Complete Thermal Characterization Research Articles

Complete thermal characterization of liquids by front photopyroelectric configuration using the reference sample method

We explored the use of the front photopyroelectric (FPPE) configuration and the reference sample method to determine the thermal properties of liquid samples such as extra virgin olive oil and aqueous glycerol (GL), ethylene glycol (EG), and sodium chloride (NaCl) solutions. The thermal diffusivity (α) and thermal conductivity (k) were determined from photopyroelectric phase and amplitude signals, respectively, using water as a reference. The thermal effusivity (e) and volumetric heat capacity (ρc) were also determined based upon both obtained thermal properties. All thermal properties of GL and EG in aqueous solutions decrease as their volume fraction increases at an average rate of 5% for concentrations higher than 20% and between 23% and 10% for concentrations less than 20%. The Matvienko and Mandelis’ model for α and our proposed expression for ρc described this trend with a reliable approximation to the experimental data with R 2 about 0.97 and 0.99, respectively. Moreover, the frequency of a specific angle is proportional to α as established by the theory for the phase signal for thermally thick samples. In the case of aqueous NaCl solutions, the α and k values were slightly below 4.6% and 3% from water values reported at room temperature. The proposed method allows the simultaneous determination of α and k by using only the FPPE configuration with test and reference liquid samples, reducing time and uncertainties from the use of more than one experimental setup, and providing the complete thermal characterization.

Non-Contact and Self-Calibrated Photopyroelectric Method for Complete Thermal Characterization of Porous Materials.

A general theory of a photopyroelectric (PPE) configuration, based on an opaque sample and transparent pyroelectric sensor, backing and coupling fluids is developed. A combined back-front detection investigation, based on a frequency scan of the phase of the PPE signals, followed by a self-normalization of the phases' behavior, leads to the possibility of simultaneously measuring both thermal effusivity and diffusivity of a solid sample. A particular case of this configuration, with no coupling fluid at the sample/backing interface and air instead of coupling fluid at the sample/sensor interface (non-contact method) is suitable for simultaneous measurement ofboth thermal diffusivity and effusivity (in fact complete thermal characterization) of porous solids. Compared with the already proposed configurations for investigations of porous materials, this novel configuration makes use of a fitting procedure with only one fitting parameter, in order to guarantee the uniqueness of the solution. The porous solids belong to a class of materials which are by far not easy to be investigated using PPE. To the best of our knowledge, porous materials represent the only type of compounds, belonging to condensed matter, which were not taken into consideration (until recently) as potential samples for PPE calorimetric investigations. Consequently, the method proposed in this paper complete the area of applications of the PPE method. Applications on some porous building materials and cellulose-based samples validate the theory.

Study of the Thermal Properties and Lattice Disorder Effects in CdTe–Based Crystals: CdBeTe, CdMnTe, and CdZnTe

Mixed semiconductor ternary crystals were grown using the Bridgman–Stockbarger method. This is a high–temperature and high–pressure crystal growth method. Cd1–xBexTe crystals were grown in the range of composition 0 < x < 0.1, such as 0.00, 0.01, 0.03, 0.05, and 0.1. The main goal of this paper was to compare the thermal properties of CdBeTe with previously grown CdMnTe and CdZnTe–mixed ternary crystals. The photopyroelectric technique was applied to examine the thermal properties. The thermal diffusivity and effusivity values were obtained after testing all the samples, and the thermal conductivity was calculated then. As such, a complete thermal characterization of the crystals was carried out. For further characterization, the thermal conductivity versus composition was checked by applying the Sadao Adachi model. Thanks to that, we were able to determine the total thermal resistivity of the crystals and the additional resistivity which arises from the lattice disorder. As such, the disorder effects arising from substituting the native atom with a foreign one were characterized for all crystals. We were looking for the best substitution of the Cd atom in the CdTe matrix based on the compounds’ thermal properties. It turned out that Zn and Mn introduce a similar disorder, with Be being the highest one.

Thermal effect in a causal diamond: Open quantum systems approach

A static observer with a finite lifetime has causal access to only a limited region of spacetime known as the causal diamond. The presence of an apparent horizon in the causal diamond, due to the observer's finite lifetime, is the origin of an Unruh-like thermal effect. Thus, even though the observer is static and the background is flat, the finite-lifetime observer experiences a thermal bath in the Minkowski vacuum. In this article, we provide an open quantum systems approach that yields a complete thermal characterization via the observer's steady-state density matrix, which is shown to be thermal with a temperature inversely proportional to its lifetime. This associated diamond temperature agrees with the established result derived from other methods. Moreover, our approach is particularly useful for designing entanglement harvesting protocols in the causal diamond. In addition, we introduce an insightful procedure that defines diamond coordinates using conformal transformations, and which leads to a more direct derivation of the thermal properties.

