Thermal Transfer Effects Research Articles

Effect of ultrasonic on thermo-hydraulic characteristics of shell and tube heat exchangers with twisted tape

Ultrasonic technology was combined with twisted tape insert technology to improve the performance of shell and tube heat exchangers. The effects of sound intensity, sound frequency, and ultrasonic transducer position on thermal transfer, resistance reduction, and overall performance of shell and tube heat exchangers with twisted tape (STHXTT) at different Reynolds numbers were investigated compared to the non-ultrasonic conditions. The experimental results show that applying ultrasonic can significantly enhance thermal transfer, reduce flow resistance, and improve the overall performance. The maximum increase of Nu is 36.53 %, the maximum decrease of f is 12.50 %, and the maximum value of PEC is 1.41. With the increase in Reynolds number, the performance is enhanced but the resistance reduction and overall performance are weak. When the ultrasonic intensity increases, the thermal transfer and resistance reduction performance is enhanced, but a critical ultrasonic intensity exists. When the ultrasonic intensity is large enough, the ability to reduce resistance is enhanced with the decrease of ultrasonic frequency. When the ultrasonic transducer is installed vertically, the thermal transfer performance is the best, however, the resistance reduction effect is the worst. When installed horizontally, the STHXTT has the best resistance reduction performance but the worst thermal transfer effect.

Highly conductive, conformable ionic laser-induced graphene electrodes for flexible iontronic devices

Iontronic devices, recognized for user-friendly soft electronics, establish an electrical double layer (EDL) at the interface between ion gels and electrodes, significantly influencing device performance. Despite extensive research on ion gels and diverse electrode materials, achieving a stable interfacial formation remains a persistent challenge. In this work, we report a solution to address this challenge by employing CO2 irradiation as a bottom-up methodology to directly fabricate highly conductive, conformable laser-induced graphene (LIG) electrodes on a polyimide (PI)-based ion gel. The PI ion gel exhibits exceptional EDL formation at the electrode interface, primarily attributable to efficient ion migration. Particularly, ionic laser-induced graphene (i-LIG) electrodes, derived from the PI ion gel as a precursor, yield high-quality graphene with enhanced crystallinity and an expanded porous structure in the upward direction. This outcome is achieved through a pronounced thermal transfer effect and intercalation phenomenon between graphene layers, facilitated by the presence of ionic liquids (ILs) within the PI ion gel. Ultimately, in comparison to alternative soft electrode-based vertical capacitors, the utilization of i-LIGs and PI ion gels in the vertical capacitor demonstrates reduced interfacial resistance and increased EDL capacitance, emphasizing the extensive potential of iontronic devices. These results not only highlight these features but also introduce a new perspective for advancing next-generation iontronic devices.

Luminescence dating of heated quartz extracted from burnt clay and pottery excavated from the Lingjiatan archaeological site, China

This study utilizes OSL-SAR, TL-SAR, and TL-MAAD methods to date heated quartz extracted from burnt clay and pottery samples from the Lingjiatan archaeological site, China. The OSL components of the heated quartz were determined by deconvoluting the CW-OSL curve, and the Fast Ratio value was used to distinguish whether the initial OSL signal was dominated by the fast component. The results show two types of quartz OSL characteristics in the initial signals: Type I is dominated by the fast component (Fast Ratio values > 10), while Type II is dominated by the medium and slow components (Fast Ratio values < 10). Type I samples show bright OSL signals, and a preheat plateau appears from a relatively low temperature. The recuperation is negligible, and reliable equivalent doses can be obtained using the conventional OSL-SAR measurement conditions. In contrast, the OSL signal of Type II samples is relatively dim, and the preheat plateau appears from a much higher temperature than in Type I samples. The recuperation of Type II samples increases significantly at higher preheat temperatures. Significant De underestimation of Type II samples was observed at lower preheat temperatures. It is noted that the thermal transfer effect can be attenuated by increasing the OSL stimulation temperature. Therefore, a modified OSL-SAR measurement condition, with higher preheat, cut-heat and stimulation temperatures, was used to date Type II samples. The OSL-SAR ages of most of these two types of samples agree well with the independent 14C ages, demonstrating that OSL-SAR can be used to date heated archaeological materials at high firing temperatures (∼900°C). The Lingjiatan archaeological site was determined to be approximately 5.4–5.8 ka BP 2022.

