Academic Journal of Science and Technology ISSN: 2771-3032 | Vol. 16, No. 3, 2025 46 A Dynamic Monitoring System for The Thermal Conductivity of Transient Hot Wire Liquids Canyan Yang1, Shuwei Yang1, 2, *, Yihan Wang1, Xiaoting Qu1, Yanyi Bian1, Hengchen Zhao1, Jinghan Fan1 1Intelligent Construction College, Zhengzhou Business University, Zhengzhou 451200, China 2Zhengzhou Intelligent Electromechanical Engineering Research Center, Zhengzhou 451200, China * Corresponding author Abstract: In this paper, the thermal conductivity measurement experimental setup built on the principle of transient short filament method was tested using liquid toluene, and the results indicated that the measurements from the experimental setup are accurate and reliable. The thermal conductivity of liquid n-dodecane was experimentally measured within the temperature range of 317.97K to 610.54K and the pressure range of 1MPa to 20MPa. The effective data from the measurements, ignoring the influence of radiation, were fitted into a function related to temperature and pressure. The experimental values were compared with the fitted values, and the relative deviations between the experimental values and the fitted values were found to be mostly within ±2%, with the maximum relative deviation being 2.6%. Keywords: Thermal properties; Thermal conductivity; Transient short wire method; n-Dodecane. 1. Introduction The scramjet engine, as an intake-type power device, has become a research hotspot worldwide due to its simple structure and the ability to enable aircraft to fly at speeds greater than Mach 5 [1]. When the scramjet engine is operating, it will be subjected to extremely high heat loads, which affect the stable operation of the engine. The regenerative cooling technology is a passive thermal protection method. It not only relies on the physical and chemical heat sinks of the fuel, but also requires good heat transfer capability. And the heat transfer capability is characterized by thermal conductivity. The thermal conductivity of hydrocarbon fuels is also very important in the transportation, storage, and combustion of the fuels. Currently, there are relatively few direct measurements of the thermal conductivity of hydrocarbon fuels (finished oil), and due to different production processes and crude oil origins, the measured thermal conductivities may vary, lacking universality. There is also an alternative method to directly measure the thermal conductivity of hydrocarbon fuels, which is to measure the thermal conductivity of the hydrocarbon compounds that make up the hydrocarbon fuels separately, and then calculate the thermal conductivity of the hydrocarbon fuels through the mixing rule based on the known main components of the hydrocarbon fuels. This method has a large workload but is universal. Tim Edwards [2] provided detailed component compositions of RP-1 and RG-1 through GC/FIMS (gas chromatography - field ionization mass spectrometry). The weight percentages of n-dodecane in RP-1 and RG-1 were 0.687% and 0.075%, respectively. And in these two fuel components, n-dodecane had the highest weight percentage among the normal alkanes. Obviously, n-dodecane has certain contribution and value. This paper measured the liquid phase thermal conductivity of n-dodecane and has important academic value and engineering application significance for the development of new fuels and the improvement of engine performance. 2. Experimental Principle and Thermal Conductivity Measurement System Figure 1. Experimental physical model 47 (1) Experimental Principle The thermal conductivity measurement experimental platform used in this paper is built based on the principle of the transient short wire method. The transient short wire method was initially proposed by the Japanese scholar Fujii [3], which is a method combining experimental measurement and numerical solution[4]. The physical model of the experiment is shown in Fig1. During the entire measurement process, the hot wire is in a central symmetrical state in the container. Therefore, only a quarter of the entire physical model can be taken for analysis. (2) Thermal Conductivity Measurement System As shown in Fig. 2, the entire thermal conductivity measurement system consists of the thermal conductivity measurement device, the data acquisition system[5], the temperature