•An OHP with external expansion structure was designed and fabricated.•The variation law of the overall and local thermal resistance was revealed.•The OHP with water shows well adaptability to the ...heat load and filling ratio.•The OHP with SRWF has smaller thermal resistance at specific range of heat load.
Aiming to combining the strength of flexibility and adaptation of oscillating heat pipe (OHP) with specific application in the field of waste heat recovery and storage, an OHP with external expansion structure was designed and fabricated. The start-up characteristic, working status, overall thermal resistance, local thermal resistance and dispersion ratio for the local thermal resistances under different filling ratios (FR), working fluids and heat loads were revealed and compared experimentally. The results showed that for the OHP with water, it exhibits well start-up performance under wide range of FRs and is able to work effectively under wide range of FR at proper heat load. Meanwhile, it also shows well adaptability to heat load under proper FR. The OHP has not obvious difference for each branch in the heat transfer performance under wide working conditions. When filled with self-rewetting fluid (SRWF), it has smaller overall thermal resistance than the water case at specific range of heat load. Comparing to the case with water, the OHP with SRWF can show better uniformity in the heat transfer capacity for each branch under appropriate condition. However, the uniformity of branch does not always contribute toincreasing the heat transfer performance.
In this letter, the impact of self-heating effect (SHE) on hot carrier degradation (HCD) in multiple-fin silicon-on-insulator (SOI) FinFETs was investigated. First, the ac conductance method has been ...utilized to extract the thermal resistance (Rth) of SOI FinFETs with different fin numbers. Then, both dc and ac stresses are applied on the gate and drain of transistors with the source grounded to characterize the HCD. It is found that the device with large fin number demonstrates high-temperature rise caused by SHE, which results in the enhanced generation of oxide bulk trapped charges. Thus, the SHE aggravates the HCD significantly. The influence of SHE on HCD is mitigated when the frequency of ac stress is above 10 MHz. Therefore, special attention to the SHE on HCD must be paid for accurate HCD prediction in FinFETs.
The thermal management of insulated-gate bipolar transistor (IGBT) modules is a critical issue in the field of power electronics. According to the minimum thermal resistance principle, this study ...proposed a rectangular heat pipe radiator with parallel heat flow structure that can be used for cooling two 1700 V/1000 A IGBT modules. The prototypes of typical and novel heat pipe radiators were produced to validate the heat transfer enhancement of the novel structure. Performance evaluation and analysis were numerically and experimentally carried out, and the numerical results agreed well with the experimental data. Parametric studies were performed to analyze the effects of inlet air temperature, air volume, and heat load on the heat dissipation capability. The study found that the novel heat pipe radiator has a good start-up characteristic due to the parallel heat flow structure. Moreover, the performance enhancement of the novel heat pipe radiator is obvious at large heat loads. Experiment results show that the two IGBT modules with 3500 W could be cooled down to 67.8 °C when the air volume is 450 m3 h−1, which is 8.9% lower than that of a typical heat pipe radiator. The proposed novel structure improves thermal performance of the novel heat pipe radiator by significantly decreasing its thermal resistance by 22% in comparison with that of a typical heat pipe radiator.
•A rectangular heat pipe radiator with parallel heat flow structure is proposed.•The energy flow model of heat pipe radiator is developed.•The prototypes of typical and novel heat pipe radiators are produced.•The thermal resistance of novel heat pipe radiator significantly decreases by 22%.
•The effect of Rint and aK on the thermal conductivity (k) of the oxide-composite is investigated.•The Rint between the SBTO and LSMO phases does not reduce k of the composite for particle size ...greater than aK.•A significant reduction in k of composite, lower than km is observed for particle size of LSMO smaller than aK.