Finite difference approximation in a non-isothermal and non-adiabatic fixed bed adsorption model: an application to n-hexane

In this work, we solved the differential equations of mass and energy balance describing the n-hexane adsorption and desorption process in 5A zeolite under non-isothermal and non-adiabatic conditions. The solution provided a theoretical model that may be used to determine the significance of the mass and thermal transfer effects applied to transient adsorption. We validated numerical results with experimental data from the literature, finding the n-hexane adsorption to be exothermic. Because the diffusion in the system is fast, the breakthrough curves showed the typical form of thermal limitation. We found desorption depends on the desorbent fluid and feed rate. We evaluated the stability of the numerical method using the eigenvalues of the matrix system. Hence, the computational code developed may be used to simulate real operating conditions for the adsorption/desorption process of gases with porous adsorbents once the process parameters are known.

Thermal fluid circulation around the Karliova triple junction: Geochemical features and volcano-tectonic implications (Eastern Turkey)

The Karlıova triple junction (KTJ) in eastern Turkey has been subjected to incremental deformation resulting in complex kinematic and mechanical interactions throughout the upper crust. These interactions have generated tectonic inversions and uplift, extensive seismicity and volcanism. The regional tectonics generate local stresses, some of which are favorable to magma transport and thermal water circulation throughout the lithosphere. Here we evalauate hydrogeochemical, geological and numerical results relating to the mechanism of thermal fluid circulation around the KTJ. Hydrogeochemistry of the samples indicates that the thermal water springs are probably heated by steam. Volcanic rocks at the site appear to be the host rock owing to the enrichment of Na+ and Cl− ions in water and the abundance of these elements in minerals of the volcanic rocks. In addition, it is clear that the thermal fluids are sourced from depth and migrate through permeable networks of faults. The effects of crustal heterogeneities, in particular the geometry and mechanical properties of many faults and layers, on thermal fluid circulation in relation to active magma chambers were investigated under a variety of different mechanical conditions. The numerical results indicate very close relationships between the stress field causing faulting and thermal fluid movement in the KTJ. The effect of thermal transfer was modeled with depth throughout the crust and along the the crustal surface. The models show that some faults encourage thermal fluid circulation below the Varto and Özenç volcanoes. Hydrogeochemical, geological and numerical results suggest that magmas residing beneath both the Varto caldera and the Özenç volcano are the main heat source for thermal fluid in the Varto region. Fluid-solid interactions and fluid circulation models show that the permeable faults are important factors affecting heat transport and fluid circulation. In a series of thermal fluid flow models we probe the mechanism for fluid and gas transport from the 900 °C ‘hot’ zone around the deep magma chambers and investigate how heat is lost throughout the crust on the way to the surface and so eventually creates water channels of temperatures between 50 to 60 °C.

Impact of thermal transfer on hydration heat of a Soundless Chemical Demolition Agent

This paper explores thermal transfer effects in Soundless Chemical Demolition Agents (SCDA). In a 10 °C water bath, quadrupling the volume of SCDA in a pipe accelerated peak hydration onset and resulted in a 700% increase in expansive pressure and a 20% increase in volumetric expansion. An equivalent sample in a constant temperature chamber showed an almost 5 °C greater hydration heat than in the water bath, which resulted in a six-fold expansive pressure difference after 4 days of testing and an order of magnitude more pressure in the first 24 h, thereby demonstrating limitations of previous SCDA experimental work and providing a temperature-based reason for discrepancies between large-scale testing and manufacturers’ predictions. Since most construction projects have scheduling requirements, understanding how to achieve sufficiently high pressures within a single work shift is important for evaluating the field viability of SCDAs on a particular project.

An extension of Oberbeck–Boussinesq approximation for thermal convection problems

