Dual-probe Heat-pulse Technique Research Articles

Measurement and prediction of thermal properties of pantoa during deep-fat frying

Thermal properties of pantoa were determined during deep-fat frying in sunflower oil at 125-145°C. Thermal conductivity (k: 0.357 to 0.199 Wm -1 K -1 ), thermal diffusivity (α: 0.105x10 -6 to 0.140x10 -6 m 2 s -1 ) and volumetric specific heat (C p : 3.275 to 1.401 MJm -3 K -1 ) were measured simultaneously using dual probe heat pulse technique. Thermal conductivity and volumetric specific heat of pantoa decreased as the moisture content decreased, while thermal diffusivity increased with the decrease in moisture content. Empirical models were also developed as a function of moisture content, fat content and temperature of frying of pantoa . It was found that moisture content was inversely related to fat content during the progress of frying. The thermal properties and the developed models would be useful in the mathematical modeling of heat transfer in pantoa during DFF.

Critical Analysis of Dual-Probe Heat-Pulse Technique Applied to Measuring Thermal Diffusivity

The paper presents an analysis of the experimental parameters involved in application of the dual-probe heat pulse technique, followed by a critical review of methods for processing thermal response data (e.g., maximum detection and nonlinear least square regression) and the consequent obtainable uncertainty. Glycerol was selected as testing liquid, and its thermal diffusivity was evaluated over the temperature range from − 20 °C to 60 °C. In addition, Monte Carlo simulation was used to assess the uncertainty propagation for maximum detection. It was concluded that maximum detection approach to process thermal response data gives the closest results to the reference data inasmuch nonlinear regression results are affected by major uncertainties due to partial correlation between the evaluated parameters. Besides, the interpolation of temperature data with a polynomial to find the maximum leads to a systematic difference between measured and reference data, as put into evidence by the Monte Carlo simulations; through its correction, this systematic error can be reduced to a negligible value, about 0.8 %.

A low-power, low-cost soil-moisture sensor using dual-probe heat-pulse technique

This paper presents the development and testing of an integrated low-power and low-cost dual-probe heat-pulse (DPHP) soil-moisture sensor in view of the electrical power consumed and affordability in developing countries. A DPHP sensor has two probes: a heater and a temperature sensor probe spaced 3mm apart from the heater probe. Supply voltage of 3.3V is given to the heater-coil having resistance of 33Ω power consumption of 330mW, which is among the lowest in this category of sensors. The heater probe is 40mm long with 2mm diameter and hence is stiff enough to be inserted into the soil. The parametric finite element simulation study was performed to ensure that the maximum temperature rise is between 1°C and 5°C for wet and dry soils, respectively. The discrepancy between the simulation and experiment is less than 3.2%. The sensor was validated with white clay and tested with red soil samples to detect volumetric water-content ranging from 0% to 30%. The sensor element is integrated with low-power electronics for amplifying the output from thermocouple sensor and TelosB mote for wireless communication. A 3.7V lithium ion battery with capacity of 1150mAh is used to power the system. The battery is charged by a 6V and 300mA solar cell array. Readings were taken in 30min intervals. The life-time of DPHP sensor node is around 3.6 days. The sensor, encased in 30mm×20mm×10mm sized box, and integrated with electronics was tested independently in two separate laboratories for validating as well as investigating the dependence of the measurement of soil-moisture on the density of the soil. The difference in the readings while repeating the experiments was found out to be less than 0.01%. Furthermore, the effect of ambient temperature on the measurement of soil-moisture is studied experimentally and computationally.

Use of the Dual‐Probe Heat‐Pulse Technique to Monitor Soil Water Content in the Vadose Zone

The dual‐probe heat‐pulse (DPHP) technique is emerging as a useful technique for measuring soil volumetric water content (θ). However, few published data are available regarding the performance of the DPHP technique under field conditions. The objective of this study is to evaluate the effectiveness of the DPHP technique for measuring θ under field conditions. We used 24 DPHP sensors to monitor θ in a soybean [Glycine max (L.) Merr.] field during the 2001 and 2002 growing seasons. The DPHP sensors demonstrated durability in field conditions and clear sensitivity to temporal and spatial variations of θ at the scale of measurement. The mean θ measured by the DPHP sensors (θDPHP) was on average 0.040 m3 m−3 larger than the mean θ measured by soil sampling (θSS). The response of the DPHP sensors was linear. Regressions of θDPHP vs. θSS yielded r2 values of 0.949 and 0.843 at depths of 7.5 and 37.5 cm. The DPHP technique showed good resolution with RMSE values for the regression of 0.009 and 0.011 m3 m−3 at the two measurement depths. The slopes of the regressions were 0.75 rather than 1.0. Errors in θSS are a likely cause of this low slope. We shifted all the θ values for each sensor up or down by a constant value to make the first θ measurement from each sensor equal θ determined from soil sampling near that sensor at the time of installation. This simple matching point procedure improved the accuracy of the DPHP technique, resulting in a −0.024 m3 m−3 average difference between θDPHP and θSS Also, the matching point procedure markedly reduced the variability between sensors, reducing the average SD from 0.063 to 0.026 m3 m−3 This procedure requires no additional soil sampling and is recommended for field applications of the DPHP technique.

