Experimentation of solar dryer with desiccant material for agricultural products

Transcription

1 Volume :2, Issue :5, 1-7 May e-issn: p-issn: Impact Factor: Khultesh S. Patil B.E.Student, Department of Mechanical Engineering, Dr.D.Y.Patil College of Engineering,Ambi Pune, Maharashtra, India Sudhir D. Mahajan B.E.Student, Department of Mechanical Engineering, Dr.D.Y.Patil College of Engineering,Ambi Pune, Maharashtra, India S.R.Burkul Assistant Professor At Department of Mechanical Engineering, Dr.D.Y.Patil College of Engineering,Ambi Pune, Maharashtra, India Correspondence: Khultesh S. Patil B.E.Student, Department of Mechanical Engineering, Dr.D.Y.Patil College of Engineering,Ambi Pune, Maharashtra, India Experimentation of solar dryer with desiccant material for agricultural products Khultesh S. Patil, Sudhir D. Mahajan, S.R.Burkul Abstract The food preservation is very important in all over. Most of the food products are obtained from agricultural so it is essential that preservation of food for long time therefore the moisture removal from agricultural products is also important. Solar Drying process is traditional process which is used for removing the moisture from agricultural grains. Drying is possible only during sunshine hours. So that time required for drying is longer. In this paper the objective is that, it can also dry the agricultural products in off sunshine hours. In off sunshine hours drying is operated by solid desiccant material which is also the adsorbent. The moisture removal rate of solid desiccant is increase by 25% and time required for drying is minimized. In short drying efficiency of increased approximately as compare to conventional process. Keywords: solar dryer, desiccant drying, thermal efficiency, forced convection 1. Introduction Let the world focus its constant attention at the centre of the planetary System where the Sun, the supreme power of the universe resides. --RigVeda (Ancient Holy Scripture) The surface of the earth receives from the sun about kw of solar energy which is approximately five orders of magnitude greater than currently being consumed from all resources. It is evident that sun will last for years. Even though the sunlight receives the energy equivalent of about 1 H.P or 1 kw. However this last amount of solar energy reaching earth is not easily convertible and certainly is not 'free'. In general, the energy produced and radiated by the sun, more specifically the term refers to the sun's energy that reaches the earth. Solar energy, received in the form of radiation, can be converted directly or indirectly into other forms of energy, such as heat and electricity, which can be utilized by man. Since the sun is expected to radiate at an essentially constant rate for a few billion years, it may be regarded as an inexhaustible source of useful energy. Experiments are underway to use this energy for power production, house heating, air conditioning, cooking and high temperature melting of metals. Energy is radiated by the sun as electromagnetic waves of which 99 per cent have wave lengths in the range of 0.2 to 4.0 micrometers. Solar energy reaching the top of the earth's atmosphere consists of about 8 per cent ultraviolet radiation (short wave length, less than 0.39 micrometer), 46 per cent visible lights (0.39 to 0.78 micrometer), [5] and 46 per cent infracted radiation (long wave length more than 0.78 micrometer).solar energy has some good advantages in comparison to the other sources of power. Solar radiation does not contaminate environment or endanger ecological balance. It avoids major problems like exploration, extraction and transportation. India receives solar energy equivalent to 5 x kwh/year potential to meet basic energy needs of teeming millions who live in rural India. The daily average incident solar energy varies from to KJ/m2 depending upon location and there are sunny days in most of the country [6]. If the country can barely tap one per cent of incident solar radiations, it can generate many times more usable energy than its demand. Prospects for harnessing solar energy in India are very bright and unlimited. India lies within the latitude of 7 N and 37 N with annual average intensity of solar radiations as 1.67 to 2.93 KJ/cm/day. 2. Problem Statement Manufacturing of a solar air dryer with regenerative desiccant material (so that we can use it during off sunshine hours), with selection of circulation of air flow with respect to absorber plate, geometry and materials for absorber plates, for domestic and industrial applications. Important criteria for selection of those parameters are: ~ 1 ~

