International Journal of Innovative Research in Engineering & Science ISSN (July 2013, issue 2 volume 7)

International Journal of Innovative Research in Engineering & Science ISSN 2319-5665 (July 2013, issue 2 volume 7) Design, Construction and Testing ...
Author: Hilary Gardner
1 downloads 1 Views 220KB Size
International Journal of Innovative Research in Engineering & Science

ISSN 2319-5665 (July 2013, issue 2 volume 7)

Design, Construction and Testing of Solar Dryer with Roughened Surface Solar Air Heater Sandeep Panchal#1, Satish Kumar solanki#1, Sunil Yadav#1, Prof Asim Kumar Tilkar#1, Prof Ravi Nagaich#2 #1 Mahakal Institute of Technology, Ujjain (M.P.) 456010 #2 Ujjain Engineering College, Ujjain (M.P) 456010 Abstract This project research reports the design, construction and testing of a simple solar dryer with roughened surface with solar air heater. It is designed in such a way that solar radiation is not incident directly on the agro products, but preheated air warmed during its flow through a low pressure thermos phonic solar energy air heater of size 1000mmx500mmx100mm, absorber plate (aluminium) sheet painted black of size 1000mmx500mm and a cover glass (5mm thickness) measuring 1000mmx500mm all arranged in this order contributed to the heating. Also the result has been tested with different arrangement of air resistors inside Like Square shaped, V-shaped, square & V-shaped combined. These resistors were aluminium strips. And it is clear from the beloved results that the combined squared and V-shaped strip arrangement took less time than else arrangements and it is quite efficient than the other arrangements. Keywords: Solar Energy, Radiation, Airflow, Collector, Absorber Plate, Glass, Mango slices. INTRODUCTION Sun drying is still the most common method used to preserve agricultural products in most tropical and subtropical countries. However, being unprotected from rain, wind-borne dirt and dust, infestation by insects, rodents and other animal, products may be seriously degraded to the extent that sometimes become inedible and the resulted loss of food quality in the dried products may have adverse economic effects on domestics and international markets. Some of the problems associated with open-air sun drying can be solved through the use of a solar dryer which is comprises of collector, a drying chamber and sometimes a chimney. (Madhlopa et al, 2002). The conditions in tropical countries make the use of solar energy for drying food practically attractive and environmentally sound. Dryers have been developed and used to dry agricultural products in order to improve shelf life (Esper and Muhlbauer, 1996). Most of these either use an expensive source of energy such as electricity (El-Shiatry et al., 1991) or a combination of solar energy and some other form of energy (Sesay and Stenning, 1997). Most projects of these nature have not been adopted by the small farmers, either because the final design and data collection procedures are frequently inappropriate or the cost has remained inaccessible and the subsequent transfer of technology from researcher to the end user has been anything but effective (Berinyuy, 2004). The total cultivated area and production of mango in Sudan , year 2003, was estimated to be about 51926 feddan (21,809 hectares) and 442,330 tonnes, respectively(Ministry of Agriculture, 2004). Mango falls into the group of fruit crops, used for food by both human being and animals. At harvest, this product usually contains too much moisture (about 25%-35%) which is a favorable environment for the growth of moulds (fungi) and insects that normally cause grain damage. In order to avoid this, drying of the mango must be done to reduce the moisture content to about (10 to 11%) for safe year-round storage. 7

International Journal of Innovative Research in Engineering & Science

ISSN 2319-5665 (July 2013, issue 2 volume 7)

