Use of R-114 as the working fluid in a flat-plate collector system for electric power generation

The use of flat-plate solar collectors for the generation of electric power is attracting the attention of engineers and scientists for its simplicity in construction and operation. The efficiency of collection is low due to the low operating temperatures of the flat-plate collectors. In the low temperature range applicable to flat-plate collectors, refrigerants can be used as working fluid. The cost of construction can be reduced by the suitable selection of collector and refrigerants. It has been shown that R-114 has suitable characteristics for use as a Rankine cycle working fluid. By using an aluminium tube-plate type collector with 0·005 m tube diameter, 10 risers per metre width of collector, it becomes light and cheap. When the emissivity of the collector is 0·1 and a single cover is used, the maximum efficiency condition is attained. Limited to a pressure drop of 2·5 bar in the collector, 16 collectors can be used in series and the overall efficiency can be as high as 7·8% under 1000 W/m² insolation conditions and for an outlet temperature of 380 K. Under these conditions 5600 collectors of 1·5 m × 1·5 m size will be required to produce 1000 kW of electricity.     

Short-term thermal performance of a built-in solar storage for frost prevention in a greenhouse

Built-in solar storage is an alternative to the traditional solar collectors. This paper explores the possibility of utilizing such solar stores for frost prevention in greenhouses. In the study, two identical NE–SW orientated greenhouses with 50 m² ground area were erected. The total ground area and volume of the water stores used in the solar greenhouse were about 6·4 and 5·4% of the total ground area and volume of the greenhouse. The short-term results showed that at times when the air temperature in the control greenhouse dropped below 0°C, it was about 3·5°C in the solar greenhouse, and sometimes this difference was more than 4·5°C. The average fraction of solar energy storage by the stores was 0·26 for a four day period. © 1998 John Wiley & Sons, Ltd.     

Performance of a solar dryer using hot air from roof-integrated solar collectors for drying herbs and spices

A solar dryer for drying herbs and spices using hot air from roof-integrated solar collectors was developed. The dryer is a bin type with a rectangular perforated floor. The bin has a dimension of 1.0 m×2.0 m×0.7 m. Hot air is supplied to the dryer from fiberglass-covered solar collectors, which also function as the roof of a farmhouse. The total area of the solar collectors is 72 m². To investigate its performance, the dryer was used to dry four batches of rosella flowers and three batches of lemon-grasses during the year 2002–2003. The dryer can be used to dry 200 kg of rosella flowers and lemon-grasses within 4 and 3 days, respectively. The products being dried in the dryer were completely protected from rains and insects and the dried products are of high quality. The solar air heater has an average daily efficiency of 35% and it performs well both as a solar collector and a roof of a farmhouse.     

Axial and radial heat transfer studies in a circulating fluidized bed

The axial and radial variation of the heat transfer coefficient in a circulating fluidized bed riser column, and the effect of operating parameters thereon, are investigated. The experimental set-up consists of a riser column of 102 mm×102 mm in bed cross-section, 5·25 m in height with a return leg of the same dimensions. The unit is fabricated with plexiglass columns of 0·6 m in length which are interchangeable with one another. Two axial heat transfer test sections of 102 mm×102 mm in cross-section, 500 mm in height, and made of mild steel, are employed for the axial heat transfer study and one horizontal tube section of 22·5 mm OD made of mild steel is employed for the radial heat transfer study. The primary air velocity is varied between 4·21 and 7·30 m s⁻¹. Local sand of mean size (d_p) 248 μm is used as the bed material. One empirical model with the help of dimensional analysis has been proposed to predict the heat transfer coefficient to a bare horizontal tube in a CFB riser column and the model results are validated with the experimental data; good agreement has been observed. © 1997 John Wiley & Sons, Ltd.     

