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

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

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

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

Supplementary information files for Super-liquid-repellent thin film materials for low temperature latent heat thermal energy storage: A comprehensive review of materials for dip-coating

CC BY 4.0 © The Authors 2024Supplementary files for article Super-liquid-repellent thin film materials for low temperature latent heat thermal energy storage: A comprehensive review of materials for dip-coatingWhen discharging latent heat thermal energy storage (LHTES) systems, performance is influenced by the formation and adherence of a solid layer of phase change material (PCM) on heat eXchange (HX) surfaces. Super‐liquid‐repellent thin films (STFs) may be able to reduce solidifying PCM adhesion on HX surfaces during discharging, delay PCM solidification to lower temperatures, and by modifying nucleation sites potentially enable long‐term seasonal thermal storage. Techniques employed previously to fabricate sintered polymeric STF coatings include chemical vapour deposition, dip‐coating, spray‐coating, spin‐coating, layer‐by‐layer (LbL) assembly, sol‐gel, anodizing, electrodeposition, electrospinning, so on. Dip‐coating is considered attractive for fabricating thin films on simple and complex surface geometries due to process maturity, scalability, flexibility and cost‐effectiveness. To identify suitable materials for preparing STFs on metal HX surfaces using the dip‐coating process, more than 200 journal articles published in English during the period 2010 to 2022 were reviewed and the potential role of STFs in LHTES applications was assessed. The review identified key areas and applications stimulating STF material developments and formulations. The dip‐coating of potential STF materials was classified under three major themes driving current research and development (R&D) activities, that is, high performance thin films, eco‐friendly thin films and fundamental research formulations. This review provides a platform from which to develop coatings and HX systems to enable the cost‐effective implementation of STFs for improved heat transfer in future mobile/stationery LHTES systems.</p

A comparative study of the effect of varying wall heat flux on melting characteristics of phase change material RT44HC in rectangular test cells

Results of an extensive experimental investigation performed to study the effect of different values of wall heat flux in a rectangular PCM (phase change material) test cell on the melting process are presented. A new experimental system consisting of a rectangular cross-section test cell formed from polycarbonate sheet, copper plates and mica heaters was constructed. During experiments uniform wall heat flux (q″wall = 675, 960 and 1295 W/m2) were applied to both the left and right sides of the test cell. Thermocouples were used to measure the temperature at different locations inside the PCM and on the surface of the copper plates and an infrared camera was used to measure the polycarbonate sheet external surface temperature distribution. The results show the expected strong correlation between the magnitude of wall heat flux and the melt fraction in the PCM as it drives the convective heat transfer. The transparent polycarbonate wall makes it possible to observe the location of the solid/liquid interface and determine melt fractions. The experiments have produced a significant experimental data set for the validation of numerical models simulating the solid/liquid phase change process and PCM melting in geometrical configurations relevant to, for example, latent heat thermal energy storage systems