Effects of Steam Heat and Dry Heat Sterilization Processes on 3D Printed Commercial Polymers Printed by Fused Deposition Modeling.

Fused deposition modeling (FDM), the most widely used additive manufacturing (AM) technology, is gaining considerable interest in the surgical sector for the production of single-use surgical devices that can be tailor-made according to specific requirements (e.g., type of patient surgery, specific shapes, etc.) due to its low cost, ease of access to materials (3D-printing filament), and the relatively low complexity. However, surgical 3D-printing parts should resist sterilization treatments without losing structural, mechanical, and dimensional accuracy. Thus, in this work, 3D-filaments based on poly(lactic acid) (PLA), poly(ethylene glycol-co-1,4-cyclohexanedimethanol terephthalate) (PETG), and a modified PETG material (CPE) were used to produce 3D-printed parts and further subjected to moist heat (MH) and dry heat (DH) sterilization processes as affordable and widely used sterilization processes in the medical field. The effect of MH and DH was evaluated by performing a complete mechanical, structural, thermal, and morphological characterization before and after both treatments. In general, the moist heat treatment produced a higher degradation of the polymeric matrix of PETG and CPE due to hydrolytic and thermal degradation, particularly affecting the tensile test and flexural properties. For instance, the linear coefficient of thermal expansion (LCTE) before glass transition temperature (Tg) increased 47% and 31% in PETG samples due to the MH and DH, respectively, while it increased 31% in CPE due to MH and was mainly maintained after the DH process. Nevertheless, in PLA, the MH produced an increase of 20% in LCTE value and the DH showed an increase of 33%. Dry heat treatment resulted in being more suitable for medical applications in which dimensional accuracy is not a key factor and there are no great mechanical demands (e.g., surgical guides).

Effect of Sunflower, Almond, and Rapeseed Oils as Additives on Thermal Properties of a Machinery Oil

Vegetable oils are considered to be eco-friendly and to offer good lubricant properties; however, their low thermo-oxidative stability makes their use as a lubricant base challenging. In this research, sunflower, almond, and rapeseed vegetable oils were added in volumes of 5, 10, 15, and 20% to a machinery oil, and the thermal properties of the resulting fluids were studied. Sunflower, almond, and rapeseed oils were chosen considering their fatty acid composition and the tocopherol content. During this investigation, thermal diffusivity was measured by using the thermal wave resonance cavity technique, while thermal effusivity was determined by the inverse photopyroelectric method, and the obtained values ranged from 4.63 to 5.75 Ws1/2m−2K−1 × 102. The thermal conductivity was calculated by obtaining a complete thermal characterization. The results showed a linear relationship between the percentage of vegetable oil and the thermal diffusivity. It was also noted that the thermal properties of diffusivity and effusivity could be tuned when using almond, sunflower, and rapeseed oils in the appropriate percentages. Hence, the influence of vegetable oils on the thermal properties of lubricating oil were closely related to the number of fatty acids.

Morphological, thermal and mechanical properties of recycled HDPE foams via rotational molding.

In this study, foamed recycled high density polyethylene (rHDPE) parts were produced by rotational molding using different concentration (0 to 1% wt.) of a chemical blowing agent (CBA) based on azodicarbonamide. From the samples produced, a complete morphological, thermal and mechanical characterization was performed. The morphological analysis showed a gradual increase in the average cell size, while the cell density firstly increased and then decreased with increasing CBA content. As expected, increasing the CBA content decreased the foam density as well as the thermal conductivity. Although increasing the CBA content decreased both tensile and flexural properties, the impact strength showed a similar trend as the cell density with an optimum CBA content around 0.1% wt. Finally, neat rHDPE samples were also produced by compression molding. The results showed negligible differences between the rotomolded and compression molded properties indicating that optimal rotomolding conditions were selected. These results confirm the possibility of using 100% recycled polymers to produce rotomolded foam parts.

