电流体力学强化水平管内凝结传热试验研究

在电流体力学(EHD)强化传热试验台上进行了水平管内凝结传热的强化试验研究，结果表明，EHD技术对水平管内的凝结传热有明显的强化效果；低热流密度时，强化效果较好，增大热流密度时，强化效果减弱；热流密度维持不变时，强化系数随强化电压的升高而增大；在本试验条件下，对凝结传热的最大强化系数为156％。     

地源热泵垂直套管式换热器传热研究

介绍了地源热泵的特性及其发展前景,分析了现有传热模型的局限性。在V．C．Mei传热模型的基础上,结合系统能量方程和热传导方程建立了套管式换热器的传热模型。采用有限元法和有限差分法对埋管周围的温度场进行了数值计算。通过与实测值的对比表明该传热模型能更好地反映出真实的传热过程和传热机理。     

地源热泵地埋管换热器传热研究(2):传热过程的完全数学描述

建立了管内流体换热和土壤换热的耦合模型,并在此基础上建立了与地面热泵模型耦合的地源热泵系统仿真模型.给出了边界条件和计算参数的确定方法,计算参数包括:流体与管内壁面的表面传热系数、地面的表面传热系数、大气温度、不同埋深土壤温度、多孔介质土壤有效导热系数.     

Numerical analysis on heat transfer characteristics of ionic liquids in a tubular heat exchanger

ABSTRACT

The efficiency of the solar thermal system depends on the performance of the solar collectors. There is a need to operate solar collector at higher possible temperature to attain maximum efficiency limits. However, the performance of the collector system is limited by the heat transfer characteristics of the working fluid called as the heat transfer fluid (HTF). Water is widely used as the HTF in the solar collector, but the major problem of using water as the HTF is its limited operating temperature. The objective of the work is to investigate the heat transfer characteristics of ionic liquids in tubular heat exchanger (HE) suitable for the solar thermal application. The HE was designed for a heat duty of 1?kW based on the thermal transport property of available ionic liquids and the computational fluid dynamics (CFD) analysis was performed. The results indicate that there is only minimal deviation between the assumed and CFD data.     

Experimental investigation on heat transfer characteristics of heat exchanger with bubble fin assistance

ABSTRACT

Heat transfer area per unit volume (m²/m³) of heat exchangers decides the size of the heat exchangers, over the period of years heat exchangers have undergone numerous development in this aspect. One such attractive design is plate heat exchanger which is very compact and has high thermal effectiveness, whereas the flow nature of fluid through this type of heat exchangers is complex. The most common type of plate heat exchanger is chevron type which suffers from large pressure drop (Δp) at higher heat transfer rates, to overcome this problem bubble finned heat exchangers are designed. In this paper the performance of bubble finned heat exchanger is studied with single phase fluid flow condition. The comparative study of finned and no fin configuration shows that the former has 1.8 times higher rate of heat transfer at lower value of Reynold’s number, further the flow remains laminar hence the Δp is minimum.     

三维高效强化传热管传热系数的试验研究(1):蒸发强化传热

试验测试了一种可用于满液式壳管换热器的管外侧强化沸腾和强化冷凝的双效强化传热管.用热阻分离法计算了使用R134a制冷剂时制冷剂侧和水侧的表面传热系数.试验结果表明,在较大的热流密度(大于20 kW/m2)下该管较传统的强化沸腾传热管具有较大的池沸腾表面传热系数;在较大的热流密度(大于15 kW/m2)下较传统的强化冷凝管具有较大的管外冷凝表面传热系数.     

Influence of conical strip inserts in heat transfer enhancement under transition flow

ABSTRACT

The performance of the concentric tube heat exchangers can be increased due to the swirl flow generation caused by the inserts which exchange heat in an effective manner. Many researchers have studied the thermal behaviour of different types of inserts, such as twisted tape and wire coil, with different geometries. This work dealt with the heat transfer and friction factor behaviour of newly fabricated staggered and non-staggered conical strip insets. The conical strip insert produces much swirl flow corresponding to the twist ratios (Y?=?2, 3 and 5). The experimental results are in good agreement with the correlations developed for Nusselt number and friction factor with the help of regression analysis.     

空冷器管组内紊流强制对流换热的热阻分离法测定

采用Ｗｉｌｓｏｎ法对１４个表面式冷却器元件进行了管内紊流强制对流换热系数的测定。实验结果表明，实测值与用ＢｏｅｌｔｅｒＤｉｔｕｓ公式计算值的偏差均在工程应用许可范围内，证实了在空冷器管组内流体紊流换热系数可按Ｄｏｅｌｔｅｒ－Ｄｉｔｕｓ公式计算。     

一种新型板式换热器的设计及其传热特性的模拟研究

设计了一种隔板为六边形的板式换热器，基于干工况平衡流换热的模拟研究表明，该换热器具有准逆流换热的特点和强化换热作用。雷诺数在300～1000范围内，随着RP的增加，传热能力增加；当Re为900时，平均换热系数提高约一倍。实验验证模拟结果是有效的。     

地源热泵的地埋管群换热特性研究

结合武汉某实际工程的地埋管群阵列布置情况和地源热泵系统的运行情况,对典型区域的地埋管群运行5年中的埋管换热特性进行了动态数值模拟和分析.提出了温度偏离度和换热保证度的概念,并研究了二者在地源热泵长期运行过程中的变化规律.建议尽量减小冷热负荷不平衡率,以保证地源热泵系统稳定可靠的运行.     

