Line Heater Research Articles

A novel preheating system in pressure reduction stations—natural gas directly flowing inside deep borehole heat exchangers

To prevent hydrates from forming during the pressure reduction process in natural gas pressure reduction stations (i.e., city gate stations, CGS), fuel-intensive preheating methods are normally adopted, leading to high fuel consumption and carbon emissions. In this study, an innovative preheating system for natural gas is proposed, which is called the “Direct Geothermal Heating System” (DGHS). The main idea is to inject high-pressure natural gas into geothermal wells before the throttling valve; thus, natural gas is directly heated by the surrounding strata when it flows through the geothermal well. A proper temperature for natural gas should be ensured, as natural gas goes back to the ground for pressure regulation. The idea is performed based on the preheating configuration using coaxial deep borehole heat exchangers (DBHE). A mathematical model describing the flow and heat transfer processes of DGHS through DBHE is established to study its heat transfer characteristics. Additionally, the environmental and economic benefits of the proposed configuration are also investigated. Through the CGS case in this paper, the findings indicate that, over the fifteen years of preheating with a DBHE depth of 2000 m and inlet flow rate of 4.39 × 107 Nm³/year, the outlet temperature of the throttling valve remains within the range of 17 °C–37 °C, meeting the heating requirement of CGS. Among fifteen preheating cycles, the average peak heating power of the DBHE reaches 105.78 kW. In addition, in the 15th year, the proposed system has a 1/3 cost of a traditional line heater, along with a reduction of 46.43 × 105 kg in CO2 emission. The DGHS for natural gas is easy to establish and operate; once it is promoted on a large scale, it will produce huge economic and environmental benefits.

An All‐In‐One Self‐Degradable Flexible Skin Patch with Thermostatic Control and Spontaneous Release of Antibacterial Ions to Accelerate Wound Healing

AbstractSmart wound dressings supply new techniques for wound management. Nevertheless, techniques to combine microenvironment control of the wound beds and spontaneous release of antibacterial agents while reducing secondary injury of the wound due to frequent replacement of wound dressings have not been sufficiently developed. Herein, this work proposes a degradable and flexible skin patch that can assist wound healing through the combined effect of thermostatic control, slow release of antibacterial metallic ions, and humidity control. The skin patch features a degradable zinc‐silver (Zn‐Ag) gird line heater and a Zn temperature sensor fabricated through screen printing and water sintering. The sintered degradable patterns of Zn‐Ag and Zn offer electrical conductivities of 307664.4 and 72400 S m−1, enabling closed‐loop thermostatic control of the wound under a temperature range of 43 ± 2 °C. The gradual degradation of the nanocomposites in a humid environment results in an antibacterial effect with more than 99% antibacterial efficiency (AE) on the wound site due to the release of Ag and Zn ions. The skin patches are demonstrated to improve wound healing in rats and rabbits by 18.35% and 51.57%, respectively. The flexible skin patch revolutionizes the wound treatment procedure by replacing traditional wound dressing with degradable materials and flexible circuits.

Heating performance of a large-scale line heater by adding synthesized carbon- nanodots to the heater bath fluid: CFD simulation and experimental study

Numerous researchers have recently become interested in nanofluids because of their potential applications in thermal systems. Herein, various concentrations of nanofluid of synthesized carbon nanodots (C-dots) were used to survey the thermal performance of a line heater as a heater bath fluid, and a numerical model was proposed to simulate all of the line heater's components for the first time. C-dots nanoparticles were manufactured with the aid of the hydrothermal method and characterized using FTIR and XRD analysis. In addition, a two-stage approach was used to prepare the nanofluid with a varying concentration of C-dot nanoparticles, ranging from 0.5 to 5 wt%. Nanofluids were also measured and compared to the base fluid in terms of thermophysical properties. Additionally, a numerical model based on the finite element method (FEM) was proposed to simulate fluid flow and heat transfer in the line heater, and validation of the numerical results revealed good agreement with earlier studies. The mesh independence analysis shows that the results are much better and more consistent when mesh number 98,946 is used instead of the others. The results illustrate that temperatures were raised from roughly 300 K near the gas tubes to around 370 K near the fire tubes. In comparison to the situation of employing water as the bath fluid, the maximum heater power consumptions derived from the experiments and numerical findings were 9.7 % and 10.3 %, respectively.

Pico-Watt Scanning Thermal Microscopy for Thermal Energy Transport Investigation in Atomic Materials.

