Film Resistance Thermometers Research Articles

Research on supersonic film cooling of hypersonic optical window under different nozzle pressure ratios

When optical imaging-guided aircraft flies at hypersonic speeds in the atmosphere, the optical window withstands severe aerodynamic heating. Conducting the thin film resistance thermometer measurements in a hypersonic gun wind tunnel with a Mach number of 7.1 and total temperature of 670 K, the study investigates the effect of nozzle pressure ratio (NPR = film exit static pressure/nearby mainstream static pressure) on supersonic (Mach 2.43) film cooling for the hypersonic optical window. By combining the flow information near the window obtained using the three-dimensional compressible Reynolds-averaged Navier–Stokes method, the study reveals the mechanism of the effect of NPR on film cooling. The results indicate that increasing NPR can enhance the momentum of the unit volume film and improve the film's ability to resist mainstream mixing. Moreover, the film with a large NPR can better maintain its own momentum, leading to an increase in the film effective cooling length and film cooling effectiveness. The film effective cooling length corresponding to the unit mass flow rate of the cooling gas increases with the increase in NPR. It verifies the nonlinear relationship between the film cooling performance and the coolant mass flow rate, indicating the additional benefits of increasing NPR on the film cooling performance. Through research, it is found that increasing NPR can increase the film thickness, thereby enhancing its ability to isolate the mainstream. Moreover, as NPR increases, the cooling film expands, objectively leading to the widening of the film flow channel, allowing the Mach number of the supersonic film to increase continually. This further reduces the static temperature of the film in the flow field, thereby enhancing its cooling capability for the mainstream.

Experimental investigation on supersonic film cooling of hypersonic optical dome under different nozzle pressure ratios

When an aircraft flies at hypersonic speeds in the atmosphere, its optical window is subjected to severe aerodynamic heating. To investigate the supersonic film cooling laws of hypersonic optical dome, three supersonic (Mach 2.35) film generation devices with different jet outlet heights (1 mm, 2 mm, 3 mm) were designed. The experiments were conducted in a hypersonic (Mach 7.1) gun wind tunnel. The NPR (nozzle pressure ratio = jet outlet static pressure/nearby mainstream static pressure) ranged from 0 to 2.3. The heat flux on the window surface was measured by the thin film resistance thermometer. Experimental results indicate that, under different jet outlet heights, the film cooling effectiveness increased gradually as the NPR increased, corresponding to an increase in effective cooling length. The existing similarity parameters for film cooling could effectively predict the effective cooling length of supersonic film when NPR = 1. However, the prediction effect deviated significantly when NPR ≠ 1. Moreover, the effective cooling length corresponding to the unit mass flow rate of the coolant first increased and then decreased with the increase of NPR, and there existed an optimal solution. Furthermore, with the same coolant mass flow rate, higher jet Mach number lead to better supersonic film cooling performance.

Gas temperature meter

Purpose: of the article is to develop a digital portable gas temperature meter in the range of -50…+600°C. To measure the temperature of dusty gas flows in the air pollution sources with the least significant digit of the digital device 1°C. Design/methodology/approach: The microprocessor measuring unit, probe and software is proposed. It leads to build a high-precision temperature meter based on a thin film sensor HM220 type "pt100". Findings: The calculation of the electrical schematic diagram parameters for signal conditioning of the sensor relative to the input range of the analog-to-digital converter. The experimental measuring unit and the probe of the gas temperature meter are assembled. The principle of the gas temperature meter calibration with the help of a precision resistance box MSR-60M is considered. The experimental gas temperature meter has a total standard uncertainty determined by type B for a maximum value of the measurement range of 1.94°C. The error of the sensor "pt100" makes the largest contribution to the total standard uncertainty, so the error increases in proportion to the value of the measured temperature. Research limitations/implications: On the basis of the proposed design of gas temperature meter it is possible to construct devices with various lengths of probes. Practical implications: The proposed meter is designed for environmental laboratories that measure the velocity, flow and sampling of dust and gas emissions from sources of air pollution. Originality/value: The device design differs due to the use of thermostable wire made of constantan as extending conductors of the temperature sensor, which is included in the unbalanced Wheatstone bridge. This solution allows the use of unipolar power supply 3.3 V for both analog and digital part of the meter. Temperature meter based on a thin film resistance thermometer is characterized by relative ease of manufacture, low material consumption, cost and high reliability.

A differential thin film resistance thermometry method for peak thermal conductivity measurements of high thermal conductivity crystals.

