'Solar Energy\r'

'A current solar powered surface assimilation refrigerator with risque performance Meunier published a comparison of those terce sorption agreements for solar engine cooling arrangement system (Meunier, 1994). The solid-gas system use in the symbolise schooling is surface assimilation. The solar surface assimilation refrigerators remove been developed in general to be apply in hot regions with no electrical push supply. There is an urgent need in the health sector (for the conservation of medicines and vaccines). These systems set about the advantage of not requiring any button other than solar energy.Regarding performance, the highest values of COPSR (0. 10-0. 12) were obtained with the surface assimilation systems zeolite + irrigate (Grenier et al. , 1988) and activated deoxycytidine monophosphate + methanol (Boubakri et al. , 1992a,b; Pons and Grenier, 1987). As methanol freighter easily evaporate at temperatures under O oc, thus favouring the production of ice, the around environmentally friendly refrigerating moldiness be water. Using water, ice john be produced within the evaporator, acting as a ‘ polar storage. Both refrigerants, water or methanol, operate at infra atmospheric pressure and therefore subscribe vacuum technology. The main urpose of the present study is to obtain what is, technically speaking, a saucer-eyed cable car.This aim seems reasonably achievable with an surface-assimilative machine, operated in a 100% solar-powered 24 h cycle with a flat-plate solar storage battery containing the adsorbent. However, when referring to the work reported higher up, both the efficiency of the solar accumulator register and that of the adsorption thermodynamic cycle could be improved. These requirements were important to the design of the ‘advanced machine. The laboratory of solar energy of the Engineering school of the Canton de Vaud (EIVD, Yverdon-lesBains, Switzerland) has been eveloping adsorptive sol ar refrigerators since 1999. The first systems built used the adsorption pair of activated carbon + methanol.For reasons of reliability and respect for the environment, this pair has been put away in favour of a silicagel + water pair. The prototype described and analyzed in this paper has been functioning since the summer of 2000 on the site of the EIVD. A thorough meter system allows us to restrict it in a complete way. During the summer of 2001, a constant procedure of thermal clog in the cold cabinet allowed us to observe the behaviour of the adsorption system over a continuous stay of 68 ays. We have highlighted the great charm of both impertinent temperature and daily rotating shaft upon the daily coefficient of performance (COPSR ). Previously, few articles were elicit in the analysis of the storage. 2.Description of adsorption and of the adsorption cooling cycle Adsorption, also cognise as physisorption, is the process by which molecules of a fluid are laid on the walls of a solid material. The adsorbed molecules undergo no chemical reaction but simply lose energy when being fixed: adsorption, the phase change from fluid to adsorbable (adsorbed phase) is exothermic. Moreover this process is reversible. In the following, we will focus on adsorption systems mainly used in cooling (or heatpumping) machines: a pure refrigerant drying up that canister easily be condensed at close temperature and a microporous adsorbent with a man-sized adsorption capacity.The main comp mavennts of an adsorptive cooling machine are the adsorber (in the present case, the solar collector itself), the condenser, the evaporator and a throttling valve amidst the last two devices, see Fig. 2. An beau ideal cycle is presented in the D‚¬hring plat (LnP vs. …I=T), Fig. 1. 2001). We can summarize it in four stages. C. Hildbrand et al. / solar Energy 77 (2004) 311-318 13 Fig. 1 . An ideal adsorption cooling cycle in the D‚¬ hring diau gram. Sat uration liquid- vapour curve for the refrigerant (EC dashed line), isoster curves (thin lines), adsorption cycle (thick lines). alter percentage point: step AB (7 a. m. fl 10 a. m. ) and step BD (10 a. m. fl 4 p. m. ); cooling period: step DF (4 p. m. fl 7 p. m. ) and step FA(7 p. m. fl 7 a. m. ). mensuration 1: isosteric heating ¶A ! BD. The system temperature and pressure increase due to solar irradiance. Step 2: desorption + compression dB ! DD. Desorption of the water steam contained in the silicagel; condensation of the water steam in the ondenser; the water in the evaporator is drained through the valve. Step 3: isosteric cooling ?D ! FP. shine of the period of sunshine; cooling of the adsorber; strike of the pressure and the temperature in the system. Step 4: adsorption + evaporation ¶F ! AD. vaporization of water contained in the evaporator; cooling of the cold cabinet; production of ice in the evaporator; readsorption of water steam by the silicagel. 3.Descripti on of the machine tested in Yverdon-les-Bains, Switzerland Adsorptive pair. The refrigerant is water, and the adsorbent is a microporous silicagel (Actigel SG¤ , Silgelac). Collector-adsorber. The solar collector (2 m2 , tilt angle of 300) is double-glazed: a polytetrafluoroethylene¤ film is installed amidst the glass and the adsorber itself. The adsorber consists of 12 parallel pipages (72. 5 mm in diameter) that contain the silicagel (78. 8 kg). The tubes are cover with an electrolytic selective layer (Chrome-black, Energie Solaire SA), which absorbs 95% of the visible solar radiation plot of land presenting an emissivity of 0. 07 in the infrared wave-lengths.A valve located between the graduated tank and the evaporator is needed on this machine. For control strategy reasons, this valve is electrically powered. 4. 5. public exposure damper management Closing: when the irradiance goes above 100 W/m2 . Opening: at the end of the afternoon when the angle of the solar beam r adiation incident upon the aperture monotonous of collector (angle of incidence) is above 500. 4. Measurements and operations The objective lens of the 2001 serial of measuring rods was to obtain a high number of beats continuously, in order to characterise he working of our adsorption machine. To do this, a system of measurement and a constant procedure of load has been established. 4. 1.Measurements The temperature is thrifty (probes Pt100) in the silicagel of a central tube of the collector-adsorber (7 sensors), on two condenser tubes and three evaporator tubes; and the ambient air temperature is also mensurable. The vapour pressure is measured by a piezogauge in the collector-adsorber, in the condenser and in the evaporator. The global irradiance in the plane of the collector is recorded by a pyranometer. A graduated tank (6. 5 1) collects the condensed water. The level of liquid water is automatically measured by a level detector. The series of measurements took place fro m July twenty-fifth to September thirtieth 2001 (68 days) in Yverdon-lesBains (altitude: 433 m, longitude: )6. 380, latitude: 46. 470). Fig. 3 shows the discover weather conditions (daily ray of light and inculpate external temperature).This graph shows two different periods: (1) From July 25th to the beginning of September: during this summer period, the beggarly external temperature is above 20 oc and the mean daily irradiation reaches 22 MJ/m2 . This o.k. weather period is interrupted between the 3rd and 9th August by ess well-heeled weather. (2) From the beginning of September to the end of the measurement: the mean external temperature and the daily irradiation are distinctly lower (13 oc and 13 MJ/m2 ). Furthermore, the conditions are very variable from one day to the next. 4. 2. Acquisition system and influence 6. Performance of the tested unit A Labview¤ program takes measurements and administers various commands (valve, dampers and load). A measurement is made eve ry 30 s.\r\n'