Principles of Transport Processes

Portable Soda Cans Solar Air HeaterJonnabelle A. ValenciaDepartment of Chemical Engineering College of Engineering, Bicol University, Legazpi City, Albay

A B S T R A C TThe fabrication of a portable solar air heater from recycled soda cans and its efficiency were discussed. The equipment enables undergraduate students to visualize, qualify, and quantify the transfer of heat from the sun to the equipment to heat the air coming in the material. The soda cans used were painted black and were assumed as a black body for maximum absorption of thermal radiation, therefore making the transfer of energy more effective. The solar air heater contains inlet and outlet wherein the air passed through the equipment. Through the experimental procedures done, the researcher acquired the ability to plan and execute a complex heat transfer operation. The process also helps to understand the principle of heat transfer, heat exchangers, and radiation. The study was made to prove the efficiency of the existing soda can solar air heater idea.Keywords: solar air heater, soda cans, heat transfer, thermal efficiency, solar radiation flux

1. IntroductionHeat transfer is a dominant aspect of the engineering world. It deals with the transport of energy from a high temperature region to a lower temperature region. The mode of transfer may be conduction, convection, or radiation. The principle of heat transfer is a great deal in the field of energy conservation as the world presently strives in looking for alternative energy sources to supply the worlds demand and to secure the futures generation. Chemical engineering students, as future chemical engineers, have the prime responsibility to seek for alternatives and fully understand the mechanism of transport processes, as one of the core courses in the chemical engineering field.

With the rapidly growing demand in energy, engineers nowadays, continue to find alternative energy sources and invent equipments that can efficiently convert abundant resources into energy reserves. And the understanding of the principle of heat transfer is a must. It is a challenge to develop equipments that shall efficiently convert other forms of energy (geothermal, hydro, wind, solar, etc.) into electricity and other useful renewable forms of energy.

In this paper, the author describes the process of constructing the solar air heater and the underlying principles incorporated in it as part of the requirement in the undergraduate Principles of Transport Processes course. The thermal efficiency of the equipment was also evaluated. Solar air heatingis a solar thermal technology in which the energy from the sun,solar insolation, is captured by an absorbing medium and used to heat air.1 It is considered as one of the most effective and economical source of renewable energy. Solar air heating is arenewable energyheating technology used to heat or condition air for buildings or process heat applications. It is typically the most cost-effective out of all the solar technologies, especially in commercial and industrial applications, and it addresses the largest usage of building energy in heating climates, which is space heating and industrial process heating.2 The equipment is existing and was inspired by Cansolair and wasinvented by a man from Newfoundland, Canada.3 A variety of applications can utilize solar air heat technologies to reduce thecarbon footprintfrom use of conventional heat sources, such asfossil fuels, to create a sustainable means to produce thermal energy. Applications such asspace heating, greenhouse season extension, pre-heating ventilation makeup air, orprocess heatcan be addressed by solar air heat devices.4

The air coming in the equipment was just heated and offered the idea of heat transfer. The incoming air is heated because of the difference in the temperature gradient between the air supplied and the heated soda cans. The thermal efficiency was computed by using the energy gain, the solar radiation flux and the area of the equipment used. The popularity of the effectiveness of the study awakened the engineering society and was tried and tested by several people because of its affordability and efficiency.

The idea that soda cans were treated as a black body also offers an understanding in the efficiency of the black body to absorb energy through radiation coming from the sun. Overall, the study provides an opportunity for the students to develop functioning, economic, and environmentally accepted process to convert the abundant solar energy into useful energy resource.

2. Experimental Details 2.1 Materials

The materials used in the study were as follows: black non-reflective spray paint, board, measuring meter or ruler, pencil, plywood, clear plastic, metal cutter, glue sticks, screws, screw driver, hammer, driller, tape, and 24 soda cans.

2.2 Equipment

The main equipment used in the study was thermometer. The device was used to measure the temperature of the incoming air and the outgoing air.

2.3 Preparation of the Soda Cans

Collect 24 soda cans. Make sure that they are in perfect condition, free from distortions and holes. Dry them and remove all the moisture content of the cans. Start making the holes on the top and bottom using the metal cutter. The hole in the top must be larger than the bottom. After cutting all the 24 cans, connect 3 soda cans on their ends using the glue stick. Wrap the ends of the connected cans with glue stick. Make sure that they are properly sealed and the air is not coming out of the connected ends. 8 columns will be assembled. Then, apply the black spray paint to the whole surface area to produce a pack of black soda cans.

