scholarly journals PoDIT: Portable Device for Indoor Temperature Stabilization: Concept and Theoretical Performance Assessment

Energies ◽  
2020 ◽  
Vol 13 (22) ◽  
pp. 5982
Author(s):  
Vítor Leal ◽  
Raul Teixeira
Keyword(s):  
Natural Convection ◽  
Forced Convection ◽  
Heat Waves ◽  
Low Cost ◽  
Building Envelope ◽  
Portable Device ◽  
Temperature Stabilization ◽  
Indoor Temperature ◽  
Solid Liquid ◽  
Change Material

This work introduces the concept of a new Portable Device for Indoor Temperature Stabilization (PoDIT), to be considered as a low-cost, quick and easy to implement remediation strategy when, for social, economic, or technical reasons, the improvement of the building envelope and/or the adoption of air conditioning are not possible. The main goal is to attenuate the maximum indoor temperature during summer and/or heat waves. The system, which is modular, consists of a certain mass of encaged phase change material (PCM) that stays indoors during the daytime and is transported to the outdoors (e.g., a balcony) during the night to discharge the heat accumulated during the daytime. Both natural convection and forced convection variants were considered. The results showed that, in the configurations and for the reference room and weather considered, the adopting 4 modules of the device can lead to reductions in the maximum room air temperature close to 3 °C, with natural convection. Adopting a fan to impose forced convection at the surfaces of the device can lead to temperature attenuations in excess of 4 °C, as it ensures full solid–liquid commuting and therefore optimal use of the PCM thermal storage capability.

Solidification of a Liquid Metal with Natural Convection in a Thick-Walled Container

1999 ◽  
Vol 15 (2) ◽  
pp. 47-55
Author(s):  
H. C. Tien ◽  
C.C. Wang
Keyword(s):  
Natural Convection ◽  
Weighting Function ◽  
Solidification Rate ◽  
Thermal Contact ◽  
Solidification Process ◽  
External Cooling ◽  
Implicit Solver ◽  
Solid Liquid Interface ◽  
Solid Liquid ◽  
Change Material

ABSTRACTThe solidification of a phase change material (PCM), exemplified by a molten metal, in a thick-walled container is analyzed in this paper. The effects of natural convection and several important controlling parameters are investigated extensively. These parameters include the initial temperature of the PCM, external cooling conditions, thickness and thermal properties of the wall, and the thermal contact resistance at the PCM/wall interface. Two representative configurations are examined in this study. A modified version of the enthalpy formulation in which the sensible heat is separated from the latent heat, is employed to construct the energy equation for the PCM. Vorticity-stream-function approach is adopted for solving the flow field. The governing equations pertinent to the problem are discretized by the weighting function scheme and finally solved by the SIS (Strongly Implicit Solver) algorithm. It is demonstrated that for both configurations natural convection has prominent effect on the temperature distribution of the liquid phase of the PCM; however, the effect of natural convection on the shape of the solid/liquid interface and the overall solid fraction is case dependent. It is also shown that the above-mentioned controlling parameters have a direct impact on the solidification process. Specifically, an increase in the Biot number (from 1 to infinity) and the thermal diffusivity of the mold (from 0.8 to 5) enhances the solidification rate. Reverse effect was found for the other controlling parameters.

NUMERICAL STUDY OF NATURAL CONVECTION DOMINATED MELTING OF A PCM WITH CONJUGATE FORCED CONVECTION

1995 ◽  
Vol 19 (4) ◽  
pp. 455-469
Author(s):  
M. Lacroix
Keyword(s):  
Thermal Conductivity ◽  
Natural Convection ◽  
Forced Convection ◽  
Numerical Study ◽  
Convection Heat Transfer ◽  
Melting Process ◽  
Reynolds Numbers ◽  
Solid Liquid Interface ◽  
Solid Liquid ◽  
Convection Dominated

This paper presents a numerical analysis of natural convection dominated melting inside a rectangular enclosure coupled with forced convection heat transfer in a transport fluid via a finite conductance heat exchanging surface. A computational methodology based on a stream function-vorticity-temperature formulation is adopted and the irregular shape of the moving solid-liquid interface is treated with body-fitted coordinates. The model is then employed to investigate the interaction between natural convection in the PCM filled cavity and forced convection in the HTF. Numerical experiments were carried out for Rayleigh numbers, Ra, between 2.08‧108 and 4.60‧109, modified Reynolds numbers, Re between 4.23 and 423.0, wall-PCM thermal diffusivity ratios, α, between 5.0 and 10.0 and dimensionless wall thickness, w, between 0.005 and 0.05. Results show that the melting process is increasingly delayed by heat conduction across a wall of decreasing thermal conductivity and/or increasing thickness. This effect is accentuated for low HTF flow rates (Re ~ 4.23). On the other hand, for a wail of given thickness and thermal conductivity, the effect of increasing the HTF flow rate on the melting process becomes imperceptible for Re ≥ 4.23.

