Liquid Crystal Thermometry Research Articles

Regulation mechanism of magnetic field on non-Newtonian melting and energy storage performance of metal foam composite nano-enhanced phase change materials

A numerical study is conduced to explore regulation mechanism of magnetic field on melting heat transfer and energy storage performance of nano-enhanced phase change material (NEPCM) composited with metal foam. The enthalpy-porosity method, Darcy-Forchheimer model and local thermal non-equilibrium model are used to describe melting process, flow in porous media and coupling heat transfer, respectively. The proposed model is then verified by experiments using thermochromic liquid crystal thermometry. Effects of nanoparticles mass fraction (0%≤Φwt≤5%), magnetic number (0≤Mn≤7×106), and Rayleigh number (104≤Ra≤106) on the non-Newtonian fluids flow, melting heat transfer and energy storage characteristics are illustrated and discussed. Results show that the addition of Fe3O4 nanoparticles can effectively promote melting and induce non-Newtonian effect of molten NEPCM, but Φwt has no significant influence on the heat transfer. With the increase of Mn, the suppression effect of magnetic field on the whole melting process of NEPCM enhances at moderate Ra = 105, and natural convection is fully developed with a “force bridge” phenomenon of Kelvin force. For lower Ra (=104), natural convection becomes weaker and magnetic field presents a “force loop” phenomenon. For larger Ra (=106), natural convective heat transfer has absolute predominance and the suppression effect of magnetic field can be ignored. Moreover, the increase of Φwt and Ra have obvious positive contributions to heat storage and heat storage efficiency. At low Ra, the suppression effect of magnetic field on heat storage and total melting time leads to decrease in energy storage efficiency.

Simultaneous optical measurement of temperature and velocity fields in solidifying liquids

We introduce a complex image processing scheme for the simultaneous application of liquid crystal thermometry (LCT), in addition to the previously established method in Anders et al. (Exp Fluids 60(4):68, 2019. https://doi.org/10.1007/s00348-019-2703-8) for particle tracking velocimetry and particle image velocimetry. This scheme was developed for an experimental study on the double-diffusive convection in an aqueous ammonium chloride solution NH4Cl(aq) during crystallization. The use of thermochromic liquid crystals (TLC) enables to visualize the flow and temperature field simultaneously. We present a color interpolation method that enhances the accuracy of the LCT by yielding RGB images only representative of the TLC’s coloration. An artificial neural network (ANN) which processes RGB triplets and spatial color dependencies transforms these images into temperature fields. The combination of the ANN system and a corresponding calibration procedure enhances the accuracy and measurable temperature range of the LCT compared to state-of-the-art procedures. By using the here established measurement scheme, quantitative global studies of the mutual influence between solidification and convection are enabled and exemplary results are presented.Graphic abstract

Heat Transfer Implications of Acoustic Resonances in Turbine Internal Cooling Channels

In an attempt to investigate the acoustic resonance effect of serpentine passages on internal convection heat transfer, the present work examines a typical high pressure turbine (HPT) blade internal cooling system, based on the geometry of the NASA E3 engine. In order to identify the associated dominant acoustic characteristics, a numerical finite-element method (FEM) simulation (two-step frequency domain analysis) is conducted to solve the Helmholtz equation with and without source terms. Mode shapes of the relevant identified eigenfrequencies (in the 0–20 kHz range) are studied with respect to induced standing sound wave patterns and the local node/antinode distributions. It is observed that despite the complexity of engine geometries, the predominant resonance behavior can be modeled by a same-ended straight duct. Therefore, capturing the physics observed in a generic geometry, the heat transfer ramifications are experimentally investigated in a scaled wind tunnel facility at a representative resonance condition. Focusing on the straight cooling channel's longitudinal eigenmode in the presence of an isolated rib element, the impact of standing sound waves on convective heat transfer and aerodynamic losses are demonstrated by liquid crystal thermometry, local static pressure and sound level measurements. The findings indicate a pronounced heat transfer influence in the rib wake separation region, without a higher pressure drop penalty. This highlights the potential of modulating the aerothermal performance of the system via acoustic resonance mode excitations.

