Evaluation Of Phase Change Research Articles

Evaluation of phase change plaster/paste composites for building envelopes

Thermal energy storage (TES) materials increase a building’s thermal mass and provide the flexibility to shave and time-shift energy use. These materials are needed to enable grid-interactive efficient buildings, allowing building occupants to lower costs by leveraging free ambient heating/cooling as well as shifting consumption to cheaper electricity periods. Phase change materials (PCMs) that store heat through a solid–liquid/solid–solid transformation are of particular interest for TES because of their ability to store large amounts of energy across a constant temperature or very small temperature range. Previous studies on PCM building envelopes evaluated products that may only be incorporated as part of new construction and are not easily applicable to existing, energy-intensive buildings. In this work, we leverage laboratory PCM characterization and whole-building energy simulation to study the energy and cost savings of PCM plaster/paste coatings, which can be applied post construction to both new builds and retrofits of existing buildings (about 40% of residential buildings in the United States fall into the retrofit category). We evaluated the energy impact of PCM plaster/paste composites for a single-family residential building in the United States, including layer design (location and thickness), composite properties (phase change temperature, energy density, and shape of the enthalpy curve), and U.S. climate zone. The enthalpy curve shape of PCM shows that phase change temperature and energy density are not the only two parameters that must be considered for PCM selection. Maximizing the energy density amid the effective TES zone is key to boosting energy savings. We also studied PCM price targets with the aim of achieving reasonable payback periods based on both block and time-of-use electricity rates. Moreover, we developed an empirical equation to provide a rough estimate of the energy savings potential of incorporating PCM without the need to perform detailed simulations. These results will help guide the selection and design of PCM plaster/paste composite elements for residential building envelopes.

Interferometric detection of 3D motion using computational subapertures in optical coherence tomography.

Doppler optical coherence tomography (OCT) quantifies axial motion with high precision, whereas lateral motion cannot be detected by a mere evaluation of phase changes. This problem was solved by the introduction of three-beam Doppler OCT, which, however, entails a high experimental effort. Here, we present the numerical analogue to this experimental approach. Phase-stable complex-valued OCT datasets, recorded with full-field swept-source OCT, are filtered in the Fourier domain to limit imaging to different computational subapertures. These are used to calculate all three components of the motion vector with interferometric precision. As known from conventional Doppler OCT for axial motion only, the achievable accuracy exceeds the actual imaging resolution by orders of magnitude in all three dimensions. The feasibility of this method is first demonstrated by quantifying micro-rotation of a scattering sample. Subsequently, a potential application is explored by recording the 3D motion vector field of tissue during laser photocoagulation in ex-vivo porcine retina.

Effect of post-cure temperature and different reinforcements in adhesive bonded repair for damaged glass/epoxy composites under multiple quasi-static indentation loading

This paper investigates the individual and associated effects of post-cure temperature and reinforcement phases on the local bending response of adhesive reinforced repairs in damaged glass/epoxy composite laminates. Multiple quasi-static indentation tests were performed on repaired composite laminates: damage propagation, absorbed energy and residual deflection data assisted in the evaluation of phase changes, which cause the transition from brittle to ductile nature and control the visco-elastic behavior the material is undergoing under the influence of temperature. Three phases of fiber reinforcements, namely particulate glass fibers, chopped short glass fibers and continuous glass fibers, were tested to study the fiber reinforcement’s effect on indentation strength and damage mechanism. The effects of post-cure temperature on the local bending response of the repaired glass/epoxy specimens were investigated by performing indentation tests on laminates exposed to post-cure at ambient temperature (30°C) and elevated temperatures up to glass transition temperature of epoxy resin (50, 70 and 90°C). Multiple quasi-static indentation test results indicated that the post-cure temperature and fiber reinforcements have considerable effect on the indentation response of the repaired specimens. Damaged glass/epoxy specimens repaired using chopped short fibers and exposed to a post-cure temperature of 50°C showed the most favorable indentation behavior.