scholarly journals A Study of Hot Climate Low-Cost Low-Energy Eco-Friendly Building Envelope with Embedded Phase Change Material

Energies ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3544
Author(s):  
Atiq Ur Rehman ◽  
Nouman Ghafoor ◽  
Shakil R. Sheikh ◽  
Zareena Kausar ◽  
Fawad Rauf ◽  
...  
Keyword(s):  
Energy Consumption ◽  
Thermal Comfort ◽  
Organic Waste ◽  
Low Cost ◽  
Building Envelope ◽  
Low Energy ◽  
Waste Materials ◽  
Indoor Temperature ◽  
Corn Husk ◽  
Low Energy Buildings

The generation and use of energy are significant contributors to CO2 emissions. Globally, approximately 30% to 40% of all energy consumption can be directly or indirectly linked to buildings. Nearly half of energy usage in buildings is linked to maintaining the thermal comfort of the inhabitants. Therefore, finding solutions that are not only technically but also economically feasible is of utmost importance. Though much research has been conducted to address this issue, most solutions are still costly for developing countries to implement practically. This study endeavors to find a less expensive yet straightforward methodology to achieve thermal comfort while conserving energy. This study takes a broader view of multiple habitat-related CO2 emission issues in developing regions and describes a hybrid solution to address them. New technologies and innovative concepts are being globally examined to benefit from the considerable potential of PCMs and their role in thermal energy storage (TES) applications for buildings. The current study numerically investigates the thermal response of a hybrid building envelope consisting of PCM and local organic waste materials for low-cost low-energy buildings. The local organic waste materials used are those whose disposal is usually done by burning, resulting in an immense amount of greenhouse gases. In the first phase, different waste materials are characterized to determine their thermophysical properties. In the second phase, a low-cost, commonly available PCM calcium chloride hexahydrate, CaCl2·6H2O, is integrated with a brick and corn husk wall to enhance the thermal storage in the building envelope to minimize energy consumption. Temperature distribution plots are primarily used for analysis. The results show a marked improvement in thermal comfort by maintaining a maximum indoor temperature of 27 °C when construction is performed with a 6% corn husk composite material embedded with the PCM, while under similar conditions, the standard brick construction maintained a 31 °C indoor temperature. It is concluded that the integration of the PCM layer with the corn husk wall provides an adequate solution for low-cost and low-energy buildings.

The Enthalpy-Transforming-Based Lattice Boltzmann Model for Solid–Liquid Phase Change

2018 ◽  
Vol 140 (10) ◽  
Author(s):  
Yutao Huo ◽  
Zhonghao Rao
Keyword(s):  
Natural Convection ◽  
Phase Change ◽  
Lattice Boltzmann ◽  
Lattice Boltzmann Model ◽  
Solid Liquid Interface ◽  
Solid Liquid ◽  
Boltzmann Model ◽  
Benchmark Solutions ◽  
Change Material ◽  
Change Problem

A new lattice Boltzmann (LB) model to solve the phase change problem, which is based on the enthalpy-transforming model has been developed in this paper. The problems of two-region phase change, natural convection of air, and phase change by convection are solved to verify the present LB model. In two-region phase change, the results of the present LB model agree well with that of analytical solution. The benchmark solutions are applied to evaluate the present LB model in natural convection of air and phase change material (PCM) as well. The results show that the present LB model is able to simulate the temperature distribution and capture the location of solid–liquid interface in the cavity accurately. Moreover, the present LB model is effective in computing owing to the fact that no iterations are necessary during the simulations.

