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1.
Solar energy is one of the most important renewable energy sources, but it is not available every time and every season. Thus, storing of solar energy is important. One of the popular methods of heat storage is use of phase change materials (PCMs) which have large thermal energy storage capacity. In this study, the heat storage tank in a domestic solar water heating system was chosen as control volume. The experiments were performed in the province of Elaz?g, Turkey, in November when solar radiation was weak due to cloudy sky. The heat storage tank of the system was modified to fill PCM between insulation and hot water part. A few PCMs which are Potassium Fluoride, Lithium Metaborate Dihydrate, Strontium Hydroxide Octahydrate, Barium Hydroxide Octahydrate, Aluminum Ammonium Sulfate, and Sodium Hydrogen Phosphate were analyzed to proper operating conditions using a Differential Scanning Calorimeter (DSC) and the best PCM was obtained with the Aluminum Ammonium Sulfate and Sodium Hydrogen Phosphate mixture. Thus, eutectic PCM was obtained and used in a heat storage tank of the solar water heating system. Energy and exergy analysis of heat storage tank was performed with and without the PCM. Energy and exergy analysis has shown that the heat storage tank with the PCM is more efficient than without the PCM and the maximum exergy efficiency was obtained as 22% with the heat storage tank with the PCM.  相似文献   

2.
ABSTRACT

This work explores the opportunities to address the setback in thermal energy storage of solar-based water heaters by uniting it with a suitable hybrid-nano composite phase change material (HNCPCM) in a static mode of operation. The experiments were conducted on a natural circulation all-glass evacuated solar water heating system (AGSWH). The investigation was steered in five cases such that the first case without any phase change material (PCM), the second with pure paraffin as PCM, and remaining three cases with three different mass percentage of HNCPCMs (0.5%, 1.0%, and 2.0% mass fraction of hybrid nanoparticles within PCM) in real-time solar exposure. The system was analyzed based on the first and second law of thermodynamics to assess the performance in all the five cases. Erstwhile, the hybrid nanoparticles were prepared by blending equal mass of SiO2 and CeO2 nanoparticles and characterized to gauge its thermal storage properties. The achieved results substantiated that the thermal conductivity had boosted with the accumulation of hybrid nanoparticles within the paraffin matrix, and maximum enhancement of 65.56% was attained with 2.0% mass fraction. The first law and second law investigations revealed that the incorporation of hybrid-nano composites improved the energy and exergy content of the system, distinctly. Among the experimented cases, HNCPCM with 1.0 mass% of hybrid nanoparticles remarkably yielded a better result of 19.4% and 1.28% improvement in energy and exergy efficiencies, respectively. Besides, it evidenced the necessity of choosing the right quantity of nanoparticles for achieving better overall results.  相似文献   

3.
ABSTRACT

According to the structure of photovoltaic/phase change material (PV/PCM), the mechanism of internal heat transfer, transmission, storage, and temperature control is analyzed, and a two-dimensional finite element analysis model of PV/PCM structure is established. This study is carried out on the effect of PCM thermal conductivity on internal temperature distribution characteristics of PV/PCM and temperature control characteristics of solar cells. The results show that the increase in thermal conductivity of PCM can prolong the temperature control time of solar cell in PV/PCM system, for example, when the thermal conductivity is increased from 0.2 W/(m·K) to1.5 W/(m·K) under a thickness of 4 cm, the duration when PV/PCM solar cell temperature is controlled below 40°C and extended from 52 min to 184 min. In addition, PV/PCM experimental prototypes are designed with the LA-SA-EG composite PCM peak melting point of 46°C and thermal conductivity of 0.8 W/(m·K) and 1.1 W/(m·K), respectively. The results indicate that compared with PCM-free solar cells, the maximum temperature of PV/PCM prototype solar cells with thermal conductivity of 0.8 W/(m·K) and 1.1 W/(m·K) is reduced by 10.8°C and 4.6°C, respectively, with average output power increased by 4.1% and 2.2%, respectively, under simulated light sources. Under natural light conditions, the average output power is increased by 6.9% and 4.3%, respectively. The results provide theoretical and experimental basis for the optimization of PV/PCM design by changing the thermal conductivity of PCM.  相似文献   

