The Experts below are selected from a list of 294 Experts worldwide ranked by ideXlab platform
A H Mosaffa - One of the best experts on this subject based on the ideXlab platform.
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energy and exergy evaluation of a multiple pcm thermal storage unit for Free Cooling applications
Renewable Energy, 2014Co-Authors: A H Mosaffa, Garousi L Farshi, C Infante A FerreiraAbstract:Latent heat thermal storage (LHTS) is a technology that can help to reduce energy consumption for Cooling applications, where the cold is stored in phase change materials (PCMs). Free Cooling is a concept developed for air conditioning applications, in which coolness is collected from ambient air during night and released into the room during the hottest hours of the day. In this work, energy and exergy analyses are performed for a Free Cooling system using a LHTS unit employing multiple PCMs. The effects of inlet air temperature and air flow rate on the performance of the system are investigated. It is observed that the increase in exergy efficiency due to reducing inlet air temperature is more significant than effect from increasing the air flow rate during the charging process.
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thermal performance optimization of Free Cooling systems using enhanced latent heat thermal storage unit
Applied Thermal Engineering, 2013Co-Authors: A H Mosaffa, C Infante A Ferreira, Marc A Rose, F TalatiAbstract:Abstract Free Cooling systems use phase change materials (PCMs) to store outdoor cold during the night and to supply it to the indoor environment during the day when the need for Cooling increases. This work presents a numerical investigation of the performance enhancement of a Free Cooling system using a latent heat thermal storage (LHTS) unit employing multiple PCMs. The PCM storage system consists of several flat PCM slabs arranged in layers with a passage in between for the heat transfer fluid (HTF). Using the effective heat capacity method, the process of melting and solidification of the PCM is predicted. The energy storage effectiveness (as a new performance parameter for LHTS units) and coefficient of performance (COP) of the system are calculated. These two performance indicators are used to optimize the system. The suitability of both methods for optimization purpose is discussed indicating the superiority of the energy based (COP) method.
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thermal performance of a multiple pcm thermal storage unit for Free Cooling
Energy Conversion and Management, 2013Co-Authors: A H Mosaffa, C Infante A Ferreira, F Talati, Marc A RoseAbstract:Abstract As demand for refrigeration and air conditioning increased during the last decade, the opportunities have expanded for using thermal energy storage (TES) systems in an economically advantageous manner in place of conventional Cooling plants. Many cool storage systems use phase change materials (PCMs) and achieve peak load shifting in buildings. This work presents numerical investigations of the performance enhancement of a Free Cooling system using a TES unit employing multiple PCMs. The TES unit is composed of a number of rectangular channels for the flowing heat transfer fluid, separated by PCM slabs. Using the effective heat capacity method, the melting and solidification of the PCM is solved. The forced convective heat transfer inside the channels is analyzed by solving the energy equation, which is coupled with the heat conduction equation in the container wall. The effect of design parameters such as PCM slab length, thickness and fluid passage gap on the storage performance is also investigated using an energy based optimization. The results show that a system which can guarantee comfort conditions for the climate of Tabriz, Iran has an optimum COP of 7.0. This could be achieved by a combination of CaCl2·6H2O with RT25 with the optimum air channel thickness of 3.2 mm, length of 1.3 m and PCM slab thickness of 10 mm.
Changqing Tia - One of the best experts on this subject based on the ideXlab platform.
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experimental investigation on a loop thermosyphon with evaporative condenser for Free Cooling of data centers
Energy, 2019Co-Authors: Shuangqua Shao, Haina Zhang, Haichao Liu, Changqing TiaAbstract:Abstract Integrating evaporative Cooling with loop thermosyphon can significantly improve the Free Cooling ability. In this paper, a loop thermosyphon with evaporative condenser is investigated experimentally. The mist water flow out of a single nozzle is observed and analyzed. The performance and annual Free Cooling potential of the system are investigated, compared with conventional loop thermosyphon. The results show that the evaporative Cooling effect of the locations below the horizontal level of the nozzle is more significant due to gravity. With the increase of horizontal distance from the nozzle, the temperature decreases and then increases and the optimal distance is 200–400 mm. The heat capacity of LTEC increases with the increase of indoor and outdoor temperature difference while it decreases with the increase of humidity. Evaporative Cooling can enhance the heat transfer of LTEC by 7%–33% compared with loop thermosyphon with conventional condenser, and this value is larger for smaller indoor and outdoor temperature difference and higher indoor temperature. LTEC can expand the annual Free Cooling time by 7%–14% compared with LTCC and the effect is more significant in regions with drier weather.
