Heat Pulse Method Research Articles

Implementation of specific-heat and NMR experiments in the 1500 ms long-pulse magnet at the Hochfeld-Magnetlabor Dresden

We report on the design and successful testing (up to 55 T) of a 60 T long-pulse (LP) magnet with a pulse duration of 1500 ms at the Hochfeld-Magnetlabor Dresden. This magnet has the capability of producing magnetic fields with time and homogeneity characteristics suitable to host specific-heat and nuclear magnetic resonance (NMR) experiments. We describe the development of a specific-heat probe for this magnet, which uses the quasi-adiabatic heat-pulse method and enables magnetocaloric-effect measurements. Furthermore, we report the implementation of a NMR setup, consisting of home-built probe and spectrometer. Both experimental devices were tested successfully in the LP magnet up to 31 and 44 T, respectively.

APPLICATION OF SAP FLOW MEASUREMENT IN REAL-TIME SOIL MOISTURE MANAGEMENT AND EXAMINATION OF SUPPLEMENTAL IRRIGATION USING AUTOMATIC DRIP SYSTEM UNDER HIGH ATMOSPHERIC DEMAND CONDITIONS

ISHS VIII International Symposium on Sap Flow APPLICATION OF SAP FLOW MEASUREMENT IN REAL-TIME SOIL MOISTURE MANAGEMENT AND EXAMINATION OF SUPPLEMENTAL IRRIGATION USING AUTOMATIC DRIP SYSTEM UNDER HIGH ATMOSPHERIC DEMAND CONDITIONS

IMPROVING HEAT-PULSE METHODS TO EXTEND THE MEASUREMENT RANGE INCLUDING REVERSE FLOWS

Traditional heat-pulse methods are not well suited to measuring either very high or very low sap flows and few methods can measure reverse flow. We have analysed two new methods that potentially extend the measurement range. Both methods can be used by modifying the analysis algorithm and adjusting the probe positions of common heat-pulse methods, with no change to existing equipment. The first method we will refer to as the Symmetrical Gradient method (HPSG). It consists of averaging the temperature difference signal of two probes (ΔT) that are equidistant from the heater. The second method we will refer to as the Symmetrical Derivative method (HPSD). It uses the same symmetrical probe configuration. However, the analysis is based on the maximum rate of change of the temperature difference curve (i.e. the derivative, ΔT’). We use computer modelling to show that these two indicators (ΔT and ΔT’max) are proportional to the heat-pulse velocity across a wide range of positive and negative flows. Hence, both metrics can be used to determine the actual sap flux density with acceptable measurement errors and good measurement sensitivity. We present results from field experiments on a willow tree (Salix alba L.) that was set up to compare our new methods against other heat-pulse techniques. We show that HPSG and HPSD both provide reliable data across a very wide range of flows. We are currently working on other field experiments to further refine our use of HPSG and HPSD to estimate tree transpiration and even to observe sap flow in roots.

A triple-probe heat-pulse method for measurement of thermal diffusivity in trees

Although thermal diffusivity is a crucial parameter for sap flow calculations in both the heat field deformation and the heat ratio method, it is seldom measured on a routine basis. This paper presents a theory based on thermodynamic principles to determine both axial and tangential diffusivity in sapwood. By measuring the temperature response after application of a heat pulse at a short axial and tangential distance from a line heater, axial and tangential thermal conductivity as well as volumetric heat capacity of the sapwood can be derived from a theoretical model. From these parameters, axial and tangential diffusivity can easily be determined. Sensitivity analysis and results of an experiment on European beech (Fagus sylvatica L.) confirm the applicability of the method. The obtained thermal diffusivities ranged from 2.7×10−7m2s−1 to 2.2×10−7m2s−1 for a relative water content (moisture per dry weight) ranging from 0.47 to 0.90, respectively. This was on average 22% lower than when applying the common methodology based on wood core sampling.