4.
The performance of the designed tilted wick solar water distillation-cum-drying unit has been tested at water flow rates of 50 and 65 ml/min in the distillation unit. Effect of water flow rates on the heat transfer coefficients of distillation and drying unit for drying ginger has been evaluated. The energy and exergy efficiency of the distillation system have also been evaluated. Average distillates of 2.36 and 2.2 l/m2 were collected from the tilted wick solar still at flow rates of 50 and 65 ml/min, respectively. Large variation in convective and evaporative heat transfer coefficients of distillation unit has been observed at given water flow rates. Water flow rate in the distillation unit significantly affects the performance of the drying unit. Average convective heat transfer coefficients of 6.56 and 3.75 W/m2 oC have been observed for drying ginger at flow rates of 50 and 65 ml/min, respectively. Energy and exergy efficiency of the distillation unit have been found to be nearly 19% and 0.9%, respectively. Experimental uncertainty has also been evaluated for distillation and drying units. The distillate cost for the developed distillation-cum-drying unit is calculated as $0.03729/l along with dried ginger of about 2.5 kg/m2/day.  相似文献   

5.
This study investigated the thin-layer drying kinetics of salted silver jewfish in a hybrid solar drying system and under open sun. Ten drying models were compared with experimental data of salted silver jewfish drying. A new model was introduced, which is an offset linear logarithmic (offset modified Page model). The fit quality of the models was evaluated using the coefficient of determination (R2), root mean square error (RMSE), and sum of squared absolute error (SSAE). The result showed that Midilli et al. model and new model were comparable with two or three-term exponential drying models. This study also analyzed energy and exergy during solar drying of salted silver jewfish. Energy analysis throughout the solar drying process was estimated on the basis of the first law of thermodynamics, whereas exergy analysis during solar drying was determined on the basis of the second law of thermodynamics. At an average solar radiation of 540 W/m2 and a mass flow rate of 0.0778 kg/sec, the collector efficiency and drying system efficiency were about 41% and 23%, respectively. Specific energy consumption was 2.92 kWh/kg. Moreover, the exergy efficiency during solar drying process ranged from 17% to 44%, with an average value of 31%. The values of improvement potential varied between 106 and 436 W, with an average of 236 W.  相似文献   

6.
Experiments are described to investigate the thermal performance of a discharging heat exchanger for a small storage tank filled with oil. Experimental results are presented in terms of the discharging energy rates (power) and the discharging exergy rates for low (~4 ml/s) and high discharging flow rates (~8 ml/s). Water heating energy rates, which are respectively maximized at approximately 600 W and 1200 W at low and high flow-rate discharging, are found to be higher than the discharging energy rates, which are respectively maximized at 450 W and 900 W. These results indicate that the energy rates do not accurately evaluate the thermal performance of the discharging heat exchanger since the energy heating rate of the water is greater than that for the oil that heats it, which is thermodynamically inconsistent. The energy rates should thus be used with caution when the thermal performance of the heat exchanger is evaluated. Water heating exergy rates, which are respectively maximized at approximately 45 W and 130 W at low and high flow-rate discharging, are generally smaller than the discharging exergy rates, which are respectively maximized at 65 W and 170 W. Exergy rate results are thus more consistent in the physical process of water heating, and an exergy factor is suggested as a proper measure for evaluating the performance of the discharging heat exchanger. The maximum value of the exergy factor is found to increase from 0.15 at low flow rates to a maximum value of approximately 0.19 at high flow rates. This implies that to extract more energy from a storage tank to a discharging heat exchanger, the flow rate has to be high, which is consistent with the physical process of heating water faster to higher temperatures. The exergy factor can thus be used as a design parameter for discharging heat exchangers.  相似文献   

