螺旋翅片强化定形机热管换热器的空气侧流动与传热性能

以螺旋翅片强化定形机热管换热器为研究对象,使用Fluent软件对空气侧流动与传热过程进行数值计算,对比分析了螺旋翅片管、平直翅片管和光管的传热性能,得到了螺旋翅片厚度、间距、横向管间距对热管管束性能的影响结果。计算分析入口风速为2～8 m/s、翅片间距为3～6 mm、翅片厚度为0.8～1.2 mm、横向管间距为50～90 mm的不同参数组合模型的努塞尔数Nu、欧拉数Eu、综合评价因子j/f。结果表明:新风入口速度增大,Nu与j/f减小,Eu增大,换热器换热性能下降,所受阻力增大,因此入口风速不宜过大;螺旋翅片的强化换热效果最好,综合评价因子j/f比平直翅片、光管提高了9.27%、202.30%;在一定范围内,减小翅片厚度和横向管间距能够提升换热器的换热性能,翅片间距为5 mm时热管管束综合性能最好。     

换热管内置塑料扭带强化传热性能的研究

换热管内置自旋扭带能够起到在线除垢、防垢和强化传热的双重作用,是换热器节能降耗的有效途径之一,但同时也带来了流体阻力的增加。为了综合评价其强化传热特性,将9根不同结构参数的塑料扭带安置到换热管中。比较了不同流速下的流体阻力和换热特性,采用多元线性回归,推导出了实验状态的摩擦阻力系数和努塞尔准数的关联式。并通过性能评价。得到了强化传热准则数φ=1．14～1．33。说明塑料扭带作为强化传热元件具有较高的应用价值。     

纤维干燥余热回收试验装置换热与阻力特性研究

对纤维干燥余热回收试验装置的换热特性与阻力特性进行了研究.研究结果表明,翅片倾角和翅片形状对余热回收换热器的换热特性和阻力损失有着显著的影响.随着翅片倾角的增加,换热器的换热性能下降,阻力损失减少.与常规的螺旋翅片相比,H型翅片热管换热器换热与阻力特性都明显改善.采用H型翅片热管换热器回收纤维干燥尾气余热可以起到较好的效果.     

螺旋扭曲扁管管外传热性能数值模拟

为了研究螺旋扭曲扁管管外强化换热性能,采用周期性边界条件对螺旋扭曲扁管管外层流流动与换热性能进行了数值模拟和理论分析,并且与圆管进行比较。通过建立不同规格的螺旋扭曲扁管换热器几何模型,得出螺旋扭曲扁管的长短轴比a/b越大、螺距s越小,其管外传热性能就越好,强化传热综合性能评价因子就越大,与此同时,其流动阻力也会增大。随着Re数的增大,强化传热综合性能增强,但趋势变缓。该研究结果对螺旋扭曲扁管换热器的设计有一定的参考价值。     

换热管内置直齿扭带的阻力与传热特性研究

为了研究直齿扭带的阻力与传热特性,将12根不同结构参数的扭带分别置入换热管内进行了冷态与热态实验。实验结果表明,直齿扭带的宽度、扭距、齿间距是影响换热系数和阻力系数的主要因素,并由此建立了实验状况下包含各影响因子的阻力系数关联式和换热系数关联式。直齿扭带比光滑扭带的阻力系数增加了约8.3%~35.4%,而努塞尔系数提高13.1%~74.1%。     

三种三角翼纵向涡翅片管换热器流动传热特性对比研究

对三角翼圆形翅片管换热器、三角翼等径长椭圆形翅片管换热器和三角翼等周长椭圆形翅片管换热器的流动传热性能分别进行了数值研究.结果表明:三角翼等周长椭圆形翅片管换热器温度场和速度场分布最为均匀,换热效果最好;三角翼等周长椭圆形翅片管换热器奴塞尔数(Nu)最大,比三角翼圆形翅片管换热器增大2.2%~6.1%,比三角翼等径长椭圆形翅片管换热器增大6.5%~8.3%,比平翅片管换热器增大29.1%~33.5%;从综合传热性能分析,三角翼纵向涡椭圆形翅片管换热器适合于中等及较大雷诺数(Re)工况.     

脉动热管传热性能模拟研究

为了提高脉动热管传热性能,文章对均匀直径脉动热管进行模拟分析。分析了1-3环路脉动热管的压力、液体体积分布、温度等参数。结果表明,均匀直径脉动热管启动时压力分布和液相流动幅度呈轴对称状态。环路数增加有助于快速形成单向循环,增加有效传热时间,而环路数的增加,降低了蒸发段温度突变程度,稳定的温度振荡使其不易达到传热极限。     

