Experimental investigation of a solar cooker based on

Experimental investigation of a solar cooker based on parabolic dish collector with phase change thermal storage unit in Indian climatic conditions Avinash Chaudhary, Amit Kumar, and Avadhesh Yadav Citation: J. Renewable Sustainable Energy 5, 023107 (2013); doi: 10.1063/1.4794962 View online: http://dx.doi.org/10.1063/1.4794962 View Table of Contents: http://jrse.aip.org/resource/1/JRSEBH/v5/i2 Published by the American Institute of Physics.

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JOURNAL OF RENEWABLE AND SUSTAINABLE ENERGY 5, 023107 (2013)

Experimental investigation of a solar cooker based on parabolic dish collector with phase change thermal storage unit in Indian climatic conditions Avinash Chaudhary,a) Amit Kumar, and Avadhesh Yadav Department of Mechanical Engineering, National Institute of Technology, Kurukshetra, Haryana 136119, India (Received 10 November 2012; accepted 22 February 2013; published online 7 March 2013)

Solar cooker based on parabolic dish collector with phase change thermal storage unit was investigated. In this experimental setup, solar cooker with phase change thermal storage unit was kept on absorber plate of parabolic dish collector. During day time, acetanilide (phase change material) stores solar heat and during evening, solar cooker is kept in the insulator box. Then, the phase change material delivers heat to the food. To enhance the performance of solar cooker, three cases have been considered: ordinary solar cooker, solar cooker with outer surface painted black, and solar cooker with outer surface painted black along with glazing. It was observed that solar cooker with outer surface painted black along with glazing performs better as compared to other cases. Also phase change material (PCM) in solar cooker with outer surface painted black stored 26.8% more heat as compared to PCM in ordinary solar cooker, whereas PCM in solar cooker with outer surface painted black along with glazing stored 32.3% more heat as compared to PCM in ordinary solar cooker. C 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4794962] V

I. INTRODUCTION

Wood, agriculture wastes, animal dung cake are the main energy sources for cooking in rural areas of India while in urban areas the main energy sources are kerosene and liquid petroleum gas (LPG). The cutting of firewood causes deforestation that leads to desertification and use of animal dung cakes pollute the environment. Also, the continuous increase in fuel price indicates that there is an urgent need to utilize the various sources of renewable energy in an effective way for cooking purpose. Fortunately, India is blessed with ample amount of solar radiation. Hence, solar cookers have good potential in India. A limitation of solar cookers is that cooking can only be done during sunshine hours. If solar cookers are provided with heat storing medium, then there is possibility of cooking food during off sunshine hours also. The different types of solar cookers used for cooking are: box type, concentrator type, and indirect type. Domanski et al.1 investigated experimentally the possibility of cooking during off sunshine hours using phase change material as storage media. They tested a solar cooker made from two concentric cylindrical vessels with the gap filled with stearic acid or magnesium nitrate hexahydrate phase change material (PCM). Solar simulator was used to provide the desired solar radiations and they found that the parameters such as solar intensity, mass of cooking medium, and the thermophysical properties of the PCM have a strong effect on cooker performance. Buddhi and Sahoo2 designed and fabricated a box type solar cooker with latent heat storage for use in climate conditions of India and also compared the experimental results with those of conventional solar cooker. They suggested that late evening cooking is possible with a solar cooker having thermal storage unit. Sharma et al.3 designed and developed a cylindrical PCM storage unit for a solar cooker and they compared the performance of this solar cooker with a standard

a)

Author to whom correspondence should be addressed. Electronic mail: [email protected].