2 Selection of circulation of air flow for solar drying Selection characteristic of absorber plate for solar drying Selection characteristic of absorber plate for solar drying Selection of dimensions of flow channel for solar drying Selection and analysis of surface of absorber plate for solar drying Selection and analysis of drying way and direction of circulation for solar drying Selection and analysis of material for solar drying 3. Objective In casting industry, core banking is one of the important operations. This operation perform with the help of many equipment, like electric oven, oil fired oven. Core baking application is selected for experimentation of solar air drying. The main motto behind it, to calculate moisture removal rate. Cores are pieces that are placed into casting moulds to form internal cavities of the casting, or to form extra section of the mould for casting that have external projections or negative draft, which, if included in the pattern, would prevent the pattern from being removed from the mould. Or simply Cores are sand shapes which form the casting contours that cannot be molded with a pattern. Multiple cores may be used in complex castings. Cores can be made from metal (in shapes that are easily removed from the casting and used in permanent mould processes) or chemically bonded sand (complex shapes, and used in all mould types) Metals cores need to be configured such that they are parallel to the mould parting line, or can be removed before the casting is removed from the mould and shaped so that is readily freed from the casting. Metal cores are typically made from cast iron or steel. Sand cores are made from materials similar to those used for chemically bonded sand moulds. These cores are formed in core boxes similar to pattern boxes used to make moulds. Core may be also made from plaster or ceramic material. As sand cores most frequently used, sand cores was chosen for baking of as an application. Cores provide the casting process its ability to make the most intricate of shapes, eliminate much machining, and provide shapes which would be impossible to machine. Following are the purpose of cores. Complete molds may be assembled of core-sand forms (intricate forms) May be used to form a part of green-sand mold. Pattern contours with back draft or projections which cannot be molded can be formed by placing a core in the mold after the pattern is drawn To strengthen or improve a mold surface. May be used as a part of gating. Ram-up cores are used for several purposes. Core sand is a mixture of sand grains and organic binders. The binders provide green strength, baked strength and collapsibility. Core making is done manually or by using machines. Cores with no flat surfaces must be supported on a core drier, until they are baked. Core baking takes place from 80 C to 250 C depending upon the type of material, application and shape. Moisture is driven off first. Then, the core oil or other binder changes chemically and molecularly from a liquid to a solid by oxygen absorption as the temperature rises. Backing cycle is for 2-6 hours. When baked, a core-oil bonded core assumes a nut-brown color, darkness indicating over baking and lightness under baking. Many types of core-baking equipment are available. Core ovens may be of batch type, continuous type, horizontal type or vertical type, dielectric type, radiant type. As this is a totally new application of solar air dryer, for deciding design parameters there is need to take review of work, done by researchers till now. 4. Heat for Agriculture Field In agricultural sector, the age old method of drying food grains and vegetables can be replaced by solar dryers to produce food quality food grains and vegetables. Almost 15 % food grains and 25 to 30 % of vegetables and fruits are lost because of inadequate storage facilities.[7] India is lacking in post harvesting. Since cold storage facilities in our country are not available at the farmers premises, the agricultural products can be dried and then preserved for longer periods. Once the product is dried up to a safe level of moisture content, it can be stored for longer time. Several food and chemical products need drying. Although, the conventional drying s are available to dry these products, solar drying may dry these products with substantial saving in energy and time. 4.1 Market Potential for Solar Heat for Industrial Processes The low temperature level complies with the temperature levels which can easily be reached with solar thermal collectors already on the market. However, for many industrial applications higher temperatures are needed. The solar thermal collectors must be specifically made to provide heat at temperature above c. [3] the most significant current SHIP application areas are in the food and beverage industries, the textile and chemical industries and for simple cleaning processes in these sectors: 30 C to 90 C. Allowing the use of commercially available flat plat or vacuum tube collectors which are very efficient in this temperature range. Solar heat is used not only to provide process heat but also to heat industrial buildings. Demand at different temperature levels for various industrial countries. These studies give a representative overview of the typical process heat demand up to 250 c. In spite of particular differences among these countries, some general conclusions were drawn out of the analysis: The studies confirm a general tendency: About 50 % of the industrial heat demand is located at temperature up to 250 c. The biggest heat demand is located in the paper and food industries. A considerable heat demand is also found in the textile and chemical industries. Table 4.1: Industrial sectors and processes with the greatest potential for solar thermal uses Industrial Sector Process Temperature level[ C] Drying Washing Food beverages Pasteurizing Boiling Sterilizing ~ 2 ~