Experimental study on dynamic performance analysis of a flat-plate solar solid-adsorption refrigeration for ice maker

A flat-plate solid-adsorption refrigeration ice maker has been built for demonstration purposes. The working pair consists of methanol used as the refrigerant and activated carbon as the adsorption medium. The adsorbent bed is constructed of two flat-plate collectors, with a total surface area of 1.5 m². Solar radiation can be simulated with quartz lamps and some important parameters such as temperature and pressure of each subsystem can be handled by a computer. The experimental results show that this machine can produce 4–5 kg of ice after receiving 14–16 MJ of radiation energy with a surface area of 0.75 m², while producing 7–10 kg of ice after receiving 28–30 MJ of radiation energy with 1.5 m². These are the most advanced results for a solar ice maker so far. All these successful achievements will speed up the commercial processing of a solar ice maker.     

Performance analysis of solar chimney using mathematical and experimental approaches

A mathematical model based on one‐dimensional energy and mass balance across the solar chimney has been developed. The air flow characteristics such as exit velocity and temperature are evaluated with respect to the collector inclination angle, hourly solar radiation, ambient temperature, and wind speed. The model is validated by comparing the performance parameters obtained, with the experimental results and also with the experimental data of different geometrical range and environmental conditions from the literature. An average deviation of 8% for exit air velocity and 1.35% for exit air temperature is obtained for the solar chimney with absorber inclination angle 30°, collector area 0.41 m², and chimney height 0.24 m. The experimental daily average and maximum exit air velocity during the month of April are 0.5 and 0.88 m/s, respectively. The predicted optimum operating conditions are 75° inclination angle, 0.63 m² absorber area, and 0.48‐m chimney height. The maximum average exit air velocity and temperature numerically obtained are 0.64 m/s and 331 K, respectively, when operating with optimum conditions. It is observed that the exit air velocity increases 33% by increasing the absorber area from 0.5 to 3 m² for a solar chimney with 0.5 m height. An increase in exit air velocity of 52% was obtained by increasing the chimney height from 0.5 to 3 m for a solar chimney with 0.64 m² absorber area. A reduction in exit air velocity of 4% was observed for the increment in wind flow over the glass cover from 1.5 to 3 m/s. These results confirm that the solar chimney could be designed based on the predicted monthly performance by the present model.     

Performance Analysis of Flat-Plate Solar Collector Having Silver Nanofluid as a Working Fluid

A study on water solar collector performance having silver nanofluid as working fluid was carried out. In this study, 20-nm silver particles mixed with water at the concentrations of 1,000 and 10,000 ppm were undertaken in 3 small identical closed-loop flat-plate solar collectors, each with an area of 0.15 m × 1.0 m. The mass flux of the working fluid varied between 0.8 and 1.2 L/min-m² and the inlet temperatures were controlled in the range of 35–65°C. The tests were performed outdoor under a steady-state condition. The experimental results showed that at the same Reynolds number, the convective heat transfer coefficient of the nanofluid inside the solar absorber tube at 1,000 ppm was slightly higher than that of water, and at 10,000 ppm, the heat transfer coefficient was about 2 times that of water. This meant that the overall heat loss coefficient of the solar collector with nanofluid could be reduced and more solar heat gain could be obtained, especially with a high inlet temperature of the working fluid. In our experiments, for 10,000 ppm concentration of silver nanoparticles, the optical characteristic and the thermal loss characteristic of the solar collector, under steady-state condition with a mass flux of 1.2 kg/min-m², were 0.691 and 4.869 W/m²-K, compared with 0.684 and 7.178 W/m²-K, respectively for 1,000 ppm concentration and 0.702 and 8.318 W/m²-K for water. When the flow rate was different from the standard value, the solar thermal characteristics were also improved with the nanofluid.     

