EXERGY LOSS ANALYSIS OF FORCED CONVECTION SOLAR DRYER

Transcription

1 International Journal of Mechanical Engineering and Technology (IJMET) Volume 9, Issue 6, June 2018, pp , Article ID: IJMET_09_06_085 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed EXERGY LOSS ANALYSIS OF FORCED CONVECTION SOLAR DRYER S. Baranitharan PRIST University, Vallam, Thanjavur , Tamilnadu, India S. Dhanushkodi 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, Pahang, Malaysia ABSTRACT A forced convection solar dryer was fabricated to improve the energy efficiency and productivity of cash crops like cashew nuts to a large extent. Energy analysis was applied to quantify the solar energy absorbed by the solar collector and drying chamber. Exergy analysis was applied to estimate the energy losses during the drying process. An exergy loss analysis of the forced convection solar dryer has been presented in this work based on the experimental analysis. Consequently, it was found that the exergy losses took place mostly in the drying chamber where the available energy was less utilized. Key words: Exergy Loss, Forced Convection, Solar Dryer, and Exergy Efficiency. Cite this Article: S. Baranitharan, S. Dhanushkodi and K.Sudhakar, Exergy Loss Analysis of Forced Convection Solar Dryer, International Journal of Mechanical Engineering and Technology, 9(6), 2018, pp INTRODUCTION Utilization of solar energy is a most viable and effective scientific method for thermal and electricity applications.[1-5]. Thermal applications like solar drying is a low-temperature process, hence solar dryers with low exergy loss and high exergy efficiency are to be selected for the practical application. The main problem with the natural convection solar dryers is the low thermal efficiency and drying performance. Forced convection dryers require a fan to pump the air through the dryer for improving the rate of heat circulation in the collector and the drying chamber. Many studies [6 15] have been attempted to study the solar radiation, solar applications in building, drying editor@iaeme.com

2 Exergy Loss Analysis of Forced Convection Solar Dryer and exergy analysis. Several studies [16 26] have been done on performance and energy analysis of solar, biomass and hybrid dryers [16 26]. The ideal thermodynamic efficiency of a dryer system is the ratio of useful available energy to the energy supplied to the system. Since the solar collector absorbs energy at a higher temperature than the ambient, the energy will be partially converted to useful heat in the system and partially lost to the surrounding. Therefore, for the assessment of the thermal performance of such a dryer system, a descriptive parameter that rates the quantity and quality of energy is required. To the best of authors knowledge, there is no work on the exergy analysis loss analysis of the solar drying systems. Therefore, this research work shall help in filling this gap. The exergy loss analysis is a more powerful tool to design and optimize the performance of energy system. In the present work an attempt has been made to perform exergy loss analysis of the forced convection solar dryer for drying cashew. 2. EXPERIMENTAL SETUP A forced convection solar dryer was constructed with absorber plate of size 2 mm thick made of aluminum and a double toughened glass of thickness 4 mm. The absorber plate is painted black to absorb solar radiation. The dryer is properly insulated with rock wool insulation to reduce heat losses. Experiments were conducted in forced convection solar dryer with 40 Kg of cashew kernel. The ambient temperature, collector inlet and outlet temperature, drying temperature are measured using RTDs. The Initial and final weight of the product is measured by using digital weight balance. The flow rate of air is taken by using hotwire anemometer connected between blower and collector inlet and energy consumption of the blower is also calculated by an energy meter. Similar experiments were repeated in natural convection solar dryer and compared with open sun drying. Table 1 shows the specification of the instruments used in the experiment. Table 1 Instrumentations Sl. No Parameter Instruments Accuracy 1 Temperature Thermocouple and RTDs 0.05 C 2 Mass Electronic Balance 0.01g 3 Solar Radiation Solar Power Meter ±5% At 2000W/m² 4 Air Velocity Hot Wire Anemometer ±2.5% 5 Power Consumption Of Blower Energy Meter ±0.1Kwh 6 Relative Humidity Thermo Hygrometer ±2.5% Figure 1 Photograph of the forced convection solar dryer editor@iaeme.com

