太陽能光伏存儲技術(shù)外文翻譯- 聚光器驅(qū)動吸收式冷水機(jī)組的熱存儲設(shè)計（英文）

1、Engineering, 2013, 5, 107-116 doi:10.4236/eng.2013.51A016 Published Online January 2013 (http://www.scirp.org/journal/eng) Design of Heat Storage for a Solar Concentrator Driving an Absorption Chiller M. A. Serag-Eldin

2、 Mechanical Engineering Department, American University in Cairo, Cairo, Egypt Email: amrserag@aucegypt.edu Received September 24, 2012; revised November 6, 2012; accepted November 15, 2012 ABSTRACT The feasibility of

3、employing stand-alone solar energy systems to meet demand-side loads depends strongly on provid- ing appropriate solar energy storage. The present paper presents an efficient and economical, underground, thermal storag

4、e design to store hot water at a temperature of around 180?C required for running a double effect absorption chiller to cool a zero-energy-house in a desert environment. The performance of the design is evaluated employ

5、ing a specially developed efficient mathematical model, for simulating the steady state radiation, convection and conduction processes occurring within the storage unit. The model is presented and analyzed, and employe

6、d to investigate the ef- fects of various design parameters on storage efficiency. It is demonstrated that high storage efficiency may be reached, providing that appropriate insulation materials are used. It is also re

7、vealed that the soil conductivity has little effect on storage efficiency. Keywords: Thermal Energy Storage; Hot Water Storage; Solar Energy; Solar Air-Conditioning; Green Buildings 1. Introduction Solar radiation varie

8、s greatly throughout the daytime hours, whereas it is completely absent during night-time hours, which poses a challenge in adapting solar energy to match stringent demand-side requirements. Thus for stand-alone oper

9、ation, resort has to be made to energy storage in order to supply the difference between input and output at all hours. The favored storage media depends on the type of so- lar collection system, and the end use. For

10、 example, when roof-top Photovoltaic modules are employed to collect solar radiation and convert it straight to electrical energy to drive an electrical vapor-compression type chiller, e.g. [1], an attractive choice

11、would be lead acid batteries. Alternatively, high temperature applications employ- ing heat as the source of energy often use concrete or ceramic storage, as well as molten salts and chemical sto- rage [2,3]. Phase

12、change energy storage, has the advan- tage of high intensity, but is restricted to the temperatures at which phase changes occur, which is a property of the material used and hence it may not be possible to find appr

13、opriate materials for all applications. In this work we are concerned with the design of a so- lar energy storage unit for a stand-alone solar energy concentrator, driving a double effect absorption chiller system to

14、 cool a two floor house in a hot desert environ- ment. The storage unit should be economical, highly ef- ficient, reliable, and easy to build and maintain on site. Previous investigations have revealed that for the t

15、ypical desert environment, a double effect absorption chiller is generally preferred to a single effect one [4], because of its higher efficiency; the latter also results in less heat rejection from the condenser, whi

16、ch may be a serious problem with the shortage of water in the desert [5]. However, double effect chillers require a heat source at approximately 170?C, thus setting the target tempera- ture for the heat storage unit

17、at 180?C for the supply to the chiller-generator, and 170?C for the return from gene- rator. For simplicity, economy, environmental friendli- ness, as well as reliability, it is proposed here to use hot water storage

18、 with water pressurized to approximately 12 bars to avoid boiling. Accurate estimation of storage efficiency is essential for proper sizing of collector equipment capacities, and the determination of the collection a

19、rea of the roof. Thus a mathematical model is developed specially for that purpose, which exploits the three-dimensional conduc- tion equation solution capabilities of a commercially available code, but introduces sp

20、ecial simplified treat- ment for radiation and convection terms to reduce un- necessary complicated computations. Although the motivation behind this work was the de- sign of appropriate storage for a specific solar

21、application, the design is equally applicable to any solar collectors Copyright © 2013 SciRes. ENG M. A. SERAG-ELDIN 109Figure 2. Cro

22、ss-sectional plan cutting through horizontal mid-plane. side air-gap of 10 - 20 mm. Thus any one tank may be lifted upwards and removed from the storage-unit sepa- rately without destroying the surrounding insulation o

23、r damaging neighboring tanks. The small width of the gap does not allow significant convective currents [9], there- fore the only mechanisms for heat transfer would be con- duction and radiation. The former is low be

24、cause of the low thermal-conductivity of air, whereas the latter is held at bay by the low emissivity (high reflectivity) of the liner, and by another shiny aluminum plate cover on the insulation side facing the line

25、r. The air-gap also allows the installation of vapor detec- tors and temperature sensors. A sudden increase of their readings would indicate a leak in the nearby storage tank, causing an alarm to be triggered. Sugg

26、ested insulation material include common glass- wool, glass fiber, or mineral-wool blankets all of which are widely available and cheap, and display a coefficient of conductivity k ≈ 0.04 W/(mK) [10]. More sophisti-

27、cated materials with superior insulation properties in- clude micro-porous insulation based on Pyrogenic silica with k = 0.022 W/(mK), at 200?C, Silica Aerogels with typical k = 0.017 W/(mK) , and Silica Aerogels wit

28、h Car- bon Black displaying a conductivity as low as k = 0.004 W/(mK) [11]. It is remarked that condensation is not an issue here, as the whole structure is air-tight, the external desert air is typically exceptionall

29、y dry, and the high in- ternal temperature in the insulation section results in very low relative humidity. The thickness of insulation between the interior tank’s surfaces is 100 mm, whereas the thickness of insulat

30、ion at the exterior surfaces is 500 mm. The insulation on the exterior tank walls wraps around all the tanks, as shown in Figure 2. Following the external surface of the insula- tion are 19 concentric radiation shiel

31、d plates formed from polished aluminum plates approximately 1 mm thick and separated by an air gap of approximately 9 mm. These introduce an effective thermal resistance between the insulation material and the 50 mm

32、thick timber covering the reinforced concrete side-walls. The heat transfer across the thermal shield is by both conduction and radiation, but not convection because of the small width of the air-gap. All the aluminu

33、m surfaces are assumed to display an emissivity of 0.07, which lies mid-way between the 0.04 - 0.1 range typical of polished commercial plates. The radiation shield is much more effective as a thermal resistances at

34、low temperatures than at higher ones, because of the dependence of radia- tion on the 4th power of temperature, and the lower con- ductivity of air at lower temperatures; thus it has been Copyright © 2013 SciRes.