The thermophysical properties at the nanoscale are key characteristics that determine the operation of nanoscale devices. Additionally, it is important to measure and verify the thermal transfer characteristics with a few nanometer or atomic-scale resolutions, as the nanomaterial research field has expanded with respect to the development of molecular and atomic-scale devices. Scanning thermal microscopy (SThM) is a well-known method for measuring the thermal transfer phenomena with the highest spatial resolution. However, considering the rapid development of atomic materials, the development of an ultra-sensitive SThM for measuring pico-watt (pW) level heat transfer is essential. In this study, to measure molecular- and atomic-scale phenomena, a pico-watt scanning thermal microscopy (pW-SThM) equipped with a calorimeter capable of measuring heat at the pW level was developed. The heat resolution of the pW-SThM was verified through an evaluation experiment, and it was confirmed that the temperature of the metal line heater sample could be quantitatively measured by using the pW-SThM. Finally, we demonstrated that pW-SThM detects ultra-small differences of local heat transfer that may arise due to differences in van der Waals interactions between the graphene sheets in highly ordered pyrolytic graphite. The pW-SThM probe is expected to significantly contribute to the discovery of new heat and energy transfer phenomena in nanodevices and two-dimensional materials that have been inaccessible through experiments.

Application of induction heaters for pumping high-wax oil from the Kyrtaelskoye field

The article discusses modern views on the problem of pipeline waxing when transporting highly paraffinic oil from the Kyrtaelskoye field in the Komi Republic via the Kyrtael - Chikshino oil pipeline and possible ways to improve the rheological properties of the pumped oil. The paper presents the results of measuring the rheological characteristics of samples from one batch of oil as it flows through the pipeline, as well as the results of modeling the operation of the pipeline in the NIPAL 3.0 program for various pumping options. It has been established that, taking into account the complex rheological properties of oil pumped through the interfield oil pipeline PPSN “Kyrtael” - PSP “Chikshino”, the operation of the oil pipeline is possible at pumping volumes of at least 2300 tons / day due to an increase in the critical operating pressure in the oil pipeline. At the moment, a Flexoil depressant is injected into the oil stream to improve the rheological parameters. In connection with a gradual decrease in the volume of oil pumping, the speed of oil movement decreases and the temperature of the pumped oil decreases below the pour point. Even with the use of a pour point depressant, the pipeline will not be able to operate at the beginning of 2024 (according to the existing operation scheme). The analysis of the problem of pumping oil through an interfield oil pipeline performed in this work shows the need to achieve optimal parameters for pumping oil during the operation of the pipeline under consideration in order to ensure the safety of oil transportation from the Kyrtaelskoye field and further pumping into the system of Transneft-Sever JSC into the Usa-Ukhta main oil pipeline. The paper considers standard methods of oil heating with the help of line heaters, as well as the method of oil heating on the linear part of the interfield oil pipeline using induction flow heaters, which were first proposed when pumping oil through the oil pipeline PPSN “Kyrtael” - PPSP “Chikshino”.

MATHEMATICAL MODEL OF THE HEATER WITH INTERMEDIATE HEAT

Track heaters are one of the technological equipment’s elements of oil and gas condensate deposits during the transportation of oil, oil products and natural gas. It was found that it is advisable to use line heaters with an intermediate heat carrier (water), which is heated during combustion associated (commercial) gas and transfers heat to the process flow through the heat exchange surface for soft heating of viscous oils and oil products to avoid hydrate formation during throttling of natural gas, with the aim of further transportation through pipelines to the place of collection, processing and consumption. A significant part of scientific publications relates to improving the efficiency of such devices with the use of various technological innovations for heat recovery from flue gases, as well as the use of high-quality control systems. On the basis of the analysis of the heater as an object of automation, the main input, disturbing factors and output parameters of control and regulation were established, and the information structure of the heater as a cybernetic system was developed. Based on the equations of the material and heat balance of the apparatus, the mathematical model of the dynamics of the process of heating technological streams has been developed, which includes the differential equations of the heat balance of the product heat exchanger, intermediate heat carrier, flue gases in the gas duct formed during gas combustion. The system of equations is supplemented by equations of heat transfer through two heat exchange surfaces from water to the target product and from flue gases to an intermediate heat carrier. The linearization of the nonlinear components of the developed model in the vicinity of the operating point is carried out. Based on the obtained mathematical description of the heater, a block diagram of the model was synthesized, which shows the relationship of input parameters, control action and output variables in deviations from the base point of the operating mode.

