Numerical Simulation And Experimental Study On Oscillation Flow And Heat Transfer In Non - Clean Water - Cooled Heat Exchanger

The development and utilization of low-grade renewable clean energy have broad prospects. It is an inevitable trend for the sustainable development of energy, buildings and environment. Sewage-source heat pump system can use the low-grade thermal energy in the waste water to provide heating, air conditioning for buildings and provide domestic hot water, with high efficiency and energy saving and significant features of environmental friend. But the waste water contains all kinds of debris. In the heat transfer process the debris would forming fouling resistance and lead to the dropping of the heat transfer efficiency of the system. The aim of this paper is to make a numerical simulation and experimental study of the oscillation flow and heat transfer of the heat pump heat exchanger, and then present a new online anti-fouling technology for the heat pump heat exchanger to improve the heat transfer performance of the system.At first, the physical and mathematical model of turbulence oscillation flow and heat transfer in a tube was established, and then a numerical simulation of turbulent pulsating flow and heat transfer was carried on. The turbulent flow conditions, the wall average convective heat transfer coefficient and the wall shear stress among the heat transfer process were analyzed using CFD software. The influence of the fluid inlet velocity, oscillatiing amplitude and frequency on the wall average convective heat transfer coefficient and wall shear stress was studied. It is shown that when the fluid is Newtonian fluid, the oscillatory flow in circular tube had no effect on turbulent heat transfer. But When the fluid is non-Newtonian, the oscillatory flow can strengthen heat transfer, significantly improve the maximum wall average shear stress values and have the descaling effectA new device of online anti-fouling technology for the non-clean water heat pump heat exchanger was developed in this thesis. The device uses periodically rotation of the valve plate within an electric rotary to achieve the effect that the fluid flow into the heat exchanger also undergoing a cyclical change and produce oscillation flow. And then this article build a heat pump heat exchanger oscillation flow and heat transfer experiment platform based on a practical project located in Qingdao. The influence of the oscillation flow to the heat transfer effect of the system was analyzed. The results show that under the experimental operating conditions, the oscillation flow has no effect on the inner tube convective heat transfer coefficient but the oscillation flow can cause falling of part of dirt deposits, played a descaling effect and the heat exchanger heat transfer coefficient increased by 22.2. The oscillation flow can not only inhibit the formation of the heat exchanger fouling but also can remove the dirt inside the heat exchanger which has been formed already and then the heat exchanger can be maintained in a high efficient state.