Air interaction around outdoor air-cooled condensers

In order to increase cooling or heating efficiency,a porous computational fluid dynamics（CFD）model is employed to predict the thermo-fluid status and optimize the placement of outdoor units.A full scale model is established to validate the accuracy of CFD simulation in terms of velocity and temperature distributions.The comparison between the measurement and the simulation shows a good agreement.By evaluating the condensers＇ sucked air temperature with CFD for three units installed in a row,it is found that the minimum separation distance among neighboring units is 0.2 m;a vertical wall should be apart from the unit line by at least 0.8 m;and large different operating pressures among units do not impact the flow rate and the heat transfer of the other units meaningfully.

Precipitation of α_2 Phase in α+β Solution-Treated and Air-cooled Ti-Al-Sn-Zr-Mo-Si-Nd Alloys

A series of Ti-Al-Sn-Zr-Mo-Si-Nd alloys with various content of Al were solution treated in α+β phase field and air-cooled. The precipitation of a2 phase in cooling was investigated by transmission electron microscopic analysis The precipitation characteristic of α2 phase was discussed. The precipitation of α2 phase would proceed by the nucleation and growth of α2 phase dependent on the diffusion of Al atoms. And a comparison on the difference of precipitation of α2 phase was carried out under the conditions of air-cooling and quenching in water. The investigation showed that the air-cooling and even quenching could supply enough time for the precipitation and growth of α2 phase when Al content reached a certain value even though far away from the stoichiometric composition of Ti3Al.

Microstructure and properties of rheo-HPDC Al-8Si alloy prepared by air-cooled stirring rod process

A new and effective semisolid slurry preparation process with air-cooled stirring rod(ACSR)is reported,in which the compressed air is constantly injected into the inner cavity of a stirring rod to cool the melt.The slurry of a newly developed high thermal conductivity Al?8Si alloy was prepared,and thin-wall heat dissipation shells were produced by the ACSR process combined with a HPDC machine.The effects of the air flow on the morphology ofα1-Al particles,mechanical properties and thermal conductivity of rheo-HPDC samples were studied.The results show that the excellent slurry of the alloy could be obtained with the air flow exceeding3L/s.Rheo-HPDC samples that were produced with the air flow of5L/s had the maximum UTS,YS,elongation,hardness and thermal conductivity of261MPa,124MPa,4.9%,HV99and153W/(m·K),respectively.Rheo-HPDC samples show improved properties compared to those formed by HPDC,and the increasing rates of UTS,YS,elongation,hardness and thermal conductivity were20%,15%,88%,13%and10%,respectively.

Effect of Chromium on CCT Diagrams of Novel Air-Cooled Bainite Steels Analyzed by Neural Network

The quantitative effects of chromium content on continuous cooling transformation （CCT） diagrams of novel air-cooled bainite steels were analyzed using artificial neural network models. The results showed that the chromium may retard the high and medium-temperature martensite transformation.

Feasibility Analysis of Back-Pressure Steam Feeding Water Pump for Direct Air-Cooled Unit

As the performance of an air-cooled condenser is apt to be affected by the fluctuating ambient condition, some difficulties are brought to the use of a steam feeding water pump in an air-cooled unit. This paper introduces a new design of for steam feeding the water pump of an air-cooled unit using the back-pressure steam turbine as the prime motor. Using variable condition analysis on a 600 MW direct air-cooled unit, and with consideration of the effect on the ambient conditions, the feasibility, economy, and adaptability of the design are verified.

Application of Air-cooled Blast Furnace Slag Aggregates as Replacement of Natural Aggregates in Cement-based Materials：A Study on Water Absorption Property

The influence of air-cooled blast furnace slag aggregates as replacement of natural aggregates on the water absorption of concrete and mortar was studied, and the mechanism was analyzed. The interface between aggregate and matrix in concrete was analyzed by using a micro-hardness tester, a laser confocal microscope and a scanning electron microscope with backscattered electron image mode. The pore structure of mortar matrixes under different curing conditions was investigated by mercury intrusion porosimetry. The results showed that when natural aggregates were replaced with air-cooled blast furnace slag aggregates in mortar or concrete, the content of the capillary pore in the mortar matrix was reduced and the interfacial structure between aggregate and matrix was improved, resulting in the lower water absorption of mortar or concrete. Compared to the concrete made with crushed limestone and natural river sand, the initial absorption coefficient, the secondary absorption coefficient and the water absorption capacity through the surface for 7 d of the concrete made from crushed air-cooled blast furnace slag and air-cooled blast furnace slag sand were reduced by 48.9%, 52.8%, and 46.5%, respectively.

