The influence of low-temperature surface induction on evacuation, pump-out hole sealing and thermal performance of composite edge-sealed vacuum insulated glazing

Hermeticity of vacuum edge-sealing materials are one of the paramount requirements, specifically, to the evolution of energy-efficient smart windows and solar thermal evacuated flat plate collectors. This study reports the design, construction and performance of high-vacuum glazing fabrication system and vacuum insulated glazing (VIG). Experimental and theoretical investigations for the development of vacuum edgeseal made of Sn-Pb-Zn-Sb-AlTiSiCu composite in the proportion ratio of 56:39:3:1:1 by % (CS-186) are presented. Experimental investigations of the seven constructed VIG samples, each of size 300mm·300mm·4 mm, showed that increasing the hot-plate surface temperatures improved the cavity vacuum pressure whilst expediting the pump-out hole sealing process but also increases temperature induced stresses. Successful pump-out hole sealing process of VIG attained at the hot-plate set point temperature of 50˚C and the approximate cavity pressure of 0.042 Pa was achieved. An experimentally and theoretically validated finite volume model (FVM) was utilised. The centre-of-pane and total thermal transmittance values are calculated to be 0.91 Wm-2K-1 and 1.05 Wm-2K-1, respectively for the VIG. FVM results predicted that by reducing the width of vacuum edge seal and emissivity of coatings the thermal performance of the VIG is improved

An experimental investigation of the heat transfer and energy storage characteristics of a latent heat thermal energy storage system with a vertically-oriented multi-pass tube heat exchanger for domestic hot water applications

This paper presents the experimental performance analysis of a latent heat energy storage system (LHESS) designed for domestic hot water (DHW) applications. The designed, fabricated and characterised thermal store comprised of a vertically-oriented multi-pass tube heat exchanger in a rectangular cross-section container filled with PCM paraffin RT44HC. The experimental investigation evaluated the heat transfer within the system, measured the transient temperature distribution, determined the cumulative thermal energy stored, charging time and the instantaneous charging power. The experimental work was conducted under controlled experimental conditions using different heat transfer fluid (HTF) inlet temperatures and different volume flow rates for store charging. It was found that during charging process natural convection in the melt played a significant role. Higher HTF inlet temperature during charging significantly decreased store charging time. Increasing HTF inlet temperature from 60 to 70 oC shortened the charging time by 3.5 hours, a further increase to 80 oC decreased melting time by a further 2 hours

An experimental investigations of the melting of RT44HC inside a horizontal rectangular test cell subject to uniform wall heat flux

This study experimentally investigates the effect of different values of wall heat flux intensity on the melting of RT44HC Phase Change Material (PCM) in a rectangular test cell. A new novel experimental test rig to provide accurate data for the validation of numerical models of phase change was developed. The designed and constructed test rig consists of a horizontal rectangular cross-section test cell formed from polycarbonate sheet with copper plates and mica heaters to provide controlled uniform wall heat flux. Experiments were performed for three constant uniform wall heat flux values (q00 wall = 675, 960 and 1295 W/m2 ) applied to both left and right sides of the test cell. An imaging technique was used to visualize and record the movement of the solid-liquid interface using a Canon EOS DSLR Camera. The results obtained show a strong correlation between the magnitude of wall heat flux which drives the convective heat transfer and melt fraction development in the PCM. The results also show that increasing the input power from 675 W/m2 to 960 W/m2 to 1295 W/m2 reduces the total time for the melting process by 26.3% and 42.10% respectively. The raw data set comprised of measured temperatures and observation of melt fraction development provide a useful data set for validation of numerical models aiming to simulate the melting process in a rectangular cross-section test cell

Numerical investigation of the influence of mushy zone parameter Amush on heat transfer characteristics in vertically and horizontally oriented thermal energy storage systems

