超声波强化传热的研究进展

对超声波强化单相对流传热、过冷沸腾传热、饱和沸腾传热的机理与研究进展进行综述,指出今后应着重研究的方向。在单相对流传热和过冷沸腾传热阶段,超声波能使传热系数得到提高,尤其单相对流传热阶段更为显著;在饱和沸腾传热阶段,超声波虽然能对传热产生一定的影响而效果并不明显,但可能会提高临界热流密度。     

基于Gebhart辐射模型的建筑壁面对流辐射传热计算方法

建筑内壁面传热是一种导热、对流和辐射共存的复合传热过程,基于Gebhart辐射模型,建立建筑壁面传热同步模型,可同步计算壁面温度和空气温度,在此基础上分析建筑壁面对流辐射传热特性。研究结果表明:传热同步模型的空气温度理论计算值小于实测值,偏差均在0.25℃以内;壁面温度计算值与实测值的偏差基本在1℃以内。并对南墙加热壁面与地板的导热传热、对流传热及辐射传热进行分析。研究结论为进一步应用Gebhart辐射模型和研究壁面的对流辐射传热提供了参考依据。     

锅壳式燃油(气)锅炉的强化传热技术

介绍了管内强化传热技术及其在锅壳式燃油燃气锅炉中的应用,分析了强化传热技术的强化传热机理和现有管内强化传热的经验计算式。通过对强化传热元件的结构特点、强化传热效果及适用工况的分析,综合考虑换热和流动阻力的因素,给出了几种强化传热元件结构的推荐参数。     

换热器的强化传热

所谓换热器传热强化或增强传热是指通过对影响传热的各种因素的分析与计算，采取某些技术措施以提高换热设备的传热量或者在满足原有传热量条件下，使它的体积缩小。换热器传热强化通常使用的手段包括三类：扩展传热面积(F)；加大传热温差；提高传热系数(K)。     

地板辐射供暖简化传热计算模型与实验研究

为简化地板辐射供暖系统的传热计算,将多表面间的辐射传热简化为地板表面与非热表面间的辐射传热,以此建立了地板辐射供暖系统的简化传热计算模型。对地板辐射供暖系统的简化传热计算模型的计算精度及地板辐射传热量占总传热量的比例进行了实验研究。通过实验研究计算得出简化传热计算模型的计算精度为±4%。地板传热量中辐射传热约占60%,在各非热表面中,屋顶面辐射传热比例最大,外墙较内墙大。     

建筑节能窗传热维数的数值分析

为准确了解建筑节能窗的传热特性,采用数值模拟方法对典型节能窗的玻璃系统和窗框系统传热维数进行分析。结果表明:玻璃系统为一维传热过程,水平窗框系统为二维传热过程,竖直窗框系统则为三维传热过程。在竖直窗框系统中三维传热模拟结果与二维传热模拟结果相差6%以上。     

分层土壤条件下竖直地埋管二维传热模型

在考虑土壤存在土质分层的实际条件下,基于竖直地埋管三维传热模型,提出简化后的二维传热模型。采用Fluent软件,基于实际工程,以地埋管进出水平均温度作为考核指标,对三维传热模型、二维传热模型模拟结果与实测值进行比较,三维传热模型的模拟结果与实测值非常接近,二维传热模型与三维传热模型、实测值的最大相对误差分别为2.33%、2.44%,证明二维传热模型可以替代三维传热模型。将地埋管进出水平均温升(进出水平均温度与水初始温度之差)作为考核指标,在总土层厚度一致、不同土层数量条件下以及土层数量相同、各土层厚度不同条件下,计算二维传热模型与三维传热模型模拟结果的相对误差。对两种模拟条件,当模拟时间大于5h后相对误差均小于4%,说明土层厚度、土层数量对二维传热模型模拟精度的影响较小。     

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。     

不完全冻结式冰盘管充气融冰的实验研究

分析了不完全冻结式冰盘管在融冰过程中的传热特性,提出了在融冰时充入空气以提高蓄冰槽传热性能的建议。实验结果表明,充气融冰可以大大提高蓄冰槽的传热性能,充气量对蓄冰槽传热性能的影响不大。     

过渡流状态下5列叉排圆柱列流动传热特性研究

为了研究小型化换热器叉排管束群在过渡流状态下的传热强化机理,对5列叉排圆柱列的流动传热特性进行了数值分析。使用Fortran自编程序,通过基于复合网格的计算方法,研究了5列叉排圆柱列在不同横向间距(Ps/D)下的流动与传热特性。结果表明:当Ps/D=3时,5列叉排圆柱列的传热强化效果最好;Ps/D=4~6时,其传热强化效果降低。在不同横向间距下,第2列圆柱列的传热强化效果最为明显,后排圆柱列的传热强化效果逐渐降低。     

Heat transfer enhancement of the latent heat storage system using different encapsulating materials with and without fins

This study is aimed at analysing the heat transfer characteristics of different encapsulating materials and the fins on the overall heat transfer in the latent heat storage system (LHSS). Experimentation is done with different phase change materials (PCMs) (d-mannitol, d-sorbitol and paraffin wax) using different encapsulating materials, i.e. copper, aluminium and brass, with and without fins. During the charging process, there is an average 15% heat loss of copper encapsulations without using fins as compared with using fins. The heat losses in aluminium and brass encapsulations are 10% and 15%, respectively. In the discharging process, 23% of heat extraction loss is seen in copper encapsulations, 5% and 18% in aluminium and brass encapsulations, respectively. The results showed that the usage of fins is an effective technique to increase the heat stored and recovered in a LHSS. The most cost-effective encapsulation is aluminium balls with fins as it has the lowest cost/kJ as compared with other two.     

