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The design calculation of shell and tube heat exchanger

To introduce the design and calculation of tubular heat exchanger.

The calculation and selection of the design steps of the shell and tube heat exchanger is basically the same, the basic steps are as follows:

1, trial and primary equipment specifications

(1) according to the heat transfer task, the heat transfer rate is calculated;

(2) the calculation of heat transfer temperature difference, and according to the temperature difference correction factor is not less than 0.8 of the principle, determine the shell number or adjust the temperature of the heating medium or cooling medium;

(3) the choice of fluid in a heat exchanger;

(4) determining the flow path of the fluid in the heat exchanger.

(5) the heat load is calculated according to the heat transfer task Q.

(6) to determine fluid in the change of the temperature of both ends of the heat exchanger, tube type heat exchanger; qualitative calculation of temperature, and to determine the nature of fluid qualitative temperature.

(7) the average temperature difference is calculated, and the number of shells is determined according to the principle that the temperature correction factor should not be less than 0.8.

(8) according to the empirical value of the total heat transfer coefficient, or the actual situation of production, the total heat transfer coefficient K.

(9) according to the basic heat transfer equation, the heat transfer area is estimated, and the basic size or the size of the heat exchanger is determined, and the flow velocity of the fluid is selected (10).

2. Calculation of tube and shell side pressure drop is according to the size of the initial equipment calculated tube and shell side fluid flow rate and pressure drop. Check calculation results are reasonable or meet process requirements. If the pressure drop does not meet the requirements, to adjust the flow rate, and then determine the number of tube or baffle plate spacing, or select another specification of the device, the re calculation of the pressure drop until meet the requirements.

3 Calculation of heat transfer coefficient, the calculation of the heat transfer area, the calculation of the heat transfer coefficient, the heat transfer coefficient, the calculation of the heat transfer coefficient and heat transfer area. Generally used for the actual heat transfer heat exchanger area than is needed to calculate the heat transfer area is 10% ~ 25%, if K/K = 1.15 ~ 1.25, or another set the total heat transfer coefficient, select heat exchanger and return to the first step, the re are checking calculation.

In general, the choice or design of the heat exchanger, should be in the premise of meeting heat transfer requirements, and then consider other issues. They are often contradictory. For example, if the total heat transfer coefficient of the heat exchanger is larger, the pressure drop (resistance) of the fluid can be increased, and the dynamic cost is increased. If the surface area of the heat exchanger is increased, the total heat transfer coefficient and the pressure drop can be reduced.

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