The effect of the value used for the mushy zone parameter (Amush) on predicted heat transfer and melting characteristics of a phase change material (PCM) Lauric acid, in both vertical and horizontal enclosures was studied. There is a lack of clarity regarding which value of this parameter should be used for accurate simulations of phase change heat transfer, addressing this will aid in accurate simulation and design of systems for LHTES (Latent heat thermal energy storage). The numerical analysis undertaken used a commercial CFD code ANSYS FLUENT 18.2 and the enthalpy-porosity formulation. The range of mushy zone parameter used was from 105 to 107. The predicted locations of the melt front were compared to published experimental data available in the literature. The simulations provided quantitative information about the amount of energy stored and the melt fraction and providing improved understanding of the heat transfer process. Comparison between predictions using different values of Amush, and experimental data showed that correct selection of the value of Amush to be used in the momentum equations is an important parameter for accurate modelling of LHTES and has a significant influence on the solid-liquid interface shape and progression. The study reveals that increasing the value of Amush leads to a decrease in fluid velocity, decreasing convection and the rate of heat transfer, therefore, proper selection of the mushy zone parameter is necessary to accurately simulate LHTES systems and provide a better understanding of the phase change behaviour and heat transfer characteristics

Characterizing contributions of glacier melt and groundwater during the dry season in a poorly gauged catchment of the Cordillera Blanca (Peru)

The retreat of glaciers in the tropics will have a significant impact on water resources. In order to overcome limitations with discontinuous to nonexistent hydrologic measurements in remote mountain watersheds, a hydrochemical and isotopic mass balance model is used to identify and characterize dry season water origins at the glacier fed Querococha basin located in southern Cordillera Blanca, Peru. Dry season water samples, collected intermittently between 1998 and 2007, were analyzed for major ions and the stable isotopes of water (δ<sup>18</sup>O and δ<sup>2</sup>H). The hydrochemical and isotopic data are analysed using conservative characteristics of selected tracers and relative contributions are calculated based on pre-identified contributing sources at mixing points sampled across the basin. The results show that during the dry-season, groundwater is the largest contributor to basin outflow and that the flux of groundwater is temporally variable. The groundwater contribution significantly correlates (P-value=0.004 to 0.044) to the antecedent precipitation regime at 3 and 18–36 months. Assuming this indicates a maximum of 4 years of precipitation accumulation in groundwater reserves, the Querococha watershed outflows are potentially vulnerable to multi-year droughts and climate related changes in the precipitation regime. The results show that the use of hydrochemical and isotopic data can contribute to hydrologic studies in remote, data poor regions, and that groundwater contribution to tropical proglacial hydrologic systems is a critical component of dry season discharge

Refurbishing the UK's 'hard to treat' dwelling stock: understanding challenges and constraints

Project CALEBRE (Consumer Appealing Low Energy technologies for Building REtrofitting) is a four year £2 million E.ON/RCUK funded project that is investigating technologies and developing solutions for the UK’s solid-wall houses to offer energy demand reduction, energy efficient heat generation and energy management combined with user appeal. Understanding how technical solutions can be aligned with householder lifestyles is central to the CALEBRE project. The technologies include: vacuum glazing to achieve exceptionally low U-values whilst being capable of retrofit in existing window frames; advanced gas and electric air source heat pumps that operate at the temperatures needed for integration with existing domestic radiator systems; innovative surface materials for buffering moisture, humidity and temperature; retrofit mechanical ventilation with heat recovery (MVHR) to manage ventilation and its associated heat loss. The technologies are being trialled in facilities that include the University of Nottingham E.ON 2016 House, a highly instrumented replica construction of a1930s dwelling. Alongside development and trialling, business case modelling of technologies is being conducted to establish mass roll-out strategies, as well as modelling to identify bespoke packages of measures for house refurbishment. This paper introduces Project CALEBRE, its content and scope, and reports some of its initial findings to highlight the challenges and constraints involved in the process of refurbishing the UK’s domestic stock

More questions than answers to the diagnosis and management of cauda equina syndrome-Authors' reply

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