2.4 Procedures

Prepare 2 boards with a length of 56.5 cm, 8.5 cm high and 1.5 cm wide. Once the cans and boards are prepared, place the cans side by side along the bottom board, leaving a small space between each can. Draw the outline of the cans on the bottom board to make the first manifold. Provide enough space from each edge to make sure that the board will not break when drilling the can-sized holes. These holes are needed as the pathway of the air travelling the equipment. While drilling, the holes on the frame can be made. The top and the bottom of the outermost casing must also be holed to serve as the vents of the equipment.

Create the frame of the box. Be sure to match the pattern left to right so that the can tubes line up and run straight within the 2 boards. Measure the frame to ensure that it will fit the 2 boards containing the soda cans painted black. The frame must be 59.5 cm long, 54 cm high, and must have a width of 8.5 cm. the bottom plywood that will contain the whole equipment must be attached to the frame. The plywood must have a dimension of 59.5 cm by 54 cm. Once framed, screw the plywood to the back of

Figure 1. Images of the Preparation of the Black Soda Cans a) Collection, b)Connecting the ends of the cans c) Spraying the black non-reflective paint in the 3 can array, d) Final output of the soda cans.

Firgure 3. Tracing and drilling the holes that will serve as vents.Figure 2 Cutting the board into the desired dimensions.

the frame and then, assemble. Paint the interior of the box with the black non-reflective spray paint. Be sure to leave enough space at the top and the bottom of the box to create an air chamber. The space must be 10 cm from the top and bottom. Figure 4 Fitting the arrays of cans in the vents on the top and bottom.

Create a barrier for the air chamber. Cut an 8.5 by 7 cm board. Make six pieces of it. It will prevent the air from escaping and controlling its path. On the top of the equipment, place the small piece of the board in between the first two holes relative to the inlet. Then, place the other two every after two holes. Do the same for the bottom part but start in between the 2nd and third hole. Spray paint the interior of the equipment. Seal the equipment with a clear hard plastic or with a clear glass. But in this study, clear plastic was used for affordability reasons.

2.4 Procedures

Experiment on the solar air heater was performed on the noon of an ordinary sunny day when the sun emits its highest solar radial energy. The experiment was conducted from 11:00 am to 1:30 pm. The equipment was first exposed to the sun for 30 minutes. After the time allotted for the exposure, a 35 watt powered fan was allowed to constantly supply air in the inlet of the air heater. After 5 minutes, the temperature of the incoming air was measured using the digital thermometer. Then, after 4 seconds (after observing that air is already coming out of the outlet, the thermometer was placed in the outlet to measure the temperature coming out of the air heater. Record the temperature for calculations.

3. Results and Discussions3.1 Determination of the Thermal Efficiency Three trials were conducted. The temperature of the incoming air remained at 26.4 while the temperature of the outgoing air varied and registered 33.2, 32.9, and 34.3.

Figure 5 Final Output of the Soda Can Solar Air Heater

Thermal efficiency () is adimensionlessperformance measure of a device that usesthermal energy, such as aninternal combustion engine, asteam turbineor asteam engine, aboiler, afurnace, or arefrigeratorfor example.5 It describes how effective and efficient a device is. In general, thermal efficiency is equal to the ratio of useful energy output and energy input in the equipment. In a solar air heater aspect, the thermal efficiency is defined by the equation: 6

Q is the useful energy absorbed per unit time, I is the solar radiation flux, and A is the surface area of the equipment. Q has the equation:Q = mCpTWherein m is the mass flow rate of the air, Cp is the specific heat capacity of the air at constant pressure, and T is the difference of the temperature of the outgoing air and the incoming air. T = Tout Tin.Mass flow rate can be calculated by multiplying the density (of the air), the cross sectional area of the cans, and the velocity of the air. Since the power of the fan is known to be 35 watts, the air velocity can be calculated. In the experiment, the air was assumed to be ideal and 1 kmol per pass. But for real scenario, anemometer must be used to measure the winds velocity.P = W = mv2P = mv2 = Pt v = v = v = 3.107 m/sSince the velocity of the air is already identified, the mass flow rate of the air can now be calculated. m = Density of air is 1.204 kg/m3, cross sectional area of the pipe is 1.96 x 10-3 m2. m = (1.204 kg/m3) (1.96 x 10-3 m2) (3.107 m/s)m = 7.332 x 10-3 kg/sThe energy absorbed per unit time can now be computed. Cp of air is 1.006 kJ/kgoC7. The differences of the temperatures for trials 1 to 3 are: 6.8, 6.5, and 7.9. The mean difference in the temperatures is 7.067 Q = (7.332 x 10-3 kg/s) (1.006 kJ/kgoC7) ( 7.067 Q = 0.0521 kJ/sQ = 52.126 J/sThe equipment acquired 52.126 J/s of useful energy. To calculate the thermal efficiency, the solar radiation flux and the area must be identified.The total surface area of the equipment is:A = l x w = (0.595 m) (0.54 m) = 0.3213 m2Radiation from the sun sustains life on earth and determines climate. The energy flow within the sun results in a surface temperature of around 5800 K. Currently accepted values are about 1360 W m-2(the NASA value given in ASTM E 490-73a is 1353 21 W m-2).8

