Cooling vests with phase change materials: the effects of melting temperature on heat strain alleviation in an extremely hot environment

2010 ◽  
Vol 111 (6) ◽  
pp. 1207-1216 ◽  
Author(s):  
Chuansi Gao ◽  
Kalev Kuklane ◽  
Ingvar Holmér
Keyword(s):  
Phase Change ◽  
Melting Temperature ◽  
Phase Change Materials ◽  
Heat Strain ◽  
Hot Environment ◽  
Extremely Hot Environment

scholarly journals Breakdown of the Stokes-Einstein relation above the melting temperature in a liquid phase-change material

2018 ◽  
Vol 4 (11) ◽  
pp. eaat8632 ◽  
Author(s):  
Shuai Wei ◽  
Zach Evenson ◽  
Moritz Stolpe ◽  
Pierre Lucas ◽  
C. Austen Angell
Keyword(s):  
Liquid Phase ◽  
Phase Change ◽  
Melting Temperature ◽  
Phase Change Materials ◽  
Dynamic Properties ◽  
Switching Behavior ◽  
Einstein Relation ◽  
Elastic Neutron ◽  
Phase Switching ◽  
Memory Applications

The dynamic properties of liquid phase-change materials (PCMs), such as viscosity η and the atomic self-diffusion coefficientD, play an essential role in the ultrafast phase switching behavior of novel nonvolatile phase-change memory applications. To connect η toD, the Stokes-Einstein relation (SER) is commonly assumed to be valid at high temperatures near or above the melting temperatureTmand is often used for assessing liquid fragility (or crystal growth velocity) of technologically important PCMs. However, using quasi-elastic neutron scattering, we provide experimental evidence for a breakdown of the SER even at temperatures aboveTmin the high–atomic mobility state of a PCM, Ge1Sb2Te4. This implies that although viscosity may have strongly increased during cooling, diffusivity can remain high owing to early decoupling, being a favorable feature for the fast phase switching behavior of the high-fluidity PCM. We discuss the origin of the observation and propose the possible connection to a metal-semiconductor and fragile-strong transition hidden belowTm.

scholarly journals Temperature Control in (Translucent) Phase Change Materials Applied in Facades: A Numerical Study

Energies ◽  
2019 ◽  
Vol 12 (17) ◽  
pp. 3286 ◽  
Author(s):  
Tenpierik ◽  
Wattez ◽  
Turrin ◽  
Cosmatu ◽  
Tsafou
Keyword(s):  
Temperature Gradient ◽  
Phase Change ◽  
Specific Heat ◽  
Melting Temperature ◽  
Phase Change Materials ◽  
Numerical Study ◽  
Melting Process ◽  
Large Temperature ◽  
Energy Efficient Buildings ◽  
High Solar Radiation

Phase change materials (PCMs) are materials that can store large amounts of heat during their phase transition from solid to liquid without a significant increase in temperature. While going from liquid to solid this heat is again released. As such, these materials can play an important role in future energy-efficient buildings. If applied in facades as part of a thermal buffer strategy, e.g., capturing and temporarily storing solar energy in so-called Trombe walls, the PCMs are exposed to high solar radiation intensities, which may easily lead to issues of overheating. This paper therefore investigates the melting process of PCM and arrives at potential solutions for countering this overheating phenomenon. This study uses the simulation program Comsol to investigate the heat transfer through, melting of and fluid flow inside a block of PCM (3 × 20 cm2) with a melting temperature of around 25 °C. The density, specific heat and dynamic viscosity of the PCM are modeled as a temperature dependent variable. The latent heat of the PCM is modeled as part of the specific heat. One side of the block of PCM is exposed to a heat flux of 300 W/m2. The simulations show that once part of the PCM has melted convection arises transporting heat from the bottom of the block to its top. As a result, the top heats up faster than the bottom speeding up the melting process there. Furthermore, in high columns of PCM a large temperature gradient may arise due to this phenomenon. Segmenting a large volume of PCM into smaller volumes in height limits this convection thereby reducing the temperature gradient along the height of the block. Moreover, using PCMs with different melting temperature along the height of a block of PCM allows for controlling the speed with which a certain part of the PCM block starts melting. Segmenting the block of PCM using PCMs with different melting temperature along its height was found to give the most promising results for minimizing this overheating effect. Selecting the optimal phase change temperatures however is critical in that case.