带有双倾斜肋片的细通道内液体流动与传热特性

为提高细通道热沉的传热性能,设计了一种内置双倾斜肋片的细通道热沉。通过数值模拟的方法对双倾斜肋片细通道的传热特性、流动特性以及综合性能进行研究。分析了在一定雷诺数范围内细通道的摩擦阻力因数、努塞尔数、综合性能评估值以及总热阻的变化情况。结果表明:在雷诺数较低时肋片长度为1.5 mm的通道综合传热性能最佳,在雷诺数较高时肋片长度为1.0 mm的通道综合传热性能最佳。综上可知加入双倾斜肋片的细通道可以增加传热,并降低总热阻从而有效地提高传热性能。     

新型空心内管换热器

介绍了一种新型空心内管换热器。该换热器的核心结构就是在管壳式换热器换热管束中的每个换热管内。各内置1根封闭的空心内管。在该内管外固定有小螺旋导流叶片．并将内管的一端或两端固定于管板或壳体上。该结构可以改善管内循环状态,提高换热强度。具有该结构形式的换热器,同时具备管壳式换热器结构强度高和板式换热器换热系数高的优点,是综合性能较为优越的换热器形式。     

合成射流冲击凹面换热特性的数值模拟

文章采用数值模拟分析了槽缝合成射流冲击凹圆柱面的流动与传热现象,从槽缝内大尺度涡结构的形成与发展的角度阐明了合成射流外围流场紊乱的原因,进而考察了靶面换热随时间的变化规律,结合流场变化特征解释了靶面有效换热区域平均努塞尔数在周期性变化过程中与入口速度之间存在的相位延迟。     

管排数对球突翅片管式换热器传热特性的影响

通过数值对比研究了不同管排数对球突翅片管式换热器的换热和流动特性的影响.结果表明:随着管排数的增加,热量/压降(Q/ΔP)和COP值逐渐减少,2排管的Q/ΔP和COP值最大.在Re=1 138~3 415范围内,2排管平均Nu数分别比3,4,5排管增大11.1%,21.7%,23.2%.流场图显示,不同管排数均因球突增强了扰动,而强化了换热,但4,5排管的温度场几乎无变化,说明管排数的增加并不能增强换热.综上2排管换热综合性能较好.     

压力条件对不同尺寸条缝喷嘴换热的影响

以条缝喷嘴型的上下冲击式速冻机内部流场为研究对象,利用计算流体力学(Computational Fluid Dynamics,CFD)数值模拟和实地测试,对比了3种尺寸的喷嘴结构分别在不同压力(190,170,160Pa)条件下3种不同尺寸的喷嘴结构,条件下内部流场及换热特性的区别。结果表明:条缝喷嘴T_0在190Pa条件下的出口风速、努塞尔特数、均匀性比在170Pa条件下的理想,同时横流风速也低。条缝喷嘴T_1在170Pa条件下的出口风速、努塞尔特数、均匀性比在160Pa条件下的理想,但横流风速反而增加。条缝喷嘴T_2与T_0在同一入口压力下相比,只有横流风速较低。在换热强度方面,当入口压力为190Pa时,条缝喷嘴T_1所对应的钢带表面的局部努塞尔特数最大,而T_0与T_1的平均努塞尔特数相差不大。在换热均匀度方面,条缝喷嘴T_0在入口压力为190Pa时的不均匀度最低,换热最均匀。故当空气的质量流量相同时,入口压力为190Pa时所对应的条缝喷嘴T_0能更好地提升换热效率,有利于提升食品的冻结速率。     

含芯棒水平换热管冷凝传热数值模拟

为提高蒸汽换热器换热效率,提出了一种在水平换热管中插入芯棒的含芯棒蒸汽换热管结构,并通过采用Fluent中两相流模型分析了该结构中芯棒直径对换热管管内冷凝换热特性的影响规律。研究结果表明,由于芯棒的插入使得管内两相流流体的平均流速与管道壁面附近速度梯度增大,故换热管的换热效率得到有效提升;定量而言,换热管的换热效率在棒径比值处于0.52~0.57区间范围内时,换热管内蒸汽冷凝率最高及通流截面内速度梯度最大,此时换热效率达到最高,可确保较低的换热管出口温度和稳定的换热效率。此外,场协同性能分析结果还表明,协同角与棒径比值?呈正相关性,且当棒径比值?>0.52后,芯棒对水平换热管的强化传热效果明显。     

Convective Heat Transfer at Particle-Liquid Interface in Continuous Tube Flow at Elevated Fluid Temperatures

Liquid-to-particle convective heat transfer coefficients are useful in developing aseptic food processing systems. They were determined for continuous flow through a holding tube at 115.5°C using liquid crystal and relative velocity methods with sodium carboxymethylcellulose solution to simulate non-Newtonian fluid characteristics. An on-line tube viscometer was used for in situ estimation of rheological characteristics. Minimum and maximum values of h_fp determined from the liquid crystal method ranged from 986 W/m²⁰K to 2270 W/m²⁰K, (Nusselt numbers from 26.4 to 54.6). Values from the relative velocity method ranged from 1143 to 2270 W/m²⁰K (Nusselt numbers from 33.2 to 63.1) when using the Ranz and Marshall relation, and from 598 to 1456 W/m²⁰C (Nusselt numbers from 13.6 to 24.1) with a flat-plate correlation. Heat transfer coefficients increased significantly with decreasing carrier medium viscosity and decreasing particle-to-tube diameter ratio and increased with flow rate.     