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numerical investigation of a co2 loop thermosyphon in an integrated air conditioning system for Free Cooling of data centers
Applied Thermal Engineering, 2017Co-Authors: Haina Zhang, Shuangqua Shao, Changqing TiaAbstract:Abstract Free Cooling based on loop thermosyphon is ideal energy-saving method for data centers. Most working fluids presently used in this field will cause greenhouse effect or destroy the ozone layer. It is necessary to investigate the applicability of environment friendly fluids. A distributed-parameter model of a CO2 loop thermosyphon in an integrated air conditioning system for Free Cooling is built and validated. The performance is compared with traditional working fluids and the effects of some key geometric parameters are evaluated. The results show that the optimal filling ratios for CO2, R22 and R134a are 120%, 100% and 90%, respectively. The circulation flow rate of CO2 is much smaller than those of R22 and R134a. For CO2 loop thermosyphon, the heat transfer rate decreases with the increase of pipe length, while increases with the increase of riser diameter and height difference. The heat transfer rate increases with the increase of tube number and length of the evaporator, while the increasing rate decreases gradually. The optimal tube number and length are 80 and 0.6 m, respectively. The relationships between the above phenomenon and the internal flow state are also analyzed.
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experimental and numerical investigation on a co2 loop thermosyphon for Free Cooling of data centers
Applied Thermal Engineering, 2017Co-Authors: Haina Zhang, Shuangqua Shao, Zichao Shi, Kaitao Liu, Changqing TiaAbstract:Free Cooling based on loop thermosyphon is an ideal method for energy-saving of data centers. In order to promote its future application, it is necessary to investigate the performance of utilizing environment friendly working fluids. In this paper, an experiment based on enthalpy difference method and thermal imaging is conducted on a CO2 loop thermosyphon with microchannel parallel-flow evaporator and condenser. The results show that the effect of filling ratio on CO2 loop thermosyphon is more significant and the optimal filling ratio is higher, compared with R22 loop thermosyphon. Thermal image of the evaporator shows that superheated region shrinks and then disappears with the increase of filling ratio. Moreover, to analyze the relationship between the phenomenon and the internal flow state, a distributed-parameter model is built and validated. The simulation results show that 150% is the optimal filling ratio for no superheating or subCooling occurs along the loop. The effects of height difference and pipe length are more significant for low filling ratio. Superheating is easier to occur at the evaporator outlet when height difference is smaller or pipe length is larger, and subCooling is easier to occur at the condenser outlet when height difference or pipe length is smaller.
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numerical investigation on integrated system of mechanical refrigeration and thermosyphon for Free Cooling of data centers
International Journal of Refrigeration-revue Internationale Du Froid, 2015Co-Authors: Haina Zhang, Shuangqua Shao, Huiming Zou, Mingsheng Tang, Changqing TiaAbstract:Abstract The Cooling energy consumption of data centers is increasing rapidly and Free Cooling attracts growing concern. To achieve the independent running of Free Cooling system all the year round, integrated system of mechanical refrigeration and thermosyphon (ISMT) is an ideal method. In this study, a distributed-parameter simulation model of an ISMT is built and validated by experimental data. The simulation results show that for thermosyphon mode, the Cooling capacity increases with increasing air flow rate, temperature difference and pipe diameter, while decreases with increasing pipe length. For refrigeration mode, decreasing outdoor air temperature or increasing indoor air flow rate will improve the Cooling capacity and reduce the input power of the compressor. For dual mode, applicable outdoor temperature range and indoor air flow rate range exist and the Cooling capacity drops below that of refrigeration mode beyond these ranges. The critical values are 19 °C and 0.5 m 3 s −1 , respectively.
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Free Cooling of data centers a review
Renewable & Sustainable Energy Reviews, 2014Co-Authors: Haina Zhang, Shuangqua Shao, Huiming Zou, Changqing TiaAbstract:The growing demand for electricity and the increasing size of the carbon footprint of data centers worldwide bring a severe challenge to sustainable development of human civilization. The Cooling energy consumption takes up around 30–50% of the total consumption of data centers due to the inefficient Cooling system. Free Cooling is an effective solution for reducing the power consumption of Cooling systems. This paper reviews the advancements of data center Free Cooling mainly focusing on configuration features and performances. Three kinds of Free Cooling methods, airside Free Cooling, waterside Free Cooling and heat pipe Free Cooling are discussed and performance characteristics of each are analyzed. Further, the criteria of performance evaluation for Free Cooling of data centers are summarized, and an overview of Free Cooling systems based on these criteria is demonstrated in order to help researchers acquire the latest developments in this area.