An extension of the Oberbeck–Boussinesq approximation (OB) with expressive thermal effects is investigated to model specific mass with a temperature-dependent approach. An expansion of OB is proposed using a mathematical formulation with null velocity divergence in the continuity equation and variable specific mass in the momentum and energy equations (NOB). The NOB method has been previously tested in the literature, and the present paper aims to carry out a quantitative analysis between NOB and OB. The specific mass is calculated based on the temperature field and a divergence-free velocity is imposed on the NOB due to the small effects of variations of the specific mass in the continuity equation, as previously demonstrated by the OB. The purpose of the NOB is to overcome the OB’s restriction to single-phase flows, as well as to model the effects of specific mass variations more accurately, especially in problems with prominent thermal transfer effects, as that occur in the turbulent regime. Since the effects of a variable specific mass in the momentum and energy equations were taken into account by the NOB, it was expected that the thermal transfer results of the NOB would be improved compared with those of the OB. Then, three-dimensional natural convection simulations for a large range of Rayleigh numbers were performed using OB and NOB in a cubic cavity. Turbulence modeling was performed using Large Eddy Simulation (LES). Numerical results from both approaches were validated and all the results presented good quality. Thermal transfer was evaluated by the calculation of the Nusselt number at the heated wall and compared to experimental data from the literature. The OB and NOB provided adequate thermal transfer rate results; however, the differences between the literature and OB were higher than for NOB. Therefore, NOB is presented as a useful mathematical formulation for modeling incompressible flows with a temperature-dependent specific mass approach in single-phase or multiphase problems instead of solving the full compressible mathematical formulation. In addition, the differences between the literature and OB results increased as the Rayleigh number was raised, especially in the turbulent regime. The results of the NOB were closer to the literature than were those of the OB for the entire range of Rayleigh numbers tested. Therefore, the numerical results confirmed the higher accuracy of NOB compared to OB despite the NOB’s still being an approximate model. Lastly, flow visualization allowed the identification of coherent turbulent structures near the cavity walls in the simulation with Rayleigh number $$10^{10}$$ . The presence of hairpin and Tollmien–Schlichting instabilities revealed the importance of modeling the three-dimensional effects of natural convection in the turbulent regime.

Study on Heat Transfer Performance of Heat Spreader depending on the Filling Rate of Working Fluid

In this paper, the effect of thermal transfer depending on the filling ratio of working fluid in heat spreader was studied. The heat spreaders were filled with working fluid (acetone) rate of 0%, 5%, 15% and 40%, respectively. The temperature distribution according to the thermal transfer direction was measured. Finally the thermal transfer was analyzed for four different filling rates of working fluid and four different LED COB input powers of 5W, 10W, 15W, 20W. Then, the thermal resistivity and thermal transfer coefficients of heat spreaders were calculated. In result, it was found that heat spreader with 15% of filling rate was most effective in terms of the thermal transfer property, which are 0.49∼0.64K/W of thermal resistivity and 2071∼2719W/㎡K of thermal transfer coefficient.

전기저항 평가법 및 접촉각을 이용한 CF/PP 복합재료 사출성형품 섬유 배열성 평가

Fiber arrangement was important for fiber reinforced thermoplastic composites using injection fabrication. In this work, fiber arrangement in CF/PP was investigated to use electrical resistance (ER) method during injection times. There were 3 types of injection products of CF/PP with different ER change ratio by fiber arrangement. High ER change ratio case of injection CF/PP products had better increased tensile strength. This reason was due to the fiber arrangement of CF/PP by injection. Fractured surface and contact angle of CF/PP products were used to evaluate for injection product quality. Uniform fiber arrangement of CF/PP by injection type exhibited the uniform heat condition of melted CF/PP. Steady thermal transfer effect occurred from melted CF/PP to steel injection mold. Steady thermal transfer effect of CF/PP was transmitted to high ER change ratio of mold. Ultimately, good condition CF/PP product by injection molding method could be predicted by using ER method.

Further investigations on ‘non-fading’ in K-Feldspar

We give a theoretical overview of non-fading infrared stimulated luminescence (IRSL) signals in feldspars, followed by intercomparison of potential methods on some sediment extracts. We observe that a more stringent thermal wash on its own is not effective in obtaining a more stable signal, suggesting that the higher the stimulation temperature in post IR-IRSL methods, the greater the ability to access distant electron hole pairs. We further find that the delayed off-time signal in time-resolved IRSL has immense potential for sampling non-fading signal and should be explored further; this signal also appears to be well reset in nature and avoids unwanted thermal transfer effects in comparison to the post IR-IRSL signal measured at 290 °C.

Historical mortars dating from OSL signals of fine grain fraction enriched in quartz

In the last years the mortar dating through Optically Stimulated Luminescence (OSL) techniques has become a viable support for chronological estimations (date of construction or restoration episodes) of historical buildings. However, the dating of mortar has still open issues mainly regarding the assessment of the bleaching degree of quartz, the analysis of the OSL processes for this type of samples and the need to do appropriate tests for the most correct evaluation of the equivalent dose. This paper discusses the results obtained by OSL dating (blue diode stimulation) on the polymineral fine grain phase, enriched in quartz, extracted from lime mortar samples collected from different sites. Thermal transfer effects, through the behaviour of Equivalent Dose (ED) and recovery tests, degree and time of bleaching were studied. For each mortar sample the adjacent brick was collected; in some cases, sampling of the bricks bracketing a mortar layer was a possibility, thus obtaining a direct comparison with the standard thermoluminescence (TL) dating on the bricks. The results obtained show, for this set of samples, the possibility of dating the mortars through the use of the fine grain fraction provided of a suitable chemical-physical preparation procedure and the verification of the bleaching conditions.

