創新式蝦池清淤系統之研發

Abstract

蝦池底淤泥的累積影響水質並且是養殖成敗的重要因素。底泥主要由殘餌、死蝦、有機物、被侵蝕的土堤所構成，經由養殖期間觀察與採樣結果發現，累積3~4天的底泥型態是屬於塊狀、黏稠的情形，超過一星期後，則會轉變為容易懸浮、擴散的碎屑。經由水車的影響，最終這些物質都會在池中央半徑約5~8m的範圍中慢慢沈積，底泥厚度由中央逐漸向外圍遞減。本研究發展的清淤概念建構於「再懸浮」的原理之上，利用泵產生噴流的力量使得沈積於池中央5 m內的池底淤泥再度懸浮移動至中央排水管附近，達成大範圍淤泥集中至小範圍區域移除的需求。同時，本研究設計的清淤模組因為具有上擋板與側擋板的構造，形成壁面噴流的情形，噴流能夠對靜態的流體產生吸入效應，加上擋板的限制功能，成功的解決底泥「再懸浮」與「擴散」二者間矛盾的問題，克服底泥移動時對水質造成危險性變動的情形。實際測試模組的參數(長：1200 mm，噴頭位置：65 mm、80 mm)是採用軟體CFdesign 模擬結果所討論出的最佳參數製作而成。軟體模擬規劃主要著重於噴頭和側擋板的相對位置與單一模組長度的測試。噴頭距離側擋板的位置分為30 mm、65 mm、250 mm、∞ mm四種模型。模組長度則是600 mm、1200 mm、1800 mm三種模型。初步測試結果顯示，噴頭距離65 mm、模組長度1200 mm，對於解決「再懸浮」與「擴散」之間的矛盾現象有較大的功效。實驗證實本系統確實可以達到清除淤泥、死蝦、殘餌的功能；結構簡單、模組化的設計則適合普通室外池使用。

關鍵字：底泥、再懸浮、CFD

Sludge accumulation in shrimp ponds is a vital factor influencing water quality and farming success. Sludge is composed of uneaten food, dead shrimp, organic matter, and soil particles. Sludge samples appear like sticky pieces after about 3 days of sedimentation, and would change to thick, foggy, easy to suspend matters after one week. Influenced by the paddlewheel, sludge would accumulate at the central zone of the pond within 5 m from the central pipe, while the thickness of sludge decreasing progressively outwards. This study is based on a resuspension principle, using a pump to produce flow to make the sludge resuspend and move to the central drain pipe, where it could be flushed away quickly, thereby resolves the contradiction of simultaneous resuspension and spreading. Since the sludge is concentrated first from a large-area to the central pipe, the removing efficiency through the central pipe is largely enhanced. The sludge removing system developed in the study covers the sludge with a top and a lateral board and could move the sludge while allowing no particles to spread out of the removing system due to the wall jet phenomenon of fluid dynamics. The sludge removing system is made up of four modules, each is 120 cm long and totally is about 5 meters so that it could sweep through the central 5 meters radius area of the pond. A computational fluid dynamics (CFD) software-CFdesign is used to simulate the flow and to find optimum parameters of the system, including the nozzle position and the length of the modules. It is shown by simulation that the current design can best achieve the resuspension and transmission of the sludge with only a 100W submersible pump. A field experiment has verified that this system can remove sludge, dead shrimp, uneaten food in about 12 minutes, and with its simple structure the sludge removing system is suitable for the ordinary use of outdoor ponds. Keywords：sludge, resuspension, CFD