Transparent Vacuum Insulation Panels

New, low-cost transparent vacuum insulation panels (TVIPs) using structured cores for the windows of existing buildings are proposed. The TVIP is produced by inserting the structured core, the low-emissivity film, and the adsorbent into the transparent gas barrier envelopes. In this chapter, the authors introduce the outlines, the design and thermal analysis method, the performance evaluation (test) method. Firstly, five spacers, namely peek, modified peek, mesh, silica aerogel, and frame, are selected as the structured core. The effective thermal conductivity of TVIPs with five different spacers is evaluated at different pressure levels by applying numerical calculation. The result indicated that TVIPs with frame and mesh spacers accomplish better insulation performance, with a center-of-panel apparent thermal conductivity of 7.0 × 10−3 W/m K at a pressure of 1 Pa. The apparent thermal conductivity is the same as the value obtained by the simultaneous evacuation thermal conductivity measurement applying the heat flux meter method. Furthermore, using a frame-type TVIP with a total thickness of 3 mm attached to an existing window as a curtain decreases the space heat loss by approximately 69.5%, whereas the light transparency decreases to 75%.

Effects of Microscopic Properties on Macroscopic Thermal Conductivity for Convective Heat Transfer in Porous Materials

Porous materials are widely used in many heat transfer applications. Modeling porous materials at the microscopic level can accurately incorporate the detailed structure and substance parameters and thus provides valuable information for the complex heat transfer processes in such media. In this study, we use the generalized periodic boundary condition for pore-scale simulations of thermal flows in porous materials. A two-dimensional porous model consisting of circular solid domains is considered, and comprehensive simulations are performed to study the influences on macroscopic thermal conductivity from several microscopic system parameters, including the porosity, Reynolds number, and periodic unit aspect ratio and the thermal conductance at the solid–fluid interface. Our results show that, even at the same porosity and Reynolds number, the aspect ratio of the periodic unit and the interfacial thermal conductance can significantly affect the macroscopic thermal behaviors of porous materials. Qualitative analysis is also provided to relate the apparent thermal conductivity to the complex flow and temperature distributions in the microscopic porous structure. The method, findings and discussions presented in this paper could be useful for fundamental studies, material development, and engineering applications of porous thermal flow systems.

Experimental Investigation of the Apparent Thermal Conductivity of Microencapsulated Phase-Change-Material Slurry at the Phase-Transition Temperature

The article presents the results of detailed studies of the thermal conductivity of the water slurry of microencapsulated PCM (mPCM) and slurry based on water–propylene glycol solutions. The starting product, MICRONAL® 5428 X, which contains about 43% microencapsulated paraffin with a transformation temperature of 28 °C, was mixed with the base liquid to obtain slurries with mass fractions of mPCM of 4.3, 8.6, 12.9, 17.2, 21.5, 25.8, 30.1, 34.4, 38.7, and 43.0%. Detailed measurements were carried out in the temperature range of 10–40 °C. It was found that: (a) an increase in the temperature of the slurry caused an increase in its thermal conductivity, both when PCM was in the form of a solid and a liquid; (b) the thermal conductivity of the mPCM slurry when the PCM was in liquid form was greater than the thermal conductivity of the slurry when the PCM was liquid; (c) during the phase transformation, a significant increase in the thermal conductivity of the slurry was observed, and its peak occurred when the temperature of the slurry reached the temperature declared by the manufacturer at which the phase-transition peak occurs.

Effect of Groundwater Flow and Thermal Conductivity on the Ground Source Heat Pump Performance at Bangkok and Hanoi: A Numerical Study

In recent decades, the fast-growing economies of Southeast Asian countries have increased the regional energy demand per capita. The statistic indicates Southeast Asian electricity consumption grows for almost 6% annually, with space cooling becoming the fastest-growing share of electricity use. The ground source heat pump technology could be one of the solutions to improve energy efficiency. However, currently, there are limited data on how a ground source heat pump could perform in such a climate. The thermal response test is widely used to evaluate the apparent thermal conductivity of the soil surrounding the ground heat exchanger. In common practice, the apparent thermal conductivity can be calculated from the test result using an analytical solution of the infinite line source method. The main limitation of this method is the negligence of the physical effect of convective heat transfer due to groundwater flow. While convection and dispersion of heat are two distinctive phenomena, failure to account for both effects separately could lead to an error, especially in high groundwater flow. This chapter discusses the numerical evaluation of thermal response test results in Bangkok, Thailand, and Hanoi, Vietnam. We applied a moving infinite line source analytical model to evaluate the value of thermal conductivity and groundwater flow velocity. While determining the ground thermal properties in a high accuracy is difficult, the moving infinite line source method fulfills the limitation of the infinite line source method. Further, we evaluated the five-year performance of the ground source heat pump system coupled with two vertical ground heat exchangers in Bangkok and Hanoi. The results suggest the importance of groundwater flow to enhance the thermal performance of the system.