Physical Properties of Crushed Air-cooled Blast Furnace Slag and Numerical Representation of Its Morphology Characteristics

Physical properties and geometrical morphologies of crushed air-cooled blast furnace slag （SCR） and crushed limestone （LCR） were comparatively investigated. The shape, angularity, surface texture and internal pore structure of aggregate particles for different size and gradation were numerically represented by sphericity （ψ） and shape index （SI）, angularity number （AN）, index of aggregate particle shape and texture （IAPST）, porosity and pore size, respectively. The results show that SCR is a porous and rough aggregate. Apparent density, void, water absorption and smashing index of SCR are obviously higher than those of LCR with the same gradation, respectively. However, bulk density of SCR is lower than that of LCR with the same gradation. SI, AN, IAPST and porosity of SCR are obviously higher than those of LCR with the same gradation, respectively. The smaller particle size of SCR, the larger of its AN, IAPST and porosity.

Thermodynamic Simulation of CCP in Air-Cooled Heat Pump Unit with HFCs and CO₂Trans-Critical

The exergy analysis and finite time thermodynamic methods had been employed to analyze the compound condensation process (CCP). It was based on the air-cooling heat pump unit. The cooling capacity of the chiller unit is about 1 kW, and the work refrigerant is R22/R407C/R410A/CO2. The MATLAB/SIMULINK software was employed to build the simulation model. The thermodynamic simulation model is significant for the optimization of parameters of the unit, such as condensation and evaporation temperature and mass flow of the sanitary hot water and size of hot water storage tank. The COP of the CCP of R410A system is about 3% - 5% higher than the CCP of the R22 system, while CCP of the R407C system is a little lower than the CCP of R22 system. And the CCP of CO2 trans-critical system has advantage in the hot supply mode. The simulation method provided a theoretical reference for developing the production of CCP with substitute refrigerant R407C/R410A/CO2.

Effect of Crushed Air-cooled Blast Furnace Slag on Mechanical Properties of Concrete

Morphology characteristics of mix aggregates with crushed air-cooled blast furnace slag（SCR） and crushed limestone（LCR） with 5-20 mm and 20-40 mm gradation were represented by numerical parameters including angularity number（AN） and index of aggregate particle shape and texture（IAPST）.The effect of mix aggregates containing SCR on compressive strength and splitting tensile strength of concrete was investigated.Fracture characteristics of concrete,interfacial structure between aggregates and matrix were analyzed.The experimental results show that porous and rough SCR increases contact area with matrix in concrete,concave holes and micro-pores on the surface of SCR are filled by mortar and hydrated cement paste,which may increase interlocking and mechanical bond between aggregate and matrix in concrete.SCR can be used to produce a high-strength concrete with better mechanical properties than corresponding concrete made with LCR.The increase of AN and IAPST of aggregate may enhance mechanical properties of concrete.

Quantitative analysis of Ni effect on CCT diagrams of novel air-cooled bainite steels using artificial neural network models

The quantitative effect of Ni content on continuous cooling transformation （CCT） diagrams of novel air-cooled bainite steels was analyzed using artificial neural network models. The results showed that Ni may retard the high- and medium-temperature transformation and martensite transformation. The results conform to the materials science theories.

The Experimental Investigation of Recirculation of Air-Cooled System for a Large Power Plant

The paper introduces thermal buoyancy effects to experimental investigation of wind tunnel simulation on direct air-cooled condenser for a large power plant. In order to get thermal flow field of air-cooled tower, PIV experiments are carried out and recirculation ratio of each condition is calculated. Results show that the thermal flow field of the cooling tower has great influence on the recirculation under the cooling tower. Ameliorating the thermal flow field of the cooling tower can reduce the recirculation under the cooling tower and improve the efficiency of air-cooled condenser also.

