Elsevier

Renewable Energy

Volume 182, January 2022, Pages 934-945
Renewable Energy

Performance evaluation of natural and forced convection indirect type solar dryers during drying ivy gourd: An experimental study

https://doi.org/10.1016/j.renene.2021.11.038Get rights and content

Abstract

The performance investigation of natural and forced convection indirect type solar dryers was performed by drying ivy gourd. The natural convection setup was modified by fitting a trapezoidal duct and central processing unit fans run by photovoltaic panels to promote forced convection. The data from the experiment was used to estimate collector and dryer efficiencies, energies, effective moisture diffusivity, transfer coefficients, specific energy consumption and specific moisture extraction rate. The average actual heat supplied was 776.6 and 997.76 W for natural and forced convections, respectively. The average collector efficiency for the same was 62.56% and 77.2%, respectively. The average drying efficiency for the same was 6.62% and 7.8%, respectively. The average values of activation energy, mass transfer, heat transfer and diffusion coefficients were estimated to be 39.85 and 35.54 kJ/mol, 7.06 × 10−9 and 8.35 × 10−9 m2/s, 0.0033 and 0.0043 m/s, and 3.85 and 4.93 W/m2 K, respectively, for natural and forced convection setups, respectively. The specific energy consumption and specific moisture extraction rate were evaluated where forced convection setup gave the best results. The drying correlations were developed for mass transfer, heat transfer and diffusion coefficients. Uncertainty analysis was performed to check the authenticity of the results.

Introduction

Renewable energy sources, more specifically, solar energy draws much focus from the global science and research communities for the fact that other energy sources are limited in nature and they are one of the major causes for environmental pollution. Additionally, high demand for energy becoming is the core issue of the globe. This is because of the rate of population growth and expansion of energy intensive technologies. These issues drive the researchers for reliable and renewable energy sources. Solar drying, solar water heating, solar cooling, solar ponds, solar cooking, solar furnaces, solar distillation, and solar thermal power generation are the main applications of solar energy. As a component of broad areas of solar energy, the solar dryer has become one of the essential applications in drying agricultural food products and other products [1]. Solar drying is a mechanism that removes moisture from the object by exposing it either directly or indirectly to solar radiation. It involves simultaneous heat and moisture transport thereby improves the shelf life and quality of the product [2].

Chauhan et al. [3] performed a comprehensive review on the studies of solar dryers and reported that solar energy is the best option to replace fossil fuel usage for drying applications. The drying time and equilibrium moisture content of potato slices were estimated experimentally by Chandramohan et al. [4]. They presented that the microbial and bacterial impact of agricultural food products can be avoided by reducing the moisture content (MC) below 10%.

Fudholi et al. [5] categorized solar drying based on the style of exposure of food products to the solar radiation as direct solar dryers, indirect type solar dryers (ITSD), mixed type dryers and hybrid type solar dryers. On their assessment, they concluded that solar drying of agricultural and sea products is very impressive and economical compared to other drying techniques. Ramadan et al. [6] studied the economic and environmental merits, demerits and pitfalls of solar dryers. They addressed the working principles, parts and categories of ITSD on their report and summarized that use of a solar dryer (during drying 120 kg of carrot) reduced 6400 kg/month CO2 emissions, saved 780$/month as compared to conventional sources of energy such as fossil fuels, and its payback period was found to be 10 months. Ong [7] theoretically analysed by formulating a drying model for tropical fruits and validated the same with experimental drying kinetics of banana slices, thereby confirmed that the model was capable of estimating drying kinetics.

Hadalgo et al. [8] made a direct solar dryer (DSD) supported by photovoltaic (PV) panels to facilitate the forced convection drying experiments of the green onion by controlling moisture and calorimetric parameters. The effective diffusivity (Deff), thermal efficiency and specific energy consumption (SEC) were estimated to be 5.15 × 10−9 and 1.15 × 10−8 m2/s, 34.2 and 38.3%, and 18.3 and 16.39 kW-h/kg for natural and forced convection setups, respectively.

