大直径圆孔翅片管结霜过程动态特性的实验研究

在入口空气温度28℃,恒温恒湿条件下,以三对称大直径圆孔翅片为研究对象,在循环式风洞中对其结霜工况下的动态性能进行了实验研究,考察了入口空气相对湿度和空气流速对换热器性能的影响,给出了换热器换热量、翅片表面传热系数和空气侧压降在结霜过程中的动态变化规律,研究结果表明:入口空气温度28℃时结霜工况下,翅片表面未覆盖满霜层时,在雷诺数Re=3602～5509,进口相对湿度φ=60％～80％范围内,不同的环境参数对结霜影响的差别较大.实验结果表明,空气相对湿度对SK型翅片的传热与流阻性能的影响大于空气流速的影响.实验结果可为优化环境参数,使制冷系统达到节能匹配提供参考.     

圆孔和半圆孔交叉翅片管的传热与流阻性能研究

本文提出一类可用于结霜和灰尘较多场合的新型翅片——圆孔和半圆孔交叉翅片。为了考察这类翅片的性能特征,对9种不同几何参数的单排肋管式换热器样件在吸风式直流热风洞内进行了实验。这些几何参数包括圆孔、半圆孔的直径和位置。通过多元线性回归法将实验数据整理为以雷诺数和换热器几何参数为自变量的j和f关联式。结果表明开孔参数对换热性能有明显影响,而对阻力影响不显著。与平片相比,样片3的平均当量换热系数提高18.3％,节约金属耗材12％。     

圆柱型翅片管换热器变工况传热性能模拟与分析

基于分排参数模型,本文建立了圆柱型翅片管换热器的性能仿真计算模型,对换热器的传热性能进行计算,并进行实验验证。结果表明:换热量的平均相对误差最大,为6.31%;出风干球温度的平均相对误差最小,为0.61%。计算所得各性能参数与实验值吻合良好。根据仿真模型,对不同制冷工况下的换热器进行计算,研究了循环风量、水质量流量、进风干球温度以及进水温度的变化对换热性能的影响。分析换热器的变工况特性可预测其非设计工况下的换热性能,并为换热器的运行工况调节提供依据。     

翅片管式换热器表面结霜特性的数值分析和实验研究

换热器表面结霜会增加传热热阻和流动阻力，为了合理确定融霜周期，必须对其结霜特性做深入地了解。本文采用了数值求解方法预测了翅片管式换热器的结霜量和霜层密度的变化过程。翅片管结霜是一个瞬变问题，为了计算方便，将其简化为准稳态过程，即在时间步长内，认为该过程是稳定的，然后把所得的霜层厚度以及霜层的表面温度作为下一时间步长内传热传质的边界条件。在研究中考虑了霜层阻力引起风量下降这一因素，计算结果与翅片管式换热器结霜的实际工况相符。     

狭缝沸腾板翅式单元传热性能的实验研究

对采用新型沸腾传热强化措施的工业用板翅式冷凝蒸发器单元试样的传热特性进行了实验研究，实验结果表明：本文的实验单元与现行的６０００ｍ＾３／ｈ空分装置的板翅式主冷凝蒸发器相比，换热系数提高了近一倍，传热温差下降了４０％－５０％。     

水-空气翅片管换热器实验研究与数值模拟

通过对翅片管式换热器的设计和实验研究,得出了该换热器的性能曲线,此外还对换热器内部流场和温度场进行了三维数值模拟计算。从实验和模拟结果分析可知,实验所得传热因子j较模拟结果有12％范围内的减小,而阻力因子,有4％～16％的增大;翅片间距和管排密集度对翅片管换热器性能影响很大,减小翅片间距和增大管排密集度均能增强换热器的换热效果,但压力损失也明显增加。     

翅片管与盘管蓄冷性能的对比实验研究

根据盘管在蓄冰期换热系数较低的情况,提出采用翅片管替代盘管做蓄冰换热器的方案;以片距12.7mm的翅片管换热器与光管换热器进行了对比实验,得到翅片管式蓄冷周期平均蓄冷量高出15.3%,蓄冰量高出25.9%的效果;实验显示,翅片管换热器在蓄冷初期,性能优势不明显,而在蓄冷后期,冰层增厚后,优势逐渐体现。     

