计算値比较试験结果図坑井九州大学

1、Thermal Response Tests Using Optical Fiber Thermometers September 13, 2006Hikari FUJII, Hiroaki OKUBO, Ryuichi ITOIGraduate School of Engineering, Kyushu University, Japan Background At Ground Heat Exchangers (GHEs) drilled in heterogeneous formations, heat exchange rates may not be uniform due the

2、variation of ground thermal conductivity (ls) with depth. Optical fiber thermometers, which measure continuous temperature distribution along optical fiber sensors, could be useful in the estimation of the distribution of ls.Estimated Vertical Distribution of Heat Exchange RatesHigh CapacityLow Capa

3、cityContents To carry out Thermal Response Tests (TRTs) using optical fiber thermometers at GHEs in Kyushu Universitys campus in Fukuoka City, Japan. To develop procedures to estimate ls distribution on the basis of measured temperature data.Installation of Optical Fiber SensorsOptical Fiber Thermom

4、eter (Hitachi Cable Ltd. FTR-070) -Resolution: 0.1K -Accuracy: 1.0K -Minimum Depth Interval: 1.0m -Minimum Time Interval: 60secExperimental Wells and Geological ColumnUnconformity (-17m)Siltstone and Silty Sandstone (Impermeable)Sand and Gravel (Permeable)Sensor PositionQuaternary SystemTertiary Sys

5、temTemperature Distribution in Co-axial and U-tube GHEs(Co-axial GHE)Large temperature difference with depth. Temperature change with depth needs to be considered in the calculation of well performance.(U-tube GHE)Nearly constant temperature with depth.Well temperatures could be treated as uniform.V

6、ertical Temperature Distribution (After 1 days Circulation)Temperature Distribution in U-tubes during CirculationMeasured TemperaturePhoto of WellheadMeasured water temperatures in U-tubes showed negligible differences with depth in Survey No.1.Water temperature in U-tubes is considered uniform unde

7、r high circulation rates.Average Temperature uw (m/s) qw (L/min) 0.55 35.0 0.33 21.0 (*)Double U-tube ID=26mmHeat exchange rates can be calculated in each sub-layer.Multi-layer Model (n=50 in this study)lnl2l1 Formation heterogeneity cannot be modeled.qavgConventional Model TinToutlavgMulti-layer Mo

8、del Apply the cylindrical source function (Ingersoll et al,1954) to each sub-layer.q1q2qn (1) Heat transfer between tubing and annulus (q1) and annulus and ground (q2) q1,n=UtAt (Ta,n-Tt,n) q2,n=UaAa (Tro,n-Ta,n) U: Heat Transfer Coefficient A:Surface Area(2) Convective heat transfer in pipes (Tt,n-

9、Tt,n+1) mwCp=q1,n (Ta,n-Ta,n+1) mwCp=q1,n -q,2,n mw: Mass Flow RateCp: Specific HeatTan-1nn+1Ttq1q2Calculation of Temperature Distribution in Co-axial GHETroEnergy Balance in Co-axial GHEEstimation of Thermal Conductivity)()1 ()(2)()(2)()(nlayercalroobsrontestnstepcaloobsoTTTTFEstimate ls by minimiz

10、ing objective function F using a nonlinear regression method, the Polytope method (Nelder and Mead, 1965).To: Water temperature at well outlet (K)Tro: Outer face temperature of GHE (K)obs: observed, cal: calculatednstep: number of timestep, nlayer: number of layerntest: number of comparison between

11、measure and calculated temperature profiles: Weighting factor (=0.1)Error in heat medium temperatureError in vertical temperature profileConditions of TRTsH-1 (Co-axial GHE)H-2 (U-tube GHE)0.62(m/s)0.31(m/s)Interpretation of TRT No.1 (Co-axial, Reverse Circulation)Outlet Temperatures of Heat MediumW

12、ell Temperatures during CirculationCalculated temperature fitted measured data reasonably well.Interpretation of TRT No.3 (Single U-tube)Outlet Temperatures of Heat MediumWell Temperatures (After Well Shut-in)Hot tubesCold tubesSensor Estimated Distribution of lsLow PermeablePermeable PermeableCompa

13、rison of Estimated Thermal ConductivityAdvection effect of groundwater flow1.63 W/m/K -15m1.21 W/m/K -42mDistribution of Heat Exchange Rates (TRT No.1)SummaryThrough interpretations of TRTs using optical fiber thermometers, following results were obtained:The application of optical fiber thermometer

14、s on TRTs will enable the optimization of GHE length in heterogeneous formations.The estimated distribution of thermal conductivity agreed with the local geological and groundwater information.Co-axial and U-tube GHEs require different modeling approaches. Interpretation of TRT No.2 (Co-axial, Norma

15、l Circulation)Using same ls distribution as TRT No.1, calculated temperature well matched measured data.Outlet Temperatures of Heat MediumWell Temperatures during CirculationCylindrical Source FunctionTemperature difference between ground and GHE Tff : farfield temperature, Tro : outer face temperature of GHE,nstep: number of timestep, qgc: heat exchange rate, ls: thermal conductivity of soil, L: well depthCylindrical source function G Z= st/r2 P=r/ro J0, J1, Y0, Y1, Y2 : Bessel functions, s : thermal diffusivity of soil, ro : outer radius