ARID ZONE JOURNAL OF ENGINEERING, TECHNOLOGY & ENVIRONMENT AZOJETE September 2021. Vol. 17(3):301-316 Published by the Faculty of Engineering, University of Maiduguri, Maiduguri, Nigeria. Print ISSN: 1596-2490, Electronic ISSN: 2545-5818 www.azojete.com.ng Corresponding author’s e-mail address: aduadeyemi@gmail.com 301 ORIGINAL RESEARCH ARTICLE INFLUENCE OF ENERGY RECOVERY SYSTEM ON THE ENERGY EFFICIENCY OF A FLAT-BED DRYER IN THE DRYING OF TURMERIC E. A. Adu1*, T. Pandiarajan2, W. Farzana3 and K. A. K. Abba4 1Postharvest Engineering Research Department, Nigerian Stored Products Research Institute (NSPRI) Kano, PMB 3032, Kano State, Nigeria. 2Department of Food and Agricultural Process Engineering, Agricultural Engineering College and Research Institute, Tamil Nadu Agricultural University, Coimbatore, India. 3Department of Agricultural Processing and Food Engineering, SVCAET and RS Indira Gandhi Agricultural University, Raipur, India. 4Postharvest Engineering Research Department, Nigerian Stored Products Research Institute (NSPRI) Maiduguri, PMB 1494, Borno State, Nigeria *Corresponding author’s email address: aduadeyemi@gmail.com 1.0 Introduction Drying is an important preservation process which reduces water activity through the decrease of water content to a level safe for avoiding potential deterioration and contamination during long storage periods (Hosain et al., 2014). The process of moisture removal requires a large amount of energy considering that one of the characteristics of agricultural production is production in large quantity and for each kilogram of water vaporized 2,257 kJ of energy is ARTICLE INFORMATION ABSTRACT Drying is one of the most energy intensive unit operations in agricultural and food processing industry. Energy costs represent a major fraction of cost of operation of a mechanical dryer, therefore, the more efficient a dryer uses its energy supply, the lesser its cost of operation and the better it impacts on profitability of drying process. A flat- bed dryer of 25kg capacity was developed and fitted with air-to-air indirect mixing heat exchanger (Heat Recovery Unit, HRU) at the vent of the drying chamber. The dryer was tested to determine the impact of exhaust vent waste heat recovery on its energy efficiency and cost of operation. Turmeric, an important spice crop was dried at three temperatures of 60°C, 65°C, and 70°C under two operating conditions; (i) without HRU (C-I) and (ii) with HRU (C-II). The result show thermal efficiency, at C-I it was found to be 28%, 27% and 27% at 60°C, 65°C and 70°C respectively and for C-II it was 42%, 42%, and 40% at 60°C, 65°C, and 70°C respectively. This indicates that the overall thermal efficiency was improved by 15% for C-II at 65°C as compared to C- I at 65°C. ANOVA show there is significant different (P< 0.05) between C-II and C-I as regards thermal efficiency. The result also showed that specific energy consumption was reduced for all drying temperatures levels of C-II as compared to C-I and the result shows that testing condition C-II, at 65°C has the lowest specific energy consumption of 1.79(kWh/kg) while C-I at 60°C has the highest value; 2.37 (kWh/kg), this showed significant different (P< 0.05).Drying curves of turmeric were plotted and it was found that C-II performed better in drying turmeric since the moisture lose was faster than in C-I and the drying time was lowered by 4hrs for C-II at 65°C compared to C-I 65°C. The average Return on Investment (ROI) of HRU was calculated considering average of 260 working days or 130 batch drying operation per annum with one drying cycle per two working days and was found to be 0.61 and the payback period was 19 months. It was concluded that the developed flatbed dryer can be used to dry 25 kg of turmeric per batch in 25 hours drying time using operating condition C-II, 65°C which showed better quality in terms of energy efficiency and drying rate. © 2021 Faculty of Engineering, University of Maiduguri, Nigeria. All rights reserved. Submitted 9 Dec., 2020 Revised 19 April, 2021 Accepted 4 May, 2021 Keywords: Flatbed dryer Energy efficiency Turmeric Heat exchanger aduadeyemi@gmail.com Adu et al: Influence of energy recovery system on the energy efficiency of a flat-bed dryer in the drying of turmeric. AZOJETE, 17(3):301- 316. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng Corresponding author’s e-mail address: aduadeyemi@gmail.com 302 required. Cost of thermal energy is a major fraction of cost which is incurred in mechanical drying (Thakur and Gupta, 2006). Therefore, the higher the thermal energy efficiency of a dryer the lesser will be its cost of operation. Use of energy resources has an obvious impact on the environment. These reasons explain the need to investigate potential energy saving options that can have impact on both economic and environmental issues (Timothy et al.,2011). Dryers are one of the most important equipment in food processing industries. Many dryers have been developed and used to dry agricultural products in order to improve their storage conditions. Most of these dryers use either expensive source of energy such as electricity, hydrocarbons (coal, propane gas, and liquefied natural gas) (Berinyuy, 2000) or a combination of solar energy and other forms of energy. Energy consumption is of interest to dryer manufacturers, as it is a key index of its market value (Kudra, 2004). Low energy consumption is critical for dryer users who deal with commodity materials and inexpensive products as it affects running costs. Factors affecting the energy requirements in drying includes, the produce moisture content (MC), the type and variety of produce, the drying air relative humidity (RH) and airflow rate; all affects the drying rate, and thus the energy requirements of the drying process, (Aviara et al., 2004). Therefore, it is relevant to specify these factors when quantifying the energy use and efficiency of a drying system The largest portion of waste thermal energy in most of the convectional drying processes appears to be in the exhaust stream (Timothy et al., 2011). Recovering and reusing energy to preheat inlet air is one way to increase energy efficiency of a dryer. One of the means of heat recovery from the exhaust air stream involves the use of heat exchangers. Conventional dryers usually operate at 30-70% efficiency levels (Jangam et al., 2010). Hence, drying is an area that is desperate for energy efficient technology. 1.1 Turmeric Turmeric was considered for this drying study because of its share production volume and its economic importance to Tamilnadu State of India as an export spice. Turmeric is usually dried as a whole or in coarsely cut form to a hygienically safe moisture level (around 10%). In the tropical and subtropical regions, the plant material is commonly spread on the ground, and sometimes on raised platforms or racks and sundried for several days and this comes with inherent problem of contamination by dust particles, animal droppings, toxins from moulds, discolouration, and long drying time (Subbulakshmi and Naik, 2002). Several mechanical dryers have been developed to accelerate the drying process, to improve the hygienic conditions and to maintain constant drying temperatures within 45oC and 60oC in order to minimize the loss of volatile oils and prevent discoloration (Ute et al., 2007). Though mechanical dryers, powered by electricity or fossil fuel, help in producing quality products in large scale, they are seldom adopted by small- scale entrepreneurs and farmers of most developing countries, due to heavy installation costs involved and large operating cost because of its being energy intensive process (Senadeera et al., 2007). The objectives of this study were to determine and compare energy efficiency and performance characteristics of a dryer with and without sensible heat recovery from the exhaust stream of the drying chamber and to analyse the economics of the drying system. Arid Zone Journal of Engineering, Technology and Environment, September, 2021; Vol. 17(3):301-316. ISSN 1596-2490; e-ISSN 2545- 5818; www.azojete.com.ng Corresponding author’s e-mail address: aduadeyemi@gmail.com 303 2. Materials and Methods A flatbed dryer with a raw product capacity of 25kg was outfitted with a heat recovery unit (HRU) heat exchanger for this study. 