空气换热器用翅片管簇的展望及换热性能的比较研究

一、翅片类型及展望翅片式空气换热器的翅片形式大体可分为:1.绕片式:园管绕园翅片,和椭园管绕椭园翅片。2.串片式:园管串园翅片,园管串矩形翅片,园管串大形板片式翅片,椭园管串矩形翅片,和椭园管串椭园翅片等。     

多孔式翅片传热与流阻特性分析

采用CFD数值模拟技术,研究了多孔式翅片传热与流阻特性,重点分析了不同孔口因素对多孔式翅片传热与流阻的影响.研究结果表明:随着孔隙率增加,多孔式翅片流阻增大,但其传热并未明显提升.同一孔隙率下,翅片传热与流阻随孔径减少而提升.开孔方式呈错列布置的流阻与传热性能高于孔口呈并行布置的情况.开孔结构对多孔式翅片传热性能影响较...     

振荡流热管汽车散热器传热性能的实验研究

对振荡流热管汽车散热器和管带式铜质汽车散热器进行了实验研究,得到了两种散热器的传热和阻力特性,对比发现振荡流热管汽车散热器具有较好的传热性能,且风阻和水阻均小于管带式铜质汽车散热器,并进行了热平衡误差分析,实验结果对开发新型汽车散热器有一定的指导意义。     

Experimental study on the heat transfer and flow characteristics of nanorefrigerants inside a corrugated tube

The heat transfer and flow characteristics of MWCNT-R141b nanorefrigerant with different mass fractions have been studied through experiments. Experimental results were compared with existing correlations. A two-step method was used to prepare the nanorefrigerants. Span-80 was used as surfactant with an average particle diameter of 20 nm. Transmittance method was used to evaluate the stability of nanorefrigerants. Results showed that the stability of MWCNT-R141b nanorefrigerant, which is the added dispersant, was good during the experiments. The 0.3 wt% MWCNT-R141b nanorefrigerants had optimal heat transfer enhancement effects compared with pure refrigerants. The maximum Nusselt number increased by 40%. The specific pressure drop of nanorefrigerant increased as the Reynolds number (Re) increased, and the specific pressure drop of the pure refrigerant was minimum, which is similar to R141b.     

Effect of fin spacing on the heat transfer and pressure drop of a two-row plate fin and tube heat exchanger

The analogy between heat and mass transfer (using the naphthalene sublimation technique to measure the mass transfer coefficient) was used to investigate the heat transfer capabilities of various two-row plate fin and tube heat exchanger configurations. Average transfer coefficients were determined from measurements of the mass transferred in an analogical system consisting of a pair of naphthalene plates and an array of spacer discs. The analogical system modelled a typical heat exchanger flow passage. Special attention was given to the effect of fin spacing on heat transfer capabilities. A physical interpretation of the experimental data has been given and new conclusions have been drawn. The pressure drop of the heat exchanger configurations has also been investigated.     

小管径椭圆管开缝翅片换热器的数值模拟

对小管径椭圆管开缝翅片换热器空气侧的流动与传热特性进行数值模拟,对影响其换热性能的2个主要参数椭圆管偏心率和开缝翅片开缝错列高度分布进行优化,与传统管翅式换热器换热性能进行比较。模拟结果表明:当椭圆管两轴之比Rx:Ry=2:3(偏心率),开缝高度分布为0.8 mm,0.6 mm和0.4 mm时,换热效果最好。与传统管翅式换热器相比,小管径椭圆管开缝翅片换热器换热系数提高10%~20%,而压降几乎相等,总体换热性能提高。     

Assessment of boiling heat transfer correlations in the modelling of fin and tube heat exchangers

A new way to assess the performance of refrigeration system models is presented in this paper, based on the estimation of cycle parameters, such as the evaporation temperature which will determine the validity of the method. This paper is the first of a series which will also study the influence of the heat transfer coefficient models on the estimation of the refrigeration cycle parameters. It focuses on fin and tube evaporators and includes the dehumidification process of humid air. The flow through the heat exchanger is considered to be steady and the refrigerant flow inside the tubes is considered one-dimensional. The evaporator model is discretised in cells where 1D mass, momentum and energy conservation equations are solved by using an iterative procedure called SEWTLE. This procedure is based on decoupling the calculation of the fluid flows from each other assuming that the tube temperature field is known at each fluid iteration. Special attention is paid to the correlations utilised for the evaluation of heat transfer coefficients as well as the friction factor on the air and on the refrigerant side. A comparison between calculated values and measured results is made on the basis of the evaporation temperature. The experimental results used in this work correspond to an air-to-water heat pump and have been obtained by using R-22 and R-290 as refrigerants.     

