PERFORMANCE STUDY OF FORCED CONVECTION SOLAR DRYER WITH REFLECTOR

International Journal of Mechanical Engineering and Technology (IJMET) Volume 9, Issue 6, June 2018, pp. 784 791, Article ID: IJMET_09_06_088 Available online at http://www.iaeme.com/ijmet/issues.asp?jtype=ijmet&vtype=9&itype=6 ISSN Print: 0976-6340 and ISSN Online: 0976-6359 IAEME Publication Scopus Indexed PERFORMANCE STUDY OF FORCED CONVECTION SOLAR DRYER WITH REFLECTOR A.Nandakumar, S.Dhanushkodi, K. Panner Selvam PRIST University, Vallam, Thanjavur, Tamilnadu, India K. Sudhakar Energy Centre, National Institute of Technology, Bhopal, M. P, India; Faculty of Mechanical Engineering, Universiti Malaysia Pahang, 26600 Pahang, Malaysia ABSTRACT The main aim of the study is to investigate the effect of the reflector on drying performance of the cashew nut in a small scale solar dryer consisting of solar flat plate collector, drying chamber and blower unit. The performance test of the dryer was carried out in forced mode by the combination of with and without a reflector. Moister content, Drying rate, collector efficiency and drying efficiency during its operation have been estimated and compared with sun drying. In forced solar drying with reflector, the average drying temperature rise is 8ºC more than without reflector. The required moisture content of 3% was achieved within 8 hours with average system efficiency estimated at 10.5% Key words: Solar Dryer, Forced Convection, Thermal Efficiency and Drying. Cite this Article: A.Nandakumar, S.Dhanushkodi, K. Panner Selvam and K. Sudhakar, Performance Study of Forced Convection Solar Dryer with Reflector, International Journal of Mechanical Engineering and Technology, 9(6), 2018, pp. 784 791. http://www.iaeme.com/ijmet/issues.asp?jtype=ijmet&vtype=9&itype=6 1. INTRODUCTION The use of solar and biomass energy as a substitute for conventional sources has gained global attention [1-6]. Various solar and biomass-based technology is developed to cater to the needs of rural as well as urban population [7-15]. The geographical location of India is highly favorable for solar PV and thermal applications [16 26]. Solar radiation in the form of solar thermal energy is an alternative source of energy for drying especially to dry fruits, vegetables, agricultural grains and other kinds of material, such as wood. Solar drying is especially appropriate in the sunny belt regions where the solar radiation intensity is high and sunshine duration is long. http://www.iaeme.com/ijmet/index.asp 784 editor@iaeme.com

Performance Study of Forced Convection Solar Dryer with Reflector The cashew industry ranks third in the world production of edible nuts. Three main cashew products are traded on the international market; these are Raw Nuts, Cashew Kernels and Cashew Nut Shell Liquid (CNSL). A Fourth product, the Cashew Apple is generally processed and consumed locally. The shelled cashew kernel is layered with the red skin testa. For easy removal ie to peel it has to undergo a drying process. It also removes tanning and reduces moisture content inside the kernel. Many different types of the solar dryer for drying agricultural products with like chilies, cauliflower, copra etc. The existing literature survey clearly indicated that so far no work has been carried out on solar drying of cashew nut in forced convection mode. Hence the present investigation is undertaken to fill the void left by the researchers. 2. EXPERIMENTAL SETUP Experiments were conducted at an optimum airflow rate of 0.042 Kg/s in forced convection mode with a reflector under loading condition of 40kg of cashew per batch (Figure 1).During the trial, for every one-hour drying duration, the temperature of the drying chamber at the bottom, middle and top trays are measured by using a thermocouple. Ambient temperatures, collector outlet temperature, drying chamber outlet temperature are measured by using RTDs. Other results observed are solar radiation by a solar power meter, relative humidity at ambient and drying chamber by thermo hygrometer. The initial and final weight of the product is measured by using digital weight balance. The flow rate of air is set by using hotwire anemometer connected between blower and collector and collector inlet. Energy consumption of the blower is also calculated by an energy meter. The same data were taken in forced convection solar mode with a reflector. Every one hour the position of the mirror is adjusted so that all the time the solar radiation falls on the collector. The collector & drying chamber inlet and outlet temperature was measured and instantaneous thermal efficiencies of the system were calculated, to analyze the performance of the solar dryer. Figure 2 shows the experimental setup of forced convection solar dryer with reflector. Figure 1 shows the cashew nut sample for drying http://www.iaeme.com/ijmet/index.asp 785 editor@iaeme.com

A.Nandakumar, S.Dhanushkodi, K. Panner Selvam and K. Sudhakar Figure 2 shows the photograph of the forced convection solar dryer with reflector 3. PERFORMANCE ANALYSIS The system performance and the drying characteristics of cashew nuts (kernel) such as moisture content, drying rate, and efficiency were calculated using the following equations. Moisture content: The moisture in cashew nuts were determined after each hour of drying. The moisture content after each hour in drying was determined by taking the initial weight and weight loss after each hour with the help of electronic balance [100]. Drying Rate: The drying rate was formed by a decrease of the water concentration during the time interval between two subsequent measurements divided by this time interval. Collector Efficiency: A measure of collector performance is the collector efficiency and it is defined as the ratio of useful heat gain over any period to the incident solar radiation over the same period. The useful heat gain by a collector can be expressed as http://www.iaeme.com/ijmet/index.asp 786 editor@iaeme.com