1941-7012/2013/5(2)/023107/13/$30.00

5, 023107-1

C 2013 American Institute of Physics V

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Chaudhary, Kumar, and Yadav

J. Renewable Sustainable Energy 5, 023107 (2013)

solar cooker. They used commercial grade acetamide as PCM. The experimental results showed that the melting temperature of PCM should be in the range of 105 to 110 C for evening cooking. Buddhi et al.4 designed and developed a PCM storage unit for a box type solar cooker having three reflectors to store energy during sunshine hours and to cook the food during the evening time in winter season. They used commercial grade acetanilide (melting point 118.9 C, latent heat of fusion 222 kJ/kg) as a latent heat storage material. The experimental results demonstrated that late evening cooking is possible in a solar cooker with reflectors and latent heat storage unit. Schwarzer and Silva5 developed a solar cooking system based on flat plate collector with or without heat storage and installed in different countries of the world, they concluded interesting features such as possibility of indoor and night cooking, heat flow control in the pots, modularity, and the possibility of further adjustments to incorporate a baking oven. Sharma et al.6 investigated the thermal performance of a prototype solar cooker based on an evacuated tube solar collector with PCM storage unit. The results demonstrated that by using erythritol as a PCM, its temperature of up to 130 C is achieved which was sufficient to cook food during late evening. Mettawee and Assassa7 experimentally investigated the performance of a compact PCM solar collector. They use paraffin wax as a PCM to store solar energy, which was discharged to cold water flowing in pipes located inside the wax. The results showed that during the charging process, with increase in molten layer thickness, the average heat transfer coefficient increases sharply as the natural convection grows strong and in the discharging process, the useful heat gain was found to increase as the water mass flow rate increases. Nallusamy et al.8 experimentally investigated a thermal energy system (TES) and integrated with constant/varying temperature source. Paraffin filled spherical capsules were filled in insulated cylindrical storage unit of TES. Charging experiments were carried out at constant and varying solar energy and effect of flow rate of inlet fluid temperature on the thermal performance of TES was examined. They also carried out discharging experiments to recover the stored heat. They concluded that at a constant inlet fluid temperature, mass flow rate has a small effect on the rate of charging and with increase in inlet temperature of heat transfer fluid, rate of heat transfer increases in direct proportion. Hussein et al.9 experimentally investigated a novel indirect solar cooker based on flat plate solar collector and having PCM thermal storage and cooking unit. Solar cooker was of elliptical cross section and wickless heat pipes were used. Magnesium nitrate hexa-hydrate having melting temperature 89 C and latent heat of fusion, 134 kJ/kg, was used as PCM. Experiments were conducted on the solar cooker without load and with load at different times and the results showed the feasibility of elliptical cross section, wickless heat pipes, and PCM in indirect solar cooker for use in evening cooking and to warm the food during off sunshine hours. Sharma et al.10 summarized the available thermal energy storage systems incorporating PCMs for use in heat storage applications and analyzed the thermal properties of various PCMs. Agyenim et al.11 examined the geometry and configurations of PCM containers and a series of numerical and experimental tests were performed. They concluded that most of the phase change problems carried out at temperature ranges between 0 C and 60 C are suitable for domestic heating applications. El-Sebaii et al.12 experimentally investigated the influences of melting/solidification fast cycling of magnesium chloride hexahydrate on its thermophysical properties; such as melting point and latent heat of fusion and found that magnesium chloride hexahydrate (MgCl2.6H2O) is a promising phase change material for cooking indoors and during low intensity solar radiation periods when it is cycled under extra water principle in a sealed container. Foong et al.13 investigated a small scale double reflector solar concentrating system with high temperature heat storage medium (NaNO3 and KNO3) and a finite element model was used to numerically analyze the latent heat storage unit. The experimental results demonstrated that the melting of phase change material occurred in 2–2.5 h and reached a temperature range of 230–260 C, suitable for cooking and baking purposes. Saxena et al.14 suggested that PCM is the best option to store the solar energy during day time and can be used for cooking in late evening/night. Many researchers have worked on solar cooker based on evacuated tube solar collector, flat plate collector with phase change thermal storage unit but none of them worked on solar cooker based on parabolic dish collector with acetanilide as the PCM in Indian climatic conditions. The objective of this paper is to study the thermal performance enhancements of a solar cooker based

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FIG. 1. Photograph of the experimental setup.

on parabolic dish collector with phase change thermal storage unit. The experimental setup is installed at NIT Kurukshetra, India (29 580 (latitude) North and 76 530 (longitude) East). II. EXPERIMENTAL SETUP

The experiment was performed to investigate the thermal performance of solar cooker with phase change thermal storage unit. The test section of solar cooker is based on parabolic dish collector. This system consists of parabolic dish collector, solar cooker, and insulator box as shown in Figure 1. Acetanilide is used as a phase change material and it is filled in between the hollow space of inner and outer wall of solar cooker. The experimental setup consists of following components: • • • •

Parabolic solar dish collector Solar cooker Phase change material Insulator box

A. Parabolic solar dish collector

The parabolic dish collector as shown in Figure 2 refers to a point focusing device which includes the concentrator and the absorber. In this system, 40 segments of the anodized aluminium are joined to form the concentrator. A flat surface works as the absorber which absorbs the solar energy concentrated on a point. The outer ring frame of the parabolic dish collector is made of the mild steel circular channel. The tracking of parabolic dish collector is done manually and for that

FIG. 2. Schematic diagram of parabolic solar dish collector.

