Design and Construction of High Concentration Solar Cooker

Ngala, G.M.1, Maina, M.B.2 and Modu Tela, B.3

1Department of Mechanical Engineering 2Centre for Entrepreneurship and Enterprise Development

University of Maiduguri, P.M.B. 1069, Maiduguri, Borno State, Nigeria 3Nigerian Nuclear Regulatory Authority, Abuja

International Journal of Research in Mechanical Engineering

Volume 3, Issue 1, January-February, 2015, pp. 01-07 ISSN Online: 2347-5188 Print: 2347-8772, DOA : 24122014

IASTER 2014, www.iaster.com

ABSTRACT Solar energy is greatly available in the north east sub region spanning to about seven to eight months as peak to average sunshine/heat period. As a renewable energy that can be obtain at less or no cost, hence, the knowledge of basics physics in the field of heat transfer is greatly adopted in this work using various means e.g. reflection, blackbody radiation, greenhouse effect, heat conservation e.t.c. to make use of available sunshine in the smallest possible time as heat to cook food items of various quantities at different time of the day. Therefore a high concentrating solar cooker was constructed and subjected to various hours of sunshine to cook different food items. The experiment conducted has yielded tremendous result with respect to cooking time and the efficiency of the system, thus giving a promising solution to our energy requirements Vis--vis environmental sustainability at an affordable cost. Keywords: Solar Energy, Heat Transfer, Cooking Time, Environmental Sustainability. 1. INTRODUCTION Different types of energy sources have been identified and various conversion methods have been designed and developed over the years in order to meet human needs. In Nigeria the sources of domestic energy are biomass, fossil fuel, electricity and solar energy (Abdulrahim et al, 2004). Fossil fuels that are the conventional energy source for everyone (Kerosene, Petrol, Diesel e.t.c.) are out of reach due to their cost, unavailability and many other unrealistic policies surrounding their provision. The only source left that is affordable and accessible is to fell trees and source energy as fuel wood or charcoal, but that is increasingly contributing to several environmental problems and the limited availability of the fuel wood means that people spend more time and energy in the search for cooking fuel (Bowman, T.E. 1985). A particular alternative is to use solar energy, which is free, pollution free and renewable. The availability of solar radiation and its accessibility even in remote places, with little access to conventional energy supplies, its higher abundance in hot, dry or arid areas with the greatest need for fuel wood substitute, makes the energy a better alternative to conventional sources of energy for cooking purposes (Dahiru et al, 2007).Nigeria is endowed with an annual average daily sunshine of 6.25 hours,

International Journal of Research in Mechanical Engineering Volume-3, Issue-1, January-February, 2015, www.iaster.com ISSN

(O) 2347-5188 (P) 2347-8772

2

ranging between about 3.5 hours at the coastal areas and 9.0 hours at the far northern boundary. Similarly, it has an annual average daily solar radiation of about 5.25 KW/m2/day, varying between about 3.5KW/m2/day at the coastal area and 7.0 KW/m2/day at the northern boundary. Nigeria receives about 4.851 x 1012 KWh of energy per day from the sun. This is equivalent to about 1.082 million tones of oil Equivalent (mtoe) per day, and is about 4 thousand times the current daily crude oil production, and about 13 thousand times that of natural gas daily production based on energy unit (Bala, et al 2000). Solar cookers have been developed, many have serious limitations, except for direct cookers most can only be used outdoors and during the day (most often only when the sun is high) most have to be adjusted every 15 20 minutes to keep pace with moving sun and most are only suitable for slow stewing/cooking. Concentrating dish shaped solar collector has been utilized to raise temperatures to boiling and above. This well known configuration has been utilized to forge metals, make steams, produce electricity and for many other purposes. All models in existence to date have been constructed of relatively affordable materials and with elaborate supporting structures and focusing arrangements. The geographical locations of the area, the climatic condition as well as the materials used for the construction are the factors that greatly affect the design and performance of solar cooker (Dahiru et al, 2007). The work being reported in this article covers the design, construction and performance evaluation of a concentrating solar cooker.

