地埋螺旋管熱交換器性能分析與應用

Abstract

本研究以實驗量測和FLUENT軟體來分析及驗證地埋螺旋管熱交換器的散熱性能和吸熱性能，並比較計算結果其趨勢相符合，此外分析土壤熱傳導係數、土壤熱容、中央直管絕熱、流體入口位置改變以及入口流體溫度改變對散熱量及土壤溫度變化的影響，其結果指出在中央直管做隔熱，在起始運轉6.5小時內其散熱量會低於中央直管未做隔熱的設計，而6.5小時後的運作時間其散熱量高於中央直管未做隔熱的設計是由於降低熱短路的效應；中央直管入水方式的散熱性能稍高於外側螺旋管入水方式，土壤熱容值越高其蓄熱能力越強而使散熱量越高；土壤熱傳導值影響土壤溫度分佈的均勻性，其值越高則散熱量越高。本研究於彰化二林實地測試螺旋管的散熱性能，進行地埋螺旋管熱交換器的測試，包含三種測試條件：當入口溫度為45℃、體積流率為12LPM，經過17小時測試運轉後，其單位長度散熱量為120W/m；當入口溫度為45℃、體積流率為3.2LPM，經過15.7小時測試運轉後，其單位長度散熱量為147.1W/m；當入口溫度為35℃、體積流率為3.2LPM，經過22.7小時測試運轉後，其單位長度散熱量為83.1W/m，另透過實驗數據驗證數學控制體積的分析模式，並透過此分析模式建立地埋螺旋管熱交換器的性能分析圖。 本研究將地埋螺旋管熱交換器應用於高功率LED的散熱，可使功率600W的LED在0.3m3燈座體積下正常運轉，並使基板溫度維持在55℃以下，另以白天關燈、晚間開燈的方式做週期運轉三天，觀測出土壤溫度會隨著操作模式形成週期，另透過實驗驗證數學控制體積所分析的散熱率和燈板溫度。

The study experimentally and theoretically investigates the heat transfer performance of the helical ground heat exchanger (HGHE). The simulation results are made with CFD code Fluent, which are found in fine agreements with the experimental data. The helical ground heat exchanger has been investigated with Fluent under different experimental parameters and working conditions. The parameters include the soil thermal conductivity, the soil heat capacity, the insulation of the center pipe, the inlet flow location and the inlet temperature of the flow. The results show that the heat dissipation rate of the HGHE with insulating the center pipe is lower than the HGHE without insulating the center pipe within 6.5 hours after start-up, but is higher than the HGHE without insulating the center pipe because avoiding the effect of the thermal interference. The heat dissipation rate of the HGHE with the inlet flow from the inside pipe is higher than from the outside pipe. Besides, the higher soil thermal conductivity and the higher soil heat capacity are benefit to elevate the heat transfer performance of the HGHE.The ground cooling is tested under the three cases. The results show that heat dissipation rates of the HGHE are 120W/m under the inlet water temperature of 45℃ and volume flow rate of 12LPM, 147.1W/m under the inlet water temperature of 45℃ and volume flow rate of 3.2LPM and 83.1W/m under the inlet water temperature of 35℃ and volume flow rate of 3.2LPM. The study constructs the relationship between the heat dissipation rate of the HGHE and soil thermal property through the 1-D model and experiment data. The thesis applies the HGHE to dissipate the heat generated from the high power LED. It keeps that the 600W LED normally works with the lamp plate of 0.3m3 and maintains the base plate temperature lower than 55℃. The ground temperature also varies periodically as the 600W LED works periodically. In addition, the base plate temperature and the heat dissipation rate of the HGHE based on a lumped model match the experimental data.