3ω method in combination with a meander shaped heater: Theoretical and experimental investigation

The 3ω-method is usually applied to a line heater because it simplifies the analytical solution of the heat transfer equation. Other potentially beneficial heater geometries, such as meandering heater structures, have not yet been addressed in the literature to date. A meandering structure is advantageous when the available space is limited. This article presents the detailed investigation on meander shaped heater structures, in combination with the 3ω-method. A theoretical approach approximated the meandering structure as several parallel strips with a certain spacing. It investigates the influence of the spacing and compares it with the conventional line heater model. It was found that the conventional model is an accurate model when the thermal diffusivity of the surrounding area of the heater is high and the spacing between the heater lines is small. This finding was used in the experimental investigation. Due to the general expressions of the theoretical model, it can be used as a tool for future investigations. An experimental approach investigated the loss of invariance along the lateral axis, which is often assumed for a line heater where its length is much larger than its width and a two-dimensional description can be used. The boundary effect of the finite length is neglected. The basic idea of the experimental work is to fabricate several meandering structures with different length-width ratios, but with the same total path length of the structures, such that the structures with different length-width ratios can be compared. The results based on platinum thin film structures showed that the straight structure with a length-to-width ratio of 300 deviates from the prediction of the two-dimensional model by about 5%. The structures with a length-to-width ratio 50 match significantly poorer with the two-dimensional model. The deviation becomes larger than 10%. A strong signal helps regarding the resolution in the application. The theoretical findings showed that the signal is highest if the distance between the heater lines is as small as possible. Moreover, the experimental work showed highest performance if the length-width ratio is around 1.4.

A CAN-Based Urea Line Heater Diagnostics Development and Experimental Validation for Selective Catalytic Reduction (SCR) System

Urea line heating system is critical for Selective Catalytic Reduction (SCR) aftertreatment system under low temperature environment. Traditionally, the Electronic Control Unit (ECU) motivates urea lines heating command and diagnostics directly. This paper illustrates a Controller Area Network (CAN)-based line heater architecture development for the SCR aftertreatment system, as well as the diagnostics generation. The CAN-based line heater diagnostics is validated on vehicle experimental with four different given cases. It can be seen from the validation results that the diagnostics logic and algorithm are reasonable, and the line heater failure modes could be detected correctly including open circuit, short circuit and inducement. In addition, the failure modes are able to set or clear for each of the urea lines according to the diagnostics logic. ECU and ECU1 could communicate well between each other by CAN. This study introduces a new line heater architecture for SCR aftertreatment system which is meaningful for the whole vehicle assembly, which could be considered in the real application in future.

Influence of short carbon fiber content on thermal properties of polyethersulfone composites

Heat dissipation plays progressively more significant role in several fields such as high-density gadgets, airplane microelectronics devices, advanced space crafts, thermal power plants, turbo-charger, due to the swiftly increasing thermal loads affects the reliability of components and limits its life span. With high stiffness, strength and low coefficient of thermal expansion (CTE), carbon fiber strengthened polymer composites have been broadly utilized in numerous engineering applications. Therefore, in the current material investigation, thermal characterizations were made on polyethersulfone (PES) material compounded with short carbon fiber (SCF) by four different weight fraction via 0, 10, 20 and 30 wt%. Specific heat (cp) was determined through differential scanning calorimeter (DSC) and thermal conductivity was measured by transient line heater method. Specific heat of PES/SCF composites decreased and conductivity was increased with the higher loading of SCF. Thermal diffusivity was in turn computed by using the relation between specific heat and thermal conductivity. In addition, numerical analysis was performed in Abaqus finite element package to simulate the transient line heater method. Temperature profiles of the composites extracted by numerical simulation matched with that of experimental temperature profile.

Exergy analysis of dual-fuel combined cycle plants

An alternative to coal technology in regions with a significant share of gas in the fuel balance can be the transition to dual-fuel combined cycle gas turbine plants. The article considers five technological profiles of cogeneration combined cycle gas turbine power unit: with a low-pressure steam generator; with coal gasification; with gas line heater; with gas line heater and freon thermotransformer; dump type with a binary coefficient equal to one. A comprehensive analysis of cogeneration plants was carried out. The perfection of the thermal design of a combined cycle gas turbine power unit of each type is evaluated by the exergy structural coefficient. An analysis the criterion of technical and economic efficiency, exergy efficiency for the supply of electricity and thermal power for combined cycle power plants in comparison with traditional cogeneration power units in the power range of 50 … 250 MW are also given.

