水平单管外混合气体对流冷凝换热的理论研究

采用修正的膜模型与Nusselt凝结理论结合的方法,对含湿混合气体自上而下横掠水平管外时的对流冷凝换热机理进行研究,建立了液膜流动和传热模型,进行数值求解并分析了雷诺数、壁面温度及水蒸汽浓度等因素对混合气体冷凝换热的影响。计算结果表明:水管外壁液膜厚度分布很大程度上受气体边界层对液膜剪切力的影响。而局部努谢尔数不同于纯蒸气的的冷凝换热,它受气相热阻的影响很大,其分布状况类似于单相气体管外的对流换热。     

混合气体横向冲刷水平管时对流冷凝换热的机理研究

采用修正的膜模型与Nusselt凝结理论相结合的方法，对含湿混合气体以一定速度冲刷水平管外时对流冷凝换热进行研究，在考虑气相边界层分离的情况下讨论了液膜流动和换热的情况，同时研究了气体来流冲刷角度对总体换热的影响。结果表明，冷凝液膜是一个相当薄的膜层，液相导热热阻在整个换热的过程中基本可以忽略。     

水平翅片管外混合气体对流冷凝传热的理论研究

以Nusselt理论为基础,结合修正的膜理论,对含湿混合气体横掠水平翅片管外时的翅片表面对流冷凝传热机理进行研究。建议了分区处理方法,建立了翅片侧壁和光管上的液膜流动和传热模型。得到了管壁温度、烟气进口温度和雷诺数对总凝结液量的影响,以及翅片侧壁液膜的厚度分布。     

水平肋片管外自然凝结换热特性研究

基于Nusselt凝结传热理论,沿肋片管圆周方向划分有限个微元角,建立了每个微元角内肋侧壁、肋间基管及肋顶三个区域的凝结传热模型,通过求解非淹没区和淹没区总传热量,推导管外平均传热系数计算式。计算不同肋片高度、肋密度时,R134a饱和蒸汽的管外平均凝结传热系数。结果表明:随肋密度的增加,平均传热系数先增大后减小,肋密度为25fpi时传热最佳;高肋片管的平均凝结传热系数大于低肋片管的,肋片高度达到一定值时,平均传热系数几乎不随肋高增加而增加。当R134a饱和蒸汽为20℃时,两种不同翅片密度的管外平均凝结传热系数随温差的增大而减小,并通过所建模型得到的计算值与Beatty-Kate模型进行了比较,平均误差分别为约16.1%和8.3%,故所建模型基本反映肋片管外蒸汽凝结传热机理。     

海水淡化系统水平管降膜蒸发器传热系数研究

针对海水淡化系统水平管降膜蒸发器,总结和分析管内冷凝侧与管外蒸发侧的换热系数关联式,比较管内径、入口蒸汽流速、蒸汽冷凝温度、出口蒸汽干度对管内蒸汽冷凝侧换热系数的影响;研究传热温差以及喷淋密度对管外蒸发侧换热系数的影响。结合不同的污垢系数,进行了总传热系数的影响因素分析,为海水淡化系统的工程设计提供依据。     

水平三维肋管外含不凝性气体的水蒸汽凝结换热的实验研究

对水平光管和三维肋管管外具有不同空气含量的水蒸汽凝结换热性能进行了实验研究。获得了不凝性气体含量和壁面过冷度对光管和三维肋管凝结换热性能的影响规律。实验结果表明：在相同的工况条件下，水平三维肋管的凝结换热系数是光管的1．7～2．9倍；不凝性气体含量越高，凝结换热系数越低；壁面过冷度越大，凝结换热系数越大。最后，获得了水平三维肋管管外凝结换热实验关系式。图8表1参9     

含湿混合气体水平管外对流冷凝换热实验研究

回收烟气中的潜热和显热在提高锅炉效率和环境保护方面都具有重要意义。主要针对含湿混合气体在水平单管管外的对流冷凝换热进行了实验研究。通过对实验数据的分析,得到了烟气进口温度、冷却水进口温度、水蒸气的质量分数以及Re的变化对含湿混合气体在水平单管管外冷凝换热的影响。     

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hi,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...     

汽-气凝结气膜分布及对换热特性的影响

基于双边界层理论,考虑气膜内诱导速度、气液界面剪切力和压力梯度等因素的影响,建立了在水平管外汽-气凝结换热过程中所形成气膜厚度的数学模型,并讨论了气膜分离情况.结果表明:沿管壁向下,气膜厚度逐渐增大;当气膜发生分离时,气膜厚度在分离点处急剧增大,且随流速增大而减小;当气膜不发生分离时,气膜厚度在管壁底部附近急剧减小,且随流速增大而增大;气膜厚度随壁温升高而增大,随不凝结气体质量分数增大而增大;气膜厚度及气膜分离对换热特性有一定的影响.     