7.
Solar drying technology is a noteworthy technique as it uses the renewable solar energy. In this study, thin slices of banana were dried by using an indirect forced solar dryer at air mass flow rates of 0.016, 0.041, and 0.082 kg s?1. In order to assess the kinetics of shrinkage and color changes, image processing technique was applied for determining area, volume, density, total color difference and browning index. Shrinkage factor of the samples was less than 1 during drying indicating non-isotropic shrinkage with contraction of inner voids. Furthermore, product shrinkage showed two descending drying steps in which the volume change was more than the evaporated water volume in the first step and equal to that in the second step. The dimensionless evaporated water volume with respect to the dimensionless volume difference of the product also revealed that two steps of volume change existed during drying separated at critical moisture ratio 0.23. The area and volume changes were only related to the product moisture content and were independent of the air mass flow rate, and hence air temperature. In contrary to the browning index, the total color difference was not influenced by air mass flow rate and the least change in browning index occurred at mass flow rate of 0.041 kg s?1.  相似文献   

8.
A numerical model for simultaneous heat and mass transfer was developed for solar drying of spherical objects and the object considered is green peas. Solar collector outlet temperature is assumed as drying chamber temperature and justified through energy balance equations. Assumptions are imposed on heat and mass transfer governing equations without losing the physics of the problem. Discretization is performed by finite difference method with implicit scheme. To generalize, the governing equation and boundary conditions are non-dimensionalized. The set of finite difference equations was solved by Tridiagonal Matrix Algorithm and a computer code in MATLAB was developed to solve them. The drying curves showed two stages of drying, initial, and secondary drying stage. At all drying temperatures and drying time, the center moisture was maximum and it was minimum at the boundary. A percentage of 85.67 surface moisture content and 25.33% center moisture was eliminated in the first 1 hr at 348 K. The product should be dried up to 7.45, 4.74, and 3.74 hr at air drying temperatures of 318, 333, and 348 K respectively, to maintain 10% of the product’s initial moisture content. The result is compared with the experimental result from literature and they are found to be in good agreement.  相似文献   

9.
In the present work, the thin layer drying kinetics of potato during natural convection solar drying was investigated experimentally. Cylindrical potato samples with length 50 mm and varying diameter of 8, 10 and 13 mm were dried in an in-house designed and fabricated laboratory scale mixed-mode solar dryer. Thirteen different thin-layer mathematical models were fitted to the experimental moisture ratio (MR) data. The obtained results indicated that the Modified Page model could satisfactorily describe the drying curve of potato cylinders with higher value of R2 and lower values of RMSE and χ2. The shrinkage parameter is incorporated in the analytical diffusion model to study the moisture transfer mechanism of potato cylinders. It was observed that the values of effective diffusion coefficient (Deff) and convective mass transfer coefficient (hm) are overestimated in the range of 85.02–90.27% and 39.11–45.11% for the range of sample diameter examined, without considering the shrinkage effect in the mass transfer analysis. A Multiphysics approach was adopted in this study to get insight into the drying behavior of potato cylinders in terms of food-moisture interactions during the solar drying process. The predicted results of MR are in close agreement with the experimental data. Moreover, the anisotropic behavior of shrinkage as well as the moisture distribution inside the potato cylinder was very well described by Multiphysics model.  相似文献   

10.

Each plant has its own optimal drying temperature, especially for the medicinal herbs, because they are sensitive to heat. If the drying temperature becomes more than the optimal value, some chemical reactions will occur and influence the quality of the dried herb, such as color, taste, and aroma. While if the drying temperature becomes lower than the optimal value, the drying process will slow down, and consequently an expected degradation in the quality of the herb may occur, due to insects and fungi infestation which increase in moist conditions. This paper presents a new temperature control technique for a medicinal herb dryer system. The technique fixes the drying temperature of the medicinal herbs at 40°C, even in cases of rapidly changing atmospheric conditions. The control of the dryer temperature is achieved through using the proportional integral (PI) controller. The designed dryer contains two systems, which are the thermal and the electrical systems. The thermal system is designed to heat the drying air by using solar energy and bio-gas fuel. Whereas the electrical system, which contains a photovoltaic (PV) modules and a battery, is designed to supply the different electrical loads of the dryer system. The control technique is investigated through simulation work by using MATLAB-SIMULINK. The simulation results indicate the high capability of the proposed technique in controlling the drying temperature, even in cases of rapidly changing atmospheric conditions.  相似文献   