2.1 Drying Chamber A double wall metal bin of size 1.15m 1.15m 0.52m was made using 18gauge M.S. sheet and angle irons of 25  25  3 mm size. The bin was covered with a hood 0.3m high and having a rectangular opening (0.36m  0.06m) at the top which the heat recovery unit fits into. The bin was built such that it could be dismantled easily for transportation. The drying chamber was insulated using polystyrene sheet with a thickness of 0.025m. A platform for tray arrangement was made 0.32m from the bottom and two doors each with dimension of 0.5m  0.2m were in-fitted. 2.2 Design of Heat Recovery Unit (HRU) The heat Recovery Unit (Figure 1) is an air-to-air indirect mixing corrugated plate heat exchanger type which is connected to the exhaust of the dryer on outlet flow channel and blower inlet in the inlet flow channel by a 152mm PVC pipe. It is a double wall metal box 0.52m  0.51m  0.18m (Figure 2), made of 18gauge M.S sheet and 25mm polystyrene sheet used in- between the walls have insulation. A grove of 0.3m  0.015m was made on both breadth sides of the wall into which corrugated aluminium sheet creates flow channel inside the metal box as inlet and outlet. Figure 1: Conceptual view of Heat Recovery Unit Figure 2: side x-ray view (dimensions are in m) Each flow channel has a two aluminium sheet 0.005m with a gap of 0.015m between them. The angle of corrugation is 37 degree. One of the breadth sides was covered to create an outlet in which a 6inch PVC elbow can fix into. The heat exchanger was connected to the blower so that the blower sucks air into the heater via the heat exchanger. Assumption were that no heat is lost to the environment that is, heat lost equals heat gain and the flow rate of both hot and cold stream is same; the following equations were used to calculate the quantity of heat transfer, and the heat transfer area required. Properties of air (at atmospheric pressure) Inlet temperature of cold stream, Tc1 ( oC) Outlet temperature of cold stream, Tc2 ( oC) Inlet temperature of hot stream, Th1 ( oC) Outlet temperature of hot stream, Th2( oC) Kinematic viscosity of air at exhaust vent, vh(m 2/s) Kinematic viscosity of air at ambient, vc(m 2/s) Thermal conductivity of air at exhaust, Kh (W/(moC) Thermal conductivity of air at ambient, Kc(W/(moC) Density of air at exhaust vent, h(kg/m3) Density of air at ambient, c(kg/m3) Velocity of hot stream, uh (m/s) Velocity of cold stream, uc (m/s) Specific heat capacity of air, Cpa (kgoC) Adu et al: Influence of energy recovery system on the energy efficiency of a flat-bed dryer in the drying of turmeric. AZOJETE, 17(3):301- 316. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng Corresponding author’s e-mail address: aduadeyemi@gmail.com 304 Thermal conductivity of Al, Ka (W/moC) According to Osborne Reynolds, for forced convection, there exist two types of flows: Laminar flow (Reynold number, NRe< 2000) Turbulent flow (Reynold number, NRe> 4000) NRe between 2000 and 4000 indicates transition from laminar to turbulent flow that is transient flow. The formula used to calculate the convective heat transfer coefficient is dependent on the type of flow, turbulent or laminar (Rajput, 2012). Reynolds number, (1) And kinematic viscosity, (2) Therefore, (3) where, d= Characteristic length (m) = Density of air (kg/m3) u= Velocity of stream (m/s) µ= Viscosity (mPa.s) According to Rajput, (2012), the characteristic length, d(mm) for a rectangular duct can be calculated by equation (4) (4) l = Height of the duct (mm) b = Breadth of the duct (mm) In other to determine the value of convective heat transfer coefficient, h, Nusselt number was used. Nusselt number, NNu is the ratio of heat flow rate by convection process under a unit temperature gradient to the heat flow rate by conduction process under a unit temperature gradient through a stationary thickness of din meters. NNu =hd/k (5) Nusselt number is also a function of Reynolds number and Prandtl number (NPr). For transient flow, Nusselt number is given by (Singh and Heldman, 2013). (6) where: (7) NRe = Reynolds number