Fin formation model during pre-roll ploughing of copper 3D outside fin tube

The mechanism of pre roll ploughing for 3D fins on the outside surface of copper tube was studied systematically, and especially the process and conditions of 3D fin formation were analyzed. The right mathematical model was also established. Based on the volume of fin ploughed out is equal to the volume of the metal extruded up by the extruding face of the tool, the relations between fin height, pre roll ploughing feed and pre roll ploughing depth have been achieved. With the increase of pre roll ploughing depth which must be equal to groove depth, the fin height gradually becomes larger. There are different critical feeds with the various depths of pre roll ploughing. The pre roll ploughing feed is the critical one, the height of fin is largest. And when the feed is above the critical one, the fin height will reduce with the increase of feed. The theoretical analysis basically accords with experimental results.

Experimental Research on Resistance Characteristics of H-type Elliptical Finned Tube Bundles

阻力特性是换热器的基本特性之一，流体横掠换热管产生的绕流扰动是换热器阻力恶化的主要因素。为分析前排绕流对后排阻力的影响规律，分别对管排数2-10不等的换热管进行阻力特性试验研究，同时为定量分析管排数对阻力特性的影响规律，定义了管排阻力修正系数，并根据实验数据给出了其在不同管排数下的取值，具有重要的工程意义；同时基于冷态阻力特性试验台进行实验研究，得到κ=1及κ=1.6的经典椭圆管的阻力特性公式Eu，并研究不同管型及布置方式对其的影响规律。

多通道平行流扁管-紧凑式翅片相变蓄热器蓄/放热性能

工业余热浪费严重、利用率较低且实际应用过程中受到时间和空间的限制,需要高效蓄热技术和装置来解决此类问题。提出一种将多通道平行流扁管与紧凑式翅片相结合的新型相变蓄热器,以水为载热流体,月桂酸为相变材料。实验研究了载热流体注入方式、流量、入口温度对蓄热器蓄/放热性能的影响,并分析小温差下蓄热器的传热特性。结果显示,该蓄热器相变材料填充率为82.5%,紧凑式翅片的采用极大强化了相变材料侧换热过程,蓄/放热性能优良。当载热流体入口温度分别为45℃和41℃时,相变材料约在270 min和75 min完成相变,最小蓄/放热温差可达2℃,最小温差时的平均蓄热比功率为25.18 W/kg,平均取热比功率为20.23 W/kg。

Heat transfer simulation of annular elliptical fin-and-tube heat exchanger by transition SST model

In this study,thermo-fluid characteristics of elliptical annular finned tube heat exchanger were numerically studied in detail.Transition SST model was utilized to simulate turbulent flow.Effects of air velocities,horizontal to vertical fin diameter ratios,and fin densities were examined in detail.The simulations indicate superior performance of elliptical fin layout.It was shown that pressure drop of annular elliptical fin can be only one half of that of a circular annular fin while containing comparable heat transfer performance.The vertical elliptical annular fin may even contain a higher heat transfer performance over circular fin.Correlations are proposed to estimate the Nu number and pressure drop based on the annular circular fin.The maximum deviations between the proposed correlations and simulations regarding pressure drop and heat transfer coefficient are 5.6%and 3.2%,respectively.For further elaboration of the superiority of the elliptical layout from the second law perspective,normalized entropy generation was also studied.In all cases,the entropy generation rate in circular fin was higher than that of an elliptical fin.

Analysis of Thermal Conductivity of Frost on Cryogenic Finned-tube Vaporizer Using Fractal Method

Thermal conductivity of frost is not only related to density, but also affected by its microstructure and environmental conditions, and it will continuously change with the formation and growth of frost. Images of frost formation and growth on the cryogenic surface in various shapes at different stages were obtained by experimental measurements, and a numerical simulation of frost formation and growth was carried out based on Diffusion Limited Aggregation (DLA) model of fractal theory in this paper. Based on the frost structure obtained by experiment, the fractal dimension of pore area distribution and porosity of frost layer on the cryogenic finned-tube?vaporizer were calculated by using fractal method, and combined with heat conduction model of frost layer obtained by thermal resistance method, the thermal conductivity of frost on the cryogenic surface was calculated. The result shows that the thermal conductivity calculated by the fractal model coincides with the range of the experimental data. Additionally, comparison with other heat conduction models indicated that it is feasible to introduce the fractal dimension of pore area distribution into heat conduction model to deduce the thermal conductivity of frost.

