Elsevier

Journal of Cleaner Production

Volume 181, 20 April 2018, Pages 352-364
Journal of Cleaner Production

Energy analysis of hybrid solar tunnel dryer with PV system and solar collector for drying mint (MenthaViridis)

https://doi.org/10.1016/j.jclepro.2018.01.229Get rights and content

Highlights

  • Energy analysis of hybrid solar tunnel dryer with PV system and solar collector.

  • Performance evaluation of mixed mode solar tunnel for drying peppermint.

  • Effect of using and without using black thermal curtain above peppermint.

  • Verification of different drying models and layer thickness for drying peppermint.

  • Effect of embodied energy of the hybrid solar tunnel dryer on the environment.

Abstract

This work aims to develop a hybrid portable solar tunnel dryer and enhance its performance using solar photovoltaic system and flat plate solar collector for drying peppermint. The solar tunnel dryer can work in mixed mode (direct and indirect thermal heating). The photovoltaic system is used to operate an axial direct current fan (forced mode). Also, the solar tunnel dryer is provided with a thermal curtain to shade mint and protect it from direct solar radiation. The solar tunnel dryer performance is evaluated by using single, double and three layers of mint, and compared with open sun drying. Predicted and experimental moisture ratio of mint leaves using developed solar tunnel dryer were compared through several models of thin-layer drying. The effect of embodied energy of the developed hybrid solar tunnel dryer on environment was studied. Results indicated that the drying time of peppermint was varied from 210 to 360 min for the developed dryer, while varied from 270 to 420 min for open sun drying. It has been noticed that peppermint drying happened in falling-rate period. The two-term model was the best model to simulate the solar thin layer drying process of peppermint for all treatments. The daily average photovoltaic efficiency was 9.38%, dryer efficiency was 30.71%, overall efficiency was 16.32%, energy payback time was 2.06 years and net carbon dioxide (CO2) mitigation over the lifetime was 31.80 tons. The quality of the dried peppermint by using black thermal curtain in the solar tunnel dryer is higher than that dried in the open sun as the natural color and the appearance are retained more under shading. This system is quite useful for people living in remote areas, where grid connectivity is not available and it can meet the demand of farmers.

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.

References (44)

  • K. Leon et al.

    Color measurements in L*a*b* units from RGB digital images

    Food Res. Int.

    (2006)
  • M.A. Machiani et al.

    Evaluation of yield, essential oil content and compositions of peppermint (Mentha piperita L.) intercropped with faba bean (Vicia faba L.)

    J. Clean. Prod.

    (2018)
  • A. Maskan et al.

    Hot air and sun drying of grape leather (pestil)

    J. Food Eng.

    (2002)
  • O. Prakash et al.

    Performance of modified greenhouse dryer with thermal energy storage

    Energy Rep.

    (2016)
  • O. Prakash et al.

    Solar Greenhouse drying: a review

    Renew. Sustain. Energy Rev.

    (2014)
  • K. Sacilik et al.

    Mathematical modelling of solar tunnel drying of thin layer organic tomato

    J. Food Eng.

    (2006)
  • V. Shanmugam et al.

    Experimental study of regenerative desiccant integrated solar dryer with and without reflective mirror

    Appl. Therm. Eng.

    (2007)
  • I.T. Togrul et al.

    Mathematical modelling of solar drying of apricots in thin layers

    J. Food Eng.

    (2002)
  • ASAE

    Standards, American Society of Agricultural Engineers

    (1991)
  • A.G. Baird et al.

    The energy embodied in building materials updated New Zealand coefficients and their significance

    IPENZ Trans.

    (1997)
  • B.K. Bala et al.

    Solar drying of fish (Bombay Duck) using solar tunnel dryer

    Int. Energy J.

    (2005)
  • D.M. Bruce

    Exposed-layer barley drying, three model fitted to new data up to 150C

    J. Agric. Eng. Res.

    (1985)
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