不锈钢螺旋槽管水平强化传热的实验研究

本文对低导热系数的水平不锈钢螺旋槽管进行了凝结换热实验研究，并对不锈钢管的壁温测量进行了探索，通过分析得到了水平单头不锈钢螺旋槽管的水测对流换热系数准则方程。     

导热油管内强制对流换热系数的计算

以一种常见导热油为例对有机热载体锅炉的对流受热面传热系数进行计算分析。     

卧式燃油燃气炉炉胆传热计算方法的比较研究

对卧式燃油燃气锅炉或加热炉,炉胆传热计算是热力计算中的重要计算,其主要目的是确定炉胆出口烟温。本文对已有的卧式内燃燃油燃气锅炉炉胆传热计算公式进行了比较,提出了适合加热炉炉胆传热计算的方法和简化算法。     

Experimental Study on the Heat Transfer Characteristics of an Evaporating Falling Film on a Horizontal Plain Tube

In this paper, an experimental investigation on the heat transfer of saturated water falling film on a single horizontal plain tube is presented. The water film falling on the outside of the tube has been heated by the condensing steam flowing in the tube, and the heat transfer coefficient between the water film and the steam has been measured. Experiments were performed at saturation temperatures of liquid film and steam as 58°C and 61°C, and 61°C and 65°C, a tube pitch of 57.16 mm, heat fluxes from 10 to 50 kW m^-2, and film flow rate per unit of length of the tube up to 0.12 kg m^?1 s^?1. Brass plain tubes with external diameters of 25.4 mm and lengths of 950 mm were used in the experiments. The experimental results show that the heat transfer coefficient increases with the increasing film flow rate and heat flux, and the quality of vapor has an obvious influence on the heat transfer performance of falling film evaporation. The coupling of condensation and evaporation heat transfer inside and outside the tube is investigated qualitatively in this paper.     

Asymmetrical Non-Uniform Heat Flux Distributions For Laminar Flow Heat Transfer With Mixed Convection In a Horizontal Circular Tube

Non-symmetric heat flux distributions in terms of gravity in solar collector tubes influence buoyancy-driven secondary flow which has an impact on the associated heat transfer and pressure drop performance. In this study the influence of the asymmetry angle (0°, 20°, 30° and 40°) with regard to gravity for non-uniform heat flux boundaries in a horizontal circular tube was investigated numerically. A stainless steel tube with an inner diameter of 62.68 mm, a wall thickness of 5.16 mm, and a length of 10 m was considered for water inlet temperatures ranging from 290 K to 360 K and inlet Reynolds numbers ranging from 130 to 2000. Conjugate heat transfer was modelled for different sinusoidal type outer surface heat flux distributions with a base-level incident heat flux intensity of 7.1 kW/m². It was found that average internal heat transfer coefficients increased with the circumferential span of the heat flux distribution. Average internal and axial local heat transfer coefficients and overall friction factors were at their highest for symmetrical heat flux cases (gravity at 0º) and lower for asymmetric cases. The internal heat transfer coefficients also increased with the inlet fluid temperature and decreased with an increase in the external heat loss transfer coefficient. Friction factors decreased with an increase in fluid inlet temperature or an increase in the external heat loss transfer coefficients of the tube model.     

对流传热计算中的烟气辐射放热系数α_1

本文提出锅炉对流传热计算中用到的烟气辐射放热系数α_(?)袭用炉内辐射传热的计算公式有误差,因为所对应的温压不同,应予改正。     

关于螺纹烟管的传热计算

十几万台新型水火管锅炉的螺纹烟管传热计算用"哈工大-之光所"的计算公式,试验及运行已表明公式的正确性.分析和讨论了有关资料推荐的其它计算公式及热有效系数ψ的选取等问题.     

非共沸混合制冷剂水平管内流动沸腾换热

近年来,非共沸混合制冷剂作为工质改善热泵和制冷设备工作效率和性能的潜力引起了广泛的重视。本文评述了非共沸混合制冷剂水平管内流动沸腾换热研究的主要问题,着重于讨论换热的计算,并提出了一些有益建议。     

Measurement of Falling Film Thickness Around a Horizontal Tube Using a Laser Measurement Technique

A new optical method for the non-intrusive measurement of falling film thickness on the perimeter of horizontal tubes is described. The technique uses a high-speed digital video camera to capture the images of the liquid interface that are illuminated by a laser sheet, with the contrast enhanced by a fluorescent powder in the fluid. The results are compared to those predicted by the Nusselt falling film theory, showing relatively good agreement around the upper perimeter of the tube but much poorer agreement on the lower perimeter. The corresponding effects on heat transfer have also been estimated.     

水平三维内微肋管在局部蒸干区的沸腾换热及其关联式

为了得到不同流型下的换热性能 ,以 R1 3 4a为实验工质在一种水平三维内微肋管内进行了流动沸腾换热实验研究 ,通过可视化等措施对得到的主要流型及其转换曲线表示在 G-x图上。对局部蒸干区的沸腾换热特点进行了讨论 ,并根据此区域换热的特点 ,沿周向管壁分成两个部分 ,即 :蒸干部分和非蒸干部分。对于非蒸干部分又分为淹没微肋的底部液体 ,且认为同环状流换热机理相同 ,而另一部分认为液休带领在沟槽中 ,从而得到了此区域的换热实验关联式 ,此换热关联式与实验值的最大偏差在± 1 6%以内