scholarly journals SINGLE-PHASE AND TWO-PHASE SECONDARY COOLANTS: SIMULATION AND EVALUATION OF THEIR THERMOPHYSICAL PROPERTIES

2011 ◽  
Vol 4 ◽  
pp. 91
Author(s):  
Pedro Samuel Gomes Medeiros ◽  
Cleiton Rubens Formiga Barbosa ◽  
Francisco De Assis Oliveira Fontes
Keyword(s):  
Thermal Conductivity ◽  
Thermophysical Properties ◽  
Dynamic Viscosity ◽  
Single Phase ◽  
Thermal Storage ◽  
Heat Transfer Fluid ◽  
Viscosity Data ◽  
Ice Slurry ◽  
Two Phase ◽  
Cooling Systems

This paper makes a comparative analysis of the thermophysical properties of ice slurry with conventional single-phase secondary fluids used in thermal storage cooling systems. The ice slurry is a two-phase fluid consisting of water, antifreeze and ice crystals. It is a new technology that has shown great energy potential. In addition to transporting energy as a heat transfer fluid, it has thermal storage properties due to the presence of ice, storing coolness by latent heat of fusion. The single-phase fluids analyzed are water-NaCl and water-propylene glycol solutions, which also operate as carrier fluids in ice slurry. The presence of ice changes the thermophysical properties of aqueous solutions and a number of these properties were determined: density, thermal conductivity and dynamic viscosity. Data were obtained by software simulation. The results show that the presence of 10% by weight of ice provides a significant increase in thermal conductivity and dynamic viscosity, without causing changes in density. The rheological behavior of ice slurries, associated with its high viscosity, requires higher pumping power; however, this was not significant because higher thermal conductivity allows a lower mass flow rate without the use of larger pumps. Thus, the ice slurry ensures its high potential as a secondary fluid in thermal storage cooling systems, proving to be more efficient than single-phase secondary fluids.

scholarly journals Improved Thermophysical Properties and Energy Efficiency of Aqueous Ionic Liquid/MXene Nanofluid in a Hybrid PV/T Solar System

Nanomaterials ◽  
2020 ◽  
Vol 10 (7) ◽  
pp. 1372 ◽  
Author(s):  
Likhan Das ◽  
Khairul Habib ◽  
R. Saidur ◽  
Navid Aslfattahi ◽  
Syed Mohd Yahya ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Ionic Liquid ◽  
Palm Oil ◽  
Thermophysical Properties ◽  
Conductivity Measurement ◽  
Optimum Concentration ◽  
Heat Transfer Fluid ◽  
Solar Pv ◽  
T System

In recent years, solar energy technologies have developed an emerging edge. The incessant research to develop a power source alternative to fossil fuel because of its scarcity and detrimental effects on the environment is the main driving force. In addition, nanofluids have gained immense interest as superior heat transfer fluid in solar technologies for the last decades. In this research, a binary solution of ionic liquid (IL) + water based ionanofluids is formulated successfully with two dimensional MXene (Ti3C2) nano additives at three distinct concentrations of 0.05, 0.10, and 0.20 wt % and the optimum concentration is used to check the performance of a hybrid solar PV/T system. The layered structure of MXene and high absorbance of prepared nanofluids have been perceived by SEM and UV–vis respectively. Rheometer and DSC are used to assess the viscosity and heat capacity respectively while transient hot wire technique is engaged for thermal conductivity measurement. A maximum improvement of 47% in thermal conductivity is observed for 0.20 wt % loading of MXene. Furthermore, the viscosity is found to rise insignificantly with addition of Ti3C2 by different concentrations. Conversely, viscosity decreases substantially as the temperature increases from 20 °C to 60 °C. However, based on their thermophysical properties, 0.20 wt % is found to be the optimum concentration. A comparative analysis in terms of heat transfer performance with three different nanofluids in PV/T system shows that, IL+ water/MXene ionanofluid exhibits highest thermal, electrical, and overall heat transfer efficiency compared to water/alumina, palm oil/MXene, and water alone. Maximum electrical efficiency and thermal efficiency are recorded as 13.95% and 81.15% respectively using IL + water/MXene, besides that, heat transfer coefficients are also noticed to increase by 12.6% and 2% when compared to water/alumina and palm oil/MXene respectively. In conclusion, it can be demonstrated that MXene dispersed ionanofluid might be great a prospect in the field of heat transfer applications since they can augment the heat transfer rate considerably which improves system efficiency.

scholarly journals Thermo-Fluidic Characteristics of Two-Phase Ice Slurry Flows Based on Comparative Numerical Methods

Processes ◽  
2019 ◽  
Vol 7 (12) ◽  
pp. 898 ◽  
Author(s):  
Shehnaz Akhtar ◽  
Haider Ali ◽  
Cheol Woo Park
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Flow Velocity ◽  
Mass Fraction ◽  
Single Phase ◽  
Ice Slurry ◽  
Two Phase ◽  
Ice Concentration ◽  
Eulerian Models