3 S. Baranitharan, S. Dhanushkodi and K.Sudhakar 3. EXERGY LOSS ANALYSIS Drying is a very complex process whose goal is to remove partially or completely the moisture contained in a product. This process involves a double transfer of heat and mass, thus it is a very inefficient operation. The energy needed for drying depends mainly on the nature of the product to be dried and the drying rate. Hence the usefulness of an energy and exergy analysis for each product to quantify the energy needed for drying and to locate the exergy losses in each step of the process. The various drying parameters needed for the loss analysis are listed below. 1. Moisture content: M = 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. R = 3. Collector efficiency: A measure of collector performance is the collector efficiency or heat collection designed or the ratio of useful heat gain over any period to the incident solar radiation over the same period. η =. The useful heat gain by a collector can be expressed as (Qu) Q = mc ( T T ) From equations 1 and 2 η =! ( " # " ) $.% 3. Overall system efficiency of forced convection solar dryer: η = &.' () $%.*+ 4. Exergy input, output, loss and efficiency [27] The exergy outflow of the drying chamber (Ex dco) = mc [(T dco -T a)-t aln " ", ] The exergy Inflow of the drying chamber (Ex dci) = mc [(T dci -T a)-t aln " ", ] The exergy loss (Ex loss)= Ex dci- Ex dco Drying chamber Efficiency (η dc)= -.-/ -.-0 The second law efficiency is estimated based on the following relations: Exergy efficiency (η EX) = RESULTS AND DISCUSSIONS Figure 2 shows a variation of moisture content with drying time in forced convection solar dryer. The initial moisture content of the cashew kernel was 9.29% (db) and the final moisture content was in the range of 3.5 to 4.6% dry basis. The drying is achieved within 6 hours in editor@iaeme.com

4 Exergy Loss Analysis of Forced Convection Solar Dryer forced convection mode, while it took 8 hours of drying in natural convection mode. The present solar system maintains the constant temperature C in 4-5hrs per day. Figure 2 variation of moisture content with drying time Figure 3 shows the variation of exergy inflow and outflow during the drying process. With the increase in temperature and flow rate, the input exergy to the drying chamber increases, and then, a large amount of the input exergy leaves without being used in water evaporation contained in the cashew. Accordingly, the highest exergy outflow and the most efficient utilization of exergy were noticed in case of the minimum exergy losses in the system. Thus, it can be inferred that it is necessary to show the variations of exergy with drying time to determine when and where the maximum and minimum values of the exergy losses took place during the solar drying process. Figure 3 Variation of exergy inflow and outflow with drying time. Figure 4 shows the variation of the exergy loss with the energy utilization in drying chamber. The drying chamber is detected as the component with the highest exergy loss and source of irreversibility. The average exergy losses of the solar dryer were found to be 434 kj/kg. Based on the amounts of the energy utilization, the exergy losses of drying chamber varied between 715 and 292 kj/kg. Moreover, they increased linearly with the rise of the ambient temperature and solar radiation. Accordingly, the exergy losses went up with the increase of the energy utilization in the drying chamber. Hence, it was noticed that the most exergy losses took place during the solar drying editor@iaeme.com

5 S. Baranitharan, S. Dhanushkodi and K.Sudhakar of cashew kernel. The seeming disadvantage of incorporating external blower is the increase in exergy destroyed as a result of increase in the mass of air. It is important to note that one of the thermodynamic inefficiencies of these drying systems is the exergy loss from the drying chamber to the environment. Figure 4 Variation of exergy loss with drying time Figure 5 shows the exergy efficiency and collector efficiency variation for the drying period Maximum instantaneous exergy efficiency of 10 % is obtained at around 11 AM. The exergy loss rate of the process decreased by the increase in the inlet drying air. The minimum exergy efficiency of 1% is obtained at around 6 PM when the drying process is almost complete. The average exergy efficiency of the forced convection solar dryer is 5 %. As can be seen, the energetic efficiency of solar dryer ranged from 55 70%, at an average value of 64%. The exergy analysis of the dryer demonstrated that the incorporation of the external blower (fan) leads to increase in the magnitude of the exergy destroyed necessitated by the increase in mass flow rate of the air Figure 5 Variation of energy efficiency and collector efficiency with drying time (hrs) editor@iaeme.com

