气瓶内部淬火过程的流动换热特性

 大直径厚壁气瓶内部淬火时的流动换热过程极其复杂，受到多种因素的影响，而研究气瓶内部压强和温度的变化规律对改善流动换热效果、提高产品组织性能具有重要的理论指导意义。以914 mm厚壁气瓶和瓶内流体为研究对象，建立了二维等效流 固耦合模型；采用多喷嘴系统对气瓶内外进行喷水淬火，研究了气瓶总长、喷水流速及淬火时间对瓶内压强及内壁温度的影响，通过间歇淬火试验验证了数学模型的正确性。结果发现，气瓶长度对瓶内压强和瓶壁温度的影响显著，喷水流速次之，当喷水流速大于8 m/s后，水量对瓶壁的冷却效果大大降低；气瓶内壁长度方向的温度梯度分别随气瓶总长的增加和淬火时间的延长而减小，但基本不受喷水量的影响。     

Mathematical model for coal conversion in supercritical water: reacting multiphase flow with conjugate heat transfer

Providing heat for supercritical water gasification (SCWG) of coal by coupling subsequent products oxidation in integrated supercritical water reactor (ISWR) provides an effective method for directional control of temperature field and avoids excessive hot spots caused by uniform heating. An exploratory numerical model incorporating particle-fluid flow dynamics, multispecies transport and thermal coupling between endothermic coal gasification and exothermic product oxidation was established to simulate the reacting multiphase flow process of coal conversion in a novel lab-scale ISWR. An eleven-lump kinetic model was proposed for the prediction of chemical reactions. And the thermal coupling relationship was described by conjugate heat transfer boundary conditions (BC). Detailed physical and chemical field distribution in ISWR were analyzed and influence factors were discussed. The results showed that oxidation of gas products as inner heat source could promote the gasification reaction with only slight or even little maximum temperature increase of the pressure-bearing wall. Coal feeding rate and oxygen supply method significantly affected the field distribution. The multi-injection compressed-air supply method provided a more uniform temperature field but would reduce heat transfer temperature difference. The carbon gasification efficiency (CGE) in the gasification zone could easily reach up to 97% under mild conditions (less than 650 °C).     

Thermal imaging of time-varying longitudinal defects in the internal coating of a tube

We deal with the mathematical model of the incremental degradation of the internal coating (e.g. a polymeric material) of a metallic pipe in which a fluid flows relatively fast. The fluid drags solid impurities so that longitudinal scratches, inaccessible to any direct inspection procedure, are produced on the coating. Time evolution of this kind of defects can be reconstructed from the knowledge of a sequence of temperature maps of the external surface. The time-varying orthogonal section of this damaged interface is determined as a function of time and polar angle through the identification of a suitable effective heat transfer coefficient by means of Thin Plate Approximation.     

Application of the Microsoft Excel Solver tool in the solution of optimization problems of heat exchanger network systems

Optimization of heat exchanger networks (HEN_S) is a field of interest in Chemical Engineering. The aim is to use the residual heat of process streams to raise the temperature of other process streams which are cold, thus minimizing the use of hot and cold utilities. The usual way to deal with this task is to pose a linear programming problem according to a transshipment model in order to minimize either the general services consumptions or the number of hot and cold stream matchings required. This optimization is subjected to several restrictions given by the energy balances corresponding to each heat exchange.The high number of variables and equations obliges the use of specific software to solve these problems, e.g. GAMS (General Algebraic Modelling System). However, this software is not intuitive and requires a long time of training and a certain level of practice for the students to adequately use it.This work describes the use of Microsoft Excel-Solver for the sequential solving of HEN_S optimization problems according to the transshipment model. Solver is a much simpler, intuitive and easily available tool for the students who, besides, usually learn how to use it in the first years of their degree, in Informatics or similar subjects. Thus, it is not necessary to spend extra time in the teaching of the software, time that may be devoted to other contents.This paper presents an example of HEN_S problem proposed in the subject Simulation and Optimization of Chemical Processes corresponding to the Joint Master in Chemical Engineering of the Rey Juan Carlos University and the Autónoma University of Madrid and solved by the students using Excel-Solver.     