Impact of twisting tapes with various pitch lengths on the exergy and entropy performances of line heaters

Water bath fire tube heaters, so-called line heaters, are commonly used for industrial applications from small scales to large scales. The main problem of such heaters is the very low effectiveness of the heater due to the inefficient heat transfer within the heater (mainly between the fire tube and gas flow). The effects of using a specific type of twisting tape on the performance of these heaters, a typical heater used in natural gas pressure reductions points, were recently investigated. This study assesses the impacts of twisting tapes with different styles placed in the gas coil of the heater on the entropy generation and exergy performance of these heaters via computational fluid dynamic methods. For this, a typical gas mixture and typical line heater were considered. The results show that twisting tapes with larger numbers of twists and shorter twist pitch better enhance the exergy efficiency of the heater and decrease the rate of entropy generation over the gas heating process. Based on the obtained results, twisting tapes with the 17 and 68 twists decrease the rate of entropy generation by 16.8% and 27.1% and decrease the Bejan number for, respectively, over 36% and 77%.

Design and Comparison of Resonant and Non-Resonant Single-Layer Microwave Heaters for Continuous Flow Microfluidics in Silicon-Glass Technology

This paper presents a novel concept for the co-design of microwave heaters and microfluidic channels for sub-microliter volumes in continuous flow microfluidics. Based on the novel co-design concept, two types of heaters are presented, co-designed and manufactured in high-resistivity silicon-glass technology, resulting in a building block for consumable and mass-producible micro total analysis systems. Resonant and non-resonant co-planar waveguide transmission line heaters are investigated for heating of sub-micro-liter liquid volumes in a channel section at 25 GHz. The heating rates of 16 and 24 °C/s are obtained with power levels of 32 dBm for the through line and the open-ended line microwave heater, respectively. The heating uniformity of developed devices is evaluated with a Rhodamine B and deionized water mixture on a micrometer scale using the microwave-optical measurement setup. Measurement results showed a good agreement with simulations and demonstrated the potential of microwave heating for microfluidics.

Optimisation of a Heat Source for Infrared Thermography Measurements: Comparison to Mehler Engineering + Service-Heater

Using an optimised heating source in active thermography can facilitate the processing of measurement results. By designing a custom heat source for dynamic line scan thermography, we reduced the excitation power needed to heat the sample and decreased the unwanted side effects originating of a wide-range heating source. The design started from a regular halogen tube lamp and a reflector is composed to provide the desired heating power in a narrow band. The reflector shape is optimised using ray-tracing software to concentrate the electromagnetic radiation along with the heat in a slim line. A comparison between the optimised heat source and a commercially available line-heater is performed. The width of the heated region from the Mehler Engineering + Service-heater is larger than prescribed in the datasheet. The optimised line heater has several advantages over the comercially available heat source.

Improving thermal performance of water bath heaters in natural gas pressure drop stations

One of the main components of a natural gas pressure drop station is the water bath heater (also known as line heater) that preheats the gas flow before its pressure is reduced through a throttling process. A major problem of this kind of heater is its low thermal efficiency, which is roughly 40–50%, making natural gas pressure drop station an exergy destructive point in the gas transmission system. This study proposes the use of a twisted flow disturber through the gas coil within the water bath heater to increase the rate of heat transfer from water to the coil, and subsequently increasing the thermal efficiency of the heater. This process is numerically simulated for a real water bath heater in a case study gas station in Iran to observe and analyze the effects of employing this type of flow disturber. The nominal capacity of the case study heater is 1000 m3/hr of gas to be heated up. The results show that the flow disturber might improve the average Nusselt number of the gas flow through the coil by about 20%, increasing the thermal efficiency of the heater and reducing its fuel consumption.

Energy and environmental analysis of a natural gas pressure reduction station equipped with turboexpander, solar collector, and storage tank

The pressure of natural gas in the transmission pipelines is high, and it is not suitable for urban consumptions. Therefore, it should be decreased to a certain lower amount in the pressure reduction stations near the urban area by the pressure reducing valves. Recently, for recovering the energy losses in these valves and generating electricity, turboexpanders are utilized. However, the pressure decrease in the turboexpander results in a sudden decrease in temperature, which leads to the formation of hydrates. To prevent the hydrate formation, preheating is required, which is conventionally done by a line heater. In this study, the required energy for preheating the natural gas entering the station is supplied from the solar energy and an auxiliary line heater for a case study of Mashhad city (Iran). Parabolic trough thermal collectors are used for the absorption of the solar radiant energy. The collector was modeled through one-dimensional implicit finite-difference method and using discretization of energy balance equation between the working fluid, the absorbent pipe, and the glass envelope. The reduction in natural gas consumption and the produced CO2 emission are computed for the pressure reduction station with a thermal collector and a storage tank. The results reveal that the presence of the thermal collector and the storage tank reduces the consumption of fuel and consequently the generation of pollutant about 90%.

