微型螺旋管蒸发器的沸腾换热与阻力特性实验研究

设计、制造并测试了一种微型螺旋管蒸发器。对微型螺旋管蒸发器的沸腾换热与阻力特性进行了实验研究。根据实验数据获得雷诺数在1460~10000范围内流阻系数与雷诺数的计算关系式。实验结果表明,这种微型蒸发器换热量超过300W。     

空气横掠管束换热实验研究

扩展传热面是提高单位体积内传热面积最常用的方法。以空气为介质,对三种给定的肋片管束(H型、纵肋肋片、螺旋肋片)进行了顺列和错列的换热和流动阻力实验。实验结果表明:错列布置的管束换热效果优于顺列布置的管束,但流动阻力相应增加;错列布置时,综合考虑换热和阻力因素,螺旋肋片管有较好的换热经济性。通过对实验数据进行拟合回归,得出了实验条件下各肋片管束顺列、错列布置的换热关联式。为肋片管束的工程应用、优化选取及进一步的实验研究提供了理论依据。     

波纹形内翅片管对流换热实验研究及其应用

通过实验的方法研究了一种新型波纹形内翅片换热管的对流换热和阻力特性,建立了所测Re范围内对流换热和阻力实验关联式,并且在相同质量流量、相同泵功率、相同阻力降的条件下比较了该翅片管与普通光管之间的传热效果.与类似的波纹管的换热效果进行了比较,结果表明,新型波纹形内翅片换热管具有较好的换热效果,特别是在较低Re条件下,效果更加明显.     

R1234ze(E)与R134a在水平双侧强化管外的凝结换热对比实验

搭建了水平单管降膜蒸发试验台,以第四代制冷剂R1234ze(E)和第三代制冷剂R134a作为工质,在新型水平双侧强化管管外分别进行了改变管内水速、热流密度和冷凝温度条件的凝结换热实验。使用Wilson-Gnielinski图解法计算得到管内表面传热系数h_i,进一步采用热阻分离法分离出两种制冷剂的管外表面传热系数,并分析了管内冷却水水速、冷凝温度和壁面过冷度的变化对其换热性能的影响。实验结果表明:同根实验管下不同制冷剂凝结换热性能的差异与制冷剂物性与强化管结构之间的匹配特性有关,实验管型下,R1234ze(E)的管外凝结换热性能高于R134a。     

轧槽管内单相对流强化换热及阻力特性的实验研究

通过实验对不同规格的轧槽管进行了强迫对流换热和阻力特性的研究。根据工程需要，选用适当的准则对这些管子的强化换热性能进行了评价，在实验范围内得出了最佳管型。     

新型复合防腐表面烟气对流凝结换热实验研究

烟气对流凝结换热强化和换热表面防腐是天然气热能动力设备烟气余热回收利用关键技术。不同防腐表面耐腐蚀性能不同,且换热性能也不同。采用CCD高速摄像仪,对烟气在新型复合防腐表面上的凝结形态和凝结过程进行了可视化观测和换热实验研究,采用对图像边缘提取法,获得凝结液的边缘曲线。研究表明,烟气在新型复合防腐表面上的凝结为珠状凝结,凝结液珠最大粒径为0.2～0.28 mm,与其他表面形成的膜状凝结相比,在实验范围内,珠状凝结换热可提高约7倍。为增强烟气对流凝结换热和开发烟气冷凝余热回收利用技术提供了参考和依据。     

凝结换热与冷凝式锅炉原理及应用(续完)

阐述了凝结换热及冷凝式锅炉原理及其应用背景,分析了制约冷凝式锅炉快速发展的技术和政策瓶颈,介绍了先进的凝结换热和冷凝式锅炉应用技术,为我国未来冷凝式锅炉技术创新指出了参考方向。     

凝结换热与冷凝式锅炉原理及应用(待续)

阐述了凝结换热及冷凝式锅炉原理及其应用背景,分析了制约冷凝式锅炉快速发展的技术和政策瓶颈,介绍了先进的凝结换热和冷凝式锅炉应用技术,为我国未来冷凝式锅炉技术创新指出了参考方向。     

