Sharif Digital Repository

One of the most important operating parameters which affects the performance and efficiency of active solar stills is brine depth. In all of the previous experimental or theoretical studies, effects of water depth were investigated during only the first 24-hour period (or even shorter periods) of the operation of active solar stills. In other words, only the first day was taken into account. However, the production of an active solar still depends on several parameters such as brine temperature at sunrise (initial temperature), which are all affected by the depth variation after the first day of operation. However, the present research experimentally investigates the long-term effects of... 

Using hybrid energy storage system is a method for increasing the storage capability of solar thermal energy. If multiple energy storage devices with complementary performance characteristics are used together, the resulting system will be a 'Hybrid Energy Storage System'. In other words, a Hybrid Energy Storage System (HESS) has several media available for storage at any time. In this way, increase in storable energy is obtained without increasing collectors' area. When there are more than one storage mediums, the system should be able to choose the best medium for storing energy according to the conditions. In the previous works, an optimizer program was used to find the proper medium... 

In the present work, effects of height, length, and width of a single-slope basin-type solar still on its distillate production was investigated. For this purpose, a radiation model was developed which accounts for the influences of all walls on quantities of received solar radiation by the base and saline water of the still. Moreover, in this radiation model, the side walls of the still were considered as the trapezoid and the diffuse as well as beam components of solar irradiance were separately taken into account for the first time. Abilities of the present model were compared with earlier ones. Furthermore, the predictions of the current model were compared with the present experimental... 

In this study, natural convection heat transfer in a vertical flat-plate solar air heater of 2.5 m height and 1 m width, with one- and two-glass covers was studied experimentally. Totally six cases of airflow (two for air heater with one glass cover and four for air heater with two-glass covers) were considered. These cases included states that air could flow within spaces between absorber plate and glass covers or air was enclosed in such spaces. Absorber plate temperature, back-plate temperature, glass cover temperatures, mass flow rates of air within channels and the solar radiation were measured. The following relations are suggested:. For channels in which air could flow:Nu = 0.7362... 

In this paper we report experimental results for the performance and rate of heat transfer in copper tubes in solar water heaters with thermosyphonic flow in continuation of experimental data reported in previous publications (Solar Energy, 2003, vol. 74, pp. 441-445, and Energy Sources, 1997, vol. 19, pp. 147-152). We also show a comparison between performances of three kinds of tubes: copper, polypropylene and steel under similar conditions. An analytical relation for calculation of rate of heat transfer in copper tubes is also presented in terms of Nusselt versus Reynolds and Prantdl numbers. A comparison of experimental data showed that performance of copper tubes is slightly better than... 

The aim of this study was to develop a predictive method for heat transfer coefficients in solar water heaters and their performance evaluation of such heaters with different materials used as heat collectors. Two approaches have been used: conventional method and an Artificial Neural Network (ANN) to predict the performance of solar water heaters and to compare these two approaches. This performance is measured in terms of outlet temperature by using a set of conventional feed forward multi-layer neural networks. The actual experimental data which were used as our network's input gathered from published literature (for polypropylene tubes) and from the experiments carried out recently using... 

In this paper, a new radiation model for a single-slope solar still has been developed which for the first time takes into account the effect of all walls of the still on the amount of incident solar radiation on the water surface and each wall. In this model, the walls are projected on the cover to calculate the amount of beam radiation received by any components inside the still. This is in contrary to the previous models in which stills' walls were projected on a horizontal surface and their shadows on the water surface and the walls were either neglected or not computed properly. The predictions of the proposed model are compared with the experimental data obtained in the present work... 

Direct steam generation (DSG) in parabolic trough collectors causes an increase to competitiveness of solar thermal power plants (STPP) by substitution of oil with direct steam generation that results in lower investment and operating costs. In this study the integrated solar combined cycle system with DSG technology is introduced and techno-economic assessment of this plant is reported compared with two conventional cases. Three considered cases are: an integrated solar combined cycle system with DSG technology (ISCCS-DSG), a solar electric generating system (SEGS), and an integrated solar combined cycle system with HTF (heat transfer fluid) technology (ISCCS-HTF).This study shows that... 

