An experimental technique based on the thermal wave approach for measuring the thermal conductivity of liquids is developed in this paper. A stainless steel strip functions as both a heating element and a sealing cover for a chamber containing a test liquid. A periodic current passing through this metal strip generates a periodic Joule heating source. An infrared detector measures the temperature response at the front surface of the stainless steel strip. The phase and magnitude of the temperature response with respect to the heating signal were measured by a lock-in amplifier at various frequencies from 22 Hz to 502 Hz. A one-dimensional, two-layered transient heat conduction model was developed to predict the temperature response on the front surface of the stainless steel strip. The phase information from this temperature response shows high sensitivity to the change in thermal properties of the liquid layer and is employed to match experimental data to find the thermal properties of the test liquid. The measured thermal conductivities of water and ethylene glycol agree quite well with the data from literature and support the validity of this measurement technique. An aqueous fluid consisting of gold nanoparticles is tested and anomalous thermal conductivity enhancement is observed. A discrepancy in the thermal transport behavior between pure liquids and nanofluids is suggested from our experimental results.

Self-heating in deep submicron transistors (e.g., silicon-on-insulator and strained-Si) and thermal engineering of many nanoscale devices such as nanocalorimeters and high-density thermomechanical data storage are strongly influenced by thermal conduction in ultra-thin silicon layers. The lateral thermal conductivity of single-crystal silicon layers of thicknesses 20 and 100 nm at temperatures between 30 and 450 K are measured using joule heating and electrical-resistance thermometry in suspended microfabricated structures. In general, a large reduction in thermal conductivity resulting from phonon-boundary scattering is observed. Thermal conductivity of the 20 nm thick silicon layer at room temperature is nearly 22 W m − 1 K − 1 , compared to the bulk value, 148 W m − 1 K − 1 . The predictions of the classical thermal conductivity theory that accounts for the reduced phonon mean free paths based on a solution of the Boltzmann transport equation along a layer agrees well with the experimental results.

Giant magnetoresistance (GMR) head technology is one of the latest advancements in the hard disk drive (HDD) storage industry. The GMR head multilayer structure consists of alternating layers of extremely thin metallic ferromagnetic and nonmagnetic films. A large decrease in the electrical resistivity from antiparallel to parallel alignment of the film magnetizations is observed, known as the GMR effect. The present work characterizes the in-plane electrical and thermal conductivities of Cu ∕ CoFe GMR multilayer structures in the temperature range of 50 K to 340 K using Joule-heating and electrical resistance thermometry on suspended bridges. The thermal conductivity of the GMR layer monotonically increases from 25 W m − 1 K − 1 (at 55 K ) to nearly 50 W m − 1 K − 1 (at room temperature). We also report a GMR ratio of 17% and a large magnetothermal resistance effect (GMTR) of 25% in the Cu ∕ CoFe multilayer structure.

The discrete Green’s function (DGF) for convective heat transfer was measured in a fully developed, turbulent pipe flow to test a new technique for simple heat transfer measurement. The 10 × 10 inverse DGF, G − 1 , was measured with an element length of approximately one pipe diameter and Reynolds numbers from 30,000 to 100,000 and compared to numerical predictions using a parabolic flow solver called STANTUBE. The advantages of using the DGF method over traditional heat transfer coefficients in predicting the thermal response for flows with nonuniform thermal boundary conditions are also demonstrated.

Hysteresis in five different Thermochromic Liquid Crystals (TLCs), both narrow-band and broad-band, has been investigated. All were found to exhibit a similar hysteresis behavior during cooling relative to heating. This hysteresis is characterized by a decrease in reflectivity and a shift in the temperature associated with the peak reflected intensity for each of the R, G, and B components during cooling. This causes a shift in the hue-temperature calibration of the TLC causing temperature biases, when cooled rather than heated, of 20–60% of the useful calibration range. The hysteresis effect increases as the peak temperature during a heating and cooling cycle is increased. Repeatable heating calibrations were obtained when the TLC was cooled below the red start temperature to an apparent low reset temperature. Somewhat repeatable cooling calibrations, different from the heating calibrations, were obtained when the TLC was heated somewhat above the blue stop temperature. A possible explanation of the hysteresis based on the texture of the liquid crystal helices is provided. In addition to hysteresis, a permanent decrease in reflectivity and a shift in the temperature associated with the peak reflected intensity was observed when the TLCs were exposed to extended higher temperatures (60°C–80°C).

