Experimental and analytical performance investigation of air to air two phase closed thermosyphon based heat exchangers

In recent years, the use of wickless heat pipes (thermosyphons) in heat exchangers has been on the rise, particularly in gas to gas heat recovery applications due to their reliability and the level of contingency they offer compared to conventional heat exchangers. Recent technological advances in the manufacturing processes and production of gravity assisted heat pipes (thermosyphons) have resulted in significant improvements in both quality and cost of industrial heat pipe heat exchangers. This in turn has broadened the potential for their usage in industrial waste heat recovery applications. In this paper, a tool to predict the performance of an air to air thermosyphon based heat exchanger using the ε-NTU method is explored. This tool allows the predetermination of variables such as the overall heat transfer coefficient, effectiveness, pressure drop and heat exchanger duty according to the flow characteristics and the thermosyphons configuration within the heat exchanger. The new tool's predictions were validated experimentally and a good correlation between the theoretical predictions and the experimental data, was observed. © 2014 Elsevier Ltd. All rights reserved

Heat pipe based thermal management systems for energy-efficient data centres

This paper investigates the potential applications for heat-pipe based heat exchangers in enhancing the efficiency of data centres’ cooling. The paper starts by assessing current industry practise and highlighting the challenges facing the data-storage industry; illustrating the legislative, technical and commercial constraints that are now, or will be prevalent in the industry as the sector continues to grow to cater for the ever increasing appetite for public sector, commercial and consumer remote data storage. The concept of free cooling and its potential application in data-centres is then introduced and analysed. A theoretical model is then constructed based on the established, proven performance characteristics of heat-pipe technologies and the weather data for a typical region in the UK. A case study has been conducted thereon and the results indicate potential energy savings of up to 75% are achievable when utilising heat pipe based free cooling systems

Three-dimensional numerical model of heat losses from district heating network pre-insulated pipes buried in the ground

The purpose of the paper is to investigate the challenges in modelling the energy losses of heating networks and to analyse the factors that influence them. The verification of the simulation was conducted on a test stand in-situ and based on the measurements of the testing station, a database for the final version of the numerical model was developed and a series of simulations were performed. Examples of the calculated results are shown in the graphs. The paper presents an innovative method of identify the energy losses of underground heating network pipelines and quantify the temperature distribution around them, in transient working conditions. The presented method makes use of numerical models and measured data of actual objects.The dimensions of the pipelines used were 6m wide, 8m high and 1m in depth, while they were simulated under conditions of zero heat flow in the ground, in the perpendicular to the sides direction of the calculated area and considering the effects of ground's thermal conductivity. The mesh was developed using advanced functions, which resulted its high quality with the average orthogonal quality of 0.99 (close to 1.00) and Skewness of 0.05 (between 0.00 and 0.25). To achieve better accuracy of the simulation model, the initial conditions were determined based on the numerical results of a three-dimensional analysis of heat losses, in steady state conditions in a single moment. The validation process confirmed the high quality of the model, as the differences between the ground temperatures were approximately 0.1°C

Investigation of the effects of thermal, oxidative and irradiation treatments on the behavior of poly(ethylene glycol) as a phase change material in thermal energy storage systems

Poly-ethylene glycol (PEG) with an average molecular weight of 2000 g/mol has been investigated as a phase change material for thermal energy storage applications. PEG ests were maintained at 80C for 861 hours in air, nitrogen, and vacuum environment; the samples maintained in vacuum were further treated with air for a period of several weeks. furthermore, another set of PEG samples was exposed to electron radiation in order to modify some of their polymer properties, such as their melting point Tm, their heat of fusion H, their crystallisation temperature T, the experiments showed that the presence of oxygen led to the degradation of the polymer and to a slight decrease of its melting temperature, while the treatment with electron radiation reduced polymer's heat of fusion. FTIR spectrum analysis showed bands assigned to carbony/carboxylate functional groups, indicating the degradation of PEG in the presence of air/oxygen

Environmental protection and nature conservation in the discourse of Newsweek and Tygodnik Powszechny

W niniejszym artykule przeprowadzona została krytyczna analiza dyskursu prasowego (KDA). W celu realizacji badań wybrane zostały dwa tygodniki: liberalno-lewicowy – Newsweek Polska (N) i liberalno-katolicki – Tygodnik Powszechny (TP). Analizie jakościowej i ilościowej poddane zostały artykuły na temat ochrony przyrody i środowiska, jakie ukazały się we wspomnianych czasopismach w ciągu ostatnich dwóch lat. Podstawową metodą badawczą wykorzystaną w badaniach była wspomniana KAD, a dokładnie – wybrane wątki wchodzące w jej skład. W jej wyniku weryfikacji poddane zostały hipotezy badawcze zakładające: że w dyskursie N częściej prezentowano kwestie ochrony przyrody; że kreowano w nim bardziej przyjazny stosunek do niej, niż w TP, a także, że w dyskursie N przeważała perspektywa globalna oraz wymiar moralny, natomiast w TP – aspekt lokalny i czynniki ekonomiczne. Wyniki badań wskazują, że w celu poprawy kondycji przyrody i środowiska potrzebne jest szersze propagowanie poprzez dyskurs prasowy , postaw proekologicznych.The purpose of this article is to conduct a critical discourse analysis (CDA). Two weeklies Newsweek Polska and Tygodnik Powszechny have been selected for the analysis. The focus was placed on texts on nature conservation and environmental protection, published in 2015 and 2016. The CDA is both a theory as well as a method of study. In the first part of article the concepts: nature conversation and environmental protection are defined and characterised using the CDA. In the second part a quantitative and qualitative analysis of discourse is performed. The results of the analysis indicate that Newsweek has published more articles on nature conservation and they promoted more broadly nature friendly attitudes in comparison with the texts published in Tygodnik Powszechny. In addition, in Newsweek there were proportionally more topics which analysed the issue from a global perspective. When it comes to motives, economic and moral arguments were presented in similar proportions in both weeklies

