The Research On Design And Calculation Of Fin-tube Heat Exchanger

Heat exchanger is commonly used in petroleum, chemical, utility power and other fields of industry. In this paper, a research on design and calculation of fin-tube heat exchanger which is widely used in low temperature fields has been carried out. A new design method is presented through the design of star-shaped fin-tube heat exchanger and an experimental confirmation.Firstly, through the brief analysis of steady-state heat conduction and unsteady-state heat conduction of fin, this paper gives the corresponding formula. Then the features of convection heat transfer in pipe are analyzed and the gasified process of cryogenic fluid is divided into four states as liquid phase forced convection heat transfer, gas-liquid two-phase forced convection heat transfer, liquid deprivation forced convection heat transfer and gas phase forced convection heat transfer. On the basis of the four states, design and calculation method of vaporizer is introduced. It is found that this method has an advantage of selecting formula with the strong adaptability and high accuracy ,and makes design more reasonable and precise.A fin-tube heat exchanger is designed with the given basic design parameter. The design goal is the length of fin-tube. This article uses the subsection design principle and takes the trial calculation method as the foundation to complete the steady-state design of vaporizer by selecting the appropriate heat transfer corresponding formula.Because of the fact that gasified process of cryogenic fluid is on the unsteady-state heat transfer condition in majority of time, the calculation result is a maximum value. Then this article uses a unsteady-state simplified model to carry on the design and get a new result. The new result is a minimum value because of the fact that the temperature of fixed section of fin-tube can tend to a stable value and the gasified process can be regarded as steady-state heat transfer after vaporizer working a not long time. And the result is proved through the experiment and analysis, although gasified process of the cryogenic fluid is at the unsteady-state heat transfer condition in majority of time.Because the steady-state heat transfer conforms to the vaporizer practical work situation, this article takes the steady-state computed result as the basis and makes the design value reduce 35% to complete the design with making reference to the unsteady-state condition computed result. Finally the experiment proves this design method is practical and feasible. The design result shows that the vaporizer can meet the practical requirements, at the sametime the design value is not too conservative. The design result saves the material and reduces the investment.The design example shows that the thermal conduction resistance of the fin-tube can be ignored, and the effects of fluid physical properties can also be ignored because of a less total pressure draw down in fin-tube so that the design can be simplified. The design method provides the reference and the basis for the subsection design of similar heat exchangers.