ENERGY AND FEASIBILITY ANALYSIS OF APPLYING BIO-BASED PHASE CHANGE MATERIALS TO BUILDINGS IN EAST ASIA

2020 ◽  
Vol 15 (2) ◽  
pp. 157-181
Author(s):  
Abdo Abdullah Ahmed Gassar ◽  
Geun Young Yun ◽  
Sumin Kim ◽  
Choong-Hee Han
Keyword(s):  
Phase Change ◽  
East Asia ◽  
Melting Temperature ◽  
Phase Change Materials ◽  
Computer Modelling ◽  
High Heat ◽  
Economic Feasibility ◽  
Key Factor ◽  
High Heat Capacity ◽  
Phase Temperature

ABSTRACT The application of phase change materials (PCMs) in building envelopes can help promote energy efficiency due to its high heat capacity. Our study aimed to provide energy and economic insights for deploying PCM to buildings in eight different regions of East Asia through a series of energy and economic analysis using computer modelling and simulations. The static payback period (SPP) and dynamic payback (DPP) methods were used to evaluate the economic feasibility of applying a PCM at different melting phase temperatures (20°C, 23°C, 25°C, 27°C and 29°C). Results show that the proper choice of a PCM melting temperature is a key factor to improve the performance of the PCM applied to buildings. A melting phase temperature of 29°C achieved the highest economic feasibility in Seoul, Tokyo; Pyongyang; Beijing; and Ulaanbaatar and a melting temperature of 23°C in Hong Kong had the highest economic feasibility. Overall, the combined economic and energy analysis presented in this study can play an important role in improving the energy and economic feasibility of PCM in buildings.

scholarly journals PEMODELAN PHASE CHANGE MATERIALS PADA DISTRIBUSI TERMAL SELUBUNG BANGUNAN HOTEL

2018 ◽  
Vol 2 (1) ◽  
Author(s):  
Solli Dwi Murtyas ◽  
Siti Nur Cholida ◽  
Muhammad Kholid Ridwan
Keyword(s):  
Phase Change ◽  
Melting Temperature ◽  
Latent Heat ◽  
Phase Change Materials ◽  
Comsol Multiphysics

Phase change materials (PCM) merupakan salah satu rekayasa selubung bangunan berupa bahan atau substan tambahan yang diaplikasikan pada selubung bangunan. Tujuan penggunaan PCM yaitu menyerap termal dari lingkungan atau melepaskan termal ke lingkungan sebelum didistribusikan kedalam bangunan. PCM sebagai penyimpanan energi termal bangunan akan menyerap dan melepaskan energi termal pada suhu yang telah ditentukan dan dijaga. Dua pemodelan ruangan dengan dan tanpa PCM dilakukan menggunakan COMSOL Multiphysics 5.0. Hasil persebaran panas ruangan dengan dan tanpa PCM akan dibandingkan. Ruangan yang disimulasikan merupakan ruangan hotel Cakra Kusuma berukuran 5 x 3,95 x 3 m. PCM dengan ketebalan 1 cm ditempatkan pada eksterior selubung bangunan yang mendapatkan sinar matahari langsung. Jenis PCM yang digunakan adalah paraffin murni dengan melting temperature sebesar 28℃ dan latent heat sebesar 244 kJ/kg. Hasilnya menunjukkan bahwa pemakaian paraffin dengan melting temperature 28℃, cocok diaplikasikan pada ruangan. Hal ini dikarenakan suhu tersebut termasuk dalam rentang suhu di Provinsi Yogyakarta. Pengaplikasian PCM dapat mengurangi suhu rata - rata ruangan sebesar 0,81℃. Suhu maksimum ruangan yang menggunakan PCM terletak di sekitar pintu, di mana tidak terdapat aktifitas penghuni. Sedangkan suhu minimum ruangan berPCM terletak di permukaan ruangan yang bersentuhan dengan PCM dan ditengah ruangan

scholarly journals Phase Change Materials for Reducing Cooling Energy Demand and Improving Indoor Comfort: A Step-by-Step Retrofit of a Mediterranean Educational Building

Energies ◽  
2019 ◽  
Vol 12 (19) ◽  
pp. 3661 ◽  
Author(s):  
Fabrizio Ascione ◽  
Nicola Bianco ◽  
Rosa Francesca De Masi ◽  
Margherita Mastellone ◽  
Giuseppe Peter Vanoli
Keyword(s):  
Thermal Comfort ◽  
Phase Change ◽  
Melting Temperature ◽  
Thermal Insulation ◽  
Energy Demand ◽  
Phase Change Materials ◽  
Cool Roof ◽  
Indoor Thermal Comfort ◽  
Innovative Solutions ◽  
Indoor Comfort

