Performance evaluation of natural and forced convection indirect type solar dryers during drying ivy gourd: An experimental study
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)
- et al.
Solar drying of agricultural products: a review
Renew. Sustain. Energy Rev.
(2012) - et al.
Review of solar dryers for agricultural and marine products
Renew. Sustain. Energy Rev.
(2010) - et al.
An investigation on solar drying: a review with economic and environmental assessment
Energy
(2018) Solar dryers in the Asia-Pacific region
Renew. Energy
(1999)- et al.
Natural and forced air convection operation in a direct solar dryer assisted by photovoltaic module for drying of green onion
Sol. Energy
(2021) - et al.
A review on indirect type solar dryers for agricultural crops – dryer setup, its performance, energy storage and important highlights
Appl. Energy
(2020) Design, experimental investigation and analysis of a solar drying system
Energy Convers. Manag.
(2013)- et al.
Experimental investigations on active solar dryers integrated with thermal storage for drying of black pepper
Renew. Energy
(2021) - 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) - et al.
Drying of red pepper slices in a solar greenhouse dryer and under open sun: experimental and mathematical investigations
Innovat. Food Sci. Emerg. Technol.
(2019)
Mathematical modeling and performance analysis of thin layer drying of bitter gourd in sensible storage based indirect solar dryer
Innovat. Food Sci. Emerg. Technol.
Mathematical modelling and experimental investigation of tropical fruits drying
Int. J. Heat Mass Tran.
Three dimensional numerical modeling of simultaneous heat and moisture transfer in a moist object subjected to convective drying
Int. J. Heat Mass Tran.
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
Exergo-environmental analysis of an indirect forced convection solar dryer for drying bitter gourd slices
Renew. Energy
A mathematical model of simultaneous heat and moisture transfer during drying of potato
J. Food Eng.
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
Conservation of Moroccan truffle (Terfezia boudieri) using solar drying method
Renew. Energy
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
Analytical model for multicomponent wall film evaporation with non-unity Lewis number
Int. J. Heat Mass Tran.
Numerical analysis of drying kinetics for shrinkable products such as fruits and vegetables
J. Food Eng.
Cited by (37)
Comparative and comprehensive experimental analysis: Performance variation of a novel hybrid dryer
2024, Applied Thermal EngineeringDevelopment and enhancement in drying performance of a novel portable greenhouse solar dryer
2024, Journal of Stored Products ResearchRenewable energy as an alternative source for energy management in agriculture
2023, Energy Reports