An Investigation into the Use of the Heat Pipe Technology in Thermal Energy Storage Heat Exchangers

Finding a solution to store industrial wasted heat for later use in order to reduce energy usage has been on the rise in recent years. This paper investigates the capability of latent heat Thermal Energy Storage (TES) system using Phase Change Material (PCM) to store/release a large amount of energy in a small volume compared to sensible heat TES system. In this work, the issue of the low conductivity of PCMs has been addressed by using an embedded finned water-charged heat pipes into the PCM bulk. Both heat pipes and the PCM tank used in this investigation were made of 316L stainless steel. The PCM used in this work was PLUSICE S89, which has a melting temperature of 89°C and crystallization point of 77°C. The evaporator section of the heat pipe was heated by condensing a steam flow. The heat that was absorbed in the evaporator section was then discharged to the PCMs by the heat pipe multi-legged finned condenser. Tests were conducted for both charging (melting) and discharging (crystallization) of PLUSICE S89. It was observed that the thermal resistance posed by PCM during the discharging stage was higher compared to that during the charging process.Spirax Sarco Engineering PL

Prediction of the gas emission from porous media with the concern of energy and environment

Measuring soil carbon dioxide efflux is a challenging task even when it is performed using respiration chambers. While gas samples are taken, measurement deviations become more evident according to the used chamber design especially when external disturbances occur. This paper studies the carbon dioxide concentration profiles within the top soil layers, and investigates the controlling factors affecting the process. The considered factors are diffusion, temperature and viscosity. The efflux equation is discussed and then it is linked with the soils geotechnical parameters, while a relationship between the Reynolds number within the soil and efflux is found. Emphasis on the importance of the external geometrical design considerations is shown through studying external boundary layer effects due to the chamber outer shell shape and how it interacts with blowing winds. Chamber stability on site of deployment is also of a significant importance considering external blowing winds. Internal geometrical considerations are linked with the flow turbulence within the dynamic chambers. It is highly recommended that respiration chamber designers need to work in parallel with a multidisciplinary team in order to make a chamber design that ensures the least disturbance to occur at the location of study

A new pH phenomenon to predict polarity reversal in lead-acid cells

This paper discusses new experimental work investigating the change in pH of the electrolyte of individual cells in Lead-Acid batteries during discharge with a view to predicting cell polarity reversal and thereby pre-empting potentially catastrophic failure in batteries. The discharge tests were carried out on batteries which were classified as ‘new’ and ‘aged’ as a means of indicating their state of health. A new pH phenomenon has been recorded for the first time in this paper as evidenced by experimental results including measurement of half-cell potentials. The trends observed during the discharge tests could be used as additional means of indicating impending cell reversal in series connected lead-acid cells

Bioprocessos e bioprodutos de espécies do gênero Ulva (Chlorophyta, Ulvophyceae) - Uma revisão

TCC(graduação) - Universidade Federal de Santa Catarina. Centro de Ciências Físicas e Matemáticas. Oceanografia.O gênero Ulva compreende um grupo de 130 espécies taxonomicamente aceitas e se distribuem em diversos locais do mundo. O cultivo das espécies de Ulva como monocultura pode gerar uma alta qualidade de biomassa que podem resultar em bioprodutos destas algas. No presente trabalho foi feita uma revisão bibliográfica com análise crítica com levantamento de estudos sobre o potencial uso de Ulva spp, utilizando bases de dados selecionadas e restrição de data para consulta das publicações a partir de 2011. Além disso, foi feita a identificação dos principais países responsáveis por estudos sobre bioprocessos e bioprodutos de espécies do gênero Ulva (Chlorophyta, Ulvophyceae). Foram encontrados diversos potenciais usos de Ulva sp. como por exemplo: biocombustíveis, ração para aquicultura, biorremediadores, biofertilizantes/bioestimulantes e para aplicações farmacêuticas. A maior quantidade de estudos ocorreu em universidades e centros de pesquisas da Europa e Ásia, continentes com universidades com maiores investimentos e também maiores problemas com o gênero Ulva nos seus corpos d’água devido as florações.The genus Ulva comprises a group of 130 taxonomically accepted species that are distributed in different parts of the world. The cultivation of Ulva species as a monoculture can generate a high quality of biomass that can be used as biproducts. This work presents a literature review performed with a survey of studies about the potential use of Ulva spp, using selected databases and date restriction (from 2011 onwards) to consult publications. In addition, the main countries responsible for studies on bioprocesses and bioproducts of species of the Ulva genus (Chlorophyta, Ulvophyceae) were identified. Multiple different potencial uses of the Ulva genus were found, for example: biofuels, aquafulture feed, bioremediator, biofertilizers/biostimulants and pharmaceutical applications. Europa and Asia were the continents with the most universities e research centers that conduct studies since the great investiments in this area and issues with Ulva spp