隧道噴霧降溫之數值模擬

Numerical Simulation on Spray Cooling for Tunnel

章永強(Yung-Chiang Chang)

指導教授 ： 柯明村

國立臺北科技大學/機電學院/能源與冷凍空調工程系碩士班/碩士(2013年)

摘要

本論文主要以數值方法來模擬隧道中架設噴霧系統所造成的溫度場變化，並改變粒徑、水量、水溫、相對濕度，探討這些參數對隧道噴霧降溫所造成的影響，以及噴霧系統的開啟時機。本文採用計算流體力學軟體ANSYS Fluent13.0來進行計算，且實地架設噴霧系統與量測設備，經由與量測數據比較，證明本論文所提出的物理模型準確度可信。模擬取隧道長度100公尺為計算域，並於入口處創建4個噴嘴，噴霧方向與車輛行駛方向為同方向，入口風速固定4m/s，壁面為絕熱。為了確保所設計的水量能夠兼顧降溫及行車安全，於高度2.2公尺處創建一監控平面對經過此平面的離散項顆粒進行統計，以監控平面沒有捕捉到任何顆粒為決定隧道噴霧水量、粒徑組合的參考項目。用六面體網格將計算區域離散化，網格數約53萬，採用k-ε紊流模式，速度與壓力耦合選擇SIMPLEC。採用離散相模型追蹤噴霧液滴。結果顯示，水量是最主要影響降溫程度的參數，當水量增加降溫效果會較好，但流量過大可能會影響行車安全。當水量3.5 LPM，其監控平面有捕捉到水滴，而1.75 LPM會使隧道降溫1℃。噴霧粒徑的大小與降溫程度沒有太大關聯，但是與蒸發速率有關，當噴霧粒徑越大，越不容易蒸發。而改變水溫對於降溫結果並沒有太大影響，由於蒸發式冷卻是靠水的蒸發潛熱降溫，所以不用刻意製造冰水噴霧。並建議在環境相對濕度70%以下開啟蒸發式冷卻，避免因濕度過高，水滴來不及蒸發影響駕駛能見度。最後加入熱源模擬，噴霧系統仍可以將隧道降溫，噴霧影響距離為35公尺，但隨著隧道長度上升，溫度還是會持續上升，因此需每隔一段間距增設一噴霧系統。

關鍵字

蒸發式冷卻 ； 噴霧降溫 ； CFD模擬

並列摘要

This paper use numerical method to simulate the change of temperature field caused by spraying system. Changing particle diameter, water quantity, water temperature and relative humidity that in order to investigate the best combination of parameters and active time of spraying system in tunnel. This study adopted Computational fluid dynamics software ANSYS Fluent 13.0 to calculate, and on-site erection spray system and measurement equipment. The numerical simulation was verified by experimental data, and prove that the proposed physical model accuracy credible. The simulation takes tunnel length of 100 meters for the computational domain, and creates four nozzles in tunnel entrance. The spray direction is the same as the vehicle traveling direction. Inlet velocity fixed 4m/s and wall is adiabatic. In order to that the design can be both cooling and traffic safety. To create a monitoring plane in height of 2.2 meters and statistics of discrete particles pass through this plane. Monitoring plane did not catch any particles to determine the best particle diameter, water quantity combination of reference for the tunnel project. Hexahedron grids were used in discretizing the computational domain. Number of grids is approximately 530000, Using k-ε turbulence model, velocity and pressure coupling selection SIMPLEC. The discrete phase model (DPM) was used to track spray droplets. The results show water quantity is the most important parameters affecting the degree of cooling. The amount of water increase the cooling effect would be better. However, much water may affect driving safety. The monitoring plane captures water droplets, when water arrive 3.5 LPM. The tunnel temperature will decrease 1℃ by 1.75 LPM. Particle diameter is not much correlation with the degree of cooling, but it is related to evaporation rate. The particle diameter is getting greater, the more difficult to evaporate. Water temperature changes did not affect the results. Since evaporative cooling is by latent heat of water evaporation, so water spray not use chilled water. Recommendations at ambient relative humidity below 70% open evaporative cooling. Avoiding excessive humidity, water droplets evaporate too late to affect driving visibility. Finally, adding a heat source simulation, Spray system also can cool tunnel. Spray influence distance of 35 meters. With the increasing in tunnel length, temperatures will continue to rise, so that it required a spray system every pitch.

並列關鍵字

Evaporative cooling ； Spray cooling ； CFD simulation

參考文獻

14.李秀娟，”雪山隧道通風系統一維流場分析與通風策略”，碩士學位論文，國立台灣大學，應用力學研究所，2006年。

5.R. Sureshkumar , S.R. Kale , P.L. Dhar , “Heat and mass transfer processes between a water spray and ambient air – I. Experimental data “,Applied Thermal Engineering,2008.

6.R. Sureshkumar , S.R. Kale , P.L. Dhar, “Heat and mass transfer processes between a water spray and ambient air – II. Simulations“,Applied Thermal Engineering,2008.

7.C.C.Hsieh, S.C.Yao“Evaporative heat transfer characteristics of a water spray on micro-structured silicon surfaces“ heat and mass transfer,2006.

8.Y.Tao ,X.Huai ,L.Wang ,Z.Guo“ Experimental characterization of heat transfer in non-boiling spray cooling with two nozzles “Applied Thermal Engineering, 2011.