Experimental Facility Development Toward Sound-Excitation Effects on Forced Convection Heat Transfer

In light of the background in periodic boundary-layer forcing as employed for flow control applications, the present work discusses the role of standing acoustic waves toward convective heat transfer modification in a turbulent straight channel flow. To this end, a dedicated low-speed wind-tunnel facility is designed, analyzed, and built, and it is specifically geared toward comprehensive investigation of sound-excited heat transfer for different aerodynamic and acoustic boundary conditions. To identify frequency ranges conducive toward exciting acoustic resonances, both in the transverse and longitudinal directions, a detailed numerical analysis of the acoustic resonance behavior is carried out. Resulting mode patterns and arising pressure nodes and antinodes are discussed in detail. On selected transverse and complex coupled modes, experimental surface temperature measurements are carried out by steady wideband liquid crystal thermometry. Findings indicate that, depending on the matched eigenfrequency and standing wave pattern, a slight elevation or reduction of heat transfer (locally and globally) is possible, whereas no change is observed for the pure traveling wave forcing. Although the acoustically induced changes are small in magnitude, the dependence on the excitation frequency is clearly quantifiable beyond the measurement error.

Acoustic resonance excitation of turbulent heat transfer and flow reattachment downstream of a fence

The current work investigates the aero-thermal impact of standing sound waves, excited in a straight channel geometry, on turbulent, separating and reattaching flow over a fence. Effects of distinct frequency resonant forcing (ReH = 10,050 and f = 122 Hz) are quantified by wall static pressure measurements and detailed convective heat transfer distributions via liquid crystal thermometry. Acoustic boundary conditions are numerically predicted and the computed longitudinal resonance mode shapes are experimentally verified by surface microphone measurements. Findings indicate the presence of a resonant sound field to exert strong influence on local heat transfer downstream of the fence, whereas the boundary layer upstream of the obstacle remains notable unaffected. Upstream shift of the maximum heat transfer location and an earlier pressure recovery indicate a reduction in time averaged flow reattachment length of up to 37 %. Although the streamwise peak Nusselt increased by only 5 %, the heat transfer level in the vicinity of the unexcited reattachment zone was locally enhanced up to 25 %. Despite prominent impact of resonant forcing on the fence wake flow, the total pressure drop penalty remained invariant. Observations demonstrate the significant aero-thermal implications of shear layer excitation by standing sound waves superimposed on the channel flow field.

Microscale thermometry: A review

Recent advancements in microelectromechanical systems (MEMS) have required state-of-the-art techniques that provide accurate information of physical parameters such as fluid velocities and temperatures, at small scales, to fully characterize fluid flows in these devices. Especially it is difficult to measure temperature fields at microscale using conventional methods due to the limitation of spatial resolution in these techniques. In this paper, we present a comprehensive review of various advanced microscale thermometry techniques for measurements of bulk fluid or wall surface temperature fields. Differing from earlier publications, this review particularly focuses on categorizing the thermometry techniques based on how they measure temperature information at the microscale, i.e., either contact or noncontact methods. The paper presents details of measurement principles for each thermometry technique and includes a broad range of their applications. For the contact-based thermometry, the most recent fabrication and measurement results with micro-thermocouples are introduced, followed by discussions for scanning temperature probes and atomic force microscope (AFM) temperature probes. On the other hand, noncontact-based thermometry techniques are broadly summarized, including optical thermometry, liquid crystal thermometry, infrared thermometry, and Raman spectroscopy. Strengths and weaknesses of each technique compared to other approaches, with information of spatial, temporal, and temperature resolutions are introduced and discussed. This review will provide a general guideline for readers regarding the advantages and disadvantages of the most recent microscale thermometry techniques considering key requirements such as tool availability, system limitations, and temperature resolution.