C Infante A Ferreira - One of the best experts on this subject based on the ideXlab platform.
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energy and exergy evaluation of a multiple pcm thermal storage unit for Free Cooling applications
Renewable Energy, 2014Co-Authors: A H Mosaffa, Garousi L Farshi, C Infante A FerreiraAbstract:Latent heat thermal storage (LHTS) is a technology that can help to reduce energy consumption for Cooling applications, where the cold is stored in phase change materials (PCMs). Free Cooling is a concept developed for air conditioning applications, in which coolness is collected from ambient air during night and released into the room during the hottest hours of the day. In this work, energy and exergy analyses are performed for a Free Cooling system using a LHTS unit employing multiple PCMs. The effects of inlet air temperature and air flow rate on the performance of the system are investigated. It is observed that the increase in exergy efficiency due to reducing inlet air temperature is more significant than effect from increasing the air flow rate during the charging process.
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thermal performance optimization of Free Cooling systems using enhanced latent heat thermal storage unit
Applied Thermal Engineering, 2013Co-Authors: A H Mosaffa, C Infante A Ferreira, Marc A Rose, F TalatiAbstract:Abstract Free Cooling systems use phase change materials (PCMs) to store outdoor cold during the night and to supply it to the indoor environment during the day when the need for Cooling increases. This work presents a numerical investigation of the performance enhancement of a Free Cooling system using a latent heat thermal storage (LHTS) unit employing multiple PCMs. The PCM storage system consists of several flat PCM slabs arranged in layers with a passage in between for the heat transfer fluid (HTF). Using the effective heat capacity method, the process of melting and solidification of the PCM is predicted. The energy storage effectiveness (as a new performance parameter for LHTS units) and coefficient of performance (COP) of the system are calculated. These two performance indicators are used to optimize the system. The suitability of both methods for optimization purpose is discussed indicating the superiority of the energy based (COP) method.
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thermal performance of a multiple pcm thermal storage unit for Free Cooling
Energy Conversion and Management, 2013Co-Authors: A H Mosaffa, C Infante A Ferreira, F Talati, Marc A RoseAbstract:Abstract As demand for refrigeration and air conditioning increased during the last decade, the opportunities have expanded for using thermal energy storage (TES) systems in an economically advantageous manner in place of conventional Cooling plants. Many cool storage systems use phase change materials (PCMs) and achieve peak load shifting in buildings. This work presents numerical investigations of the performance enhancement of a Free Cooling system using a TES unit employing multiple PCMs. The TES unit is composed of a number of rectangular channels for the flowing heat transfer fluid, separated by PCM slabs. Using the effective heat capacity method, the melting and solidification of the PCM is solved. The forced convective heat transfer inside the channels is analyzed by solving the energy equation, which is coupled with the heat conduction equation in the container wall. The effect of design parameters such as PCM slab length, thickness and fluid passage gap on the storage performance is also investigated using an energy based optimization. The results show that a system which can guarantee comfort conditions for the climate of Tabriz, Iran has an optimum COP of 7.0. This could be achieved by a combination of CaCl2·6H2O with RT25 with the optimum air channel thickness of 3.2 mm, length of 1.3 m and PCM slab thickness of 10 mm.
Harald Mehling - One of the best experts on this subject based on the ideXlab platform.
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improvement of a thermal energy storage using plates with paraffin graphite composite
International Journal of Heat and Mass Transfer, 2005Co-Authors: Jose M Marin, Belen Zalba, Luisa F Cabeza, Harald MehlingAbstract:Abstract This work aims at designing a thermal energy storage (TES) using air as heat transfer medium, efficient mainly for Free-Cooling but also for other applications, improving the low heat transfer rates dues to the thermal conductivity of the materials usually employed in these systems, phase change materials (PCM). In this paper, Free-Cooling means the storage of cold from the night to be used during the day to cool down a room. An experimental set-up has been constructed to simulate the application. The loading and unloading processes (melting and Freezing of the PCM) have two disadvantages: a relative long duration, in the range from 3 to 8 h, and a very high power consumption of the fans. Using a porous matrix of graphite where the PCM is embedded, both handicaps can be noticeably overcome. The application is studied, both experimentally and numerically.
