套管式CO_2蒸发器的优化设计计算

为了设计出结构紧凑、具有更好换热性能的CO_2蒸发器,本文建立了套管式CO_2蒸发器的计算模型,论述了套管式换热器的计算方法和步骤,并最终确定了套管式换热器的结构尺寸和型式。结果表明:传热系数随管束内径的增大先增大后减小,CO_2侧压降随管束内径的增大而减小;管束个数增加,换热系数和CO_2侧压降都减小。研究成果可为今后套管式CO_2蒸发器的优化设计提供理论依据。     

铜翅片管热水器的特性研究

以铜翅片管换热器为研究对象,通过合理的简化模型,以相邻2片换热片(取半片)及其之间的烟气通道作为计算区域,利用流体力学软件CFX对烟气通道的流动状况和换热情况进行了数值模拟。研究了管径、翅片厚度和翅片间距对排烟温度的影响,结果表明随着管径和翅片间距的增大排烟温度升高,随着翅片厚度增大排烟温度降低,排烟温度的升高或降低将影响排烟损失的大小,从而影响热效率。该数值模拟结果对改进翅片结构以提高热效率有一定指导意义。     

单流程蒸发器表面温度场均匀性的影响因素研究

改善蒸发器表面温度场的均匀性对提高其换热效率具有决定性作用。设计出一种类似平行流蒸发器的圆管单流程蒸发器,改变其集液管和蒸发管衔接处的孔径大小以及制冷剂入口流速,并进行了蒸发器管路的水力计算和相应的实验研究,得出管路中间截面的温度分布。模拟结果表明:在结构一定的条件下,集液管内的制冷剂来流速度具有决定性作用。当集液管内的来流速度在0.04m/s时,蒸发器各支管的温度分布最为均匀;同时在制冷剂流量一定时,支管数及各蒸发管与集液管衔接处的孔径大小也影响着温度分布。试验结果证明了此结论:在一定的液态制冷剂集管入口流速下,最小孔径为0.4mm时,具有8根支管的单流程蒸发器比10根支管的单流程蒸发器具有均匀的温度场。研究结果为研发高效率的平行流蒸发器提供了一定的理论和试验基础。     

再循环重力供液制冷系统换热性能可视化研究

建立了再循环重力供液制冷系统可视化试验台,在不同工况下对制冷系统进行实验研究,观察玻璃蒸发管内制冷剂的沸腾换热流动状态,研究分析重力供液蒸发器的传热特性。试验表明:再循环重力供液蒸发器内,制冷剂的沸腾换热出现了气泡流、气塞流、气弹流、分层流、波状分层流等流型。通过编程计算得到,经过修正的J.Chawla关联式和Kandlikar关系式分别在低温及高温工况下对沸腾换热系数有较好的预测,计算结果与试验值的偏差均在12.5%以内,采用两种关联式相结合的方法能较好地对重力供液蒸发器管内沸腾换热进行预测。     

R290家用空调制热特性研究

出于安全的考虑,R290应用于家用空调,充注量会受到限制,由此对制热量产生了不利的影响。本文以直流变频热泵空调为测试样机充注R290制冷剂,通过调整换热器的翅片宽度和内螺纹铜管管径大小,研究制热量的变化。研究发现改变换热器的翅片宽度影响较小,但将蒸发器的内螺纹铜管的管径从7mm减小到5mm,制热量可提升约3%。     

CFD analysis of fin tube heat exchanger with a pair of delta winglet vortex generators

Among tubular heat exchangers, fin-tube types are the most widely used in refrigeration and air-conditioning equipment. Efforts to enhance the performance of these heat exchangers included variations in the fin shape from a plain fin to a slit and louver type. In the context of heat transfer augmentation, the performance of vortex generators has also been investigated. Delta winglet vortex generators have recently attracted research interest, partly due to experimental data showing that their addition to fin-tube heat exchangers considerably reduces pressure loss at heat transfer capacity of nearly the same level. The efficiency of the delta winglet vortex generators widely varies depending on their size and shape, as well as the locations where they are implemented. In this paper, the flow field around delta winglet vortex generators in a common flow up arrangement was analyzed in terms of flow characteristics and heat transfer using computational fluid dynamics methods. Flow mixing due to vortices and delayed separation due to acceleration influence the overall fin performance. The fin with delta winglet vortex generators exhibited a pressure loss lower than that of a plain fin, and the heat transfer performance was enhanced at high air velocity or Reynolds number.     