Non-contact photopyroelectric approach for complete thermal characterization of porous building materials

The suitability of two photopyroelectric (PPE) methods for measuring the thermal diffusivity and effusivity of porous solids is described. The main characteristic of both methods, associated with the possibility of investigating porous solids, is the absence of coupling fluid between the pyroelectric sensor and sample. The first method (proposed initially by Salazar et al., Measurement 121, 96 (2018) [1]) relies on the front detection configuration with opaque pyroelectric sensor and thermally thick sample. Based on the phase frequency scan of the PPE signal, this method leads to the direct measurement of the sample’s thermal effusivity. The second method (proposed initially by Zammit et al., J. Appl. Phys. 117, 105,104 (2015) [2]) is based on two successive measurements (frequency scans), one in back and one in front PPE configuration, followed by a self-normalization of the phase vs. modulation frequency dependence. This method uses transparent pyroelectric sensor and backing material, allowing the direct measurement of the sample thermal diffusivity. In the paper, both methods were adapted and improved for investigating some porous building materials of interest: old bricks with unknown values of thermal parameters.

Integrated Approach for Detecting Convection Effects in Geothermal Environments Based on TIR Camera Measurements

Thermal characterization of soils is essential for many applications, including design of geothermal systems. Traditional devices focus on the computation of thermal conductivity, omitting the analysis of the convection effect, which is important for horizontal geothermal systems. In this paper, a procedure based on the monitoring of the surface of the soil with a thermal infrared (TIR) camera is developed for the evaluation of the global thermal imbalance on the surface and in-depth. This procedure allows for the computation of thermal conductivity and global convection heat rate, consequently constituting a complete thermal characterization of the geothermal system. The validation of the results is performed through the evaluation of the radiometric calibration of the thermal infrared camera used for the monitoring and the comparison of the thermal conductivity values obtained in-depth, with traditional methods, and for the surface of the system.

Recyclable Organocatalyzed Poly(Thiourethane) Covalent Adaptable Networks.

A new type of tetraphenylborate salts derived from highly basic and nucleophilic amines, namely 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), 1,8-diazabicyclo(5.4.0)undec-7-ene (DBU) and triazabicyclodecene (TBD), was applied to the preparation of networked poly(thiourethane)s (PTUs), which showed a vitrimer-like behavior, with higher stress-relaxation rates than PTUs prepared by using dibutyl thin dilaurate (DBTDL) as the catalyst. The use of these salts, which release the amines when heated, instead of the pure amines, allows the formulation to be easily manipulated to prepare any type of samples. The materials prepared from stoichiometric mixtures of hexamethylene diisocyanate (HDI), trithiol (S3) and with a 10% of molar excess of isocyanate or thiol were characterized by FTIR, thermomechanical analysis, thermogravimetry, stress-relaxation tests and tensile tests, thus obtaining a complete thermal and mechanical characterization of the materials. The recycled materials obtained by grinding the original PTUs and hot-pressing the small pieces in the optimized time and temperature conditions were fully characterized by mechanical, thermomechanical and FTIR studies. This allowed us to confirm their recyclability, without appreciable changes in the network structure and performance. From several observations, the dissociative interchange trans-thiocarbamoylation mechanism was evidenced as the main responsible of the topological rearrangements at high temperature, resulting in a vitrimeric-like behavior.

Comprehensive analysis of the thermal properties of capric-myristic, lauric-myristic and palmitic-stearic acids and their shape-stabilization in an inorganic support

Complete thermal characterization was performed to the binary eutectics capric-myristic (CA:MA), lauric-myristic (LA:MA) and palmitic-stearic (PA:SA). The obtained thermophysical properties included theoretical calculus along with experimental measurements as phase change temperatures, latent heats, specific heat capacities and degradation temperatures, through modulated differential scanning calorimetry (MDSC) and thermogravimetry analysis (TGA). Likewise, vacuum-assisted method was successfully employed to produce novel shape-stabilized phase change materials (SS-PCMs), with a porous clay mineral as a support, using different impregnation percentages (25%, 35% and 40%) of CA:MA, LA:MA and PA:SA. Thermal properties were obtained in the same manner as for the binary eutectic mixtures, besides, scanning electron microscope (SEM) was used to study the SS-PCMs morphologies and leakage test performed. From the MDSC measurements, empirical equations of specific heat capacity as a function of temperature were proposed for the binary eutectics and SS-PCMs. The results of this work revealed that the optimal percentage of CA:MA, LA:MA and PA:SA was 35%, in terms of low leakage (<2%), latent heats around 45 kJ kg−1 and average heat capacities of 1.4 J g−1°C−1. As the new composites presented a wide range of phase change temperatures then SS-CAMA (23°C), SS-LAMA (36°C) and SS-PASA (55°C) can be used for diverse applications as in construction, food industry and domestic hot water tanks.

