管板式太陽能加熱器為一種結構簡單、容易維護的加熱器。一般利用管板式太陽能集熱器於熱水器、蒸餾系統、流體加熱及乾燥之用途。影響管板式太陽能集熱器集熱效率的因素中，以流體流量、迴流比值與集熱器之流體流動組數的影響最為顯著。 本研究乃針對具迴流之管板式太陽能集熱器，探討(一)具迴流效應;(二)集熱器流體流動組數;(三)圓管內加翅;(四)流體總流量;(五)流體進口溫度;(六)太陽光入射量等參數對集熱效率之影響，並且討論因迴流操作而增加之水力消耗增加量，以求得在經濟效益考量下之最佳管板式太陽能集熱器的設計與操作參數，及求得在固定流量下，最佳集熱器流體流動組數之設計參數。並將結果與傳統之無迴流管板式太陽能集熱器作比較。研究結果顯示，具迴流效應之管板式太陽能集熱器之集熱效率隨著迴流比增加而增加，而管內加翅型比無加翅型之管板式太陽能集熱器有較高之集熱效率 The study presents a theoretical prediction of the device performance of a sheet-and-tube solar water heater with external recycle, and a comparison of the device performance was made between these two device with and without external recycle. The device with internal fins attached in each tube is also discussed. Analytical results show that the recycle effect can effectively enhance the collector efficiency compared with that in a single-pass device with the same flow rate. The desirable effect of increasing convective transfer rate and the undesirable effect of reducing heat transfer driving force are the two conflict effects produced by the recycle operation. It was found that the convective transfer-rate increment by increasing the recycle ratio could generally compensate for the temperature driving force decrement, leading to improved performance, especially for low flow rate. Also, the collector efficiency increases with increasing collector aspect ratio (i.e., either increasing the tube length or decreasing tube number) for a specified collector area and the distance between tubes.