Phase change dispersion properties, modeling apparent heat capacity

2017 ◽  
Vol 74 ◽  
pp. 240-253 ◽  
Author(s):  
L.J. Fischer ◽  
S. von Arx ◽  
U. Wechsler ◽  
S. Züst ◽  
J. Worlitschek
Keyword(s):  
Heat Capacity ◽  
Phase Change ◽  
Dispersion Properties ◽  
Apparent Heat Capacity

Thermal Modeling Solid-Liquid Phase Change Materials (PCMs)

2013 ◽  
Vol 746 ◽  
pp. 161-166
Author(s):  
Tao Hu ◽  
Yan Li ◽  
Duo Su ◽  
Hai Xia Lv
Keyword(s):  
Heat Capacity ◽  
Phase Change ◽  
Temperature Control ◽  
Phase Change Materials ◽  
Thermal Modeling ◽  
Effective Heat Capacity ◽  
Apparent Heat Capacity ◽  
Effective Heat ◽  
Solid Liquid ◽  
Capacity Method

Three thermal modeling methods for phase change materials (PCMs): enthalpy-based method, effective heat capacity method and apparent heat capacity method, are presented in details. Their characteristics and application limitations are compared and discussed. We found that enthalpy-based method and effective heat capacity method are both approximation treatments, and can be well used in steady state problems, while apparent heat capacity method tracks the moving phase change boundary in PCMs, and it is the most accurate and applicable method of the three for dealing with transient processes. This work might provide useful information for the study of using PCMs in temperature control field, especially in aircraft environmental temperature control and thermal management.

Nitrous oxide fluxes related to soil freeze and thaw periods identified using heat pulse probes

2010 ◽  
Vol 90 (3) ◽  
pp. 409-418 ◽  
Author(s):  
C. Wagner-Riddle ◽  
J. Rapai ◽  
J. Warland ◽  
A. Furon
Keyword(s):  
Heat Capacity ◽  
Nitrous Oxide ◽  
Phase Change ◽  
Conventional Tillage ◽  
Heat Pulse ◽  
Tunable Diode Laser ◽  
Water Phase ◽  
No Tillage ◽  
Apparent Heat Capacity

Surface N2O fluxes have not been unequivocally linked to soil profile conditions, in particular the timing of water phase change. The heated needle probe is a sensor that has the potential to monitor in situ apparent volumetric heat capacity (Ca), which considers latent heat transfer, during freezing and thawing. The objective of this study was to relate the timing of N2O flux to the occurrence of soil water phase change between liquid and ice as determined by Ca in no-tillage (NT) and conventional tillage (CT) plots monitored from fall to spring. Half-hourly micrometeorological N2O fluxes were measured using a tunable diode laser trace gas analyzer. Apparent heat capacity was measured at 5-cm depth using three 4-cm-long parallel needles, two equipped with thermistors and one with a heater. Two N2O flux events were observed for CT in January, followed by the main emission event in early March. For NT, only one emission event occurred, with lower magnitude than the CT event, and a later starting and ending date. The apparent heat capacity measured in situ with HPP showed a different temporal pattern between NT and CT, with CT presenting more phase change events. Two out of the three N2O emission events in CT that occurred during winter and early spring occurred immediately after phase change from ice to liquid water at 5-cm depth. The N2O flux associated with the phase change during the main thaw event in CT was an exponential function of the soil surface temperature increasing sharply when T > 0°C, but with smaller fluxes once T was > 5°C. The temperature response observed is consistent with the suggestion of a breakdown in the N2O reduction process in the 0 to 5°C range, while the N2O production enzymes are less affected by low temperature.Key words: Nitrous oxide flux, freeze-thaw cycles, heat pulse probes, no-tillage, conventional tillage

scholarly journals Testing a Gypsum Composite Based on Raw Gypsum with a Direct Admixture of Paraffin and Polymer to Improve Thermal Properties

Materials ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3241
Author(s):  
Krzysztof Powała ◽  
Andrzej Obraniak ◽  
Dariusz Heim
Keyword(s):  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermal Properties ◽  
Phase Change ◽  
Large Scale ◽  
Building Materials ◽  
Residential Buildings ◽  
Energy Performance ◽  
Polymer Content ◽  
Volumetric Heat Capacity