control and measurement system, the pressure measurement system, and the vacuum system. Figure 2. Schematic diagram of the thermal conductivity measurement system A: Sample fluid; B: Filter valve; C: High-pressure pump; D, I, L: Shut-off valve; E: Pressure relief valve; F: Recovery tank; G: High-pressure safety valve; H: Low-pressure safety valve; J: Low-pressure sensor; K: High-pressure sensor; M: Vacuum pump; N: High-temperature constant temperature bath; O: PT100; P: First-class standard platinum resistance thermometer; Q:Insulation layer; R: Heating plate The thermal conductivity measurement device of this article is shown in Fig.3. The structure of this measurement device is cylindrical and the material used is 316 stainless steel. It adopts a flange and bolt sealing structure. In the figure, 7, 8, 9, and 10 belong to the core measurement device. Quartz fixtures are used to fix a platinum rod with a diameter of 1mm, and a point-welding method is used to weld a platinum wire with a diameter of 0.025mm at the center of the two platinum rods. Figure 3. Thermal Conductivity Measurement Device 1: Valve; 2: Wires; 3: Wire sealing component; 4: Bolt; 5: Flange; 6: Copper seal gasket; 7: Quartz fastener; 8: Pt rod; 9: Pt hot wire; 10: Support cylinder; 11: Pressure vessel body. The data acquisition system in this article is the core component. As shown in Fig. 4, a platinum wire, a standard resistor, a variable resistor box, and a power meter constitute a series circuit. The Keithley 2400 power meter and the Agilent 34410A digital multimeter are all connected to the industrial computer via GPIB cables, and the power meter and the digital multimeter are connected through a trigger line. Before the formal measurement experiment, the resistance value of the variable resistor box needs to be adjusted so that the sum of its resistance value and the resistance value of the standard resistor is approximately the same as the initial resistance of the platinum wire. This ensures that the electric 48 heating power through the platinum wire remains basically constant during the measurement process. Figure 4. Data Acquisition System Rw: Heating wire resistor; R1: Standard resistor; R2, R3: Variable resistors; DVM: Agilent 34410A digital multimeter The constant temperature system adopted in this article is a large-capacity high-temperature and high-precision constant temperature bath using air as the medium, with a temperature control accuracy of ±10mk/20min[6]. The pressure measurement system is divided into a high-pressure measurement system and a low-pressure measurement system to achieve segmented pressure transmission measurement. 3. Inspection of the Experimental System For this experimental system, an initial liquid phase toluene with a purity of 99.5% was experimentally verified within a temperature range of 317.44K to 635.82K. The critical temperature of toluene is 591.79K. Fig.5-1 Fig.5-2 and presents the distribution maps and relative deviation graphs of the thermal conductivity of toluene according to isobaric lines and isothermal lines. From Fig.5-3 and 5-4, it can be seen that the relative deviation of the thermal conductivity of toluene from NIST is within ±3%, with the maximum deviation being -3.75%, indicating that this experimental system is accurate and reliable. Figure 5-1. Distribution map of toluene thermal conductivity according to isobaric lines Figure 5-2. Relative deviation of toluene thermal conductivity from NIST data 49 Figure 5-3. Distribution map of toluene thermal conductivity according to isothermal lines Figure 5-4. Relative deviation of toluene thermal conductivity from NIST data 4. Experimental Measurement of the Liquid Phase Thermal Conductivity of Tetradecane Using the measurement system of this experiment, the liquid phase thermal conductivity of n-dodecane was measured. The temperature range was from 317.97K to 610.54K, and the pressure range was from 1MPa to 20MPa. A total of 159 thermal conductivity data along 13 isothermal lines were obtained. The results are listed in Table 3-2. The thermal conductivity data obtained were fitted to a relationship between temperature and pressure, and the formula is as follows: λ W⁄ m⁄ K⁄ ∑ ∑ 𝛼 𝑇 𝐾⁄ 𝑝/𝑀𝑃𝑎 (1) The values of each coefficient in this equation are shown in Table 1: Table 1. Coefficient Values of the Fitting Relationship