Electrospinning of PCL-Based Blends: Processing Optimization for Their Scalable Production

In this work poly(ε-caprolactone) (PCL) based electrospun mats were prepared by blending PCL with microcrystalline cellulose (MCC) and poly(3-hydroxybutyrate) (PHB). The electrospinning processing parameters were firstly optimized with the aim to obtain scalable PCL-based electrospun mats to be used in the industrial sector. Neat PCL as well as PCL-MCC and PCL-PHB based mats in different proportions (99:1; 95:5; 90:10) were prepared. A complete morphological, thermal and mechanical characterization of the developed materials was carried out. Scanning electron microscopy (SEM) observations showed that the addition of PHB to the PCL matrix considerably reduced the formation of beads. Both the addition of MCC and PHB reduced the thermal stability of PCL, but obtained materials with enough thermal stability for the intended use. The electrospun PCL fibers show greatly reduced flexibility with respect to the PCL bulk material, however when PCL is blended with PHB their stretchability is increased, changing their elongation at break from 35% to 70% when 10 wt% of PHB is blended with PCL. However, the mechanical response of the different blends increases with respect to the neat electrospun PCL, offering the possibility to modulate their properties according to the required industrial applications.

Crystalline Characteristics and Their Influence in the Mechanical Performance in Poly(ε-Caprolactone) / High Density Polyethylene Blends.

Blends of poly(ε-caprolactone) (PCL) and high-density polyethylene (HDPE) have been prepared at different compositions in order to assess the effect of HDPE on gas transport and mechanical behaviors of PCL. Previous to this evaluation, a complete morphological, structural, and thermal characterization were performed using techniques, including SEM, contact angle, FTIR, differential scanning calorimetry, and X-ray diffraction with synchrotron radiation at small and wide angles. Low HDPE incorporations allow interactions to be established at interfaces in the amorphous regions and the enhancement of the mechanical performance. Consequently, the addition of a small amount of HDPE (ranging from 5 to 10 wt%) appears to be appropriate in certain bio-applications where a higher mechanical behavior is required.

Sustainable polymer-based Phase Change Materials for energy efficiency in buildings and their application in aerial lime mortars

An experimental study aimed at investigating the possibility to produce a Phase Change Material (PCM) for mortars by incorporating through the “form-stable method” a thermoplastic low-melting polymer (PEG 1000) into a porous inert substrate (i.e., Lecce Stone), obtained as residue from processing stone, is reported. The viscosity of pure PEG at different temperatures was first assessed to identify an appropriate processing temperature to introduce fluid PEG into the pores of the stone. A complete (chemical, thermal and morphological) characterization was performed on the developed PCM composites, varying the impregnation times. Aerial lime-based mortars were produced with the addition of the selected experimental PCM composite, taking as comparison the mortar containing only the stone as inert aggregate. On the different mortars, mechanical tests were performed in both compression and bending mode and the thermal conductivity was measured.

Enhancing the Thermal Stability of Polypropylene by Blending with Low Amounts of Natural Antioxidants

AbstractNatural antioxidants are added in very low amounts to protect a polypropylene (PP) matrix against thermo‐oxidative degradation during processing. Thus, PP is melt‐blended with caffeic, chlorogenic, trans‐ferrulic, and p‐coumaric acids, and also with flavone and 3‐hydroxyflavone at 0.1 wt% with respect to the PP matrix. Neat PP and PP blended with three traditional antioxidants are prepared for comparison. A complete structural, thermal, and mechanical characterization is conducted. Ferrulic acid and particularly caffeic acid increases the thermal stability, showing also the highest activation energy. The structural changes of PP‐based films due to the polymer thermal degradation at high temperature (i.e., 400 °C) followed by FTIR reveal that antioxidants effectively delay the thermal degradation process. The wettability and the mechanical performance are also studied to get information regarding the industrial application of such films. While caffeic acid provides a more flexible material, ferrulic acid provides higher water resistance. Finally, AFM‐QNM shows that PP with caffeic acid has the highest miscibility.

Miniature ammonia loop heat pipe for terrestrial applications: Experiments and modeling

Thermal management is always an exigent topic in various applications like electronic equipment cooling, aerospace, and avionics, defence electronics, etc. Loop Heat Pipes (LHPs) are highly efficient, robust, two-phase, passive heat-transfer devices, increasingly becoming popular for thermal management of terrestrial and avionics applications. Miniaturization of the device and its ability to perform well in different orientations with respect to the gravitational vector are essential for its employment in terrestrial applications. In the present study, complete thermal characterization of the developed ammonia miniature loop heat pipe (mLHP) in different orientations, keeping into view possible terrestrial applications, has been carried out utilizing infrared thermography coupled with conventional thermometry. The maximum capacity obtained is about 225 W (for maximum evaporator temperature of 70 °C) and the thermal resistance was better than 0.5 K/W in all experimental trials irrespective of the orientations. The effect of orientation on the operation of mLHP is insignificant because of its small dimensions and the device can be safely considered to be orientation-free. From the results of the study, mLHP can regard as a quite promising thermal management technology for terrestrial applications. A mathematical model is developed to predict the steady-state evaporator temperature of the mLHP for a given heat load, sink temperature and surrounding temperature. The model has been validated with the experimental results and a good match is obtained.