Design performance and economics of a low-cost solar wax melter for the candle industry

Solar thermal energy is a viable energy option for low-temperature applications (< 100 °C), especially in developing countries, where at present fossil fuels (coal and petroleum products) and firewood are inefficiently being used for such applications. The candle-making industry requires solid wax to be melted at about 62 °C. Flat-plate solar thermal collectors can be advantageously used for this purpose. This article describes the conventional method of melting wax and the solar alternative proposed. Experiments conducted using the fabricated solar wax melter of collector area 0·64 m² shows that about 13–15 kg of solid wax could be melted per day. An economic analysis done to compare the cost of the solar wax melter with that of the conventional methods of melting wax indicates the economic viability of the proposed system. It has also been shown how such renewable energy devices could be used for generating gainful employment in rural areas owing to its simple technology, easy use and economics.     

Efficiency investigation of a new-design air solar plate collector used in a humidification–dehumidification desalination process

The aim of this research is to experimentally study the efficiency of a new-design plate collector used to heat air in a new desalination humidification–dehumidification process. In fact, in such processes, the air solar collectors work at unusual experimental parameters (forced convection, elevated air humidity, high solar irradiation…). At these stressed experimental conditions, few published works are available in literature. Furthermore, the comparison of the efficiency of collectors running with normal air humidity content (about 10–20 g kg⁻¹) and air of elevated humidity (20–50 g kg⁻¹) were not yet published as our knowledge. In the present investigation, a new air solar plate collector was designed and developed for its use in a desalination process. Moreover, a characterization of such collector was performed under different experimental conditions. The effect of different parameters, namely: the solar radiation, the wind velocity, the ambient temperature, the air mass flow rate, the inlet air humidity and temperature, on the collector efficiency was also investigated. The collector was optimized for its use in a new solar desalination process. In fact, the air solar collector was designed in order to lower its economic cost making them applicable for water desalination.     

Investigation of the bubble behaviour at the free surface of a large three-dimensional gas fluidized bed

Gas fluidization is generally associated with the formation of bubbles that critically influence the performance of fluidized bed processes (FBPs). Therefore, in the design, simulation and operation of FBPs, it is very essential to know the behaviour of the bubbles at the free surface. The size and growth of bubbles play an important role for determining properties such as bed expansion, solids entraiment, in-bed heat transfer and solid mixing. This paper presents a study on the behaviour of bubbles at the free surface of a large three dimensional gas-fluidized bed with square section of 61×61 cm². Measurements were carried out to determine the effects of bed height and excess air velocity on the bubble eruption diameter, frequency and bubble fraction. All experiments were performed at freely bubbling mode and the flow characteristics of bubbles were recorded by a video camera. Bed materials used were 593 μm raw perlite and 1233 μm sand falling within the categories of Geldarts Groups B and D, respectively. The fixed bed height ranged from about 8–18 cm for raw perlite and 9–26 cm for sand. The excess air velocity was varied between 0·5 and 1·75 cm s⁻¹ for raw perlite and 13 and 25 cm s⁻¹ for sand. Equations related to the bubble count, frequency, flow area shape factor and through-flow coefficient were given using a modified form of two-phase theory of fluidisation. Observations were made to validate the two-phase theory for two different particles. The flow area shape factor was in the range of 0·47–0·81 for raw perlite and 0·20 to 0·57 for sand, with mean values of 0·6 and 0·4, respectively. The through-flow coefficient was found to be between −0·68 and 2·82 for raw perlite and between 3·27 to 15·87 for sand, and was larger than predicted values of classical bubble models. © 1998 John Wiley & Sons, Ltd.     

Solar passive heating through a thermosyphon air panel

Thermosyphon air panels installed on the south wall of a building are being used for solar space heating in the cold desert climates of North India. This paper presents a simulation model to predict the performance of such panels; a numerical evaluation of the performance has been made, using the meteorological data for January (having maximum and minimum temperatures equal to ?2·°C and ?14·2°C, respectively, and an insolation of 4·58 kWh/m² day on the horizontal surface). For typical weather condition in January a 1·62 m² thermosyphon air panel is seen to collect about 2·3 kWh of energy per day with a rise of temperature of about 2·5°C to 13·5°C (with room air at 18°C as inlet air) and a working efficiency of approximately 32·5 per cent.     

