The accuracy of the liquid thermal conductivity testing device is highly dependent on the sensor performance and temperature control technology. The two work together to achieve precise capture of small heat flow signals and dynamic compensation for environmental interference. The following analysis is conducted from the perspectives of technical principles and engineering implementation:
1、 Sensor selection: Multi parameter fusion measurement system
Heat Flow Sensor (HFS)
Using a thin film heat flux sensor (such as platinum foil or copper foil) with a thickness of ≤ 50 μ m and a response time of<10ms, it can monitor the small heat flux density on the wall of the test chamber in real time (range 0.1-10kW/m ²). For example, when measuring the thermal conductivity of liquid metals, it is necessary to choose a platinum rhodium alloy heat flux sensor that is resistant to high temperatures (>500 ℃) to avoid signal drift caused by thermal expansion.
Temperature sensor array
Main control temperature sensor: Platinum resistance thermometer (PT100, accuracy ± 0.01 ℃) is selected and arranged at the center of the hot and cold ends of the test chamber, directly participating in the calculation of thermal conductivity.
Auxiliary temperature sensor: using N-type thermocouples (accuracy ± 0.1 ℃), evenly distributed along the axial direction of the test chamber (spacing ≤ 10mm), used to monitor the uniformity of temperature gradients. For example, in non Newtonian fluid testing, temperature distortion caused by internal convection of the fluid needs to be corrected through auxiliary sensor data.
Pressure and liquid level sensors
Integrated piezoresistive pressure sensor (range 0-10MPa, accuracy ± 0.05% FS) and capacitive liquid level sensor (resolution 0.01mm), real-time monitoring of pressure fluctuations and liquid level changes caused by liquid evaporation in the testing chamber, avoiding measurement errors caused by cavitation effects.
2、 Temperature Control: Dynamic Balance and Precise Control Technology
Dual zone independent temperature control system
The cold end adopts a combination of semiconductor cooling elements (TEC) and circulating water cooling, while the hot end uses high-frequency induction heating or thin film heating elements, achieving temperature stability of ± 0.05 ℃ through PID algorithm. For example, when testing low-temperature liquids such as liquid nitrogen, it is necessary to add a liquid nitrogen Dewar flask and a vacuum insulation layer at the cold end to reduce environmental heat leakage.
Construction of gradient temperature field
By using multi-stage heating/cooling modules (each with independent temperature control) and filling with thermal conductive silicone grease, a linear temperature gradient (Δ T=5-20 ℃ adjustable) is formed in the test chamber. For example, using finite element analysis (FEA) to optimize the layout of heating plates, the temperature gradient deviation within a 100mm long test chamber is ≤ 0.2 ℃/cm.
Active compensation and anti-interference design
Environmental temperature compensation: A temperature sensor is embedded in the device casing to correct the impact of environmental temperature fluctuations (such as laboratory air conditioning on/off) on the testing chamber through software algorithms.
Electromagnetic interference shielding: The heating module power line adopts a twisted pair structure and is wrapped with an aluminum foil shielding layer to reduce the impact of 50Hz power frequency interference on the temperature sensor signal (signal-to-noise ratio improvement>30dB).
3、 Technical collaboration and error suppression
Sensors and temperature control systems achieve error closed-loop control through the following mechanisms:
Heat flow temperature coupling correction: dynamically adjust the temperature gradient setting value using heat flow sensor data to compensate for heat loss caused by liquid convection or phase change. For example, when testing high viscosity fluids, the system automatically reduces the heating power to maintain a stable temperature gradient.
Self diagnosis and fault tolerance mechanism: When the deviation of any temperature sensor exceeds the threshold (such as ± 0.5 ℃), the system switches to the backup sensor and triggers an alarm, while recording abnormal data segments for subsequent analysis.
By integrating high-precision sensor arrays with intelligent temperature control technology, modern liquid thermal conductivity testing devices can achieve measurement repeatability of ≤± 0.3% and long-term stability of ≤± 0.5%/year within the range of 0.01-10W/(m · K), meeting the testing needs of cutting-edge fields such as aerospace fuels and nanofluids.