This work presents the use of laser induced fluorescence for instantaneous temperature measurements of 200 μm water droplets in a monodisperse stream while traveling downward in a standard stagnant atmosphere. The droplets are doped with small concentrations of a natural fluorescence dye (Pyrene), and with a surfactant substance, cetyldimetylbenzylammoniumchloride (CDBAC) to improve the fluorescence emission and the rate of its two band emission (excimer to monomer) is used to determine the temperature. The temperature distribution along the stream of droplets was determined for three different initial temperatures: 30°C, 40°C, and 50°C at the exit of the nozzle and it is compared very favorably with numerical results.

The present paper addresses the measurement errors in temperature due to the effects of surface-mounted temperature sensors like thermocouples. Heat conduction into or from the installed thermocouple wires can alter the temperature at the thermocouple junction as well as in its immediate vicinity. As a result, the emf appearing at the thermocouple terminals does not correspond to the actual surface temperature. In this paper, we present a dual-scale computational method that can be used to calculate the transient temperatures at the multiple thermocouple junctions during heating or cooling of an object. The basis of the method is a thermocouple submodel embedded in a FEM model for the parent object. The numerical results of the dual-scale computational model are compared with that of the conventional FEM models as well as the analytical solutions available. This paper also discusses the characteristics of surface-mounted thermocouples in a range of configurations.

The local time-averaged temperature θ s ¯ and its fluctuating component θ s on the surface of a heated circular cylinder immersed in a cylinder near-wake were measured using a fiber-optic Bragg grating (FBG) sensor. Three cylinder center-to-center spacing, i.e., L / d = 5.20 , 2.50, and 1.18, were investigated. In order to validate the FBG sensor measurement, a thermocouple and a single hot-wire were employed to measure θ s ¯ on the heated cylinder and streamwise fluctuating velocity u in the near-wake of the downstream cylinder, respectively. The FBG sensor measurement of θ s ¯ is in good agreement with that simultaneously obtained by the thermocouple. The measured θ s is closely correlated to the hot-wire measurement; the θ s -spectrum exhibits a pronounced peak at the vortex shedding frequency, as identified in E u , for each L / d . The results suggest that the FBG sensor can be used to measure reliably both time-averaged and fluctuating temperatures. The heat transfer characteristics of the heated cylinder are examined for different L / d and further compared with the case of an isolated cylinder.

We have batch-fabricated a microdevice consisting of two adjacent symmetric silicon nitride membranes suspended by long silicon nitride beams for measuring thermophysical properties of one-dimensional nanostructures (nanotubes, nanowires, and nanobelts) bridging the two membranes. A platinum resistance heater/thermometer is fabricated on each membrane. One membrane can be Joule heated to cause heat conduction through the sample to the other membrane. Thermal conductance, electrical conductance, and Seebeck coefficient can be measured using this microdevice in the temperature range of 4–400 K of an evacuated Helium cryostat. Measurement sensitivity, errors, and uncertainty are discussed. Measurement results of a 148 nm and a 10 nm-diameter single wall carbon nanotube bundle are presented.

The present study addresses the effects of thermocouples on the measured temperature when such thermocouples are mounted directly on the surface of the object. A surface-mounted thermocouple is a very convenient way of measuring the surface temperature. However, the heat conduction into/from the thermocouple wire changes the local temperature at the thermocouple junctions along with the immediate vicinity of the thermocouple. As a consequence, the emf appearing at the thermocouple terminals does not correspond to the actual surface temperature. In this paper, we first discuss the general characteristics of the enhanced heating/cooling due to the so-called “fin effects” associated with the surface-mounted thermocouples. An embedded computational model is then developed so that the model can be used in conjunction with a regular FEM model for the multidimensional calculation of the heating or cooling of a part. The embedded computational model is shown to offer very accurate calculation of the temperature at the junction of thermocouple wire. The developed computational model is further used in the inverse heat transfer calculation for a Jominy end quench experiment.

Numerical investigations of the heat transfer from hot wires in near-wall measurements were carried out. Special attention was paid to the effect of the wall thickness, the flow conditions below the wall and the shear velocity connected to different wall materials. Compared with previous studies, an improved physical model taking into account the flow region below the wall in the computational domain was applied. The results obtained agree well with experimental data in the literature for walls consisting of both highly and poorly conducting materials. The investigation showed that the shear velocity U τ has a significant influence on hot-wire measurements in the vicinity of a wall. Nevertheless, discernible effects of the wall thickness and the flow condition below the wall were found only in the case of a poorly conducting wall. In addition, the results also suggest a weak effect of the overheat ratio for a wire with an infinitely large aspect ratio.