Use of the correct heat conduction–convection equation as basis for heat-pulse sap flow methods in anisotropic wood

Heat-pulse methods to determine sap flux density in trees are founded on the theory of heat conduction and heat convection in an isotropic medium. However, sapwood is clearly anisotropic, implying a difference in thermal conductivity along and across the grain, and hence necessitates the theory for an anisotropic medium. This difference in thermal conductivities, which can be up to 50%, is, however, not taken into account in the key equation leading to the currently available heat-pulse methods. Despite this major flaw, the methods remain theoretically correct as they are based on derivations of the key equation, ruling out any anisotropic aspects. The importance of specifying the thermal characteristics of the sapwood according to axial, tangential or radial direction is revealed as well as referring to and using the proper anisotropic theory in order to avoid confusion and misinterpretation of thermal properties when dealing with sap flux density measurements or erroneous results when modelling heat transport in sapwood.

Evaluation of compensated heat-pulse velocity method to determine vine transpiration using combined measurements of eddy covariance system and microlysimeters

A field experiment was carried out with the objective to evaluate the compensated heat-pulse velocity (CHPV) method used to determine vine transpiration (Tsap). The performance of the CHPV method was evaluated using daily values of residual transpiration (Tr), obtained as the difference between actual evapotranspiration (ETa) and soil evaporation (Es) (Tr=ETa−Es) measured from an eddy covariance (EC) system and microlysimeters, respectively. Data used in this study were collected over a drip-irrigated Merlot vineyard trained on a vertical shoot positioned (VSP) system during three consecutive growing seasons (2006/2007, 2007/2008 and 2008/2009). Results showed that the best agreement between Tsap and Tr was obtained using correction coefficients for a wound size of 2.4mm. The comparison between Tsap and Tr indicated that the index of agreement (d) was 0.97, and root mean square error (RMSE), mean absolute error (MAE) and mean bias error (MBE) were 0.22, 0.18 and −0.04mmday−1, respectively. Also, the sensitivity analysis of fraction of wood (FM), fraction of water (FL) and factor of thermal properties of the woody matrix (k) suggested that the changes of ±30% have a little effect in the final estimation of daily vine transpiration with variations less than 12%. Finally, major disagreements between Tr and Tsap were observed on partially cloudy days where rapid changes (on 30min time intervals) of solar radiation produced extreme values of volumetric sap flux density.

Probe Body and Thermal Contact Conductivity Affect Error of Heat Pulse Method Based on Infinite Line Source Approximation

Probe Body and Thermal Contact Conductivity Affect Error of Heat Pulse Method Based on Infinite Line Source Approximation

Trunk sap flow characteristics during two growth stages of apple tree and its relationships with affecting factors in an arid region of northwest China

a b s t r a c t Sap flow is an important parameter for orchard irrigation scheduling. According to seasonal variation of trunk diameter and leaf area index (LAI), the whole growth stage of apple tree was divided into stage I (rapid leaf and trunk growing) and stage II (rapid fruit enlarging and maturing). Trunk sap flow (SF) of apple tree irrigated with 100% evapotranspiration (ET) was measured using the compensation heat-pulse method, and meteorological variables, soil water content (� ), LAI, maximum daily stem shrinkage (MDS) and leaf water potential (ϕl) were monitored during the whole stages from 2008 to 2010 in an apple orchard of arid region of northwest China. The relationships between SF and affecting factors were also analyzed. The results show that LAI increased rapidly at stage I, and SF was mainly determined by vapor pressure deficit (VPD), LAI and reference evapotranspiration (ET0). However, LAI was relatively stable at stage II, and SF was affected by VPD, ET0 and � . Under the condition of border irrigation with 100% ET, tree SF could be calculated using VPD, ET0 and LAI at stage I, and VPD, ET0 andat stage II. Moreover, SF had significantly negative linear relationship with ϕl and exponential relationship with MDS. Therefore, it is beneficial for more accurate modeling of truck sap flow and orchard water management under border irrigation by analyzing major factors affecting sap flow during two stages of apple tree. © 2011 Elsevier B.V. All rights reserved.