Convective heat transfer investigation of acoustically excited flow over an isolated rib obstacle

The research effort investigates the aero-thermal ramifications of acoustically excited turbulent reattaching shear flow in the wake of an isolated fence obstacle. In order to contrast the effectiveness of traveling and standing sound wave excitations towards surface heat transfer modulation, the flow is stimulated with forcing frequencies and amplitudes, in the ranges of 70–270Hz (St=0.1–0.38) and 103–131dB respectively. Along with local static pressure measurements, the consequent convective heat transfer distributions are quantified by liquid crystal thermometry. Subjected to a standing wave (resonance conditions) within a conductive Strouhal regime in the St=0.17–0.22 range, the separated flow behind the rib is observed to be significantly affected. This is evidenced by size reduction in the time averaged reattachment length of up to 37%. The ensuing local heat transfer enhancement is ∼25%. Conversely, when the flow is excited with acoustic frequencies which do not correspond to resonances (traveling wave forcing), the local heat transfer distributions remained unchanged; however, limited variations in local static pressure are observed. For conditions that yield improved thermal performance, a minimum source amplitude threshold (∼121dB) is found; above this level, the aero-thermal effectiveness of the forcing rises monotonously with increased sound pressure. Even under thermally favorable excitation conditions, the integral pressure drop penalty (total net loss) remains invariant.

1020 小型インタークーラの乱れ構造制御と感温液晶による対流熱伝達計測

Recently, heat transfer enhancement in an automotive heat exchanger becomes one of key technologies. Then, a flow in tube of heat exchanger has a low Re number. For heat transfer enhancement, the saliences are designed on the inner surface of tube. Saliences promote turbulent flow and mixing effect, at low Re number, even though a turbulent flow is vanished by viscous effect. The saliences which promotes continuous turbulence is needed. For this reason, we have carried out a flow visualization experiment. Temperature contour has been visualized with liquid crystal thermometry. And, 3D particle tracking velocimetry has also conducted for visualization of turbulent generation. So, heat transfer performance has been evaluated with the experimental results.

Film Cooling Extraction Effects on the Aero-Thermal Characteristics of Rib Roughened Cooling Channel Flow

The present study is geared towards quantifying the effects of film cooling holes on turbine internal cooling passages. In this regard, tests are conducted in a generic stationary model, with evenly distributed rib-type perturbators at 90 deg, constituting a passage blockage ratio of H/Dh = 0.3 and pitch-to-height ratio of P/H = 10. The 1/3H diameter surface-perpendicular film cooling holes are employed at a distance of 5/3H downstream of the preceding rib. Through liquid crystal thermometry measurements, the aero-thermal effects of a change in suction ratio are contrasted for various configurations (Re = 40,000 SR = 0–6), and compared with the analogous aerodynamic literature, enabling heat transfer distributions to be associated with distinct flow structures. At increased suction ratio, the size of the separation bubble downstream of the rib is observed to diminish, triggering globally an earlier reattachment; in addition to low-momentum hot fluid extraction via film cooling suction. Hence, in the presence of active flow extraction, higher overall heat transfer characteristics are observed throughout the channel. Moreover, the findings are generalized via friction factor and Nusselt number correlations, along with an analytical 20-pitch passage model. SR ∼ 3.5 is observed to provide favorable characteristics of pitch-to-pitch uniform suction ratio, lack of hot fluid ingestion and to sustain the highest passage averaged heat transfer.

Measuring the temperature of fluid in a micro-channel using thermochromic liquid crystals

Thermochromic liquid crystal (TLC) thermometry, which has been previously used at the macro-scale, is applied quantitatively in a microfluidic device for the first time. Much like the micro-scale version of the PIV technique, TLC thermometry implementation at the micro-scale must account for constraints on imaging and illumination configurations and the proximity of the measurements to interfaces and surfaces from which light scatters. Unlike μPIV, TLC thermometry requires the use of white light, so unwanted reflections are managed using circular polarization filtering, which is implemented for the first time and may also have applications at the macro-scale. The validity and precision of the TLC thermometry technique are tested by imposing a linear temperature gradient along a micro-channel filled with stationary fluid. Additional work is required to develop the technique into a fully functional form and to realize the potential for use in various microfluidic applications including “lab-on-a-chip” devices, MEMS switches, inkjet printer nozzles, and for use with simultaneous velocity measurements.