Detailed heat transfer coefficient distributions on a squealer tip of a gas turbine blade were measured using a hue detection based transient liquid crystals technique. The heat transfer coefficients on the shroud and near tip regions of the pressure and suction sides of a blade were also measured. Tests were performed on a five-bladed linear cascade with a blow-down facility. The blade was a two-dimensional model of a first stage gas turbine rotor blade with a profile of a GE-E 3 aircraft gas turbine engine rotor blade. The Reynolds number based on the cascade exit velocity and axial chord length of a blade was 1.1 × 10 6 and the total turning angle of the blade was 97.7 deg. The overall pressure ratio was 1.2 and the inlet and exit Mach number were 0.25 and 0.59, respectively. The turbulence intensity level at the cascade inlet was 9.7 percent. The heat transfer measurements were taken at the three different tip gap clearances of 1.0 percent, 1.5 percent, and 2.5 percent of blade span. Results showed that the overall heat transfer coefficients on the squealer tip were higher than that on the shroud surface and the near tip regions of the pressure and suction sides. Results also showed that the heat transfer coefficients on the squealer tip and its shroud were lower than that on the plane tip and shroud. However, the reductions of heat transfer coefficients near the tip regions of the pressure and suction sides were not remarkable.

A blackbody optical fiber thermometer consists of an optical fiber whose sensing tip is given a metallic coating. The sensing tip of the fiber forms an isothermal cavity and the emission from this cavity is approximately equal to the emission from a blackbody. When a short length of the fiber is exposed to a high temperature environment, the temperature at the sensing tip can be inferred using the standard two-color approach. If, however, more than a short length of the fiber is exposed to elevated temperatures, emission by the fiber will result in erroneous temperature measurements. This paper presents experimental results that show it is possible to use additional spectral measurements to eliminate errors due to emission by the fiber and measure the tip temperature. In addition, the technique described in this paper can be used to obtain an estimate of the temperature profile along the fiber.

The detailed distributions of heat transfer coefficient and film cooling effectiveness on a gas turbine blade tip were measured using a hue detection based transient liquid crystals technique. Tests were performed on a five-bladed linear cascade with blow-down facility. The Reynolds number based on cascade exit velocity and axial chord length was 1.1 × 10 6 and the total turning angle of the blade was 97.7°. The overall pressure ratio was 1.2 and the inlet and exit Mach numbers were 0.25 and 0.59, respectively. The turbulence intensity level at the cascade inlet was 9.7%. The blade model was equipped with a single row of film cooling holes at both the tip portion along the camber line and near the tip region of the pressure side. All measurements were made at the three different tip gap clearances of 1.0%, 1.5%, and 2.5% of blade span and the three blowing ratios of 0.5, 1, and 2. Results showed that, in general, heat transfer coefficient and film effectiveness increased with increasing tip gap clearance. As blowing ratio increased, heat transfer coefficient decreased, while film effectiveness increased. Results also showed that adding pressure side coolant injection would further decrease the blade tip heat transfer coefficient but increase film-cooling effectiveness.

In the satellite or energy conversion industries flat heat pipes may be utilized to transfer heat to the thermal sink. In this investigation, a large flat heat pipe, 1.22 m × 0.305 m × 0.0127 m , fabricated from 50 mil Monel 400 metal sheets and Monel 400 screens was videographed at horizontal and vertical orientations with an infrared video camera. The heat pipe evaporator section consisted of a 0.305 m × 0.305 m area (one heated side only) while the side opposite the heated section was insulated. The remaining area of the heat pipe served as the condenser. In the horizontal orientation the heated section was on the bottom. In the vertical orientation the evaporator was aligned below the condenser. The sequence of photographs depicts heat inputs ranging from 200 W to 800 W, and the effect of air infiltration on heat pipe operation for both orientations. For the horizontal orientation, the air is seen to recede towards the small fill pipe as the heat input is increased. For the vertical orientation, the air and water vapor exhibit a buoyant interaction with the result that the air presence inhibits heat transfer by rendering sections of the condenser surface ineffective. The effects depicted in this paper set the stage for future analytical and experimental work in flat heat pipe operation for both normal and variable conductance modes.