Hydrogen production by oxidative steam reforming of methanol over anodic aluminum oxide-supported Cu-Zn catalyst

Oxidative steam reforming of methanol (OSRM), which is a convenient reaction for producing hydrogen, suffers from the hot spot formation problem when conventional particle catalysts are used. Recently, an anodic aluminum oxide (AAO)-supported Cu-Zn catalyst was proposed as an OSRM catalyst for its high thermal conductivity through the aluminum metal body. In this study, OSRM was conducted in a prototype reactor packed with the AAO plate catalyst strips. It was verified that the high thermal conductivity of the catalyst effectively suppresses the hot spot formation and makes the temperature profile smooth along the reactor. The start-up time of the reactor depended on the preheating temperature and was very short (less than 2 min) for preheating over 503 K. The methanol conversion and reactor temperature increased with increasing O₂/CH₃OH mole ratio, indicating that the mole ratio can be used as a control variable to operate the reactor at desired conditions. Further, a reactor model was developed and verified, and the simulation showed that for a given total reactor volume, an optimal reactor configuration could be achieved by shortening the reactor length while widening the cross-sectional area.     

基于(火用)效率目标的环冷机余热回收系统操作参数优化

摘要：针对烧结环冷机余热回收利用率不高的难题，采用分析法建立了评价某钢铁厂烧结环冷机余热回收系统运行效率的效率模型。基于多孔介质模型、局部非热平衡方程、真实气体SRK方程建立环冷机内气固两相换热模型。通过CFD仿真模拟，探究料层高度、循环风机输入烟气温度、烧结矿底部入口风速三项可控环冷机运行工艺参数对系统效率的影响规律。结果表明，料层厚度在1～1.5 m区间每增加0.1 m，效率增加0.8%～1.1%；循环风温在100～140℃之间每增加10℃，效率增加1.4%～1.5%；烧结矿底部入口风速在0.9～1.9 m/s之间每增加0.1 m/s，效率降低0.18%～0.24%。在此基础上，基于工业运行数据建立效率正交试验优化模型，提高了该余热回收系统3.42%的效率。     

Thermal hydraulic analysis of supercritical water reactor cooled by TiO2 nanofluid

Heat transfer study of nanofluids as coolant in SCWRs core has been performed at Helwan University. A thermal hydraulic code has been produced to study the effect of TiO₂ nanofluid water based as a coolant with comparison with pure water as a coolant. Various volume fractions of nanoparticles TiO₂ (2, 6 and 10%) were used in order to investigate its effects on reactor thermalhydraulic characteristics. Based on Parameters of a SCW Canadian Deuterium Uranium nuclear reactor (CANDU), the fuel assembly was modeled to study the effect of nanoparticles volume fraction on thermos-physical properties of basic fluid and the temperature distribution of fuel, cladding surface and coolant in axial direction. The theoretical results showed that the density, viscosity and thermal conductivity of the coolant increases with the increase of nanoparticles volume fraction, contrasting to specific heat, which decreases with the increase in nanoparticles volume fraction.     

二次侧非能动余热排出系统流动不稳定性研究

二次侧非能动余热排出（ASP）系统是压水堆核电厂应对全厂断电事故的重要措施之一。为研究ASP系统的运行特性，设计建造了ASP系统试验装置（ASPTF）。在ASPTF上开展了ASP系统运行稳定性影响试验，并对试验结果进行了理论分析。试验研究与理论分析结果表明：低压低功率下ASP系统中出现流动不稳定性；增加蒸汽管线或回水管线阻力系数可抑制ASP系统出现流动不稳定性；降低加热功率时ASP系统更易出现流动不稳定性；主泵运行状态影响ASP系统的输入功率进而影响系统的流动不稳定性。