Introduction:

In vigyan ashram 2-3 student calculated efficiency of solar water heater on the roof of memorial hall and DIC boy’s hostel. But they all observe different efficiency for solar water heater on DIC boy’s hostel.  To find out problem behind this efficiency difference dixit sir gave us new assignment of calculation of efficiency of solar water heater.

18/04/2023:

Next day on April 18 we took first observation which given below,

Length of tube= 174 cm

Diameter of tube = 5.5cm

Area of one tube = 174×5.5 = 957 per tube   

Capacity of storage water tank (m) = 500LPD   (all this observation taken from previous blog)

Now the total number of tubes = 32

Out of these 32 tubes two tubes are not in working so we count only 30 tubes so that total area of evacuated tube = 957×30= 28710 cm2= 2.87 m2

Temperature of water at 10 am (input temp) = 210C

Temperature of water at 4 pm (output temp) = 610C

Therefore temperature difference  = 61-21 = 400C

Incident Energy in 1 m2 = 25.04×106J/m2

Now the input energy = Area of ETC × Energy in 1 m2× Time

                                     = 2.87×25.04×106

                                     =71.86×106 J

Output energy = mcp × temperature difference 

                           = 500000×4.187×40

                           = 83740000

                           = 83.74×106 J

  • Efficiency = output energy / input energy ×100

                  = 83.74 / 71.86 × 100

                  = 1.165×100

                   =116.5%

Discussion:

Our efficiency cross 100% which totally wrong so that we went to Dixit sir and told them about this after some discussion sir told us that there was two section present inside the tank cold water & hot water region. And we took reading of only one region so that we observe 400C temperature difference. To overcome this problem sir suggested us to take circulation of water from cold region to hot region by using motor for 2-3 times a day when the water mixed well then we get proper output temperature.

21/04/2023

With help of Mahesh sir and DIC student Dnyaneshwar Dongre we made connection and placed motor as shown in following figure.

Observations:

Input temperature = 280C

Output temperature = 570C

Temperature difference = 290C

    Calculation:

    Input energy = 2.87×25.04×106= 71.86×106 J

    Output energy = 500000×4.187×29= 60.71×106J

    Efficiency = 60.71/71.86×100

                      = 0.8448 ×100

                      = 84.48%

    After the pumping we forget to close the pumping cock due this all the water in tank get drain out. So that we took another reading of temperature on next day 22 April 2023.

    22/04/2023

    Observations:

    1.Input temperature= 260C

    2.Output temperature = 570C

    3.Temperature difference = 310C

      Calculations:

      Input energy = 2.87×25.04×106

                              = 71.86×106 J

      Output energy = 500000×4.187×31

                                  = 64.81×106 J

      Efficiency = 64.81/71.86 ×100

                         = 90.30%

      Result:

      Efficiency of solar water heater on the roof of DIC boys hostel = 90.30%