ICONE23-1279 NUMERICAL COMPARISON OF FLOW BEHAVIOR AND HEAT TRANSFER ASPECTS OF SUPERCRITICAL CO2 AND SUBCRITICAL WATER BASED NATURAL CIRCULATION LOOP

Experiments were conducted to investigate the heat transfer characteristics of water-based suspensions of phase change nanocapsules in a natural circulation loop with mini-channel heat sinks and heat sources. A total of 23 and 34 rectangular mini-channels, each with width 0.8 mm, depth 1.2 mm, length 50 mm and hydraulic diameter 0.96 mm, were evenly placed on the copper blocks as the heat source and heat sink, respectively. The adiabatic sections of the circulation loop were constructed using PMMA tubes with an outer diameter of 6 mm and an inner diameter of 4 mm, which were fabricated and assembled to construct a rectangular loop with a height of 630 mm and a width of 220 mm. Using a core material of n-eicosane and a shell of urea-formaldehyde resin, the phase change material nanocapsules of mean particle size 150 nm were fabricated successfully and then dispersed in pure water as the working fluid to form the water-based suspensions with mass fractions of the nanocapsules in the range 0.1–1 wt.%. The results clearly indicate that water-based suspensions of phase change nanocapsules can markedly enhance the heat transfer performance of the natural circulation loop considered.

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Numerical study on heat transfer characteristics of nanofluid based natural circulation loop

Thermal Science ◽

10.2298/tsci160826087b ◽

2018 ◽

Vol 22 (2) ◽

pp. 885-897 ◽

Cited By ~ 4

Author(s):

Ramesh Bejjam ◽

Kiran Kumar

Keyword(s):

Heat Transfer ◽

Numerical Study ◽

Natural Circulation ◽

Flow Behavior ◽

Circulation Loop ◽

Heat Transfer Characteristics ◽

Step Size ◽

Particle Volume ◽

Transfer Characteristics ◽

Natural Circulation Loop

In this paper the steady-state analysis has been carried out on single phase natural circulation loop with water and water based Al2O3 (Al2O3-water) nanofluid at 1%, 3%, 5%, and 6% particle volume concentrations. For this study, a 3-D geometry of natural circulation loop is developed and simulated by using the software, ANSYS (FLUENT) 14.5. Based on the Stokes number, mixture model is adopted to simulate the nanofluid based natural circulation loop. For the simulations, the imposed thermal boundary conditions are: constant heat input over the range of 200-1000 W with step size of 200 W at the heat source and isothermal wall temperature of 293 K at the heat sink. Adiabatic boundary condition is imposed to the riser and down-comer. The heat transfer characteristics and fluid-flow behavior of the loop fluid in natural circulation loop for different heat inputs and particle concentrations are presented. The result shows that the mass-flow rate of loop fluid in natural circulation loop is enhanced by 26% and effectiveness of the natural circulation loop is improved by 15% with Al2O3-water nanofluid when compared with water. All the simulation results are validated with the open literature in terms of Reynolds number and modified Grashof number. These comparisons confidently say that the present 3-D numerical model could be useful to estimate the performance of natural circulation loop.

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Effect of Pressure on Steady State and Heat Transfer Characteristics in Supercritical CO2 Natural Circulation Loop

Procedia Engineering ◽

10.1016/j.proeng.2015.11.355 ◽

2015 ◽

Vol 127 ◽

pp. 636-644 ◽

Cited By ~ 1

Author(s):

Archana V. ◽

A.M. Vaidya ◽

P.K. Vijayan

Keyword(s):

Heat Transfer ◽

Steady State ◽

Supercritical Co2 ◽

Natural Circulation ◽

Circulation Loop ◽

Heat Transfer Characteristics ◽

Effect Of Pressure ◽

Transfer Characteristics ◽

Natural Circulation Loop

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Effect of Loop Tilting on the Heat Transfer and Pressure Drop in Two-Phase CO2 Based Natural Circulation Loop: An Experimental Study

Journal of Thermal Science and Engineering Applications ◽

10.1115/1.4047820 ◽

2020 ◽

Vol 13 (2) ◽

Cited By ~ 1

Author(s):

L. R. Thippeswamy ◽

Ajay Kumar Yadav

Keyword(s):

Heat Transfer ◽

Pressure Drop ◽

Heat Transfer Rate ◽

Transfer Rate ◽

Natural Circulation ◽

Flow Behavior ◽

Experimental Studies ◽

Circulation Loop ◽

Two Phase ◽

Natural Circulation Loop

Abstract The natural circulation loop (NCL) is widely used where the safe and economic heat transfer device is desired. However, the instability associated with the regular change in fluid flow behavior due to the imbalance between friction and buoyant forces is a major disadvantage. One of the erudite solutions to overcome this is to tilt the entire loop by a certain angle, with an inherent penalty in heat transfer and pressure drop. In the present study, experimental studies have been carried out on two-phase carbon dioxide (CO2) based NCL, which has gained popularity because of its compactness and higher heat transfer rate. Pressure drop and heat transfer performance of the loop for various tilt angles (0 deg, 30 deg, and 45 deg) in different planes (XY and YZ planes) have been investigated. Methanol is used as the external fluid in cold and hot heat exchangers in order to maintain low operating temperature in the loop. Results show that the tilting of the loop causes a marginal drop in the heat transfer rate of two-phase CO2 based NCL. Hence, tilting of the loop could be a solution to instability problem without conceding the performance of the loop.

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