R410A在内螺纹强化管管内冷凝的传热性能试验研究

为了研究水平强化单管的管内冷凝性能,搭建了实验台。研究了在冷却水量不变的情况下,R410A在不同冷凝温度(35℃和40℃)和不同管径(5mm和9.52mm)下的换热情况。结果表明:总换热系数和压降随工质质量流量的增大而增大,质量流量对管内换热系数影响不是很大。冷凝温度40℃,5mm铜管的换热系数最高;冷凝温度40℃,9.52mm铜管的压降最小。     

螺旋折流板管壳式换热器的传热计算及连接结构改进

利用不同规格螺旋折流板换热器试验设备所得传热数据,推导出传热系数的变化规律,确定出不同角度的折流板传热修正系数。将修正系数引入传热计算公式中,解决了螺旋折流板换热器的传热计算问题,改进了传统换热器总传热系数低、壳程存在流动死区、所需换热面积大等不良因素。此外,对换热管与管板连接结构进行了优化,可降低设备泄漏质量事故的发生。     

Investigation of boiling heat transfer characteristics of two-phase closed thermosyphons with various internal grooves

The boiling heat transfer characteristics of two-phase closed thermosyphons with internal grooves are studied experimentally and a simple mathematical model is developed to predict the performance of such thermosyphons. The study focuses on the boiling heat transfer characteristics of a two-phase closed thermosyphons with copper tubes having 50, 60, 70, 80, 90 internal grooves. A two-phase closed thermosyphon with plain copper tube having the same inner and outer diameter as those of grooved tube is also tested for comparison. Methanol is used as working fluid. The effects of the number of grooves, the operating temperature, the heat flux are investigated experimentally. From these experimental results, a simple mathematical model is developed. In the present model, boiling of liquid pool in the evaporator is considered for the heat transfer mechanism of the thermosyphon. And also the effects of the number of grooves, the operating temperature, the heat flux are brought into consideration. A good agreement between the boiling heat transfer coefficient of the thermosyphon estimated from experimental results and the predictions from the present mathematical model is obtained. The experimental results show that the number of grooves and the amount of the working fluid are very important factors for the operation of thermosyphons. The two-phase closed thermosyphon with copper tubes having 60 internal grooves shows the best boiling heat transfer performance.     

高效节能钢带式果蔬绿色干燥装备翅片管换热器的传热计算

翅片管换热器是高效节能钢带式果蔬绿色干燥装备的供热装置,通过对翅片管换热器的翅化比、对流换热系数、传热系数及阻力的计算,得到了翅片管换热器的压降及翅片管的管数,计算结果表明翅片管换热器换热能力强,传热系数高。     

Efficiency analysis of straight fin with variable heat transfer coefficient and thermal conductivity

In this study, one type of applicable analytical method, differential transformation method (DTM), is used to evaluate the efficiency and behavior of a straight fin with variable thermal conductivity and heat transfer coefficient. Fins are widely used to enhance heat transfer between primary surface and the environment in many industrial applications. The performance of such a surface is significantly affected by variable thermal conductivity and heat transfer coefficient, particularly for large temperature differences. General heat transfer equation related to the fin is derived and dimensionalized. The concept of differential transformation is briefly introduced, and then this method is employed to derive solutions of nonlinear equations. Results are evaluated for several cases such as: laminar film boiling or condensation, forced convection, laminar natural convection, turbulent natural convection, nucleate boiling, and radiation. The obtained results from DTM are compared with the numerical solution to verify the accuracy of the proposed method. The effects of design parameters on temperature and efficiency are evaluated by some figures. The major aim of the present study, which is exclusive for this article, is to find the effect of the modes of heat transfer on fin efficiency. It has been shown that for radiation heat transfer, thermal efficiency reaches its maximum value.     