Cumulative Soil Water Evaporation as a Function of Depth and Time

Soil water evaporation is an important component of the surface water balance and the surface energy balance. Accurate and dynamic measurements of soil water evaporation enhance the understanding of water and energy partitioning at the land–atmosphere interface. The objective of this study was to measure the cumulative soil water evaporation with time and depth in a bare field. Cumulative water evaporation at the soil surface was measured by the Bowen ratio method. Subsurface cumulative soil water evaporation was determined with the heat pulse method at fine‐scale depth increments. Following rainfall, the subsurface cumulative evaporation curves followed a pattern similar to the surface cumulative evaporation curve, with approximately a 2‐d lag before evaporation was indicated at the 3‐ and 9‐mm soil depths, and several more days' delay in deeper soil layers. For a 21‐d period in 2007, the cumulative evaporation totals at soil depths of 0, 3, 9, 15, and 21 mm were 60, 44, 29, 13, and 8 mm, respectively. For a 16‐d period in 2008, the cumulative evaporation totals at soil depths of 0, 3, 9, 15, and 21 mm were 32, 25, 16, 10, and 5 mm, respectively. Cumulative evaporation results from the Bowen ratio and heat pulse methods indicated a consistent dynamic pattern for surface and subsurface water evaporation with both time and depth. These findings suggest that heat pulse sensors can accurately measure subsurface soil water evaporation during several wetting–drying cycles.

Single- and Dual-Probe Heat Pulse Probe for Determining Thermal Properties of Dry Soils

Heat pulse methods include the dual-probe (DP) and single-probe (SP) methods. The DP method is a widely used method for determining the thermal conductivity (K) and thermal diffusivity (β) of soil. The SP method has been traditionally used for measuring K only. The objective of this study was to examine if the SP method can be used to estimate the thermal properties of air-dried soils. The thermal properties of three sands were measured using differential scanning calorimetry (DSC) and the DP and SP methods. For the SP method, the small-time and large-time solutions of the perfect conductor model and hollow cylindrical probe model were fitted to the respective small-time and large-time temperature vs. time curves. Both K and β of the soil were determined by the SP method. The DP and SP methods yielded similar K values for the three air-dried soils with a relative deviation <6.1%. In comparison with the DSC measurements, the DP method overestimated the specific heat (c) by 19 to 29%, while the SP method with the hollow cylindrical probe model underestimated c by 21 to 8%, and the SP method with the perfect conductor model resulted in −4 to 7% error. Therefore, the SP method with the perfect conductor model gave the most accurate estimate of c.

Systematic Study of the 4f Electronic State in RRhIn5 and RCu2Si2 (R: Rare Earth)

Systematic study of the 4ƒ electronic state in RRhIn5 and RCu2Si2 has been done by using single crystalline samples which were successfully grown by the flux method. Most of RRhIn5 compounds order antiferromagnetically at low temperatures, except when R=Y, La, Pr and Yb. The observed anisotropic features in the magnetic susceptibility and magnetization have been analyzed on the basis of the crystalline electric field (CEF) model. The observed anisotropy in the magnetic susceptibility in the paramagnetic state is well explained by the CEF effect. Specific heat measurements on a series of ternary compound RCu2Si2 have been performed by the quasi-adiabatic heat pulse method in the temperature range down to 100 mK. We observed the nuclear specific heat at low temperatures and estimated the magnitude of internal effective magnetic field Heff at the nucleus in RCu2Si2. [DOI: 10.1380/ejssnt.2011.446]

Spatial sap flow and xylem anatomical characteristics in olive trees under different irrigation regimes

The compensation heat pulse (CHP) method is widely used to estimate sap flow and transpiration in conducting organs of woody plants. Previous studies have reported a natural azimuthal variability in sap flow, which could have practical implications in locating the CHP probes and integrating their output. Sap flow of several olive trees (Olea europaea L. cv. 'Arbequina') previously grown under different irrigation treatments were monitored by the CHP method, and their xylem anatomical characteristics were analyzed from wood samples taken at the same location in which the probes were installed. A significant azimuthal variability in the sap flow was found in a well-irrigated olive tree monitored by eight CHP probes. The azimuthal variability was well related to crown architecture, but poorly to azimuthal differences in the xylem anatomical characteristics. Well-irrigated and deficit-irrigated olive trees showed similar xylem anatomical characteristics, but they differed in xylem growth and in the ratio of nocturnal-to-diurnal sap flow (N/D index). The results of this work indicate that transpiration cannot be accurately estimated by the CHP method in olive trees if a small number of sensors are employed and that the N/D index could be used as a sensitive water status indicator.