The implemented new legal regulations regarding thermal comfort, the energy performance of residential buildings, and proecological requirements require the design of new building materials, the use of which will improve the thermal efficiency of newly built and renovated buildings. Therefore, many companies producing building materials strive to improve the properties of their products by reducing the weight of the materials, increasing their mechanical properties, and improving their insulating properties. Currently, there are solutions in phase-change materials (PCM) production technology, such as microencapsulation, but its application on a large scale is extremely costly. This paper presents a solution to the abovementioned problem through the creation and testing of a composite, i.e., a new mixture of gypsum, paraffin, and polymer, which can be used in the production of plasterboard. The presented solution uses a material (PCM) which improves the thermal properties of the composite by taking advantage of the phase-change phenomenon. The study analyzes the influence of polymer content in the total mass of a composite in relation to its thermal conductivity, volumetric heat capacity, and diffusivity. Based on the results contained in this article, the best solution appears to be a mixture with 0.1% polymer content. It is definitely visible in the tests which use drying, hardening time, and paraffin absorption. It differs slightly from the best result in the thermal conductivity test, while it is comparable in terms of volumetric heat capacity and differs slightly from the best result in the thermal diffusivity test.

Thermal Analysis of Phase Change Material Based Heat Transfer Fluid in Solar Thermal Collector

2020 ◽  
Author(s):  
Tyler J. E. O’Neil ◽  
Celine S. L. Lim ◽  
Sarvenaz Sobhansarbandi
Keyword(s):  
Heat Capacity ◽  
Phase Change ◽  
Specific Heat ◽  
Specific Heat Capacity ◽  
Phase Change Materials ◽  
Solar Thermal ◽  
Heat Transfer Fluid ◽  
Liquid Form ◽  
High Specific Heat ◽  
Multi Walled Carbon Nanotubes

Abstract Phase change materials (PCMs) are commonly used as energy storage mediums in solar thermal systems. This paper investigates the mixture of PCM doped with nanoparticles to be used as HTFs directly integrated in a U-pipe ETC to be applied in solar thermal collectors. The selected type of PCM-HTF in this study is erythritol (C4H10O4), with high specific heat capacity in liquid form, as well as its unique sub-cooling behavior. In order to overcome the low thermal conductivity of erythritol and further enhance specific heat capacity, a weight concentration of 1% multi-walled carbon nanotubes (MWCNT) is added. Additionally, to insure even distribution of MWCNT and consistent properties of the HTF, triethanolamine (TEA) is proposed to be incorporated as a dispersant. The samples were each tested in a Thermogravimetric Analyzer (TGA) and Differential Scanning Calorimeter (DSC) to analyze their thermal properties. The results from the DSC tests show 12.4% enhancement of specific heat capacity of the proposed HTF mixture as well as nearly 5° C depression of freezing onset temperature. This study allows for the optimization of the operating temperature range of the collector when integrated with these materials, where direct heat gain can be obtained in the collector.

An experimental study of reflected liquefaction shock waves with near-critical downstream states in a test fluid of large molar heat capacity

1994 ◽  
Vol 277 ◽  
pp. 163-196 ◽  
Author(s):  
Seyfettin C. Gülen ◽  
Philip A. Thompson ◽  
Hung-Jai Cho
Keyword(s):  
Shock Wave ◽  
Heat Capacity ◽  
Phase Change ◽  
Molar Heat Capacity ◽  
Continuous Process ◽  
Nucleation And Growth ◽  
Test Fluid ◽  
Average Lifetime ◽  
Wave System ◽  
Two Phase

Near-critical states have been achieved downstream of a liquefaction shock wave, which is a shock reflected from the endwall of a shock tube. Photographs of the shocked test fluid (iso-octane) reveal a rich variety of phase-change phenomena. In addition to the existence of two-phase toroidal rings which have been previously reported, two-phase structures with a striking resemblance to dandelions and orange slices have been frequently observed. A model coupling the flow and nucleation dynamics is introduced to study the two-wave system of shock-induced condensation and the liquefaction shock wave in fluids of large molar heat capacity. In analogy to the one-dimensional Zeldovich–von Neumann–Döring (ZND) model of detonation waves, the leading part of the liquefaction shock wave is a gasdynamic pressure discontinuity (Δ ≈ 0.1 μm, τ ≈ 1 ns) which supersaturates the test fluid, and the phase transition takes place in the condensation relaxation zone (Δ ≈ 1–103 μm, τ ≈ 0.1–100 μs) via dropwise condensation. At weak to moderate shock strengths, the average lifetime of the metastable state, τ ∞ 1/J, is long such that the reaction zone is spatially decoupled from the forerunner shock wave, and J is the homogeneous nucleation rate. With increasing shock strength, a transition in the phase-change mechanism from nucleation and growth to spinodal decomposition is anticipated based on statistical mechanical arguments. In particular, within a complete liquefaction shock the metastable region is entirely bypassed, and the vapour decomposes inside the unstable region. This mechanism of unmixing in which nucleation and growth become one continuous process provides a consistent framework within which the observed irregularities can be explained.

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