High thermal conductivity materials are useful for thermal management applications and fundamental studies of phonon transport. Past measurements of several ultrahigh thermal conductivity materials were not able to obtain the peak thermal conductivity, which is expected to appear at a low temperature and contains insight into the competition between extrinsic phonon-defect and phonon-boundary scattering with intrinsic phonon-phonon processes. Here, we report a peak thermal conductivity measurement method based on differential Wheatstone bridge measurement of the small temperature drop between two thin film resistance thermometers patterned directly on the sample. With the use of a mesoscale silicon bar sample as the calibration standard, this method is able to obtain results that agree with past measurements of large bulk silicon crystals at high temperatures and first-principles calculation results that account for additional phonon-boundary scattering in the sample. The agreement demonstrates the accuracy of this measurement method for peak thermal conductivity measurements of high thermal conductivity materials.

Thin film resistance thermometer with simple package for cryogenic application

In this paper, we proposed a novel simple package based on micro-machining for thin-film cryogenic temperature sensors. The substrate with temperature sensitive element fabricated by micro-machining process, directly used as the package substrate. Then, the silicon cover soldered on the substrate, providing vacuum encapsulation with high air tightness. Subsequently, we researched the reliability of the package by leak rate detection, shear force test and scanning electron microscope. Lastly, the temperature response curves, measurement fluctuation, thermal response time and short-term stability of the thermometers had been researched. Compared to the traditional package, the simple package simplified manufacturing process, reduced cost. Furthermore, the temperature sensitive element directly deposited on the package substrate, reduced sensor mass and improved thermal response speed.

Intellectual Precise Temperature Sensor with Wireless Interface

Intellectual precise temperature sensor with wireless interface (ITWS) for contact measurements with absolute error of ±0.05 ◦C in the temperature range from 5 to 95 ◦C was developed. Platinum thin film resistance thermometer was used as the sensitive unit. High accuracy of measurements is supported by following. Investigations and modeling of temperature dependence of resistivity for sensitive unit allowed to develop mathematical model ensuring calculation of temperature with the error not exceeding 5× 10−3 ◦C. Original patented design, and hardware and software solutions for ITWS were developed. Method and mathematical models for thermocompensation of electronic components of ITWS were elaborated, which allowed sufficient decrease of measurement error during measurements and exploitation. Methodology, and hardware and software measuring system for individual ITWS calibration in automatic regime were developed, which include correction of mathematical model for the calculation of temperature for each sensor. ITWS has several design and technological solutions, and is developed for the temperature measurements of heat transfer agent in the pipelines of heating and hot water supply systems, independently of pipeline diameter. Measured data are transferred by radio channel to the recording and display devices. ITWS are used in automated systems for energy carrier controlling and determination of individual heat consumption. ITWS consists of following modules: sensitive unit, analog-to-digital converter, microcontroller, radio transceiver (carrier frequency is 434 or 868 MHz, output power of transmitter is not more than 10 mW), antenna and power supply (3.6 V).

Ge-on-GaAs film resistance thermometers: Low-temperature conduction and magnetoresistance

We investigated and generalized the resistance temperature and magnetic field dependences for various versions of cryogenic resistance thermometers based on Ge films on semi-insulating GaAs substrates. It is shown that, at low temperatures, the conductivity mechanism that is responsible for Ge film heat and magnetic field sensitivity is variable-range hopping (VRH). We found that the exponent x in VRH-type temperature law may take different values (fall between 0.25 and 0.67) for different versions of Ge-on-GaAs film thermometers. The magnetoresistance of Ge films depends strongly on the nature of hopping conductivity. It may be positive and negative as well as high and low. We found that, in the 1.8−4.2 K temperature range studied, the Ge films with x ≅ 0.25 (that corresponds to nonzero constant density of states at the Fermi level) demonstrate high positive magnetoresistance. The films with x > 0.4 (that corresponds to presence of a gap in the density of states at the Fermi level) have negative magnetoresistance component that predominates at magnetic induction up to 3–5 Т. The parameters describing VRH conductivity in the Ge-on-GaAs films thermometers were determined. From practical point of view for thermometry, the possibility to describe the R = f( T) dependence by an analytical equation (VRH-type temperature law) does not require the fitting procedure and makes calibration and thermometry more simple and convenient.

Dual function sensors for concurrent measurement of temperature and magnetic field in cryogenic applications

Dual function sensors (DFSs) for concurrent measurement of temperature and magnetic field in cryogenic applications have been developed and characterized. The DFS consists of a Ge-on-GaAs film resistance thermometer and an InSb-on-GaAs film Hall-effect magnetic field sensor combined in a single package with dimensions: 3.5 mm wide, 2.2 mm thick and 10.1 mm long. The construction and characteristics of two models of the DFSs; which are intended to provide measurements of temperature in the 1.5–400 K and 0.1–400 K ranges, and magnetic fields up to 30 T, are presented.