Feasibility of soil moisture monitoring with heated fiber optics

Accurate methods are needed to measure changing soil water content from meter to kilometer scales. Laboratory results demonstrate the feasibility of the heat pulse method implemented with fiber optic temperature sensing to obtain accurate distributed measurements of soil water content. A fiber optic cable with an electrically conductive armoring was buried in variably saturated sand and heated via electrical resistance to create thermal pulses monitored by observing the distributed Raman backscatter. A new and simple interpretation of heat data that takes advantage of the characteristics of fiber optic temperature measurements is presented. The accuracy of the soil water content measurements varied approximately linearly with water content. At volumetric moisture content of 0.05 m3/m3 the standard deviation of the readings was 0.001 m3/m3, and at 0.41 m3/m3 volumetric moisture content the standard deviation was 0.046 m3/m3. This uncertainty could be further reduced by averaging several heat pulse interrogations and through use of a higher‐performance fiber optic sensing system.

Water use by Tabor and Kermes oaks growing in their respective habitats in the Lower Galilee region of Israel

We estimated water use by the two main oak species of the Lower Galilee region of Israel—Tabor ( Quercus ithaburensis) and Kermes ( Quercus calliprinos)—to develop management options for climate-change scenarios. The trees were studied in their typical phytosociological associations on different bedrock formations at two sites with the same climatic conditions. Using the heat-pulse method, sap flow velocity was measured in eight trunks (trees) of each species during a number of periods in 2001, 2002 and 2003. Hourly sap flux was integrated to daily transpiration per tree and up-scaled to transpiration at the forest canopy level. The annual courses of daytime transpiration rate were estimated using fitted functions, and annual totals were calculated. Sap flow velocity was higher in Tabor than in Kermes oak, and it was highest in the youngest xylem, declining with depth into the older xylem. Average daytime transpiration rate was 67.9 ± 4.9 l tree −1 d −1, or 0.95 ± 0.07 mm d −1, for Tabor oak, and 22.0 ± 1.7 l tree −1d −1, or 0.73 ± 0.05 mm d −1, for Kermes oak. Differences between the two oak species in their forest canopy transpiration rates occurred mainly between the end of April and the beginning of October. Annual daytime transpiration was estimated to be 244 mm year −1 for Tabor oak and 213 mm year −1 for Kermes oak. Adding nocturnal water fluxes, estimated to be 20% of the daytime transpiration, resulted in total annual transpiration of 293 and 256 mm year −1 by Tabor and Kermes oaks, respectively. These amounts constituted 51% and 44%, respectively, of the 578 mm year −1 average annual rainfall in the region. The two species differed in their root morphology. Tabor oak roots did not penetrate the bedrock but were concentrated along the soil–rock interface within soil pockets. In contrast, the root system of Kermes oak grew deeper via fissures and crevices in the bedrock system and achieved direct contact with the deeper bedrock layers. Despite differences between the two sites in soil–bedrock lithological properties, and differences in the woody structure, annual water use by the two forest types was fairly similar. Because stocking density of the Tabor oak forests is strongly related to bedrock characteristics, thinning as a management tool will not change partitioning of the rainfall between different soil pockets, and hence soil water availability to the trees. In contrast, thinning of Kermes oak forests is expected to raise water availability to the remaining trees.

An external heat pulse method for measurement of sap flow through fruit pedicels, leaf petioles and other small‐diameter stems

The external heat ratio method is described for measurement of low rates of sap flow in both directions through stems and other plant organs, including fruit pedicels, with diameters up to 5 mm and flows less than 2 g h(-1). Calibration was empirical, with heat pulse velocity (v(h)) compared to gravimetric measurements of sap flow. In the four stem types tested (Actinidia sp. fruit pedicels, Schefflera arboricola petioles, Pittosporum crassifolium stems and Fagus sylvatica stems), v(h) was linearly correlated with sap velocity (v(s)) up to a v(s) of approximately 0.007 cm s(-1), equivalent to a flow of 1.8 g h(-1) through a 3-mm-diameter stem. Minimum detectable v(s) was approximately 0.0001 cm s(-1), equivalent to 0.025 g h(-1) through a 3-mm-diameter stem. Sensitivity increased with bark removal. Girdling had no effect on short-term measurements of in vivo sap flow, suggesting that phloem flows were too low to be separated from xylem flows. Fluctuating ambient temperatures increased variability in outdoor sap flow measurements. However, a consistent diurnal time-course of fruit pedicel sap flow was obtained, with flows towards 75-day-old kiwifruit lagging behind evaporative demand and peaking at 0.3 g h(-1) in the late afternoon.

