solar oven design engr 102 fall 2008 class notes
TRANSCRIPT
General Categories of EnergyGeneral Categories of Energy
KINETIC ENERGYKINETIC ENERGY
Energy in motionEnergy in motionPOTENTIAL ENERGYPOTENTIAL ENERGY
Stored energyStored energy
Forms of EnergyForms of EnergySolar/Light/Radiant Solar/Light/Radiant
EnergyEnergyEnergy from the sunEnergy from the sun
1000 Watts/m1000 Watts/m22 at the at the earth’s surface !!!!!earth’s surface !!!!!
Electrical EnergyElectrical EnergyEnergy as a result of the flow Energy as a result of the flow
of charged particles called of charged particles called electrons or ionselectrons or ions
Forms of EnergyForms of Energy
Mechanical EnergyMechanical EnergyEnergy produced from Energy produced from
mechanical devicesmechanical devices
Chemical EnergyChemical EnergyEnergy that is stored in Energy that is stored in
molecular bonds, the molecular bonds, the forces that hold molecules forces that hold molecules togethertogether
Forms of EnergyForms of Energy
Thermal (Heat) Thermal (Heat) EnergyEnergy
energy in the process of energy in the process of being transferred from one being transferred from one object to another because object to another because of the temperature of the temperature
difference between them.difference between them.
Nuclear EnergyNuclear EnergyEnergy that is trapped inside
each atom
Heat TransferHeat Transfer
Conduction - solidsConduction - solids Convection – gases and liquidsConvection – gases and liquids RadiationRadiation
• Trap heat/solar energy inside a Trap heat/solar energy inside a containercontainer
• Black surfaces adsorb and radiate Black surfaces adsorb and radiate energyenergy
• Shiny surfaces reflect light Shiny surfaces reflect light
Solar OvensSolar Ovens
Not just an Academic ExerciseNot just an Academic Exercise• Water/milk pasteurizationWater/milk pasteurization• CookingCooking
Designed by solar engineers to be used Designed by solar engineers to be used in sun rich but fuel poor areas in the in sun rich but fuel poor areas in the world to improve the quality of life and world to improve the quality of life and nutrition of some of the 2.4 billion nutrition of some of the 2.4 billion people who lack adequate cooking fuel people who lack adequate cooking fuel
Solar Oven SocietySolar Oven Society
handout Designhandout Design Flat bottom, flat topFlat bottom, flat top
• Not all sun gets inNot all sun gets in
Alternative:-Aimed OvenAlternative:-Aimed Oven• Incident width = window Incident width = window
width, W= Lwidth, W= L
Solar Oven – Theory Solar Oven – Theory
First law of thermodynamicsFirst law of thermodynamics• Energy in = Energy outEnergy in = Energy out
Joules, BTUs, caloriesJoules, BTUs, calories
• Power out = Power absorbedPower out = Power absorbed Energy/timeEnergy/time Joules/sec, BTU/s, hp, WattsJoules/sec, BTU/s, hp, Watts
• Goal is to determine Power absorbed Goal is to determine Power absorbed and Power out and ultimately to predict and Power out and ultimately to predict Oven Temperature TioOven Temperature Tio
Power Absorbed - factorsPower Absorbed - factors
SunSun• II00 – incident solar power (W/m – incident solar power (W/m22))SS – angle of sun rays with horizon – angle of sun rays with horizon
Size or Area (ASize or Area (Aww))• W – width of glazingW – width of glazing• L – length of glazingL – length of glazing– – angle of window with horizonangle of window with horizon
Material properties of window, ovenMaterial properties of window, oven – – transmissivitytransmissivity• a - absorptivitya - absorptivity
Power AbsorbedPower Absorbed
Sun
Radiation, conduction and Convection
Insulation
swoabsorbed aAIP sin
Power outPower out
Radiation, Conduction, and Radiation, Conduction, and ConvectionConvection
FactorsFactors• A – Area through which energy flowsA – Area through which energy flows
● ● T – temperature gradient from inside to T – temperature gradient from inside to outsideoutside
• MaterialMaterial U – heat transfer coefficient (radiation, U – heat transfer coefficient (radiation,
conduction, and convection)conduction, and convection)
Power out- detailsPower out- details
PPoutout = UA = UATT sb = Sides and sb = Sides and
BottomBottom w – Windoww – Window io – interior ovenio – interior oven ambient – outside ambient – outside
ovenovenSides/Bottom
Window/glazing
ambientiowwsbsbout TTAUAUP
Balancing Energy (out = in)Balancing Energy (out = in)
Power out = Power absorbedPower out = Power absorbed
swoabsorbed aAIP sin
ambientiowwsbsbout TTAUAUP
Predict Final Oven Temp TPredict Final Oven Temp T ioio
Use an Excel Spreadsheet II0 0 – fixed– fixed Angle of sun – fixedAngle of sun – fixed Position the ovenPosition the oven Window areaWindow area
• Bigger window but Bigger window but heat loss increaseheat loss increase
InsulationInsulation ReflectorsReflectors
Uw = f(Tio)
Tio = f(Uw)
ReflectorsReflectors
Goal is to capture more light and Goal is to capture more light and allow less heat to escapeallow less heat to escape
ReflectorsReflectors
Energy GainEnergy Gain• Some solar energy reflected is adsorbed by reflector Some solar energy reflected is adsorbed by reflector
and more heat (energy) retained in ovenand more heat (energy) retained in oven
• PPabsorbed with a reflectorabsorbed with a reflector = G P = G Pabsorbed without a reflectorabsorbed without a reflector
r – reflectivity of reflector
M – height of reflector
– angle of reflected light
N - # of reflectors
90sin1L
MrNG
wwsbsb
woambientio AUAU
aGAITT
M/L RatioM/L Ratio Cannot merely make a Wide/Squat Cannot merely make a Wide/Squat
vs. Tall skinny Pyramidvs. Tall skinny Pyramid• Much of the sun’s rays would miss Much of the sun’s rays would miss
windowwindow