A professional non-standard equipment design and manufacturing company must have a very strong technical force to support the complex and changeable customized customer needs.
Nantong Safe Machinery Equipment Co., Ltd. is such a non-standard equipment customization unit with strong technical force and strong production capacity integrating R&D, design, manufacturing and service.
Today, what we want to Amway is "the design steps of shell and tube heat exchanger".
When designing a heat exchanger, if you only blindly increase the safety factor of the heat transfer area or simply estimate it, it will cause a serious waste of resources. Only by carrying out very detailed calculations, can it be possible to obtain a reliable and powerful guarantee for the safety and economy of the heat exchanger put into operation.
In fact, many factors in the design are related to each other and the design process is intricate. Therefore, the design procedure should be different depending on the design tasks and original conditions. For example, in the calculation of heat transfer and resistance, the structure is inevitably involved, so it is often necessary Preliminarily select the heat transfer coefficient to obtain the initially estimated heat transfer area, so as to make a structural arrangement, and then perform further heat transfer calculations to obtain the calculated value of the heat transfer coefficient and the required heat transfer area. Generally, when the required heat transfer area calculated by the ratio of the heat transfer area determined by the structure has a margin of 10% to 20%, the heat transfer calculation and the structure calculation are successful.
If there are still problems with resistance calculation, strength calculation, and vibration correction, some parts have to be changed or even re-selected.
The general design procedure is as follows:
Collect relevant original data according to the design task, and select the type of heat exchanger, etc.
The original data should include: the physical and chemical properties of the fluid (such as fouling, corrosive, explosive, chemical action, etc.), the flow, pressure, temperature, thermal load of the fluid, the restriction of the equipment installation place, the restriction of the material, and the pressure drop Restrictions and so on.
Determine the qualitative temperature and check physical data;
Calculate the heat load and the flow of hot fluid or cold fluid from the heat balance;
Choose the material of the shell and tube;
Select the flow mode and determine the fluid flow space;
Find the average temperature difference;
Initially select the heat transfer coefficient K', and calculate the heat transfer area F';
Design the structure of the heat exchanger (or select a standard type of heat exchanger), including:
①Select pipe diameter and pipe side fluid
②Determine the number, length and total number of tubes in each pass;
③Determine the pipe arrangement, pipe spacing, shell inner diameter and connecting pipe diameter, etc.;
④Determine the number and size of the shell side passes and the number and size of the longitudinal partitions, or the number, spacing, and size of the baffles and other shell side structure dimensions.
In this step, it is best to determine the relevant data and the heat transfer area F" through the sketch (F" is generally not exactly equal to F').
It should be noted that when determining the size of the structure, many factors affect each other, and finally are reflected in the diameter and length of the shell. Often the shorter shell has a larger diameter, and the long shell has a smaller diameter. Generally speaking, The latter is more economical. This is because:
①The small diameter shell may be made of standard pipes;
②For given operating conditions, if the diameter of the shell is small, the thickness of the shell, flange, end cover and other parts can also be reduced;
③The processing cost of the tube sheet is relatively high. If the diameter of the shell is small, the thickness and diameter of the tube sheet can be reduced accordingly, so that the manufacturing cost can be reduced;
④The cost per unit length of pipe is low.
Of course, the choice of a small shell and a long shell must first meet the requirements of allowable pressure drop, and also take into account the possibility of equipment arrangement, installation and maintenance in the existing space.
Tube side heat transfer calculation and resistance calculation. When the heat transfer coefficient is much greater than the primary heat transfer coefficient and the pressure drop is less than the allowable pressure drop, the next step can be calculated, otherwise K'must be reselected and the structure adjusted.
Shell side heat transfer calculation. According to the adopted structure, the wall temperature is assumed and the heat transfer coefficient is calculated. If it is unreasonable, the shell side structure should be adjusted until satisfactory.
S Check the heat transfer coefficient and heat transfer area. Calculate the heat transfer coefficient K and the heat transfer area F according to the heat transfer coefficient of the tube and the shell side, the thermal resistance of fouling, and the thermal resistance of the wall. Taking into account the uncertain factors in the heat transfer calculation formula, the difference between the operating conditions and the design conditions, some pipes will have to be blocked due to severe fouling or leakage in the future, and the fluid parameters may change in a short period of time under emergency and abnormal conditions. Therefore, it is required that the heat transfer area F" determined by the structural calculation is 10% to 20% larger than the calculated required heat transfer area F to meet the requirements.
Calculate the wall temperature. The requirement corresponds to the assumed wall temperature.
Calculate the shell side resistance to make it less than the allowable pressure drop. If the pressure drop does not meet the requirements, adjust the flow rate or structure size.
Calculate the strength of the parts of the heat exchanger. For example, the thickness of the shell, the thickness and size of the tube sheet, head and flange, the type and size of the support, the size and number of screws, and so on.
Calculate the thermal stress of the tube and the shell and the pull-off force at the tube interface, consider the thermal compensation measures and check and calculate the vibration.
Draw formal drawings, prepare material lists, etc.
In summary, the above steps can be adjusted appropriately depending on the specific circumstances, and the design results should be analyzed. If unreasonable parts are found, there must be a certain amount of repetition and repetition to ensure the standard of the implementation results.
For example, if a certain thermal resistance dominates, if possible, measures should be taken to reduce the thermal resistance.
For another example, the allowable pressure drop must be used as much as possible. If there is a substantial difference between the calculated pressure drop and the allowable pressure drop, you should try to change the design parameters or structure size or even change the structure type. Sometimes in order to save investment, several schemes should be used for comparison, which shows that the design process is quite complicated and time-consuming.
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