적외선 윈도우용 가스식 냉각장치 해석 기법

In this paper, a post-analysis of cooling system for infrared(IR) window was performed based on heating experiment of IR window system. We applied the same experimental conditions to analysis, and then validated the analysis technique by comparing numerical and experimental results. For an analysis software, we used a professional heat/fluid analysis program and the numerical and experimental results were in fairly good agreement. We investigated the effect of thermal transfer between the frame and IR window and also a cooling efficiency between fluid and structure in order to determine the proper parameters for the analysis. In this study, 100 % thermal transfer between the frame and IR window and 30 % cooling efficiency between fluid and structure have been proposed, which can be used in the future conceptual design and analysis of similar IR windows.

Potential of quartz OSL dating on moraine deposits from eastern Tibetan Plateau using SAR protocol

Optically stimulated luminescence (OSL) dating methods have been widely applied in Quaternary glaciology. However, glacigenic deposits are considered in general as problematic for OSL dating, mainly because they are transported shorter distances prior to burial and are usually partially bleached. Thus, most researchers choose glaciofluvial and glaciolacustrine sediments (with relatively longer transportation times) for OSL dating when constraining the age of glaciation. In this study, four samples were collected from a lateral moraine series at Zhuqing Village, northern margin of Queer Shan Mountain, eastern Tibetan Plateau, in order to investigate the applicability of OSL dating for morainic deposits. Quartz grains (38–63 μm) were extracted and measured using single aliquot regenerative-dose (SAR) protocol. Internal checks and dose recovery test show that the SAR protocol is appropriate for equivalent dose (D e) determination. The effect of thermal transfer is small for all samples and the recycling ratio for each individual sample is close to unity. The symmetry in the D e distributions indicates that quartz grains were well-bleached prior to burial. OSL ages show good agreement with geomorphological and field investigations, and are also concordant with an independent ESR age. It is concluded that: (a) the morainic deposits in Zhuqing were well-bleached and suitable for OSL dating; (b) SAR protocol can be applied to morainic deposits for samples under study.

Correlation between TL and OSL properties of CaF2:N

Natural CaF2 is very well known thermoluminescent (TL) material, since it has been extensively used as a dosimeter. Its basic advantage is the exhibited high TL sensitivity. In the present work, the optically stimulated luminescence (OSL) sensitivity of this material was studied by exposing it to environmental radiation for time intervals of few hours up to a few days, and was found to be very high. By analyzing the TL glow curves and the OSL decay curves into their individual glow-peaks and components respectively, a relation between specific glow-peaks and OSL components was established. An intense thermal transfer effect occurring during optical stimulation at high temperature was observed and an explanation is offered according to existing models.

Nonlinear absorption in biological tissue for high intensity focused ultrasound

In recent years the propagation of the high intensity focused ultrasound (HIFU) in biological tissue is an interesting area due to its potential applications in non-invasive treatment of disease. The base principle of these applications is the heat effect generated by ultrasound absorption. In order to control therapeutic efficiency, it is important to evaluate the heat generation in biological tissue irradiated by ultrasound. In his paper, based on the Khokhlov–Zabolotkaya–Kuznetsov (KZK) equation in frequency-domain, the numerical simulations of nonlinear absorption in biological tissues for high intensity focused ultrasound are performed. We find that ultrasound thermal transfer effect will be enhanced with the increasing of initial acoustic intensity due to the high harmonic generation. The concept of extra absorption factor is introduced to describe nonlinear absorption in biological tissue for HIFU. The theoretical results show that the heat deposition induced by the nonlinear theory can be nearly two times as large as that predicated by linear theory. Then, the influence of the diffraction effect on the position of the focus in HIFU is investigated. It is shown that the sound focus moves toward the transducer compared with the geometry focus because of the diffraction of the sound wave. The position of the maximum heat deposition is shifted to the geometry focus with the increase of initial acoustic intensity because the high harmonics are less diffraction. Finally, the temperature in the porcine fat tissue changing with the time is predicated by Pennes’ equation and the experimental results verify the nonlinear theoretical prediction.