Influence of Particle Size Distribution on the Physical Characteristics of Pore-Filling Hydrate-Bearing Sediment

Nature gas hydrates (NGHs) are regarded as a potential alternative energy source due to their huge reserves and wide distribution. According to the geophysical surveys, the pore-filling hydrates occupy a large proportion of the global hydrate reserves, especially for the marine regions. Therefore, with a novel pore-scale 3D morphological modeling algorithm, this study systematically studied the effect of the particle size on the physical characteristics of the pore-filling hydrate-bearing sediment (HBS). The pore system evaluations and permeability simulations were performed by utilizing pore network modeling (PNM), and the thermal and electrical simulations were conducted by utilizing a finite volume method (FVM). The results show that for the HBS with smaller particle size, the average radius of the pores and throats would also be reduced, and the fractal dimension of the pore system would be increased. In addition, with the increasing hydrate saturation, the fractal dimension of the pore system will increase firstly and then decrease. And these parameter evolutions could impact the physical properties correspondingly; specifically, the decreasing particle size in the HBS would reduce the permeability and electrical conductivity of HBS and enhance the apparent thermal conductivity of HBS.

Experimental And Numerical Invetigation Of Dependence Of Soil Thermal Conductivity On Temperature Water Content, And Soil Texture

Comprehensive set of thermal conductivity data for a loam soil was generated, for temperature variations from 5ºC to 92ºC and water content variations from dry to saturation, and compared to two other soil textures. The results exhibited similar characteristics as those of the other textures, where a significant change in soil thermal conductivity was. Using the thermal conductivity data sets, a model representing heat and mass transfer in soil was used to study the apparent thermal conductivity due to vapour migration. In addition, a computer simulation of a ground source heat pump system was developed, where the experimental data was used to investigate the impact of water content and soil texture variation on the GSHP performance. It was observed that the GSHP energy consumption varied more prominently when the soil wetness varied from dryness to full saturation and less significantly when the soil type varied from coarse to finer texture.

Experimental And Numerical Invetigation Of Dependence Of Soil Thermal Conductivity On Temperature Water Content, And Soil Texture

Comprehensive set of thermal conductivity data for a loam soil was generated, for temperature variations from 5ºC to 92ºC and water content variations from dry to saturation, and compared to two other soil textures. The results exhibited similar characteristics as those of the other textures, where a significant change in soil thermal conductivity was. Using the thermal conductivity data sets, a model representing heat and mass transfer in soil was used to study the apparent thermal conductivity due to vapour migration. In addition, a computer simulation of a ground source heat pump system was developed, where the experimental data was used to investigate the impact of water content and soil texture variation on the GSHP performance. It was observed that the GSHP energy consumption varied more prominently when the soil wetness varied from dryness to full saturation and less significantly when the soil type varied from coarse to finer texture.

Experimental Study of the Thermal Behavior of a Watercress Planted Roofed Cubic Cell to be Watered with Domestic Wastewater

One of the virtues of watercress is its ability to grow in wastewater. This work aims at experimentally studying the thermal behavior of a watercress planted roofed cubic cell. To do this, the temperatures of various components of the cell and the solar radiation received by this cell were measured in order to compare the watercress roof performance with that of the conventional concrete roof. Then, the influence of the opening applied on the door of the studied cell was analyzed. As results, the fluctuation amplitude of the indoor ambient temperature of the concrete roofed cell is wider than that of the green roofed cell. Moreover, the last opening applied to the facades of the cell was the optimum area that the ambient temperature indoor was more attenuated. The LAI’s crop was worth 1.2. In addition, the low value of the canopy apparent thermal conductivity revealed that this layer plays a role of thermal insulation. The rooftop greening allows energy savings of about 85% compared to the consumed energy with conventional roofing. An extension of this work could be the energy performance analysis of a system using renewable energy for pumping domestic wastewater produced in or around green roofed housing.

Assessing the time-step dependency of calculating supraglacial debris thermal diffusivity from vertical temperature profiles

<p>Debris thermal conductivity is a critical parameter in calculating a glacier’s sub-debris ice melt. The method widely used in publications to calculate apparent thermal conductivity of supraglacial debris layers is based on an estimate of volumetric heat capacity of the debris and simple heat diffusion principles and is presented in . The analysis of heat diffusion requires a vertical array of temperature measurements through the supraglacial debris cover. This study explores the effect of the temperature sampling interval on the thermal conductivity values derived using this method. Initial results indicate that the thermal diffusivity decreases linearly with an increasing sampling time from 30min to 6h by 0.2-0.4 mm²/s for glaciers in high mountain Asia during the monsoon season. These results suggest that care must be taken in choosing the analysis time interval for computing debris thermal conductivity and for comparing values between datasets sampled at different intervals. Current research aims to further investigate the cause of the artifact and determine how this problem can be solved. An open-source web application is therefore developed to help other scientists investigate the effect of the sampling interval on their calculated sub-debris ice melt. This study falls under the remit of the on debris-covered glaciers and is supported by data provided from within this group.</p>