Energy and Exergy Analysis of a Greenhouse Heating System Equipped with a Parabolic Trough Concentrator and a Flat -Plate Solar Collector
Journal Title: Journal of Agricultural Machinery - Year 2019, Vol 9, Issue 2
Abstract
Introduction Greenhouse cultivation has been increased in response to population growth, reduction in available supplies and arable lands and raising the standards of living. The quality and quantity of the products are profoundly affected by the greenhouse temperature. Therefore, providing an appropriate heating system is an elementary requirement for greenhouse cultivation. A number of factors such as glazing material, greenhouse configuration, product type, and climate conditions should be considered to design a greenhouse heating system. Due to the environmental concerns associated with the fossil fuels, renewable energy-powered heating systems such as geothermal, solar and biomass- are increasingly considered as the alternative or supplementary to the traditional fossil fuel heating equipment in greenhouses. In this way, a number of researchers have developed different greenhouse heating systems to reduce fossil fuel consumption. In Iran, because of appropriate available solar irradiance, the solar heating systems can be efficiently employed for greenhouse cultivation. A compound solar greenhouse heating system was experimentally and analytically investigated in the present study. To verify the obtained heat transfer equations, a set of experiments were carried out at Biosystems Engineering Campus of the Shahid Bahonar University of Kerman. Â Materials and Methods The designed system was comprised of a Parabolic Trough solar Collector (PTC), a dual-purpose modified Flat Plate solar Collector (FPC) and a heat storage tank. The modified FPC was located inside the greenhouse to act as a heat exchanger to transfer the stored heat to the greenhouse atmosphere during the night. The FPC also collects the solar radiations during the sunshine hours to enhance the thermal energy generation. Heat transfer equations of the PTC and the FPC were written and the useful energy gain of the heating system was determined at the quasi-static condition during the day. Experimental verification of the analytical models was conducted using regression coefficient (r) and root mean square percent deviation (e) criteria as follows: where Xi and Yi are respectively the ith analytical and experimental data and n shows the number of observations. Â Exergy analysis of the PTC and the FPC were carried out and the effect of the different fluid flow rates through the PTC on the exergy efficiency of the different components was investigated using the experimental data. Results and Discussion Increasing the fluid flow rate increased outlet temperature of the PTC due to the increase in heat removal factor and inlet temperature; whereas, caused a reduction in outlet temperature of the FPC. Since the thermal efficiency of the PTC improved with the fluid flow rate, the PTC fraction enhanced when the flow rate increased from 0.5 to 1.5 kg min-1. However, the PTC fraction values were less than 50% and sometimes have dropped below zero. The exergy efficiency of the PTC improved with increasing the flow rate. The reason was that the difference between the inlet and outlet temperatures of the PTC increased with the flow rate at the similar conditions of solar irradiance and ambient temperature. The highest exergy efficiency of the FPC was observed at the flow rate of 0.5 kg min-1. Conclusion The results of the study revealed that: There was a suitable agreement between the obtained analytical expressions and the experimental data based on root mean square percent deviation and regression coefficient criteria. The highest stored energy in the tank was around 40.02 MJ at the flow rate of 0.5 kg min-1. Increasing the flow rate improved the PTC exergy efficiency.
Authors and Affiliations
A. Ziaaddini,H. Mortezapour,M. Shamsi,A. Sarafi,
Study on Drying Process of Farmed Shrimp Meat in a Hot Air Convective Dryer and Variation of Some Related Parameters
IntroductionDrying shrimp is one of the storage methods that, while increasing the shelf life, leads to the production of a versatile product with various uses, from consumption as snacks to use as one of the main compon...
Evaluation of Two Types of Cotton Pickers in Terms of the Functionality and Quality of the Harvested Fibers
IntroductionCotton, as one of the most widely used products in various industries, has always been considered by leading countries in agriculture. The applications of this plant range from the food industry to the milita...
Study of Primary Tillage Timeliness Cost for Irrigated Wheat in Fars Province Using System Dynamics
Delay in irrigated wheat primary tillage operations causes yield reduction and hidden timeliness cost in Fars province. Mechanization of primary tillage operations for irrigated wheat in Fars province was simulated using...
Simulation of Heat and Mass Transfer in a Refractance Window Dryer for Aloe vera gel
IntroductionDrying is one of the oldest methods of food preservation. To increase the efficiency of heat and mass transfer while maintaining product quality, the study of the drying process is crucial scientifically and...
Comparison of Fiber Reinforced Polymer (FRP) Composite Blade with Steel Blade Performance Used in Chisel Plow
All over the world, farmers choose different implements for tillage, which depend on crop type, soil type, the amount of plant residue from the previous crop, etc. Tillage implement selection is also affected by the avai...