Lingayat et al. [9] systematically surveyed the overall being of ITSDs and presented that ITSDs (passive dryers) are easy to fabricate. It was mentioned that ITSD dryers are more preferable as they overcome the limitations of DSD dryers. Abuska et al. [10] briefly discussed the working principles, basic components and instrumentations of ITSDs in their experimental study. They examined with two setups, one with a flat plate absorber in solar air collector (SAC) and the other with conical springs on the absorber plate. They presented that the thermal efficiency was significantly improved by the conical spring mounted absorber plate.

Sevik [11] reported that the ITSD dryers were predominantly utilized for drying leafy foods and the eventual outcome would be perfect and sterile if all the important care and precautions were made during drying. They designed and fabricated a double-pass SAC supported by a heat pump and PV unit to perform an experimental study by drying carrot slices. It took 220 min to reduce the moisture content of the carrot from 7.76 to 0.1 g per g of db, and the thermal efficiency was estimated to be 60%–78%. Kulkarni and Vijayanand [12] presented that ivy gourd (Coccinia Indica L.) produced in India was categorized under the Cucurbitaceae family, which is a well-known tropical vegetable with important nutritional qualities such as hypoglycaemic effect and contains an ample amount of ascorbic acid. Its local name is ‘Dondakaya’ in Warangal, India. They executed an experimental study to investigate the quality characteristics of an ivy gourd which was pre-treated by potassium meta-bisulfate and dehydrated 4.6% MC at 50 ± 1 °C. They claimed that the dehydrated and packed foods in low density polyethylene covers preserved for 4–6 months with highly acceptable quality. Hussein et al. [13] dried apricot fruits (Prunus Armeniaca L.) in Indian semi-arid altitude and the result showed that drying the fruit improved the shelf life which also enhanced the lifestyle of the producers because the dried fruits were exported.

In general, studies on solar drying of red chilli by Murali et al. [14], mushroom by Mustayen et al. [15], green peas by Godireddy et al. [16], black pepper by Lakshmi et al. [17], carob seeds (Ceratonia siliqua L.) by Tagnamas et al. [18], green chilli by Mugi et al. [19], apple and watermelon by Lingayat et al. [20] plainly showed a promising future. All the studies proved that ITSD is an effective dryer compared to other dryers as it produces more hygienic final products [3]. Among the literature, few studies on solar drying dealt with natural convection [11,20] and few others dealt with forced convection [21,22]. There is no data found on the comparative study made between natural and forced convection setups. There are some studies on estimating the drying parameters such as drying rate [22,23], actual heat supplied [25], diffusion coefficient [8,26] and surface transfer coefficients [27,28] during solar drying of food products. Still, there is no study on the results of drying parameters for comparison of natural and forced convection ITSDs. Very few studies estimated and analysed the performance parameters such as drying efficiency [22,29], collector efficiency [10,22], activation energy (Ea), specific energy consumption (SEC) [8,30] and specific moisture extraction rate (SMER) [19,20]. But no comparative data of these output parameters of natural and forced convection ITSDs. There is no data exist on drying correlation for Deff, h and hm during drying of ivy gourd for both natural and forced convection procedures. These research gaps inspire authors to investigate more on results comparison on natural and forced convection ITSDs so that these outcomes reach industries and researchers.

This work contributes to fulfilling the above said research gaps. The objectives of this work are, i) to conduct the drying experiments and estimate the parameters such as drying rate, actual heat supplied, effective diffusion coefficient (Deff), mass transfer coefficient (hm), heat transfer coefficient (h) of ivy gourd using natural convection ITSD, ii) to perform and estimate all the above mentioned parameters using a forced convection ITSD setup, iii) to analyse and compare the above mentioned parameters for natural and forced ITSDs, iv) to estimate and compare the performance parameters such as collector and drying efficiencies (ηc and ηd) of both setups, v) to evaluate and compare the specific energy consumptions (SEC) and specific moisture extraction rates (SMER) for both setups and vi) to generate correlations for Deff, h and hm for both setups.

