Phase change in multi-tube heat exchangers

Investigation of nano powders influence on melting process within a storage unit

A comprehensive review on positive cold energy storage technologies and applications in air conditioning with phase change materials

A comparative thermal performance assessment is reported for vertical and horizontal orientation of shell and tube type Latent Heat Storage Unit (LHSU) using stearic acid (melting point of 55.7–56.6 °C) as Phase Change Material (PCM) and water as Heat Transfer Fluid (HTF). Total 45 thermocouples are used in radial, axial and angular directions to measure the temperature distribution in the PCM. In horizontal LHSU, temperature in the upper half of the horizontal diametric plane reaches the melting point faster due to natural convection. As a result, the upper half melts earlier than the lower half. In order to demonstrate the motion of solid-liquid interface, liquid fraction contours are presented. For vertical LHSU, melting front moves in a conical fashion around the vertical plane with faster melting at upper axial locations. Experimental analysis suggests that horizontal LHSU is better for part load operation as compared to vertical LHSU, as it requires lesser time to melt half of the PCM mass. Energy storage/retrieval rate during melting and solidification is also compared for both the LHSU configurations.

Thermal performance of shell and tube latent heat storage unit: Comparative assessment of horizontal and vertical orientation

An experimental study is conducted to investigate the melting and solidification processes of paraffin wax as a phase change material (PCM) in horizontal double pipe heat latent heat storage unit. The present work on phase change process includes study of temperature variations along the axial distances in PCM, determination of heat transfer coefficient as well as the heat flow rate. A series of experiments was conducted to investigate the effect of increasing the inlet temperature and the mass flow rate of the heat transfer fluid (HTF) both on the charging and discharging processes of the PCM. The experimental results show that the PCM melts and solidifies congruently, and the melting front moves from the left to right side of the PCM container whereas the solidification front moves from right to the left along the axial distances in the PCM container. The results indicate that natural convection dominates the melting process in the liquid phase due to buoyancy effects. On the other hand, the solidification process is dominated by conduction. The flow rate and inlet temperature of the HTF in the experiment range has a significant effect on the phase change processes. The results also indicate that the heat transfer coefficient between the HTF and the PCM was affected by the Reynolds number more during the melting process than during the solidification process. Heat flow rate during the melting and solidification process increased by 25% and 11%, respectively, in the case of increase or decrease by 2 °C of the inlet HTF temperature. The results of this study show that by increasing the inlet water temperature from 70 °C to 74 °C, total melting time can be decreased by 31%.

An experimental study on heat transfer characteristics of paraffin wax in horizontal double pipe heat latent heat storage unit

Experimentally validated two dimensional numerical model for the solidification of PCM along a horizontal long tube

This paper presents the results of an experimental study on the
 solidification along a long horizontal tube submersed in liquid PCM and the
 enhancements due to the use of a turbulence promoter. The experimental rig
 consists of a long copper tube fixed coaxially inside a larger PVC tube
 filled with liquid PCM (water). The working fluid at a temperature lower than
 the PCM phase change temperature flows inside the copper tube provoking the
 solidification of PCM over its surface. The PVC tube is fitted with three
 windows along its length for observation and photographing the solidified PCM
 interface. The tests were realized for values of Reynolds number from 741 to
 2280 and temperatures varying from -5 to - 20oC with and without turbulence
 promoter showed their effects on the interface position, the solidification
 velocity and how they were enhanced because of the turbulence promoter.

/pdf/enhancement-of-phase-change-along-the-long-tubes-of-a-latent-vikumom0tc.pdf

Enhancement of phase change along the long tubes of a latent heat storage unit

Embalagem produzidas de biopolímeros vêm crescendo atualmente para atender a demanda de conservação de alimentos com reduzido impacto ambiental. O objetivo deste trabalho foi desenvolver e caracterizar filmes poliméricos incorporados com pólen apícola para uso em embalagem de alimentos. Nesta pesquisa foi utilizado planejamento experimental de misturas, com quatorze ensaios, analisando as variáveis independentes (concentrações de alginato, pectina e amido) sobre os aspectos subjetivos e as características de umidade (ω), espessura (δ), solubilidade em água (S) e permeabilidade ao vapor de água (PVA). Foram fixadas concentrações de 10g de pólen, 3ml de glicerol e 30ml de cloreto de cálcio dihidratado à 1%, em todos os ensaios. Com base nos melhores resultados de homogeneidade, continuidade, transparência, flexibilidade, juntamente com menor valor de ω, δ, S e PVA, selecionou-se cinco ensaios (G4, G6, G7, G8 e G10) que foram caracterizados quanto as propriedades mecânicas e microscopia óptica. Os resultados mostraram que o filme G6 (1/3g de pectina + 2/3g de amido) apresentou o melhor resultado de tensão de ruptura (2,83Mpa), porém obteve o menor valor de alongamento de ruptura (4,05%) mostrando ser mais rígido. Em contrapartida, o filme G8 (2/3g de alginato + 1/3g de amido) alcançou melhor elongação (9,60%). O módulo de Young variou de 35,05 a 137,06MPa. Quanto a microscopia óptica, foi possível observar nitidamente os grânulos de pólen em todas as formulações otimizadas. As características observadas nos filmes otimizados são promissoras para utilização como embalagem comestível e biodegradáveis, porém, recomenda-se a realização de mais testes.

Louryval C. Paixão

Papers

Experimentally validated two dimensional numerical model for the solidification of PCM along a horizontal long tube

Enhancement of phase change along the long tubes of a latent heat storage unit

Incorporação de pólen de abelha Tubi (Scaptotrigona sp) em filmes biodegradáveis de alginato, pectina e amido

Biopolymers of Alginate Using Buriti Extracts: Mathematical Modeling and Antioxidant Release Optimization