Comparison of Two Laboratory Methods for Measuring the Critical Temperature of Sandy Soils

Simplified two-step, cross-sectional approach for coupled heat and moisture transfer modeling of shallow, horizontal, ground-based heat Exchangers

“…The soil-water characteristic curve (SWCC) describes the relationship between matric suction and moisture content, and the thermal conductivity dry-out curve (TCDC) defines the relationship between soil thermal conductivity (λ) and moisture content (commonly represented as volumetric or gravimetric water content, or as degree of saturation). As the SWCC and TCDC provide required information for modeling coupled heat and moisture transfer in unsaturated soil [24,[28][29][30], these relationships for SP and SM samples were measured using multiple specimen and modified Tempe cell tests, which have been widely used by previous researchers [14][15]. In the multiple specimen tests, the soil thermal conductivity was repeatedly measured at various moisture contents and soil densities (e.g., 3% moisture content compacted to 90% γdmax).…”

Modeling of shallow, horizontal, unsaturated, ground-based heat exchangers with consideration of dry zone formation

“…Table 1 summarizes index properties-soil particle diameters corresponding to 10% and 50% finer (D10) and (D50), respectively; coefficient of uniformity (Cu); and coefficient of curvature (Cc)-and γdmax. Coupled heat and moisture transfer in soil (e.g., dry zone formation) depends on the hydraulic and thermal properties of the soil [12]. The hydraulic and thermal behaviors of unsaturated soil can be predicted using the soil-water characteristic curve (SWCC), which is a relationship between matric suction and degree of saturation, and the thermal conductivity dry-out curve (TCDC) that represents thermal conductivity (λ) at variously saturated conditions [8,[13][14][15][16].…”

“…Gravimetric moisture content near the boundary was about 1%. In this study, physical properties of the backfill were adapted from one sample used in [12], and modeling results indicated similarly that VWC around a boundary between dry and wet zones is about 0.04 m 3 /m 3 , which is about 1% gravimetric moisture content. In contrast to the rapid heat and moisture transfer around the GHX, more gradual gradients of temperature and VWC were observed at distance from the GHX.…”

“…2, potentially resulting in a decrease in the GHX efficiency. According to [12], soil thermal behavior significantly changed near a boundary between dry and wet zones. Specifically, heat transfer gradually occurred through wet soil that has a relatively higher thermal conductivity while rapid heat transfer was observed in dry soil near the GHX due to a relatively lower thermal conductivity.…”

“…6 also shows isotherms for the same case (GHX temperature of 35 °C after 258 days) to more precisely quantify heat dissipation from the GHX. Oh and Tinjum (2017) reported that a boundary between dry and wet zones is observed where the heater temperature of about 30% to 50% dissipated (depending soil thermal properties). Similarly, in this modeling, the isotherm where 50% of the delta between pipe temperature and undisturbed ground temperature was dissipated (i.e., T50) approximately indicated the boundary between moist and dry soils (i.e., 27.5 °C isotherm in Fig.…”