Two temperatures can be detected in a hot gas laden with water droplets. The lower one is the temperature read by a sensor immersed in the flow. This measurement is affected by significant evaporative cooling resulting in readings much below the real gas temperature. The higher one is the temperature of the gas. The difference between these two temperatures is proportional to the water volumetric fraction in the flow. On this basis, a new technique for the measurement of the water volumetric fraction is proposed. The results are compared with a conventional measurement technique based on optical methods. A novel approach to the gas temperature measurement is also introduced. The sensing device is kept at temperatures exceeding the Leidenfrost transition and therefore it is insensitive to the presence of the water droplets. Independent measurement techniques developed at the Evaporative Cooling Sensor Accuracy Test (ECSAT) facility provide the data to validate the measurements obtained with the Above Leidenfrost Temperature and Evaporative Cooling (ALTEC) sensor.

A procedure using a long-wavelength pyrometer is developed for the measurement of surface temperatures on materials that are semitransparent at shorter wavelengths, and specific application is made to a dense zirconia ceramic (Mg-PSZ) undergoing laser-assisted machining (LAM). The pyrometer operates in a waveband between 11 and 14 μm, and a detailed description of measurement uncertainties is provided. The largest uncertainties relate to knowledge of the surface emissivity and the large temperature gradients generated by the LAM process. Repeatability of the measurements is demonstrated, and a parametric study of three LAM parameters reveals expected trends.

The time and space development of the fluid bulk temperature in a transient heat transfer experiment for internal channel cooling investigations using heater foils is addressed. An analytical solution for uniform heat transfer coefficients is derived which shows the effect of wall heating on the bulk temperature during a transient test run. A simplified model is proposed for characterizing the bulk temperature development by introducing an upstream heat transfer parameter. With this, analytical solutions for the local wall temperature history can be derived. The presented solution can be used for data reduction of transient tests of this kind.

Laser interferometry can be used in a three dimensional temperature field to measure the average fluid temperature and heat transfer rate, integrated over the length of an experimental model. However, such measurements are inherently approximate when the surface temperature varies in the direction of the test/object beam. In this study an analysis is performed to determine the accuracy of beam-averaged heat transfer rate measurements made in ideal gases. Two analysis methods are considered. The first method is based on extrapolation of the near-wall temperature field to obtain the surface gradient. In the second method, the temperature gradient at the surface is obtained directly from the gradient of the fringe field. The results show that the intrinsic error in the measurements depends strongly upon the form and magnitude of the temperature variation in the light beam direction. Although the error in the measured heat transfer rate is shown to be small for many commonly encountered conditions, it can be greater than ten percent in extreme cases.

We review recent advances in experimental methods for high spatial-resolution and high time-resolution thermometry, and the application of these and related methods for measurements of thermal transport in low-dimensional structures. Scanning thermal microscopy (SThM) achieves lateral resolutions of 50 nm and a measurement bandwidth of 100 kHz; SThM has been used to characterize differences in energy dissipation in single-wall and multi-wall carbon nanotubes. Picosecond thermoreflectance enables ultrahigh time-resolution in thermal diffusion experiments and characterization of heat flow across interfaces between materials; the thermal conductance G of interfaces between dissimilar materials spans a relatively small range, 20< G <200 MW m − 2 K − 1 near room temperature. Scanning thermoreflectance microscopy provides nanosecond time resolution and submicron lateral resolution needed for studies of heat transfer in microelectronic, optoelectronic and micromechanical systems. A fully-micromachined solid immersion lens has been demonstrated and achieves thermal-radiation imaging with lateral resolution at far below the diffraction limit, <2 μm. Microfabricated metal bridges using electrical resistance thermometry and joule heating give precise data for thermal conductivity of single crystal films, multilayer thin films, epitaxial superlattices, polycrystalline films, and interlayer dielectrics. The room temperature thermal conductivity of single crystal films of Si is strongly reduced for layer thickness below 100 nm. The through-thickness thermal conductivity of Si-Ge and GaAs-AlAs superlattices has recently been shown to be smaller than the conductivity of the corresponding alloy. The 3ω method has been recently extended to measurements of anisotropic conduction in polyimide and superlattices. Data for carbon nanotubes measured using micromachined and suspended heaters and thermometers indicate a conductivity near room temperature greater than diamond.