A Granite Bed Storage for a Small Solar Dryer

Nemś, Magdalena; Nemś, Artur; Pacyga, Paweł

doi:10.3390/ma11101969

Cited by 10 publications

(5 citation statements)

References 36 publications

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“…Previous experimental studies, which concerned a granite bed storage and which were carried out by the author of this paper, showed a different nature of the storage process in relation to the shape of the tested material [14]. Different characteristics of the working medium's outlet temperature from the heat storage were obtained for the same testing conditions.…”

Section: Introductionmentioning

confidence: 59%

Experimental Determination of the Influence of Shape on the Heat Transfer Process in a Crushed Granite Storage Bed

Nemś¹

2020

Energies

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The article presents the problem of modelling the charging of a constant-phase bed storage in the first hours of the process. The places of errors in the heat transfer calculations for the packed beds were indicated. Granite in the shape of spheres and crushed rocks, with a characteristic dimension of 50 mm, was used for the experimental tests. The material was subjected to tomographic examination and then used as a storage material. The charging process was carried out for three flow rates: 0.006, 0.008 and 0.010 m3/s. After three hours of testing, the temperature of the outlet air for the granite sphere as the storage material was the same as for the granite crushed rock. However, the biggest differences occurred after 1 h of charging. They were equal to: 40.4% for the flow rate of 0.006 m3/s, 22.0% for the flow rate of 0.008 m3/s, and 18.5% for the flow rate of 0.010 m3/s. The differences were greater than the uncertainty of the measurements. As a result, different temperatures of the storage material were obtained. After three hours, they were equal to: 25.2%, 12.3% and 8.6% for the lowest, medium, and highest airflow, respectively. The conducted heat transfer analysis and the relationship Nu = f(Re) was determined. The influence of the calculated and actual surface of the crushed rock on the heat exchange process was explained. For all the tested air flow rates through the bed, higher thermal parameters were obtained for the crushed rock than for the sphere. The maximum differences in the Nu number were: 222.6%, 151.4% and 161.3% for the flow of 0.006, 0.008 and 0.010 m3/s, respectively. This means that the description of the heat exchange process in the piled beds would require a parameter that takes into account the geometry of the storage material.

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Section: Introductionmentioning

confidence: 59%

Experimental Determination of the Influence of Shape on the Heat Transfer Process in a Crushed Granite Storage Bed

Nemś¹

2020

Energies

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“…The specific heat of this material is equal to 780 J/(kg•K), which makes it attractive in terms of heat storage. It is also resistant to working in high temperatures of even several hundred degrees Celsius [19].…”

Section: Methodsmentioning

confidence: 99%

“…V air . The design of the Hartley experiment, which was described in detail in [19,20], was selected for the investigation. It enabled the tests to be carried out for three input factors at three levels of variation.…”

Section: Test Stand and Experiments Planmentioning

confidence: 99%

The Influence of the Shape of Granite on the Heat Storage Process in a Rock Bed

Nemś

Gębarowska

2020

Energies

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Granite is one of those materials that due to its thermal parameters is used as a filling for storage beds, including high-temperature ones. The article analyzes local material that was extracted in Strzegom, Poland. The purpose of the paper is the assessment of storage material with regard to its cooperation with a heat source that is available for a short time, e.g., a solar installation. Three different shapes of granite material were tested: rock, cube and sphere. Each shape has its advantages and disadvantages, which are associated with economic and strength aspects. The article presents experimental tests of the material, which were conducted in order to determine the efficiency of the charging process. The results show that rock-shaped granite filling elements are characterized with the best parameters during the charging process, and that they obtained the highest first- and second-law efficiency in the entire tested range of inlet air temperature and flow rate. The efficiency of the cube-shaped granite was lower than the sphere-shaped granite. This means that the efficiency does not directly depend on the coefficient of sphericity of the elements that fill the storage bed. The determination of the second law efficiency showed that the highest use of energy supplied with hot air occurs after 1 h of charging the accumulator in the case of all the analyzed geometries. At the end of the paper, the influence of the obtained results on the process of modelling the charging of a storage bed filled with elements of non-spherical geometry is also discussed.

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“…According to the authors, all the evaluated systems presented high performance and stable output temperature suitable for drying process up to 60 °C. Nems et al (2018) presented a concept of vertical flow high temperature solar dryer with granite balls in the bed of the dryer acting as thermal storage. Experimental results have shown that granite can prolong the operation of the dryer in two hours.…”

Section: State Of the Artmentioning

confidence: 99%

Proposal Solar Drying With Heat Storage Applied to Medicinal Plants

Diaz¹,

Reimbrecht²,

Jahn³

et al. 2019

JAS

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In this work, a proposal of an indirect solar dryer with a vacuum solar collector and storage of water-sensitive heater is presented. A mathematical model is presented as the first approximation to evaluate the performance. The test climatic conditions are based on the city of Cascavel (Paraná, Brazil) and the resolution of the model was aided by the EES program. In order to analyze the performance of the system, a model load was created based on the references found in the literature, sample of 80 kg with initial water content of 75% w.b and final of 10% w.b, for drying time of 4 h and 3 h with air velocity of 0.7 m/s and 1.1 m/s respectively. It was possible to simulate the variation of the temperature of the reservoir during the day, as well as the response of the heat exchanger to the variation of temperature of entrance of the fluids and the climatic influence, radiation and ambient temperature in the participation of the solar energy in the total energy consumption of the drying. The simulations suggest good results with solar fraction between 20 and 47 %, meanwhile in the literature the values reported are between 10 and 25%.

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A Granite Bed Storage for a Small Solar Dryer

Cited by 10 publications

References 36 publications

Experimental Determination of the Influence of Shape on the Heat Transfer Process in a Crushed Granite Storage Bed

Experimental Determination of the Influence of Shape on the Heat Transfer Process in a Crushed Granite Storage Bed

The Influence of the Shape of Granite on the Heat Storage Process in a Rock Bed

Proposal Solar Drying With Heat Storage Applied to Medicinal Plants

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