NPr = Prandtl number For turbulent flow over a plate the Nusselt number from Colburn analogy is given by (Rajput, 2012). (8) Prandtl number, NPr is the ratio of kinematic viscosity (v) to thermal diffusivity () Arid Zone Journal of Engineering, Technology and Environment, September, 2021; Vol. 17(3):301-316. ISSN 1596-2490; e-ISSN 2545- 5818; www.azojete.com.ng Corresponding author’s e-mail address: aduadeyemi@gmail.com 305 NPr = vCP/k (9) 1) Calculating overall heat transfer coefficient, U (10) where U = Over all heat transfer coefficient (Wm-2oC) hc =Convective heat transfer coefficient of cold stream (Wm-2oC) ka =Thermal conductivity of aluminium (W/moC) hh = Convective heat transfer coefficient of hot stream (Wm-2oC) 2) Calculation heat transfer area, quantity of heat transfer, Q is given as (11) Tlm(CF) = Log mean temperature difference for counter-flow heat exchanger (12) TA = difference between the hot inlet and cold outlet stream temperature TB = difference between the hot outlet and cold inlet stream temperature Tlm for cross flow is calculated by incorporating correction factor (F) to the expression of log mean temperature difference of counter flow heat exchanger. (13) The correction factor was obtained from the calculation of two ratios P and R associated with the inlet and outlet temperatures of the two fluids using the standard graph (Holman, 2002). If no heat is lost in the heat exchanger, then quantity of heat transfer (14) Therefore, using equation (11), heat transfer area, A was calculated. 3) Calculating the required insulation thickness The casing of the exchanger was fabricated using composite wall with three layers made up of, mild steel - glass wool - mild steel. Using mild steel of 0.0012m thickness (xm), and T1 and T4 were taken as Th1 and Tc1 respectively. Insulation thickness, (xi) was calculated by Fourier’s law. (15) where: Q = Quantity of heat transferred (W/m2) xm= Thickness of mild steel (m) xi = Thickness of insulation material (m) T1= Inlet temperature of hot stream (oC) T4 =Inlet temperature of cold stream(oC) km= Thermal conductivity of mild steel(W/moC) kg =Thermal conductivity of insulation(W/moC) 2.3 Dryer layout The dryer is an electric powered flatbed dryer with configuration including the dryer chamber, heating chamber, electric blower, heat recovery unit (HRU) and control panel (Figure 3). A centrifugal type air blower powered by a three phase 1hp electric motor was used. A supply shunt was made at the blower’s suck-in opening to vary the inlet air flow rate. The blower has Adu et al: Influence of energy recovery system on the energy efficiency of a flat-bed dryer in the drying of turmeric. AZOJETE, 17(3):301- 316. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng Corresponding author’s e-mail address: aduadeyemi@gmail.com 306 the capacity to move air flow rate up to 2.5m3/min. Electric heaters was required to heat the air moved by the blower before the heated is moved to the plenum chamber. Four coils, 1.5kW each were mounted concentrically inside a M.S. sheet (18gauge) cylinder of 0.285m diameter and 1.1m length to for the heating chamber. The cylinder was insulated by using asbestos rope and Plaster of Paris to reduce the heat loss due to radiation. The control panel consist of switches for both the blower and the heaters and a thermostat to regulate temperature. The dryer was fitted with HRU as shown in Figure 4 Figure 3: Conceptual front view of Flat-bed dryer with HRU Figure 4:Flat-bed Dryer fitted with HRU 2.4 Raw Material Procurement and Preparation The testing of the dryer was conducted using the PTS-10 variety of turmeric (Curcuma longa) as this variety is grown in large quantity in Erode and other areas of Tamilnadu. Turmeric were procured directly from famer at Erode and washed thoroughly in a turmeric washer using tap water at normal temperature to remove the adhering extraneous matter then it was boiled in a Arid Zone Journal of Engineering, Technology and Environment, September, 2021; Vol. 17(3):301-316. ISSN 1596-2490; e-ISSN 2545- 5818; www.azojete.com.ng Corresponding author’s e-mail address: aduadeyemi@gmail.com 307 turmeric steam boiler for 5min to achieve softening of the produce and afterwards it was dried in the developed dryer. 