Floating offshore wind turbines (FOWTs) face a major challenge when focusing on the effect of biofouling: biofouling by mussels on bottom-surface mobile connections, such as dynamic submarine electrical cables and mooring lines. Mussels are one of the dominant species in offshore wind farms in North Atlantic area. Amongst other effects, mussels can cause significant thermal impacts on dynamic power cables, which can lead to reduced performance or even failure. To address this issue, it is essential to thermally characterize mussels, including estimating their thermal resistance, so that they can be properly incorporated into the design and maintenance phases of the submarine dynamic power cables. This study investigates three key factors that could affect mussel thermal resistance, including mussel water filtering, imposed power during measurement, porosity (mussel's age). Results reveal that the thermal resistance of living mussels is smaller than that of dead mussels due to the metabolic process of water filtering. Additionally, thermal resistance decreases as mussel age (porosity) and imposed power during measurement increase. The results of this study offer novel insights into the thermal properties of mussels and their impact on submarine dynamic electrical cables used in FOWTs. The findings have practical implications for the design and maintenance of FOWTs, enhancing the sustainability of offshore wind energy production and provide a complete protocol for further investigations.

This article introduces an ultrafast transient hot-bridge (THB) technique for the microscale measurement of thermal properties. The system comprises microfabricated heaters and resistance thermometers, arranged in a Wheatstone bridge configuration, deposited on sample surface. These components are used in order to generate and detect electrical pulses, leading to temperature increases on micro- and nanosecond scales. The design and performance of various probes are discussed, with an evaluation of their capabilities in terms of time response, precision, and resolution. Electrical pulses are applied via metalized probes, and the resultant temperature increases are analyzed within selected time periods ranging from 10 ns to 100 mu s. By ensuring a self-balanced condition for all Wheatstone bridges, the technique facilitates the detection of rapid, time-dependent changes in thermal properties due to temperature evolution or structural transformations. This innovative method enables the measurement of thermal conductivity in very thin films and demonstrates the potential for measuring thermal properties at micrometric or even nanometric scales.

Floating offshore wind turbine (FOWT) plays a significant role in meeting emission targets over the next 20 years. The dynamic submarine electrical cable (DSEC) is a key component of FOWT. Its electric insulation system is intended to withstand a maximum conductor temperature of 90°C. However, biofouling growth, particularly mussel growth, can modify heat transfer around the cable and thus the maximum conductor temperature, as well as temperature fluctuation, affecting fatigue lifetime. In our work, we thermally characterize mussels of various ages. The results revealed that the effective thermal conductivity of juvenile mussels is lower than that of mixed and only adult mussels. This variation in effective thermal conductivity with mussel's age is related to the water porosity of the mussel's layer. Using a numerical simulation, it founds that the thermal effect of the resulting global thermal resistance can lead the DSEC conductor wire to either overheat or cool down depending on the mussel's age.

The prediction of the effective thermal conductivity of composites filled with carbon fibers requires the knowledge of the microstructure, the relative amount and thermal properties of filler and matrix materials, the orientation of non-isometric filler phases and the thermal contact resistances between fibers and matrix and also between fibers. However, information at small scale are often missing especially thermal contact resistances. The present work describes the measurement of the thermal contact resistance (TCR) between two crossed carbon fibers which is performed by an adaptation of the T-type 3? method for thermal conductivity measurement of wires. The first carbon fiber is connected to two copper blocks supplied by a modulated electrical current providing a volumetric heating. The second fiber fixed on a U-shape holder is delicately implemented over the first one. After performing a secondary vacuum, the 3? voltage V3? of the first fiber is recorded as function of the frequency of the modulated current. Knowing the applied force, the contact area between the two carbon fibers is calculated from bending and deformations then a 3D numerical model describing heat transfer in two crossed carbon fibers is used to estimate the TCR at their intersection. In addition, a detailed sensitivity analysis of the unknown parameter TCR is performed allowing to find optimal operating conditions especially the frequency range. Measurements are performed with PAN type carbon fibers (FT300B) picked up from the same bundle. Different TCR estimations were performed by fitting numerical and computed V3? voltage as function of fre-quency. Finally, values of TCR between crossed carbon fibers were found equal (10.4 & PLUSMN; 10.1) 105 kW-1 which provides an order of magnitude for such phenomenon.

There are potential alternatives to cold production by vapor compression. Among these possibilities, one may consider solid refrigeration based on the elastocaloric effect of materials with a low environmental footprint such as natural rubber. After a state of the art on refrigeration systems using caloric materials (barocaloric, magnetocaloric, electrocaloric, elastocaloric), this article presents the principles of cold production by regenerative systems (with heat transfer fluid) and by recovery systems (direct contact between the heat exchangers and the caloric material). Two recovery systems were designed and tested. The first system has a single actuator and operates in sequence in 2.5 times, a power of 0.2 W/g and a temperature span of 1.3 K were obtained. The second system uses two actuators, and its sequencing is in 4 times, a temperature difference of 3.5 K.