不同材质花瓣形扁通道内翅换热管的实验研究

通过实验的方法研究了一种花瓣形扁通道内翅换热管的对流换热和阻力特性,拟合了所测Re范围内对流换热和阻力实验关联式,并运用相同质量流量、相同泵功率和相同阻力降这3种准则比较了采用不同材质时翅片管与普通光管之间的传热效果。结果表明,翅片材质对换热强化效果有较大影响,无论采用哪种材质,花瓣形扁通道内翅管均有较强的换热效果,特别是在低盅条件下,强化效果更加明显。     

超临界CO_2在螺旋管中换热特性的数值模拟

数值模拟超临界CO_2在竖直螺旋管内加热过程的换热特性。4种湍流模型的计算结果与实验数据对比,表明SST模型的计算结果与实验数据吻合较好。基于SST模型研究重力、热流密度以及压力对换热系数的影响。由于离心力的作用导致局部换热系数峰值点向左偏移,压力越大,偏离度越大。在计算工况中,浮升力对超临界CO_2在螺旋管中的换热影响可以忽略不计,而直管中必须考虑。     

Condensation heat transfer and pressure drop characteristics of R-134a in an annular helical pipe

Condensation heat transfer and pressure drop data of R-134a in annular helical pipes is of significant importance to the effective design and reliable operation of helical pipe heat exchangers for refrigeration, air-conditioning, and many other applications. This paper presents the experimental investigation on condensation heat transfer and pressure drop characteristics of R-134a in an annular helical pipe. The average condensation heat transfer coefficients and pressure drops were experimentally determined for R-134a at three different saturated temperatures (35 °C, 40 °C, and 46 °C). The experimental results are compared with the data available in the literature for helical and straight pipes.     

Flow boiling and condensation of tetrary refrigerant mixtures inside water/refrigerant enhanced surface tubing

This work presents the results of an experimental study concerning the heat transfer characteristics of two-phase flow condensation and boiling of tetrary (R-32/R-125/R143a/R134a) refrigerant mixtures inside water/refrigerant horizontal enhanced surface tubing. Heat transfer characteristics such as average heat transfer coefficients, as well as pressure drops of the tetrary refrigerant mixtures, have been predicted and compared with other mixtures during flow condensation and boiling inside enhanced surface tubing. It was found that the tetrary refrigerant blend has higher transfer coefficients than R-502, and the lowest pressure drop among the refrigerants studied. © 1997 by John Wiley & Sons, Ltd.     

Influence of Spiral Angle on Heat Transfer during Condensation inside Spiralled Micro-Fin Tubes

This paper reports the influence of the spiral angle on the heat transfer performance during condensation inside spiraled micro-fin tubes having constant geometric parameters such as fin height, pitch, shape (apex angle), and fin number, as various papers previously published in this field had not clearly established this influence. Tests were conducted for condensation of R-22, R-134a, and R-407C inside a smooth tube (9.52 mm outer diameter) and three micro-fin tubes with approximately the same diameter and spiral angles of 10°, 18°, and 37°, respectively. Experimental results indicated a heat transfer augmentation with spiral angle increase. A new semi-empirical predictive correlation was developed for the practical design of spiraled micro-fin tubes. The proposed new correlation predicted the majority of experimental results of the present study within a deviation zone of ±20 percent.     

Performance of a R-134a-filled thermosyphon

Heat pipes are low cost and efficient heat exchange equipment. They are suitable for low temperature heat or cold recovery systems. The latter could be employed to cool incoming warm fresh air in air-conditioned ventilation systems. R-134a is an environmentally friendly refrigerant and has been generally accepted as a substitute for R-12 and R-22. The thermal performance of a thermosyphon filled with R-134a was investigated. The effects of temperature difference between bath and condenser section, fill ratio and coolant mass flow rates on the performance of the thermosyphon were determined. The experimental results indicate that the heat flux transferred increased with increasing coolant mass flow rate, fill ratio and temperature difference between bath and condenser section.     