A survey was carried out on ordinary sun drying method and it was found out that the existing method was very tedious, time wasting, wastage, in terms of produce and consequently having a very low hygienic level. The direct exposure to sunlight, or more precisely ultraviolet radiation, can greatly reduce the level of nutrients such as vitamins in the dried product. As a solution to these problems enumerated above, an idea was conceived and a Distribution Passive Solar Energy Maize Dryer was designed, fabricated, and tested. The aim of this research work therefore, is to design, construct and test a Simple Solar Dryer with roughened surface air heater to dry at least 1kg of mango slices. The design consists of two major sections made in one unit: a. the flat collector upon which solar energy is incident, transmitted and absorbed to heat air which is passed by natural convection to the drying chamber; b. the drying chamber which contains the grains being dried. The air having passed over the grains becomes saturated with water and is discharged through the chimney to avoid condensation of water vapor in the event that the system temperature falls. EXPERIMENTAL SETUP 2.1 Material and Method: The solar dryer considered in this research paper is the Distributed Passive Solar Dryer (DPSD) or Hybrid Dryer (HD). Here the product is located on trays or shelves inside an opaque drying chamber. Solar radiation is thus not incident directly on the crop. Preheated air warmed during its flow through a low-pressure thermos phonic solar energy air heater, is ducted to the drying chamber to dry the product. Because the products are not subjected to direct sunshine, Localized heat damage, do not occur. A typical Distributed Passive Solar Energy Dryer is made up of the following basic units: (a) A Drying chamber. (b) An air-heating solar energy collector, which consists of cover plate, absorber plate and insulator (wood). 2.1.1 Drying Chamber: The drying chambers made of a highly polished plywood box held in place by angle irons. The material has been chosen since wood is a poor conductor of heat and it has smooth surface finish; heat loss by radiation is minimized. To further reduce heat loss by radiation and to avoid moisture absorption by the wood, aluminium foil is wrapped on the inside of the chamber. 2.1.2 Cover Plate: This is transparent sheet used to cover the absorber, thereby preventing dust and rain from coming in contact with the absorber. It also retards the heat from escaping (i.e. forming a confinement for heated air) It is placed about 25.4mm above the absorber. Common materials used for cover plates are glass, flexi glass, fiberglass, reinforced polyester, thin plastic films and plastics. 2.1.3 Absorber Plate: This is a metal plate painted black and placed about 25.4mm below the cover to absorb the incident solar radiation transmitted by the cover thereby heating the air between it and the cover. In its plainest form, it is no more than a blackened metal plate exposed to the sun. 2.1.4 Insulator: This is used to minimize heat loss from the system. It is placed under the absorber plate. The insulator must be able to withstand stagnation temperature, should be fire resistant and not subject to out-going gassing; and should not be damageable by moisture or insect. Insulating materials are usually fiberglass, mineral wool, Styrofoam and urethanes. 8

International Journal of Innovative Research in Engineering & Science

ISSN 2319-5665 (July 2013, issue 2 volume 7)

Figure1. Representation of the Solar Dryer DESIGN EXPERIMENTAL SPECIFICATION 3.1 Design Features of the Dryer: The solar dryer has the shape of a home cabinet with tilted transparent top. The angle of the slope of the dryer cover is 24º for the latitude of location Ujjain, MP (India). It is provided with air inlet and outlet holes at the front and back, respectively. The outlet vent is at higher level. The vents have fix covers which control air inflow and outflow. The movement of air through the vents, when the dryer is placed in the path of airflow, brings about a thermo siphon effect which creates an updraft of solar heated air laden with moisture out of the drying chamber. The source of air is natural flow. 3.2 Solar Dryer Design Considerations: The following point has been considered in the design of the natural convection solar dryer system: a- The amount of moisture to be removed from a given quantity of wet mango. b- Harvesting period during which the drying is needed. c- The daily sunshine hours for the selection of the total drying time. d- The quantity of air needed for drying. e- Daily solar radiation to determine energy received by the dryer per day. f- Wind speed for the calculation of air vent dimensions. 3.3 Design procedure: The size of the dryer was determined as a function of the drying area needed per kilogram of pulp of fruit. The drying temperature was established as a function of the maximum limit of temperature the fruit might support. From the climatic data (Ujjain MP) the mean average day temperature in April is 30ºC and RH is 15 %. From the psychometric chart the humidity ratio is 0.0039kg H2O/kg dry air. From the result of preliminary experiments on the crop, the optimal drying temperature was 70ºC and final moisture content of mango for storage is 10% w.b. the corresponding relative humidity is 51%(sorption isotherms equation). 3.4 Design Calculations: To carry out design calculations and size of the dryer, the design conditions applicable to Khartoum are required. The conditions and assumptions summarized in Table 1 are used for the design of the mango dryer. From the conditions, assumptions and relationships, the 9