Tethering Luminescent Thermometry and Plasmonics: Light Manipulation to Assess Real-Time Thermal Flow in Nanoarchitectures.

The past decade has seen significant progresses in the ability to fabricate new mesoporous thin films with highly controlled pore systems and emerging applications in sensing, electrical and thermal isolation, microfluidics, solar cells engineering, energy storage, and catalysis. Heat management at the micro- and nanoscale is a key issue in most of these applications, requiring a complete thermal characterization of the films that is commonly performed using electrical methods. Here, plasmonic-induced heating (through Au NPs) is combined with Tb3+/Eu3+ luminescence thermometry to measure the thermal conductivity of silica and titania mesoporous nanolayers. This innovative method yields values in accord with those measured by the evasive and destructive conventional 3ω-electrical method, simultaneously overcoming their main limitations, for example, a mandatory deposition of additional isolating and metal layers over the films and the previous knowledge of the thermal contact resistance between the heating and the mesoporous layers.

Antimicrobial properties of polypropylene films containing AgSiO2, AgZn and AgZ for returnable packaging in seafood distribution

Active antimicrobial films were prepared by incorporating AgSiO2, AgZn and AgZ at 1, 3, 5 and 10 % (w/w) into a polypropylene (PP) matrix. Complete thermal, structural, mechanical and functional characterization as well as antimicrobial efficiency and returnable antimicrobial efficiency were determined according to the Japanese Industrial Standard method. The morphology of the films showed agglomerates of particles in the composites. The active formulation had decreased elongation compared to the pure PP sample. Thermal analyses indicated that the active formulation compositions had increased thermal stability. The films showed 50 % antimicrobial properties after the fifth wash against the tested microorganisms, presenting better activity against Gram negative organisms than Gram positive ones. These findings suggest that PP films with AgSiO2, AgZn and AgZ particles can provide a significant contribution to the quality and safety of seafood in the distribution chain.

Active wheat gluten films obtained by thermoplastic processing

Abstract Active films based on glycerol-plasticized wheat gluten protein containing different thyme oil concentrations (0–15 wt.%) were prepared by a thermoplastic process involving relatively high temperature and pressure. A complete thermal, structural, mechanical, antimicrobial and antioxidant characterization of all formulations was carried out. Antimicrobial activity tests showed that neat thyme oil presented a meaningful antimicrobial activity. The addition of thyme essential oil to formulations based on gluten protein allowed to prepare biodegradable and edible films with increased in vitro antioxidant and antimicrobial properties for the most concentrated samples. However, increasing essential oil concentration led to a continuous decrease in the tensile and storage modulus but to an increase in the deformability of the films. Only films containing 10 and 15 wt.% thyme oil showed reduced moisture sorption with respect to the control film (0% thyme oil), while the water vapor permeability and total soluble matter were not markedly affected by its addition. These changes were attributed to the interference of the oil in the formation of the protein molecular network, and were corroborated by the analysis of the films microstructures by SEM.

Thermal Characterization Using Optical Methods of AlGaN/GaN HEMTs on SiC Substrate in RF Operating Conditions

Performance and reliability of wide bandgap high-power amplifiers are correlated with their thermal behavior. Thermal model development and suitable temperature measurement systems are necessary to quantify the channel temperature of devices in real operating conditions. As a direct temperature measurement within a channel is most of the time not achievable, the common approach is to measure the device temperature at different locations close to the hotspot and then to use simulations to estimate the channel temperature. This paper describes a complete thermal characterization of AlGaN/gallium nitride (GaN) on silicon carbide high electron-mobility transistors (HEMTs) when devices are operating in dc bias, pulsed, and continuous wave. Infrared thermography, charge-coupled device-based thermoreflectance microscopy, and micro-Raman spectroscopy have been performed to extract the thermal resistance of the components. Results have been compared with simulations using a 3-D finite-element model to estimate the operating channel temperature. Measurements have shown that the RF-biased thermal resistance and the dc-biased thermal resistance of GaN HEMTs are similar.