太阳能与热泵技术应用在暖通空调中的进展

热泵是一项重要的节能技术,但因自身的缺陷使得它的应用遇到一定的困难。随着太阳能利用技术不断进步,太阳能系统集热效率逐渐提高,太阳能与热泵之间可以优势互补的特点逐渐显现。越来越多的专家、学者和企业的工程人员投入到对太阳能技术和热泵技术联合应用的研究之中,并取得了一定的成果。本文综述了太阳能热泵的一般原理及其各种模式控制方案,介绍了目前国内外的研究情况和一些有代表性的成果,并对将来太阳能热泵复合技术的发展进行了一些讨论。     

多斜孔气膜冷却传热特性数值研究

对三种不同结构的多斜孔气膜冷却结构进行了数值研究。多斜孔均为叉排结构,斜孔与平板表面夹角均为30,°重点研究了不同相邻孔间距与孔径比Pm/dm(3.0～5.0)和不同吹风比M(0.5～1.5)对热侧壁面绝热温比和换热系数的影响规律。     

An experimentally validated thermo-mechanical model for the prediction of thermal contact conductance

A predictive model for estimating thermal contact conductance between two nominally flat metallic rough surfaces has been developed and experimentally validated. The predictive model consists of two complementary parts, the first of which is a surface deformation analysis to calculate the actual area of contact for each contact spot, while the second accounts for the effects of constriction resistance and gas gap conductance between the contacting surfaces. A surface characterization technique is developed which generates an equivalent 3-D surface profile from multiple 2-D profiles and determines the unique wavelengths of importance for the surface deformation and constriction resistance models. For given surface profiles and material properties of two contacting surfaces, and a specified contact pressure, the surface characterization technique filters out non-essential wavelengths on the surface, after which the surface deformation analysis calculates the deformation and contact area of each contacting asperity by considering three different modes of deformation, namely, elastic, elastic–plastic, and plastic. The constriction resistance model is then used to calculate the constriction resistance for each contacting asperity based on the area of contact and radius of curvature of the asperity. The constriction resistance values for all the contacting asperities are then used to calculate the total thermal contact conductance. An experimental facility has also been constructed to measure thermal contact conductance of interfaces to verify the results of the predictive model. Good agreement has been found between the model predictions and experimental measurements, validating the modeling approach.     

An experimental study of film cooling in a negatively bowed cascade with a large turning angle

Transverse measurements are carried out at the outlet of the straight and negatively bowed turbine cascades with a 106° turning angle respectively with and without cooling air injection. The air injection is from single or multiple rows of ten holes (26 schemes in all). Experimental results show that the negatively bowed cascade produces more energy loss than the straight one without cooling air injection. Cooling air injection from the holes on both the pressure and the suction surface near the trailing edge can reduce energy losses in both the straight and the negatively bowed cascades. The increase in loss is less in the negatively bowed cascade than that in the straight one with cooling air injection from holes of multiple rows at the leading edge, whereas cooling air injection from holes of multiple rows at the trailing edge reduces the energy loss in the negatively bowed cascade. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(1): 1–8, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20042     

Distribution of heat sources in vertical open channels with natural convection

In this paper we use the constructal method to determine the optimal distribution and sizes of discrete heat sources in a vertical open channel cooled by natural convection. Two classes of geometries are considered: (i) heat sources with fixed size and fixed heat flux, and (ii) single heat source with variable size and fixed total heat current. In both classes, the objective is the maximization of the global thermal conductance between the discretely heated wall and the cold fluid. This objective is equivalent to minimizing temperature of the hot spot that occurs at a point on the wall. The numerical results show that for low Rayleigh numbers (∼10²), the heat sources select as optimal location the inlet plane of the channel. For configuration (i), the optimal location changes as the Rayleigh number increases, and the last (downstream) heat source tends to migrate toward the exit plane, which results in a non-uniform distribution of heat sources on the wall. For configuration (ii) we also show that at low and moderate Rayleigh numbers (Ra_M ∼ 10² and 10³) the thermal performance is maximized when the heat source does not cover the entire wall. As the flow intensity increases, the optimal heat source size approaches the height of the wall. The importance to free the flow geometry to morph toward the configuration of minimal global resistance (maximal flow access) is also discussed.     

Spray impingement cooling with single- and multiple-nozzle arrays. Part I: Heat transfer data using FC-72

With electronic packages becoming more dense and powerful, traditional methods of thermal energy removal are reaching their limits. One method of direct contact cooling capable of removing high heat fluxes while still being compact in size is spray impingement cooling, but its heat transfer behavior is not understood well enough to enable systematic, practical system design. This work presents the results of a large parametric study of spray cooling using a number of different nozzle patterns. It was found that nozzles that use the fluid most efficiently to remove thermal energy were limited by low peak heat fluxes and that the highest peak heat fluxes were obtained when phase change was avoided. Multiple nozzle arrays allowed for higher peak heat fluxes but used fluid inefficiently due to interactions between neighboring sprays. In general, the geometric pattern of the nozzle arrays had little effect on overall heat transfer performance.     

发电厂直接空冷系统的可行性探讨

根据我国目前水资源的基本情况 ,阐明了建造空冷发电厂的必要性 ,多方面比较了直接空冷系统与湿冷系统的特点 ,以及由此带来的相应主设备选型上的差异。从技术经济学角度出发分析了水源对于冷却系统的重要性 ,结合具体实例分析了建设直接空冷机组的可行性 ,最后提出了一些探讨性的见解     

Comfort criteria for passively cooled buildings a pascool task

The application of passive cooling techniques to buildings in warm climates creates the need for appropriate comfort criteria. Conventional comfort criteria, usually based upon laboratory experiments, seem to be unnecessarily severe. The paper describes preliminary findings of the PASCOOL Thermal Comfort task which, responding to renewed interest in behavioural aspets of thermal comfort, sets out to establish appropriate limits by field studies and theoretical considerations.     

一种新型高效敞开式空调系统

报道了一种应用于敞开吸收式空调系统的新型空气循环方式，它可以显著地改善系统进行特性，提高效率，减小设备尺寸，降低造价，同时还可提高系统致冷贮存能力。     

基于热传导技术的数据中心冷却系统的研究与应用

随着近年来国内外数据中心建设和运营的蓬勃发展,数据中心能耗问题也日益突出,如何有效减少能源浪费、增加能源使用效率成为数据中心节能减排工作重点。本文针对数据中心能耗占比较高的空调系统,提出了“液冷为主、风冷为辅”的双通道冷却系统架构,通过建立基于热传导技术的低热阻高效率导热通道,实现大部分热量的高效传导、自然冷却,同时大幅减少制冷系统能耗。