燃气-蒸汽联合循环机组余热锅炉尾部受热面锈蚀对烟道阻力的影响

在某燃气 蒸汽联合循环机组长期停机备用期间,针对其余热锅炉尾部受热面开齿螺旋鳍片管锈蚀导致烟气流动阻力升高,影响燃气轮机带负荷的问题,通过现场数据监测、数值模拟及小型试验台试验,研究鳍片管表面锈蚀状态对流动阻力特性的影响。结果表明:余热锅炉尾部模块5、模块6的阻力上升明显;鳍片管背风侧的锈蚀堆积不会导致流动阻力的上升,两侧锈蚀厚度增加是流动阻力上升的主要原因;鳍片管除锈后鳍片减薄,流通截面积增大,阻力特性优于新鳍片管。

椭圆型套管-管翅式蒸发式冷凝器传热传质性能及实验研究

介绍了一种椭圆型套管-管翅式蒸发式冷凝器,通过搭建的蒸发式冷凝器性能测试实验系统,研究该蒸发式冷凝器在不同循环水配比、不同地区环境以及“风冷”“水冷”“蒸发冷凝”和“全工况”4种不同运行模式下的传热传质性能与运行特性的变化规律。结果表明:在相同条件下“全工况”模式的热流密度高于“风冷”和“蒸发冷凝”两种模式,而“水冷”模式由于其传热面积远小于其它模式,所以其热流密度最高;“全工况”模式在保持配风量及循环水总量一定的条件下,热流密度随循环水配比的增大而先增大后减小,喷淋水与冷却水的流量最佳配比为2∶5;“全工况”模式在严寒干燥地区、寒冷地区以及夏热冬暖地区的总热流密度分别为5879.64、3964.28及2933.05 W/m^(2),因此不同地区环境运行的传热性能相差较大,该冷凝器“全工况”模式在空气干燥的地区,喷淋冷却水温度范围为13~18℃运行时传热性能较优。在相同的条件下,“蒸发冷凝”模式的水膜传质系数高于“全工况”模式,且两者均随喷淋密度的增大先增大后减小。

Surface treatment of 3D outside serrated integral-fin tube manufactured by rolling and extrusion

The outside serrated integral-fin tubes fabricated by rolling-plowing-extrusion processing were surface-treated through different processes of annealing in hydrogen atmosphere,electrochemical corrosion or sandblasting.The purpose was to eliminate residual stress,clear secondary micro-fins and enhance heat transfer performance.By comparing the surface characteristics,it is found that the finned tubes treated by electrochemical corrosion have the most glabrous surfaces where the fins are almost perfectly reserved.Clear layer cracks can be observed on the top of the fins.These structures are effective in enhancing heat transfer performance when being applied to flow heat exchange.Therefore,the finned tubes treated by electrochemical corrosion are proper for the tubular exchanger with water coolant.The finned tubes treated by sandblasting have rougher surfaces with layer cracks and micro gaps removed.As these structures are useful to clearing adhesive feculence,the tubes are more suitable for the tubular heat exchanger with oil coolant.

Compound forming technology of outside 3D integral fin of copper tubes

Using rolling-ploughing-extrusion compound processing methods,a 3D integral-fin structure on outside surface of red copper tube with diameter of 16.0 mm and wall thickness of 1.5 mm was obtained. When both rolling depth and ploughing-extrusion(P-E) depth were 0.2 mm,rotating speed was 50 r/min,feed speed was 0.16 mm/r,3D fin structures with height of 0.25 mm were gotten. Two different fin structures were obtained in grooves formed with rolling-ploughing-extrusion compound forming technology and observed by scanning electron microscope(SEM). One is the compound structure with V-shaped groove and U-shaped groove,and the other is the single structure with V-shaped grooves. Two kinds of groove structures obtained by rolling processing and ploughing extrusion processing are restricted together by groove interval and rolling depth,and pitch and P-E depth,respectively. Based on the analysis of interaction of rolling and P-E processing,it is found from the result that the outside 3D integral-fin can be achieved by rolling-ploughing-extrusion compound processing when single V-shaped groove structures are formed by both rolling and P-E processing.