Wind energy is expected to play a significant role in meeting emission targets over the next 20 years. Offshore wind turbines in deep water (>150 m) must be developed due to resource quality, environmental, and activity constraints. Floating offshore wind turbines (FOWT) will be the best technology for reaching these targets. The dynamic submarine electrical cable (DSEC) is a key component of FOWT. Its electric insulation system is intended to withstand a maximum conductor temperature of 90 °C. However, biofouling growth, particularly mussels, can modify the heat transfer around the cable and thus its maximum conductor temperature, as well as temperature fluctuation, affecting the fatigue lifetime. In our work we estimate the effective thermal conductivity of mussels of various ages, as well as the heat transfer coefficient of the water around them. The results revealed that the effective thermal conductivity of juvenile mussels is lower than that of mix (both juvenile and adult) and only adult mussels. This variation in effective thermal conductivity with mussel age is related to the water porosity of the mussel’s layer. Then, the thermal effect of the resulting global thermal resistance can lead the DSEC conductor wire to either overheat (colonized by juvenile and mixed mussels) or cool down (colonized by adult mussels). Numerical simulations are used to quantify this effect.

The prediction of the effective thermal conductivity of composites filled with carbon fibers requires the knowledge of the microstructure and composition of the composite, the orientation of nonisometric filler, the thermal conductivities of both phases and the thermal contact resistances between fibers and also between fibers and matrix. Due to the anisotropy of carbon fibers, one should know both their axial and radial thermal conductivities. Contrary to the axial thermal conductivity of carbon fiber, there are not much work on the radial one. The present work describes the characterization of the thermal conductivity of carbon fiber in the radial direction using the 3 Omega method with a constant current source. One key point is the use of de-ionized water around the carbon fibers to enhance radial heat transfer. An appropriate thermal model is required in order to estimate the radial thermal conductivity. Therefore, analytical 1D and 2D thermal models are developed using quadrupole methods to describe heat transfer in the carbon fiber using periodic regime and are compared with a 2D numerical model. It appeared that the use of a 1D heat transfer model induces some bias until 50.3% on the estimation of the radial thermal conductivity showing that residual axial heat transfer still occurs. Therefore the 2D thermal model is more appropriate and is used with the experimental data to estimate the radial thermal conductivity. In addition, a detailed sensitivity analysis of the unknown parameter is performed that allows to find the best range of operating conditions especially the frequency range and the effect of the type of surrounding material. Measurements are performed with PAN type carbon fiber (FT300B) of 6-8 mu m diameter and various lengths from 0.5 to 2.5 mm embedded in de-ionized water. Finally, radial thermal conductivity values are shown to be about 10 times smaller than the axial one, revealing strong anisotropy of the studied carbon fiber.

Photochromic azo materials have stirred considerable interest for their ability to mechanically respond to polarized light through large photoinduced migration and orientation processes. In order to apprehend the microscopic dynamics behind the extensive mass transport occurring under interferential illumination, two azo compounds differing by their propensity to form hydrogen bonds are synthesized and processed as nondoped glassy thin films. Interferential irradiation using polarization and intensity patterns reveals fully distinct responses. Regular nanometer-high surface relief gratings transform into micrometer superstructures with an amplitude ten times higher than the initial film thickness when using the latter polarization. Systematic comparisons between the azo materials in terms of thermal properties, photochromism in solution and in the solid state, and photomigration are carried out. The progressive formation of superstructures is ascribed to two successive processes. The first one relates to fast photoinduced migration due to the impinging structured light, and the second one is promoted by slower thermally activated "zig-zag"-like diffusion and Z-E thermal relaxation, which in turn requests high orientational mobility of the azo compounds and causes large nanomechanical changes. Such studies should provide novel structural guidelines in terms of material fluidity to rapidly achieve highly structured and rewritable materials at low light irradiance.

In this study, phenol formaldehyde/reduced graphene oxide (PF/RGO) foam nanocomposites were prepared. Here, RGO was obtained by the reduction of graphene oxide using an eco-friendly reducing agent potato starch. The scanning electron microscopic images of RGO reinforced foams exhibited smaller cells with thick cell walls as compared to neat PF foam that confirms the incorporation of filler material. The thermal and dielectric properties of the PF/RGO foams were improved with increasing the wt% of RGO. The incorporation of RGO improved the thermal conductivity of the PF matrix (11.3% for 0.15 wt% of RGO) to a small extent. The prepared foams are efficient thermal insulation materials as well as efficient electrical conductors. wt% RGO shows cells of uniform size and shape. From the TGA results, it is found that there is an improvement in the thermal stability of PF foams. The dielectric properties of the PF foams increase with an increase in wt% of RGO. The thermal conductivity study of the prepared foams shows that the introduction of RGO into the PF matrix increases

