Energy analysis of hybrid solar tunnel dryer with PV system and solar collector for drying mint (MenthaViridis)
Introduction
Improving product shelf life, reducing packing costs, lowering shipping weights, enhancement of the product appearance, capturing original flavor, and maintenance of nutritional value are some advantages of drying food products (Kadam and Samuel, 2006). It is widely trend to implement thin layer drying in agricultural commodities to extend their shelf life period. Simplicity of thin layer drying models has made them used mostly among other drying models. Contrary to some common complex representation models, in thin layers models, drying process is illustrated in an integrated manner as many parameters' evaluation are not necessary.
For fruits and vegetables, the thin layer drying models are basically time dependent moisture content due to drying parameters variation (Togrul and Pehlivan, 2002). In order to improve dried product quality, it is essential to conduct the drying process in a closed system which is entirely dependent on various unit operations (Ertekin and Yaldiz, 2004).
Peppermint is one of the indispensable commodities that is used year around for wide range of industries. Its oil is mainly used as flavoring in toothpaste, ice cream, confectionery, soft drinks, chewing gum, and other varieties of foods and in medicinal treatments. It can also be used in shampoos, soaps, balms and liniments. The oil has a cooling effect for fevers. For industrial applications, the vital mint oil is extricated mainly from freshly harvested peppermint leaves or semi dried and dried leaves through distillation process. The use of mint leaves in assortment of dishes such as vegetable and fruit salads, dressings, soups, desserts, juices, and sherbets are also indicated by several researchers (Park et al., 2002). Machiani et al. (2018) reported that intercropping of peppermint with faba bean could improve the essential oil quality by increasing the content of menthol and decreasing the content of menthofuran and pulegone.
The increased awareness of the global warming and the need to mitigate the environmental pollution by reducing fossil fuel use has already driven middle eastern countries to participate in the world climate change conferences.
The wide and continuous use fossil fuel causes air pollution and CO2 emissions effects. Therefore, it is mandatory to explore other renewable energy sources. Photovoltaic (PV) has gained worldwide recognition as a reliable and environment friendly renewable source of energy which can contribute significantly to a sustainable development. The abundant solar radiation in Middle Eastern countries made it most appropriate for development of solar PV system. Drying food products by solar energy can reduce up to 27%–80% of fossil fuel cost (Prakash and Kumar, 2013). Labed et al. (2016) mentioned that the use of solar dryers leads to avoid the mixture of product with the ground during drying and also prevents the penetration of insects and scorpions in the dried samples.
The amount of the energy required to remove 1 kg of water from wet substance is known as specific energy consumption (Fatouh et al., 2006). The specific energy consumption of dryers is directly affected by the methods of drying represented by heat transfer, dryer throughput, and mixing of the bed material. Some other factors such as physical and chemical properties of wet materials, climatic conditions, and operating options also affect the specific energy consumption (Tarhan et al., 2011).
The present research aims to develop a hybrid portable solar tunnel dryer (STD) and enhance its performance using PV system and flat plate solar collector for drying peppermint. The STD performance was evaluated by using three layers of mint, and compared with open sun drying. Predicted and experimental moisture ratio of mint leaves using developed STD were compared through several thin-layer drying models. Energy analysis of the hybrid STD such as effect of embodied energy on the environment was studied.
Section snippets
Materials and methods
The experimental work was done at College of Agricultural and Food Sciences, King Faisal University, Al Ahsa (25°18′ N Latitude, 49° 29′ E Longitude), Saudi Arabia.
PV performance
Since the performance of PV system in outdoor is quite different from the standard conditions, the performance is evaluated under ambient conditions. Results indicated that the PV power output and module temperature were directly proportional to insolation and ambient temperature. The daily average ambient conditions that affect the performance of PV system powered the mixed mode tunnel dryer is presented in Table 3.
Results of the experimental tests without load indicated that, the average
Conclusion
The hybrid solar tunnel dryer (STD) with PV system and flat plate solar collector was constructed and used for drying peppermint. The STD was operated under mixed mode and evaluated by using three layers of mint and thermal curtain for shading. The drying performance of the STD was compared with natural open sun drying. The energy analysis including CO2 emissions per year, embodied energy, energy payback time, carbon mitigation and carbon credit has been carried out. The average PV module
Acknowledgement
The authors acknowledge the Deanship of scientific research at King Faisal University, Saudi Arabia for the financial support under grant 150018.
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