Influence of thermal flow field of cooling tower on recirculation ratio of a direct air-cooled system for a power plant

In order to get thermal flow field of direct air-cooled system,the hot water was supplied to the model of direct air-cooled condenser(ACC). The particle image velocimetery (PIV) experiments were carried out to get thermal flow field of a ACC under different conditions in low velocity wind tunnel,at the same time,the recirculation ratio at cooling tower was measured,so the relationship between flow field characteristics and recirculation ratio of cooling tower can be discussed. From the results we can see that the flow field configuration around cooling tower has great effects on average recirculation ratio under cooling tower. The eddy formed around cooling tower is a key reason that recirculation produces. The eddy intensity relates to velocity magnitude and direction angle,and the configuration of eddy lies on the geometry size of cooling tower. So changing the flow field configuration around cooling tower reasonably can decrease recirculation ratio under cooling tower,and heat dispel effect of ACC can also be improved.

Water, Air Emissions, and Cost Impacts of Air-Cooled Microturbines for Combined Cooling, Heating, and Power Systems： A Case Study in the Atlanta Region

The increasing pace of urbanization means that cities and global organizations are looking for ways to increase energy efficiency and reduce emissions. Combined cooling, heating, and power （CCHP） systems have the potential to improve the energy generation efficiency of a city or urban region by providing energy for heating, cooling, and electricity simultaneously. The purpose of this study is to estimate the water consumption for energy generation use, carbon dioxide （CO2） and NOx emissions, and economic impact of implementing CCHP systems for five generic building types within the Atlanta metropolitan region, under various operational scenarios following the building thermal （heating and cooling） demands. Operating the CCHP system to follow the hourly thermal demand reduces CO2 emissions for most building types both with and without net metering. The system can be economically beneficial for all building types depending on the price of natural gas, the implementation of net metering, and the cost structure assumed for the CCHP system. The greatest reduction in water consumption for energy production and NOx emissions occurs when there is net metering and when the system is operated to meet the maximum yearly thermal demand, although this scenario also results in an increase in greenhouse gas emissions and, in some cases, cost. CCHP systems are more economical for medium office, large office, and multifamilv residential buildings.

Influence of syngas components and ash particles on the radiative heat transfer in a radiant syngas cooler

Radiant syngas cooler(RSC)is widely used as a waste heat recovery equipment in industrial gasification.In this work,an RSC with radiation screens is established and the impact of gaseous radiative property models,gas components,and ash particles on heat transfer is investigated by the numerical simulation method.Considering the syngas components and the pressure environment of the RSC,a modified weighted-sum-of-gray-gases model was developed.The modified model shows high accuracy in validation.In computational fluid dynamics simulation,the calculated steam production is only 0.63%in error with the industrial data.Compared with Smith's model,the temperature decay along the axial direction calculated by the modified model is faster.Syngas components are of great significance to heat recovery capacity,especially when the absorbing gas fraction is less than 10%.After considering the influence of particles,the outlet temperature and the proportion of radiative heat transfer are less affected,but the difference in steam output reaches 2.7 t·h^(-1).The particle deposition on the wall greatly reduces the heat recovery performance of an RSC.

Analysis of the Erosion-Corrosion Mechanism of the Air Cooler in a Hydrocracking Unit:A Numerical and Experimental Study

Corrosion leakages often occur in the air cooler of a hydrocracking unit,with the failure sites mainly located in the entrance area of the tubes.An analysis of the macroscopic morphology and corrosion products confirmed that the damage was caused by erosion-corrosion(E-C).Numerical and experimental methods were applied to investigate the E-C mechanism in the air cooler.Computational fluid dynamics(CFD)was used to calculate the hydrodynamic parameters of the air cooler.The results showed that there was a biased flow in the air cooler,which led to a significant increase in velocity,turbulent kinetic energy and wall shear within 0.2 m of the tube entrance.A visualization experiment was then performed to determine the principles of migration and transformation of multiphase flow in the air cooler tubes.Various flow patterns(pure droplet flow,mist flow,and annular flow)and their evolutionary processes were clearly depicted experimentally.The initiation mechanism and processes leading to the development of E-C in the air cooler were also determined.This study provided a comprehensive explanation for the E-C failures that occur in air coolers during operation.