2.5 Condition of Operating the dryer In the process for determining the efficiency of the dryer, different operating conditions were used. Table 1 shows the operation temperatures and inlet air velocity at which efficiency of the dryer was determined. Table 1: Description of operating conditions for drying runs Air velocity (m/s) Temp (°C) Description Parameters determined C-I (Without HRU) 1.5 60, 65, 70 Exhaust air vented into the atmosphere - Heat utilization factor of turmeric - Overall thermal efficiency - Specific energy consumption - Drying characteristics of turmeric - Economy analysis of the dryer C-II (With HRU) 1.5 60, 65, 70 Energy in exhaust air recovered using Heat recovery unit. 2.6 Performance Evaluation Experiments were conducted to evaluate the performance of the drier. First idle run test was conducted on the dryer with heat recovery unit (pre-heating), the heater was switch on with the thermostat set using optimum drying temperature of 650C (Gursewak et al., 2010) and the blower was operated at the rated speed but the inlet chute of the blower was adjusted to create four selected air velocities of 1, 1.5, 2, 2.5m/s. Data generated from the preliminary studies were used to determine the air velocity having the best heat recovery efficiency of the HRU. The parameters measured and recorded includes the come up time, air flow rate and temperature into and out of the heat exchanger (cold and hot stream), and the external temperature of the drying chamber. Drying runs were performed on the dryer by drying of steamed-boiled turmeric rhizomes according to the conditions of drying operations as presented in Table 1. Temperature and relative humidity of the drying chamber was measure using data logger (Equinox® EQ-171). The performance of the dryer was evaluated in terms of drying efficiency (d), heat utilization factor (HUF), Temperature transfer efficiency (TTE) and overall thermal efficiency (th). These were estimated by the method adopted by Sahay and Singh (2001) as discussed below. 1) Drying efficiency, Drying efficiency is defined as the ratio of the energy utilized for heating the sample for moisture evaporation to the total consumed energy (Vieira et al., 2007). Sensible heat of drying air was considered as being the effective heat for drying; therefore, drying efficiency is mathematically defined as follows (16) Td = dry bulb temperature of the heated air, oC Te = dry bulb temp of the exhaust air,oC Tdw = wet bulb temperature of the heated air, oC Adu et al: Influence of energy recovery system on the energy efficiency of a flat-bed dryer in the drying of turmeric. AZOJETE, 17(3):301- 316. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng Corresponding author’s e-mail address: aduadeyemi@gmail.com 308 The dry bulb temperature of the heated and exhaust air for each trial was measured using mercury-in-glass thermometer of 0-1500C range and Equinox data logger. The wet bulb temperature of the exhaust air was determined from the psychrometric chart using dry bulb temperature and relative humidity. 2) Heat utilization factor, HUF Heat utilization factor is defined as the ratio of heat utilized by the turmeric to heat supplied by the hot air (Sahay and Singh 2001). = (17) 3) Overall thermal efficiency Overall thermal efficiency (th) is the ratio of energy required to evaporate moisture and the energy supplied to the dryer and it can be calculated according to equation (18), (Toneli, 2013). (18) Mw=Water evaporation flow (kgs-1), ΔH =vaporization enthalpy (kJkg-1), M = Air mass flow (kgs-1), Cpa= specific heat of air (kJkg-1°C-1), Td and Ta are the absolute temperature of the drying and ambient air respectively. 