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

Experimental investigation of small diameter two-phase closed thermosyphons charged with water, FC-84, FC-77 and FC-3283

Copyright © 2009 Elsevier Ltd. All rights reserved.An experimental investigation of the performance of thermosyphons charged with water as well as the dielectric heat transfer liquids FC-84, FC-77 and FC-3283 has been carried out. The copper thermosyphon was 200 mm long with an inner diameter of 6 mm, which can be considered quite small compared with the vast majority of thermosyphons reported in the open literature. The evaporator length was 40 mm and the condenser length was 60 mm which corresponds with what might be expected in compact heat exchangers. With water as the working fluid two fluid loadings were investigated, that being 0.6 ml and 1.8 ml, corresponding to approximately half filled and overfilled evaporator section in order to ensure combined pool boiling and thin film evaporation/boiling and pool boiling only conditions, respectively. For the Fluorinert™ liquids, only the higher fill volume was tested as the aim was to investigate pool boiling opposed to thin film evaporation. Generally, the water-charged thermosyphon evaporator and condenser heat transfer characteristics compared well with available predictive correlations and theories. The thermal performance of the water-charged thermosyphon also outperformed the other three working fluids in both the effective thermal resistance as well as maximum heat transport capabilities. Even so, FC-84, the lowest saturation temperature fluid tested, shows marginal improvement in the heat transfer at low operating temperatures. All of the tested Fluorinert™ liquids offer the advantage of being dielectric fluids, which may be better suited for sensitive electronics cooling applications and were all found to provide adequate thermal performance up to approximately 30–50 W after which liquid entrainment compromised their performance

Experimental and numerical investigation of an air-to-water heat pipe-based heat exchanger

An experimental and analytical investigation was conducted on an air-to-water heat exchanger equipped with six wickless heat pipes (thermosyphons) charged with water as the working fluid. The flow pattern consisted of a double pass on the evaporator and condenser sections. The six thermosyphons were all made from carbon steel, measured 2m in length and were installed in a staggered arrangement. The objectives of the reported experimental investigation were to analyse the effect of multiple air passes at different air inlet temperatures (100 to 250°C) and air mass flow rates (0.05 to 0.14kg/s) on the thermal performance of the heat exchanger unit including the heat pipes. The results were compared with a CFD model that assumed the heat pipes were solid rods with a constant conductivity. The conductivity of the pipes was extracted from modifications of correlations available in the literature based around the theory of Thermal Resistance. The results proved to be very accurate within 10% of the experimental values

Numerical modelling of the temperature distribution in a two-phase closed thermosyphon

Interest in the use of heat pipe technology for heat recovery and energy saving in a vast range of engineering applications has been on the rise in recent years. Heat pipes are playing a more important role in many industrial applications, particularly in improving the thermal performance of heat exchangers and increasing energy savings in applications with commercial use. In this paper, a comprehensive CFD modelling was built to simulate the details of the two-phase flow and heat transfer phenomena during the operation of a wickless heat pipe or thermosyphon, that otherwise could not be visualised by empirical or experimental work. Water was used as the working fluid. The volume of the fluid (VOF) model in ANSYS FLUENT was used for the simulation. The evaporation, condensation and phase change processes in a thermosyphon were dealt with by adding a user-defined function (UDF) to the FLUENT code. The simulation results were compared with experimental measurements at the same condition. The simulation was successful in reproducing the heat and mass transfer processes in a thermosyphon. Good agreement was observed between CFD predicted temperature profiles and experimental temperature data.The Saudi Cultural Bureau in London, the Ministry of Higher Education and the Mechanical Engineering Department, Umm Al-Qura University

Analysis of energy use in crisp frying processes

Copyright @ 2010 Politecnico di Bari - BB PressWith increasing energy costs in industrial food frying processes it is essential to identify inefficiencies and minimise them. A way of achieving this is through the application of energy analysis and modelling techniques to characterise the process and investigate the interactions between the various operating and control parameters. The overall objective is to reduce energy consumption without compromising product throughput and quality. This paper provides a review of published work on heat and mass transfer in frying processes. Based on this, a simplified analysis of the key processes has been carried out using an energy balance model. The outputs of this model have been validated using data from an industrial crisp frying facility. The knowledge gained from this validation will be used to better understand and appreciate the energy flows in industrial frying processes and should lead to identification of losses and opportunities for energy recovery.The authors would like to acknowledge the financial support from the UK Engineering and Physical Sciences Research Council (EPSRC), Grant NO. EP/G059799/1, for this project as well as the input from the industrial collaborators and academic collaborators from the Universities of Newcastle and Northumbria

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

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

Advanced Heat Exchangers for Waste Heat Recovery Applications

EditorialCopyright © 2023 by the author. The incentive for industrial waste heat recovery, which has attracted much research interest in recent years, has been twofold: the obligation to reduce greenhouse gas emissions in line with climate change targets and the need for processes to reduce overall energy consumption in order to remain commercially competitive [...

Cryopreservation: Methods, equipment and critical concerns

The technique of cryopreservation aims to maintain the biological samples in a metabolic suspension state, by which all chemical, physical and biological changes are diminished. The biology principles behind cryopreservation are widely investigated in the literature. However, little scientific interest has been focused to the current equipment used as cryogenic storages and how they affect the viability and functionality of the cells during their preservation. This review paper attempts to bridge the gap between the biology and engineering aspects of cryopreservation. The basic principles of cryobiology, the cryoinjury mechanisms, the role of cryoprotective agents, the state of the art cryopreservation methods and equipment, and concerns regarding the use of liquid nitrogen as cryogenic refrigerant are covered. Further to our knowledge there is no complete review in the literature describing the connection between the current cryogenic equipment and the physical events taking place during cryopreservation. The paper aims to provide researchers with the key knowledge of cryopreservation, not only from a biological point of view, but from a technical aspect, too, in order to contribute to the development of the cryobiology field.This work was funded by Air Products PLC