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TABLE I. Specifications of the parabolic dish collector. Diameter of outer ring

1.4 m

Focal length of dish

0.2 m

Dish rim angle Aperture area of dish

120.5 1.539 m2

Concentration ratio of dish

33

tracking screw is provided at the top of outer ring. The parabolic dish collector is adjusted in such a way that the shadow of tracking screw does not visible. After setting this position, the parabolic dish collector is locked in that position by the holding screw provided at the bottom of tracking screw. A wheel is provided at the bottom of parabolic dish so that the dish can be tracked with the movement of sun. Specifications of the parabolic dish collector are shown in Table I. B. Solar cooker

Solar cooker as shown in Figure 3 is made up of two hollow concentric cylinders of aluminium. Its inner and outer diameters are 0.20 m and 0.245 m, respectively, and are 0.24 m deep and 0.0225 m thick. The hollow space between the cylinders is filled with 2.5 kg of commercial grade acetanilide having melting point 118.9 C and latent heat of fusion 222 kJ/kg. Enough space is left in the solar cooker to allow the volumetric expansion of PCM. C. Phase change material

The selection of phase change material depends upon its properties such as melting temperature, latent heat of fusion, toxicity, etc. In this paper, the phase change material used is commercial grade acetanilide with its thermophysical properties given in Table II. D. Insulator box

A box made up of wood is used for insulation. Its dimension (l b h) are 0.375 m, 0.375 m, and 0.35 m, respectively, as shown in Figure 4. The box is filled with glasswool for better insulation and in the centre of box a space of diameter 0.26 m is provided for placing solar cooker. The bottom side of space is also filled with thermocoal. The cover of insulator box is made up of GI sheet with thermocoal sheet at inside surface. III. MEASURING DEVICES AND INSTRUMENTS

Different parameters are measured, these are: •

Outer surface temperature of solar cooker, inner surface temperature of solar cooker, PCM temperature, and cooking medium temperature

FIG. 3. (a) Schematic diagram of front view of solar cooker. (b) Photograph of solar cooker.

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TABLE II. Thermophysical properties of commercial grade acetanilide. Melting temperature of acetanilide (commercial grade)

• •

118.9 C

Latent heat of fusion of acetanilide (commercial grade)

222 kJ/kg

Specific heat of acetanilide

2 kJ/kg C

Ambient temperature Solar radiation intensity

Outer surface temperature of solar cooker, inner surface temperature of solar cooker, PCM temperature, and cooking medium temperature are measured with RTD PT100 thermocouples which are connected with a digital temperature indicator that shows the temperature with a resolution of 0.1 C. Dry bulb temperature of ambient air was measured with a handheld digital hygrothermometer (model RHT-200 C, Elinco Innovations, India) with a high-accuracy probe that had a temperature range from 10 to 60 C. The humidity multimeter measured the temperature with a resolution of 0.1 C and accuracy 60.3 C. The solar radiation intensity is measured during the day time with a Pyranometer-model CM11, supplied by Kipp and Zonen, Holland. During charging and discharging periods, the experimental data is recorded at an interval of 30 min. The experiments were carried out in mostly clear sky days in the month of October 2012. IV. SYSTEM OPERATION

In the experimental setup, acetanilide as phase change material is filled in between the hollow space of inner and outer wall of solar cooker and thermocouples are used for measuring the outer surface temperature of solar cooker, inner surface temperature of solar cooker, PCM temperature, and cooking medium temperature. Initially, at the start of the experiment, PCM was at ambient temperature (31–34 C). Solar cooker is placed on the absorbing plate of dish collector and the system is exposed to solar radiation. Solar radiations as well as various temperatures are measured from 9 am to 4 pm, at an interval of 30 min. The dish collector is tracked manually in every 15 min with the movement of sun. After 4 pm, the solar cooker is lifted from the dish collector with the help of handle and placed in the insulator box and readings are taken without load. Next day, for the same case, readings are taken with load in which water is used as cooking medium. Two liters of water having temperature 30 C is poured in the solar cooker. A thermocouple is hanged in the water to measure its temperature during discharging process of PCM. The insulator box is then covered with lid and temperatures are measured at an interval of 30 min, from 4 pm to late night.

FIG. 4. (a) Schematic diagram of insulator box. (b) Photograph of insulator box.