International Journal of Innovative Research in Engineering & Science

ISSN 2319-5665 (July 2013, issue 2 volume 7)

values of the design parameters were calculated. The result of calculations is summarized in Table 2. I-Amount of moisture to be removed from a given quantity of wet mango slices to bring the moisture content to a safe storage level in a specified time. The amount of moisture to be removed from the product, mw, in kg was calculated using the following equation: mw = mp(Mi – Mf) / (100- Mf) ………………..(1) Where: mp is the initial mass of product to be dried, kg; Mi is the initial moisture content, % wet basis and Mf is the final moisture content, % wet basis. II-Final or equilibrium relative humidity: Final relative humidity or equilibrium relative humidity was calculated using sorption isotherms equation for mango given by Hernandez et al (2000) as follows: aw = 1- exp[-exp(0.914+0.5639lnM)]………….(2) Where: aw = water activity, decimal M = moisture content dry basis, kg water/kg dry solids aw = ERH/100………………………………...(3) III-Quantity of heat needed to evaporate the H2O: The quantity of heat required to evaporate the H2O would be: Q = mw x hfg …………………………….…..(4) Where: Q = the amount of energy required for the drying process, kJ mw = mass of water, kg hfg = latent heat of evaporation, kJ/kg H2O The amount needed is a function of temperature and moisture content of the crop. The latent heat of vaporization was calculated using equation given by Youcef-Ali as follows: hfg = 4.186*103(597-0.56(Tpr))………….….(5) Where: Tpr = product temperature ºC Moreover, the total heat energy, E(kJ) required to evaporate water was calculated as follows: E = m` (hf -hi)td…………………………….(6) Where: E = total heat energy, kJ m` = mass flow rate of air, kg/hr hf and hi = final and initial enthalpy of drying and ambient air, respectively, kJ/kg dry air. td = drying time, hrs The enthalpy (h) of moist air in J/kg dry air at temperature T (ºC) can be approximated as (Booker et al., 1992): h = 1006.9T +w[2512131.0 +1552.4T]…….(7) IV- Average drying rate: Average drying rate, mdr, was determined from the mass of moisture to be removed by solar heat and drying time by the following equation: mdr = mw/ td………………………………(8) The mass of air needed for drying was calculated using equation given by Sodha et al. (1987) as follows: m`= mdr / [wf –wi]………………………..(9) Where: 10

International Journal of Innovative Research in Engineering & Science

ISSN 2319-5665 (July 2013, issue 2 volume 7)

mdr = average drying rate, kg/hr wf –wi , final and initial humidity ratio, respectively, kg H2O/kg dry air From the total useful heat energy required to evaporate moisture and the net radiation received by the tilted collector, the solar drying system collector area Ac, in m2 can be calculated from the following equation: AcIη = E = m` (hf -hi)td ……………….(10) Therefore, area of the solar collector is: Ac = E/Iη ……………………………...(11) Where: E is th total useful energy received by the drying air, kJ; I is the total global radiation on the horizontal surface during the drying period, kJ/ m2 and η is the collector efficiency, 30 to50%. Volumetric airflow rate, Va was obtained by dividing ma by density of air which is 1.2 kg/m3 V-Air vents dimensions: The air vent was calculated by dividing the volumetric airflow rate by wind speed: Av = Va/Vw ………………………… (12) Where: Av is the area of the air vent, m2, Vw wind speed, m/s.The length of air vent , Lv, m, will be equal to the length of the dryer. The width of the air vent can be given by: Bv = Av/Lv ……………………..…... (13) Where: Bv is the width of air vent, m VI-Required pressure: Velocity = Va/A Va = volumetric flow rate m3/sec. The pressure difference across the mango slices bed will be solely due to the density difference between the hot air inside the dryer and the ambient air. Air pressure can be determined by equation given by Jindal and Gunasekaran (1982): P = 0.00308 g(Ti- Tam)H ………….(14) Where: H is the pressure head (height of the hot air column from the base of the dryer to the point of air discharge from the dryer), m; P is the air pressure, Pa; g is the acceleration due gravity 9.81m/s2; Tam is the ambient temperature, C. The prototype solar dryer was sized to have a minimum area of 1m2 to be used in experimental drying tests. Table1. Design conditions and assumptions Items Location Crop Variety Drying period Drying per batch Loading rate (mp) Initial moisture content (moisture content At harvest), Mi Final moisture content (moisture content For storage) , Mf Ambient air temperature, Tam Ambient relative humidity, RHam