Section snippets

The experimental setup

The experimental setup contains a solar air collector (SAC), drying chamber with four trays and a chimney at the top. The schematic of the experimental setup was shown in Fig. 1. The experimental setup used for natural convection ITSD is mentioned Fig. 2 (a). With this setup, a trapezoidal duct with three inlet CPU fans was provided at the entrance of SAC to conduct forced convection experiments as shown in Fig. 2 (b). The CPU fans were run using solar PV panels. Therefore, there was no

Solar radiation

Solar radiation was recorded for the consecutive days during drying of ivy gourd in natural and forced convection ITSDs and shown in Fig. 4. The experiment was started at 8:00 h and completed at 18:00 h which are represented as 0 h and 10 h, respectively, in the X-axis of Fig. 4. The minimum values of solar radiation were observed to be 178 and 184 W/m2 and the maximum values were recorded to be 990 and 1020 W/m2 for natural and forced convections, respectively. The average radiations were

Conclusions

The experiments were performed to examine the drying kinetics and performance of a natural and a forced convection indirect type solar dryer (ITSD). Forced convection was facilitated by fitting a trapezoidal duct with three fans aided by PV panels. From the test results, the major findings inferred are:

  • The moisture content (MC) of the ivy gourd was decreased from 15.32 (db) to 0.144 (db) and it took 16 and 13 h for natural and forced convection ITSDs, respectively.

  • The average solar radiations

CRediT authorship contribution statement

Mulatu C. Gilago: Experimentation, Data collection, Formal analysis, Investigation, Writing – original draft, Preparation. Chandramohan V.P.: Conceptualization, Supervision, Writing – review & editing.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The authors indebted to thank Department of Mechanical Engineering, NIT Warangal, India for supporting the project in finance which is referred as: NITW/MED/Head/2015/408 dated Dec. 3, 2015.

References (42)

  • S. Vijayan et al.

    Mathematical modeling and performance analysis of thin layer drying of bitter gourd in sensible storage based indirect solar dryer

    Innovat. Food Sci. Emerg. Technol.

    (2016)
  • M.A. Karim et al.

    Mathematical modelling and experimental investigation of tropical fruits drying

    Int. J. Heat Mass Tran.

    (2005)
  • V.P. Chandra Mohan et al.

    Three dimensional numerical modeling of simultaneous heat and moisture transfer in a moist object subjected to convective drying

    Int. J. Heat Mass Tran.

    (2010)
  • V. Reddy Mugi et al.

    Energy, exergy and economic analysis of an indirect type solar dryer using green chilli: a comparative assessment of forced and natural convection

    Thermal Science and Engineering Progress

    (2021)
  • S. Vijayan et al.

    Exergo-environmental analysis of an indirect forced convection solar dryer for drying bitter gourd slices

    Renew. Energy

    (2020)
  • N. Wang et al.

    A mathematical model of simultaneous heat and moisture transfer during drying of potato

    J. Food Eng.

    (1995)
  • A.K. Bhardwaj et al.

    Energy and exergy analyses of drying medicinal herb in a novel forced convection solar dryer integrated with SHSM and PCM

    Sustainable Energy Technologies and Assessments

    (2021)
  • Z. Tagnamas et al.

    Conservation of Moroccan truffle (Terfezia boudieri) using solar drying method

    Renew. Energy

    (2020)
  • M. Goud et al.

    A novel indirect solar dryer with inlet fans powered by solar PV panels: drying kinetics of Capsicum Annum and Abelmoschus esculentus with dryer performance

    Sol. Energy

    (2019)
  • A. Ullal et al.

    Analytical model for multicomponent wall film evaporation with non-unity Lewis number

    Int. J. Heat Mass Tran.

    (2021)
  • S.J. Kowalski et al.

    Numerical analysis of drying kinetics for shrinkable products such as fruits and vegetables

    J. Food Eng.

    (2013)
  • Cited by (37)

    View all citing articles on Scopus
    View full text