4) Specific energy consumption According to Ashok, (2014) another method to estimate the energy efficiency of a drying system is to calculate its specific energy consumption. It is the amount of energy used in removing one kg of moisture from a food material in kWh/kg 5) Drying rate The duration of the drying process is the most important parameter to be considered in evaluating a dryer. It is estimated from the time when the dryer is loaded with fresh product until when the product dries to the required moisture level, usually given as hours or days. Drying rate was calculated using equation (19) (19) k = Drying rate, kg/h WL= amount of moisture evaporated, kg t = time, h 2.7 Economic Analysis Drying operation as a commercial enterprise requires cost analysis of the process to prove its economic viability (Krokida et al., 2004). The Cost analysis that was conducted to determine if the expenses of installing and operating a waste heat recovery system is justified is the Return on Investment (ROI) analysis (Gene, 2002). The main aim of understanding ROI of a particular process is to identify if the process generates profit or loss. Arid Zone Journal of Engineering, Technology and Environment, September, 2021; Vol. 17(3):301-316. ISSN 1596-2490; e-ISSN 2545- 5818; www.azojete.com.ng Corresponding author’s e-mail address: aduadeyemi@gmail.com 309 Return on investment analysis was carried out according to (Raghavendra, 2010) and is given by. (20) Where Ceq = Additional equipment cost S = Annual Savings and is given by, (21) where: TAC = Total annual cost Cea = Annual costs from electrical energy = Ceti Cet = Savings from the energy reduced through shorter drying time. (22) ts = Time saved due to shorter drying times (hr) Ce = Cost of kWh of electricity consumed per hour ti= Annual operation time. (hr) Total annual cost when the system is operated in C-I or C-II is given by (Raghavendra, 2010), (23) where: e = depreciation and is given by (Raghavendra, 2010), (24) For C-II, Ceq= Additional equipment cost = Cost of HRU + Cost of air recirculation ducts Cop = Operation Cost (Electricity) (Rupee/kWh) ir = Interest rate L = Life span of equipment. The cost analysis was calculated based on the drying time of the product and the total energy utilized in the drying process at different conditions. Annual return on investment (ROI) was calculated considering average of 10 working hours per day and 260 working days or 130 batch drying operation per annum with one drying cycle per two working days. The kWh cost of electricity was taken as indicated by Tamil Nādu Electricity Regulation Commission (TNERC). A cost of 5.75 rupees per unit electricity was selected for this calculation. Assuming the number of batches of drying operation in a year is 130, the cost of operation is shown on Table 2 and the cost of additional equipment in Indian rupee is shown in Table 3 Table 2: Cost of Operation (Electricity) Condition 65oC (C-I) 65oC(C-II) Drying time/batch (h) 24 20 Batch per year 130 130 Hrs per year 3120 2600 Energy consumed per batch (kWh) 35.2 28 Energy consumer per year (kWh) 4576 3640 Electricity cost per year (Rs) 26312 20930 Adu et al: Influence of energy recovery system on the energy efficiency of a flat-bed dryer in the drying of turmeric. AZOJETE, 17(3):301- 316. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng Corresponding author’s e-mail address: aduadeyemi@gmail.com 310 Table 3: Cost of Addition Equipment (HRU) S/N Material Quantity Price/unit (Rs) Cost (Rs) 1 Mild steel plate 2.1m2 560/m2 1176 2 Aluminium sheet 1m2 460/m2 460 3 PVC pipe 2m 315/m2 630 4 PVC elbow 2 180 360 5 Workmanship - 5000 Total 7626 1) Return on Investment ir = Interest Rate = 7% L = Lifetime of equipment = 20 years Therefore, e = [0.07(1+0.07)20] / [(1+0.07)20 -1] = 0.0944 For Condition (C-II), Ceq = Equipment cost = Cost of Heat Recovery Unit + Cost of Recycle ducts =Rs 7,626 Cost of operation, Cop = Cost of electricity used for the process Total Annual Cost for C-II, 65OC = (0.0944  7626) + 20930 = 21650 rupees Annual savings S, due to energy reduced through shorter drying time and more effective heat utilization = 26312 - 21650 = 4662 rupees Return over investment = S/Ceq = 4662/7626 ROI = 0.6114 This procedure was repeated for comparing C-I and C-II for drying temperature of 60 and 70oC and ROI calculated were 0.6207 and 0.5965. Therefore, average value of ROI is 0.61. 