Mechanical Engineering - Heat Transfer, Refrigeration and Air Conditioning - Discussion

Bypass factor is independent of velocity.

By pass factor suggest the un-contacted air therefore if the speed will be high the air will not be able to contact the coil and hence bpf increases.

Let t1 = air before entering coil.

t2 = mean coil temperature.

t3 = air temperature cooling coil.

So bpf = (t1-t2)/(t3-t2).

So if the velocity of air will increase then the numerator will decrease which will result in a increase in bpf.

Wrong buddy, by pass factor would reduced because time available low to make contact and enough heat will taken by air.

The by-pass factor can be increased by increasing the number of rows in a cooling coil or by decreasing the air velocity or by reducing the fin pitch.

I'm totally agree with You (@Raju) with increase in velocity forced convection increase and with this the temperature decreases which should decrease the bypass factor.

As velocity increases Reynolds number increases which result in increase in heat transfer coefficient (turbulent) then bypass factor should increase?

Bypass factor is the (Amount of air bypassing the coil) divided by (the total amount of air passing the coil).

So a higher velocity of the passing air will decrease the time of contact for effective heat transfer and hence decrease the amount of heat transfer.

So it can be assumed that a greater portion of air is bypassing the coil without any heat transfer with the coil. So increasing the velocity of air decreases the Bypass factor.

With increase in velocity temp. Decreases & bypass factor increases.