Productivity enhancements of compound parabolic concentrator tubular solar stills

The performance of compound parabolic concentrator assisted tubular solar still (CPC-TSS) and compound parabolic concentrator-concentric tubular solar still (CPC-CTSS) (to allow cooling water) with different augmentation systems were studied. A rectangular saline water trough of dimension 2 m × 0.03 m × 0.025 m was designed and fabricated. The effective collector area of the still is 2 m × 1 m with five sets of tubular still – CPC collectors placed horizontally with north-south orientation. Hot water taken from the CPC-CTSS was integrated to a pyramid type and single slope solar still. Diurnal variations of water temperature, air temperature, cover temperature and distillate yield were recorded. The results showed that, the productivity of the un-augmented CPC-TSS and CPC-CTSS were 3710 ml/day and 4960 ml/day, respectively. With the heat extraction technique, the productivity of CPC-CTSS with a single slope solar still and CPC-CTSS with a pyramid solar still were found as 6460 ml/day and 7770 ml/day, respectively. The process integration with different systems cost was found slightly higher but the overall efficiency and the produced distilled water yield was found augmented.     

Experimental investigation of the effect of using the cylindrical parabolic collector,different solar panels and their cooling on seawater desalination in double-slope solar still

ABSTRACT

The present study was aimed at examining the effect of using solar panels and cylindrical parabolic collectors, or CPCs, on solar still unit. Cooling of the solar panels up to 25°C has been also conducted in order to rise the amount of produced freshwater. In the first setup, the solar still unit has been made up of 300 W and 600 W solar panels along with the CPC devices of lengths 1 m and 2 m outside for water heating. The second setup was designed in a way that water is heated by the solar panels as well as the CPC device with the copper pipe circulation inside the solar still unit, so the hot water within the pipe has raised the temperature of the water as a heat exchanger inside the solar still. Based on the results, the second setup had a higher efficiency than the first setup. Moreover, the highest amount of fresh water was 4.215 kg and 5.091 kg during one day in the first setup and the second setup, respectively. Cases 1 to 6 are related to the first setup and cases 7 to 12 are related to the second setup. The lowest fresh water production in case 1 was 2.852 kg. the highest water temperature in experimental setup 1 was 71.9 °C and in experimental setup 2 was 84.8°C.     

Experimental study with operational solar‐sorption cooling

Building integrated solar systems have been considered as a reasonable system for building heating, cooling and hot water supply. Various types of solar collectors, such as plate type, evacuated tube type and solar air collector, have been used as the heat source, whereas adsorption chillers, absorption chillers and desiccant dehumidification systems have been considered to match the above solar heat sources. Now, such sorption chillers are more matured, but their coupling with suitable solar heat source is not well researched. Experimental study has been done in this paper to analyse four kinds of typical solar air‐conditioning system with different sorption chillers and solar collectors. Copyright © 2012 John Wiley & Sons, Ltd.     

Estimation of bed expansions in a freely-bubbling three-dimensional gas-fluidized bed

Knowledge of bed expansions is important in the design and operation of gas–solid fluidized beds. This paper presents a study on the estimation of expanded bed height in a large three-dimensional gas-fluidized bed with a square section of 0·61×0·61 m². All experiments were performed at the freely bubbling mode and the bed expansions were recorded by a video camera. Bed materials were used 593 μm raw perlite and 1233 μm sand falling within the categories of Geldart's Groups B and D, respectively. The bed height at minimum fluidization ranged from 0·0398 to 0·3176 m, while the excess air velocity from 0·034 m s⁻¹to 0·7453 m s⁻¹. Equations related to the bed expansion were given using a modified form of two-phase theory of fluidization. A correlation for the average bed expansion (void fraction) was also presented that has been derived from the principal form found successful in gas–liquid systems as follows: R=0·5482 d^−0·129_p(U_o−U_mf)^0·111 with an average deviation of less than 1%. The experimental findings were compared with previously reported results and were discussed in the light of available correlations. © 1998 John Wiley & Sons, Ltd.     