Equation aij j=0 j=1 j=2 j=3 i=0 0.15528 0.0069 3.74E-04 -1.92E-05 i=1 1.26E-04 -5.29E-05 -2.46E-06 1.40E-07 i=2 -1.01E-06 1.41E-07 4.80E-09 -3.18E-10 i=3 9.65E-10 -1.18E-10 -2.92E-12 2.32E-13 50 Table 2. Data on the Liquid Phase Thermal Conductivity of n-Dodecane T/ K p/ MPa λ⁄ W ∙ m ∙ k T/ K p/ MPa λ⁄ W ∙ m ∙ k T/ K p/ MPa λ⁄ W ∙ m ∙ k 317.97 21.06 0.13498 479.79 15.27 0.09926 550.49 20.26 0.09239 317.98 21.06 0.13256 479.67 15.27 0.10016 550.64 15.16 0.0905 318 15.79 0.13031 479.76 10.3 0.0963 550.9 15.16 0.08992 317.97 15.79 0.13115 479.84 10.3 0.09592 550.74 15.16 0.08999 318.06 10.74 0.12884 479.86 10.3 0.09675 550.79 10.16 0.08791 318.1 10.74 0.12863 479.99 5.33 0.09464 550.82 10.16 0.08854 318.23 5.3 0.12625 480.1 5.33 0.09382 550.85 10.16 0.08756 318.19 5.3 0.12672 480.03 5.33 0.09412 551.04 5.25 0.08451 318.27 1.22 0.12511 480.2 1.65 0.09143 550.96 5.25 0.08389 318.33 1.22 0.12522 480.15 1.65 0.09086 550.87 5.25 0.08475 347.83 19.78 0.12591 480.12 1.65 0.09091 551.27 1.24 0.08128 347.85 19.78 0.12539 489.39 21.71 0.1011 551.27 1.24 0.08139 347.92 15.16 0.12423 489.47 21.71 0.1018 569.81 20.18 0.08957 347.95 15.16 0.12262 489.59 15.02 0.09854 569.96 20.18 0.08845 347.87 10.81 0.12201 489.39 15.02 0.0975 569.9 20.18 0.08788 348.01 10.81 0.12082 489.61 15.02 0.09864 570.19 15.12 0.08539 347.99 5.12 0.1199 489.65 10.62 0.09581 570.07 15.12 0.0857 348.04 5.12 0.11906 490.06 10.62 0.09498 570.02 15.12 0.08547 348.07 1.1 0.11708 490.08 10.62 0.09421 570.25 10.09 0.08251 348.07 1.1 0.11728 490.15 5.21 0.09077 570.18 10.09 0.08196 378.51 19.92 0.11965 490.14 5.21 0.09118 570.12 10.09 0.08292 378.6 19.92 0.11935 490.07 5.21 0.09257 570.28 5.19 0.07888 378.71 15.15 0.11734 490.22 1.13 0.08859 570.3 5.19 0.07959 378.69 15.15 0.11768 490.34 1.13 0.08875 570.19 5.19 0.07992 378.8 10.64 0.1152 490.29 1.13 0.08899 570.21 1.2 0.07821 Fig.6-1 shows the variation of thermal conductivity of n- dodecane along 5 isobaric lines with temperature. Fig.6-2 presents the relative deviation of the experimental thermal conductivity of n-dodecane from the calculated thermal conductivity according to Equation (3-1). From Figure 6-2, it can be seen that the relative deviation between the experimental thermal conductivity and the calculated thermal conductivity based on the fitting formula is basically within 2%, with an average relative deviation of -0.0082% and the maximum relative deviation of 2.6%. Figure 6-1. Graph showing the variation of the thermal conductivity of n-decane with temperature 51 Figure 6-2. Graph showing the relative deviation between the experimental values and the fitted values 5. Summary The experimental platform was improved based on the original design, making it more convenient for filling and exchanging working fluids. The liquid-phase toluene was used to test the thermal conductivity measurement experimental platform built based on the transient filament method. The results showed that the measurement results of this experimental platform were accurate and reliable. Experiments were conducted to measure the liquid-phase thermal conductivity of n-dodecane within the temperature range of 317.97K to 610.54K and the pressure range of 1MPa to 20MPa. Acknowledgements This research was supported by The Undergraduate Innovation Key Program in 2025(No.240084470105), Henan Science and Technology Attack Project (No. 252102230094). References [1] Xia Youcai, Dai Shun'an, Su Yan. Research Status and Trends of Superalloy Ramjet Engines [J]. Journal of Aeronautical Missiles. 2016(08): 59-63. [2] Edwards T. "Kerosene" Fuels for Aerospace Propulsion - Composition and Properties[J].38th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit. 2002. [3] Fujii M, Zhang X, Imaishi N, et al. Simultaneous measurements of thermal conductivity and thermal diffusivity of liquids under microgravity conditions[J]. International Journal of Thermophysics, 1997, 18 (2): 327-339. [4] Zeng Fanjian. Development of a Thermal Conductivity Measurement System Using the Transient Short Wire Method [D]. Xi'an: Xi'an Jiaotong University, 2013. [5] Healy JJ, De Groot JJ, Kestin J. The Theory of the Transient Hot-Wire Method for Measuring Thermal Conductivity[J], Physica, 1976, 82: 392-408. [6] Marcia L. Huber ,* Arno Laesecke , and Richard Perkins. Transport Properties of n-Dodecane[J]. Energy Fuels, 2004, 18 (4), 968–975.