We present a novel approach to reduce the thermal conductivity (k) in thermoelectric composite materials using acoustic impedance mismatch and the Debye model. Also, the correlation between interface thermal resistance (Rint) and the particle size of the dispersed phase on the k of the composite is discussed. In particular, the k of an oxide composite, which consists of a natural superlattice Aurivillius phase (SrBi4Ti4O15) as a matrix and perovskite (La0.7Sr0.3MnO3) as a dispersed phase, is investigated. A significant reduction in k of composite, even lower than the k of the matrix when the particle size of La0.7Sr0.3MnO3 is smaller than the Kapitza radius (aK) is observed, depicting that Rint dominates for particle size lower than aK due to increased surface to volume ratio. The obtained results have the potential to provide new directions for engineering composite thermoelectric systems with desired thermal conductivity and promising in the field of energy harvesting.
Interfacial thermal resistance (ITR) is the main obstacle for heat flows from one material to another. Understanding ITR becomes essential for the removal of redundant heat from fast and powerful ...electronic and photonic devices, batteries, etc. In this review, a comprehensive examination of ITR is conducted. Particular focus is placed on the theoretical, computational, and experimental developments in the 30 years after the last review given by Swartz and Pohl in 1989. To be self-consistent, the fundamental theories, such as the acoustic mismatch model, the diffuse mismatch model, and the two-temperature model, are reviewed. The most popular computational methods, including lattice dynamics, molecular dynamics, the Green's function method, and the Boltzmann transport equation method, are discussed in detail. Various experimental tools in probing ITR, such as the time-domain thermoreflectance, the thermal bridge method, the 3ω method, and the electron-beam self-heating method, are illustrated. This review covers ITR (also known as the thermal boundary resistance or Kapitza resistance) of solid-solid, solid-liquid, and solid-gas interfaces. Such fundamental challenges as how to define the interface, temperature, etc. when the materials scale down to the nanoscale or atomic scale and the opportunities for future studies are also pointed out.
•First systematic comparative study of methods for calculating borehole resistance.•Of 10 methods, only 1st order multipole method gives high accuracy for all cases.•Similarly for internal ...resistance, only one method gives acceptable accuracy.•Grout resistance is shown to vary with pipe resistance and ground conductivity.
The borehole thermal resistance – that is, the thermal resistance between the fluid in the U-tube and the borehole wall – is both a key performance characteristic of a closed-loop borehole ground heat exchanger and an important design parameter. Lower borehole thermal resistance leads to better system performance and/or lower total borehole length and possibly lower installation costs. Borehole thermal resistance may be determined using in situ thermal response testing, but for design purposes, it is important to be able to predict the borehole thermal resistance prior to installation. Due to the complexity of calculating it, numerous simplified methods have been proposed. This paper reviews published methods for calculating borehole thermal resistance for grouted boreholes with single U-tubes and compares their results against a rigorous analytical method.
Another quantity that is particularly important for deep boreholes is the internal thermal resistance – that is, the thermal resistance between the upward-flowing and downward-flowing fluid paths in the borehole. Short-circuiting between the two legs has the effect of reducing the total heat transfer and can be quantified as an adjustment to the borehole thermal resistance, resulting in an effective borehole thermal resistance. A few simplified methods for calculating internal thermal resistance are compared against a rigorous analytical method.
The simplified methods for calculating both borehole thermal resistance and internal thermal resistance are compared in parametric studies spanning the range of borehole diameters, pipe spacing, ground thermal conductivities and grout thermal conductivities found in practice. Many of the simplified methods work well with some combinations of parameters and poorly with others. The first-order multipole expressions are closed-form algebraic expressions that give results within 2% (for borehole thermal resistance) and 6% (for internal thermal resistance) over the entire range of parameters. This represents significantly better accuracy than any of the other simplified methods and, therefore, the first-order multipole algorithm is recommended for single U-tube applications when the tubes are symmetrically placed.
The out-plane thermal conductivity of hexagonal boron nitride nanosheet (hBNNS)/epoxy resin (EP) composites in the perpendicular to the lamellar layers direction as well as the interface thermal ...resistance (ITR) between EP and hBNNS in nanocomposites are investigated via molecular dynamics (MD) simulations, and compared with those of the graphene nanosheet (GNS)/epoxy nanocomposites and experimental results. Results show that the out-plane thermal conductivity of the hBNNS/EP is higher than that of GNS/EP at the same volume fraction of the fillers. The obtained ITR between EP and GNS is (4.48-8.43)×10−9 m2KW−1, consistent with the previous reported experimental and simulation results. Interestingly, the calculated ITR between EP and hBNNS is (2.42–3.62)×10−9 m2KW−1, smaller than that between EP and GNS. The ITRs exponentially decay with the number of layers of hBNNS (or GNS). This work provides insights into predicting and understanding the thermal conductivity of hBN and graphene-based nanocomposites using computational approaches.
