Numerical Simulation Of Heat Transfer Enhancement With Pulsating Flow

With the development of technology and shortage of energy source, more and more emphasis was put upon the enhancement of heat transfer. The pulsating flow has absorbed more attention of people. Many paper have proved by experiment and calculation that the pulsating flow can enhance heat transfer. Heat transfer performance and economic characteristics for laminar and turbulent pulsating pipe flow under different conditions of pulsation frequency, amplitude and different fluid were numerically investigated by applying Fluent 6.0 computer software in this paper. The velocity of the inlet flow was periodically varied. And by analyzing the velocity distribution on any section along the pipe, the paper explains the reason of the effect of frequency and amplitude on flow and heat transfer. The results are as follows: 1. The effect of pulsation on heat transfer When the flow is turbulent, the heat transfer performance coefficient E (k)before and after introducing the pulsation will increase with the increase of the frequency firstly, and then decrease to an asymptotical value. It will increase gradually with non-dimensional amplitude. For different fluid, the tendency of the change of heat transfer with frequency is basically similar, but the corresponding optimum frequencies are different, and the asymptotical values of them are different. When the flow is laminar, the heat transfer performance coefficient E (k)before and after introducing the pulsation will increase with the increase of the frequency. With the increase of the non-dimensional amplitude, it will decrease firstly, and then increase gradually. For different fluid, the tendency of the change of E (k) with frequency is basically similar, but the corresponding optimum frequencies are different, and the asymptotical values of them are different. When the frequency or the non-dimensional amplitude is small enough, the heat transfer will be weakened. 2. The effect of pulsation on flow When the flow is turbulent, with the increase of the frequency the ratio of the friction coefficients E (λ)before and after introducing the pulsation increase firstly, and then gradually decrease, and finally increase to an asymptotical value. With the increase of the non-dimensional amplitude, coefficient E (λ) will decrease firstly and then increase gradually. For different fluid, the tendency of the change of friction coefficient with frequency is similar, but the corresponding optimum frequencies are different, and the asymptotical values are different. But when the non-dimensional amplitude is small enough, the friction coefficient will be weakened. When the flow is laminar, the ratio of the friction coefficients E (λ)before and after introducing the pulsation gradually increases with the increase of the frequency. And with increase of the non-dimensional amplitude, it increases firstly, then decreases and increases again gradually. For different fluid, the tendency of the change of E (λ) with frequency is basically similar, but the corresponding optimum frequencies are different. 3. The effect of pulsation on the performance of heat exchanger When the flow is turbulent, with the increase of the frequency, the criterion of the performance of a heat exchanger (E) decreases gradually firstly, then increases and finally decreases gradually. When the frequency is high enough, we have E >0. With the increase of the non-dimensional amplitude, it increases firstly and then decreases gradually. For different fluid, the tendency of the change of E with frequency is basically similar, but the corresponding optimum frequencies are different. When the flow is laminar, E increases firstly and then decreases gradually with the increase of the non-dimensional amplitude. For different fluid, the tendency of the change of E with frequency is different: when the fluid is ammonia (liquid), E decrease gradually with increase of the frequency, and E is always less than zero; when the fluid is water, E gradually increases firstly and then decreases with the increase of the frequency, and when the frequency is high enough, then E >0. 4. The explanations of the effect of pulsation on the heat transfer and flow: When the frequency and the non-dimensional amplitude are high enough, there is an overflow nearly the wall. And with the increase of the frequency and non-dimensional amplitude, the spatial and time range of the influence will increase gradually.