Effects of the amount and mode of input energy to an active multi-stage solar still were investigated in this work. To control the input energy, an electrical heater controlled by a PLC was utilized to simulate the energy absorbed by solar collectors. The study of the amount of input energy indicated that the freshwater production was a quadratic function of the collector over basin area (CBA) ratio. It was also found that stages 1 to 4 produced about 36%, 26%, 20% and 18% of the overall yield, respectively. Moreover, the effect of employing a thermal energy storage (TES) on the system performance was studied by comparing the mode of feeding energy according to the daily solar radiation... 

The present work investigated the outdoor performance of a basin type multi-stage solar still as well as the effect of collector over basin area (CBA) ratio on the distillate production. The effect of CBA was studied in outdoor experiments for the first time. The system consisted of a still coupled with one, two or three flat-plate solar collectors. In order to study the effect of CBA more accurately, the experiments were conducted in both winter and summer. In these experiments, the distilled water production of the multi-stage still was measured during the whole 24. h of a day on an hourly basis. The results revealed that in the winter, the basin coupled to one solar collector (CBA. =... 

The performance of the tower based concentrated solar thermal (CST-tower) plant is very sensitive to the operation strategy of the plant and the incident heat flux on the receiver. To date, most studies have been examined only the design mode characteristics of the cavity receivers, but this paper significantly expands the literature by considering non-design operating conditions of this important sub-component of the CST-tower plants. A feasible non-design operating conditions of the cavity receivers that was considered in this study is the storage mode of operation. Two practical dynamic control strategies were examined then to find the most efficient approach: fixed solar field mass... 

In this article, a novel solar still which is equipped with thermoelectric modules to utilize the heat of vapor condensation is experimentally investigated. The use of thermoelectric modules as devices for generating electricity from the temperature difference between two environments (hot vapor steam and cold ambient air) as well as taking outstanding advantages of evacuated tubes as collectors with high performances in adverse climatic conditions, led to utilizing of the energy dissipated due to vapor condensation and a considerable increase in the performance of the system. The effect of using the generated electricity to operate a small propeller fan for inducing forced convection was... 

In this study, a novel idea of storing the latent heat of condensing vapor in solar stills by means of phase change materials (PCMs) as a thermal storage is experimentally investigated. During the daytime, the generated water vapor by the solar energy, is conducted to an external condenser filled with PCM to be condensed. The wasted latent heat is absorbed by PCM and thereby stored. It is worth noting that there is no direct contact between the saline water and the PCM, therefore, the solar energy is not directly stored in the PCM. In the evening, the energy stored in the PCM is transferred as heat to the saline water by heat pipes and enables the desalination process to continue. Several... 

In recent years, increasing attention has been paid to the use of renewable energy sources in building sector. The ground source heat pumps are a promising alternative for heating and cooling applications. Despite the high coefficients of performance and significant environmental benefits, their performance may deteriorate over the long-term operation if the annual ground loads are not well balanced. An appropriate solution is the use of hybrid ground source heat pump system through which some portion of the thermal loads can be offset by supplemental components. The aim of this study is to assess the feasibility of a solar-assisted ground source heat pump system for heating a detached house... 

In recent years, increasing attention has been paid to the use of renewable energy sources in building sector. The ground source heat pumps are a promising alternative for heating and cooling applications. Despite the high coefficients of performance and significant environmental benefits, their performance may deteriorate over the long-term operation if the annual ground loads are not well balanced. An appropriate solution is the use of hybrid ground source heat pump system through which some portion of the thermal loads can be offset by supplemental components. The aim of this study is to assess the feasibility of a solar-assisted ground source heat pump system for heating a detached house... 

Wettability is one of the most important factors which significantly influences solar still efficiency. Moreover, it determines the condensation mode, i.e., filmwise or dropwise condensation. In the present study, materials with different wettability were applied as the condensing surface to evaluate the effect of wettability on the distillate production of a single slope solar still. To compare the effects of dropwise and filmwise condensation on the condensate yield, the wettability of the condensing surface was changed by applying a nano-silicon solution according to a dip coating technique. All the experiments were conducted at three surface inclination angles. The results revealed that... 

Greenhouses require energy in order to provide a proper environment for crop production. Utilizing solar energy in solar greenhouses is a sustainable solution to face this problem. In this study, a solar greenhouse concept is considered, and a dynamic thermal model is developed to predict the inside air temperature. The model is integrated into an optimization procedure to find the optimal greenhouse design that has the best thermal performance by adjusting its structural parameters. This optimization procedure provides a tool to find the optimal solar greenhouse design for each climate condition and predict its performance. For instance, for the case study of Tehran (Iran), the optimal...