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This work investigates interfacial thermal transport in phononic‐mismatched heterostructures that consists of pristine black phosphorene and its phononic crystal. It is found that the presence of the ...sub‐periodic structure results in reduced thermal conductivity in phononic crystals. As opposed to intuitive expectations, a slight temperature jump is observed at the interface of nanophononic heterostructures, which is only about 10% of that at conventional interfaces consisting of dissimilar materials. Consequently, contact thermal conductance in the nanophononic heterostructure is 10−30 times higher than that of mass‐mismatched interfaces in a comparative study. Moreover, in contrast to conventional heterostructures achieved by interfacing dissimilar materials, weak temperature dependence is observed in interfacial thermal conductance, and thermal rectification is sharply suppressed. These phenomena are well explained based on lattice dynamic insights. This work not only enhances the understanding of the fundamental physics of phonons transport across interface, but also facilitates the possible spectrum of application ranges from thermoelectrics, thermal management, to thermal cloak.
As opposed to intuitive expectation, a slight temperature jump is observed at the interface of nanophononic heterostructures, which is about 10% of that at the interface of dissimilar materials. Consequently, its contact thermal conductance is 10−30 times higher than that of mass‐mismatched interfaces. This work enhances the understanding of phonon transport, and facilitates the possible spectrum of application ranges from thermoelectrics, thermal management, to thermal cloaks.
•Rough nanostructured surface can effectively delay the bubble nucleation and growth.•Atomic-scale roughness affects the solid-liquid interfacial thermal resistance.•High roughness element shows a ...better thermal performance with a larger CHF
The concave nanostructure presents a better boiling performance compared to convex one, however, the surface roughness plays a key role in thermal transport at solid-fluid interface. In this work, we adopted the non-equilibrium molecular dynamics simulation to investigate the effect of the internal surface roughness on the boiling heat transfer performance in concave nanostructure. It shows that the presence of atomic-scale roughness leads to heat transfer deterioration and enhancement during the evaporation and the explosive boiling processes, respectively. This finding, which is contradictory with the general understanding, is attributed to the difference in interfacial thermal resistance. It shows that the heat transfer performance is strongly dependent on the configuration of roughness elements. The low solid fraction configuration has a better heat transfer performance and can postpone the start of boiling process.
•A detailed thermal resistance analysis of the PV-TE hybrid system is proposed.•c-Si PV and p-Si PV cells are proved to be inapplicable for the PV-TE hybrid system.•Some criteria for selecting ...coupling devices and optimal design are obtained.•A detailed process of designing the practical PV-TE hybrid system is provided.
The thermal resistance theory is introduced into the theoretical model of the photovoltaic-thermoelectric (PV-TE) hybrid system. A detailed thermal resistance analysis is proposed to optimize the design of the coupled system in terms of optimal total conversion efficiency. Systems using four types of photovoltaic cells are investigated, including monocrystalline silicon photovoltaic cell, polycrystalline silicon photovoltaic cell, amorphous silicon photovoltaic cell and polymer photovoltaic cell. Three cooling methods, including natural cooling, forced air cooling and water cooling, are compared, which demonstrates a significant superiority of water cooling for the concentrating photovoltaic-thermoelectric hybrid system. Influences of the optical concentrating ratio and velocity of water are studied together and the optimal values are revealed. The impacts of the thermal resistances of the contact surface, TE generator and the upper heat loss thermal resistance on the property of the coupled system are investigated, respectively. The results indicate that amorphous silicon PV cell and polymer PV cell are more appropriate for the concentrating hybrid system. Enlarging the thermal resistance of the thermoelectric generator can significantly increase the performance of the coupled system using amorphous silicon PV cell or polymer PV cell.
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