The Performance of a Scaled-Down Fluidized Loop Seal

2003 ◽  
Author(s):  
Andreas Johansson ◽  
Filip Johnsson ◽  
Bengt-A˚ke Andersson
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Scaling Laws ◽  
Tube Bundle ◽  
Flow Behavior ◽  
Cross Flow ◽  
Operating Conditions ◽  
Cfb Boiler ◽  
Super Heater

This work investigates the solids cross flow in a super-heater tube bundle immersed in the loop seal of a cold CFB unit. The loop seal and the tube bundle are scaled to a 1/3rd of the size of a loop seal and a super-heater located in a 30 MWth CFB boiler. The simplified scaling laws proposed by Glicksman et al. [1] are applied to the flow in the seal. The loop seal was built into an existing CFB unit with riser dimensions 0.7 m × 0.12 m × 8.5 m. The riser is not scaled but the pressure distribution in the CFB loop is similar to that in the boiler. The solids flow through the tube bundle was studied by means of visual observations, pressure drop and tube-temperatures, corresponding to the overall heat transfer rate to each tube. The loop seal was operated under various conditions, including those typical for the boiler. Thus, the recirculation flux of solids through the loop seal, as well as the fluidization velocity in the seal, were varied. In addition, the fraction of the bottom area that is fluidized was varied. The overall flow behavior of the CFB loop with the scaled loop seal was found to be similar to that of the boiler. The temperature measurements showed that the heat transfer rate to the tubes in the bundle differed depending on operating conditions and on the position of the tube, both laterally and vertically. The recirculation flux could be maintained with a substantial decrease of the fluidization flow in the seal compared to the conditions corresponding to full load in the boiler. In addition, it was possible to significantly decrease the fraction of the bottom of the seal that was fluidized. However, if the area beneath the tube bundle is not fluidized, the heat transfer rate to the tubes decreased.

Dynamic simulation of the circulating fluidized bed loop performance under the various operating conditions

2019 ◽  
Vol 233 (7) ◽  
pp. 901-913 ◽  
Author(s):  
Seongil Kim ◽  
Sangmin Choi ◽  
Jari Lappalainen ◽  
Tae-Ho Song
Keyword(s):  
Heat Transfer ◽  
Fluidized Bed ◽  
Heat Transfer Rate ◽  
Dynamic Simulation ◽  
Transfer Rate ◽  
Gas Flow ◽  
Circulating Fluidized Bed ◽  
Operating Conditions ◽  
Temperature Behavior ◽  
Furnace Temperature

In a circulating fluidized bed boiler, the large thermal mass and flow characteristics of the solids strongly affect the transient response of the circulating fluidized bed loop temperature, which determines the heat transfer rate to steam flow. Therefore, it is essential to interpret the dynamic response of the solid behavior in the circulating fluidized bed loop for the stable and efficient operation of the circulating fluidized bed boiler. In this study, the dynamic simulation of the solid behavior along with the flue gas flow in a circulating fluidized bed loop was performed by applying the core-annulus approach for the solid-gas flow inside the furnace and selected models for other physical phenomena of the fluidized bed. The circulating fluidized bed loop of a commercial boiler was selected as the target system. Especially, the model simulates the characteristics of the solid behavior, such as the local solid mass distribution, and the solid flow inside the furnace and the circulating solid according to the various operating conditions. These aspects are difficult to measure and quantify in a real power plant. In this paper, the simulated furnace temperature behavior as the representative performance parameter of the circulating fluidized bed loop was discussed along with the qualitative operation experiences reported in the literature. The operating conditions include the feed rate of fuel and air, the particle size, the solid inventory and the solid circulation rate. Furnace temperature behavior was reproduced through the simulation for each operating case in the literature and was analyzed with the solid behavior along with the combustion rate and heat transfer rate of the circulating fluidized bed loop. The simulation enables quantitative evaluation of the effect of the solid behavior on the temperatures of the furnace and return part in the various operating conditions.

