SIMULATION of SOLAR DRYER UTILIZING GREEN HOUSE EFFECT for COCOA BEAN DRYING M.Manoj 1, A
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M. Manoj et al., International Journal of Advanced Engineering Technology E-ISSN 0976-3945 Research Paper SIMULATION OF SOLAR DRYER UTILIZING GREEN HOUSE EFFECT FOR COCOA BEAN DRYING M.Manoj 1, A. Manivannan 2 Address for Correspondence 1Department of Energy Engineering, Regional Centre, Anna University Tirunelveli Region, Tirunelveli-627 007. 2 Assistant Professor, Department of Energy Engineering, Regional Centre, Anna University Tirunelveli Region, Tirunelveli- 627 007. ABSTRACT Drying is an excellent way to preserve food and solar food dryers are appropriate food preservation technology for sustainable development. The aim of the work is to develop a MATLAB-based modeling and simulation to predict the air flow properties, equilibrium moisture content of the solar dryer technology for food crop drying especially cocoa and other cash crops. In the model practical and technological ways by which the Crank – Nicholson equation is applied to heat equations using finite difference method to develop a solar dryer utilizing Green House Effect (GHE) for drying cocoa beans. The mathematical model for the general case of the 3D (three-dimensional) conduction equation for green house dryer has been derived and simulated by Matlab program.The results show that the dryer performed at it optimal range and dried beans within 7 days to a moisture content of 7% to the weight of the bean. A mathematical model was developed to predict the performance of the green house effect type solar dryer and the 3D modeling was drawn using ProE. KEYWORDS : Cocoa, Green house effect, MATLAB, Simulation, Solar dryer. I. INTRODUCTION processing, statistics and data analysis, control design Cocoa beans are the seeds of Theobroma cacao and mathematical modeling. Technical computing (Sterculiaceae family), a tropical tree which is grown with MATLAB allowed us to accelerate our research mostly in the wet tropical forest climate countries work, costs, reduce development time and deliver such as Ivory Coast, Nigeria, Brazil and Malaysia. better cocoa products[21]. The three varieties are Trinitarios Forasteros, and II. DESCRIPTION OF A GREEN HOUSE Criollos; but Criollos has become negligible in world EFFECT SOLAR DRYER trade. Cocoa is used in the production of milk The initial cost of a solar drying system can be chocolate, chocolate bars, cocoa powder, cosmetics further reduced by using a Green House Effect(GHE) and pharmaceutical products. The cocoa shells are mechanism since the function of solar collector unit used for stock feed and manure. It is also a source of can be substituted by transparent structure which also theobromine, vitamin D and shell fat. The pod simultaneously function as the drying chamber . The contains rich in potash and is used for soap entire wall is made of transparent materials such as production. Then, after harvesting of ripe cocoa pods, fiberglass, UV stabilized plastic or polycarbonate fresh cocoa beans are fermented for 5-7 days and sheets. The transparent sheets are fixed on steel frame dried immediately after fermentation to safe moisture support or pillars with bolts and nuts and rubber level of 7.5% (wet basis). At these stages the cocoa packing to prevent humid air leaking into the beans undergo various chemical and biochemical chamber other than those introduced from the changes that form the necessary flavour precursors opening of the inlet. Blackened steel plates is needed during processing. Drying is usually carried provided to enhanced solar radiation absorption out using natural sun drying. The solar powered within the structure and are located either on the cocoa bean dryer has advantage over the traditional upper section of the structure or at both sides near the method of drying because it brings more hygienic wall. Based on the type of commodity to be dried, way of drying cocoa beans in lesser time, with less cabinets or drying bin the racks can be placed at the foreign materials. center section of the transparent structure so that maximum access to drying air can be obtained. Inlet and exhaust fan are placed at proper position within the structure to ensure even distribution of the drying air within the chamber. can be installed. Whenever necessary, auxiliary heating system using kerosene stove with heat exchanger unit can also be installed. Fig 1: Cocoa beans. In this work, the technological ways by which the green house type of solar dryer is used in drying cocoa beans is modeled and simulated using MATLAB programming. The software for modeling and simulation was MATLAB R2010a. With a Pentium IV that had processor speed of 2.0 GHz, Fig 2: The greenhouse solar dryer. RAM of 2.O GB and hard disk drive of 520 GB. III. GREEN HOUSE EFFECT