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Thermal illusion device, which can change an arbitrary object into another one when observed from an infrared vision, recently has attracted considerable attention amongst a series of innovative thermal phenomena by resorting to the unique thermal metamaterial. To enhance the illusion deceptiveness, current thermal illusion devices mostly change the location or shape of the target, but seldom deal with the number of heat signatures. In this paper, we develop a general formula to enhance the illusion deceptiveness by splitting the thermal target to appear like thermal bilocation with twinborn distinct heat signatures. The exhaustive design process based on transformation thermodynamics is rigorously introduced in order to realize thermal bilocation. Simulative and experimental results agree well with each other and validate the conception of thermal bilocation. Additionally, the influence of three structure parameters on the bilocation effects has been considered for further optimization. Our device can thermally camouflage the original target with twinborn signatures at different locations, improving the deceptiveness greatly compared with only moving or reshaping. The present thermal bilocation not only can fortify the performance of thermal camouflage, but also can stimulate the extension of illusion thermodynamics to further physical applications.

Solid–liquid phase change materials (PCMs) are attractive candidates for thermal energy storage and electronics cooling applications, but once all the PCMs have completely phase-changed and approximate their thermal storage limit, they will become the bottleneck for heat dissipation on the contrary and the electronics have to stop working. In this paper, a modularized thermal storage unit (MTSU) was proposed to overcome such fatal drawback. Once the PCMs reach their limit, the completely phase-changed MTSU will be replaced by a new one due to the modularization. Such online thermal charging and offline thermal discharging working characteristics enable the continuous working of electronics. The proposed MTSU is fabricated by encapsulating paraffin with epoxy resin, and the paraffin is thermally enhanced via copper or nickel foams. Theoretical and experimental validations reveal that the ETC is increased by 376% via copper foam with the porosity of 95.52%, and by 205% for nickel foam with the porosity of 95.61% due to the relatively lower skeleton thermal conductivity of nickel foam. The cycled test revealed that the proposed MTSU has good thermal stability. Compared with the conventional TSU, the proposed MTSU avoids the slow re-solidification process and exhibits potential for continuous thermal storage over long periods of time. The proposed MTSU is expected to be applied in the field of driving batteries and solar-thermal conversion system.

Laser-excited remote phosphor (LERP) has been reported to be an effective approach to produce high-luminance white light based on laser diodes (LDs). However, the local phosphor temperature may easily reach thermal quenching point due to the local high light power density, resulting in a significant drop/deterioration of efficiency, reliability and lifetime. In this paper, we focused on the phosphor thermal quenching and developed an optical-thermal coupling model to predict the high phosphor temperature of LERP. From this model, both accurate phosphor heating and temperature can be obtained by iteration. For validation, experiments were performed to verify the model and good agreement was observed between the measurements and the theoretical predictions. Based on the validated model, the critical incident power against thermal quenching under various factors was systematically studied. It was found in the experiments that when a 680 mW laser spot with a diameter of 1.0 mm was projected onto a phosphor layer, the phosphor temperature was as high as 549.0 °C, which would result in severe thermal quenching and even silicone carbonization. It was also found that increasing pump spot from 0.5 mm to 3.0 mm can dramatically enhance critical power by 19 times. The effect of decreasing phosphor layer thickness on critical power enhancement was explained by the model. Some suggestions were also provided to prevent thermal quenching and improve the optical/thermal performance of LERP.

Thermal metamaterials have been extensively studied due to their extraordinary properties beyond natural materials and offered great flexibilities to tune heat flow for desired thermal functionalities, like thermal cloaking, concentrating, rotating, etc. Whereas, the thermal properties of thermal metamaterials are usually fixed once the configuration and the constituent materials are designed and fabricated. For instance, the thermal cloaking effect may be deteriorated when background changes, which limits its practical application significantly. By deducing the effective thermal conductivities of rotating objects, we propose an adaptive thermal cloaking metadevice that is composed by three rotating layers with different roles. The joint effect of three rotating layers makes the effective thermal conductivity a real number on the reciprocity line for feasible implementation. When background changes, we only need change the angular velocities rather than change the configuration or the constituent materials to restore the cloaking effect, which is much more convenient and real-time for practical applications. The underlying physics of the rotating thermal cloak is discussed to identify the key parameters and upper and lower limits of the effective thermal conductivity for further improving the cloaking effect. The present study can trigger more rotating metadevices for novel applications beyond thermal cloaking.

Besides the junction temperature, phosphor temperature is another key parameter to characterize the thermal behavior of phosphor-converted light-emitting diodes (pc-LEDs). However, the measurement of phosphor temperature remains a challenge. In this paper, we proposed a modified bidirectional thermal resistance model for the junction and phosphor temperature estimation. Compared with the conventional thermal resistance model, both the heat generation of the phosphor layer and the heat flow through the phosphor layer were further considered in this model. Three LED packaging structures were fabricated and measured to complete the model. The heat generation of the chip and phosphor layer was measured. With varying driving current from 0.05 A to 0.65 A with an increment of 0.1 A, the maximum deviation of the predicted and measured junction and phosphor temperature is less than 1% and 9.2%, respectively, which proves the feasibility of the proposed model for the junction and phosphor temperature estimation.

The diffusive nature of heat flow lays a formidable obstacle for directional heat manipulation, not akin to the wave-governed electromagnetics that can be well controlled in intensity and direction. By modulating the near-field radiative heat transfer among graphene/SiC core-shell (GSCS) nanoparticles, we propose the concept of thermal routing to address the directional heat manipulation in a particular many-body setup. The graphene shell introduces a minor polarizability peak and remarkably modifies the localized surface resonance of the particle, which plays a significant role in the radiative heat transfer within the many-body system consisting of GSCS nanoparticles. Consequently, Fermi levels of graphene shells matching allows directional radiative heat flow, thus enabling thermal routing manifested by variant designated temperature distributions. The proposed thermal routing could be used to dynamically tune heat flow in integrated nano-objects for thermal manipulation, and also opens avenues for exploiting novel thermal functionalities via radiative heat transfer at the nanoscale.

In this study, genetic algorithm (GA) was utilized to optimize the phosphor distribution to decrease the junction temperature of white phosphor-converted light-emitting diodes (pc-LEDs). The key steps of the GA were introduced, including selection, crossover, and mutation. Both the junction temperature and the entransy dissipation of each evolution were calculated. It was found that with evolutions, the phosphor particles tend to build a “thermal bridge” between the chip and the convective boundary and spread along the convective boundary. The junction temperature decreases from ∼157.5 °C to ∼150 °C and the entransy dissipation decreases from ∼18 W K to ∼6 W K. The least entransy dissipation principle was demonstrated to be the rule that governs the optimization processes.

Phosphor heat generation in phosphor-converted light-emitting diodes (pc-LEDs) plays an important role in affecting the optical and thermal performance of LEDs, but it is hard to measure directly. In this paper, we developed a method to calculate the phosphor heat generation by modifying the Kubelka–Munk theory. With full consideration of light scattering, absorption and conversion inside the phosphor layer simultaneously, we calculated the phosphor heat generation and analyzed its trend with changing the phosphor quantum efficiency and phosphor parameters (concentration, thickness, particle size). Experiments were also conducted to validate the calculations. It was found that with the increase of phosphor concentration from 0.11 to 0.34 g/cm 3 , the total energy loss increases by 54.11%. The phosphor concentration and thickness played similar roles in affecting the phosphor heat generation. The maximum phosphor heat generation corresponded to the phosphor particle size of around 2 μm, which is denoted as the critical size.