2. MATERIALS AND METHODS The Effect of Geographical Location and the Climatic Condition: The latitude of the location could significantly affect the design of solar cooker as reported by Pelemo et al (2002). For locations near the equator, a simple parabolic concentrator is desirable. The sunshine hours available and seasonal variations are also very important and can significantly affect the performance of the cooker. On clear days, the performance of solar energy equipment is higher (Dahiru et al, 2007). Figures 3, 4 and 5 show the monthly average solar sunshine hours, monthly average solar radiation and monthly average maximum temperature for the location under study (1998-2007) Description of the Solar Cooker A picture of the high concentrating solar cooker is shown in Figures 1 and 2 and is made of the following components: A Parabolic Concentrator, Reflecting Mirror, Glass, Oven, and Support. The concentrator has an aperture diameter of 1.0 m that concentrates the solar radiation on to a focal point. The reflecting material is made of glass mirrors, and adhesive glue was used to stick the glass pieces on to the parabolic concentrator. The reflectivity of glass is about 90% and will last for a period of about ten years (Dahiru et al, 2007). The absorber is the oven that has glass base and made of Aluminum sheet completely painted with black lacquer, it has the capacity of taking two pots. The adjustable tracking device is used to continuously adjust the concentrator after every ten to fifteen minutes during cooking as the sun moves away. The frame gives the stability and the support needed to hold the entire concentrator. Design of the Solar Cooker: The principal focal point of the system for solar collection is the parabolic mirror. This optical surface forms a point image on the optical axis and provides a maximum possible

International Journal of Research in Mechanical Engineering Volume-3, Issue-1, January-February, 2015, www.iaster.com ISSN

(O) 2347-5188 (P) 2347-8772

3

brightness of the solar image. The aperture of the solar concentrator is obtained to be 0.8m as reported by Sayigh; (1977)

21

4

aHHD

(1)

Where; H= Solar intensity within the suns image at the focus, Ha = Amount of solar radiation of the area under study (W/m2) Determination of the Maximum Concentration Ratio of the Solar Cooker: Concentration ratio is defined as the ratio of the area of the collector to that of the receiver, or the intensity of the solar radiation to that of the incident solar radiation (Magal, 1999).

2

2

2

2 161614

nnCm

(2)

Where; = reflectivity of the applied system Determination of the Internal Surface Area of the Paraboloid: The internal surface area of the paraboloid is determined, (Stroud, 1995).

dydydxA

y

yP

21

22

1

12

.. (3)

And for the equation of a parabola is given as yx 22 (4)

Determination of Focal Length of the Concentrator: The focal length of the concentrator is approximately 0.5m as sighted by Sayigh; (1977),

nDf (5)

Where; D= Aperture diameter of the concentrator (m) n=Aperture ratio 3. CONSTRUCTION MATERIALS AND PROCEDURE Materials: The concentrator of the paraboloid mirror consist of mild steel rods, sheet metals and segments of back silvered mirror used to form the reflecting surface. The frame was made of angle iron and the absorber which is the oven, is made of aluminium sheet and glass; the entire structure can be moved around with the help of four wheels, two drivers and two followers. A square pipe is used as the adjuster and a mild steel rod is used to hold the concentrator on the frame. Parabolic Concentrator; A circular ring was formed using one length of square pipes. The ring is 1m in diameter after welding the edges. Three length of square pipes were bent into the required parabolic shape using a parabolic path constructed on steel plate with studs along the curve. Plane mirrors were cut into small square and V- shapes. These small mirrors were glued to the internal surface of the paraboloid using adhesive glue with the larger mirrors at the periphery and the small one extending to the apex.

International Journal of Research in Mechanical Engineering Volume-3, Issue-1, January-February, 2015, www.iaster.com ISSN

(O) 2347-5188 (P) 2347-8772

4

Absorber Unit; the oven in this case is the absorber, it is made of aluminium box with glazed base, it was formed by riveting the sheets together and the entire aluminium sheet is painted with black paint to enhance absorption of the solar radiation, the combination of the black colour and glass base enhances heat generation due to black body radiation and green house effect. The pot used is also painted black and the ovens interior was packed with few materials to help conserve heat generation. See figure. 2. Supporting Frame; the entire frame is made from angle iron, the concentrator and the cooking oven are positioned symmetrical to it. It is also wheeled for easy transportation to and from cooking area back to its storage, while the concentrator is hung to swing to allow adjustment to go in pace with the sun, the oven is permanent on its position above the concentrator supported by the upper part of the frame.