冷库用空气冷却器的经济性计算模型

为了优化结霜工况下翅片管式空气冷却器的结构设计,提出经济性分析计算模型。综合考虑换热性能、材料成本及运行费用,以单位制冷量的费用年值为目标函数,以费用年值最小为优化目标求解经济模型得到合理的空气冷却器的结构参数,分析了翅片间距、换热管管径、管排数变化对目标函数的影响,并通过一冷库案例进行实际测试验证。计算及试验结果表明:随着翅片间距的增大,目标函数先减小后增大,翅片间距为10时目标函数取极小值;在相同翅片间距的情况下管径越大,其目标函数值也越大;综合考虑换热管直径、翅片间距和管排数的影响,翅片间距为10,换热管外径为9.52,管排数为6时,目标函数取极小值。     

Thermal performance analysis of heat exchanger for closed wet cooling tower using heat and mass transfer analogy

In closed wet cooling towers, the heat transfer between the air and external tube surfaces can be composed of the sensible heat transfer and the latent heat transfer. The heat transfer coefficient can be obtained from the equation for external heat transfer of tube banks. According to experimental data, the mass transfer coefficient was affected by the air velocity and spray water flow rate. This study provides the correlation equation for mass transfer coefficient based on the analogy of the heat and mass transfer and the experimental data. The results from this correlation equation showed fairly good agreement with experimental data. The cooling capacity and thermal efficiency of the closed wet cooling tower were calculated from the correlation equation to analyze the performance of heat exchanger for the tower.     

Effect on boiling heat transfer of horizontal smooth minichannel for R-410A and R-407C

An experimental study of boiling heat transfer with refrigerants R-410A and R-407C is presented. The present paper is focused on pressure drop and boiling heat transfer coefficient of the refrigerants inside a horizontal smooth minichannel. To evaluate the diameter size effect on pressure and heat transfer characteristics, minichannels with inner diameters of 1.5 mm and 3.0 mm and with lengths of 1500 mm and 3000 mm respectively are used. The pressure drop increases with mass flux and heat flux for both inner tube diameters and for both the refrigerants. The pressure drop of R-407C is higher than that of R-410A, but the heat transfer coefficient of R-410A is higher than of R-407C at the low quality region. The heat transfer coefficient in the tube with an inner diameter of 1.5 mm is higher than that of 3.0 mm diameter tube at the low quality region. The comparison of present heat transfer coefficient with the predictions of some previous correlations shows a large deviation. Therefore, there is a necessity to develop a new correlation.     

板式蒸发器的工业应用概述

板式蒸发器是一种新型高效节能设备,具有传热系数高、结构紧凑等特点,广泛应用于冶金、食品、造纸、空调制冷以及化工等行业.本文介绍了板式蒸发器在各行业中的应用,对其使用过程中存在的问题进行了总结.同时,对板式蒸发器的前景进行了展望.     

Application of thermosyphon air-preheater for energy thrift from a furnace in a hot forging process

This research studied the heat transfer of the thermosyphon air-preheater. An empirical model was developed to predict heat transfer and applied to compute the thermosyphon air-preheater in a hot brass forging process. The thermosyphon air-preheater was designed, constructed and tested under medium temperature operating conditions with inlet hot gases, ranging between 390–440 °C in terms of using water as the working fluid with a 50 % fill by volume of the evaporator section. The experimental setup was comprised of a circular fin with 0.013 and 0.020 m internal diameter bare stainless steel tubes, with 0.015 m long evaporator and condenser sections. The thermosyphon air-preheater model had 6 rows, each composed of 4 columns. Experimental results found that the hot gas temperature was increased from 390 to 440 °C, the heat transfer rate increased. If the internal diameter changed from 0.013 to 0.020 m, the heat transfer rate slightly increased. The predicted results agreed well with the experimental data. This thermosyphon air-preheater has been designed, manufactured and tested for heat recovery in industry using medium temperatures ranging between 300-500 °C to recover flue gas energy from the furnace in a hot brass forging process.     

