Why is the design area of the heat exchanger specified
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This is the assignment sheet for the graduation project given by the teacher. Original data: Design requirements: The heat exchange area of the heat exchanger must be 250 square meters. Media used in the heat exchanger: High-temperature medium – lubricating oil; inlet temperature: 250°C, outlet temperature: 200°C, pressure: 6 MPa. Low-temperature medium – diesel; inlet temperature: 100°C, outlet temperature: 120°C, pressure: 2 MPa. Mass flow rate: 200 KG of lubricating oil per minute. The medium is considered clean. I’m confused – why is it necessary to specify the area of the heat exchanger? With the information provided earlier, couldn’t we simply design the heat exchanger directly?
Regarding the issue of specialized division of labor, the heat exchange area is determined by the process engineering team; therefore, there is no need to conduct further process calculations when designing the equipment. Moreover, it may not even be necessary to do so for equipment design. The key parameter in heat exchanger design is the heat exchange area; it is necessary to have this value in order to carry out the design
There is no flow rate for the low-temperature medium; that’s correct
Hehe, the design of a heat exchanger is generally aimed at determining its heat exchange area! ! If the heat exchange area is determined, then operation calculations are the main thing to focus on! ! It can’t be called design!
Heat balance can be calculated. The possible reason for the issue is that your team specializes in equipment design; the area has already been calculated by the process engineering team.
If you’re not given a specific area, can you design it however large you want? Then who are you designing it for? All of this is designed based on the user’s requirements; you need to create it in the size they require, providing them with something that is both practical and cost-effective.
Generally, in design, an exchange coefficient is chosen based on experience, and then the heat exchange area is estimated. Now that you already have the value for the heat exchange area, there’s no need for estimation anymore; you can simply select the appropriate option. Subsequently, a comparison is made to determine whether there is a sufficient margin between the selected area and the calculated area. The area value provided by your teacher is meant to reduce your workload, as it prevents repeated calculations caused by inaccurate estimates of the exchange coefficient, thus saving time. That’s my opinion
To reduce the workload and make it less difficult!
What the teacher means: 1. To have you determine the diameter and length of the heat exchange tubes, as well as the diameter of the shell； 2 To help you determine the number of stages and the spacing between baffle plates ； 3 Determine whether the heat exchange area meets the 250 square meter requirement based on the previous two calculations (including a 10% margin) ； 4 In conditional cases, the pressure drop across the shell and tube sides should also be checked (provided by the instructor). Higher requirements: If time permits, several options should be developed, with the lowest cost being preferred!
There are no flow rates for the tube side or the shell side; actually it’s the same, and this makes things easier for you, doesn’t it?
Hehe, my graduation project was also related to heat exchangers (design of a distillation column heater). Let’s compare our initial data: the heat exchange area is 8 m2. The pressures are 0.05 MPa inside the tubes and 0.1 MPa outside them. The temperatures are 73 degrees inside the tubes and 120 degrees outside them. (I’ve temporarily chosen acetic acid and water vapor as the working media.) I went to see my professor this afternoon, and his general idea was that once the heat exchange area is known, the average temperature difference can be calculated directly. Of course, my current approach is to work backwards based on the given heat exchange area: there is a margin of 10%-20% between the actual heat exchange area and the designed one, and this margin can be used to determine the tube length and diameter, thereby deciding on the appropriate type of tube! !
First of all, it should be noted that process calculations cannot be carried out based on your given conditions, as the physical properties of the materials on both sides (density, viscosity, specific heat, thermal conductivity) are not available. Courses or graduation projects are not that complex; I agree with the view expressed on floor 9. The main task is to design a reasonable length-to-diameter ratio, determine the specifications of the heat exchange tubes, select appropriate flow rates for the tube side and shell side, as well as decide on the type of baffle, its inclination, and spacing
How did you carry out the calculations for the heat transfer part?
When the heat dissipation area is specified, this sets a fixed parameter; it means that the radiator you design must achieve the corresponding efficiency
This post was last edited by wanlirn on 2017-5-4 10:31. It’s a question from the teacher regarding the optimized design of heat exchangers