11.
In this communication, a new design of solar-energy-based water distillation cum drying unit with parabolic reflector has been designed, fabricated, and tested. Bitter gourd and potato slices are chosen as a drying commodity. Thermal performance of the developed system has been evaluated based on the experimental results and using linear regression analysis. Heat transfer coefficients (convective, evaporative, and radiative) for solar distillation system have been observed to be 2.48–4.09, 13.25–52.38, and 8.75–9.66 W/m2°C, respectively. Overall thermal efficiency and exergy efficiency for the distillation system has been found to be 18.77% and 1.2%, respectively. The convective heat transfer coefficient for potato slices are observed higher for initial hours and decreases as the day progresses. The average convective heat transfer coefficients for bitter gourd and potato slices have been observed as 2.18 and 5.04 W/m2°C, respectively. Experimental error in terms of percent uncertainty for bitter gourd and potato slices are found to be 42.93% and 37.06%, respectively. The present design of solar distillation and drying in a single unit could be beneficial for the development of remote, arid, and rural areas.  相似文献   

12.
ABSTRACT

In this paper, a novel evacuated tube solar collector (ETSC) is first designed and built. Then, the impact of adding reflector, reflector plus single-axis sun tracker and reflector plus two-axis sun tracker to the built ETSC on the thermal efficiency of the ETSC is evaluated both theoretically and experimentally. In this regard, four identical versions of the proposed ETSC have been built and utilized in four collectors built and presented in this research work. The first collector is the same proposed built ETSC, the second collector is a parabolic trough solar collector comprising one built ETSC and a reflector (ETSC+R), the third collector is composed of one built ETSC, a reflector and a single-axis sun tracker all built in this study (ETSC+R+ ST), and the fourth collector consists of one built ETSC, a reflector and a two-axis sun tracker all built in this study (ETSC+R+ DT). Theoretical basis and concepts of the four collectors are formulated and analyzed in separate subsections. Theoretical results are outlined and highlighted at the end of each subsection. Experimental measurements and data obtained from the operation of the four collectors in the four seasons are presented that point by point verify theoretical results obtained in this study. To provide a comprehensive view, a techno-economic numerical comparison is performed between the four collectors. The following points, which are also the novelty and contributions of this work, are deduced from theoretical concepts, experimental data, and comparison provided in this study:

?There is no technical and economic justification for adding a reflector to an ETSC that results in forming a parabolic trough solar collector (ETSC+R) without any sun tracker.

?There is no economic justification for adding a single-axis sun tracker to a parabolic trough solar collector (ETSC+R).

?There is no economic justification for adding a two-axis sun tracker to a parabolic trough solar collector (ETSC+R).

?Comparing between a two-axis sun tracker and a single-axis sun tracker, adding the single-axis type to a parabolic trough solar collector (ETSC+R) is more advantageous.  相似文献   

13.
Variation in drying material and their biological differences, coupled with heat supply method in different dryers, makes mathematical modeling of drying complicated. Attempt was made to simulate a drying process and to identify best suitable model out of six selected drying models, for drying of ginger slices in a solar-biomass integrated drying system designed and developed for spice drying. Moisture content data were converted into the moisture ratio (MR) expressions and curve fitting with drying time for the selected drying models was analyzed. Sigma Plot software was used for nonlinear regression to the data obtained during drying and for modeling of drying curves. The suitability of the models was evaluated in terms of statistical parameters such as coefficient of determination (R2), mean percentage error (P), and standard error estimate. Drying air temperature was in the range of 47–55°C and air velocity was between 1.0 and 1.3 m s?1. Ginger slices were dried from 88.13% to 7.65 ± 0.65% (wb) in 16 h. Trays were interchanged in a predetermined matrix sequence from 4 h onwards when moisture content was reduced to 60–70% (wb), for uniformity in drying. Highest value of R2 (0.997), lowest value of SEE (0.020), and P value < 0.0001 established Page model as the best suitable model for the developed drying system. The predicted MRs were in good agreement with the experimental values and the effective moisture diffusivity for ginger was found to be 2.97 × 10–7 m2 s?1.  相似文献   

