An experimental investigation of heat transfer in the thermally developing region of a pulsating pipe flow.

Abstract

The effect of pulsation on heat transfer coefficient in the thermally developing region of turbulent air flow in a pipe was investigated. The pipe wall was electrically heated to provide uniform heat flux. Reynolds number was varied from 6387 to 41947 while frequencies of pulsation ranged from 1 to 13 Hz in an almostsinusoidal form. The displacement amplitude of pulsation inducing mechanism was kept constant throughout the experiment. The behavior of local Nusselt number under the influence of pulsation was studied. The results show enhancement in the mean Nusselt number up to 9% at frequency of 2 Hz for Reynolds number of about 15000. The rate of enhancement decreases as Re increases and the frequency band at which enhancement is observed widens and lies between 1.5 and 3.5 Hz for Re between 15000 and 33000. Reduction of heat transfer coefficient is encountered at higher frequencies and the effect of the pulsation becomes insignificant as Re becomes very high. It can be concluded that the effect of pulsation on the heat transfer coefficient is less significant in the thermally developing region of turbulent air flow in pipes. This may be due to the already high heat transfer coefficient which exists in this region of developing thermal boundary layer. The effect of pulsation on heat transfer coefficient in the thermally developing region of turbulent air flow in a pipe was investigated. The pipe wall was electrically heated to provide uniform heat flux. Reynolds number was varied from 6387 to 41947 while frequencies of pulsation ranged from 1 to 13 Hz in an almostsinusoidal form. The displacement amplitude of pulsation inducing mechanism was kept constant throughout the experiment. The behavior of local Nusselt number under the influence of pulsation was studied. The results show enhancement in the mean Nusselt number up to 9% at frequency of 2 Hz for Reynolds number of about 15000. The rate of enhancement decreases as Re increases and the frequency band at which enhancement is observed widens and lies between 1.5 and 3.5 Hz for Re between 15000 and 33000. Reduction of heat transfer coefficient is encountered at higher frequencies and the effect of the pulsation becomes insignificant as Re becomes very high. It can be concluded that the effect of pulsation on the heat transfer coefficient is less significant in the thermally developing region of turbulent air flow in pipes. This may be due to the already high heat transfer coefficient which exists in this region of developing thermal boundary layer.