Impact of increasing the heat exchange area (without process fluid adjustment)!
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This post was last edited by YunDanFengYeQing on December 8, 2016, at 21:16. Currently, the design involves a fixed tube-sheet vaporizer. The shell-side fluid is ambient-temperature water (at atmospheric pressure; inlet temperature: 15°C), while the tube-side fluid is liquid nitrogen (at 10 MPa; inlet temperature: -168.4°C)℃； Exit temperature -90°C) ； The heat transfer coefficient of water is set at a conservative value of 300 W/㎡·K; the liquid nitrogen is calculated in segments: 1. Before supercritical state, that is, at 10 Mpa, -168.4°C to 10 Mpa, -147℃ ； 2. After supercritical state: 10 Mpa, -147°C to 10 Mpa, -90℃ ； The heat transfer coefficients are almost identical, at 1157.5 W/㎡·K and 1121 W/㎡·K respectively ； Due to the leadership’s requirement for a higher safety factor, it was determined that Q_needed = Q_absorbed * 1.5; as a result, it was found that a heat exchanger with a surface area of 50㎡ is sufficient to meet the process requirements! Since the heat exchanger operates at high pressure, its design diameter is DN400, and it is approximately 5 meters long! The leader requested a design of 10 to 12 meters. 1. Here comes the problem! The leader requires a design for 100㎡! (The heat exchange area is doubled.) What effects will using it in this way have? 2. Since liquid nitrogen is the process fluid and its outlet temperature and flow rate need to be determined and controlled, how should the water flow be adjusted to maintain balance? 3. From a superficial perspective, a heat exchanger 5 meters long would be sufficient to meet the requirements, with an outlet temperature of around 3.5–4°C; however, since the design now calls for a 10-meter-long heat exchanger, I’m worried that the water might freeze severely! I’m just starting to work with heat exchanger design, and my understanding of some issues is still limited; I hope experts here can help provide a thorough analysis!
This heat exchanger design has many problems: 1. Your management decided to double the heat exchange area in order to prevent the temperature on the water side from dropping too low, which results in increased costs for the equipment. 2. A self-standing pressure regulator should be used on the liquid nitrogen side to ensure stable vaporization of nitrogen. 3. Since freezing is a risk on the water side, safety measures against freezing must be in place to maintain an outlet water temperature of over 10 degrees Celsius during heat balance calculations.
Please explain item 1.2 in detail! :handshake 1. How can the temperature be kept from dropping too much when the heat exchange area is doubled? 2. Is the purpose of the pressure control valve to address the high pressure fluctuations inside the heat exchanger? Use a pressure reducing valve to control the outlet pressure? Our nitrogen outlet has a direct nozzle; if the operating conditions don’t change significantly, it doesn’t have much impact, but it is necessary to include control at 10 MPa.
This post was last edited by YunDanFengYeQing on 2016-12-8 at 22:12. @cl6119, @QingChengJun, @Grizzly, @humanrzm, @XiaoJie, @YaMei, @great.wang – Apologies, all of you! Could you help analyze it and give some suggestions!
As the flow rate increases, the heat also increases, and consequently the temperature at the nitrogen outlet on the tube side rises as well.
The leader doesn’t understand the situation; they just say to increase the area – can’t they say a bit more?~
The management is not confident in the heat transfer coefficient, and freezing occurs after long periods of operation; therefore, they recommend going for a larger size instead! It seems that the only thing we can do now is adjust the K value! I don’t know how to make adjustments
The management is not confident in the heat transfer coefficient, and freezing occurs after long periods of operation; therefore, they recommend going for a larger size instead! It seems that the only thing we can do now is adjust the K value! I don’t know how to make adjustments
You don’t need to spend too much effort on these details either; after all, you are engaged in research work. If there are no problems, how would you have the opportunity to write articles? Research involves creating problems and solving them – you can first make a rough estimate, conduct an experiment, and once it’s run, you’ll know what’s going on. Sure, I’ll tell you, but make sure your boss doesn’t see it. . . :lol
:L is like this! I’m a beginner; a heat exchange area of 50㎡ calculated this way should be sufficient. In reality, the larger it is, the better! But without figuring it out, one can’t be confident!