The present work concerns the energy retrofit of a public educational building at the University of Molise, located in Termoli, South Italy. The study provides a comparison of the results obtained by different dynamic simulations of passive strategies to improve thermal comfort and energy behavior of the building during the summer regime. Firstly, the building model was calibrated against historical consumption data. Then, a subsequent step involves the technical-economic analysis, by means of building performance simulations, of energy upgrading scenarios, specifically, cool roof and green roof technologies for the horizontal opaque envelope and thermal insulation, vented façade, and phase change materials’ applications for the vertical opaque envelope. Improving the indoor thermal comfort and reducing the thermal energy demand during summertime through innovative solutions will be the primary objective of the present study. The energy efficiency measures are compared from the energy, emissions, costs, and indoor comfort points of view. Phase Change Materials applied to the inner side of the external walls are analyzed in depth and, by varying their melting temperature, optimization of design is performed too. This innovative material, with a melting temperature of 23 °C and a freezing temperature of 21 °C, determines the reduction of summer energy consumption of 11.7% and the increase of summer indoor comfort of 215 h. Even if consolidated, other solutions, like the cool roof, green roof, thermal insulation, and vented façade induce improvements in terms of summer energy saving, and the percentage difference compared to the basic building is less than 2%. For this case study, a Mediterranean building, with construction characteristics typical of the 1990s, traditional passive technologies are not very efficient in improving the energy performance, so the investigation focused on the adoption of innovative solutions such as PCMs, for reducing summer energy demand and improving indoor thermal comfort.

scholarly journals Fabrication and Characterization of Novel Shape-Stabilized Phase Change Materials Based on P(TDA-co-HDA)/GO Composites

Polymers ◽  
2019 ◽  
Vol 11 (7) ◽  
pp. 1113
Author(s):  
Sai Chen ◽  
Yue Yu ◽  
Ruirui Cao ◽  
Haihui Liu ◽  
Xingxiang Zhang
Keyword(s):  
Energy Storage ◽  
Phase Change ◽  
Melting Temperature ◽  
Phase Change Materials ◽  
Molar Ratio ◽  
Energy Storage Materials ◽  
The Novel ◽  
Acrylate Copolymer ◽  
Solution Blending ◽  
Blending Method

Shape-stabilized phase change materials (SPCMs) are green, reusable energy storage materials. Because the melting temperature of n-alkyl acrylate copolymer is adjustable by controlling the side-chain length, the appropriate melting temperature can be achieved. Poly(tetradecyl acrylate-co-hexadecyl acrylate) (P(TDA-co-HDA)) with a molar ratio of 1:1 and SPCMs were fabricated via an atom transfer radical polymerization (ATRP) method and a solution blending method with P(TDA-co-HDA) as a thermal storage material and graphene oxide (GO) as a supporting substance. In this composite, an SPCM was achieved, which absorbed heat at 29.9 °C and released it at 12.1 °C with a heat storage capacity of 70 J/g at a mass ratio of GO of 10%. The material retained its shape without any leakage at 60 °C, which was much higher than that of the melting temperature of P(TDA-co-HDA). The SPCMs exhibited good crystallization behaviors and excellent thermal reliabilities after 100 thermal cycles. The thermal properties of the P(TDA-co-HDA)/GO composite PCMs with various GO loadings were also investigated. The novel shape-stabilized PCMs fabricated in this study have potential uses in thermal energy storage applications.

Numerical Study of Phase Change of PCM in Spherical Cavities

2017 ◽  
Vol 372 ◽  
pp. 21-30 ◽  
Author(s):  
Fábio Faistauer ◽  
Petros Rodrigues ◽  
Rejane de Césaro Oliveski
Keyword(s):  
Phase Change ◽  
Melting Temperature ◽  
Wall Temperature ◽  
Phase Change Materials ◽  
Numerical Study ◽  
Liquid Fraction ◽  
Fluid Dynamic ◽  
Melting Process ◽  
Constant Wall Temperature ◽  
Spherical Cavities

This work presents a numerical study of the phase change process of PCM (Phase Change Materials) stored in spherical cavities. The numerical model is two-dimensional and it is composed by the equations of conservation of mass, momentum, energy and volumetric fraction, which are modeled using the enthalpy-porosity technique. The computational mesh is tetrahedral, with refinements on regions that have large thermic and fluid dynamic gradients. The numeric model was validated with result from literature. It was studied the melting process of PCM RT35, RT 55 and RT 82 in spherical cavity with constant wall temperature. Four diameters of spheres D were used (40, 60, 80 and 100 mm) and three temperature differences ΔT (10, 20 and 30 oC) between the wall temperature and the melting temperature of the PCM. Liquid fraction results from the 36 cases studied are presented. It was observed that the time required to reach a certain liquid fraction increases with the diameter and reduces with the increment of ΔT, being possible to predict the fusion time by knowing the characteristic length of the sphere. The largest percentage reduction of the fusion time was obtained with ΔT = 10 oC – 20 oC for all the D considered. The shortest fusion time was obtained with the largest ΔT combined with the smallest D. It is possible to see the dependence of the liquid fraction results in relation with the PCM properties and the its independence in relation its melting temperature, since all the PCM studied presented equal fusion time for the same ΔT and D.

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