地埋管换热器运行工况下换热量变化特性的研究

通过对土壤热阻的理论计算和地埋管换热器的数值模拟计算,获得了地埋管换热器的温差-换热量的变化关系。理论分析与现场实测结果均表明地埋管换热器的换热量随时间的变化分为快速变化段、平缓变化段、线性变化段三个阶段,拟合出了平缓变化段和线性变化段的单位延米换热量随介质与土壤传热温差的变化公式。     

Convective heat transfer prediction in large rectangular cross-sectional area Earth-to-Air Heat Exchangers

An Earth-to-Air Heat Exchanger (ETAHE) uses the ground's thermal storage capacity to dampen ambient air temperature oscillations by delivering the outdoor air to the indoors through a horizontally buried duct. With their lower airflow resistance, large cross-sectional area ETAHEs have been found to be more energy efficient than the conventional small ones, especially when integrated in hybrid ventilation systems. However, the lack of available methods for determining the heat convection at the duct surfaces has made accurate energy simulation and proper system design overly difficult. In this study, numerical experiments using computational fluid dynamics (CFD) were conducted to investigate the airflow and thermal behavior in the large ducts. A two-layer turbulence model was used to ensure accuracy in resolving the flow information in the near-wall region, which is critical for predicting accurate heat convection. The modeling method was verified by comparing its results with measurements from literature. Parametric studies were conducted to identify the influential design and operation variables for the heat convection. Thirty numerical experimental setups designed with the Latin Hypercube Sampling method were simulated to prepare a database with six design parameters as the simulation inputs and average Nusselt numbers over the duct ceiling, wall, and floor as the outputs. Based on the database an artificial neural network (ANN) model was trained to build a mathematical relation between the design variables and the Nusselt numbers. The developed ANN model showed very accurate prediction when compared with test data.     

Experimental investigation on heat transfer enhancement in a minichannel using CuO-water nanofluid

In this work, CuO-water nanofluid with an average size of nanoparticles (24?nm) and volume concentrations of 0.1% and 0.5% is used. For the computer microprocessor cooling, an aluminium minichannel of dimension (40?×?1?×?3) mm³ is fabricated instead of an aluminium heat sink and a cooling fan. It is shown that the dispersion of nanoparticles into the distilled water has produced a considerable enhancement of the cooling of the minichannel. Experiments were conducted for Reynolds number ranging from 25 to 800 under a laminar regime. From the experiments, it is found that better heat transfer is achieved when CuO-water nanofluid is used as the working fluid.     

基于层换热理论的竖直地埋管换热器设计方法

建立了地源热泵竖直地埋管换热器的三维传热温度场数学模型,模拟计算了不同季节不同工况下地埋管换热器内的水温分布。提出了层换热理论,竖直地埋管换热器及其周围岩土可以分为三个换热层——饱和换热层、换热层、未换热层。通过实测验证了该层换热理论。介绍了地埋管换热器埋深的确定、出水管的保温及流量的确定等。     

多孔建筑材料热湿传递过程的研究

从理论计算和实验研究等方面对国内外多孔建筑材料的传热、传湿及热湿耦合传递研究方面的进展进行了综合分析。指出了目前多孔建筑材料热湿传递过程研究中存在的问题，并对未来的研究方向进行了展望。     

外掠单排矩形翅片管的强化换热实验研究

本文以冷风机蒸发器普遍采用的矩形平翅片管作为比较对象，对三种不同片型的新型翅片管在吸风式直流风洞中进行了空气外掠单排翅片管的对比性实验研究。     

Airflow and heat transfer in double skin facades

Airflow and heat transfer simulation was conducted for a DSF system equipped with a venetian blind, using computational fluid dynamics (CFD) with RNG turbulence model, for a three-level combination of slat tilt angle and blind position. The CFD prediction was validated using experimental data collected for a mechanically ventilated DSF equipped with venetian blinds. The predicted trends in glass and blind surface temperatures of the CFD model are compared well with the experimental measurements. The present study indicates that the presence of venetian blinds influences the surface heat transfer coefficients (SHTCs), the temperature and the air distribution in the DSF system. For the cases considered, the changes in the position of the blinds (outer, middle, and inner) have more effect on the distribution of temperature, velocity, and SHTCs compared to the changes in the slat angles (θ = 0°, 45°, 90°).     

双级压缩高温热泵换热器型号优化设计仿真

介绍了高温热泵系统形式及换热器初步设计,编制了系统仿真程序,得到了8种换热器型号下系统COP、换热器传热系数、水侧压降等关键参数随换热面积的变化关系。针对该热泵系统,给出了一定换热面积范围内较优的换热器型号。     

A theoretical study of Cu-H2O nano-fluid effect on heat transfer enhancement of a solar water heater

In the present work, an attempt has been made to enhance the heat transfer in a solar water heater by using Cu nano-particles dispersed in water for various concentrations ranging from 0% to 5%. Considerable improvement in the solar collector efficiency is obtained by increasing the nano-particle concentration up to 17.5 for a concentration of 5% and for a mass flow rate ratio of 10. The outlet water temperature increases by increasing the nano-particle concentration up to 8.35% for a concentration of 5% and for a mass flow rate ratio of 5. The study showed that the solar heater collecting area takes into account significant factors for increasing the outlet temperature. An increase in the collecting area of the solar water heater by 6 times could increase the water temperature by 39% for a 5% nano-particle volume fraction. The helical heat exchanger effectiveness is increased up to 65.71 for a concentration of 5% for a mass flow rate ratio of 10.     

地下水渗流对地埋管换热影响的分析

基于对单井地埋管换热器的数值模拟,本文分析了地下水渗流对地埋管周围土壤温度场及传热热阻的影响.