Ge-on-GaAs film resistance thermometers for cryogenic applications

Our paper discusses and reviews the properties of a range of semiconductor sensors, which have been developed for thermometry in cryogenic applications. The range of sensors developed includes a family of single and dual element resistance thermometers based on Ge-on-GaAs films. The thin film devices were produced using standard semiconductor processing techniques and provide high device sensitivity within the range 0.03–500 K. The construction and characteristics of the sensors are presented together with a discussion of their sensitivities to magnetic fields and ionising radiation.

Wind tunnel evaluation of novel interferometric optical fibre heat transfer gauges

Short length ( approximately 2 mm) fibre Fabry-Perot interferometers embedded in test models have been used as calorimeter heat transfer gauges in transient wind tunnel experiments. Four sensors were multiplexed to a single laser diode source by a fibre optic coupler network. Results are presented from wind tunnel evaluations with comparison against conventional thin film resistance thermometers in the measurement of heat fluxes of approximately 50 kW m-2 and 20 ms duration.

Interferometric fibre sensors for measurement of surface heat transfer rates on turbine blades

We describe a prototype sensor for surface heat transfer measurements based on a miniature fibre Fabry-Perot (FFP) interferometer. These sensors are being developed for a particular application where heat transfer data are currently obtained using conventional platinum thin film resistance thermometers. The specification that the sensors must exceed is: (i) temperature resolution of 25 mK over a 50 K range; (ii) temporal response of 10 μs; (iii) an ability to operate as a calorimetric heat transfer gauge. The sensor consists of a short length of single mode optical fibre (∼ 3 mm) to which low reflectivity coatings have been applied at each end. It is illuminated and interrogated by an arbitrary length of addressing fibre. A laser diode is used as the source and we have exploited the facility to frequency modulate the diode in a novel signal processing scheme. To determine the performance of the sensor, short duration heat pulses derived from a pulsed Nd: YAG laser were applied to one end of the FFP. The response time was found to be 8 μs and the sensor operation as a calorimeter was verified.

磁場中の比熱計測技術の開発 （２） 熱緩和法システムと磁場中特性評価

A heat-capacity measurement system has been developed to establish a reliable calorimetric study under magnetic fields. The system is based on the thermal relaxation method by use of a temperature-difference detection system, which incorporates a pair of small thin film resistance thermometers, PTF-7 and is little affected by magnetic fields. Its performance under magnetic fields has been studied by use of a reference sample, whose heat capacity is independent of magnetic fields. SRM 720 provided by NIST, which is made of synthesized sapphire, was selected for this purpose. As this material is non-magnetic insulator, its heat capacity is expected to have small field dependence. The performance of the total system has been studied between 40 and 90K under magnetic fields of up to 7T. The resolution of the system was estimated to be about 2% and independent of the magnitude of magnetic fields. The measured heat capacities under magnetic fields of 0T, 5T and 7T agreed with each other within the resolution of the measurement.

Nature of the surface heart transfer fluctuation in a hypersonic separated turbulent flow

This paper presents the results of an experimental study of the unsteady nature of a hypersonic separated turbulent flow. The nomimal test conditions were a freestream Mach number of 7.8 and a unit Reynolds number of 3.5×107/m. The separated flow was generated using finite span forward facing steps. An array of flush mounted high spatial resolution and fast response platinum film resistance thermometers was used to make multi-channel measurements of the fluctuating surface heat trtansfer within the separated flow. Conditional sampling analysis of the signals shows that the root of separation shock wave consists of a series of compression wave extending over a streamwise length about one half of the incoming boundary layer thickness. The compression waves converge into a single leading shock beyond the boundary layer. The shock structure is unsteady and undergoes large-scale motion in the streamwise direction. The length scale of the motion is about 22 percent of the upstream influence length of the separation shock wave. There exists a wide band of frequency of oscillations of the shock system. Most of the frequencies are in the range of 1–3 kHz. The heat transfer fluctuates intermittently between the undisturbed level and the disturbed level within the range of motion of the separation shock wave. This intermittent phenomenon is considered as the consequence of the large-scale shock system oscillations. Downstream of the range of shock wave motion there is a separated region where the flow experiences continuous compression and no intermittency phenomenon is observed.