Evaluating Forced Versus Natural Convection for Solar Concentrating Hybrid Photovoltaic-Thermoelectric Power Systems Made From Small Up-Cycled Satellite Dishes

2017 ◽  
Author(s):  
Said Alamri ◽  
Turki Alamri ◽  
Saud Almutairi ◽  
Muhammad K. Akbar ◽  
Fatemeh Hadi ◽  
...  
Keyword(s):  
Steady State ◽  
Natural Convection ◽  
Power Systems ◽  
Forced Convection ◽  
Power Output ◽  
Focal Point ◽  
Low Cost ◽  
Cold Side ◽  
Pv Module ◽  
Satellite Dish

Design processes and analytical modeling are presented showing creation of a low-cost concentrating photovoltaic-thermoelectric (PV/TE) hybrid power system for research and laboratory teaching built using a small upcycled satellite dish. Today, concentrated solar hybrid PV/TE systems are drawing significant research attention and funding investment. However, the literature lacks examples of how this cutting-edge energy technology can be made accessible at low cost for STEAEM education at universities, vocational institutions, and high schools. By applying Energy Engineering Laboratory Module (EELM™) design principles and pedagogy, a process is presented to make this technology easily accessible at low cost. The concentrating solar hybrid PV/TE system presented here is divided into four subsystems: 1) a concentrator, 2) a PV/TE generator, 3) data acquisition, and 4) a cooling system. The key engineering decisions governing the design for each sub-system are described. In addition, a thermodynamic analysis is presented to predict the on-sun steady-state temperature profile of the PV/TE generator at the focus of the concentrator and to determine how much electrical power it will produce. The concentrator used is a salvaged miniature satellite dish, which is coated with mirrored tape to reflect sunlight upon a focal point. Scavenged at no cost, the satellite dish is a sectioned paraboloid of rotation offset from the vertex and the axis of symmetry. However, which paraboloid section the dish represents is unknown. A technique is presented to find the focal point and to use this information to correctly position a shadow-casting gnomon to ensure proper on-sun alignment. A method to experimentally confirm the focal location and size the PV is also provided. A key research question for solar concentrating hybrid PV/TE power systems at this size scale is whether it is better to actively cool the TE cold side via forced convection or simply allow cooling via natural convection. The thermodynamic heat balance analysis presented to address this question finds that while forced convection does better cool the PV module, increasing its efficiency and power output, the parasitic energy expenditure of the cooling fan far exceeds the additional power produced. It is therefore more beneficial to rely on natural convection on the TE cold side to maximize power production of the overall PV/TE module. Two experimental apparatuses were built consisting of a PV module backed by TE generators and instrumented with thermocouples to determine the internal temperature gradient while multi-meters read steady-state PV and TE power output. A halogen lamp placed at various distances from this array approximates concentrated sunlight, which is measured via pyranometer. These experiments validate conclusions drawn from the theoretical model.

Numerical Performances Study of Curved Photovoltaic Panel Integrated with Phase Change Material

2020 ◽  
Vol 22 (4) ◽  
pp. 1439-1452
Author(s):  
Mohamed L. Benlekkam ◽  
Driss Nehari ◽  
Habib Y. Madani
Keyword(s):  
Phase Change ◽  
Phase Change Material ◽  
Numerical Study ◽  
Numerical Data ◽  
Navier Stokes ◽  
Photovoltaic Panel ◽  
Pv Panel ◽  
Energy Equations ◽  
Solid Liquid ◽  
Change Material

AbstractThe temperature rise of photovoltaic’s cells deteriorates its conversion efficiency. The use of a phase change material (PCM) layer linked to a curved photovoltaic PV panel so-called PV-mirror to control its temperature elevation has been numerically studied. This numerical study was carried out to explore the effect of inner fins length on the thermal and electrical improvement of curved PV panel. So a numerical model of heat transfer with solid-liquid phase change has been developed to solve the Navier–Stokes and energy equations. The predicted results are validated with an available experimental and numerical data. Results shows that the use of fins improve the thermal load distribution presented on the upper front of PV/PCM system and maintained it under 42°C compared with another without fins and enhance the PV cells efficiency by more than 2%.

Gallium–indium nanoparticles as phase change material additives for tunable thermal fluids

Nanoscale ◽  
2021 ◽  
Author(s):  
Jacob Mingear ◽  
Zachary Farrell ◽  
Darren Hartl ◽  
Christopher Tabor
Keyword(s):  
Thermal Diffusivity ◽  
Phase Change ◽  
Phase Change Material ◽  
Wide Temperature Range ◽  
Alloy Nanoparticles ◽  
Thermal Fluids ◽  
Indium Nanoparticles ◽  
Solid Liquid ◽  
Change Material ◽  
Transport Fluid

Inorganic Ga–In alloy nanoparticles suspended in a traditional thermal transport fluid simultaneously increase the overall thermal diffusivity of the fluid and serve as a cyclable solid–liquid PCM slurry, providing a thermal sink definable over a wide temperature range.

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