Design calculation of porous ceramics tube type dew point indirect evaporative cooler

To improve the wall surface hydrophilicity of a tube type indirect evaporative cooler,a new method adopting porous ceramics is proposed.This method realizes the combination of porous ceramics and the evaporative cooling technique.The design calculation of the porous ceramics tube type dew point indirect evaporative cooler are carried out from such aspects as the volumes and status parameters of the primary and secondary air,the cooler structure,the heat transfer of the solid porous ceramic tubes and the resistance of the cooler.The calculation results show that the design is reasonable.Finally,based on the design calculation,the porous ceramics tube type dew point indirect evaporative cooler is successfully manufactured.

Influence of regenerator flow resistance on stability of pulse tube cooler

Based on the fluid network theory,the possibility of utilizing regenerator flow resistance to suppress the direct current （DC） flow induced by the introduction of a double-inlet in a pulse tube cooler is investigated theoretically. The calculation results show that increasing regenerator flow resistance can lead to a smaller extent of DC flow.Therefore,a better stability performance of the cooler can be realized.On this basis,the stability characteristics of the cooler with various regenerator matrix arrangements are studied by experiments.By replacing 30% space of 247 screens of stainless steel mesh at the cold part of the regenerator by lead balls of 0.25 mm diameter,a long-time stable temperature output at 80 K region is achieved. This achievement provides a new way to obtain stable performance for pulse tube coolers at high temperature and is helpful for its application.

首钢股份360 m^(2)烧结环冷机节能改造及余热烟气超温分析

钢铁企业烧结工序中,环冷机冷却烧结矿的同时,会产生大量高品位余热余能,其中约30%烧结工序总能耗在冷却系统散失,利用好这部分能耗是烧结工序节能降耗的重点。本文通过改造首钢股份有限公司炼铁作业部二烧结415 m^(2)环冷机减少环冷机的漏风,提升烟气温度,增加锅炉产汽量,并针对余热烟气超温等问题进行了研究分析,采取了相应措施,取得了较好的效果。

Effect of sinter layer porosity distribution on flow and temperature fields in a sinter cooler

When sinters are filled into the sinter cooler from the sintering machine, it is commonly seen that, due to segregation effects, sinters of larger size usually accumulate closer to the inner wall of the sinter cooler, whereas those of smaller size are to the outer wall. This nonuniform distribution of sinters has led to uneven cooling effect throughout the cooler. This causes the sinters leaving the cooler at a large temperature difference. This undesired temperature difference leads to the deformation and even the destruction of the conveyors. The computational fluid dynamics （CFD） technique was used in the present work to investigate the heat and fluid flow phenomena within the sinter cooler corresponding to the different distribution of sinter layer porosity, which was highly dependent on the arrangement and orientation of sinters within the sinter cooler. It is confirmed that a high mass flow rate within the sinter layer causes a low temperature region and vice versa. The flow fields for vertically reducing porosity distribution and random distribution are almost identical indicating the relative insignificance of convective heat transfer mechanism.

Designing for Long Campaign Life Blast Furnace (1)──The Mathematical Model of Temperature Field for Blast Furnace Lining and Cooling Apparatus and New Concept of Long Campaignship Blast Furnace Cooler Design

The physical and mathematical model of temperature field for blast furnace stave coolers was established. The computation results show that the heat resistance of 2-6 mm water scale within the cooling pipe is about 7%-20% of the total heat resistance of cooling stave body, as for drilling duct type, the heat resistance of 2-6 mm water scale is about 88%-98% of the total heat resistance. Using drilling duct or full cast pipe can eliminate gas clearance and coating layer between pipes and cast iron body and reduce the heat resistance of the cooler sharply and improve the coefficient of heat transfer to a great extent. The water velocity within coolers can be kept at the 1evel of 0.5- 1 .5 m/s, the higher water velocity can not decrease the hot surface temperature, but can increase energy consumption for cooling water.