摘要 本研究以熱再循環燃燒技術為主要核心，使用瑞士捲燃燒器(Swiss-roll burner，簡稱SRB)，將不同當量比(equivalence ratio)與流速的丙烷/空氣預混氣體燃燒轉換成高溫生成物，並採用不同的熱交換設計概念，目的是設計出省能熱水器。接著以燃氣雷諾數(Re)、當量比(ψ)對水溫與水熱效率(ηthermal)的影響，來做新一代熱水器的改良與評估標準，並量測燃燒生成物之濃度，如CO和NOx等，藉以判斷熱水器系統與燃燒器彼此結合後是否會導致燃燒熱釋放的效率降低。熱水器的設計概念有三：(1)結合鰭管式熱交換器，使用市售電腦用水冷系統鰭管散熱組，透過其良好的熱交換特性，將瑞士捲燃燒器高溫生成氣體之熱量與冷水轉換；(2)使用自研發銅材水渠道為燃燒器上板，藉由高溫火焰接觸來傳熱，並於水渠道上板中加入鰭片增加熱交換面積；(3)加入延伸銅管，由燃燒器排氣流道出口延伸到中心燃燒室出口處再轉折返迴。實驗結果顯示，使用鰭管式熱交換器必須先解決高溫廢氣水冷凝於熱交換器面板上而使熱交換效率下降的問題，特別是在高流速下會更加速冷凝水之產生。而使用銅材質上板能克服冷凝水問題，並直接由燃燒室的高火焰溫度透過銅板直接傳遞到水流中，使用捲數1.5圈之瑞士捲燃燒器，燃燒器出口處仍有500oC以上的高溫氣體排出。結合了延伸銅管的概念，可使出口氣體之溫度下降到100oC左右，證明延伸銅管置於燃燒器生成物流道內是有效的設計概念。我們進一步地使用捲數為2.5圈之瑞士捲燃燒器，可有效增加熱再循環率，提高熱水水量。本論文另一重點，以熱再循環燃燒器為對象，首度建立用熱損失為參數之數學模型，藉由實驗量測結果佐以建立符合操作條件下之熱損失參數，做為日後設計改良熱水器之參考。 The purpose of this research is to design an energy-saving geyser using heat-recirculating lean premixed combustion technique in the Swiss-roll burner (SRB). The burner uses lean premixed C3H8/air mixtures as a fuel. The effects of Reynolds number (Re) and equivalence ratio (ψ) on the hot water temperature and the heat efficiency of the geyser are investigated in order to judge and improve design. Emissions, such as CO and NOx are measured by the flow gas analyzer. Three different designs of the heat exchangers inside and outside the SRB are proposed, (1) a fin-tube heat exchanger similar to that used by the personal computer, (2) a self-designed copper water plate with fins which is used as the upper plate of the SRB, and (3) similar to (2) but plugging the extended copper tubes along the flow channel of the products to increase heat transfer for water heating. Experiment results show that the water condense problem on the fin-tube surface, as the first design, can degrade the heat transfer efficiency especially at high Re. The second and third designs are free from the water condensed problem. The second design with 1.5 turns of the SRB is not good enough, because the exit temperature of the products is still high, over 500oC. In order to fully utilize the hot temperature of the products, we use the third design, and the exit temperature of the SRB can be reduced to about 100oC. Furthermore, a bigger SRB with 2.5 turns is also built for increasing higher hot water flow rates in the geyser. Probably, the most important point in this thesis is to develop a simple mathematic model based on several heat loss parameters in the heat-recirculating system to predict the performance of the geyser and thus improve its design. Finally, this simple mathematical model is proposed.
