Fabrication of Direct Evaporative Cooler and its Performance Analysis for Different Materials In Hot and Dry Climates Utkarsh Tripathi 1, Dr. R.M.Sarviya 2, Veeresh Fuskele 3 1Department of Mechanical Engineering, MANIT, Bhopal, India 2Professor & Dean S/W, Department of Mechanical Engineering, MANIT, Bhopal, India 3Department of Mechanical Engineering, MANIT, Bhopal, India Abstract This paper studies the performance analysis of different evaporative pad materials such as Charcoal, Activated Charcoal, Sponge of Sponge Guard ( Gilki in Hindi), brick bats and a combination of Wood Wool and Charcoal has been done in a specially design and fabricated evaporative cooling system. The objective is to analyse cooling effectiveness and cooling capacity at different velocities of air. Indore MP and nearby places where temperature is in the range of 39 C to 42 C in summer days with relative humidity 22% to 29 %, in this scenario evaporative cooling is a good option. This analysis has been done on a special evaporative cooler maintains cool interior temperature for food preservation purpose. While these devices are not typically capable of maintaining temperatures of 2-3 degrees Celsius, they can be significantly cooler than ambient temperature. An evaporative cooler uses the principal of evaporative cooling to maintain a cool interior temperature for refrigeration and food preservation. The device is constructed from an open timber frame with evaporative pad material filled sides, which is kept continually moist. As warm, dry air flows through the moist material, water is evaporated into the air and it is cooled. Keywords Evaporative Cooling, Direct and Indirect Evaporative Cooling, Cooling Effectiveness and Cooling Capacity. Activated charcoal I. INTRODUCTION 1.1 Evaporative Cooling: The principle underlying evaporative cooling is the fact that water must have heat applied to it to change from a liquid to a vapor. During evaporation, this heat is given to the water from dry air in the form of sensible heat when it comes in contact with water. Water takes this heat in the form of latent heat to convert its phase. 1.1.1 Direct Evaporative Cooling: In direct evaporative cooling the air to be cooled comes in direct contact with water. In such a process air gets humidified. 1.1.2 Indirect Evaporative Cooling: In indirect evaporative cooling, the air to be cooled does not come in direct contact with water. Instead, it is in indirect contact with a surface that is maintained at lower temperature with flow of water. In such a process its absolute humidity is not affected. 1.2 Activated charcoal It is a powerful adsorbent known. It is basically a solid material consisting mainly of pure carbon. A characteristic feature is its porous structure and the resulting immense surface area which may be large as 1500 sq m / gm. The surface area of Charcoal in present study is 200 sq m / gm. Activated Charcoal works on the principle of adsorption. Adsorption is an interfacial process involving the collection of gaseous or solute components on the surface of adsorbent solids. This phenomenon is associated with physical attractive forces that bind gaseous and solute molecules commonly known as Vander wall forces. Activated Charcoal for Evaporative cooling- Fig. 1: Pore structure of Activated Charcoal The adsorption power and rate is determined by the kind of activated charcoal, the particle size, the pore size and its distribution. Pore size and its distribution: When the carbon is activated it leads to opening of various pores in its structure. The pores with diameter exceeding 500 A are called macro pores or the transport pores. These pores are larger pores and are not responsible for adsorption directly but they act as wide paths through which organic molecules penetrates. Thus they transport the adsorbent to the smallest adsorption pore site. Pores with diameter below 50 A are called micro pores or adsorption pores. These are the finest pores, which are located inside the carbon particle where the adsorption actually takes place. www.ijaers.com Page 6
For activated carbon to give good performance it needs to have both these pores in good proportion. II. DEVICE CONSTRUCTION AND EXPERIMENT METHODOLOGY The device is a cube or cuboid shaped hollow box constructed from an open timber frame with its four side walls are made of sieves on framed pillars forming a space for filling the evaporative material. The base is closed and insulated and the top face is also insulated except for a 150mm dia exhaust fan fitment The exhaust fan location was optimized using CFD analysis. The results were found better on top facing exhaust fan fitment rather than side facing exhaust fan fitment. Since side facing exhaust would lead to only three effective cooling faces. Also the exhaust fan provided with variable wind velocity scope. Fig.2 CFD Analysis of the design and optimization In all the four side faces different evaporative materials were placed one by one and in combinations also. A water circulation arrangement is also provided ( using both gravity circulation and forced circulation using pumps), and flow rate optimised in such a way that rate of circulation equals to rate of evaporation using number of hole and dia of holes in the pipes. The evaporative material is kept continually moist. As warm, dry air flows through the moist material, water is evaporated extracting the required latent heat from the air and air gets cooled and in turn maintains the interior cooler. Fig. 3: A Schematic explanation of the Construction On complete