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Three cases are considered to enhance the thermal performance of solar cooker and for each case; the readings are taken for two days, i.e., without cooking load and with cooking load. • • •

Ordinary solar cooker Solar cooker with outer surface painted black Solar cooker with outer surface painted black along with glazing.

A. Ordinary solar cooker

The photograph of ordinary solar cooker is shown in Figure 5(a). A handle is provided at the solar cooker so that it can be lifted properly from the collector for placing in the insulator box. B. Solar cooker with outer surface painted black

The photograph of solar cooker with outer surface painted black is shown in Figure 5(b). In this type, outer surface of solar cooker is painted black for maximum absorption of solar radiation. C. Solar cooker with outer surface painted black along with glazing

The photograph of solar cooker with outer surface painted black along with glazing is shown in Figure 5(c). In this type, a glazing of acrylic sheet of dimension 0.30 m 0.28 m 0.30 m (l b h) is placed on to solar cooker to minimize the convection losses. V. ANALYSIS OF EXPERIMENTAL DATA

Heat stored by the PCM is given by Sharma et al.,3 QPCM ¼ mPCM ½CPCM ðTm Ti Þ þ L þ CPCM ðTPCM; max Tm Þ: It is assumed that specific heat for solid and liquid phase of PCM is same. VI. EXPERIMENTAL RESULTS AND DISCUSSION

In the experimental setup, cooking experiments were conducted using a solar cooker based on parabolic dish collector with thermal storage unit. The readings were taken for without cooking load and with cooking load on October 1 to October 7, 2012. Three cases are considered and the various results are obtained: Case 1: Ordinary solar cooker (a)

Ordinary solar cooker without cooking load; October 1, 2012: Figure 6 shows that as the solar intensity increases, outer surface temperature of solar cooker, inner surface temperature of solar cooker, PCM temperature increases reaching to a

FIG. 5. Photograph of (a) ordinary solar cooker, (b) solar cooker with outer surface painted black, (c) solar cooker with outer surface painted black along with glazing.

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FIG. 6. Variation of temperature and solar radiation intensity with time in case of ordinary solar cooker; without cooking load.

(b)

maximum value of 145.9 C at 13:30 h, 122.4 C at 14:00 h, and 119 C at 14:00 h, respectively. During the day, maximum solar intensity is 927 W/m2 at 11:30 h and the ambient temperature lies in the range of 28.1 C to 35.8 C. During discharging period of PCM, PCM temperature decreases from 110.8 C to 63.7 C in a duration of 4 h, i.e., from 16:00 h to 20:00 h. Ordinary solar cooker with cooking load; October 2, 2012 Figure 7 shows that with increase in solar intensity, outer surface temperature of solar cooker, inner surface temperature of solar cooker, PCM temperature increases reaching to a maximum value of 92.2 C at 10:30 h, 108 C at 11:30 h, and 108.2 C at 11:00 h, respectively. Due to a little bit cloudy day, the maximum temperature achieved in this case is less than the case of without loading. Maximum solar intensity is 896 W/m2 at 12:00 h and the ambient temperature lies in the range of 28.2 C to 34.2 C. During discharging period, 2 l of

FIG. 7. Variation of temperature and solar radiation intensity with time in case of ordinary solar cooker; with cooking load.

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water at temperature of 30 C is poured in the solar cooker and the solar cooker is placed in insulator box. In the first half hour of discharging process, PCM temperature decreases at a faster rate and then decrease slowly to 43.7 C till 20:00 h while the cooking medium temperature initially increases at a faster rate reaching to a maximum value of 52.2 C and then decreases slowly to 45.7 C till 20:00 h. Case 2: Solar cooker with outer surface painted black (a)

(b)