Performance Study of Forced Convection Solar Dryer with Reflector Drying chamber efficiency: It can be defined as the ratio of the difference between the drying chamber inlet and drying chamber outlet temperature to the difference between the drying chamber inlet and ambient temperature. Overall system efficiency is the ratio of the energy required to evaporate moisture from the product to the heat supplied to the dryer.the system drying efficiency is a measure of the overall effectiveness of a drying system. Energy consumed by the blower is taken into account for forced convection mode. System efficiency can be expressed as. (Forced convection solar dryer) (Natural convection solar dryer) Effectiveness factor: It can be defined as ratio of drying rate in the particular mode of the dryer to the drying rate in the open sun drying. Drying rate in the particular mode of dryer Effectiveness factor = Drying rate in open sun drying 4. RESULTS AND DISCUSSIONS The thermal performance of the system was studied with and without using reflector and found the maximum collector outlet temperature was 75.5 C and 70 C (Figure 3). There was an increase in temperature of 5.5 % with reflectors than in the dryer without reflectors. The ambient air temperature ranged from 28-34 C. The maximum and minimum drying air temperatures recorded at the collector outlet were 50 C and 90 C. The temperature in the dryer varied between 35-78 C. The average drying chamber temperatures recorded were 64 C. The drying air temperature at collector outlet and inside the drying chamber obtained in this system is comparatively higher than the temperature obtained in the forced system without a reflector. Figure 3 Variation of solar radiation, ambient temperature, drying chamber, collector temperature with time http://www.iaeme.com/ijmet/index.asp 787 editor@iaeme.com

A.Nandakumar, S.Dhanushkodi, K. Panner Selvam and K. Sudhakar A sample calculation is provided for the better understanding of the analysis. 1. Moisture Content: =1.00 Initial moisture content = 9.29% Reduced moisture = 1.00% Moisture content present at time t = 8.29% 2 Drying Rate: mi md Rd = t = 500 495 = 0.0013kg/s 3600 3. Collector Efficiency: mcp( T 0 Ti) ηc = X100 IA 0.0298 x 1005 x (62 29.5) = x 100 675 x 2.2 = 65.54% For mass flow rate: m a = ρa x Va = 1.2754 23.39 10-3 = 0.0298 kg/s 4. Dryer Efficiency: mwhfg ηd = x100 IAt + E = (675 X = 16.12% 0.4 X 2394.8 X10 X100 3 2.2 3600) 0.1 X10 X + 3600 3 Figure 4 Variation of moisture content with drying time The data on weight loss and the moisture content variation of the cashew nut along with drying time are shown in Fig.4. The initial moisture content of cashew nut was 9.5 % (w.b.). The time required to dry cashew kernel to the required moisture content of 3.5 % was around http://www.iaeme.com/ijmet/index.asp 788 editor@iaeme.com

Performance Study of Forced Convection Solar Dryer with Reflector 8.5 hrs in forced convection with a reflector. It was observed that the reduction in moisture content was high at the beginning and reduced gradually with drying time. It shows that the drying rate of cashew in forced convection mode is higher when compared to the other two methods. Also the cashew nut dried with the solar dryer in forced mode showed a variation in drying rate. The moisture content of cashew kernel reached to 3.5 % from 9.5% in 8.5 h of drying while it took 15 hours of drying time in open sun drying (Figure 5). The drying time is reduced by 43 % in forced convection solar dryer with a reflector. The drying rate was high initially but decreased gradually with a reduction in moisture content. The drying rate was found to decrease with increase in drying time. Drying rate decreases due to decrease in collector outlet air temperature and gets increased due to increase in collector outlet air temperature. The plots indicate that the rate of moisture loss decreases as the drying time increases, until finally the cashew nut approach the equilibrium moisture content (MR=0). The drying mainly occurs in the falling rate period which indicates a diffusion-controlled type of mechanism of drying Figure 5 Variation of drying chamber and collector efficiency with time The average thermal efficiency of the dryer system, using reflector was nearly 10% whereas the thermal efficiency of the system without using reflector was around 8.5 % 5. CONCLUSION From the above-summarized results, the following conclusions could be drawn: The temperature in the dryer varied between 35-78 C corresponding to the ambient temperature of 28-34 C during experimentation The drying time required for drying cashew nut to reduce moisture content from 9.5% to 3.5% (wb) was found to be 8 hrs in the cabinet solar dryer equipped with reflector, whereas it took 15 h in the open sun drying. The thermal efficiency of the solar dryer with reflector system was found to be 10% whereas it is 8.5 % for solar dryer without a reflector. The forced convection solar dryer integrated with glass reflectors was found suitable for drying cashew nut. The results showed that integration of the reflector enhanced the performance of the solar dryer Further investigations are underway to bring out the better comparison with variation in load and other agricultural products. http://www.iaeme.com/ijmet/index.asp 789 editor@iaeme.com

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