14.
We studied stormwater detention basins where woody vegetation removal was suspended for 2 years in Virginia, USA to determine if woody vegetation can control Typha populations and how early woody plant succession interacts with Typha, other herbaceous vegetation, and site factors. Distribution and composition of woody vegetation, Typha and non-Typha herbaceous vegetation biomass, and site factors were assessed at 100 plots in four basins ranging in age from 7 to 17 years. A greenhouse study examined the interaction of shade and soil moisture on Typha biomass and persistence. Principal component analysis identified an environmental gradient associated with greater water table depths and decreased elevation that favored Typha but negatively influenced woody vegetation. Elevation was correlated with litter layer distribution, suggesting that initial topography influences subsequent environmental characteristics and thus plant communities. Soil organic matter at 0–10 cm ranged from 5.4 to 12.7 %. Woody plants present were native species with the exception of Ailanthus altissima and Pyrus calleryana. In the greenhouse, shade and reduced soil moisture decreased Typha biomass and rhizome length. The shade effect was strongest in flooded plants and the soil moisture effect was strongest for plants in full sun. Typha in dry soil and heavy shade had 95 % less total biomass and 83 % smaller rhizomes than Typha in flooded soil and full sun, but even moderate soil moisture reductions decreased above- and below-ground biomass by 63 and 56 %, respectively. Suspending maintenance allows restoration of woody vegetation dominated by native species and may suppress Typha invasion.  相似文献   

15.
In this paper, we have proposed a thermal cycle with the integration of chemical-looping combustion and solar thermal energy with the temperature of about 500-600°C. Chemical-looping combustion may be carried out in two successive reactions between a reduction of hydrocarbon fuel with metal oxides and a reduced metal with oxygen in the air. This loop of chemical reactions is substituted for conventional combustion of fuel. Methane as a fuel and nickel oxides as an oxygen carrier were employed in this cycle. Collected high-temperature solar thermal energy is provided for the endothermic reduction reaction. The feature of the proposed cycle is investigated through Energy-Utilization Diagram methodology. As a result, at the turbine inlet temperature of 1200°C, the exergy efficiency of the proposed cycle would be expected to be about 4 percentage points higher than that of a conventional gas turbine combined cycle. Compared to the previous study of chemical-looping combustion energy systems, the proposed cycle with the integration of green energy and traditional hydrocarbon fuels will offer the possibility of both greenhouse gas mitigation, with green energy, and a new approach to the efficient use of solar energy.  相似文献   

16.
Phase change materials (PCMs) that can store and release heat energy over the temperature range from 363 to 393 K are crucial for solar absorption cooling, and it is worthy to seek new solid-liquid PCMs candidates that melt and crystallize in this temperature range. In this paper, (E)-3-m-tolylbut-2-enoic acid (mTBEA) was applied as a PCM candidate. Its thermal energy storage properties and thermal stability were systematically investigated. The results showed that mTBEA melted at 382.9 ± 0.5 K and crystallized at about 364 K, with a melting enthalpy (ΔfusH) of 138.4 ± 6.9 J g?1 and showed good long-term cyclic stability and thermal stability. The supercooling of mTBEA was stabilized at about 20 K, indicating that the conservation condition of melted mTBEA could be simple. In addition, the melted mTBEA could release all the absorbed thermal energy upon crystallizing. Besides, mTBEA exhibited good thermal stability for it to be applied as PCM. Hence, mTBEA is a promising PCM candidate for solar absorption cooling. Furthermore, the heat capacity of mTBEA was measured by modulated temperature differential scanning calorimetry (MTDSC) over the temperature range from 198.15 to 431.15 K, and the molar thermodynamic functions, [HT-H298.15]m and [ST-S298.15]m, were calculated based on the fitted molar heat capacity data.  相似文献   

