隱藏式風扇是採用較新的設計概念，不同於傳統式的吊扇，其中最大的優點是採用隠藏式設計，可簡易的安裝於天花板之中，不但可以有效地節省安裝空間，最重要是不會有壓迫與不安全感的問題。由於是採用隱藏式設計，外殼除了包覆單體風扇外，尚須將整體隱藏於天花板之中，因此，如何在狹窄有限的空間內開發出高性能風扇，即成為是本研究的目標。本文為完整評估隱藏式風扇，選用市面上常見款式十四吋軸流隱藏式風扇為研究對象，首先將此風扇之各參數進行完整的流場分析、性能評估、風扇效率計算、扭力估算與噪音分析，藉由數值模擬與實驗方式，詳細地作一整合式探討，以釐清回吸現象與遮蔽效應等不良影響。結果顯示風扇性能之數值計算與實驗量測結果具有良好之趨勢一致性，充分證實此整合之探討方法，可提供進一步性能改善設計之參考。
在性能改善上，本研究將隱藏式風扇分為單體軸流扇與風扇外殼進行設計，首先在單體軸流扇方面，使用正向設計方法之最適化流程，採用數個NACA4系列的二維翼形，結合成三維複合式翼形，並調整風扇相關的重要參數，以確立出高流量之軸流扇為目標。接著參考先前整合式探討之結果，進行新的外殼設計以提昇其性能表現，期間採用數值模擬之可視化，逐一對參數進行觀察與修正；以設計出提高風扇效率之外殼為目標，最後再建立風扇實體模型以進行實驗量測與數值模擬作比較。
最後結果顯示，所得模擬值與實驗值之趨勢相當一致，而且在風扇流量的改善上已經大幅的提升，新設計的隱藏式風扇在結合新的軸流扇與新的外殼後，其最大流量有效的提升64.57%。此外，在內部單體軸流扇設計上，其最大靜壓高於市售樣品33.7%、最大流量則提升了55.48%。綜合上述之研究成果顯示，本文所設計之隱藏式風扇，不論是內部軸流扇或是風扇外殼設計皆已達到整體性能提升目標。再者於設計過程中，同時提供了一套完整風扇性能評估方式，風扇設計者亦可從相關評估資訊中擬定性能改善方案；此完整之評估方法與設計流程能大幅擴增風扇工程師的設計視野，並提升高效能之風扇設計。

The hidden ceiling fan is installed itself deeply behind the ceiling floor to save the room space, eliminate the suppression sense and the possible insecurity. Because the majority part of hidden ceiling fan is embedded in the ceiling floor, the enclosing case is constructed to contain the axial-flow fan in the constrained space. Thus, the hidden ceiling fan is different from conventional ceiling fan that usually without an enclosing housing. To meet with the demand for a high-quality living circumstance, the development of a high-performance fan becomes an essential task and the topic of this research. Here, a hidden ceiling fan equipped with the 14-inch axial-flow impeller is selected from the market for a comprehensive investigation, which is integrated with flow visualization, performance evaluation, calculated efficiency, torque estimation, and acoustic analysis with the aids of numerical simulation and experimental measurement.
Firstly, serious inhale-return phenomenon and blockage effect are numerical and experimentally identified in analyzing this commercial product. Also, a great agreement on the fan performances attained from CFD calculation and measurement is found to verify the reliability of this integrated effort. The approach for performance enhancement is composed of the redesigns on the axial-flow rotor and the housing. In the beginning, an optimal procedure is applied to construct the multi-airfoil impeller which is formed by several NACA four-digital airfoils. Several critical parameters are adjusted to obtain the high airflow rate from this axial-flow rotor. Next this rotor is installed in the original housing to check its aerodynamic performance numerically. Moreover, careful flow visualization and step-by-step modification are incorporated to eliminate the inhale-return phenomenon and other undesired flow pattern associated with the ceiling fan. After these modifications, a CNC-fabricated prototype including new housing and axial-flow rotor are prepared for experimental verification its aerodynamic and acoustic characteristics in AMCA test chamber and semi-anechoic room, respectively.
Consequently, the results from experiment and simulation have the same trend and an acceptable deviation. Also, the test outcomes indicate that the maximum static pressure and airflow rate of the optimized axial-flow fan are increased by 33.7% and 55.48%, respectively. Moreover, the airflow rate of prototype has significantly improved by 64.57% after combining the new designs of rotor and housing. In conclusion, the accomplishment of this work not only attains a substantial improvement on the hidden ceiling fan, but also establishes a systematic and comprehensive design procedure for fan engineers.

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