Heat exchange between gas and cylinder wall
The influence of heat exchange between gas and cylinder wall can be easily seen from the figure; here P1 represents the starting pressure of gas entering the cylinder of Fusheng air compressor, P2 represents the ending pressure; curve BC represents the compression line.
At point E, the heat transfer from the cylinder wall to the air stops, and at this point the gas releases heat (the EC line is inclined to the left of the adiabatic line).
When discharging (c d), the gas cools from point C to point D. When it expands from point d to point F, it transfers out heat, and when it expands from point F to point a, it absorbs heat. The temperature Ta at the end of expansion is higher than the temperature T1 at the suction.
At the time of suction, the temperature of the gas will increase due to its mixing with the gas remaining in the clearance volume and the heating of the cylinder wall. Therefore, the temperature at the beginning of compression is higher than that of the gas at the inlet, so the weight productivity of the compressor will be reduced and the work consumed in the compression will be increased.
The temperature of the cylinder wall, said along the centerline, is higher in the area of the valve; and lower in the center of the cylinder, which causes the gas to be heated.
Especially remarkable is the heat exchange between gas and piston. The expansion variable index N2 decreases with the increase of heating, which is why when N2
The test shows that the heating caused by the contact of gas with the hot cylinder wall and valve wall will greatly reduce the productivity, which may be up to 10% in some cases.
It should be noted that this figure is from the compressor with small test size. In the case of large channel size, the velocity of gas flow may be very small, so the corresponding thermal conductivity will be reduced.
It can be seen from the above that the quality of cooling should be paid attention to in design, operation and repair.
The effect of air heating in suction is calculated by the heating coefficient λ t.