Cost of Manufacture and Materials

Materials Quantity Unit cost =N= Total cost

=N= Sheet metal, 0.5 mm thickness Angle iron 0.2 x 2 cm Plane mirrors 0.4 x 1.2 m Cedar Gum Square pipe Mild steel rod of 10 mm diameter Flat bar Black Paint Blue Paint Welding electrodes Wheels Oven Labour Cost

One sheet Three lengths of 4m 2 1 tin 6m, 2 length 0.5m length 1 length Litre

Litre 15 piece 4 sheet --

3,000.00 1,550:00

700:00 500:00 700:00 300:00 650:00 200:00 400:00

20:00 500:00 500:00

2,000:00

3,000.00 6,200:00 1,750:00

500:00 1,400:00

300:00 650:00 200:00 400:00 300:00

2,000:00 500:00

2,000:00 TOTAL 19,200:00

Testing; After constructing the solar cooker, it is put to test by cooking the following food items, 0.4 kg of yam, 0.35kg, 0.65 kg of rice and boiling 0.15 kg of water. The test was conducted at University of Maiduguri Mechanical Teaching workshop, this test was conducted in the month of November. Results of the test are shown in table 1. 4. RESULTS

Table 1

Item Rice1 0.35kg Rice2

0.65kg Water 0.15kg

Yam 0.4 kg

Oven 2kg

Q(kJ) Glass, Mirror 133.788 196.75 154.186 115.428 84.364 1 (oC) 27 26 42 27 34 2 (oC) 82 61 74 80 80 T (Min) 80 150 30 46 30 C (kJ/kgK) 3.35 3.35 4.2 3.84 917

International Journal of Research in Mechanical Engineering Volume-3, Issue-1, January-February, 2015, www.iaster.com ISSN

(O) 2347-5188 (P) 2347-8772

5

5. CONCLUSION

The aim and objective of this work has been achieved, which is to reduce the cooking time (day long) to an average of one and half to two hours for a cooking session (Table, 1). Since the experiment was conducted during hazy periods (November), it is believed that the efficiency will increase during dry season (February to June), which means shorter cooking time. The average wind speed of Maiduguri is 3m/s (Ngala et al, 2004), wind speed affects the efficiency of solar cooker, higher efficiency is observed on a calm day. The problem of cutting down of trees will be reduced, if government could adopt and encourage the use of renewable energy and hence sustainable environmental development. The cost of the prototype production is just below =N=20,000:00 and surely the cost will drop for mass production. REFERENCES [1] Abdulrahim, A.T. Ngala, G.M. and Mshelia, A.B. (2004), Performance Evaluation of An Improved

Abiola Saw Dust Cooking Stove, Faculty of Engineering Seminar Series, University of Maiduguri, Nigeria, Vol. 3 No 1, pp 58 62.

[2] Bala, E.J., Ojosu, J.O. and Umar, I. H. (2000). Government Policies and Programmes on the

Development of Solar-PV Sub-sector in Nigeria. Nigerian Journal of Renewable Energy, Vol. 8, No. 1&2, pp. 1-6.

[3] Bowman, T.E. (1985), Understanding Solar Oven and Cookers, Understanding Technology

Services, Technical Paper, No. 36, Florida, pp120-123. [4] Dahiru, D.Y. Malachy, S and Asera, A.A. (2007), The Development of Concentrating Solar Energy

Cooker Under Hazy Weather Condition, Journal of Scientific and Industrial Studies, Duncan Science Company, Vol.5 No. 2, pp25 29.

[5] K.A. Stroud,(1995), Engineering Mathematics, Fourth Edition, Macmillan Press Limited, UK. [6] Magal, B.S. (1999), Solar Power Engineering, Tata-McGraw Hill Publishing Company Ltd. New Delhi, pp 18. [7] Ngala, G.M., Liman, B.S. and Abdulrahim, A.T.(2004), An Assessment of Wind Energy Potential

of Borno state, Nigeria, Journal of Life and Environmental Sciences, Volume 6 No.1, PP 381-386. [8] Pelemo, D.A.,Fassi, M.K., Owolabi, S.A.,and Shaniyi, J.A; (2002), Effective Utilization of Solar

Energy for Cooking, Nigerian Journal of Engineering Management, Vol. 3 No. 1, pp 13 18. [9] Sayigh, A.A.M. (1977), Solar Energy Engineering, Academic Press Publishing Co. London, pp 242

262.

International Journal of Research in Mechanical Engineering Volume-3, Issue-1, January-February, 2015, www.iaster.com ISSN

(O) 2347-5188 (P) 2347-8772

6

APPENDIX Fig.1 Assembled Picture of Complete Cooker with Oven

Figure 2. Solar Cooker Showing the Pot Inside the Oven

International Journal of Research in Mechanical Engineering Volume-3, Issue-1, January-February, 2015, www.iaster.com ISSN

(O) 2347-5188 (P) 2347-8772

7

Figure. 3 Sources: Department of Meotrological Services, Federal Ministry of Aviation

Figure.4 Sources: Department of Meotrological Services, Federal Ministry of Aviation

Figure.5 Sources: Department of Meotrological Services, Federal Ministry of Aviation