| Author: | Wu, Qian |
| Title: | Effects of different falling film dehumidifiers on the flow morphology with CFD simulations |
| Advisors: | Lu, Lin (BSE) |
| Degree: | M.Eng. |
| Year: | 2020 |
| Subject: | Humidity -- Control Energy conservation Air conditioning Energy consumption Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Building Services Engineering |
| Pages: | xiii, 83 pages : color illustrations |
| Language: | English |
| Abstract: | Energy consumption has been one of the most concerned questions all over the world. The electricity consumption of air conditioning systems contributes to the largest part in residential and commercial buildings. Then, liquid desiccant dehumidification technology was introduced to decrease the power consumption and to achieve better temperature and humidity control. Many previous researches focused on the influence of macroscopic parameters on the dehumidification performance of dehumidifiers. However, the flow mechanism in the dehumidifier interior was seldom studied. With a more comprehensive understanding of flow mechanism, the enhancement of moisture removal capability can be proposed from a more essential perspective. Therefore, the effects of several types of modified dehumidifiers on the flow morphology were studied in the thesis. Firstly, the flow processes on the flat and corrugated plates were studied with CFD 3D models. It was found that the minimunm wetting rate of the corrugated plate was almost twice higher than that of the flat plate, but it had much larger wetted area. Then, because of the fluctuation in flow process, the liquid-gas interface can be larger than the physical plate surface in certain cases. Besides, the axial velocity plays a more important role in the corrugated plate and causes a longer contact time and a more stable flow on the plate. However, with the increase of plate height, the wetted width on corrugated plate would contract because the liquid is easier to gather at the caving part. Then, a 3D model with film-reverting plates was also established to study the flow characteristics on the reverting plates. Although the average film thick increases with the rise of liquid velocity, it decreases along with each plate, which means the ability of absorption also declined gradually. Besides, the influence of contact angle on the wettability of falling film is notable. Smaller contact angle contributes to a larger wetted area on both of the plate. Moreover, the lower contact angles of 10° to 50° contributes to larger wetted area in the corrugated plate, however, when the range of contact angle is 50° to 90° , the difference of wetted area is small on both vertical plates, which means that higher contact angles lead to more serious decrements of wetted area in the corrugated plate. Finally, several enhancement methods of dehumidifier performance are proposed. For the dehumidifier with corrugated plate, the plate can not be too high to avoid the contract of wetted width, which would largely enhance the wettability of falling film. For the dehumidifier with film-reverting plate, there should be a minimal liquid velocity to make sure that the both sides of liquid desiccant can be used for absorption. The axial and radial velocities in the reverting plates need further investigation. In addition, the structure with higher contact angle is recommended to be designed as corrugated plate, while the flat plate is more appropriate if the contact angle is low. |
| Rights: | All rights reserved |
| Access: | restricted access |
Files in This Item:
| File | Description | Size | Format | |
|---|---|---|---|---|
| 5344.pdf | For All Users (off-campus access for PolyU Staff & Students only) | 1.73 MB | Adobe PDF | View/Open |
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