Detailed comparison of the performance of flat-plate and vacuum tube solar collectors for domestic hot water heating

The performance of a DHW system fitted with flat-plate and vacuum collectors has been analysed. Simulations were carried out on the basis of equal aperture or gross areas of basis using TMY data for hour-by-hour dynamic simulation generated for 1036 sites located in different regions of the world. The performance indicators of solar fractions and number of days were determined for specific water mean temperatures in the storage tank of 37 °C, 45 °C and 55 °C. It has been shown that vacuum tube collectors provide slightly better DHW performance indicators than typical flat-plate collectors having the same aperture area. However, since the space that needs to be provided and directly or indirectly paid for is what matters to the user of solar heating systems, the analysis was also carried out on equal gross area basis; on this basis, the advantages of using vacuum collectors are not obvious.     

Design of a solar collector for year-round climatization

Solar heating systems in buildings have increasingly been studied in the past two decades. In several applications the primary energy demand is now for both heating and cooling, and modern solar collectors should be designed to provide climatization during the whole year. Solar systems are seldom applied in Europe, and large buildings, such as office buildings and schools, continue to be built with mechanical ventilation systems.The study presented in this paper is part of a European XVII Thermie project entitled “Pilot project for photovoltaic, energetic and biohousing retrieval in a school”, whose aim was to install a photovoltaic plant and solar air collectors coupled with a sun breaker structure at a scientific high school in Umbertide, in central Italy.This paper describes the research and development activities concerning a solar air collector suited for winter heating and summer ventilation, which was installed at the high school. The collector physical and numerical modelling of heat transfer and fluid flow in winter operation is presented. The system performance has been estimated as a function of different parameters in order to provide a tool for the design process. Furthermore, the climate in the area has been simulated through the available experimental data, and the system behavior under these conditions is presented.The collectors were installed at the scientific high school in Umbertide in spring 2001. Summer ventilation cooling is under testing and an experimental test period is foreseen next winter to validate the design of the collectors and their performance.     

无盖板渗透型太阳能空气集热器热性能的实验研究

无盖板渗透型太阳能空气集热器是一种易于实现建筑一体化的高效新风预热及干燥装置。为了掌握无盖板渗透型集热器在实际工况下的热性能,建造了集热面积为2.2 m2的太阳能空气加热系统实验台,并在2009年2月至2009年4月对其热性能进行了户外瞬态实验研究。实验结果表明出口空气温度随辐射强度的增加而升高,太阳辐射强度是影响集热器出口空气温度的最重要因素,而室外空气温度的影响极小。空气温升随风量的增加而减小,集热器热效率随风量的增加而增大。在三个测试日中集热器的平均热效率分别为58%、63%和72%,高于普通平板太阳能空气集热器。     

Efficiency of fresnel lenses with respect to thermal losses

Experimental observations and heat loss calculations for a Fresnel lens under forced and natural convection have both been obtained. A lens with a 2·0 mm step width and 325·99 cm² area when exposed to solar radiation and kept normal to solar radiation with an intensity of 43·116 cal/cm²/h has given a steady-state temperature of 187·5°C at its focus.     

Factors influencing solar energy collector efficiency

The effects of glazing, solar flux, emissivity and absorptivity of the absorber surface on collector performance have been predicted for different plate temperatures (60°C and 100°C). At low solar flux levels (200–600 W m^?2) double- or triple-glazed collectors are superior to single-glazed collectors. For collectors with selective absorber coatings, the optimal number of glazing panes is two. Higher values of absorptivity and lower values of emissivity are more effective for single-glazed than for double-glazed collectors.