Calculations

Dimensions of vessel

Bulk density-

          Bulk density of kitchen waste was necessary to find out for deciding the dimensions of vessel. First the waste from kitchen was taken in tray. The weight and dimensions of tray was taken. Then weight of waste was taken. The waste was taken in tray as there is no too much space between waste particles. The care taken was the waste does not overflow from tray. The weight of waste was taken and recorded.

            Dimensions of tray were 36 x 25 x 7 cm.

 Volume of tray = 36 x 25 x 7

                                         = 6300 cm³

                                        = 0.006300 m³

Weight of waste = 1.334 kg

Density = 211.74 kg/m³

Vessel

          The vessel shape was selected as circular truncated cone, so as the waste should not throw out of vessel while chopping. The vessel capacity should be 5 kg. Therefore the calculations are given as following,

Theoretical volume for 5 kg waste,

To find the calculated volume of vessel the base radius was assumed 25 cm, upper radius was assumed 27 cm and height was assumed as 25 cm. calculating the volume for these dimensions.

The calculated volume is greater than theoretical volume. Therefore, dimensions of vessel as base radius 25 cm, upper radius 27 cm and height 25 cm were selected.

Chopper

            From trials it was decided to take chopper of weight 5 kg for effective cutting of waste layer of 15 cm. Force applied by chopper was calculated as follows,

                        F = m x a

            Where,

                        F = force, N

                        m = mass, kg

                        a = acceleration, m/s²

                        F = 5 x 9.81

                           = 50 N

            Therefore force applied by chopper was 50 N.

            Now, length of chopper can be given as,

                        Total length = stroke length + extra length

                                           = 30 cm + 20 cm

                                           = 50 cm

            The extra length was kept for uniform operation of chopping during work. Also the distance between top of vessel and bottom of chopper blades was taken into account while deciding extra length, so as the waste should not throw out of vessel.

            The blade size was 20 x 10 cm.

Chopper drive mechanism

Velocity and power calculations

            The number of strokes required for chopping were 360 in 30 minutes.

Therefore,

            No. of strokes per minute = 360 / 30

                                                      = 12

Now, time required per stroke (sec) = 60 / 12

                                                            = 5 sec

Here, we know that displacement is 30 cm.

Power requirement

Since, the factor of safety is taken as 2, therefore the force was taken as 50 x 2 = 100

Drive mechanism

            Here the main part of this dynamic system is to convert rotary motion into reciprocating motion. Therefore a crank connecting rod mechanism was selected.

            Now, we have to decide the dimensions of crank and connecting rod.        

We found that for displacement, from fig. 1.

Hence, the length of crank is 15 cm and length of connecting rod was 23.84 cm was fixed.

Structure

          The structure i.e. supporting system was designed so as the system should be compact and reliable for operation. The height was kept 100 cm and width was kept 70 cm.