An experimental setup for 3ω method with a constant current source and two differential amplifiers was built to measure the thermal conductivity and the volumetric heat capacity of single polyacrylonitrile (PAN)-based carbon fiber. In complement to a well-known analytical thermal model, a numerical one was developed that can check the validity of the analytical one and can also take into account the effect of convective heat loss on the measurements. A detailed sensitivity analysis of the unknown parameters was presented that would finally help in the better design of the setup for 3ω method. The tests were performed under vacuum and atmospheric pressure for chromel wire as a reference sample and under vacuum for two types of PAN-based carbon fiber. Detailed measurements were performed displaying the influence of convective loss and the thermal contact resistance between fiber and copper electrodes on the estimation of thermal properties of carbon fiber.

In this work, we report the implementation of the ultra-fast transient hot strip (THS) technique for measuring the anisotropic thermal conductivity of aluminum nitride (AlN) thin-films. AlN films were produced by reactive DC magnetron sputtering grown at low temperature (>250 degrees C) on silicon oxide (SiO2) thin-film produced on a silicon substrate. Precise measurement of thermal conductivity was performed with an experimental device generating ultra-short electrical pulses, and subsequent temperature increases were electrically measured on nanosecond and microsecond time scales. The electrical pulses were applied within metalized strips patterned on SiO2 before AlN elaboration and the temperature increases were analyzed within time periods selected in the range [0.1-10 mu s]. AlN thermal conductivity of cross-plane (in-plane) increased from 60 to 90 W m(-1) K-1 (33-44 W m(-1) K-1) when thickness was raised from 1 to 2 mu m, respectively. This shows clearly the anisotropy in thermal conductivity of AlN films. In addition, the volumetric heat capacity of AlN was estimated to be similar to 2.5 x 10 6 J K-1 m(-3).

This study investigated the morphology, tensile properties, thermal conductivity, and thermal stability of short carbon fiber reinforced polypropylene (CF/PP) composites. CF/PP composites were prepared with varying amounts of short carbon fiber (9, 15, 20, 25, and 30 wt%) in PP matrix with and without maleic anhydride grafting PP as a coupling agent. Samples were prepared by extrusion blending followed by injection molding. Results showed that the addition of CFs significantly improved the tensile modulus and tensile strength of composites by 455% and 168%, respectively, at 30 wt% loading compared with pure PP. Thermogravimetric analysis results indicated that increasing the CF content improved the thermal stability of composites compared with PP. In addition, thermal conductivity increased with increasing CF weight fraction. The microstructural analysis results showed that maleic anhydride grafting PP improved the adhesion between carbon fibers and PP matrix. POLYM. COMPOS., 39:E664–E670, 2018. © 2016 Society of Plastics Engineers

Heat flux distribution measurement is very useful in concentrated solar application. It allows improvement in the overall energy collected and the control of the heat flux profile. However, heat flux distribution measurement is not straight forward with existing heat flux sensors. In this work, a new heat flux sensor for heat flux distribution measurement is designed calibrated and tested. The new sensor is based on a normal gradient technique where thermoelectric thin films on both sides of a machinable glass ceramic substrate provide temperature discrepancies and therefore heat flux measurements using Fourier's law. An original nickel and copper electric pattern allows heat flux measurements at 9x9 locations on a 100x100 mm(2) ceramic substrate. The calibration is performed with temperature discrepancy measurement or prescribed heat flux using Joule effect. Finally the new device is tested using an infrared lamp and a radiative screen to obtain various heat flux profiles.

Flat glass temperature at the vicinity of the grinding wheel during grinding can become very high and reach that of the glass transition (typically around 550-600 degrees C). In such cases, the mechanical strength of glass is greatly affected and the grinding process cannot be carried out properly. Hence, thermal phenomena must be managed by adjusting the machining parameters to avoid overheating. For this purpose, it is very important to be able to measure the glass temperature, especially at the grinding interface. However, measuring the interfacial glass temperature is difficult and none of the existing methods for metal grinding is adequate for glass grinding. This work shows a novel temperature method that uses constantan and copper strips on both sides of the glass plates; thermoelectric contact being provided by the metallic binder of diamond particles in the grinding wheel. This new technique allows the measurement of the glass edge temperature during the wheel displacement around the glass plate. The experimental results show an average glass edge temperature between 300 and 600 degrees C depending on the value of the machining parameters such as work speed, wheel speed, depth of cut and water coolant flow rate. As this new thermal instrumentation is rather intrusive, glass temperature biases were analysed using a 3D heat transfer model with a moving source. Model computations performed using finite elements show that the temperature biases are less than 70 degrees C, which is smaller than the standard deviation of the glass edge temperatures measured during grinding.