3 Textile industry Chemical Industry All sectors Heat treatment Washing Bleaching Dyeing Boiling Distilling Various Chemical processes Pre-heating of boiler feed water Drying of sleeves Table 4.1 also shows that, alongside the low temperature processes up to 80 C there is also significant potential for processes in the medium temperature range up to around 250 C. Industrial process heat is one of the least developed solar thermal applications so far. The potential is huge, but the variety of industrial application makes it difficult to standardize solar thermal s. Without suitable support measures solar thermal will only penetrate the industrial heat market slowly. Focusing on the demand side, industry is huge consumer of energy. 5. Details of Test Rig of Solar Air Dryer with desiccant Solar dryer test rig is solely in- house manufactured. Schematic diagram for test rig of active mode solar air dryer with regenerative desiccant material is as shown in (Fig. 5.1). Solar air dryer setup consists of mainly solar collector, drying cabinet and piping and fittings. Fig 5.1: Schematic Diagram for test rig of Solar dryer with Desiccant material Collector will be fitted in South North direction at about 30 angles. Solar collector is made of Plywood. Material is selected on cost and trial basis. In between Plywood and Absorber sheet thermocole is used as a thermal insulation, to minimize the losses. The absorber plates are made of Aluminum sheets, painted with dull back paint. Rubber gasket is attached on top of plywood panel to avoid leakage between top of ply and acrylic glass. Clamping clips are attached to outer surface of plywood panel. These clamping clips take care of proper clamping pressure on acrylic glass thought the trial. Solar cabinet is attached using simple 1 pipe fittings. Thermocole is used as insulation in this cabinet. On one side of dryer, patti valve is attached. Using this vale, we can cut off air flow during off sunshine hours. Also for convince in assembly and transportation, one union joint is used between panel and drying chamber.drying chamber has inside dimensions 500 x 360 x 500 mm.[1] It is kept approximately at 450 mm distance from solar collector. The distance between two trays is mm. inside box is made up of plywood and outer is also from plywood. In between thermocole is placed. Stand can be removed from cabinet. Trays are sliding type and can remove completely from stand. Door of drying cabinet can open in 180⁰. Total eight sensors are fitted inside solar collector panel. One sensor is supported by base stand bracket on acrylic glass. To measure drying cabinet temperature one sensor is fitted. One sensor is put suspended below collector for measuring atmospheric temperature. ~ 3 ~

4 Photo 5.1: Photo of pasting thermocole sheets inside plywood solar panel. Photo 5.2: Photo of absorber sheets. All sensors are in varying in lengths from 50 to 90 mm and having 6mm diameter. For fitting sensors inside collector and box, drills are made at location. To avoid leakage, Sensors are pushed inside forcefully, so that surely no gap exists between them. All sensors are attached to indicators for indicating observations. Measurement at Different Parameters of Solar Dryer In this experimentation two different types of readings are focused. First is temperature measurement and another is moisture measurement. For temperature measurement total 11 no. of simplex type resistance temperature detector (RTD) sensors are fitted at different locations for taking readings. These sensors are also called as PT 100 sensors, which are having different lengths. While for calculating moisture content weights are taken on analytical balance. Cut section of collector plate is as shown in below (figure 6.1). Sensor locations are given by S1 to S11.All the details about sensors is given in table 6.1 Fig 6.1: Locations of sensors Table 6.1: Details about RTD sensors used for measurements Sr.No: Code Sr.No.of Manufacturer Probe Length (mm) Location of sensors 1 S Above plate, at 360 mm from bottom header 2 S Above plate, at 720 mm from bottom header 3 S Above plate, at 1080 mm from bottom header 4 S Bottom header ~ 4 ~

5 5 S Top header 6 S In the drying cabinet 7 S On the plate, at 360 mm from bottom header 8 S On the plate, at 720 mm from bottom header 9 S On the plate, at 1080 mm from bottom header 10 S In the shadow collector 11 S On acrylic glass All the sensors are of 0.00 C to C range. These probe type sensors having protective sheath of SS316. Extension cables provided with each sensor are 1.5 to 3m in length, with hard coating of Teflon sheet. All sensors are calibrated in standard laboratory. Sensors S1, S2, and S3 are placed above S7, S8, S9 respectively and exactly middle of absorber plate. Potential temperature difference shown with the help of these Sensors. This difference is main motive force of heat transfer from plate to the circulating air. S4 is placed in bottom header. Bottom header is a place where, air is distributed widthwise evenly over the absorber plate. S4 indicates temperature of inlet air to the absorber plate. Similarly, S5 plays same role in top header, indicating outlet temperature from absorber plate. S10 tells us about temperature of atmosphere during trial. To avoid direct sun radiation effect, it is kept in the shadow of collector box. It is measured by S11. The temperature rise in drying cabinet is shown by S6. All the sensors have different probe length as per installation requirement at that location. Temperature indicator is used. This is having the range of 0 to 199.9⁰C.It has total 24 no. of inputs. This is also calibrated in standard laboratory. Second measurement is taken for weights of samples. For weighing purpose Shimadzu Analytical balance model AUX 220 is used. This balance can weigh up to one thousandth part of one gram (0.1 mg) Table 6.2: Error value for sensors and indicator as per calibration report Sr.No: Codes Actual sensor Manufacturer Error in C length(mm) Sr.No: 100⁰ c 200 c⁰ 1 S S S S S S S S S S S Indicator Plus 1 Let PD1 is the temperature potential difference between location S7 and S1. PD1 = S7 S1 (i) PD2 = S8 S2 (ii) PD3 = S9 S3 (iii) Avg. PD = (PD1 + PD2 +PD3) / 3 (iv) Where, PD1 = Temperature potential difference between location S8 and S2 PD3 = Temperature potential difference between location S9 and S3 PD Avg.= average temperature potential difference on absorber plate Let Temperature difference between inlet and outlet header = IO Δ avg. = S5 - S4 (v) Let ML is the percentage loss of moisture weight of products with respect to wet products ML = (X1 - X2 ) X 100 /X1 (vi) Where, X1 = Initial weight of the products X2 = Final weight of the products Using relations from (i) to (vi) and by accounting sensors error results of calculations written. The instantaneous moisture content Mt at any given time t on dry basis is computed using the following expression [2] M (vii) The main characteristics, which are generally used for performance estimation of any solar drying, are dryer thermal efficiency and pick-up efficiency [3]. Pick-up efficiency determines the efficiency of moisture removal by the drying air from the product. Dryer thermal efficiency is the ratio of the energy used to evaporate the moisture from the product to the energy supplied to the dryer and can be expressed as Pick-up efficiency:- η (ix) Dryer thermal efficiency:- η (x) Table 6.3: Result table for day one of absorber Plate Date : 26/3/2015 Time and Sensors Readings Time S* S1 S2 S3 S4 S5 S9 S7 S8 S6 S10 S11 9:30 AM 10:30 AM :30 AM :30 PM ~ 5 ~