Condition or assumption Ujjain (latitude 24º N) Mango Kitchener April (2days / batch), 1kg sliced mango 60 % w.b. 10 % w.b. 30ºC (Average for April) 15% (Average for April) 11

International Journal of Innovative Research in Engineering & Science

Maximum allowable temperature, Tmax Drying time (sunshine hours)td Incident solar radiation, I past 30 years) Collector efficiency, η Wind speed Thickness of sliced mango Vertical distance between two adjacent trays

Parameter Initial humidity ratio, wi Initial enthalpy, hi, Equilibrium relative Humidity, RHf Final enthalpy, hf Final humidity ratio, wf Mass of water to be Evaporated, mw Average drying rate, mdr Air flow rate, ma Volumetric airflow rate, Va Total useful energy, E Solar collector area, Ac Vent area, Av Air pressure, P Vent length Vent width

ISSN 2319-5665 (July 2013, issue 2 volume 7)

70ºC 7 hours (Average for April) 13MJ/m2/day (average for 30% . 19km/hr 3mm 250mm

Table 2. Values of design parameters Value Data or Equation used 0.0039kgH2O/kg dry air Tam, RHam 40kJ/kg dry air Tam, RHam 51% Mf and isotherms equation 75kJ/kg dry air wi and Tf 0.014kgH2O/kg dry air RHf and hf 0.560kg Equation (1) 0.08kgH2O/hr 7.920kg dry air/hr 0.055m3/s 2MJ 0.50m2 0.0140m2 0.32Pa 0.13m 0.080m

Equation (8) Equation (9) ma,air density (ρ) Equation (6) Equation (11) Va,wind speed Equation (14) Equation (12) Equation (13)

EXPERIMENT CALCULATIONS The testing of the solar mango dryer was done in the month of April for two days with each arrangement of strips. The solar Dryer was placed outside with the collector facing the direction of the sun. The collector has been rigidly fixed to the dryer at an angle 24ºc approximately to the horizontal to obtain approximately perpendicular beam of sun rays to avoid damage in transit. About 1kg of fresh mango was arranged on the drying bed in a single layer to avoid moisture being trapped in the lower layer. The dryer chamber door was closed and seals placed in position. The result obtained for hourly reading of 7hours everyday for every arrangement of strips is tabulated in tables 1-8 From table1 to table8 the dryer has been tested with different arrangements of aluminium strips for the period of two days depend on requirement conditions and got the results. Notifications: Tsurr - Temperature of surroundings. º C (varying with time). Tduct - Temperature of air inside duct, º C. Tbb - Temperature of air below bed, º C. Tab - Temperature of air above bed, º C. w.b. - Wet basis.

12

International Journal of Innovative Research in Engineering & Science

ISSN 2319-5665 (July 2013, issue 2 volume 7)

4.1 For the solar air heater having no aluminium strips inside. Results on 15th April 2013. Table1. Variation of Temperature with Time on the First day Day1 Time Tsurr Tduct Tbb Tab M(kg) Mango slices

9am 30 35

10am 31 37

11am 33 37.4

12pm 35 40

13pm 35 40.1

14pm 36 40

15pm 33 38

16pm 32 36

34 33

37 36.2

37 36

41 39

41 40

39.8 38

38 37.1

36 35

1kg

0.61kg

Mango weight (initial)=1 kg Mango weight (final)=0.61kg Moisture removed=0.39kg Results on 16th April 2013. Table2. Variation of Temperature with Time on the Second day Day2 Time Tsurr Tduct Tbb Tab M(kg) Mango slices

9am 31 37 36.4 35.2

10am 31 37.5 36 34

0.61kg

11am 32 38 37.3 36

12pm

13pm

14pm

15pm

16pm

0.52kg

Mango weight (initial)=0.61kg Mango weight (final)=0.52kg Moisture removed=0.09kg This arrangement took total 9.6 hrs approx. to get the desired result i.e. from 60% wb to 10% wb moisture content. 4.2 For the solar air heater having Square shaped aluminium strips inside. Results on 17th April 2013. Table3. Variation of Temperature with Time on the First day Day1 Time Tsurr Tduct Tbb Tab M(kg) Mango slices

