Journal of the Korea Academia-Industrial cooperation Society (한국산학기술학회논문지)

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An Experimental Study on the Effect of Air Temperature and Humidity on Humidification Performance of the Humidifying Element Used for Air Conditioning

공기 온습도가 공조용 가습 소자의 가습 성능에 미치는 영향에 대한 실험 연구

  • Kim, Nae-Hyun (Division of Mechanical Engineering, Incheon National University)
  • Received : 2018.10.10
  • Accepted : 2019.02.01
  • Published : 2019.02.28
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Abstract

Evaporative humidification using a humidifying element is widely used for humidification of a building or a data center. The performance of a humidifying element is commonly expressed as humidification efficiency, which is used independent of air temperature, humidity and water temperature. In this study, a series of tests were conducted at two air conditions (data center and commercial building) using two different humidifying elements (cellulose/PET and Glasdek) changing the frontal air velocity and water temperature. Results showed that the measured humidification efficiency was dependent on the air condition and water temperature. In fact, even dehumidification occurred at the inlet of the humidifying element at the air condition of commercial building. The reason was due to the inlet water temperature, which was lower than the dew point air temperature. As the difference between the inlet water and the dew point air temperature increased, the humidification efficiency decreased. This suggest that proper thermal model should account for the inlet region, where the amount of moisture transfer may be different from the other part of the humidification element. A simple analysis on the thermal performance of the cellulose/PET humidification element showed that the Sherwood number was adequately predicted, whereas the friction factor was ovepredicted, probably due to the simplification of the channel geometry and the neglection of the water film on the element surface.

가습 소자를 이용한 증발식 가습은 건물이나 데이터 센터의 공조에 널리 사용되고 있다. 가습 소자의 성능은 가습 효율로 나타내는데 이 효율은 공기의 온습도나 물 온도에 무관하게 사용되고 있다. 본 연구에서는 데이터 센터와 건물 공조의 두 공기 조건에 대하여 셀룰로오스/PET, Glasdek의 두 소자를 사용하여 전벙 풍속과 물 온도를 변화시키며 일련의 실험을 수행하였다. 실험 결과 측정된 가습 효율은 공기 조건과 물 온도에 따라 다르게 나타났다. 심지어 건물 조건에서는 소자의 입구부에서 감습이 나타나기도 하였는데 그 이유는 공급수 온도가 입구 공기의 노점온도보다 낮았기 때문이었다. 건물 조건에서는 공급수 온도와 공기의 노점 온도 차이가 증가할수록 가습 효율은 감소하였다. 이로부터 가습 효율 모델을 적절히 세우려면 길이 방향으로 수분 전달량이 변화하는 입구 영역에 대한 해석이 중요하다고 판단된다. 셀룰로오스/PET 소자에 대하여 성능 해석을 수행한 결과 Sherwood 수는 적절히 예측하였으나 마찰 손실은 과대 예측하였다. 이는 해석시 채널 형상을 단순한 삼각형으로 가정하고 소자 표면에 형성된 액막의 영향을 무시한 때문으로 판단된다.

Keywords

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Fig. 1. A photo of a Cellulose/PET humidifying element

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Fig. 2. A photo of a Glasdek humidifying element

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Fig. 3. Humidification test apparatus shown in ASHRAE 133 [10]

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Fig. 4. Schematic diagram showing the air and water property change during humidification

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Fig. 5. SEM photos of the raw material

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Fig. 6. Experimental apparatus

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Fig. 7. A photo and a graph showing the absorption performance of humidifying elements[16]

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Fig. 8. Flow distribution at the header pipe

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Fig. 9. Humidification efficiencies as a function of water flow rate (frontal air velocity: 2.0 m/s)

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Fig. 10. Humidification efficiencies as a function of frontal velocity

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Fig. 11. Pressure drops as a function of frontal air velocity

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Fig. 12. Humidification efficiencies at different inlet water temperatures

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Fig. 13. Sherwood numbers (Cellulose/PET) and friction factors predicted by the model

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