FLUID to PARTICLE CONVECTIVE HEAT TRANSFER COEFFICIENT IN A HORIZONTAL SCRAPED SURFACE HEAT EXCHANGER DETERMINED FROM RELATIVE VELOCITY MEASUREMENT1

Liquid-to-particle convective heat transfer coefficient (h_fp) between fluid and particle was investigated in continuous flow through a horizontal scraped surface heat exchanger. the relative velocities between fluid and particle were measured, and h_fp calculated from well known correlations. Heat transfer coefficients increased with increasing flow rate, rotational speed, and decreased with increasing carrier medium viscosity and particle size. the measured relative velocities during flow visualization studies ranged from 0.04 to 0.29 m/s with corresponding h_fp values of 597 W/m²°K and 1975 W/m²°K, respectively. Even with the most conservative correlation, Nusselt numbers ranged from 12.1 to 49.7; significantly greater than the value of 2.0 for a sphere in a stagnant fluid.     

管壳式换热器强化传热的数值模拟分析

阐述了换热器管程强化传热强化管和管内插入物两种结构及其性能特点 ,并用场协同原理和数值模拟方法分析了其强化传热机理。模拟分析的结果为 :光滑管内速度矢量与温度矢量两者之间的夹角接近 90° ,传热效果较差 ;在管内插入物情况下 ,两者之间的夹角小于 90° ,流场和温度场的协同性更好 ,从而实现了强化传热     

Heating Rates of Peach Juice in an Agitated Jacketed Vessel

Heat transfer characteristics were studied on clarified depectinized peach juices heated in an agitated jacketed vessel. Four types of agitators and several agitation rates were analyzed. Two equations were derived for the density and rheological behavior of peach juice based on the combined effects of temperature and soluble solids content. Overall and internal heat transfer coefficients were also determined. For each agitator, Nusselt number was statistically correlated as a function of the Reynolds and Prandtl numbers, and as the ratio of the fluid viscosity at the bulk temperature to the fluid viscosity at the wall temperature. The power number also correlated with the Reynolds, Froude, and time numbers.     

A new arrangement of blades in scraped surface heat exchangers for food pastes

The present study analyses the performance of a scraped surface heat exchanger (SSHE) equipped with a new arrangement of blades to achieve higher thermal efficiencies than the conventional SSHE. This new design of exchanger, named here as scraped surface heat exchanger with alternate blades, A-SSHE, may be particularly suited to treat high viscous fluids, like food pastes. Experimental and numerical tests were carried out on an industrial scale A-SSHE used to heat hazelnut paste, an intermediate product widely used in Italian confectionery industry. Experimental tests include physical, chemical and rheological characterization of the hazelnut paste and the evaluation of the overall heat transfer coefficient as a function of rotational speeds and mass flow rates. Three-dimensional axial-symmetric CFD simulations of the A-SSHE were performed by using the software Fluent 6.2. For comparison, the same numerical tests were carried out for an equivalent SSHE with a conventional blades design (C-SSHE). Our studies show that the A-SSHE gives heat transfer coefficient values almost twice that of an equivalent C-SSHE, and that the numerical results are consistent with the experimental observations. The analysis of the fluid dynamics and of the thermal profiles suggests that the higher heat transfer efficiency of A-SSHE may be attributed to the occurrence of backmixing phenomena.     

逆流式三套管换热器的传热计算

三重套管换热器适用于食品、化学等行业冷却（加热）工作介质,并兼作输送管路.本文根据传热基本方程推导纯逆流传热套管的总传热系数,沿传热管长度的流体轴向温度分布,模拟二重套管的对数平均温差和有效总传热系数以便于工程设计计算.     

HEAT TRANSFER IN A VERTICAL, LIQUID-FULL SCRAPED-SURFACE HEAT EXCHANGER. APPLICATION OF THE PENETRATION THEORY AND WILSON PLOTS MODELS

Heat transfer characteristics of a scraped-surface heat exchanger (Contherm Model 6 × 2) were evaluated at ultra high temperatures using water and soybean water extracts as model systems. The resistance equation was used to calculate internal (scraped-side) heat transfer coefficients (h_i) from the overall heat transfer coefficient, the wall coefficient and the external (steam-side) coefficient (calculated from the Nusselt Theory using an iteration procedure). The Penetration Theory of Harriot (1958) predicted h_i values quite well at low axial mass flow rates, where laminar flow conditions prevail. However, turbulent axial flow resulted in experimental higreater than predicted by the theory. A correction factor based on Prandtl number suggested by Trommelen et al. (1971) did not improve the prediction. The Wilson Plots method was useful for explicitly accounting for axial and rotational velocity effects, both of which significantly affected heat transfer, especially at high values of either variable.