Ice slurry is a potential secondary refrigerant for commercial refrigeration systems because of its remarkable thermal properties. It is necessary to optimize the heat transfer process of ice slurry to reduce the energy consumption of the refrigeration system. Thus, this study investigates the heat transfer performance of single-phase (aqueous solution) and two-phase (ice slurry) refrigerants in a straight horizontal tube. The numerical simulations for ice slurry were performed with ice mass fraction ranging from 5% to 20%. The effects of flow velocity and ice concentration on the heat transfer coefficient were examined. The results showed that heat transfer coefficient of ice slurry is considerably higher than those of single-phase flow, particularly at high flow velocity and ice content, where increase in heat transfer with a factor of two was observed. The present results confirmed that ice slurry heat transfer ability is considerably affected by flow velocity and ice concentration in laminar range. Moreover, the second part of this paper reports on the credibility three distinct two-phase Eulerian–Eulerian models (volume of fluid (VOF), mixture, and Eulerian) for the experimental conditions reported in the literature. All two-phase models accurately predict the thermal field at low ice mass fraction but underestimate that at high ice mass fractions. Regardless of the thermal discrepancies, the Eulerian–Eulerian models provide quite reasonable estimation of pressure drop with reference to experimental data. The numerical predictions from the VOF model are more accordant with the experimental results and the maximum percentage error is limited to ~20% and ~13% for thermal and pressure drop predictions, respectively.

scholarly journals Using analytic hierarchy process for evaluating different types of nanofluids for engine cooling systems

2019 ◽  
Vol 23 (5 Part B) ◽  
pp. 3199-3208
Author(s):  
Asli Abdulvahitoglu
Keyword(s):  
Thermal Conductivity ◽  
Analytic Hierarchy Process ◽  
Automotive Industry ◽  
Thermophysical Properties ◽  
Analytic Hierarchy ◽  
Cooling Systems ◽  
Attribute Weights ◽  
Engine Cooling ◽  
Different Types ◽  
Hierarchy Process

The radiator is an important heat exchanger for cooling the engine. Usually, water and ethylene glycol are used in vehicles as cooling fluids. However, these fluids have lower thermal conductivity. In the automotive industry, coolants with better characteristics are being searched to develop more efficient engines. In recent years, nanofluids have become more attractive to car manufacturers, with higher thermal conductivity to increase heat transfer. In this study, the analytic hierarchy process is used to structure the decision problem and to attribute weights to criteria. Three types of nanofluid (Cu-water, NiO-water, and CuO-water) were evaluated. Among the thermophysical properties of nanofluid, the most important one is calculated as the thermal conductivity and also the Cu-water is determined as the most suitable coolant in terms of thermophysical properties among the evaluated nanofluid.

scholarly journals Enhancement of heat transfer coefficient multi-metallic nanofluid with ANFIS modeling for thermophysical properties

2015 ◽  
Vol 19 (5) ◽  
pp. 1613-1620 ◽  
Author(s):  
Hyder Balla ◽  
Shahrir Abdullah ◽  
Wan Faizal ◽  
Rozli Zulkifli ◽  
Kamaruzaman Sopian
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Thermophysical Properties ◽  
Dynamic Viscosity ◽  
Base Fluid ◽  
Volume Fractions ◽  
The Heat Transfer Coefficient ◽  
Cu And Zn

Cu and Zn-water nanofluid is a suspension of the Cu and Zn nanoparticles with the size 50 nm in the water base fluid for different volume fractions to enhance its Thermophysical properties. The determination and measuring the enhancement of Thermophysical properties depends on many limitations. Nanoparticles were suspended in a base fluid to prepare a nanofluid. A coated transient hot wire apparatus was calibrated after the building of the all systems. The vibro-viscometer was used to measure the dynamic viscosity. The measured dynamic viscosity and thermal conductivity with all parameters affected on the measurements such as base fluids thermal conductivity, volume factions, and the temperatures of the base fluid were used as input to the Artificial Neural Fuzzy inference system to modeling both dynamic viscosity and thermal conductivity of the nanofluids. Then, the ANFIS modeling equations were used to calculate the enhancement in heat transfer coefficient using CFD software. The heat transfer coefficient was determined for flowing flow in a circular pipe at constant heat flux. It was found that the thermal conductivity of the nanofluid was highly affected by the volume fraction of nanoparticles. A comparison of the thermal conductivity ratio for different volume fractions was undertaken. The heat transfer coefficient of nanofluid was found to be higher than its base fluid. Comparisons of convective heat transfer coefficients for Cu and Zn nanofluids with the other correlation for the nanofluids heat transfer enhancement are presented. Moreover, the flow demonstrates anomalous enhancement in heat transfer nanofluids.