6 Exergy Loss Analysis of Forced Convection Solar Dryer 5. CONCLUSION In the present work, experiments were conducted on a forced convection solar dryer to evaluate the exergy loss. The various measured parameters were solar radiation intensity, wind speed, ambient temperature, humidity, and collector inlet and outlet temperature, drying chamber inlet and outlet temperature, of air. The highest exergy loss was observed in forced convection solar dryers systems. It is important to note that one of the thermodynamic inefficiencies of these drying systems is the exergy loss from the drying chamber to the environment. The daily exergy loss of forced convection solar dryer increases with drying time and then decreases. The exergy efficiency of the dryer is very low when compared to the thermal efficiency of the solar collector. REFERENCES [1] A.K. Shukla, K. Sudhakar, P. Baredar, Exergetic assessment of BIPV module using parametric and photonic energy methods: a review, Energy Build. 119, 2016,pp [2] Sreenath Sukumaran, K. Sudhakar, Performance analysis of Solar powered airport based on energy and exergy analysis, Energy, 2018, doi: /j.energy [3] A.K. Shukla, K. Sudhakar, P. Baredar, Exergetic assessment of BIPV module using parametric and photonic energy methods: a review, Energy Build. 119, 2016,pp [4] P Kumar, AK Shukla, K Sudhakar, R Mamat. Experimental exergy analysis of watercooled PV module. International Journal of Exergy 23,2017,pp, [5] Akash Kumar Shukla, K.Sudhakar, Prashant Baredar, Exergetic analysis of building integrated semitransparent photovoltaic module in clear sky condition at Bhopal India, Case Studies in Thermal Engineering 8, 2016, pp [6] Hyder, F., Sudhakar, K., & Mamat, R. Solar PV tree design: A review. Renewable and Sustainable Energy Reviews, 82, 2018, pp [7] Sreenath Sukumaran, K. Sudhakar, Fully solar powered airport: A case study of Cochin International airport, Journal of Air Transport Management, 62, 2017, pp [8] Shukla, K.N., Sudhakar, K., Rangnekar, S., A comparative study of exergetic performance of amorphous and polycrystalline solar PV modules. Int. J. Exergy 17,2015,pp [9] K. Sudhakar, M. Premalatha: Characterization of micro algal biomass through FTIR/TGA/CHN analysis: Application to Scenedesmus sp.. Energy Sources Part A Recovery Utilization and Environmental Effects 10, 2015, pp 1-8., [10] K Sudhakar, M Premalatha, M Rajesh: Large-scale open pond algae biomass yield analysis in India: A case study. International Journal of Sustainable Energy 08, 2012, pp-., DOI: / [11] K Sudhakar, M Rajesh, M Premalatha: A Mathematical Model to Assess the Potential of Algal Bio-fuels in India. Energy Sources Part A Recovery Utilization and Environmental Effects 04, 2012, pp , [12] K.Sudhakar, Tulika Srivastava, Guddy Satpathy, M.Premalatha: Modelling and estimation of photosynthetically active incident radiation based on global irradiance in Indian latitudes. International Journal of Energy and Environmental Engineering, 04, 2013;pp 1-19., [13] M.Debbarma,K. Sudhakar, P. Baredar Thermal modeling, exergy analysis, performance of BIPV and BIPVT: A review, Renewable and Sustainable Energy Reviews, 73, 2017, pp, [14] Shukla, K.N., Rangnekar, S., Sudhakar, K., Mathematical modelling of solar radiation incident on tilted surface for photovoltaic application at Bhopal, M.P., India. Int. J. Amb. Energy. 04,2015,pp [15] Rajput, D.S., Sudhakar, K., Effect of dust on the performance of solar PV panel. Int. J. Chem. Technol. Res. 5, 2013, pp editor@iaeme.com