(Invited) Monocrystalline Si Thin Film By High Speed Zone Melting / Heating Crystallization with Controlling Nano-Surface Roughness for Cost-Cutting Solar Cells with High Efficiency

Recent development in monocrystalline Si (c-Si) solar cell technology is significant both for reducing the cell cost andfor increasing the photoelectric conversion efficiency. The recent improved efficiency and cost-cutting of c-Si solar cell is mainly due to technology that (a) improves the carrier lifetime via surface passivation, (b) uses higher quality crystalline Si, and (c) reduces wafer thickness. A challenge in achieving further cost reduction, however, is reducing the thickness of c-Si while maintaining its crystallinity. Fabrication of c-Si is commonly attained by wire-saw slicing of a crystalline ingot or by a layer transfer process (peeled off). The wire-saw slicing can keep high quality of c-Si but, cause kerf loss and the limitation of reducing thickness. In contrast, technical challenges for layer transfer processes are 1) the formation of a high-quality thin film Si, 2) achieving a structure that can easily be peeled off from Si substrate, 3) improving the growth rate and Si raw material yield (necessary equipment costs are determined by the growth rate), and 4) being able to use the substrate after layer transfer without any waste. In the paper, I will introduce the zone melting / heating (re-) crystallization (ZMC/ZHR), shown in Fig.1, to fabricate monocrystalline Si thin film as a key technology in two different kinds of layer transfer process for cost-cutting solar cells with high efficiency. In both layer transfer processes, the control of nano-surface roughness was crucial to improve the crystal quality of Si thin film. Fabrication of quasi-monocrystalline Si thin film without seed layer by high-speed ZMC[1~3] Silicon-on-insulator (SOI) films for solar cells were fabricated by high-speed ZMC. For ZMC, amorphous Si films were deposited on SiO2layers by rf sputtering. After SOI (Si/SiO2) was covered with another SiO2layer (forming a sandwich structure of SiO2/Si/SiO2), the SOI films were crystallized by ZMC. In ZMC, monocrystalline Si thin film was prepared by melting and crystallizing in a line (using a lamp line heater) and then scanning in one direction. Due to the stability at the SiO2/melted Si interface, the result is quasi-monocrystalline Si without requiring any seed for crystal growth. The surface roughness (several ten nanometer) of deposited Si film determined the crystal defect density of the ZMC film. Monocrystalline Si thin film with 10 times faster growth rate on nano smoothing porous Si by ZHR for cost-cutting solar cells with high efficiency[4~6] A high-quality thin film monocrystallinesilicon was developed for solar cells. The crystal defect density of the film could be reduced to the silicon wafer level at a growth rate that is more than 10 times higher than typical CVD. First, double-layer nano-order porous Si was formed from Siwafer using an electrochemical oxidation. Subsequently, the surface was smoothed to a roughness of 0.2 to 0.3 nm by ZHR. This substrate was used for high-speed growth of monocrystalline Si by Rapid vapor deposition (RVD), developed by S. Noda et al.[7]. The grown film can easily be peeled off using the double-layer porous Si layer, and the substrate can be reused or used as an evaporation source for RVD, which significantly reduces material loss. When the surface roughness of the porous Si substrate is reduced by changing the ZHR conditions, the defect density of the Si thin film, measured by ESR, could be reduced to the Si wafer level of about 1/10th. The results showed that a surface roughness in the range of only 0.1-0.2 nm (level of atoms to several tens of layers) has an important impact on the formation of crystal defects, which is also of interest as a crystal growth mechanism. (Figure 1 showed the outline of these results.) Acknowledgement I summarized the results of reference papers [1~6] focusing on zone melting / heating (re-) crystallization and surface roughness control as an invited talk in the 234thMeeting of The Electrochemical society (ECS). I appreciate for Prof. S. Noda, Dr. K. Hasegawa, Dr. A. Lukianov, Ms. C. Takazawa and all authors of these papers. Figure 1

Increasing the Operation Efficiency of Low Pressure Cylinders of Cogeneration Turbines

