The exponential rise of power dissipation in electric devices has so far vastly surpassed the performance of power converter systems. New thermal management solutions are therefore in high demand to ...maintain devices at their optimal temperature and efficiency. Here, we present an innovative magnetically actuated thermal switch (MATS) based on nanofluids capable of controlling both the magnitude and direction of the heat flux. When in the OFF state (zero applied magnetic field), the nanofluid captures the heat being generated at the heat source. When an external magnetic field is applied (ON state), the nanofluid is transported from the heat source to the heat sink where it releases the carried heat. This work (i) provides a detailed description of the MATS operating principles, (ii) studies the effect of thickness and operation frequency in its cooling power, (iii) presents numerical simulations to forecast MATS behavior and (iv) demonstrates the MATS applicability in the thermal management of a 10W Light Emitting Diode. The versatility, simple design, unique operating mode and high performance of the MATS suggests that the proposed approach is a promising technology to be used in a vast number of electronic devices, thermal storage systems and thermal management applications.
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•A novel remotely operated magnetic thermal switch was developed based on ferrofluids.•The temperature difference between hot and cold sides is significantly reduced.•The temperature control of a high power Light Emitting Diode was demonstrated.•We discuss the prospects and challenges of the MATS for future developments.
Polydimethylsiloxane (PDMS)-based flexible films have substantiated advantages in various sensing applications. Here, we demonstrate the highly sensitive and programmable thermal-sensing capability ...(thermal index, B, up to 126 × 103 K) of flexible films with tunable sandwiched microstructures (PDMS/cracked single-walled carbon nanotube (SWCNT) film/PDMS) when a thermal stimulus is applied. We found that this excellent performance results from the following features of the film’s structural and material design: (1) the sandwiched structure allows the film to switch from a three-dimensional to a two-dimensional in-plane deformation and (2) the stiffness of the SWCNT film is decreased by introducing microcracks that make deformation easy and that promote the macroscopic piezoresistive behavior of SWCNT crack islands and the microscopic piezoresistive behavior of SWCNT bundles. The PDMS layer is characterized by a high coefficient of thermal expansion (α = 310 × 10–6 K–1) and low stiffness (∼2 MPa) that allow for greater flexibility and higher temperature sensitivity. We determined the efficacy of our sandwiched, cracked, flexible films in monitoring and switching flexible devices when subjected to various stimuli, including thermal conduction, thermal radiation, and light radiation.
In recent years, intensive studies on thermal control devices have been conducted for the thermal management of electronics and computers as well as for applications in energy conversion, chemistry, ...sensors, buildings, and outer space. Conventional cooling or heating techniques realized using traditional thermal resistors and capacitors cannot meet the thermal requirements of advanced systems. Therefore, new thermal control devices are being investigated to satisfy these requirements. These devices include thermal diodes, thermal switches, thermal regulators, and thermal transistors, all of which manage heat in a manner analogous to how electronic devices and circuits control electricity. To design or apply these novel devices as well as thermal control principles, this paper presents a systematic and comprehensive review of the state‐of‐the‐art of fluidic and mechanical thermal control devices that have already been implemented in various applications for different size scales and temperature ranges. Operation principles, working parameters, and limitations are discussed and the most important features for a particular device are identified.
The paper presents an up‐to‐date review of fluidic and mechanical thermal control devices, including thermal switches, thermal diodes, thermal regulators, and thermal transistors, that have been used for various thermal management applications.
•We have investigated the spin analog of the Thomson effect.•The heat conduction equation was derived in the presence of magnetic/electric fields.•Heat transfer by spins leads to the appearance of a ...heat flux.•The spin Thomson coefficient was found for a yttrium-iron garnet plate.•Feasibility of using in heat switches of solid-state coolers is analyzed.
The study of novel thermal effects associated with spin current is fundamental to understanding the relationship between magnetoelectric and thermal phenomena. The central focus of attention of our research is on the spin analog of the Thomson effect as the most promising in terms of its use in heat switches of solid-state coolers. In order to model heat flows, the heat conduction equation is derived in the presence of magnetic and electric fields. Applying the developed theoretical framework, the spin Thomson coefficient is calculated for a yttrium-iron garnet plate. It is demonstrated that this coefficient strongly depends on the thickness of the plate. The corresponding estimates of the heat flux carried by the spins are also obtained. For a 200 nm plate, it is 6.81 W/cm2, which is comparable to the heat fluxes in the best thermal switches. Moreover, the results of the paper indicate at the possibility of further increase in the flux by an optimal choice of plate thickness and magnitude of magnetic field.
This paper studies one of the magnetic analogs of well-known thermoelectric effects, the spin Thomson effect. This effect consists in the existence of a heat flux caused by the spin current and is ...described by a modified heat equation. When comparing the published experimental data and the theoretical model, it was possible to find the Thomson spin coefficient for iron-yttrium garnet. From a viewpoint of thermal conductivity, the presence of a magnetic field of 1750 Oe turns out to be equivalent to the motion of the medium at a rate of 6.5 mm/s and leads to the existence of a giant heat flux of 18.9 kW/m 2 due to the transfer of heat by spins. The ability to control heat fluxes by means of a magnetic field allows the use of materials based on iron-yttrium garnet for practical applications as thermal switches for solid-state cooling.
Magnetic heat pumps, refrigerators and energy conversion prototypes, with an operation based on the magnetocaloric effect, usually show a restriction in their frequency of operation to a few Hertz. ...In 2010 it was proposed to apply thermal switches to overcome this barrier. In this article thermal switches built with Ni-nanowire Peltier elements are presented and the performance of such elements is discussed on a theoretical and experimental basis. Finally an approximate estimate of the performance of a magnetic refrigerator of the types built up to present is compared to that of a magnetic refrigerator applying nanowire thermal switches.
•A new alternative method for magnetic refrigeration.•High-frequency device is more efficient and economical.•Applicable to magnetic heating, refrigeration and energy conversion.
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