17.
Due to the existing huge biogas resource in the rural area of China, biogas is widely used for production and living. Cogeneration system provides an opportunity to realize the balanced utilization of the renewable energy such as biogas and solar energy. This article presented a numerical investigation of a hybrid energy-driven organic Rankine cycle (ORC) cogeneration system, involving a solar ORC and a biogas boiler. The biogas boiler with a module of solar parabolic trough collectors (PTCs) is employed to provide heat source to the ORC via two distinct intermediate pressurized circuits. The cogeneration supplied the power to the air-condition in summer condition and hot water, which is heated in the condenser, in winter condition. The system performance under the subcritical pressures has been assessed according to the energy–exergy and economic analysis with the organic working fluid R123. The effects of various parameters such as the evaporation and condensation temperatures on system performance were investigated. The net power generation efficiency of the cogeneration system is 11.17%, which is 25.8% higher than that of the base system at an evaporation temperature 110°C. The exergy efficiency of ORC system increases from 35.2% to 38.2%. Moreover, an economic analysis of the system is carried out. The results demonstrate that the profits generated from the reduction of biogas fuel and electricity consumption can lead to a significant saving, resulting in an approximate annual saving from $1,700 to $3,000. Finally, a case study based on the consideration of typical rural residence was performed, which needs a payback period of 7.8 years under the best case.  相似文献   

18.
Drying characteristics of Zingiber officinale (Ginger) under the open sun and direct type natural convection solar biomass (hybrid) drying were studied. It has been observed that under open sun drying conditions, the drying rate depends on the product thickness and climatic conditions. The results have been drawn for both the summer (April-May, 2004) and winter (November-January, 2003–04) months of Delhi, in India. In the hybrid drier, the ginger, with a thickness of 0.008 m, dried in 33 hours in comparison to 96 hours in open-sun drying. The overall drying efficiency of the hybrid drier was found to be 18% and 13% under summer and winter climatic conditions respectively. The loss of volatile oil content of the ginger is less in hybrid drier in comparison to open sun drying. It was found that the average drying air temperature of 60°C with average air velocity of 0.6m/sec was sufficient for the drying of ginger in the hybrid drier. Ginger quality after drying is better and drying time is less in the hybrid drier in comparison to open-sun drying. The hybrid drier is a simple device, which can be manufactured with locally available materials and can be used for drying of other spices, vegetables and fruits etc.  相似文献   

19.
Abstract

Thermal energy storage (TES) technologies in general and phase change materials (PCMs) in particular, have been topic in research for the last 20 years. Traditionally, available heat has been stored in the form of sensible heat (typically by raising temperature of water, rocks, etc). Latent heat storage on the other hand, is a novel and developing technology, which has found considerable interest due to its operational advantages of smaller temperature swing, smaller size, and lower weight per unit of storage capacity. The interest on thermal energy storage by using fatty acids as PCM has risen in recent times since they have desired thermodynamic and kinetic criteria for low temperature latent heat storage. An added advantage is that fatty acids are derived from the vegetable and animals oil that provides an assurance of continuous supply. This article will review the development of fatty acids as PCMs for solar thermal energy storage application.  相似文献   

20.
A novel design of twin-chamber community solar (TCCS) cooker is presented as a replacement of biomass-based cooking. The novelty of separating a single rectangular cooking chamber into separate twin chambers (of 1-m2 aperture area each) improves the cooking performance as opening of one chamber for unloading of food cooked in lesser time (rice) does not disturb the stagnation temperature of the other chamber (pulses and meat) needing more time to cook besides resulting in reduction in side heat loss coefficient due to common wall. Aperture area and cooking volume of TCCS cooker are 9.54 and 35.33 times more as compared to single-chamber domestic solar (SCDS) cooker which makes it a community-scale large-capacity solar cooker. The developed solar radiation capture model and overall heat loss coefficient (Ul) computed for TCCS cooker have been used in a thermal model developed between various interactive components. First (F1) and second figures of merit (F2) values are 0.13 and 0.42, respectively, for TCCS cooker at par with ‘A’ grade category SCDS cooker. Techno-economic analysis shows that the net present value of TCCS cooker is Rs. 83,253 with break-even point occurring after cooking 43,461 meals with payback period of only 25, 50, and 72 months if used as a replacement for LPG, cow dung cakes, and wood-based cooking, respectively. Environmental impact analysis shows that the use of the proposed cooker can mitigate 2, 5.9, and 4.1 tonnes of CO2 emissions every year by not burning LPG, cow dung cakes, and wood respectively.  相似文献   

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