Solar cooker with outer surface painted black; without cooking load; October 4, 2012 Figure 8 shows that as the intensity increases, outer surface temperature of solar cooker, inner surface temperature of solar cooker, PCM temperature increases reaching to a maximum value of 165.6 C at 15:00 h, 151.5 C at 15:00 h, and 151.4 C at 11:30 h, respectively. During the day, maximum solar intensity is 933 W/m2 at 14:00 h and the ambient temperature lies in the range of 28.4 C to 35 C. Compared to the case of ordinary solar cooker, in this case, melting temperature of PCM is achieved at 10:30 h, i.e., in 1.5 h of start of experiment. During discharging period of PCM, PCM temperature decreases from 141 C to 64 C in a duration of 5.5 h, i.e., from 16:00 h to 21:30 h. In this case, PCM temperature at 21:30 h is 64 C which is more than the temperature achieved in case of ordinary solar cooker; without cooking load in which PCM temperature was 63.7 C at 20:00 h. Solar cooker with outer surface painted black; with cooking load; October 5, 2012 Figure 9 shows that with increase in solar intensity, outer surface temperature of solar cooker, inner surface temperature of solar cooker, PCM temperature increases reaching to a maximum value of 159.5 C at 14:00 h, 168.3 C at 11:30 h, and 175.4 C at 11:30 h. Maximum solar intensity is 930 W/m2 at 12:00 h and the ambient temperature lies in the range of 27.2 C to 34.6 C. Melting temperature of PCM is achieved at 10:00 h, i.e., in 1 h of start of experiment. In the first half hour of discharging process, PCM temperature decreases at a faster rate and then decrease slowly to 50.1 C till 23:00 h while the cooking medium temperature initially increases at a faster rate reaching to a maximum value of 84.3 C and then decreases slowly to 51.9 C till 23:00 h. In this case, PCM temperature at 23:00 h is 50.1 C which is more than the temperature achieved in case of ordinary solar cooker; with cooking load in which PCM temperature was 45.7 C at 20:00 h.

FIG. 8. Variation of temperature and solar radiation intensity with time in case of solar cooker with outer surface painted black; without cooking load.

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FIG. 9. Variation of temperature and solar radiation intensity with time in case of solar cooker with outer surface painted black; with cooking load.

Case 3: Solar cooker with outer surface painted black along with glazing (a)

Solar cooker with outer surface painted black along with glazing; without cooking load; October 6, 2012 Figure 10 shows that, maximum temperature of outer surface of solar cooker, inner surface of solar cooker, PCM is 184.2 C at 11:00 h, 177.2 C at 14:00 h, and 179.5 C at 14:00 h, respectively. During the day, maximum solar intensity is 893 W/m2 at 13:00 h and the ambient temperature lies in the range of 28.1 C to 34.6 C. Compared to the case of solar cooker with outer surface painted black, in this case, melting temperature of PCM is achieved at 10:00 h, i.e., in 1 h of start of experiment. During discharging period of PCM, PCM temperature decreases from 163.8 C to 57.2 C in a duration of 6.5 h, i.e., from 16:00 h to 22:30 h. In this case, PCM temperature at 21:30 h is 67.1 C, which is more than

FIG. 10. Variation of temperature and solar radiation intensity with time in case of solar cooker with outer surface painted black along with glazing; without cooking load.

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FIG. 11. Variation of temperature and solar radiation intensity with time in case of solar cooker with outer surface painted black along with glazing; with cooking load.

(b)

the temperature achieved in case of solar cooker with outer surface painted black; without cooking load in which PCM temperature was 64 C at 21:30 h. Solar cooker with outer surface painted black along with glazing; with cooking load; October 7, 2012 Figure 11 shows that maximum temperature of outer surface of solar cooker, inner surface of solar cooker, PCM is 196.1 C at 14:00 h, 185.6 C at 11:30 h, and 186.3 C at 11:30 h, respectively. Maximum solar intensity is 912 W/m2 at 12:00 h and the ambient temperature lies in the range of 27 C to 34.5 C. Melting temperature of PCM is achieved at 9:30 h, i.e., in 0.5 h of start of experiment. In the first half hour of discharging process, PCM temperature decreases at a faster rate and then decrease slowly to 53.5 C till 23:00 h while the cooking medium temperature initially increases at a faster rate reaching to a maximum value of 88.4 C and then decreases slowly to 55.3 C till 23:00 h. In this case, PCM temperature at 23:00 h is 53.5 C, which is more than the temperature achieved in case of solar cooker with outer surface painted black; with cooking load in which PCM temperature was 50.1 C at 23:00 h.

VII. ESTIMATION OF COSTS AND BENEFITS OF SOLAR COOKER

The use of a solar cooker depends on its cost effectiveness. In financial terms, investment is made towards the cost of solar cooker to reduce the bill on conventional fuels. The return on investment depends upon the saving in conventional fuels. The economics of solar cooker can be looked at different angles: 1. With an increase in cost of conventional fuels and due to their shortage; there is an urgent need to utilize the source of renewable energy like solar energy for cooking purpose. 2. Solar cooking is pollution free and it preserves the nutrition value of food. In the following sections, the costs associated with solar cooker and benefits of solar cooker are discussed: A. Total cost

Total cost of the system consists of: 1. The cost of solar cooker including sub components if any.

