arXiv subjects

W. Imamura

Publications and source records attributed to W. Imamura.

6 recordsLinked to original sources

arXiv2023

A comprehensive thermodynamic model for temperature change in i-caloric effects

Solid-state cooling based on i-caloric effects may be an alternative to conventional vapor-compression refrigeration systems. The adiabatic temperature change ($\Delta T_{S}$) is one of the parameters that characterize the i-caloric effects, therefore it is important to obtain the correct $\Delta T_{S}$ values and, whenever possible, to correlate this parameter with thermodynamic and microscopic quantities. In this work, we propose a comprehensive thermodynamic model that allows us to determine the adiabatic temperature change from non-adiabatic measurements of temperature change induced by a field change. Our model fits efficiently temperature versus time and temperature change versus the inverse of the field change rate data for three different materials presenting different i-caloric effects. The results indicate the present model is a very useful and robust tool to obtain the correct $\Delta T_{S}$ values and to correlate $\Delta T_{S}$ with other thermodynamic quantities.

cond-mat.mtrl-sci↗

arXiv2021

High-field specific heat and entropy obtained from adiabatic temperature change

Specific heat and entropy are relevant thermodynamic properties, which may be used as macroscopic probes to microscopic properties of materials under ambient conditions and under high applied fields. However, the measurement of specific heat under intense external fields can be a challenging task, as well as to obtain the entropy in the same conditions. Here, we describe a method to obtain high-field specific heat and entropy from measurements of specific heat under ambient conditions and direct temperature change induced by adiabatic field changes. We derive straightforward thermodynamic equations to calculate the specific heat and entropy and our results agree satisfactorily with experimental data of specific heat under magnetic field, electric field, and pressure.

cond-mat.stat-mech↗

arXiv2020

Supergiant Barocaloric Effects in Acetoxy Silicone Rubber over a Wide Temperature Range: Great Potential for Solid-state Cooling

Solid-state cooling based on caloric effects is considered a viable alternative to replace the conventional vapor-compression refrigeration systems. Regarding barocaloric materials, recent results show that elastomers are promising candidates for cooling applications around room-temperature. In the present paper, we report supergiant barocaloric effects observed in acetoxy silicone rubber - a very popular, low-cost and environmentally friendly elastomer. Huge values of adiabatic temperature change and reversible isothermal entropy change were obtained upon moderate applied pressures and relatively low strains. These huge barocaloric changes are associated both to the polymer chains rearrangements induced by confined compression and to the first-order structural transition. The results are comparable to the best barocaloric materials reported so far, opening encouraging prospects for the application of elastomers in near future solid-state cooling devices.

cond-mat.mtrl-sci↗

arXiv2018

Giant reversible barocaloric effects in Nitrile Butadiene Rubber around room temperature

Elastomers have shown to be promising barocaloric materials, being suitable candidates for solid-state cooling devices. Moreover, this family of polymers presents additional advantages, such as their low cost and long fatigue life. In this context, we investigated the barocaloric effects in Nitrile Butadiene Rubber (NBR) in a large range around room temperature. Moderated applied pressures on NBR yield giant temperature change (ΔTS) and entropy change (ΔST), reaching the maximum values of 16.4(2) K at 323 K and 59(6) J kg-1K-1 at 314 K, respectively, for a pressure change of 390 MPa. Besides, both ΔTS and ΔST have shown to be rather reversible. An influence of the glass transition on the barocaloric effects was verified: the glassy state tends to diminish the entropy and temperature changes in comparison with the rubbery state. Furthermore, we calculated the pressure coefficient of glass transition (dTg/dP) obtained from different processes. Our study evidences the potential of NBR for cooling applications based on barocaloric effect, but also points out the glass transition must be avoided for a better barocaloric performance.

cond-mat.mtrl-sci↗

arXiv2018

Giant barocaloric effects in natural rubber: A relevant step toward solid-state cooling

Solid-state cooling based on i-caloric effects has shown to be a promising alternative to the conventional refrigeration devices. Only very recently, the research on barocaloric materials is receiving a deal of attention due to the demonstration of giant barocaloric effects in shape-memory alloys. Regarding polymers, there is still a lack of literature, despite their high caloric potential. Thus, we present here giant barocaloric effects in natural rubber, a low-cost and environmental friendly elastomer polymer. The maximum values of entropy and temperature changes are larger than those previously reported for any promising barocaloric material. Moreover, the huge normalized temperature change and refrigerant capacity exhibited by natural rubber confirm its high potential for cooling applications. We also verify a relevant dependence of the barocaloric effect on the glass transition in natural rubber. Our findings suggest that commercial refrigeration devices based on barocaloric effects from elastomer polymers can be envisaged in the near future.

cond-mat.mtrl-sci↗

arXiv2018

Giant room-temperature barocaloric effects in PDMS rubber at low pressures

The barocaloric effect is still an incipient scientific topic, but it has been attracting an increasing attention in the last years due to the promising perspectives for its application in alternative cooling devices. Here, we present giant values of barocaloric entropy change and temperature change induced by low pressures in PDMS elastomer around room temperature. Adiabatic temperature changes of 12.0 K and 28.5 K were directly measured for pressure changes of 173 MPa and 390 MPa, respectively, associated with large normalized temperature changes (~70 K GPa-1). From adiabatic temperature change data, we obtained entropy change values larger than 140 J kg-1 K-1. We found barocaloric effect values that exceed those previously reported for any promising barocaloric materials from direct measurements of temperature change around room temperature. Our results stimulate the study of the barocaloric effect in elastomeric polymers and broaden the pathway to use this effect in solid-state cooling technologies.

cond-mat.mtrl-sci↗