- #1
physicso
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Hi..I joined this forum a couple of days ago and I find that this is the best place for newb like me to share and seek some ideas.
I have a question to ask and I don't know if this had been asked before. Would it be possible to heat water to its boiling point by solar?
The idea is to collect the energy from sun by photovoltaic panel and store it in a 12V 7.2A-hour rechargeable battery and from that battery, I want to heat water to it's boiling point.
I have made a few calculations, correct me if I'm wrong.
Water = 350ml = 0.35kg
Water Specific Heat = 4186 joule kg-1 C-1
Tf - Ti = (100 - 30)C = 70C
*assuming Ti is 30 degree Celsius.
Q = 0.35*4186*70 = 102557 J = 102.6kJ
let say the heating period is around 3 hours (I don't mind about the time taken, as for now, the main objective is to get water boils.)
P = Q/t = 102.6kJ/(3x60x60) = 9.49 Watt ~= 10 Watt.
Power supplied from battery
1) for first hour
P = VI = 12V*7.2A-hour*(1/1hour) = 86.4 Watt
2) for second hour
P = VI = 12V*7.2A-hour*(1/2hour) = 43.2 Watt
3) for third hour
P = VI = 12V*7.2A-hour*(1/3hour) = 28.8 Watt
to support my calculation, I try to figure out the length of the heating element needed.
P = I2*R
R = P/I2 where P = 10 watt, I = (7.2A-hour)*(1/3hour) = 2.4A
R = 1.736 ohm
material used is nichrome with resistivity 1.5 x 10-6 ohm-m.
R = resistivity*(Length/Cross Area)
Length/Cross Area = R/resistivity = 1.736/(1.5 x 10-6) = 1,157,407 m/m2
Length = Cross Area * 1,157,407 m/m2 where Cross Area = 1000 circular mils = 0.506707479 mm3
Length = 0.586 m *approx. half a meter
*it seems to me that the power supplied by 12V 7.2A-hour battery is more than enough to boil 350ml water but I never build it yet because I have to finish the paperwork/calculations first before start assemble. My teacher told me that it is not possible to boil water using battery. He told me something about start up energy/power/heat that requires a lot of power. Anyone can explain this to me?
Questions.
1. Is the calculation right?
2. Any other idea to heat water with minimum power?
Thank You. Really appreciate your help.
I have a question to ask and I don't know if this had been asked before. Would it be possible to heat water to its boiling point by solar?
The idea is to collect the energy from sun by photovoltaic panel and store it in a 12V 7.2A-hour rechargeable battery and from that battery, I want to heat water to it's boiling point.
I have made a few calculations, correct me if I'm wrong.
Water = 350ml = 0.35kg
Water Specific Heat = 4186 joule kg-1 C-1
Tf - Ti = (100 - 30)C = 70C
*assuming Ti is 30 degree Celsius.
Q = 0.35*4186*70 = 102557 J = 102.6kJ
let say the heating period is around 3 hours (I don't mind about the time taken, as for now, the main objective is to get water boils.)
P = Q/t = 102.6kJ/(3x60x60) = 9.49 Watt ~= 10 Watt.
Power supplied from battery
1) for first hour
P = VI = 12V*7.2A-hour*(1/1hour) = 86.4 Watt
2) for second hour
P = VI = 12V*7.2A-hour*(1/2hour) = 43.2 Watt
3) for third hour
P = VI = 12V*7.2A-hour*(1/3hour) = 28.8 Watt
to support my calculation, I try to figure out the length of the heating element needed.
P = I2*R
R = P/I2 where P = 10 watt, I = (7.2A-hour)*(1/3hour) = 2.4A
R = 1.736 ohm
material used is nichrome with resistivity 1.5 x 10-6 ohm-m.
R = resistivity*(Length/Cross Area)
Length/Cross Area = R/resistivity = 1.736/(1.5 x 10-6) = 1,157,407 m/m2
Length = Cross Area * 1,157,407 m/m2 where Cross Area = 1000 circular mils = 0.506707479 mm3
Length = 0.586 m *approx. half a meter
*it seems to me that the power supplied by 12V 7.2A-hour battery is more than enough to boil 350ml water but I never build it yet because I have to finish the paperwork/calculations first before start assemble. My teacher told me that it is not possible to boil water using battery. He told me something about start up energy/power/heat that requires a lot of power. Anyone can explain this to me?
Questions.
1. Is the calculation right?
2. Any other idea to heat water with minimum power?
Thank You. Really appreciate your help.