ERROR ANALYSIS OF HEAT PULSE METHOD FOR MEASURING SOIL HEAT-CAPACITY,DIFFUSIVITY, AND CONDUCTIVITY

A dual-probe heat pulse (DPHP) method was developed recently that allo ws for the simultaneous, automated measurement of soil thermal diffusi vity (kappa), volumetric heat capacity (rho c), and thermal conductivi ty lambda). Estimation of thermal properties is based on theory for th e conduction of heat away from an infinite line source (ILS) that is h eated for a short period of time. In this study, we examined possible sources of error in the use of the ILS theory by comparing it with oth er models that explicitly account for finite length and cylindrical sh ape of the actual heater. For probe geometry and heating times typical of our experimental work, the analysis of model error showed that ass uming an infinite length for a heat source of finite length caused err ors < 2% in the estimated thermal properties. Assuming the cylindrical ly shaped heater to be a line heat source caused errors of < 0.6% in t he estimated thermal properties. Thus, the ILS theory appears to be ap propriate for use in the DPHP method if probe geometry is considered c arefully. However, small changes in probe geometry tan lead to large m odel errors. First-order error analysis also was used to predict how t hermal property estimates will be affected by experimental errors in t he measured inputs to the ILS model. The analysis shows that kappa and rho c estimates are sensitive to measurement error in probe spacing ( r), but lambda is unaffected by error in r. Estimates of kappa and lam bda. were shown to be sensitive to measurement error in the time to th e temperature maximum (t(m)), whereas pc was affected only slightly by such error.