Use of the Dual-Probe Heat-Pulse Technique to Monitor Soil Water Content in the Vadose Zone

Use of the Dual-Probe Heat-Pulse Technique to Monitor Soil Water Content in the Vadose Zone

Use of the Dual-Probe Heat-Pulse Technique to Monitor Soil Water Content in the Vadose Zone

Use of the Dual-Probe Heat-Pulse Technique to Monitor Soil Water Content in the Vadose Zone

Measuring peat moisture content using the dual-probe heat pulse technique

The dual-probe heat pulse (DPHP) technique for measuring soil volumetric moisture content (Θv) is evaluated for use in peat soils with very high organic matter contents. The method has a greater sensitivity in peat soils compared with mineral soils and excellent resolution is possible, even at moisture contents as high as 90% by volume. Advantages of the DPHP technique are that sensors are simple to construct from inexpensive parts and calibration is not required since the method is based on a physical model of radial heat flow in soil. A multiplexer method was developed to allow multiple probes to be deployed in the field. DPHP measurements of Θv for small peat samples compared closely to reference measurements made using the gravimetric method, and in the field were similar to results obtained using a time domain reflectometry (TDR) method. Peat soils display a high level of spatial variation in Θv at the scales of both DPHP and TDR probes, so that multiple probes of each type are required for adequate spatial sampling of Θv. Rapid changes in peat moisture content were recorded following rainfall infiltration events yet moisture storage did not remain elevated following rainfall, even for peat that was very dry. wetlands, hydrology, soil moisture.

On Measuring Soil Thermal Properties with a Dual-Probe Heat-Pulse Technique

On Measuring Soil Thermal Properties with a Dual-Probe Heat-Pulse Technique

Root-zone hydraulic lift evaluated with the dual-probe heat-pulse technique

Roots are movers of water in the soil. One method of movement is through hydraulic lift, which occurs when plants extract water from a moist subsoil and release it into a dry topsoil. Detection of hydraulic lift has been hampered by the lack of instruments sensitive enough to measure the small amount of water moved. Recently, the dual-probe heat-pulse (DPHP) technique has been used to monitor with fine spatial resolution the soil water content in root-zones. The objective of this research was to determine if water is released by hydraulic lift, using the DPHP technique. Sunflower (Helianthus annuus L.) was grown in a column (38 cm height; 25 cm diam.; bulk density = 1.45 Mg/m3) packed with a Haynie very fine sandy loam (coarse-silty, mixed, calcareous, mesic Mollic Udifluvents; FAO-Eutric Fluvisols) with its roots divided between a top dry layer and a lower wet layer. Eight DPHP sensors installed in the soil column were used to monitor soil water content. During 24 measurement days, hydraulic lift was evident only when the plant was wilted. This occurred when the lower ‘wet’ layer had been allowed to dry and then it was re-watered. At this time, the roots in the upper dry layer released water, increasing the soil water content in the centre of the root mass by 0.019 m3/m3 (increase from 0.121 m3/m3 to 0.140 m3/m3). The soil-water increase was similar to other values reported in the literature and show it to be small.

Dual probe heat pulse technique for measuring soil water content and sunflower water uptake

Soil water content is the most sought-after soil physical parameter. Recent experiments have shown that dual probe heat pulse (DPHP) sensors can be used to determine volumetric water content of soil without roots. Little work has been done to document the performance of DPHP sensors in the presence of roots, and no work has been done with a taprooted plant. Thus, the objective of this experiment was to determine the accuracy of DPHP sensors in measuring volumetric water content ( θ v) and changes in volumetric soil water content (Δ θ v) in soil with a branched taproot system. Another objective was to determine plant water use. A sunflower plant ( Helianthus annuus L. `Hysun 354') was grown in a column (0.20 m in diameter and height) with Haynie very fine sandy loam (coarse-silty, mixed, calcareous, mesic Mollic Udifluvents; FAO-Eutric Fluvisols) containing 11 DPHP sensors. Results from the sensors were compared with those from the gravimetric method. Discrepancies between measurements of soil volumetric water content and changes of soil volumetric water by the DPHP and gravimetric methods were small (within 0.018 and 0.01 m 3 m −3, respectively). The sunflower had a small amount of nocturnal transpiration, and roots took up water at a higher rate near the surface of the soil than at deeper depths. The results showed that the DPHP technique can monitor volumetric soil water content in the presence of a taproot.

Measuring Soil Water Content under Turfgrass Using the Dual-probe Heat-pulse Technique

Measurements of soil water content near the soil surface often are required for efficient turfgrass water management. Experiments were conducted in a greenhouse to determine if the dual-probe heat-pulse (DPHP) technique can be used to monitor changes in soil volumetric water content (θv) and turfgrass water use. `Kentucky 31' Tall fescue (Festuca arundinacea Schreb.) was planted in 20-cm-diameter containers packed with Haynie sandy loam (coarse-silty, mixed, calcareous, mesic Typic Udifluvents). Water content was measured with the DPHP sensors that were placed horizontally at different depths between 1.5 and 14.4 cm from the surface in the soil column. Water content also was monitored gravimetrically from changes in container mass. Measurements started when the soil surface was covered completely by tall fescue. Hence, changes in θv could be attributed entirely to water being taken up by roots of tall fescue. Daily measurements were taken over multiple 6- or 7-day drying cycles. Each drying cycle was preceded by an irrigation, and free drainage had ceased before measurements were initiated. Soil water content dropped from ≈0.35 to 0.10 m3·m-3 during each drying cycle. Correlation was excellent between θv and changes in water content determined by the DPHP and gravimetric methods. Comparisons with the gravimetric method showed that the DPHP sensors could measure average container θv within 0.03 m3·m-3 and changes in soil water content within 0.01 m3·m-3.