Numerical Simulation Of Heat Transfer Of Spiral Coiledheat Exchanger

The spiral coiled heat exchanger is a high efficient and compact heat exchanger, with the advantages of high surface heat transfer coefficient, compact structure, high heat transfer area per unit volume, undertake the high pressure of the working fluid, easy approach to multi-stream heat transfer and some others. To develop and use this kind of heat exchanger, the cost of metal material can be decreased and the space for the process can be reduced. The spiral coiled heat exchanger has a good prospect to meet the market needs. In this paper, it is firstly studied the performance of shell-side fluid flow and heat transfer of the spiral coiled round tube heat exchanger, including the effect of structure size, operating conditions and material properties. At this base, the new spiral coiled tube heat exchanger structure is introduced, the spiral coiled elliptic tube and spiral coiled trifoliate tube, and the flow and heat transfer performance of both shell-side and tube-side for the new structure are researched numerically. The following are the main work and conclusions for this paper:(1)After analyzing the advantages and disadvantages of all kinds of turbulent model, the Realizable k-two-equation turbulent model is selected as the turbulent model for simulation in the developed turbulent flow region; for the low velocity region near the wall of the coiled tube, the Scalable wall functions is adopted to refinement the turbulent model. The Nusselt number and skin friction coefficient f calculated for the shell fluid flow in this paper is agreed with the empirical correlation in Tube Bank model.(2)Through carrying out orthogonal experiment research of five factors, of which contains parameters of geometry model structure size(such as the outer diameter of spiral coiled tube, the radical distance of nearby spiral coils and the axial distance of nearby spiral coils), the operating condition parameter Reynolds number and the physical property parameters Pr number, it is concluded the weight of this five considered factors is Re>Pr>Pr>Pl>Dtube. This results indicates the operating condition parameter Reynolds number and physical property parameter Pr number has a great significance to the shell fluid flow. The single factor analysis show the pressure drop, temperature drop between inlet and outlet, surface heat transfer coefficient, Nusselt number of the coiled tube in the shell fluid flow are increased as the Reynolds number increases. With the increase of the physical property parameters Pr number, the pressure drop between inlet and outlet, surface Nusselt number, skin friction coefficient and surface heat transfer coefficient is increased, but the temperature drop between inlet and outlet is decreased. At last, the regression analysis depending on the data of orthogonal experimental and single factor experimental is is carried out, the Nusselt number and skin friction coefficient regression equation is obtained.(3)The new structure of spiral coiled elliptic tube and spiral coiled trifoliate tube are developed and researched about the heat transfer and skin friction coefficient performance both the tube flow and the shell flow, the effect of the geometry parameters of spiral coiled elliptic tube and spiral coiled trifoliate tube are also considered in this paper. It is concluded that there also exists a secondary flow in the tube flow of the spiral coiled elliptic tube and spiral coiled trifoliate tube flow, which similar to the tube flow of spiral coiled round tube, but the direction and the shape of the secondary flow are great different from spiral coiled round tube. Through the analysis of the flow and skin friction performance of the tube-side flow and shell-side flow for spiral coiled elliptic tube, it is indicated that the shell-side comprehensive heat transfer performance of spiral coiled elliptic tube is a little weak, compared to the spiral coiled round tube, but the comprehensive heat transfer performance and the synergy performance in tube-side flow is good, so in a comprehensive thinking the spiral coiled elliptic tube heat exchanger can enhanced the heat transfer. To the same both the comprehensive heat transfer performance and synergy performance of both shell-side and tube-side flow for spiral coiled trifoliate tube heat exchanger are good, so the structure of spiral coiled trifoliate tube heat exchanger can enhanced both tube-side and shell-side flow heat transfer performance in the meaning time, and the spiral coiled trifoliate tube is an excellent structure for enhanced heat transfer.