Color theory perception of steady wide band liquid crystal thermometry

A color theory perspective to steady wide-band thermochromic liquid crystals (TLCs) is presented towards application in surface temperature measurements. In this regard, TLC color response experiments are conducted on an ex situ calibration plate under various illuminant spectra, and for a broad range of camera angle and white balance configurations.The findings indicate that by color theory guided application of eligible background image subtraction technique, in conjunction with appropriate camera white balance selection, accurate, illuminant and viewing angle invariant hue-temperature relations can be established. This yields more practical, robust and generalized calibration methodologies. The importance of an adequate processing technique, along with its implications in color theory and consequences on hue-temperature relation is addressed in detail towards applicability in a broad spectrum of experimental arrangements.

Fluid Flow and Heat Transfer of Opposing Mixed Convection around Rectangular Cylinder Placed in Uniform Downward Flow of Forced Convection

Experimental investigations have been carried out on opposing mixed convective flows of water induced around a horizontal rectangular cylinder in the range of the Reynolds and modified Rayleigh numbers, ReD =500-3000 and RaD*=7x107-1010. The flow and temperature fields around the cylinder were first visualized with dye and liquid crystal thermometry. The results showed that longitudinal vortices of which axes parallel to the flow direction appear over the upper surface of the cylinder when the buoyancy force beyond critical. The flow along the upper surface, then, separates at the edges of the cylinder. Thus, the side and bottom surfaces of the cylinder are covered by separation bubbles and wake. The local and overall heat transfer coefficients from the cylinder were subsequently measured. The coefficients from the upper and side surfaces showed marked increase with the buoyancy force. This yields higher overall Nusselt numbers than those of the forced convections. It was also found that the non-dimensional parameter (GrD*/ReD2.5) well correlates the present overall Nusselt numbers.

Visualization of turbulence structure in unsteady non-penetrative thermal convection using liquid crystal thermometry and stereo velocimetry

Temperature and velocity fields in unsteady non-penetrative turbulent thermal convection of a horizontal fluid layer are measured in horizontal and vertical planes simultaneously using the combined liquid-crystal thermometry and stereo particle image velocimetry (PIV) with high spatial and temporal resolution. The result shows the formation of convection pattern across the fluid layer, which originates from the spoke structure over the heated surface. The upward fluid motion is generated from the intersection of the bursting lines of the spoke structure, while the downward motion is induced by the low temperature fluid directing toward the center of the spoke structure. Thus, the large-scale convective motion is produced in the fluid layer through the motion of spoke structure. The POD analysis of the temperature and velocity eigenfunctions shows the existence of large-scale motion in the fluid layer, which supports the observed convection pattern near the heated boundary and in the middle of the fluid layer.

Liquid crystal thermometry for early detection of hypothermia in newborns in neonatology ward, Sardjito Hospital, Yogyakarta

Background Hypothermia in neonates increases the risk ofmortality and morbidity such as infection, coagulation disorders,acidosis and hyaline membrane disease. Mercury thermometer iscommonly used to detect hypothermia in newborns, but it has itis not ecological acceptable, difficult to be sterilized, easily broken,difficult to find in some developing countries and needs sometraining before use. A simple, effective and easily used tool fordetection of hypothermia in newborns is needed.Objective To evaluate the ability of liquid crystal thermometry(LCT) in early detection of newborn hypothermia.Methods This study was conducted in the neonatology ward,Sardjito Hospital. The LCT was placed on the abdominal wall.Digital thermometer measurement and LCT observation wereconducted three times in each patient. LCT’s color and bodytemperature were documented by using a pre-coded questionnaire.Results A total of 268 newborns met the inclusion and exclusioncriteria. The pilot study showed that the inter-observer agreementof LCT was 0.75. Positive likelihood ratio during threemeasurements were 22.9 (95%CI 11.47;45.78), 18.97 (95%CI9.43;38.16) and 22.8 (95%CI 11.34;45.83) respectively.Conclusion LCT exhibits good accuracy and is safe to diagnosehypothermia in newborn.