3. Results and Discussion Drying runs at operating conditions of C-I and C-II were conducted and observations are stated and discussed below. 3.1 Effect of HRU on drying efficiency HRU was observed to increase drying efficiency of the dryer at all temperatures. The mean drying efficiency of the dryer was increased from 0.263 to 0.413 at 60oC, 0.240 to 0.423 at 65oC and 0.196 to 0.363 at 70oC as shown in Table 4 and expressed in Figure 5. It was also observed that there was decrease in drying efficiency at 70°C. As discussed by (Sahay and Singh, 2001), this may be due to the fact that there is no increase in moisture diffusion within the produce to correspond to the increase in heat energy available. The result showed significant different (P<0.05) between C-I and C-II and the test data and ANOVA for both C-I and C-II is given in Table 4 and Table 5 respectively. Arid Zone Journal of Engineering, Technology and Environment, September, 2021; Vol. 17(3):301-316. ISSN 1596-2490; e-ISSN 2545- 5818; www.azojete.com.ng Corresponding author’s e-mail address: aduadeyemi@gmail.com 311 Figure 5: Drying efficiency at different operating conditions Table 4: Mean Tables of Drying Efficiency T1 T2 T3 C-I 0.2633 0.2400 0.1967 C-II 0.4133 0.4233 0.3633 Table 5: ANOVA for Effect on Operating Conditions on Drying Efficiency Source df SS MS F PROB TOT 17 0.14640 0.0086 12.4009 Trt 5 0.1380 0.0276 39.7632 0.452 NS Err 12 0.00833 0.0006 1.0000 C 1 0.12500 0.1250 180.000 0.000 ** T 2 0.01223 0.0061 8.8080 0.102 NS CT 2 0.00083 0.0004 0.6000 0.625 NS Err 12 0.00833 0.0006 1.0000 3.2 Effect of HRU on Heat utilization factor HRU was observed to significantly increased heat utilization factor of the dryer at all temperatures as shown in table 6. The HUF of the dryer at all temperatures is shown in Figure 6. Sahay and Singh, (2001) stated that the ability to increase the heat utilisation factor of a drying process implies that there will be increase in the percentage of the heat supplied utilized, thus, an improvement in the thermal efficiency of the dryer. The result showed significant different (P<0.05)between C-I and C-II and the ANOVA for both C-I and C-II are show in Table 7 D ry in g Ef fi ci en cy Temperature, 0C Adu et al: Influence of energy recovery system on the energy efficiency of a flat-bed dryer in the drying of turmeric. AZOJETE, 17(3):301- 316. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng Corresponding author’s e-mail address: aduadeyemi@gmail.com 312 Figure 6: Heat utilization factor at different operating conditions Table 6: Mean Tables of Heat Utilization Factor (HUF) T1 T2 T3 C-I 0.3933 0.3500 0.2600 C-II 0.6100 0.6300 0.5633 Table 7: ANOVA of Effect of Operating Conditions on Heat Utilization Factor (HUF) Source df SS MS F PROB TOT 17 0.372511 0.021912 14.8280 Trt 5 0.354778 0.070956 48.0150 0.439 NS Err 12 0.017733 0.001478 1.0000 C 1 0.320000 0.320000 216.544 0.000 ** T 2 0.028744 0.014372 9.7256 0.093 NS CT 2 0.006033 0.003017 2.0414 0.329 NS Err 12 0.017733 0.001478 1.0000 3.3 Effect of operating conditions on overall thermal efficiency HRU was observed to increased thermal efficiency of the dryer at all temperatures (table 8) and by 15% at operating temperature of 65oC. Operating temperature had no significant effect on thermal efficiency of the dryer. The overall thermal efficiency of the dryer at all temperatures was shown in Figure 7. In an experiment conducted by (Timothy, 2011), Heat recovery ventilator was attached to a low-cost meat dehydrator and an increase in efficiency of 20% was achieved. The ANOVA result given in (Table 9) showed that there significant different (P<0.05) between treatments C- I and C-II. Since the HRU can be attached to any dyer with little or no modification, this means that thermal efficiency of commercially available dryers can be increased by at least 15% with investing in HRU. H ea t u ti liz at io n f ac to r Temperature, 0C Arid Zone Journal of Engineering, Technology and Environment, September, 2021; Vol. 17(3):301-316. ISSN 1596-2490; e-ISSN 2545- 5818; www.azojete.com.ng Corresponding author’s e-mail address: aduadeyemi@gmail.com 313 Figure 7: Overall thermal efficiencies at different operating conditions