Solar energy is an alternative source of nonrenewable energy in Oman. Sultanate of Oman government showed initiation into utilization of solar energy for domestic applications. Conversion of solar radiation into useful heat is the simplest application of solar energy, in which it can be used for late evening cooking. In this context, present work highlighted the design and development of solar cooker for Oman climatic conditions. The current work signifies usage of solar cooker for late evening cooking using stearic acid and acetanilide as phase change materials (PCM). Solar cooker parts are developed in-house and connected to water heating system compounded with evacuated tubes solar collector and storage tank. The circumference of cooker unit is incorporated with spiral stainless steel heat exchanger and annulus area of the pot is filled with PCM material. PCM releases heat at late evening and effective cooking up to 7:30 PM is noticed. The experimental results indicated the cooker efficiency of 30% and collector efficiency of 60–65% during the study. Overall, experiments showed satisfactory performance on the developed cooker.
According to statistics, 50% of the commercial sources of energy like petrol, gas, and electricity are used in our daily consumption. Humans should take advantage of other sources of energy; renewable energy is one of the alternative available energy sources. It is also essential to encourage the community to start using alternative energy sources for the sake of cleaner environment. Solar cooker is now an invention that uses solar energy for late evening cooking.
In the late 1950s, the scientist Maria Telkes was the person who worked on box type solar cooker. Later, the mid of the 20th century showed a number of individuals and groups experimenting projects on solar cookers. The technical concept of solar cooker can be evaluated by thermal storage potential and energy is stored by raising the temperature of a storage medium; therefore, phase change materials (PCM) play important role in the present scenario. These materials have the ability to store large amounts of thermal energy under isothermal conditions, which means they can deliver or store energy at constant temperature and excrete the heat whenever there is a difference in the degree of the temperature.
Sharma et al. [
With this thought, present work signifies the design, development, and comparison of the performance of the solar cooker using stearic acid and acetanilide as phase change materials for Oman conditions. Thermal calculations are made for evacuated tube collector, PCM storage system, and studying the performance at different loadings.
The placement of earth’s orbit around the sun is such that sun-earth distance varies by 1.7 percent and solar radiation outside the earth’s atmosphere is nearly of fixed intensity; the radiant energy flux received per second by a surface of unit area held normal to the direction of sun’s rays at the mean earth-sun distance is constant throughout the year. This is called as solar constant,
Normally, evacuated tube collector with heat pipe consists of a metal fin and is used for maximum heat transfer from absorbed solar energy at the absorber. The evaporator is exposed to solar radiation and condenser is attached with tube in configuration plate. The working fluid flows through tube flat plate of condenser.
A schematic view of an evacuated tube collector with heat pipe and the condenser is shown in Figure
Schematic diagram of evacuated tube collector [
Under steady condition, the rate of useful energy available with evacuated tube solar collector can be represented by the equation
The thermal efficiency of collector is calculated from
Phase change materials are latent heat storage materials and energy release occurs when a material changes its phase from solid to liquid or vice versa. In general, they absorb and release heat at constant temperature and can store more heat per unit volume than sensible heat storage materials. Fatty acids have high heat of fusion values comparable to that of paraffin’s and their major drawback is 2–2.5 times costlier than paraffin’s. In the current work stearic acid and acetanilide is used as PCM.
Similarly, acetanilide is a solid chemical used to store the thermal heat energy in the form of latent heat. It is also known as N-phenylacetamide, acetanil, and acetanilide. Table
Thermophysical properties of the phase change materials.
Name | Stearic acid | Acetanilide |
---|---|---|
Chemical structure | C17H35CO2H | C8H9NO |
Molecular weight, g/mol | 284.4772 | 135.17 |
Melting point, °C | 69.5 | 114–116 |
Heat of fusion, J/g | 192.09 | 162.90 |
Density, kg/m3 | 847 | 1219 |
Enthalpy curves of phase change materials. Orange, blue, and purple lines in Figure
Stearic acid [
Acetanilide [
Before starting the experiment, solar intensity calculation has been carried out to determine intensity of solar radiation in Oman. The study highlighted that the solar intensity in the summer period is nearer to 1000 W/m2 in Oman.
Solar intensity data (dated: May 9, 2016).
Similarly, from theoretical relations, the parameters like useful energy, final temperature of water, and efficiency of evacuated tube solar collector are calculated. Refer to Table
Thermal analysis results for evacuated tube solar collector.
Parameter | Values |
---|---|
Useful energy, W | 90.474 |
Final temperature of water, °C | 134.4 |
Efficiency of evacuated tube solar collector, % | 63.4 |
Specification of evacuated tube solar collector.
Item | Specification |
---|---|
Number of collector tubes | 10 tubes |
Outer diameter of the collector tube | 58 mm |
Tube length | 500 mm |
Total area of evacuated tube | 84 cm × 58 cm, 58 cm height |
Figure
Assembly of evacuated tube solar water heater.
In the present work, a storage unit is provided with two hollow concentric aluminum cylinders; its inner and outer diameters are 250 mm and 350 mm, respectively, and 300 mm deep. The space between the inner diameter and outer diameter is filled with PCM materials; see Figure
In-house developed parts of solar cooker.
PCM storage unit
Stainless steel heat exchanger
Complete setup of solar cooker.
The late evening cooking of rice.
In addition, other parameters like water outlet and PCM storage temperatures are recorded at regular intervals. In addition, solar cooker is studied for different loadings of water in the vessel. Figure
Variation of PCM temperature at different loadings in the vessel.
1 kg water in the vessel
2 kg water in the vessel
3 kg water in the vessel
Variation of water outlet temperature.
From the test results, it is observed that, until 3 PM, the temperature of PCM material is lower than water outlet temperature. However, in late evening, water temperature drops substantially as compared to PCM temperature. It is due to the fact that heat content of PCM is high, so fewer drops are noticed in the evening and this helped to cook the rice effectively.
Observed values of heat gained by water and heat stored by PCM.
Date | Load, kg | Max. solar intensity W/m2 | Acetanilide | Stearic acid | ||||||
---|---|---|---|---|---|---|---|---|---|---|
| | | | | | | | |||
| 1 | 900 | 1.99 | 4.03 | 63 | 31 | — | — | — | — |
| 2 | 938 | 2.02 | 4.12 | 65 | 31 | — | — | — | — |
| 3 | 890 | 1.99 | 2.66 | 63 | 31 | — | — | — | — |
| 1 | 895 | — | — | — | — | 1.57 | 4.03 | 64 | 25 |
| 2 | 906 | — | — | — | — | 1.60 | 4.21 | 65 | 25 |
| 3 | 885 | — | — | — | — | 1.55 | 3.67 | 60 | 25 |
In the present study, thermal performance of a solar cooker coupled with PCM heat storage unit and evacuated tube solar collector is studied for Oman conditions. A simple cylindrical PCM heat storage unit is designed to store solar energy during sunshine hours and to cook food in the late evening. The experiment results from the present setup drives the following conclusions. The solar cooker system is able to cook successfully in evening time up to 7:30 PM by providing PCM storage unit, and PCM material temperature reached more than 120°C at 3 PM, which is sufficient to cook the food in the evening time. The study results indicated that acetanilide would be better than stearic acid from the performance point of view. During the experiment, collector efficiency of 60~65% and cooker efficiency of 30% are noticed with acetanilide as PCM. Overall, the present study showed satisfactory performance under Oman conditions.
The authors declare that they have no competing interests.