加熱Lコーナまわりに生じる自然対流

Experimental investigations have been carried out on natural convective flows over a heated L-corner in which the vertical plate was shorter than the horizontal plate. Special interest was paid to the fluid flow and heat transfer around the vertical plate. The height of vertical plates, H, were varied as H=10-150mm. The width of horizontal plate was 350mm constant. The test fluid was water. The flow fields and the surface temperatures were visualized with fluorescent dye and liquid crystal thermometry, respectively. The local heat transfer coefficients of the vertical plate were also measured. The result shows that the recirculating flow appears irregularly around the vertical plate when H is less than 30mm. It is also found that the local heat transfer coefficients show a maximum at H/2 when the recirculating flow appears around the vertical plate.

A207 感温液晶を用いたレーリーベナール対流のエネルギーバランスの計測に関する研究

A207 感温液晶を用いたレーリーベナール対流のエネルギーバランスの計測に関する研究

B217 感温液晶法を用いた温度・速度同時計測法による乱流自然対流の組織構造研究

In order to understand the formation and the development of the plume structure in turbulent thermal convection, the temporal and spatial variations of temperature and velocity field are measured in the non-penetrative thermal convection of the horizontal fluid layer using the combined liquid crystal thermometry and stereo-velocimetry. It is found that the spoke structure is generated near the heated surface and moves along the heated surface unsteadily changing the cell size. The thermal plume is generated from the high temperature region of the spoke structure, where the vertical velocity component is clearly observed near the heated surfaces.

Neonatal hypothermia detection by ThermoSpot in Indian urban slum dwellings

Objective: To look at the performance of ThermoSpot liquid crystal thermometry in detecting neonatal hypothermia. Design: A comparison was made between skin temperatures taken by ThermoSpot and axillary temperatures taken...

In situ thermal diagnostics of the micro-PCR system using liquid crystals

A simple, reliable liquid crystal (LC) thermometry of a polymerase chain reaction (PCR) chip that has a microchamber inside the chip and a film heater and a film sensor patterned on the surface is firstly introduced. The silicon-based PCR chip is made by MEMS technology. A non-linear feedback proportional-integral control scheme adjusts the power input of the Pt heater to control the surface temperature of the micro-PCR chip measured by the Pt sensor with an accuracy of less than ±0.1 °C at steady state. We use the LC thermometry to analyze the temperature distribution in the microchamber of the micro-PCR chip. The reflected colors of LC's inside the microchamber are captured through a charge-coupled device (CCD) camera, subsequently analyzed using a hue-based color analysis system. Two LC's of which individual working range is near the typical PCR temperature of 55 °C and 72 °C are calibrated in a constant temperature bath with a resolution of less than ±0.3 °C. While the average microchamber temperature near the annealing temperature is similar to the surface temperature, it is lower than the surface temperature by ca. 1 °C in the range of the extension temperature. Also, the temperature variations along the center of the microchamber, are less than 1.5 ± 0.5 °C and 3 ± 0.3 °C in the range of the annealing and the extension temperature, respectively.

A212 感温液晶温度・速度同時計測法を用いたレーリーベナール対流のエネルギーバランスの計測

As a purpose to know the mechanism of energy transportation in turbulent Rayleigh Benard convection, the measurement experiment of temperature and velocity at turbulent thermal convection field is carried out by the liquid crystal thermometry and velocimetry. From these experimental results, the distribution of mean and fluctuation of temperature and velocity, Reynolds stress, turbulent head flux and dissipation are obtained. These values indicate a balanced distribution of turbulence energy at spacious field without neighboring wall boundary.