Evaluation of Key Design Parameters of an Encapsulated Latent Heat Thermal Storage Unit

2016 ◽  
Vol 852 ◽  
pp. 652-658
Author(s):  
N. Lakshmi Narasimhan ◽  
P. Karthik
Keyword(s):  
Thermal Conductivity ◽  
Specific Heat ◽  
Latent Heat ◽  
Thermal Response ◽  
Thermal Storage ◽  
Heat Transfer Fluid ◽  
Design Parameters ◽  
Inlet Temperature ◽  
Storage Unit ◽  
Melting Temperatures

The present work numerically investigates for a latent heat thermal storage (LHTS) unit, the effect of key design parameters such as the inlet temperature of the heat transfer fluid (HTF), initial and melting temperatures of the PCM, thermophysical parameters such as specific heat, thermal conductivity etc., on its performance. A numerical model has been developed considering the discharging mode of operation and solved employing finite difference technique. The parametric study reveals that the effect of HTF inlet temperature on the unit's thermal response is more compared to initial temperature of the PCM and the influence of thermal conductivity of the PCM is very strong compared to specific heat capacity of the solid PCM

Liquid Cooling Network Systems for Energy Conservation in Data Centers

2011 ◽  
Author(s):  
Mayumi Ouchi ◽  
Yoshiyuki Abe ◽  
Masato Fukagaya ◽  
Haruhiko Ohta ◽  
Yasuhisa Shinmoto ◽  
...  
Keyword(s):  
Heat Exchanger ◽  
Data Center ◽  
Single Phase ◽  
Cooling System ◽  
Heat Pipes ◽  
Air Cooling ◽  
Liquid Cooling ◽  
Two Phase ◽  
Cooling Systems ◽  
Cooling Methods

Energy consumption in data center has been drastically increasing in recent years. In data center, server racks are cooled down by air conditioning for the whole room in a roundabout way. This air cooling method is inefficient in cooling and it causes hotspot problem that IT equipments are not cooled down enough, but the room is overcooled. On the other hand, countermeasure against the heat of the IT equipments is also one of the big issues. We therefore proposed new liquid cooling systems which IT equipments themselves are cooled down and exhaust heat is not radiated into the server room. For our liquid cooling systems, three kinds of cooling methods have been developed simultaneously. Two of them are direct cooling methods that the cooling jacket is directly attached to heat source, or CPU in this case. Single-phase heat exchanger or two-phase heat exchanger is used as cooling jackets. The other is indirect cooling methods that the heat generated from CPU is transported to the outside of the chassis through flat heat pipes, and condensation sections of the heat pipes are cooled down by liquid. Verification tests have been conducted by use of real server racks equipped with these cooling techniques while pushing ahead with five R&D subjects which constitute our liquid cooling system, which single-phase heat exchanger, two-phase heat exchanger, high performance flat heat pipes, nanofluids technology, and plug-in connector. As a result, the energy saving effect of 50∼60% comparing with conventional air cooling system was provided in direct cooling technique with single-phase heat exchanger.

Preparation and Thermophysical Properties of (La0.4Sm0.5Yb0.1)2(Zr0.7Ce0.3)2O7 Ceramic for Thermal Barrier Coatings

2008 ◽  
Vol 368-372 ◽  
pp. 1334-1336
Author(s):  
Ling Liu ◽  
Qiang Xu ◽  
Fu Chi Wang ◽  
Hong Song Zhang
Keyword(s):  
Thermal Conductivity ◽  
Thermal Expansion ◽  
Rare Earth ◽  
Phase Composition ◽  
Thermal Barrier Coatings ◽  
Thermophysical Properties ◽  
Single Phase ◽  
Pyrochlore Structure ◽  
Thermal Barrier ◽  
Barrier Coatings

A complex rare-earth zirconate (La0.4Sm0.5Yb0.1)2(Zr0.7Ce0.3)2O7 powder for thermal barrier coatings (TBCs) was synthesized by coprecipitation method. The phase composition, microstructure and the thermophysical properties were investigated. XRD results revealed that single phase (La0.4Sm0.5Yb0.1)2(Zr0.7Ce0.3)2O7 with pyrochlore structure was prepared and the SEM result showed that the microstructure of the product was dense and no other phases existed among the particles. With the temperature increasing, the thermal expansion coefficient (CTE) of the ceramic increased, while the thermal conductivity decreased. The results indicated that CTE of the ceramic was slightly higher than that of La2Zr2O7 and the thermal conductivity of the ceramic was lower than that of La2Zr2O7. These results imply that (La0.4Sm0.5Yb0.1)2(Zr0.7Ce0.3)2O7 can be explored as the candidate material for the ceramic layer in TBCs system.

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