Table 8: Mean Tables of Thermal Efficiency T1 T2 T3 C-I 28.0000 27.0000 26.9967 C-II 42.0000 42.0033 40.0000 Table 9: ANOVA of Effect of Operating Conditions on Thermal Efficiency Source df SS MS F PROB TOT 17 986.7892 58.04642 7.3718 Trt 5 892.3000 178.4600 22.6642 0.474 NS Err 12 94.48913 7.874094 1.0000 C 1 882.2800 882.2800 112.0484 0.000 ** T 2 7.020033 3.510017 0.4458 0.692 NS CT 2 3.000011 1.500006 0.1905 0.840 NS Err 12 94.48913 7.874094 1.0000 3.4 Effect of operating conditions on specific energy consumption The specific energy consumption of the dryer at all temperatures decreased with HRU. The specific energy consumption of the dryer at all temperatures was shown in Figure 8. The test data for both C-I and C-II is given in Table 10. Table 10: Specific Energy Consumption at Different Operating Conditions Operating condition Energy used (kWh) Mass of water removed (kg) Specific energy consumption (kWh/kg|) C-I, T1 Without HRU and at 60oC 35.2 14.8 2.38 C-I, T2 Without HRU and at 65oC 35.3 15.4 2.30 C-I, T3 Without HRU and at 70oC 32.3 14.8 2.18 C-II, T1 With HRU and at 60oC 29.7 15.3 1.94 C-II, T2 With HRU and at 65oC 27.0 15.1 1.79 C-II, T3 With HRU and at 70oC 27.0 14.9 1.80 Th e rm al E ff ic ie n cy Temperature, 0C Adu et al: Influence of energy recovery system on the energy efficiency of a flat-bed dryer in the drying of turmeric. AZOJETE, 17(3):301- 316. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng Corresponding author’s e-mail address: aduadeyemi@gmail.com 314 Figure 8: Specific energy consumption at different operating conditions 3.5 Effect of Operating Condition on Drying Rate The drying rate of turmeric inside the dryer at the different operating condition C-I and C-II is shown in the Figure 9 and 10 respectively. Temperature showed effect on drying rate, but no trend was observed with ‘with’ or ‘with-out’ HRU on rate of drying as shown. Drying was observed to occur mainly at falling rate period and also it was observed that samples in C-II reached safe moisture range before samples in C-I at all temperature levels of T1, T2 and T3 that is 60oC, 65oC and 70oC respectively therefore drying time for samples in C-II were shorter. Figure 9: Drying rate at C-I operating condition Figure 10: Drying rate at C-II operating condition 3.6 Cost Analysis 1) Return of Investment The calculated Return-On-Investment for C-II, at drying temperature of 65oCis 0.6114. The procedure used to calculate ROI for C-II, 65oC was repeated to calculate C-II for drying temperature of 60oC and 70oC and ROI calculated were 0.6207 and 0.5965 respectively. Therefore average value of ROI is 0.61. Sp e ci fi c e n e rg y co n su m p ti o n ( kW h /k g) Arid Zone Journal of Engineering, Technology and Environment, September, 2021; Vol. 17(3):301-316. ISSN 1596-2490; e-ISSN 2545- 5818; www.azojete.com.ng Corresponding author’s e-mail address: aduadeyemi@gmail.com 315 2) Payback Period The calculated payback period is approximately 19months, therefore it can be said that investing in the Heat recovery unit with a lifespan of 30 to 50 years is a profitable investment.4. Conclusion A flatbed dryer with a heat reclamation system was developed. Evaluation of the dryer was carried out with ‘No-load’ test and drying runs of turmeric at conditions C-I and C-II, indicating without and with heat-recovery-unit respectively at temperatures of 60oC, 65oC and 70oC.Thermal Efficiency of the dryer was determined, at C-I it was found to be 28, 27 and 27% at 60oC, 65oC and 70oC respectively and at C-II it was 42, 42, and 40% for 60oC, 65oC, and 70oC respectively. Effectiveness of using a HRU to recover the waste heat from the exhaust stream of the dryer was studied and found that by using C-II the overall thermal efficiency was increased at all the temperatures. 15% increase in thermal efficiency was achieved. Specific energy consumption was reduced for all levels of C-II as compared to C-I and the result shows that testing condition C-II, 65oC has the lowest value of specific energy consumption of 1.79 while C-I, 60oC has the highest value; 2.37. 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