We consider energy transfer between non-equal nanoparticles mediated by a quantum system. The nanoparticles are considered as thermal reservoirs described as ensembles of finite numbers of harmonic oscillators within the Drude-Ullersma model having mode spacings Δ1 and Δ2. Our approach is based on the generalized quantum Langevin equation. The quasi-static energy transport between the thermal reservoirs is investigated. As is shown, the double degeneracy of the mode frequencies, which occurred in the previously considered case when Δ1 = Δ2, is removed in the present case of non-equal mode spacings. Equations describing long-time (t ∼1/Δ1,2) relaxation for the mode temperatures (or the ensemble averaged mode energies) are solved and the resulting expression for the total energy current between the nanoparticles is derived and explored.

Synthesis, structural, magnetic properties and heating efficiency of γ-Fe2O3 nanoparticles have been investigated. X-ray diffraction (XRD) and Mössbauer spectroscopy show that the obtained nanoparticles are mainly composed of maghemite phase (γ-Fe2O3). Williamson-Hall method shows that the crystallite is around 14nm.The specific absorption rate (SAR) under an alternating magnetic field is investigated as a function of frequency. A highest SAR value of 12W/g for frequency 523 kHz was obtained.

One approach to treating atrial fibrillation relies on freezing tissue of the heart wall. This surgical technology requires sub-millimeter spatial resolution when dynamically tracking the freezing of pulmonary vein; conventional techniques such as ultrasound lack the necessary precision. Here we use an electrothermal “3ω” method to track propagating freezing fronts in nearly real time. The heater line is excited with multiple frequencies simultaneously, and the freezing front detected as it passes through the various penetration depths due to the contrast between thermal conductivities on either side of the front. Comparison of water freezing experiments with video images further suggests the accuracy of the method. Analysis and experiments show how the uncertainty, time response, and measurement range depend on the frequencies and thermal conductivity contrast. Finally, the method is demonstrated on biological tissue as further proof of principle for medical applications.

Using our newly proposed interface conductance modal analysis (ICMA) formalism, we study the modal contributions to thermal interface conductance (G ) across the interface of crystalline silicon and crystalline germanium. We present the accumulation functions of G at different temperatures and predict G as a function of temperature after proper quantum-corrections have been applied. Different classes of vibration are identified across the interface, among which interfacial modes are determined to have the highest per mode contribution to G . The results demonstrate the ability of ICMA in not only calculating the spectral contributions to G but exactly pinpointing the shape of each vibrational eigen state.

As the major heat carriers in dielectrics and semiconductors, phonons are strongly scattered by boundaries and interfaces at the nanoscale, which can lead to a significantly reduced lattice thermal conductivity kL. In recent years, such phonon size effects have been used to enhance the thermoelectric performance of various nanostructured materials. With dramatically reduced kL and bulk-like electrical properties, high thermoelectric performance has been demonstrated for nanoporous Si films at room temperature. Despite these encouraging results, however, challenges still exist in the theoretical explanation of the observed low kL values. Existing studies mainly attribute the observed low kL to phononic effects and/or amorphous pore edges. These two effects can be separated when the specific heat of the film can be measured along with kL to provide more insight into the phonon dispersion modification. In this work, both the specific heat and k of a suspended nanoporous Si film is extracted from the 3ω measurements. The result is compared to the reported kL values of various porous Si films. The influence of employed phonon mean free path spectrum on the data analysis is discussed.

Lithographically fabricated gold nanowires are optically excited with 532nm CW laser and the local temperature change is measured in air, pure water and various concentration aqueous solutions of ionic solutes NaCl, Na2SO4 and MgSO4 using the thermal sensor film of Al0.94Ga0.06N embedded with Er3+ ions. The interface thermal resistance for heat transfer from the excited nanowires into the surrounding liquid is determined from the slopes of the temperature change versus laser intensity plots obtained for the nanowire excitation under various solutions. Addition of ionic solute molecules into the solution decreases the interface thermal resistance and hence leads to increased heat dissipation into the surrounding liquid. Interface thermal resistance decreases exponentially with the ionic strength of solution and saturates around zero for solution ionic strength of 0.3M and higher.

