Explore the vast range of titles available.

Phase-change materials (PCM) play off their advantages over conventional heat storage media when used within narrow temperature ranges. Many cooling and temperature buffering applications, such as cold storage and battery cooling, are operated within small temperature differences, and therefore, they are well-suited for the application of these promising materials. In this study, the storage capacities of different phase-change material emulsions are analysed under consideration of the phase transition behaviour and supercooling effect, which are caused by the submicron size scale of the PCM particles in the emulsion. For comparison reasons, the same formulation for the emulsions was used to emulsify 35 wt.% of different paraffins with different purities and melting temperatures between 16 and 40 °C. Enthalpy curves based on differential scanning calorimeter (DSC) measurements are used to calculate the storage capacities within the characteristic and defined temperatures. The enthalpy differences for the emulsions, including the first phase transition, are in a range between 69 and 96 kJ/kg within temperature differences between 6.5 and 10 K. This led to an increase of the storage capacity by a factor of 2–2.7 in comparison to water operated within the same temperature intervals. The study also shows that purer paraffins, which have a much higher enthalpy than blends, reveal, in some cases, a lower increase of the storage capacity in the comparison due to unfavourable crystallisation behaviour when emulsified. In a second analysis, the stability of emulsions was investigated by applying 100 thermal cycles with defined mechanical stress at the same time. An analysis of the viscosity, particle size and melting crystallisation behaviour was done by showing the changes in each property due to the cycling.

Background In the development process of holographic displays like holographic Head-Mounted Displays (hHMD) the simulation of the complete optical system is strongly required. This especially includes the correct behaviour of the volume holographic grating (VHG) in terms of its optical function and its diffraction efficiency. The latter is not supported by the current version of Zemax®; OpticStudio 17, one of the most popular optic simulation tools. Methods To solve this problem we implemented a C++ code for each raytracing mode of Zemax®;, namely the sequential and non-sequential. The C++ code calculates the grating vector for every single ray traced. Based on the k-sphere formalism the propagation direction of the diffracted light is determined. Furthermore, its diffraction efficiency is defined according to Kogelnik’s coupled-wave theory. The C++ code is compiled and linked into Zemax®; using the Windows Dynamic Link Library (DLL). Results and discussion The aforementioned DLL enables the simulation of planar and arbitrarily spherical curved VHG and their diffraction efficiency within Zemax®; OpticStudio. This allows the fast, easy and reliable simulation of optical systems which include holograms or holographic optical elements, e.g. hHMD. Especially the simulation of VHG in non-sequential mode can be helpful in order to identify possible stray light paths. Conclusion The implemented C++ code enables the user to simulate VHG and its diffraction efficiency within Zemax®; Optic Studio.

Ice slurries effectively utilize latent heat, but are generally restricted to temperatures around 0°C. Below this threshold, oil‐based cooling is often used, yet oil alone offers limited sensible heat capacity and is expensive compared to water. To overcome these limitations, this study aims to create a water‐in‐oil (W/O) phase change emulsion that combines the benefits of the high latent heat of (salt) water with an oil‐based matrix to maintain flowability at subzero temperatures. The freezing temperature of an aqueous ammonium sulfate solution is reduced to −18°C and shows additional supercooling when dispersed in oil, pushing the solidification temperature below −48°C. Adding polyethylene glycol (PEG‐600) as a nucleation agent mitigates supercooling from over 30 to about 3 K as proven by thermal analysis. A tailored surfactant system based on Tween 80 (T80) and Span 85 (S85) with a hydrophilic–lipophilic balance (HLB) near 7 stabilizes a 30 wt% water phase in thermal oil, thus, harnessing the latent heat of water without compromising pumpability. Measured enthalpy values reach about half the theoretical maximum of 116 J g −1 in a 10 K wide phase change region, offering more than three times the storage capacity of pure oil. Thermomechanical investigations show the emulsions’ capability to withstand repeated freeze–thaw cycles, ensuring kinetic stability for cold transport applications. This study demonstrates how W/O emulsions provide outstanding thermal performance and remain flowable below 0°C. Thereby, key shortcomings of both ice slurries and oil‐based coolants are resolved, unlocking the potential for future high‐performance solutions in cold storage and transport.