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Free Cooling of buildings with phase change materials
International Journal of Refrigeration-revue Internationale Du Froid, 2004Co-Authors: Belen Zalba, Jose M Marin, Luisa F Cabeza, Harald MehlingAbstract:Abstract In this paper, the application of phase change materials (PCM) in Free-Cooling systems is studied. Free-Cooling is understood as a means to store outdoors coolness during the night, to supply indoors Cooling during the day. The use of PCMs is suitable because of the small temperature difference between day indoors and night outdoors. An installation that allows testing the performance of PCMs in such systems was designed and constructed. The main influence parameters like ratio of energy/volume in the encapsulates, load/unload rate of the storage, and cost of the installation were determined, and experiments were performed following the design of experiments strategy. The statistical analysis showed that the effects with significant influence in the solidification process are the thickness of the encapsulation, the inlet temperature of the air, the air flow, and the interaction thickness×temperature. For the melting process the same holds, but the inlet air temperature had a higher influence than the thickness of the encapsulation. With the empirical model developed in this work, a real Free-Cooling system was designed and economically evaluated.
R Velraj - One of the best experts on this subject based on the ideXlab platform.
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analysis of the heat transfer mechanisms during energy storage in a phase change material filled vertical finned cylindrical unit for Free Cooling application
Energy Conversion and Management, 2013Co-Authors: Gnanadurai Ravikuma Solomo, R VelrajAbstract:Abstract The heat transfer performance of the Phase Change Material (PCM) used in Free Cooling application is low due to poor thermal conductivity. The addition of fins to enhance the heat transfer during solidification process is commonly employed, to address this. However for application such as Free Cooling, where the driving temperature potential is very less, the present experimental study is intended to investigate the sensible and subCooling phenomena during the outward cylindrical solidification of the PCM stored on the annulus side, along with 8 longitudinal uniformly spaced copper fins of different heights. The performance of the fins during solidification is analyzed, and the best suitable height is arrived at. The addition of fins plays a contradicting role during the sensible Cooling of the liquid PCM, due to the suppression of Free convection. The external Cooling conditions along with the effect of the fin, vary the sensible Cooling rate of the liquid PCM, that influences the subCooling effect, and also drifts the temperature at which major phase change occurs. In addition, the effects due to the inlet velocity of the heat transfer fluid, and its temperature on heat transfer are investigated and reported. The increase in velocity decreases the duration of solidification, and this effect is more pronounced towards the entry region, due to the higher local convective heat transfer co-efficient and a comparatively higher driving temperature potential.
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heat transfer and pressure drop studies on a pcm heat exchanger module for Free Cooling applications
International Journal of Thermal Sciences, 2011Co-Authors: Antony Aroul V Raj, R VelrajAbstract:Free Cooling/Night ventilation is the process of storing the cool energy available in the night time ambient air in a storage device. During the day time the cool energy is retrieved from the storage device in order to cool the building using mechanical ventilation system. The modular heat exchanger developed in this work is a shell and tube type with phase change materials in the shell portion of the module and passage for the flow of air through the tubes. The modules of the modular heat exchanger are stacked one over other with air spacers in between each module. This modular heat exchanger arrangement is suitable for Free Cooling application where the diurnal temperature variation is low. Transient and steady state CFD modeling is carried out for a single module and two air spacers. Conjugate heat transfer analysis is carried out for the fluid and PCM of heat exchanger module. The latent heat value of the PCM is modeled using apparent heat capacity method with suitable profile approximated from the experimental results. The CFD results are validated with the experimental results. The steady state CFD analysis is useful to determine the pressure drop across the module and the spacers and to know the flow and temperature variation of heat transfer fluid in the module so as to select the geometrical and flow parameters for a given surface temperature and inlet condition. The transient analysis results are useful to determine the PCM solidification characteristics and to verify the suitability of the selected geometrical dimensions. The air spacers provided between the module increases the retention time of the air for better heat transfer and its effect is more pronounced at the lower velocities and decreases as the frontal velocity increases and its effect is negligible above the frontal velocity of 2 m/s.
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review on Free Cooling of buildings using phase change materials
Renewable & Sustainable Energy Reviews, 2010Co-Authors: Antony Aroul V Raj, R VelrajAbstract:The concept of Green building is gaining importance in the present energy scenario and related environmental issues. Free Cooling or ventilation Cooling is truly a green concept since even 1Â g of carbon is not burnt for the purpose of Cooling. Also it ensures that a good indoor air quality is maintained in the building. In this paper a detailed review of work carried out by various researchers on Free Cooling or ventilation Cooling is presented. In addition the major challenges and facts posed in the use of phase change material for Free Cooling system design such as thermal resistance of air and phase change materials, geometry of encapsulation are discussed in detail. Also the method of energy efficient charging and discharging, effect of phase change temperature, insulation and geographical location are also discussed in this paper. This paper also provides lists the PCM candidates used for Free Cooling.
