并对比分析不同伴热方式下的伴热效果,根据管线长度,优化选择伴热方式。     

Numerical simulations of temperature field of an oil pipeline when transportation is stopped

对于高凝点原油,管线停输后很容易出现凝管现象,确定安全停输时间是保证安全启动的重要条件.原油的储热能力,管道系统向周围土壤传热能力及土壤的温度场分布决定着管线安全停输时间,研究热油管线停输期间温降规律显得尤为重要.利用CFD软件,在非稳态传热条件下,模拟出不同停输时刻管道温度场分布及温降曲线.结果表明:停输初期管内原油自然对流传热强烈,温度下降较快,后期下降缓慢,这种变化趋势和传热方式的变化相对应.当停输21 h时,原油温度降为38 ℃(高于凝点3 ℃),即安全停输时间为21 h.     

含蜡原油热输管道轴向温降计算在大港石化公司的应用

根据含蜡原油在三个不同温度区域的比热容表达式,从能量平衡关系式出发,推导出了含蜡原油热输管道轴向温降的计算公式,并与苏霍夫温降公式进行了比较。得出了实际运行情况下,原有的外输油起点温度范围已不再是最佳的选择。应用本文提供的计算方法予以调整,可以大大降低不必要的能量消耗。     

油油换热器投运及节能效果的探讨

为实现节能减排,西部原油管道在首站原有加热系统的基础上增加了油油换热器装置,针对投运过程中遇到的问题,如泵不满足启泵条件、部分高凝油进入管道等,提出了相应的解决措施.同时,探讨油油换热器装置投用前后对管道的影响,如停输出站油温下降或启输油温回升速度对外输物性的影响,冬季运行加热炉节能效果等.运行结果表明:较投用前停输温降速度慢,出站油温变化不大,节能效果显著,备用加热炉增加,更有利于管道的冬季运行.     

原油外输

<正>原油外输是原油集输系统的最后一个环节。管道输送是用油泵将原油从外输站直接向外输送,具有输油成本低、密闭连续运行等优点,是最主要的原油外输方法。也有采用装铁路油罐车的运输方法,还有采用装油船(驳)的水道运输方法。用铁路油罐车或油船(驳)     

基于PCA-GRNN模型的原油管道减阻剂减阻率预测研究

针对原油管道减阻剂减阻率的计算问题,首先对影响减阻剂减阻率的相关因素进行系统分析,介绍PCA(主成分分析)算法、GRNN(广义回归神经网络)算法以及PCA-GRNN模型的组合过程,使用国内某管道公司的实验数据,将135组数据作为学习数据,对20组数据进行预测,并将预测结果和Frank Vejahati、Karami所提出的方法、倒数方程法以及负指数方程法的计算结果进行误差对比,以此证明PCA-GRNN模型的可行性。研究表明:加剂浓度、管道直径、管道长度、平均输量、平均速度以及雷诺数是影响原油管道减阻剂减阻率的主要因素;使用PCA-GRNN模型的预测平均绝对误差为3.832%,远小于其他方法的计算结果,证明该方法完全适用于原油管道减阻剂减阻率预测。     

A new general model for phase-change heat transfer of waxy crude oil during the ambient-induced cooling process

The thermal process during shutdown (a stoppage state of the pipeline), of which the essence is an irregular phase-change process accompanied by natural convection, non-Newtonian behavior, and sometimes turbulence, is a critical problem in crude oil transportation engineering. An accurate calculation of the thermal process during shutdown is more than necessary for the safety of crude oil pipeline; however, it faces some challenges due to the complexity of the phase change. In this study, the phase change of waxy crude oil during the cooling process is divided into four stages, which includes a pure liquid natural convection, solid/liquid dispersion natural convection, coexistence of dispersion system natural convection and porous media natural convection, and pure porous media convection, according to different heat transfer mechanisms on different stages. Based on this division, a general phase-change heat transfer model is proposed for the thermal calculation of waxy crude oil during shutdown. Compared with the previous research, this model appropriately includes the influences of non-Newtonian behavior, phase evolution as well as turbulence. With the proposed model, the temperature drop characteristic of a sample pipeline is analyzed and the influencing factors are investigated.     

Transient natural convective heat transfer in porous medium with solidification of binary mixture

In this paper an enthalpy porosity method associated with finite control volume scheme and SIMPLE iteration was employed to solve Navier–Stokes equation coupled with energy equation through Ergun equation and Boussinesq approximation for studying the effect of two-dimensional transient natural convective heat transfer from a closed region of porous medium with the different porosity on solidification in carbon–iron system. As shown in the results, it is fund that the thickness of solidification layer is increased with time due to thermal coupled flow induced by natural convection; and the wall temperature is faster changed in porous medium with larger porosity, which corresponds to slow the growth of the solidification layer in binary system.     

