Experimental Characterization of Heat Transfer to Vertical Dense Granular Flows Across Wide Temperature Range

2019 ◽  
Vol 141 (3) ◽  
Author(s):  
Megan F. Watkins ◽  
Richard D. Gould
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Rate ◽  
Convective Heat Transfer Coefficient ◽  
Granular Flows ◽  
Effect Of Temperature ◽  
Cylindrical Tubes ◽  
Operating Temperatures ◽  
Dense Granular Flows

Particle-based heat transfer fluids for concentrated solar power (CSP) tower applications offer a unique advantage over traditional fluids, as they have the potential to reach very high operating temperatures. Gravity-driven dense granular flows through cylindrical tubes demonstrate potential for CSP applications and are the focus of the present study. The heat transfer capabilities of such a flow system were experimentally studied using a bench-scale apparatus. The effect of the flow rate and other system parameters on the heat transfer to the flow was studied at low operating temperatures (<200 °C), using the convective heat transfer coefficient and Nusselt number to quantify the behavior. For flows ranging from 0.015 to 0.09 m/s, the flow rate appeared to have negligible effect on the heat transfer. The effect of temperature on the flow's heat transfer capabilities was also studied, examining the flows at temperatures up to 1000 °C. As expected, the heat transfer coefficient increased with the increasing temperature due to enhanced thermal properties. Radiation did not appear to be a key contributor for the small particle diameters tested (approximately 300 μm in diameter) but may play a bigger role for larger particle diameters. The experimental results from all trials corroborate the observations of other researchers; namely, that particulate flows demonstrate inferior heat transfer as compared with a continuum flow due to an increased thermal resistance adjacent to the tube wall resulting from the discrete nature of the flow.

Heat Transfer to Vertical Dense Granular Flows at High Operating Temperatures

2017 ◽  
Author(s):  
Megan F. Watkins ◽  
Richard D. Gould
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Granular Flows ◽  
Concentrated Solar Power ◽  
Ceramic Particles ◽  
Dense Flows ◽  
Operating Temperatures ◽  
The Heat Transfer Coefficient ◽  
Dense Granular Flows

Ceramic particles as a heat transfer fluid for concentrated solar power towers offers a variety of advantages over traditional heat transfer fluids. Ceramic particles permit the use of very high operating temperatures, being limited only by the working temperatures of the receiver components, as well as demonstrate the potential to be used for thermal energy storage. A variety of system configurations utilizing ceramic particles are currently being studied, including upward circulating beds of particles, falling particle curtains, and flows of particles over an array of absorber tubes. The present work investigates the use of gravity-driven dense granular flows through cylindrical tubes, which demonstrate solid packing fractions of approximately 60%. Previous work demonstrated encouraging results for the use of dense flows for heat transfer applications and examined the effect of various parameters on the overall heat transfer for low temperatures. The present work examined the heat transfer to dense flows at high operating temperatures more characteristic of concentrated solar power tower applications. For a given flow rate, the heat transfer coefficient was examined as a function of the mean flow temperature by steadily increasing the input heat flux over a series of trials. The heat transfer coefficient increased almost linearly with temperature below approximately 600°C. Above 600°C, the heat transfer coefficient increased at a faster rate, suggesting an increased radiation heat transfer contribution.

Effect of Flow Rate and Particle Size on Heat Transfer to Dense Granular Flows

2016 ◽  
Author(s):  
Megan F. Watkins ◽  
Richard D. Gould
Keyword(s):  
Heat Transfer ◽  
Particle Size ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Rate ◽  
Granular Flows ◽  
Heat Transfer Fluid ◽  
Storage Medium ◽  
Flow Rates ◽  
Dense Granular Flows