An increase in the operation efficiency of cogeneration turbines used by big heat and power plants is conditioned by the need of a maximum use of the fuel heat, mainly that of natural gas. The generation of two types of energy, in particular electric and thermal by cogeneration turbines for outside consumers is closely related to turbine operation modes and first of all to those for low pressure section in which the permanent heat loss occurs. The purpose of this research was to analyze the operation of low pressure cylinders used by operating cogeneration turbines of Т-100/120-130 and Т-250/300-240 types in a wide range of changes in electric and thermal loads. At high heat consumption according to the thermal schedule and low steam rate in the LPC the cascades of it operate consuming power at high ventilation losses. The joint operation of supply line heaters and low pressure cylinders was analyzed using the method of mathematical simulation of the turbine unit, experimental investigation of the models of LPC cascades and full-scale test data of cogeneration turbines built by different organizations. The relationships for the determination of power losses by LPC cascades when operating in low rate modes and additional generation of electric power by the turbine with the rational distribution of thermal load between the supply-line heaters have been given. It has been shown that the choice of heat release mode by the turbine unit can be defined by the optimization problem that requires the comparative estimation of power losses in the LPC and a gain in electric power due to the rational distribution of thermal load between the supply-line heaters.

Determination of heat transfer properties of media with a single-needle probe

Needle probes with a line heater inside are often used in studying the heat transfer properties of loose rocks. The key problem of contact methods of measuring thermal properties of various media consists in finding thermal contact resistance at the probe/medium interface which must be taken into account in determining the thermal diffusivity of the medium. We describe a mathematical model of heating of a long needle probe in the medium under study, taking into account dimensions and thermal properties of the needle source and assuming that thermal contact between the source and the medium is not ideal. Based on the proposed model, we formulate and solve the inverse problem of finding the thermal diffusivity coefficient of the medium and the heat exchange coefficient at the probe/medium interface. The purpose of the article is to create methodology for determining thermal properties of various media in the field.

Sub-Beam Size Temperature Measurement of Heavily Doped Silicon Heater Using Two-Wavelength Thermoreflectance Microscopy

This work describes a novel technique for simultaneously determining local temperature and thickness of a heavily doped Si heater having a submicron width by using two-wavelength thermoreflectance microscopy. The doped silicon line heater, whose thickness and width are, respectively, 480 nm and 900 nm, is fabricated by conventional microfabrication techniques on a fused silica wafer. The full width at half maximum (FWHM) of the focused laser beam is measured to be 2.00 μm and 2.28 μm for green (λ = 516 nm) and red (λ = 640 nm) lasers, respectively. Because the heater width is narrower than the focused laser beam size, the reflected beam contains background information (i.e., reflection from the fused silica substrate) in addition to the thermoreflectance signal from the doped silicon heater. With precise knowledge of the laser beam size, heater width, and exact location of the laser beam spot on the heater, one can quantitatively model the reflectance. In reality, however, due to the difficulty of aligning the laser beam with respect to the submicron-wide Si heater, precise determination of local temperature from thermoreflectance signal is not easily attained. In the present study, instead of aligning the laser beam to the center of the submicron silicon heater, the probe laser horizontally scans over a region of the heater. By taking into account the size of the focused laser beam and the width of the doped silicon heater, it is possible to determine the absolute temperature of a local region of the heater from the measured reflectance during the scanning, even though the width of the heater line is only 39% of the size of the laser beam.

Use of a Pre-Drilled Hole for Implementing Thermal Needle Probe Method for Soils and Rocks

The thermal needle probe method, which is widely used for measuring the thermal conductivity λ of soils, deploys a long and thin metallic probe that houses a line heater and a temperature sensor. However, inserting such probes into consolidated or densely compacted soils or rocks is difficult, frequently causing buckling of the probe and severe disturbance to the surrounding ground, leading to unreliable measurements. We found that the use of a pre-drilled hole filled with thermally conductive grease for installing a thermal needle probe was feasible to overcome such challenges, and still yielded reliable measurements of thermal conductivity. The proposed method, i.e., the pre-drilling thermal needle probe method, was verified by finite element calculations and laboratory experiments by varying various parameters, such as the pre-drilled hole diameter, probe diameter, and thermal conductivity of thermal grease. It was observed that increases in the pre-drilled hole diameter and probe diameter and a decrease in the thermal conductivity of the thermal grease caused delays in temperature increase owing to the slowed heat transfer. Nevertheless, all the estimated λ values agreed well with the reference λ values with acceptable errors. Thus, the proposed method yields reliable measurements and can be applied for a wide range of soils from compacted soils to hard rocks.