Coupled radiation and solidification heat transfer inside a graded index medium by finite element method

Effects of thermal radiation on solidification heat transfer must be considered inside semitransparent media. This paper investigates coupled heat transfer of solidification and radiation within a two-dimensional rectangular semitransparent medium having gradient index. Solidification process is supposed to happen at some temperature range, and accordingly three zones including liquid-, solid- and mushy-zones exist in phase-change media. In different phase field, parameters of thermophysical property are assumed different and those of radiative property are assumed same. Governing equation includes conduction, radiation and phase-change terms, and radiation and phase-change are treated as source terms in the equation, respectively. A Galerkin finite element method is used to solve energy equation of coupled radiation and phase-change heat transfer. This paper analyzes effect of thermal radiation on phase-change heat transfer and those of refractive index distributions on temperature fields and liquid fraction distributions during radiation–solidification coupled heat transfer. From the results, we can find that refractive index gradient has a major influence on phase-change process and compared with the case of smaller index gradient, bigger gradient can speed up phase-change heat transfer in semitransparent media.     

Numerical and experimental investigation of paper drying: Heat and mass transfer with phase change in porous media

The physics of paper drying combines heat and mass transfer with phase change in wet porous media. The drying processes can be modeled with the liquid and vapor mass conservation equation, the liquid–gas mixture mass conservation equation, and the energy conservation equation. The drying model of paper includes the convection and the capillary transport of liquid and the convection and the diffusion transport of gas and vapor. Numerical simulation and experimental investigation of whole paper drying are done on an actual paper machine. The drying parameters in boundary conditions including the temperature of outer surface of the cylinder, the temperature and the relative humidity of the air pocket were measured. The numerical results of paper sheet temperature of the first 26th cylinders and the final moisture content after 78 cylinders agree well with experimental data, which means the drying model is valid to predict the performance of paper drying.     

Numerical investigation of the thermal mechanism of the solid-liquid phase changing process

由于相变换热储能技术可以协调能量在时间和空间尺度的分配,成为了目前研究的热点问题。本工作用焓值法分别对充填低温无机盐相变材料的二维和三维管壳式相变储能换热器模型的储/放热特性进行了模拟研究,采用Boussinesq近似研究了液相区密度变化引起的自然对流的影响。研究表明换热器的入口温度对相变换热效率影响显著;在储热过程中自然对流发挥了重要作用,换热效率与液相区的运动状态直接相关,而放热过程中的热交换主要依靠热传导完成;三维模拟的结果表明换热管出口温度与管壁的平均努赛尔数高度相关,且换热管水平放置的换热效率略低于竖直放置。     

Further study on the thermal characteristic of a buried waxy crude oil pipeline during its cooling process after a shutdown

Since the temperature drop of waxy crude oil after a shutdown determines whether the pipeline is able to restart successfully or not, it is necessary to calculate the temperature drop and clarify the characteristic of the thermal process of waxy crude oil pipeline after the shutdown. However, the relevant techniques proposed in the previous researches for this calculation are not accurate enough, due to the complex phase change, non-Newtonian behavior of the fluid, and the transition of different heat transfer mechanisms involved within the physical problem. Therefore, in a companion piece to this paper, a general and accurate mathematical model was proposed for the phase-change heat transfer of waxy crude oil. In this paper, the mathematical model of the waxy crude oil pipeline system after its shutdown is established, based on the phase-change heat transfer model proposed in the companion piece, and the numerical procedure is established for the calculation of the model. With the proposed techniques, the thermal process of the shutdown of waxy crude oil is investigated in detail, and the temperature drop characteristic is clarified on the level of heat transfer mechanism. The research will provide theoretical support for the establishment of shutdown scheme and thermal preservation method for waxy crude pipeline.     

Conjugate forced convection-conduction plate fin in power law fluids

The heat transfer characteristics of laminar, forced convection flow for power law fluids from a vertical plate fin are studied analytically based on the conjugate convection and conduction theory. The resulting boundary layer equations of fluids are coupled with the one-dimensional heat conduction equation of fin through interfacial conditions. Numerical results for the local heat flux, local heat transfer coefficient, and temperature distribution along the fin surface and overall heat transfer rate under the effects of the conjugate convection-conduction parameter, generalized Prandtl number and fluid flow index are illustrated. The results obtained of the non-Newtonian power law fluid are found to have trends similar to those of the Newtonian fluids.     

凝固层界面上局部对流换热系数的确定

依据实测的固液界面的运动规律和界面上的能量守恒。讨论了一种确定国管外凝国层界面上局部对流换热系数的方法。凝固实验中局部对流换热系数的推算表明：凝固时的局部对流换热系数不同于圆管外单相介质的稳定局部对流换热系数。