6 1:30 PM :30 PM :30 PM :30 PM Fig 6.2: Variation in loss of moisture weight of product A for 1 day box drying Figure 6.3: Variation in loss of moisture weight of product B for 1 day box drying 6. Conclusions In India there is abundance potential for solar energy available. Solar air heating can be an appropriate energy solution in the right application. Solar air dryers are used for drying agricultural and industrial products, and for space heating. Though solar drying having versatile appearance but still it has some disadvantage, which restrict its use in industry. Available devices are not more efficient as user will like it. Considering location constraint, the results of solar drying are analyzed in three parts, first solar collector performance, second drying process and third drying process with desiccant material. Following inferences are drawn from results of this experimentation. a) For Corrugations across air flow direction (C type plate) heat transferred to the air is higher at 360 mm distance (at location S1) on absorber plate. b) For duct ratio, unity, after length 720 mm (at location S2), efficiency of transferring heat to air goes on decreasing for Flat plate (A type) and C type absorber plate. c) For Corrugations along air flow direction (B type plate), efficiency of transferring heat to air goes on increasing (compare to S1 and S2) up to 1440 mm length. d) Due to typical, geometry, lowest radiation losses back at atmosphere from top cover are found in type B and highest radiation losses observed in plate A between 10:30 a.m. to 12:30 p.m. e) For selected geometry of absorber surface type A, B, and C gives best average temperature at about 700, 1100, 400 mm length of absorber plate respectively. ~ 6 ~ f) For circular and square cross section products, type C and A type absorber plate respectively are more suitable to remove moisture for one day drying. g) For two day drying (7 hrs/day), plate B shows steady and reliable results over a period, soaking least moisture during night period for both samples. h) For three days drying, in case of A type products plate A, B, and C can remove maximum 10%, 9%, and 8% moisture about 16, 13, and 13 hours respectively and in case B type products plate A, B, and C can remove maximum 11%, 13%, and 12% moisture about 18 hours. i) In open sun drying moisture removal rate is tolerable for circular then cross section at the cost of loss in strength and color due to absorbing more moisture form atmosphere. j) In the off sunshine hours, the dryer is operated by circulating the air inside the drying chamber through the desiccant bed by a reversible fan. The drying efficiency varies between 48 % to 56% and pickup efficiency varies between 52% to 63% respectively. k) Approximately in all drying experiment 68% of moisture is removed by air heated using solar energy and the remaining by the desiccant material. Although the benefits of solar air heating need to be quantified more thoroughly by collecting actual energy use date for each installation, there is sufficient evidence that the pilot solar air heating installations are saving resources and money. The options like switching from oil to solar should be made available with consideration of economics behind it and providing energy alternatives.

7 7. References 1. R. Hodali, J. Bougard, Integration of desiccant unit in crops solar drying installation: optimization by numerical simulation, Energy Conversion and Management 42 (2001),pp T.F.N. Thoruwa, C.M. John stone, A.D. Grant, J.E. Smith, Novel, low cost CaCl2 based desiccants for crop drying applications, Renewable Energy 19 (2000),pp M.A. Leon, S. Kumar, S.C. Bhattacharya, A comprehensive procedure for performance evaluation of solar food dryers, Renewable and Sustainable Energy Reviews 6 (2002), pp Sukhatme S.P. & Nayak J.K., Solar energy in western Rajasthan, Current science, Jan1997, Vol. 72, No. 1, pp Hassan E. S. Fath, Thermal performance of a simple design solar air heater with built-in thermal energy storage, Renewable Energy Vol. 6, No. 8, 1995, pp Hassan E. S. Fath, Transient Analysis of Thermosyphon Solar air heater with Built in latent heat thermal energy storage, Renewable Energy Vol. 6, No. 2, 1995, pp ~ 7 ~