working setup, results were observed using specific high accuracy instruments. The instruments used were: Fig. 4: Instruments used in the experiment 1) Mercury Thermometer; 2) Wet bulb thermometer 3) Anemometer; 4) Digital contact type thermometer Some Assumptions were made and tried to achieve at the time of experimentation: The conditions are at steady state The cooler will be placed in a shaded region and radiation effects are negligible The top (Except for Exhaust Fan area)and bottom of the cooler are insulated The entire system operates at atmospheric pressure (101.325kPa) The material is kept continually moist (water consumption rate = rate of evaporation) III. NOMENCLATURE AND THEORY T1 Dry Bulb Temperature ( C ) T2 Temperature inside cooler ( C ) Twet Wet Bulb temperature ( C ) Ec Cpu Cpv Cpa Wi RH Wi ṁa Cooling Effectiveness Specific Heat of Moist Air (KJ/KgK) Specific Heat of water vapor (KJ/KgK) Specific Heat of inlet air (KJ/KgK) Specific Humidity of inlet air ( Kg/Kg of inlet air) Relative Humidity Specific humidity of inlet air (kg/kg of inlet air) Mass flow rate of inlet air ( Kg / Sec) 3.1 Cooling Effectiveness: Instruments E c = Actual Cooling = T 1 - T 2 www.ijaers.com Maximum Cooling T 1 - T wet Page 7
3.2 Cooling Capacity: Q= ṁ a *C pu * (T 1 -T 2 ) C pu (moist air) = C pa (inlet air) +W i *C pv 3.3 Factors affecting evaporation Evaporation depends on the following factors Ambient Temperature (DBT) Ambient Specific Humidity (outside air) Surface Area Evaporative Media ( Density) Air Flow Rate Water Temperature The heat removed from a space due to the evaporation of water is given by following equation Where; Q. is the heat removed in kw ṁ e is the rate of evaporation of water in k kg/s h e is the latent heat of evaporation for water (~2270kJ/kg). 3.4 Density of various materials: (Table 1) Material Density (kg/m 3 ) Material Density (kg/m 3 ) Sample Bulk (Whole fruit & Veg) 25g Testing Conditions: Ambient 31 c/70% RH Inside cooler 21 c/90% Sample Bulk (Leafy veg) 5g Charcoal 208 Coconut shredded 352 Carbon solid 2146 Cork solid 240 Cardboard 689 Cotton seeds not de linted 320 Clay wet 1602 Cotton wood 416 Bark wood 240 Lime hydrated 481 Clay dry lump 1073 Mud 1906 Coal Bituminous broken Sugarcane 272 833 Sawdust 210 3.5 Ambient Specific Humidity Average weather data at Bhopal, India (April, May & some part of June-2011) is shown in table no.2. The most frequently occurring condition is B of average maximum DBT 40.1 C and average RH 22.14% is selected for the analysis. All the properties of air are referred at this temperature. (Table 2) Fig. 5: Materials used in the experiment IV. REVIEW OF EXPERIMENTAL WORK AND OBSERVATIONS 4.1CHARCOAL 4.2 ACTIVATED CHARCOAL 3.6 Shelf life of Fruits and Vegetables: ( Table 3) www.ijaers.com Page 8
4.3 SPONGE -SPONGE GUARD ( GILKI IN HINDI): 4.6 WOOD WOOL & CHARCOAL 4.4 BRICK BAT 4.7 Comparative Analysis Of Different Evaporative Pad Materials 4.5 KHAS Hence with varying wind velocity and evaporative material, the combination of Wood Wool and Charcoal has given the highest cooling effectiveness in the setup. www.ijaers.com Page 9
V. CONCLUSION & PROPOSED WORK Fabrication of Direct Evaporative Cooler has been done. The study has been done on in the month of November and December 2012 and March- April 2012. The cooling effectiveness is coming out to be 80.5% for Charcoal, 73.8% for Activated Charcoal, 85.16% for Sponge of Sponge Guard, 74.48% for Brick bats, 84.12 % for Khas and 97.32% for combination of Wood Wool and Charcoal at air velocity 5 m/s. The cooling capacity is 4.85 kj/h for Charcoal, 1.87 kj/h for Activated Charcoal, 5.18 kj/h for Sponge of Sponge Guard, 3.62 kj/h for Brick bats, 4.78 kj/h for Khas and 4.85 kj/h for combination of Wood Wool and Charcoal at air velocity 5 m/s. In hot and dry climate of India, based on summer weather data, most frequently occurring condition of average maximum DBT 40.1 C and average RH 22.14% evaporative cooling is good option. With present efficiency the temperature difference in hot and dry climate of Bhopal is estimated to be 13 C to 15 C. VI. AKNOWLEDGEMENT This research was supported by MANIT, BHOPAL. Special thanks to Dr. R.M.Sarviya, Prof & Dean Mech. Engg. Dept, MANIT, for his guidance and motivation, and Mr. Veeresh Fuskele, Research Scholar, Mech. Engg. Dept, MANIT for his assistance and comments that greatly improved the manuscript We thank our colleague Ms Neelam Dubey, from MITM, INDORE who provided insight and expertise that greatly assisted the research. REFERENCES Literature Review: Different researchers have made the efforts to clear the concept of evaporative cooling and to search an appropriate media, design and process to make the evaporation most effective [1] R.K.KULKARNI and S.P.S.RAJPUT -Theoretical Performance Analysis of Indirect-Direct Evaporative Cooler in Hot and Dry Climates. [2] http://www.academicjournals.org/ajfs -Development of an Evaporative Cooling system for the preservation of Fresh Vegetables: R.K. Kulkarni and S.P.S. Rajput-Comparative performance of evaporative cooling pads of alternative materials. [3] Understanding Evaporative Cooling by Eric Rusten. [4] http://aurocarbon.com/activatedcarbon.html Understanding Activated Charcoal. [5] Mass, weight & density of bulk materials www.simetric.co.uk/ si_materials.html [6] 7.CFM calculation for room http://ag.arizona.edu/pubs/consumer/az9145.pdf [7] Bhopal weather data retrieved from www.tutiempo.net. [8] Mr. S.K. Varde, Chartered Engineers, HVAC & R consultants, Govt. Certified Energy Auditors. www.ijaers.com Page 10