The increasing demand for renewable energy sources necessitates the development of more efficient technologies. Concentrated solar power (CSP) towers exhibit promising qualities, as temperatures greater than 1000°C are possible. The heat transfer fluid implemented to capture the sun’s energy significantly impacts the overall performance of a CSP system. Current fluids, such as molten nitrate salts and steam, have limitations; molten salts are limited by their small operational temperature range while steam requires high pressures and is unable to act as an effective storage medium. As a result, a new heat transfer fluid composed of ceramic particles is being investigated, as ceramic particles demonstrate no practical limit on operation temperature and have the ability to act as a storage medium. This study sought to further investigate the use of dense granular flows as a new heat transfer fluid. Previous work validated the use of such flows as a heat transfer fluid; the present work examined the effect of flow rate, as well as the particle size and type on the heat transfer to the particle fluid. Three different types of particles were tested, along with two different diameter particles. Of the three materials tested, the particle type did not appear to effect the heat transfer. Particle diameter, however, did effect the heat transfer, as a smaller diameter particle yielded slightly higher heat transfer to the fluid. Flow rates ranging from 30 to 200 kg/m2-s were tested. Initially, the heat transfer to the flow, characterized by the convective heat transfer coefficient, decreased with increasing flow rate. However, at approximately 80 kg/m2-s, the heat transfer coefficient began to increase with increasing flow rate. These results indicate that a dense granular flow consisting of small diameter particles and traveling at very slow or fast flow rates yields the best wall to “fluid” heat transfer.

scholarly journals Experimental study on heat transfer of an engine radiator with TiO2/EG-water nano-coolant

2021 ◽  
Vol 3 (4) ◽  
Author(s):  
Mohd Muzammil Zubair ◽  
Md. Seraj ◽  
Mohd. Faizan ◽  
Mohd Anas ◽  
Syed Mohd. Yahya
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Ethylene Glycol ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Flow Rate ◽  
Volume Flow Rate ◽  
Convective Heat Transfer Coefficient ◽  
Volume Flow ◽  
Nanoparticle Concentration

AbstractNanofluid as a transport medium displays a great potential in engineering applications involving heat transfer. In this paper, the execution of water and ethylene glycol-based TiO2 nanofluid as a radiator coolant is resolved experimentally. The convective heat transfer coefficient of TiO2/EG-Water nanocoolant has been estimated and contrasted with the information acquired experimentally. Nanocoolant were set up by taking 25% ethylene glycol and 75% water with low volume concentration of TiO2 nanoparticles. All the experiments were led for the distinctive volume flow rates in the range going from 30 to 180 L/h (LPH). The nanocoolant made to flow through curved radiator tubes in every experiment, so that it can exchange heat effectively. Result shows that increasing the volume flow rate of nanocoolant flowing in the radiator tubes, increases the heat transfer as well as the convective heat transfer coefficient of nanocooant. Maximum heat transfer enhancement of 29.5% was recorded for nanocoolant with 0.03% nanoparticle concentration as compared to water at 150 LPH. Apart from this nanoparticle concentration into the base fluid, no further enhancement in heat transfer has been observed at any volume flow rate.

Numerical Investigation of Convective Heat Transfer on a Dynamic Wall Heat Exchanger With Varying Amplitude and Frequency

2020 ◽  
Author(s):  
Md. Habibur Rahman ◽  
Emdadul Haque Chowdhury ◽  
Didarul Ahasan Redwan ◽  
Hasib Ahmed Prince ◽  
M. Ruhul Amin
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Mass Flow Rate ◽  
Convective Heat ◽  
Mass Flow ◽  
Flow Rate ◽  
Convective Heat Transfer Coefficient ◽  
Liquid Temperature

Abstract The current work aims to investigate the thermo-hydraulic performances of a dynamic wall heat exchanger by varying amplitude and frequency of the oscillating waveform. The lower wall of the channel is exposed to constant heat flux, the upper insulating wall is deforming in a sinusoidal waveform, and water is taken as the working fluid. The governing partial differential equations are solved by using the Arbitrary Lagrangian-Eulerian finite element method. The study has been performed in the transient regime for up to 1.0 second. At first the effects of frequency variation over the average mass flow rate, convective heat transfer coefficient, and the average liquid temperature have been observed for a particular amplitude of the dynamic wall. It has been found that the mass flow rate of water increases linearly with increasing frequency. Convective heat transfer coefficient decreases with increasing frequency up to 50 Hz, then starts to increase notably. Interestingly, the fluctuating average liquid temperature decreases and reaches a steady-state faster with increasing frequency. To explore the effect of amplitude over heat transfer characteristics, the amplitude ratio of the sinusoidal wave is varied maintaining a constant frequency of oscillation. It has been observed that with increasing amplitude, both mass flow rate and convective heat transfer coefficient increase exponentially. Increasing amplitude ratio from 0.5 to 0.9 results in an increment in the convective heat transfer coefficient by about 5 times. Although, the average liquid temperature decreases and reaches a steady state faster with increasing amplitude, initially the peak temperature of the water is recorded for the highest amplitude.

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