Dynamic measuring error correction of encapsulated auxiliary wall heat flux sensors made of film resistance thermometers

A mathematical correction of the dynamic measuring error associated with encapsulated heat flux sensors can normally be obtained by solving the inverse heat conduction problem. An approximation using information theory is considered here. In contrast to a temperature sensor, the time constant of a heat flux sensor is assumed to be independent of the heat transfer coefficient.

Converse thermal conductivity problems and calorimetry of transparent bodies

The problem of measuring temperature of transparent bodies can be solved by use of transparent thin film resistance thermometers. Such sensors have been developed using tin and indium oxide. They are used to perform calorimetry of the properties of partially transparent bodies and laser radiation.

Unsteady Interaction Effects on a Transitional Turbine Blade Boundary Layer

Results are presented illustrating the detailed behavior of the suction surface boundary layer of a transonic gas turbine rotor in a two-dimensional cascade under the influence of both free-stream turbulence and simulated nozzle guide vane wakes and shocks. The instrumentation included thin film resistance thermometers along with electrical analogues of the one-dimensional heat conduction equations to obtain wide bandwidth heat transfer rate measurements in a short duration wind tunnel. This instrumentation provides sufficient time resolution to track individual wake and shock-related events and also the turbulent bursts of a transitional boundary layer. Wide bandwidth surface pressure transducers and spark Schlieren photography were used in support of these heat transfer measurements. The results showed a direct relationship between the passage of wake disturbances and transient surface heat transfer enhancements. It was possible to track both wake and transitional events along the surface and to compare these with the expected convection rates. Analysis of the signals allowed direct calculations of intermittency factors, which compared well with predictions. Additional effects due to a moving shock/boundary layer interaction were investigated. These resulted in marked variations in heat transfer rate both above and below the laminar values. These excursions were associated with separation and re-attachment phenomena.

The theory of advanced multi-layer thin film heat transfer gauges

This paper describes the theory of a transient method of measuring heat transfer rate to metal substrates coated with an electrical insulator, using thin film resistance thermometers. This builds on the already well-established system which uses semi-infinite insulating substrates. It is intended that the new technique will have application in rotating turbine test rigs, since there is at present a lack of suitable instrumentation which can be easily manufactured, and which does not interfere with the flow. The new system described here shows that multi-layer substrate gauges can be used. This paper presents analyses of layered gauges and gives sample predictions and calibrations.

High-frequency response heat-flux gauge

A double-sided, high-frequency response heat-flux gauge has been developed which allows measurement of heat flux from dc to 100 kHz. The instrument is designed for heat-flux magnitudes ranging from one to several hundred kW/m2 at temperatures up to 400 °C and is independent of the test article material. The gauges consist of a metal film (1500 Å) resistance thermometers sputtered on both sides of a thin (25 μm) polyimide sheet. The sheet, which can contain many gauges, is then adhesively bonded to a test article. The temperature difference across the polyimide is a direct measure of the heat flux at low frequencies, while a quasi-1D analysis is used to infer the high-frequency heat flux from the upper surface temperature history. The design criteria, construction and application techniques, and a novel, ratiometric calibration procedure are discussed in detail.

A high sensitivity, fast response heat flux sensor

A high sensitivity, fast response heat flux sensor was developed for heat flux measurement at a moving surface subjected to rapidly fluctuating heat flux. The sensor is a gold thin film resistance thermometer on a non-conducting substrate. Mounted flush with the moving surface, the sensor measures instantaneous surface temperature with a resolution of about 0.002°C at sampling speeds up to 5000 s −1. Local heat flux is obtained through solution of the unsteady heat conduction equation. Heat transfer profiles are generated with this technique for the case of plane jets impinging on surfaces moving at speeds up to 12 m s −1.

Unsteady heat transfer during laminar flame quenching

Measurements were made of the unsteady heat transfer to a wall during the quenching of premixed, methane-air flames. One dimensional laminar flames were produced in a constant volume chamber and the heat transfer into the quenching surface was measured by means of a platinum thin film resistance thermometer. The experiments were performed at pressures near atmospheric over a range of equivalence ratios from 0.7 to 1.2. Predictions of the heat transfer were made with two numerical finite difference models, one with detailed kinetics and the other with single step kinetics. The main experimental results are: 1) the data are successfully correlated using the heat release rate of the flame prior to quenching; 2) the maximum heat flux is related to the quenching distance and thus it may be possible to use measurements of the quenching distance to predict the maximum heat flux. A comparison of the experimental results and the numerical calculations revealed that: 1) a single step reaction model predicts the heat transfer as well as a detailed kinetics model, to within 15% of the experimental results; 2) thermal diffusion and the chemical reaction rate of combustion are the dominant processes which determine the heat flux during quenching.