The Research On Heat Transfer Of The Vertical Concentric Tube Heat Exchanger In Ground Sourse Heat Pump System

The ground-source heat pump system (GSHP) is an effective and energy-saving heat pump system which takes the soil as the source of heating and chilling instead of asmospheric environment. GSHP with the adoption of the vertical concentric tube heat exchanger has become increasingly popular because of such outstanding advantages as fewer area requirement, fewer limits, more steady and effective performance, lower costs on system maintenance etc. As the only instrument for the heat exchange between the tube and the soil, the effect of the vertical concentric tube heat exchanger is of vital importance for the system's COP. With the in-depth researches on the vertical heat exchanger, it becomes greatly necessary to set up a more precise heat transfer model in order to further analyze the process of the heat exchange and to find efficient ways to promote the efficiency of the heat exchanger. Therefore, the present thesis is focused on the following aspects:1 To analyze the characteristics and applicable conditions of the existing heat transfer model and to study the cylinder heat transfer model deeply, referring to the differentiated rules of heat transfer, put forward the criterion for the inside bore.2 Based on the analysis of the existing heat transfer model and the theory of energy balance as well as the equations of differential coefficient heat conduction, this thesis attempts to build up the more precise model for the vertical concentric tube heat exchanger under the condition of long-term running. This model takes into account the factors such as the tube configuration, the liquid temperature and the soil temperature distribution, and the differentical physical charateristic of the back-filled and the soil to describ the actual heat transfer process;3 The formulae of temperature distribution of the fuild in the vertical concentric tube are worked out under the two different flow conditions;4 To make analysis on the influential factors of the performance of the vertical concentric tube heat exchanger and the effect of the "heat short-circuit";5 To put forward the common process of the heat exchanger design.The stable running of the GHSP system, the attenuation and delay function of the soil to the surface temperature make reazonable the steady long-term heat tranfer mathmatic model presented in this thesis. The model describes parts of the heat transtfer process of the vertical concentric tube heat exchanger, and is able to analyze such influncial factors as flow rate, pipe length, pipe diameter and material features made of pipe and the back-filled, the soil characters and the patterns of...