Solar & Wind Technology最新文献

The aim of this paper is two fold. Firstly, to predict two methods for estimating the monthly daily and monthly hourly diffused solar radiation on a horizontal surface on clear days. Measurements of the total and diffused solar radiation, available in Baghdad during the period 1967–1985, are used to obtain the regional regression coefficients. The second aim of this paper is to deal with the effect of dust on energy recieved from solar systems. A dirt correction factor is estimated by carrying out a comparison study on a pair of glass sheets placed horizontally. The study is carried out at a topical location in Iraq during the period 1971–1980. The rising dust frequencies distribution with wind speed is studied.

One of the most significant factors limiting the performance of solar powered solid absorption refrigeration systems is the low rates of heat and mass transfer within the absorbant pellet. Solutions to these problems are discussed in this paper. They include the use of suitable additives or treatments, and the dispersion of the absorbent in an inert liquid which has a high absorption capacity for the refrigerant without impeding the absorption and generation reactions. With particular reference to the calcium chloride/ammonia system, the experimental investigation of the idea of dispersing the absorbent in an inert liquid is reported here. The tests were performed by simulating the absorption and generation reactions in two mild steel pressure vessels, one acting as the absorber/generator, and the other as the receiver of the condensed refrigerant. Normal heptanol was used as the inert liquid. The novel feature of the investigation is the use of a bubble agitation device in order to dispense with mechanical stirring of the dispersion. Heating was done electrically, pressure, temperature and mass measurements being taken. The results indicate that the absorption and generation reactions were at least five times faster with the dispersion. The practical problems of utilizing the absorbent in this form in solar refrigeration systems are considered.

A solar driven, high efficiency, compound refrigeration system is considered, made up of two cooperating absorption parts, which use NH₃/H₂O and H₂O/LiBr solutions, respectively. Solar heat is given to the vapour generator of the NH₃/H₂O unit, and the heat produced by the absorber and the condenser of this unit is supplied to the vapour generator of the H₂O/LiBr unit. A method for simulating the operation of the compound system has been developed and applied for predicting the hour by hour performance of the system operating during the typical year in Athens, for which solar radiation and ambient temperature data are available. An optimization study for the compound and the individual cycles has also been made. Very high performance of the system has been predicted. For example, on 21 May, the calculated theoretical coefficient of performance is 219% while the corresponding theoretical values of single H₂O/LiBr and NH₃/H₂O units are 93% and 65% respectively. The corresponding calculated cooling power produced by the system is 543 W/m²-collector. An annual analysis shows that the cooling produced by a NH₃/H₂O unit in Athens is 0.87 GJ/m²-year, while the present compound system gives an impressive increase to 3 GJ/m²-year.

Rural development policies in India have rarely been designed for women as beneficiaries of development schemes. This is despite the fact that the women in rural communities, especially the very isolated, play a crucial role towards maintaining families at a subsistance level. The economics of womens' contribution in terms of energy, goods and income supplement is not clearly understood and often overlooked by planning authorities. An attempt is being made here to demonstrate the major role played by women in energy usage and expenditure, by quantifying womens' work in terms of household income distribution. The point being made is that womens' work should not be regarded as only drudgery to be eliminated. One should work towards reducing womens' workload by bringing in appropriate technology to ease her work and not eliminate the work itself by importing a substitute. If this is not done we end up getting rid of women as important contributors to society.

The effect of wind suppressors on the performance of a 4 m² solar pond, operating under the environment of the Arabian Gulf area characterized by windy, hot and humid conditions, is investigated experimentally. In addition to using screen nets on the pond's perimeter, two arrangements of wind suppressors of PVC floating pipes are considered. Climatological data relevant to the operation of solar ponds in this area namely wind speeds and evaporation rates are presented. Results of both salinity and temperature over a one year period are presented to evaluate the effect of wind suppressors and thermal insulation on the performance of the pond. The gradient zone was disturbed by invoking localized convective zones of different thicknesses to examine the effect of wind suppressors on the healing of those zones. Results show that wind suppressors of the floating piping type, can considerably slow down the movement of the upper convective-gradient zone interface and prohibit any formation of localized convective zones. Thermal insulation is a prerequisite for operating small solar ponds even in hot climates.

A method is presented for predicting the performance of solar H₂OLiBr absorption heat transformers, which receive solar heat at an intermediate-temperature level, reject a part of it in the ambient at a low-temperature level and deliver the remaining useful heat at a high-temperature level. Simple relations are derived, which define the exact thermodynamic cycle of heat transformer and allow calculation of characteristic temperatures and heat quantities exchanged in terms of the main parameters of the unit. A correlation linking the heat gain factor to the main parameters is presented, which may be used for calculating the optimum cycle. The procedure developed has been employed for predicting the hour-by-hour performance of solar driven absorption heat transformers in the Athens area along a typical year, using mean climatological conditions obtained by processing of 20 years hourly measurements. The theoretical heat gain factor has been found to be practically constant (≅51%) along the typical year. With usual flat plate collectors, the calculated maximum values of the specific heat gain for January, March, May, July, September and November are 79, 143, 232, 247, 185 and 107 W/m²-collector, respectively, obtained at 13 or 14 h under a maximum temperature of about 100°C.