NOCTURNAL HEAT-PULSE SAP FLOW AS A SENSITIVE SYSTEM TO ASSESS DROUGHT EFFECTS ON GRAPEVINES: AN IRRIGATION SCHEDULING APPLICATION?

The compensated heat-pulse method, New Zealand (cHP) was tested on grapevines (Vitis vinifera L. cv. Shiraz) under a PRD trial in Benalla, Victoria (season 2003-2004). Results showed that vines (all treatments) where in constant stress during the season and PRD treatments were able to maintain an almost constant transpiration rate, independently of atmospheric demand, which could indicate a better stomatal control. Other whole-tree water status monitoring methods were midday stem water potential (Ψs) and infrared thermography (IR). The cHP offered a continuous and sensitive physiological technique to monitor the effect of watering at very low transpiration rates. Therefore, the sensors used were able to register night time sap flow (SN), which was more evident after irrigations and decreased gradually over time until the next irrigation. SN was significantly correlated to Ψs obtained from the day before. Monitoring SN could be a suitable method to assess grapevine water status and the capacity of vines to recover from the daily water stress. We propose SN as a possible irrigation scheduling technique.

Estimation of water use of mature coconut (Cocos nucifera L.) cultivars (CRIC 60 and CRIC 65) grown in the low country intermediate zone using the compensation heat pulse method (CHPM)

The compensation heat pulse method (CHPM) was used to determine the diurnal variation and daily total water use of two coconut varieties (i.e. CRIC 60 and CRIC 65) growing on two contrasting land suitability classes (i.e. S2, Kurunegala series, and S4, Kuliyapitiya series) in the low- country intermediate zone (IL1) of Sri Lanka. The average daily total sap sow (F d ) of CRIC 60 and CRIC 65 on S2 were 120 and 90 L d -1 while on S4 it was 92 and 79 L d -1 respectively.

Superconductivity in a Ternary Silicide Ca2Pt3Si5

Superconductivity in the non-centrosymmetric crystal structure has been attracting a considerable interest since Bauer et al. reported superconductivity in CePt3Si which lacks inversion symmetry in the tetragonal crystal structure. Recently the pressure-induced superconductivity was observed in some uraniumand cerium-based compounds with non-centrosymmetric crystal structures. Many unconventional superconducting properties were found in these heavy fermion superconductors. It is, however, still unclear how the strong antisymmetric spin–orbit interaction (ASOI) due to the lack of inversion symmetry in the crystal affects on superconductivity. In order to elucidate the intrinsic effect of the strong ASOI on superconductivity, it is desirable to develop new non-centrosymmetric superconductors with weakly correlated electrons. Very recently, Oikawa et al. reported new ternary silicide superconductors ATSi3 (A: Ca, Sr and Ba, and T: transition metal) with the BaNiSn3-type tetragonal crystal structure. 5) For example, polycrystalline CaPtSi3 was found to show superconductivity below 2.1K. Since we succeeded in growing single crystals of CeTX3 (X: Si and Ge) compounds with the same BaNiSn3-type crystal structure by the flux method, the same method was applied to ATSi3 compounds. We could not, however, grow single crystals of CaPtSi3, but succeeded in growing single crystals of Ca2Pt3Si5, which were found to be a superconductor. The existence of Ca2Pt3Si5 was clarified in the present paper. Single crystals of Ca2Pt3Si5 were grown by the Sn-flux method. The starting elements were 4N (99.99% pure)-Ca, 4N-Pt, and 5N-Si. These materials with a stoichiometric composition of Ca : Pt : Si : Sn 1⁄4 1 : 1 : 3 : 20 for CaPtSi3 were inserted in an alumina crucible and sealed in a quartz tube with a partial pressure of argon gas. The temperature of the furnace was raised to 1050 C. After homogenization for about 24 h, the furnace was cooled down to 600 C over a period of two weeks and finally cooled down to room temperature at a faster rate. After removing the excess Sn flux by centrifuging, we found many single crystals with a characteristic shape and size of the crystal, as shown in Fig. 1. We randomly chose the crystal and measured the electrical resistivity. All the measured crystals showed superconductivity at the same temperature, as shown later. The obtained single crystals were not CaPtSi3 but Ca2Pt3Si5 with the flat plane of (001) or c-plane, as shown in Fig. 1. Structural parameters of Ca2Pt3Si5 were analyzed by the single crystal X-ray diffraction experiment with Mo K radiation. We confirmed that Ca2Pt3Si5 crystallizes in the U2Co3Si5-type orthorhombic crystal structure (Ibam #72). Atomic coordinates are shown in Table I. Note that this crystal structure has an inversion center. The lattice parameters were determined as a 1⁄4 10:0676 A, b 1⁄4 11:5469 A, and c 1⁄4 5:9237 A. We measured the electrical resistivity for the current along the [010] direction or the b-axis and the specific heat C at low temperatures, and found that Ca2Pt3Si5 shows a superconducting transition at Tc 1⁄4 1:3K, as shown in Fig. 2. Here, the specific heat was measured by using ten single crystals by means of the quasi-adiabatic heat pulse method. Ca2Pt3Si5