Parametric study of natural convection over horizontal annular finned tube

Natural convection heat transfer from annular finned tubes was studied numerically. Effects of fin spacing, temperature difference and tube diameter on flow pathlines and local heat transfer were also studied. It was shown that pathlines remain mostly circular for different geometries. Moreover, the contributions of fin periphery, fin side and bare tube to heat transfer were specified. It was shown that the heat transfer per unit area of fin periphery can be several times that of other parts. Moreover, in higher finspacing, the heat transfer from the bare tube can be more important than fin sides.

Forming mechanism of integral serrated high fins by plowing-extruding based on variational feed

Plowing-extruding tool was designed and plowing-extruding process was investigated.Then,a manufacturing method of integral serrated high-finned tube,plowing-extruding based on variational feed was proposed,in which plowing-extruding tool moved forward at two different feeds,f1 and f2,in turn.In this method,overlaps that are usually avoided in practical application were utilized to manufacture high fins and average height of fins was up to 1.58 mm.The critical feed(fc) of overlaps forming and terms of high fins forming were analyzed.The main technical parameters that affect the fins height were discussed.The experimental results show that the fins height increases with extruding inclination angle and plowing-extruding depth,and the fins height increases with f1 increasing when f1 is smaller than fc,and decreases with f1 increasing if f1 is larger than fc.

Deformation behaviors of 21-6-9 stainless steel tube numerical control bending under different friction conditions

For contact dominated numerical control(NC) bending process of tube, the effect of friction on bending deformation behaviors should be focused on to achieve precision bending forming. A three dimensional(3D) elastic-plastic finite element(FE) model of NC bending process was established under ABAQUS/Explicit platform, and its reliability was validated by the experiment. Then, numerical study on bending deformation behaviors under different frictions between tube and various dies was explored from multiple aspects such as wrinkling, wall thickness change and cross section deformation. The results show that the large friction of wiper die-tube reduces the wrinkling wave ratio η and cross section deformation degree ΔD and increases the wall thinning degree Δt. The large friction of mandrel-tube causes large η, Δt and ΔD, and the onset of wrinkling near clamp die. The large friction of pressure die-tube reduces Δt and ΔD, and the friction on this interface has little effect on η. The large friction of bending die-tube reduces η and ΔD, and the friction on this interface has little effect on Δt. The reasonable friction coefficients on wiper die-tube, mandrel-tube, pressure die-tube and bending die-tube of 21-6-9(0Cr21Ni6Mn9N) stainless steel tube in NC bending are 0.05-0.15, 0.05-0.15, 0.25-0.35 and 0.25-0.35, respectively. The results can provide a guideline for applying the friction conditions to establish the robust bending environment for stable and precise bending deformation of tube bending.

内肋-光滑组合式圆管内流动沸腾换热试验

为探究分段结构对管内流动沸腾过程的影响,采用试验方法分析了制冷剂R245fa在光滑管、内肋管以及采用前肋-后光滑组合管中的流动沸腾换热特性。以质量流速为100~350 kg/(m^(2)·s)、热流密度为9.36~55.84 kW/m^(2)、试验管进口过冷度约为2℃进行试验,并以光滑管的流动换热特性为基准,对比不同试验管的换热系数增强比例(enhancement factor,EF)和价值因子(merit factor,MF)。研究结果表明:内肋管和前肋-后光滑组合管的换热性能均优于全光滑管;在低质量流速时,内肋管的EF高于前肋-后光滑组合管,即内肋管换热效果更好;而随着质量流速的增加,前肋-后光滑组合管的EF逐渐高于内肋管,达到1.7左右;内肋管的MF在低质量流速时高于前肋-后光滑组合管,但在较高质量流速以及较高热流密度条件下,前肋-后光滑组合管的MF要高于内肋管,即前肋-后光滑组合管的综合性能更好。

A Numerical Study on Fully Developed Fluid Flow and Heat Transfer in a Spiral Finned Tube

In this paper, the standard k-ε two-equation model is adopted to numerically simulate fully developed fluid flow and heat transfer in a spiral finned tube within a cracking furnace for ethylene manufacturing. By variable transformation, the original 3-D problem is converted into a 2-D problem in spiral coordinates. The algorithm of SIMPLEC is used to study the fully developed fluid flow and heat transfer in the spiral finned tube at constant periphery temperature and constant axial heat flux. The computed results agree pretty well with the experimental data obtained from the industry. Further studies on the fluid flows and temperature profiles at different Reynolds numbers within straight and spiral finned tubes are conducted and the mechanisms involved are explored. It is found that with the spiral finned tube, pressure drop increases to a great extent whereas heat transfer tends to be decreased.