9am 30.5 38 35 34.5

10am 33 41 40 39

1kg

11am 36 40 39.5 39

12pm 36 43 43 42.6

13pm 37 44 42 41.8

14pm 36 43.2 43 42.6

15pm 34 42 42.6 41.5

16pm 33 41 40.8 40 0.53kg

Mango weight (initial)=1kg Mango weight (final)=0.53kg 13

International Journal of Innovative Research in Engineering & Science

ISSN 2319-5665 (July 2013, issue 2 volume 7)

Moisture removed=0.47kg

Results on 18th April 2013. Table4. Variation of Temperature with Time on the Second day Day2 Time Tsurr Tduct Tbb Tab M(kg) Mango slices

9am 32 38 37 36

10am 34 40 38.2 37.1

0.53kg

0.49kg

11am

12pm

13pm

14pm

15pm

16pm

Mango weight (initial)=0.53kg Mango weight (final)=0.49kg Moisture removed=0.04kg This arrangement took total 8.5 hrs approx. to get the desired result i.e. from 60% wb to 10% wb moisture content. 4.3 For the solar air heater having V-shaped aluminium strips inside. Results on 19th April 2013. Table5. Variation of Temperature with Time on the First day Day1 Time Tsurr Tduct Tbb Tab M(kg) Mango slices

9am 30 38 37 35.7

10am 32 41.4 41 40

11am 37 43 41.7 40

12pm 36 43.5 43 42

13pm 38 45 44.7 44

14pm 37.5 44.3 44 43

15pm 36 44 43.6 42.4

1kg

16pm 33.3 42 40 39 0.52kg

Mango weight (initial)=1kg Mango weight (final)=0.52kg Moisture removed=0.48kg Results on 20th April 2013. Table6. Variation of Temperature with Time on the Second day Day2 Time Tsurr Tduct Tbb Tab M(kg) Mango slices

9am 31 38 36.9 36

10am 32 39 38.3 37.8

0.52kg

0.47kg

11am

12pm

13pm

14pm

15pm

16pm

Mango weight (initial)=0.52kg 14

International Journal of Innovative Research in Engineering & Science

ISSN 2319-5665 (July 2013, issue 2 volume 7)

Mango weight (final)=0.47kg Moisture removed=0.05kg This arrangement took total 8.4 hrs approx. to get the desired result i.e. from 60% wb to 10% wb moisture content. 4.4 For the solar air heater having square and V-shaped(combined) aluminium strips inside. Results on 22nd April 2013. Table7. Variation of Temperature with Time on the First day Day1 Time Tsurr Tduct Tbb Tab M(kg) Mango slices

9am 31 40 39 38

10am 33 42 41.3 41

11am 35 43.3 43 42

12pm 37 45.6 44.8 44.3

13pm 39 47 46 44.8

14pm 38 46 45.3 44.3

15pm 36 45 45 44

16pm 33 44 42.7 40

1kg

0.49kg

Mango weight (initial)=1kg Mango weight (final)=0.49kg Moisture removed=0.51kg Results on 23rd April 2013. Table8. Variation of Temperature with Time on the Second day Day2 Time Tsurr Tduct Tbb Tab M(kg) Mango slices

9am 31 38.3 38 36.8

10am 33 41 40.2 39.8

0.49kg

0.41kg

11am

12pm

13pm

14pm

15pm

16pm

Mango weight (initial)=0.49kg Mango weight (final)=0.41kg Moisture removed=0.08kg This arrangement took total 8.1 hrs approx. to get the desired result i.e. from 60% w.b. to 10% w.b. moisture content. RESULT AND DISCUSSION In order to reduce moisture content from 60% wb to 10% wb in 1 kg mango slices here tests have been performed using solar air heater with different arrangements and the results have been found out likeExperimental Setup No aluminium strips Squared shaped aluminium strips