SOLAR DRYER MATLAB was selected as the modeling and A solar dryer with greenhouse as a collector is shown simulation software because it produces immediate in Fig.3. It consists of a greenhouse of length 50 m, access to good performance of numerical computing. as a collector linked to a wooden stack chamber. The The functionality of MATLAB is extended with solar dryer has trays stacked inside a wooden shed. interactive graphical capability for creating images, Trays of size 2 m x 2 m are fixed in the wooden surfaces, plots and volumetric representation. chamber to spread cocoa beans. The fan and plastic Furthermore, toolbox algorithms enhance MATLAB film together forms an efficient solar collector system functionality in domains such as signal and image that shows no need of separate collector unit, which IJAET/Vol. IV/ Issue II/April-June, 2013/24-27 M. Manoj et al., International Journal of Advanced Engineering Technology E-ISSN 0976-3945 can increase the air temperature inside the where h 1,h 2,h 3 and τ are the steps of discretization greenhouse by about 250C. Heated air inside the with respect to x,y,z,t. The equation 3 has the greenhouse passes through the trays stacked in the numerical scheme which is the Crank-Nicholson wooden chamber. With respect to obtain a regular air method of the 3-D conduction equation is an implicit flow through the trays, a fan is placed on the rear side numerical scheme because the values at the previous of the stack chamber. For practical purpose of time step which are not readily available. This needs loading, the size of the dryer shed is fixed at 2 m3. In us to solve a set of simultaneous linear equations at order to avoid saturation of the outlet air and to keep every time step. The Crank-Nicholson method is the water gradient of the cocoa beans small, the superior to finite difference scheme, because of length of the shed is maintained at 2 m. It is observed accuracy, stability and convergence [19]. The that recycling of air is not financially viable in this simulated graph of equation 3 is shown in figure 4 type of dryer. and 5 explains the heat conduction mechanism during drying of the beans. V. MATHEMATICAL MODELING A mathematical model was developed for foretelling the performance of this type of green house effect solar dryer. 1. Mass of water to be lost from the product. The mass of water to be lost from the product is, ʚͫ$ Ǝ ͫ!ʛ ͡2 Ɣ ͡ Ɛ ʚ100 Ǝ ͫ!ʛ where Fig 3: 2D of Green House Solar Dryer. mw = Mass of water loss IV. EQUATIONS TO SOLVE PDE IN PDE mc = Mass of product to be dried TOOL BOX OF MATLAB wi = Initial moisture content The system was assumed to be in a steady flow 0 process and thus the mass flow rate of dry air remains constant during the entire process. The numerical solution of Partial Differential Equations is a topic of wf = Final moisture content great importance in science and engineering because 2. The mass flow rate of air. of many applications. Finite Volumes, Finite The mass flow rate of air is, $- !'*2 -/ Differences, Finite Elements, Boundary Elements are ͡ Ɣ among the most valuable numerical tools that we can .+ $!$ 1*'0( where Air flow rate=Air flow x Drying area use in order to approximate the theoretical solution Specific volume is obtained from psychometric chart. with a numerical one. Suppose that we have to solve 3. The amount of moisture removed per hour. the 1-D (one-dimensional) conduction equation. The amount of moisture removed per hour is, iv! &i! (1) i3v Ɣ i/ ͇͌ ʚ͇͙ͣͧͨͩͦ͝ ͙͕͌ͣͪ͡͠ ʛ Ɣ ͡ Ɛ ʚ͂͌̓ Ǝ ̻͂͌ʛ We consider the grid of the points ʚ͝ ͝ ʛ Ǩ ͔ͬ ͦ as a where ͥ, ͦ 2 discretization of the continuous space of x,t of R HRI = Humidity Ratio Increase where the function f(i 1,i 2) which approximates the HRA= Humidity Ratio of Air f(x,t). These finite difference scheme suffers from 4. The approximate time for the cocoa beans to be convergence problems, errors and instability, dried using the green house solar dryer. therefore another better method the so called Crank- The drying time is calculated using the formula ͡2 Nicholson method is applied. The Crank-Nicholson ̾͌ ʚ̾ͦͭ͛͢͝ ͎͙͝͡ ʛ Ɣ method for the general case of the 3-D (three- ͇͌ Where mw=Mass of water loss dimensional) conduction equation is applied to the MR=Amount of moisture removed parabolic equation: 5. Pickup efficiency. v v v i ! i ! i ! &i! (2) The pickup efficiency is given by i3v ƍ i4v ƍ i5v Ɣ i/ ℎ* Ǝ ℎ$ A point that does not belong to the grid of the points Ɣ ͥ ℎ Ǝ ℎ$ (i 1,i 2,i 3,i 4) is considered. It is the at where ʚͥ͝, ͦ͝,ͧ͝, ͨ͝ ƍ ͦʛ this point we approximate to numerical scheme ho =absolute humidity of air leaving the drying chamber below: hi = absolute humidity of air entering the drying chamber h = adiabatic saturation humidity of the air entering the ͥ !ʚ$ ͯͥ,$ ,$ ,$ ʛͮ!Ƴ$ ͮͥ,$ $ ,$ Ʒͯͦ!ʚ$ ,$ ,$ ,$ ʛ a u v w x u v, w x u v w x dryer.