Air-flow Analysis for BCF Texturing Tube

In this paper,the Reynolds number,velocity,pressureand kinetic energy of the BCF processing hot air-floware analyzed with the help of the aero-dynamic theory,and their distributions inside the texturing tube are ob-tained by pressure measuring.

基于NSGA-III算法的小管径翅片管式蒸发器高维多目标优化

以稳态分布参数法和NSGA-III算法为基础,提出一种翅片管式蒸发器结构参数与流路参数混合寻优的方法,并依此展开小管径蒸发器结构和流路参数的影响分析与流路的高维多目标设计优化。建立的小管径翅片管式蒸发器模型与实测数据的误差在4%以内,可以较好地用于小管径翅片管式蒸发器的计算。基于该模型进一步建立以结构参数与流路参数为自变量,换热量、制冷剂侧压降、空气侧压降以及成本为因变量的神经网络模型,并利用NSGA-III算法对模型进行优化求解,得到小管径翅片管式蒸发器在一定的结构参数变化范围内的最优结构参数及最佳流路。研究结果显示:管外径对小管径翅片管式蒸发器的换热量、制冷剂侧压降以及成本的影响程度最大;翅片间距对小管径翅片管式蒸发器的空气侧压降影响程度最大;翅片厚度对换热量、制冷剂侧压降、空气侧压降以及成本的影响程度均最小;流路主要影响蒸发器的换热量及制冷剂侧压降;制冷剂流路为二支路、三支路和四支路时,模型可输出综合性能最优的结构及流路特征。

SA-192高频焊翅片管漏水原因

某SA-192高频焊翅片管发生漏水,采用宏观观察、尺寸测量、化学成分分析、金相检验、扫描电镜和能谱分析、硬度测试等方法对其漏水原因进行分析。结果表明:漏水的主要原因是焊接时高频电流集中在钢管表面,输入功率大而焊接速率小,造成表面局部受热严重,出现过烧缺陷;过烧缺陷导致钢管表面堆积大量焊渣,降低了基体材料的塑性和韧性,促使表面凹坑和孔洞的形成。

Decoupled thermal–hydraulic analysis of an air-cooled separated heat pipe for spent fuel pools under natural convection

An investigation of the decoupled thermal–hydraulic analysis of a separated heat pipe spent fuel pool passive cooling system(SFS)is essential for practical engineering applications.Based on the principles of thermal and mass balance,this study decoupled the heat transfer processes in the SFS.In accordance with the decoupling conditions,we modeled the spent fuel pool of the CAP1400 pressurized water reactor in Weihai and used computational fluid dynamics to explore the heat dissipation capacity of the SFS under different air temperatures and wind speeds.The results show that the air-cooled separated heat pipe radiator achieved optimal performance at an air temperature of 10℃ or wind speed of 8 m/s.Fitted equations for the equivalent thermal conductivity of the separated heat pipes with the wind speed and air temperature we obtained according to the thermal resistance network model.This study is instructive for the actual operation of an SFS.

强制对流下翅片管蒸发器表面结霜实验

翅片管蒸发器表面结霜是阻碍制冷系统高效运行的主要不利因素之一。利用恒温恒湿箱搭建强制对流下蒸发器翅片管表面结霜可视化实验平台,在环境温度0~8℃、相对湿度55%~75%及迎面风速0.8~2.4 m/s时,实时记录霜层动态生长过程,研究了环境温度、相对湿度和迎面风速对霜层生长特性及蒸发器换热性能的影响规律。结果表明:环境温度和迎面风速是影响蒸发器结霜的主要因素,结霜50 min,环境温度为0℃的霜层厚度比环境温度为8℃的提高了12.78%,迎面风速为2.4 m/s的霜层厚度比迎面风速为0.8 m/s的提高了14.66%,结霜量与换热量提高趋势相同。在结霜初期,相对湿度越大,换热量越大;结霜后期,相对湿度越小,换热量越大,并得到了换热量关于环境参数与时间的相关关系。