Initial weight

Final weight

Time required

0.52 kg

% of moisture removed 48%

1 kg 1kg

0.49 kg

51%

8.5 hours

9.2 hours

15

International Journal of Innovative Research in Engineering & Science

ISSN 2319-5665 (July 2013, issue 2 volume 7)

V-shaped 1kg 0.47 kg 53% 8.4 hours aluminium strips Square and V1kg 0.41 kg 59% 8.1 hours shaped aluminium strips And it is clear from the above results that the combined squared and V-shaped strip arrangement took less time than else arrangements and it is quite efficient than the other arrangements. CONCLUSION A solar dryer was designed and constructed based on preliminary investigations of mango slices drying under controlled conditions (laboratory dryer).The constructed dryer to be used to dry mango slices under controlled and protected conditions. The designed dryer with a collector area of 0.5m2 is expected to dry 1kg fresh mango(1kg of sliced mango) from 60% to 10% wet basis in two days under ambient conditions during harvesting period in the month of April. REFERENCES [1] Afriyie, J.K., Rajakaruna, H., Nazha, M. A. A., Forson, F.K., 2011, Simulation and optimization of the ventilation in a chimney-dependent solar crop dryer, Solar Energy, 85, pp.15601573. [2] Ministry of Agriculture and Forestry (2004). Department of Horticulture. Khartoum,

Sudan. [3] Sodha, M. S.; Bansal, N. K.; Kumar, A.; Bansal, P. K and Malik, M. A. (1987). Solar crop drying. Vol. I and II. CPR press, Boca Raton, Florida, USA. [4] Amer, B.M.A., Hossain, M.A. , Gottschalk, K., 2010, Design and performance evaluation of a new hybrid solar dryer for banana, Energy Conversion and Management, 51, pp.813-820. [5] Anderson, R.B., 1946, Modification of the BET equation, Journal of the American Chemical Society, 68, pp. 656–691. [6] Arinze, E. A., Sokhansanj S., Schoenau, G. J., Trauttmans dorff, F. G., 1996, Experimental evaluation, simulation and optimization of a commercial heated-air batch hay drier, Journal of Agricultural Engineering Research, 63, pp. 301–314. [7] Jindal, V. K. and Gunasekaran, S. (1982). Estimating air flow and drying rate due to natural convection in solar rice dryers. Renewable energy review, 4(2): 1-9. [8] Hernandez, J. A.; Pavon, G. and Garcia, M.A. (2000). Analytical solution of mass

transferequation considering shrinkage for modeling food-drying kinetics. Journal of food engineering, 45(1): 1-10. [9] Brooker, D. B.; Bakker-Arkema, F. W. and Hall, C. W. (1992). Drying and storage of grains and oilseeds. Avi, Van Nostrand Reinhold. USA. [10] Ampratwum,D.B. (1998). Design of solar dryer for dates. AMA, 29(3): 59-62 Basunia, M. A. and Abe .T. (2001). [11] Design and construction of a simple three-shelf solar rough rice dryer. AMA, 32 (3): 54-5 Berinyuy, J. E. (2004). [12] A solar tunnel dryer for natural convection drying of vegetables and other commodities in Cameroon. AMA, 35(2): 31-35. Brett, A; Cox, D.R. ; Simmons, R. and Anstee,G. (1996). [13] Producing solar dried fruit and vegetables for micro and small-scale rural enterprise development. [14] Hand book3: Practical aspect of processing. Natural Resources Institute, Chatham, UK.

[15] Madhlopa, A.; Jones, S. A. and Kalenga Saka, J. D. (2002). A solar air heater with compositeabsorbersystems for food dehydration. Renewable energy, 27:27-37.

16

International Journal of Innovative Research in Engineering & Science

ISSN 2319-5665 (July 2013, issue 2 volume 7)

[16] Esper, A. and Muhlbauer, W. (1996). Solar tunnel dryer. Plant Res. And development, 44(4):16-64. [17] El-Shiatry, M.A.; Muller, J. and Muhlbauer, W. (1991). Drying fruits and vegetables with solar energy in Egypt. AMA, 22(4): 61-64 [18] Sesay, K. and Stenning, B. C. (1997). A free-convective fruit and vegetable hybrid tray dryer for developing countries. Cited by Berinyuy, J. E. (2004).

17

Suggest Documents