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TABLE III. Cost analysis for solar cooker with thermal storage unit. Components Parabolic solar dish collector

Specification Outer ring frame material—mild steel

Cost (Rs.) 2500

Concentrator material—anodized aluminium Segments of anodized aluminium 40 Manual tracking Focal length 0.2 m Dish rim angle 120.5 Aperture area of dish 1.539 m2 Concentration ratio of dish 33 Acetanilide (PCM)

Melting point of acetanilide (commercial grade) 118.9 C

2.5 720 ¼ 1800

Latent heat of fusion of acetanilide (commercial grade) 222 kJ/kg Specific heat of acetanilide 2 kJ/kg C Quantity of PCM used 2.5 kg Solar cooker

Material—aluminium Inner diameter 0.20 m

500

Outer diameter 0.245 m Depth 0.24 m Thickness 0.0225 m Paint

Manufacturer Asian paints

70

Dark black colour Quantity used 100 ml Insulator

Box material wood Cover material of insulator box GI sheet

350

Dimension 0.375 m 0.375 m 0.35 m (lbh) Insulation glasswool Glazing

Material acrylic sheet

400

Dimension 0.30 m 0.28 m 0.30 m (l b h)

2. Cost of components provided on subsidy basis/ loan basis by various agencies like Indian renewable energy development agency limited (IREDA). 3. If the system has parts which undergo wear and tear, then maintenance cost must be added to the total cost. B. Costs and benefits

The economic benefit of solar cooker is obviously the money saved each month on conventional fuels. Cooking based on LPG is costly, as 1 LPG cylinder costs around Rs. 920. Electricity can be used for cooking as in induction cooker, but in India mainly electricity comes from thermal power plant where coal is used and coal is considered as non renewable resource. Moreover, induction based cooking depends upon the domestic electricity tariff which varies from state to state. Thus solar cooker is a viable option in terms of cost saving. C. Payback period

Payback period represents the amount of time that it takes for a system to recover its total cost. The concept of payback period emphasizes the need to install such systems that provide a reasonable return on the investment made. Payback period (days) ¼ Total cost/saving per day.

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Payback period depends upon: 1. 2. 3. 4.

Type of the solar cooker installed. Mode of payment—self financing or loan through agencies like IREDA. Interest payable on investments made and loan availed. Tax benefits.

D. Cost analysis

The capital outlay for the installation of solar cooker with thermal storage unit is shown in Table III. Total cost of experimental setup Rs. 5620. Unsubsidized cost of 1 LPG cylinder Rs. 920. Average running period of 1 LPG cylinder for a family of 3 member 45 days. Cost per day for cooking considering 1 LPG cylinder ¼ 920/45 ¼ Rs 20.44. If solar cooking with PCM storage unit is used for cooking food, then saving per day for cooking ¼ Rs 20.44. Payback period ¼ Total cost/saving per day ¼ 5620/20.44 ¼ 274.9 days ¼ 9 months. VIII. CONCLUSIONS

1. The maximum temperature of PCM achieved in case of ordinary solar cooker, solar cooker with outer surface painted black, solar cooker with outer surface painted black along with glazing is 119 C, 175.4 C, and 186.3 C, respectively. 2. The melting temperature of PCM achieved in case of ordinary solar cooker, solar cooker with outer surface painted black, solar cooker with outer surface painted black along with glazing is at 14:00 h, 10:00 h, and 9:30 h. 3. During discharging process of PCM, the maximum temperature of cooking medium achieved in case of ordinary solar cooker, solar cooker with outer surface painted black, solar cooker with outer surface painted black along with glazing is 52.2 C, 84.3 C, and 88.4 C, respectively. 4. PCM in solar cooker with outer surface painted black stored 26.8% more heat as compared to PCM in ordinary solar cooker whereas PCM in solar cooker with outer surface painted black along with glazing stored 32.3% more heat as compared to PCM in ordinary solar cooker. 5. The above results show the feasibility of solar cooker based on parabolic dish collector with thermal storage unit for late evening cooking in Indian climatic conditions. NOMENCLATURE

QPCM mPCM CPCM Tm Ti L TPCM;max

1

heat stored by PCM, kJ mass of PCM, kg specific heat of PCM, kJ/kg C melting temperature of PCM, C initial temperature of PCM, C latent heat of fusion, kJ/kg maximum temperature of PCM, C

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