Evaporation heat transfer and pressure drop characteristics of R-290 (propane), R-600 (butane), and a mixture of R-290/R-600 in the three-lines serpentine small-tube bank

This paper reports an experimental investigation of heat-transfer and pressure-drop behavior of R-290, R-600, and R-290/R-600 in the three-lines serpentine small-diameter (2.46 mm) tube bank. Heat transfer coefficients and pressure drop characteristics are measured for a range of heat flux (5–21 kW/m²), mass flux (250–500 kg/m² s), equilibrium mass quality (0–0.86), and the fixed mixture composition ((R-290/R-600 (55 wt.%/45 wt.%)). The results show that the flow boiling heat transfer coefficients for R-290, R-600, and R-290/R-600 are 1.66–1.96-fold, 1.28–1.38-fold and 1.57–1.88-fold greater as compared with those for R-134a under equal heat and mass fluxes. Also, the two-phase flow frictional pressure drop for R-600, R-290/R-600 and R-290 are 1.41–1.60-fold, 1.32–1.50-fold and 1.22–1.40-fold smaller as compared with that for R-134a. A new heat transfer correlation was presented by using a superposition model to predict the experimental data for both pure refrigerants and refrigerant mixtures. Experimental results were compared with several correlations which predict the evaporative heat transfer, which are in good agreement with experimental data.     

含不凝气体的蒸汽冷凝换热系数的关联式

本文建立了含不凝气体的蒸汽冷凝换热的换热模型,应用该模型和大量换热数据,得到含空气的蒸汽与水平光滑圆管外表面之间冷凝换热系数的关联式,该式应用方便,具有应用价值。     

R134a在水平内微翅管管内凝结换热的实验研究

对制冷剂R134a在水平强化换热管管内的凝结换热性能进行了实验研究。实验管为两种内微翅管,分别命名为A管和B管。实验件采用套管结构,强化内管外表面和外管内表面之间(管间)走乙二醇水溶液。实验过程中管内冷凝温度为51℃,管间乙二醇水溶液的流速为3.35 m/s,乙二醇水溶液的进口温度根据制冷剂的质量流速做相应调整,以保证试件出口制冷剂有一定的过冷度。实验结果表明:两种水平强化管的管内冷凝换热系数均随着制冷剂质量流速的增加而增大,在制冷剂质量流速从300 kg/(m2.s)增加到700kg/(m2.s)时,A管的管内冷凝换热系数比B管高1.87%到6.28%,而B管的制冷剂流动阻力比A管高9.56%到11.05%,A管的结构优于B管。     

Prediction of condensation characteristics of alternatives to R-502 inside air–refrigerant enhanced surface tubing

In this paper, an experimental study on the heat transfer characteristics of two-phase flow condensation of alternative azeotropic refrigerant mixtures to R-502, on air/refrigerant horizontal enhanced surface tubing, is presented. The condensation data indicated that the heat transfer coefficient on the blend R-408A has the highest heat transfer rate among the blends under investigation. The condensation data also showed that R-502 and R-407B have similar heat transfer rates when plotted against the refrigerant mass flow rate. It also can be observed that, as the mass flux increases, heat transfer coefficient increases. Correlations were proposed to predict the heat transfer characteristics such as average heat transfer coefficients, as well as pressure drops of alternatives to R-502; such as R507, R404A, R407B and R408A in two-phase flow condensation inside enhanced surface tubing. In addition, proposed correlations were found to fairly predict the two-phase flow heat transfer condensation data.     

T型沸腾强化换热管传热性能的实验研究

对一种T型翅片内螺纹沸腾强化换热管进行换热性能实验研究,管外以制冷剂R134a为工质,管内以水为介质,在定热流密度(q=9 000 W/m2)与定水流速(v=1.5 m/s,v=2.6 m/s)的工况下得到一系列实验数据.利用Wilson图解法得到管内外的换热系数,并与理论光管计算值进行比较,得出T型翅片管管内外沸腾换...     

A Comprehensive Study of Modified Wilson Plot Technique to Determine the Heat Transfer Coefficient during Condensation of Steam and R-134a over Single Horizontal Plain and Finned Tubes

In the present investigation a comprehensive study of the modified Wilson plot technique has been made and a stepwise methodology has been evolved. This technique can be used to determine the condensing-side heat transfer coefficient during condensation of vapor over a horizontal tube. The necessary experimental data have been acquired by conducting experiments for the condensation of steam and R-134a over a plain tube and different finned tubes (CIFTs and SIFTs). The experimental heat transfer coefficient, based on the test-section wall temperature measurement (wall temperature was measured with thermocouples), h_o, has been compared with that predicted by the modified Wilson plot technique, h_mw. The modified Wilson plot technique underpredicted the condensing-side heat transfer coefficient for the condensation of steam in a range of 7.5-15%. The heat transfer coefficient for the condensation of R-134a is also underpredicted in a range of 13-25% by this technique.