7 S. Baranitharan, S. Dhanushkodi and K.Sudhakar [16] Shukla, K.N., Sudhakar, K., Rangnekar, S., A comparative study of exergetic performance of amorphous and polycrystalline solar PV modules. Int. J. Exergy 17, 2015, pp [17] K.Sudhakar, T.Srivastava, Energy and exergy analysis of 36W solar photovoltaic module, Int.J. Ambient Energy 35, 2014, pp [18] A.K. Shukla, K. Sudhakar, P. Baredar, Exergetic assessment of BIPV module using parametric and photonic energy methods: a review, Energy Build. 119, 2016, pp [19] Dhanushkodi, S., Wilson, V. H., & Sudhakar, K. Energy analysis of cashew nut processing agro industries: a case study.bulgarian Journal of Agricultural Science, 22, 2016,pp [20] Dhanushkodi, S., Wilson, V. H., & Sudhakar, K. Mathematical modeling of drying behavior of cashew in a solar biomass hybrid dryer. Resource-Efficient Technologies, 3, 2017,pp [21] Dhanushkodi, S., Wilson, V. H., & Sudhakar, K. Simulation of Solar biomass hybrid dryer for drying cashew kernel.advances in Applied Science Research, 6,2015,pp [22] Dhanuskodi, S., Wilson, V., & Kumarasamy, S. Design and thermal performance of the solar biomass hybrid dryer for cashew drying. Facta Universitatis, Series: Mechanical Engineering, 12, 2014,pp [23] Dhanushkodi, S., H Wilson, V., & Sudhakar, K. Life Cycle Cost of Solar Biomass Hybrid Dryer Systems for Cashew Drying of Nuts in India. Environmental and Climate Technologies, 15,2015,pp, [24] Dhanushkodi, S., Wilson, V.H, & Sudhakar, K.Energy analysis of cashew nut processing agro industries: a case study. Bulgarian Journal of Agricultural Science, 22, 2016, pp [25] Dhanushkodi, S., Wilson, V. H., & Sudhakar, K.Thermal Performance evaluation of Indirect forced cabinet solar dryer for cashew drying. American-Eurasian Journal of Agricultural and Environmental Science, 14, 2014, pp [26] Dhanushkodi, S., Wilson, V. H., & Sudhakar, K. Design and performance evaluation of biomass dryer for cashewnut processing. Advances in Applied Science Research, 6, 2015, pp [27] A. Fudholi, K. Sopian, M.H. Yazdi, M.H. Ruslan, M. Gabbasa and H.A. Kazem, Performance analysis of solar drying system for red chili, Solar Energy, 99 (2014), [28] Dinesh Acharya and Prof. Dr. Tri Ratna Bajracharya, Performance Evaluation of Rack Type Solar Dryer. International Journal of Mechanical Engineering and Technology, 7(6), 2016, pp [29] Yogesh Dhote and S.B. Thombre, A Review on Natural Convection Heat Transfer Through Inclined Parallel Plates, Volume 4, Issue 7, November - December 2013, pp , International Journal of Advanced Research in Engineering and Technology (IJARET). [30] AjeetKumar Rai, SarfarajAhamadIdrisi and Shahbaz Ahmad, An Experimental Study of Forced Convection Green House Drying, Volume 4, Issue 5, July August 2013, pp , International Journal of Advanced Research in Engineering and Technology (IJARET). [31] Tunguntla Samuel and Y.V Hanumantha Rao. CFD Analysis on Nano Fluids Turbulent Convection Heat Transfer. International Journal of Mechanical Engineering and Technology, 8(7), 2017, pp [32] M N Raja Shekar and Shaik Magbul Hussain, Effect of Viscous Dissipation On Mhd Flow Of A Free Convection Power-Law Fluid With A Pressure Gradient, Volume 4, Issue 3, April 2013, pp , International Journal of Advanced Research in Engineering and Technology (IJARET) editor@iaeme.com