Assessment of condensation heat transfer correlations in the modelling of fin and tube heat exchangers

This is the second paper of a series that assesses the performance of a refrigeration system model by means of cycle parameters. In this case, the condensation temperature is the parameter to study and it is focused on fin and tube condensers. It also studies the influence of the heat transfer models on the estimation of this refrigeration cycle parameter and different correlations for the heat transfer coefficients have been implemented in order to characterise the heat transfer in the heat exchangers. The flow inside the heat exchangers is considered one-dimensional as in previous works. In the cycle definition, other submodels for all the cycle component have been taken into account to complete the system of equations that characterises the behaviour of the refrigeration cycle. This global system is solved by means of a Newton–Raphson algorithm and a known technique called SEWTLE is used to model the heat exchangers. Some experimental results are employed to compare the condensation temperatures provided by the numerical procedure and to evaluate the performance of each heat transfer coefficient. These experimental results correspond to an air-to-water heat pump and are obtained by using R-22 and R-290 as refrigerants.     

一种新型高效传热铜管的冷凝传热性能实验研究

建立无润滑油实验台，以R22。R134a和R410A为工质。测试新型铜管Turbo-DWT和常规内螺纹铜管Turbo—A的冷凝传热性能，并进行比较。从实验数据可知。新管型Turbo-DWT的冷凝传热系数高于Turbo-A约42％，且压降低于Turbo-A约65％（R134a）。三种制冷荆相比，R22的传热系数最高，R410A的压降最小。Turbo-DWT是一种更高效的冷凝传热管，且适用于各种冷媒。     

喷雾冷却临界传热特性试验研究

为了进行极限热工况下的喷雾冷却传热特性研究,设计并搭建采用蒸馏水及乙醇溶液喷雾冷却试验台,分析结构参数、喷雾流量、喷雾腔内压力等对喷雾冷却临界热流密度的影响。试验结果表明:临界热流密度随槽道深度增加先增大后减小,最佳槽道深度为0.8 mm,此时临界热流密度达到326 W/cm^2;随着喷雾流量的增加,临界热流密度始终增大;喷雾腔内压力对临界热流密度基本没有影响。计算结果表明,喷雾冷却效率随槽道深度增加而提升,随喷雾流量的增加而减弱。     

Experimental study on the heat and mass transfer characteristics in a refrigerated truck

An experimental study on the heat and mass transfer characteristics in the body of a refrigerated truck for cases without an air curtain, with a fan air curtain and with a plastic strip curtain have been carried out. The variations in temperature and relative humidity inside the stationary truck during a short duration after the door is opened are the present focus. The average air temperature inside is found to increase to 14, 7 and 8°C from an initial temperature of −10°C, for cases without an air curtain, with a fan air curtain and with a plastic strip curtain, respectively, within 2 min after the door is opened. It is found that using an air curtain can have energy savings up to 40 and 11%, respectively, compared to the cases without an air curtain and using plastic strip curtain. Comparison between the experiment and numerical results also shows reasonable agreement in terms of average temperature inside the body.     

Experimental study of turbulent single-phase flow and heat transfer inside a micro-finned tube

Single-phase heat transfer and pressure drop characteristics of a commercially available internally micro-finned tube with a nominal outside diameter of 7.94 mm were studied. Experiments were conducted in a double pipe heat exchanger with water as the cooling as well as the heating fluid for six sets of runs. The pressure drop data were collected under isothermal conditions. Data were taken for turbulent flow with 3300 ≤ Re ≤ 22,500 and 2.9 ≤ Pr ≤ 4.7. The heat transfer data were correlated by a Dittus–Boelter type correlation, while the pressure drop data were correlated by a Blasius type correlation. The correlation predicted values for both the Nusselt number and the friction factors were compared with other studies. It was found that the Nusselt numbers obtained from the present correlation fall in the middle region between the Copetti et al. and the Gnielinski smooth tube correlation predicted Nusselt number values. For pressure drop results, the present correlation predicted friction factors values were nearly double that of the Blasius smooth tube correlation predicted friction factors. It was also found that the rough tube Gnielinski and Haaland correlations can be used as a good approximation to predict the finned tube Nusselt number and ffriction factor, respectively, in the tested Reynolds number range.