= 0.1193

= 11.93 %

3.2 Heat Transfer from the Sun

Heat transfer through radiation takes place in form of electromagnetic waves mainly in the infrared region. Radiation emitted by a body is a consequence of thermal agitation of its composing molecules.9 The solar energy coming from the sun was absorbed by the solar air heater as a black body through radiation. A black body is the one that absorbs all the radiant energy and reflects none. A black body is a hypothetic body that completely absorbs all wavelengths of thermal radiation incident on it. Such bodies do not reflect light, and therefore appear black if their temperatures are low enough so as not to be self-luminous. All blackbodies heated to a given temperature emit thermal radiation.9 Although the concept was just ideal and not realistic, it still plays a great role in the field of radiation and is accepted for its close approximation. The radiant energy was transferred to the solar air heater due to the temperature difference between the two bodies. Heat is always transferred from a hotter body to a colder one.

After absorbing the solar energy, a constant pressure air was blown into the device to be heated. The air travelled and passed through the pipes and the air chamber. The heat will transfer from the soda cans which absorbed the radiant energy coming from the sun to the air passing through the tubes. The air exited heated by means of convection. The flow of fluid may be forced by external processes, or sometimes (in gravitational fields) by buoyancy forces caused when thermal energy expands the fluid (for example in a fire plume), thus influencing its own transfer. The latter process is often called "natural convection". All convective processes also move heat partly by diffusion, as well. Another form of convection is forced convection. In this case the fluid is forced to flow by use of a pump, fan or other mechanical means.10 The transfer of energy started from the sun, to the solar air heater, specifically in the soda cans, and finally to the air. The device can also be used to convert solar energy into electricity by means of injecting a solar cell in the equipment.

4. ConclusionThe soda can solar air heater has proven to be an effective equipment in the conversion of the abundant solar energy into other forms of energy. The equipment can also be a power generating device which will help prolong the non-renewable sources of energy and give birth to renewable energy sources. With a proven high thermal efficiency, the soda can solar air heater is really a great help to the engineering society. 5. Recommendations After conducting the study, the following points can be noted to be included: Include a solar cell to store up the solar energy and convert it into electrical energy. Better insulate the equipment with a clear glass than a clear plastic to fully avoid air escape. In determining the velocity, use anemometer for better accuracy. The highest radial energy emitted by the sun is in the noon so when trying to store up great energy, it is best to do it on noon.

AcknowledgementsThe author expresses her greatest gratitude to the people who helped her made into completion this study. To her family for the emotional, moral, spiritual and financial support, Mr. Jesus Roy D. Valencia, her father, for exerting all his effort to help the author materialize the equipment and for financing the study; Mrs. Marvelous Grace A. Valencia, her mother, for the continuous support, care and encouragement; Ms. Jenelyn A. Valencia, her sister, for the great love and support To her best friend, Ms. Jann Marie A. Cabug, for lending her a laptop to finish the paper and for the cheers and words of encouragement To Engr. Junel Bon Borbo, for constant guidance and advices he imparts and for the knowledge he shared about the subject matter To her friends and classmates for the emotional support And above all, to her Almighty Father, Creator of heaven and earth, who provided her everything she needsReferences1. "Solar Thermal Collectors - Energy Explained, Your Guide To Understanding Energy - Energy Information Administration". Tonto.eia.doe.gov. 2013-05-29. Retrieved2014-05-04.2. "Advanced Manufacturing Office: Industrial Distributed Energy". Eere.energy.gov.3. http://stonehavenlife.com/7-diy-pop-can-solar-heaters/4. Rural Renewable Energy Alliance."Solar Air Heat Basics"5. http://en.wikipedia.org/wiki/Thermal_efficiency6. Filiz Ozgen, Mehmet Esen andHikmet Esen.Experimentalinvestigation of thermal performance ofa doubleflow solar air heater havingaluminium cans. Renewable Energy 34(2009) 23912398.7. http://www.engineeringtoolbox.com/air-specific-heat-capacity-d_705.html8. https://www.newport.com/Introduction-to-Solar-Radiation/411919/1033/content.aspx9. The Engineering Toolbox10. http://en.wikipedia.org/wiki/Heat_transfer#Convection