The specific heat and thermal conductivity of Eccosorb CR-124 between 800 mK and 6 K

Eccosorb CR-124 is a castable iron-loaded epoxy resin with excellent absorption properties for electromagnetic waves in the GHz range. It is commonly used in low temperature instruments to absorb thermal radiation. The specific heat c ( T ) of Eccosorb CR-124 was measured between 800 mK and 6 K with the heat pulse method. The results were fitted to the function c ( T ) = ( 0.132 ± 0.003 ) · T + ( 0.0053 ± 0.0003 ) · T 3 J kg - 1 K - 1 , with T being the temperature in Kelvin. In addition, the thermal diffusivity D ( T ) of Eccosorb CR-124 was determined. At a temperature of 2.3 K, a peak is observed in D ( T ) . Consequently, the thermal conductivity λ ( T ) of Eccosorb CR-124 features two distinct regimes. Below 2.3 K, it fits the function λ ( T < 2.3 K ) = ( 0.0038 ± 0.0003 ) · T 2 ± 0.1 W m - 1 K - 1 . Above 2.3 K, it fits the function λ ( T > 2.3 K ) = ( 0.0057 ± 0.0004 ) · T 1.4 ± 0.04 W m - 1 K - 1 .

Evaluation of sap flow methods to determine water use by cultivated palms

Sustainable management of water resources allocated to palm crops requires reliable tools for measuring palm water use. Thermometric sap flow methods developed for woody dicot plants hold great potential for use in palms, but there have been few investigations to determine whether such methods can be used successfully in ‘woody’ monocots. Here, we evaluate two sap flow methods for measuring whole-plant water use by potted cocos palms ( Syagrus romanzoffiana): the Heat Ratio Method (HRM) and the Compensation Heat Pulse Method (CHPM). Measurements of whole-plant water use from the HRM and the CHPM were compared to gravimetric measurements acquired from an electronic balance. Of the two methods, the HRM gave the most accurate results and it most precisely described patterns of transpiration with respect to environmental conditions and leaf morphology. Estimates of total daily water use from the HRM and the balance were highly correlated ( R 2 = 0.92; P < 0.0001) and very near to a 1:1 relationship—an excellent result given the potential for error associated with each method. As expected, the CHPM was seriously limited at low flow rates, but it agreed well with the HRM at higher flow rates (heat pulse velocity >4 cm h −1). Anatomical investigations revealed that vascular bundles in measured palm fronds were evenly distributed and the distance between bundles was comparable in scale to the diameter of probes of HRM sensors, and most likely an order of magnitude smaller than the probable zone of thermal influence for HRM measurements. This contention was supported by results of mathematical modeling suggesting that HRM heat pulse velocities in palm-like sapwood remain largely unaffected by increases in heterogeneity caused by larger xylem vessels and wider interstitial tissues. Although wounding models for heat pulse sap flow methods have not historically catered for the effects of discrete vascular bundles, they are sufficiently approximate given our empirical validations, and we conclude that palm sapwood is thermally homogenous enough for the HRM and the CHPM to be used without modification. Overall, we present strong evidence that heat pulse methods such as the HRM and the CHPM can be used successfully in woody monocots. Finally, we note that the CHPM is likely to perform better in cases of very high flow rates, while the HRM provides more comprehensive monitoring of the usual range of flow rates including at night, early morning and during water deficit.