The heat transfer coefficients of homogeneous and hybrid micro-porous copper foams, produced by the Lost Carbonate Sintering (LCS) process, were measured under one-dimensional forced convection conditions using water coolant. In general, increasing the water flow rate led to an increase in the heat transfer coefficients. For homogeneous samples, the optimum heat transfer performance was observed for samples with 60% porosity. Different trends in the heat transfer coefficients were found in samples with hybrid structures. Firstly, for horizontal bilayer structures, placing the high porosity layer by the heater gave a higher heat transfer coefficient than the other way round. Secondly, for integrated vertical bilayer structures, having the high porosity layer by the water inlet gave a better heat transfer performance. Lastly, for segmented vertical bilayer samples, having the low porosity layer by the water inlet offered the greatest heat transfer coefficient overall, which is five times higher than its homogeneous counterpart.

The impact of mass and lattice difference on thermal boundary conductance is investigated using non-equilibrium molecular dynamics with the Lennard-Jones interatomic potential. Results show that the maximum thermal boundary conductance is achieved when the mass and the lattice of two dissimilar materials are matched, although the composite thermal conductance is not necessarily a maximum. It is observed that the small difference in mass and potential well depth has as significant an impact as large differences, and that the frequency mismatch is an important factor that affects thermal boundary conductance. It is, also, found that inelastic scattering begins to play a role at the interface as the temperature increases.

Selectively-absorbing nanofluids were synthesized and evaluated for spectrum splitting PV/T collector applications. Core-shell silver-silica (Ag-SiO2) nanodiscs and multi-walled carbon nanotubes (MWCNTs) were suspended in water at varying dilutions and then tested as an optical filter placed between a light source and silicon solar cell. A concentrated Ag-SiO2 solution diluted with an aqueous MWCNT solution yielded higher thermal efficiencies than when diluted by the same volume of water. However, AgSiO2-MWCNT mixtures yielded a lower electrical output than aqueous AgSiO2 dilutions due to the non-selective absorption of MWCNTs. The most concentrated Ag-SiO2 nanofluid (0.026wt%) yielded a peak thermal efficiency of 65%, to deliver the greatest combined efficiency of ∼72%.

A new thermal imaging technique is characterized that uses an optically trapped erbium oxide nanoparticle cluster of approximately 150 nm. This technique can measure absolute temperature and has an imaging spatial resolution of the trapped particle. Scanning optical probe thermometry has been used to thermally image a cluster of gold nanowires that were excited with the trapping laser. Following a deconvolution of the measured thermal profile, a point spread function of the imaging technique has been determined to be a Gaussian with a FWHM of 165 nm. This width is a function of the clustering of Er2O3 nanoparticles used to image the nanowire. Optical probe thermometry has further been used to measure the temperature of nucleation events where a dichotomy of temperature for nucleated water occurs from degassed water and native water. Degassed water has been measured to nucleate at 555K confirming water adjacent to the gold nanoparticle superheats to the spinodal decomposition temperature before nucleating into a water vapor bubble. Following this event, the temperature inside the vapor bubble rises to the melting point of the gold nanoparticle, 1300 K which is followed by temperature stabilization. The rapid and significant temperature increase is attributed to the loss of a thermal dissipation pathway, to the surrounding water, previously available to the gold nanoparticle due to the insulator nature of the growing vapor envelope around the gold nanoparticle.

The present work reports on the fabrication, experimental and theoretical investigation of thermal conductivity (TC) and viscosity of ethylene glycol (EG) based nanofluids/microfluids (NFs/MFs) containing copper nanoparticles (Cu NPs) and copper microparticles (Cu MPs). Cu NPs (20-40 nm) and Cu MPs (0.5-1.5 μm) were dispersed in EG with particle concentration from 1 wt% to 3 wt% using powerful ultrasonic agitation, and to study the real impact of dispersed particles the use of surface modifier was avoided. The objectives were to study the effect of concentration and impact of size of Cu particles on thermo-physical properties, including thermal TC and viscosity, of EG based Cu NFs/MFs. The physicochemical properties of NPs/MPs and NFs/MFs were characterized by using various techniques. The experimental results exhibited higher TC of NFs and MFs than the EG base liquid. Moreover, Cu NFs displayed higher TC than MFs showing their potential for use in some heat transfer applications. Maxwell effective medium theory as well as Einstein law of viscosity was used to compare the experimental data with the predicted values for estimating the TC and viscosity of Cu NFs/MFs, respectively.