含翅片矩形腔体内相变材料传热特性研究

相变材料低导热特性影响相变传热进程,添加金属翅片可有效提高相变材料传热速率.本文通过使用有限元软件模拟相变材料的熔化过程.通过改变翅片高度、翅片厚度、翅片个数、加热壁面的温度以及将铝片换为导热性能更好的铜片来研究相变材料熔化过程.研究结果表明:增加翅片高度、翅片个数和提高热源壁面温度对强化换热效果具有显著的作用,增加翅...     

翅片管的传热分析及其表面几何参数的优化

对翅片管的强化传热过程进行了分析。建立了以单位传热量下翅片管的体积最小为目标函数的最优化薮学模型，并对翅片管的最佳表面几何参数(翅片高度、翅片节距、翅片厚度)进行了分析，这些研究对翅片管的应用具有一定指导作用。     

多元平行流蒸发器空气侧百叶窗翅片的数值模拟

对多元平行流蒸发器空气侧百叶窗翅片流动和传热进行了数值模拟。得到了不同迎面风速下的空气温度场、压力场、翅片表面局部换热系数。计算得出的空气侧换热系数和压降与实验关联式一致。分析研究了翅片间距和百叶窗角度对空气侧传热和阻力特性的影响,研究结果对多元平行流蒸发器的设计和优化有重要的指导意义。     

新型高效低阻外翅管的研究

通过对外翅管绕流阻力及绕流谱的分析,提出利用翅片的外伸作用对基管进行近体扰流增效减阻的方法。单管的实验研究证实,选用合理的绊条扰流结构,可使环翅管的绕流阻力降低４０％,换热增强１０％。     

Experimental investigation and heat transfer process on longitudinal fins with different notch configuration

Heat transfer enhancement can be achieved by surface modification of fins using different notches. Fin arrays find wide applications in heat transfer studies and other fluid flow processes. The key factor is the fin geometry, which is much significant in the fin arrays. An experimental investigation of mixed convection heat transfer on rectangular fins with triangular notch, circular notch and without notch in a horizontal rectangular channel for a wide range of modified Rayleigh numbers and different flow rates has been carried out. From this investigation, it has been found that circular notch plays efficiently in heat transfer rate.     

Modelling and thermal analysis of air-cooling system with fin pitch in IC engines

ABSTRACT

Excessive heat from the system in IC engines is removed by using the air-cooling system in order to avoid damaging and overheating of IC engines. Fins are most preferably used now to enhance convective heat transfer without the use of an excessive amount of the primary surface area. Choosing the configuration of the fin is very important in order to attain maximum effectiveness of the fin. The heat transfer from surfaces in general is enhanced by increasing the heat transfer area of the surface or the heat transfer coefficient between the surface and its surrounding. Extended fins are well known for enhancing the heat transfer in IC engines. Therefore, it is important for an air-cooled engine to utilise the fins more effectively to obtain uniform temperature distribution in the cylinder periphery. The aim of this paper is to investigate the thermal behaviour of the cooling system with fin pitch and surface geometry in ANSYS and modelling is done using solid works software, in order to compare its performance over the conventional fin design.     

Experimental analysis of the performance of a solar flat plate water heater with and without internal fins

Generally increasing, an increase in the surface area will increase the heat transfer capability of a solar collector and possibly its efficiency. Conventional solar water heaters have longitudinal fins attached externally to the collector tubes for reaping the benefits of enhanced heat transfer. Attempts have been made towards providing internal fins (spirally grooved copper tubes), in addition to the existing external fins for analysing its influence on efficiency and outlet temperature. Two identical solar water heaters with a capacity of 25?L per day were designed and fabricated, one with a collector with plain (unfinned) internals and another with internal grooving (finned tube). The paper details the temperature profile observed in the two collectors, variation of thermo-siphon mechanism and change in efficiency of the solar water heaters with respect to time. It has been observed that providing internal fins had led to an increase in efficiency of about 4.5% as compared to conventional plain tubes.     

Thermal convection in double glazed windows with structured gap

Convective heat transfer inside the gap of double glazed windows is studied numerically using a commercial CFD code (Fluent v6.3), for different Rayleigh numbers and aspect ratios. A reference window with empty gap is compared with windows where the gap contains fins arranged in such a way as to reduce heat transfer. The effects of convective air flow inside the cavities were estimated both at the onset of convection and at steady-state in real environmental conditions. The global Nusselt numbers were calculated for different configurations of the fins in the window gap, in order to apply the standard heat loss estimation method to this type of windows.     

主动式冷梁性能实验研究

针对某主动式冷梁搭建实验台,在一次风量200 m3/h以内,供水温度15~17℃条件下进行实验,研究了:(1)诱导规律,(2)换热器翅片间流动状态、换热系数及压降,可评价冷梁性能的影响因素。实验结果表明,随着一次风量的增加,诱导比呈先增加后稳定的趋势;在二次风速0.8 m/s内微风速下,换热器翅片上的流态为层流;换热器各测试工况点的换热系数保持在15~28 W/(m2·K)范围内,随二次风量和水流量的增加而提高,但供水水温的增加导致换热系数降低;在二次风速0.6 m/s以内,二次风经过换热器的压降在2 Pa以内,呈指数增长。实验数据及结果对冷梁的设计人员具有直观参考价值。