Observations of thermal transfer OSL signals in glacigenic quartz

The conclusions of Rhodes and Pownall (Rhodes, E.J., Pownall, L., 1994. Zeroing of the OSL signal in quartz from young glaciofluvial sediments. Radiation Measurements 23, 329–333) were somewhat discouraging for the prospects of using quartz OSL for dating glacigenic sediments, while the more detailed study of Rhodes and Bailey (Rhodes, E.J., Bailey, R.M., 1997. The effect of thermal transfer on the zeroing of the luminescence of quartz from recent glaciofluvial sediments. Quaternary Science Reviews (Quaternary Geochronology) 16, 291–298) provided more encouragement. Specifically, the latter authors were able to account for the relatively high D e values observed for recent glacigenic (dominantly glaciofluvial) sediments in terms of an anomalously high thermal transfer effect, rather than simply insufficient bleaching prior to deposition. In other locations, the OSL of quartz from glacigenic material appears to provide reliable age estimates, and does not suffer from these effects (Owen, L.A., Richards, B., Rhodes, E.J., Cunningham, W.D., Windley, B.F., Badamgarav, J., Dorjnamjaa, D., 1998. Relic permofrost structures in the Gobi of Mongolia: age and significance. Journal of Quaternary Science 13 (16), 539–548; Richards, B.W., Owen, L.A., Rhodes, E.J., 2000. Timing of Late Quaternary glaciations in the Himalayas of northern Pakistan. Journal of Quaternary Science 15, 283–297). In this paper, laboratory bleached samples from both the above studies are remeasured, using an experimental design to correct for OSL sensitivity changes, which has some similarities to the single aliquot regenerative dose (SAR) protocol of Murray and Wintle (Murray A.S., Wintle A.G., 2000. Luminescence dating of quartz using an improved single-aliquot regenerative-dose protocol. Radiation Measurements 32, 57–73). Clear evidence of thermal transfer OSL signals, generated during the preheating procedure, is presented. Further measurements, using the full SAR protocol, demonstrate that the source of this charge is related to natural dosing. For one sample, the apparent effect is subtracted effectively by the SAR protocol. Another sample studied in detail shows a striking relationship between the thermally transferred OSL signal and the total TL observed during the ramping of the preceding preheat treatment.

The effect of thermal transfer on the zeroing of the luminescence of quartz from recent glaciofluvial sediments

The natural optically stimulated luminescence (OSL) response of quartz grains extracted from a range of recent glaciofluvial and other glaciogenic sediments from Western Greenland is presented. All samples were deposited within the last 10 years, many only days or hours before collection. Consequently we would expect to measure zero or very small D E values had optical resetting of the OSL signal been complete. In the case of most samples. D E values in the range 0.5–10 Gy are observed, while higher values are observed for a handful of samples. However, the regenerated OSL growth curves, constructed after daylight exposure of at least several hours, also show large apparent D E values (negative x-axis intercepts). Corresponding samples from four different locations in the Indian Himalaya display similar OSL characteristics. The measurement of several regenerated OSL growth curves omitting the preheat procedure which normally precedes OSL measurement, confirms that a significant degree of thermal transfer is occurring during the preheating. It is this thermal transfer of charge during the preheat which is responsible for a significant contribution to the large apparent D E values observed for the regenerated OSL growth. In this paper we describe combined OSL and TL measurements which have been used to monitor the charge transfer in detail for one sample. An attempt is made to describe the charge transfer behaviour, and we discuss methods appropriate to eliminating the unwanted effects of this phenomenon during OSL dating. Preliminary results from the application of these techniques are presented, and the implications of these observations for the OSL dating of glaciogenic sediments are discussed.

DIRECTIONAL SOLIDIFICATION OF LAMELLAR EUTECTIC

Directional solidification of lamellar eutectic has been studied both theoretically and experimentally. This process has been modeled through comparing it with directional solidification of an array of cells in binary alloys and developing of the Saffman-Taylor viscous fin-gerinig in a Hele-Shaw cell in an unitied framework. A coupling relation among the solute diffusion, the thermal transfer and the capillary effect of the growing interface has been derived. The well known scaling law λ2V = const can be derived from this relation. Directional solidification of regular Al-Al2Cu eutectic and irregular Al-Si eutectic has been investigated experimentally, the coupling relation has been verified. The solidifying interface profile and thermal transfer effect of solidification have also been discussed.