Some aspects of experimental in-tube evaporation

The heat transfer characteristics of refrigerant-oil mixture for horizontal in-tube evaporator have been investigated experimentally. A smooth copper tube and a micro-fin tube with nominal 9.5 mm outer diameter and 1500 mm length were tested. For the pure refrigerant flow, the dependence of the axial heat transfer coefficient on quality was weak in the smooth tube, but in the micro-fin tube, the coefficients were 3 to 10 times greater as quality increases. Oil addition to pure refrigerant in the smooth tube altered the flow pattern dramatically at low mass fluxes, with a resultant enhancement of the wetting area by vigorous foaming. The heat transfer coefficients of the mixture for low and medium qualities were increased at low mass fluxes. In the micro-fin tube, however, the addition of oil deteriorates the local heat transfer performance for most of the quality range, except for low quality. The micro-fin tube consequently loses its advantage of high heat transfer performance for an oil fraction of 5%. Results are presented as plots of local heat transfer coefficient versus quality.     

平直翅片热管散热器的正交数值模拟优化

文中以平直翅片热管散热器为研究对象,研究了翅片厚度、翅片间距、翅片高度、翅片宽度和热管直径 5 个结构参数对翅片换热性能和阻力特性的影响,采用正交实验设计的方法设计了上述结构参数的 15 个组合方案,利用 CFD 数值模拟的方法对每个组合方案下翅片的流动换热性能进行了模拟。以努塞尔数 Nu 、阻力系数f、传热性能综合评价指标(Performance Evaluation Criteria, PEC)作为评价指标,在每个评价指标下利用极差分析挑选出性能最优的组合方案。 该方法能快速获得散热器结构的优化方案,并分析出主要影响因素,对工程应用有一定的指导意义。 结果表明:影响 Nu 和 f 的最主要因素是热管直径,影响 PEC 的最主要因素是翅片厚度。 对于本文研究的散热器,其最优参数组合方案为:翅片厚度为 0. 6 mm,翅片间距为 2. 2 mm,热管直径为 6 mm,翅片高度为 65 mm,翅片宽度为 28 mm。     

Thermal analysis of heat pipe shell-fin structures with selective coatings under radiation

The purpose of this study is to investigate the thermal response of a heat pipe shell-fin structure that is selectively coated and is subject to uneven radiation from upper and lower sides. Such a structure would arise when fins are attached to opposing sides of the condenser or evaporator section of heat pipes to enhance the heat transfer performance. Typical examples include radiators for space applications and solar energy collectors for water heating. The temperature distribution in the circumferential direction of the heat pipe shell as well as that in the fin is examined via theoretical modeling and numerical analysis. The model accounts for the effects of selective coatings. Both steady-state and transient solution procedures are presented. Examination of the steady-state results justifies the use of a thermally-lumped formulation for the heat pipe shell region. The effect of fin width is investigated as a typical design variable. The fin efficiency and the collector efficiency are also presented as functions of heat pipe operating temperature and fin widith. The influence of the surface properties on the thermal performance of the heat pipe shell-fin structure are also examined.     

肋片焊接方式对其传热的影响

通过改变肋片的焊接尺寸以及焊接形状建立肋片传热模型,采用CFD(Computational Fluid Dynamic)模拟的方法,将模拟结果与传统铸造肋片的传热情况进行对比,研究不同焊接方式以及焊接尺寸对整个肋片的换热量以及换热系数的影响.结果显示,肋片焊接后,对整个肋片的换热量和换热系数有一定的影响,但影响较小.其中换热量根据焊接尺寸的增加先减小后增大;而换热系数呈波浪形变化,但有减小的趋势.