Numerical Study of Fluid Flow and Heat Transfer Enhancement of Nanofluids over Tube Bank

2013 ◽  
Vol 388 ◽  
pp. 149-155 ◽  
Author(s):  
Mazlan Abdul Wahid ◽  
Ahmad Ali Gholami ◽  
H.A. Mohammed
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Pressure Drop ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Cross Flow ◽  
Bulk Temperature ◽  
Compact Heat Exchanger ◽  
Pure Fluid ◽  
Tube Banks

In the present work, laminar cross flow forced convective heat transfer of nanofluid over tube banks with various geometry under constant wall temperature condition is investigated numerically. We used nanofluid instead of pure fluid ,as external cross flow, because of its potential to increase heat transfer of system. The effect of the nanofluid on the compact heat exchanger performance was studied and compared to that of a conventional fluid.The two-dimensional steady state Navier-Stokes equations and the energy equation governing laminar incompressible flow are solved using a Finite volume method for the case of flow across an in-line bundle of tube banks as commercial compact heat exchanger. The nanofluid used was alumina-water 4% and the performance was compared with water. In this paper, the effect of parameters such as various tube shapes ( flat, circle, elliptic), and heat transfer comparison between nanofluid and pure fluid is studied. Temperature profile, heat transfer coefficient and pressure profile were obtained from the simulations and the performance was discussed in terms of heat transfer rate and performance index. Results indicated enhanced performance in the use of a nanofluid, and slight penalty in pressure drop. The increase in Reynolds number caused an increase in the heat transfer rate and a decrease in the overall bulk temperature of the cold fluid. The results show that, for a given heat duty, a mas flow rate required of the nanofluid is lower than that of water causing lower pressure drop. Consequently, smaller equipment and less pumping power are required.

Performance Evaluation of Tube-in-Tube Heat Exchanger Using Nanofluids

2015 ◽  
Vol 787 ◽  
pp. 72-76 ◽  
Author(s):  
V. Naveen Prabhu ◽  
M. Suresh
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Pressure Drop ◽  
Heat Transfer Rate ◽  
Thermal Performance ◽  
Transfer Rate ◽  
Flow Characteristics ◽  
Operating Conditions ◽  
Element Analysis ◽  
Tube Heat Exchanger

Nanofluids are fluids containing nanometer-sized particles of metals, oxides, carbides, nitrides, or nanotubes. They exhibit enhanced thermal performance when used in a heat exchanger as heat transfer fluids. Alumina (Al2O3) is the most commonly used nanoparticle due to its enhanced thermal conductivity. The work presented here, deals with numerical simulations performed in a tube-in-tube heat exchanger to study and compare flow characteristics and thermal performance of a tube-in-tube heat exchanger using water and Al2O3/water nanofluid. A local element-by-element analysis utilizing e-NTU method is employed for simulating the heat exchanger. Profiles of hot and cooling fluid temperatures, pressure drop, heat transfer rate along the length of the heat exchanger are studied. Results show that heat exchanger with nanofluid gives improved heat transfer rate when compared with water. However, the pressure drop is more, which puts a limit on the operating conditions.

scholarly journals Experimental Study for Counter to Cross Flow Air Cooled Heat Exchanger in Concentric Tube using Rectangular Copper Fins Spacing with Internal Spiral Grooving

2021 ◽  
pp. 203-208
Author(s):  
Rakesh Kumar Tiwari ◽  
Ajay Singh ◽  
Parag Mishra
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Natural Convection ◽  
Heat Exchanger ◽  
Forced Convection ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Cross Flow ◽  
Variable Number ◽  
Air Cooled Heat Exchanger

In this manuscript we have presented eight variation of Air-Cooled Heat Exchanger (ACHE) design with internal spiral grooving, all of them are having variable number of rectangular copper fins with different distances between the fins. In the proposed design we get the value of heat transfer rate of a counter to cross flow ACHE is 7833.77 watt, 4068.13 watt, 2736.95 watt, 2161.49 watt, 1802.89 watt, 1546.44 watt, 1336.51 watt and 1165.74 watt in natural convection (without fan) for 0.5 cm, 1.0 cm, 1.5 cm, 2.0 cm, 2.5 cm, 3.0 cm, 3.5 cm and 4.0 cm respectively. Then again, value of rate of heat transfer in forced convection (with fan) are 8007.46 watt, 4084.81 watt, 2754.69 watt, 2205.98 watt, 1809.24 watt, 1555.39 watt, 1352.88 watt and 1172.78 watt for 0.5 cm, 1.0 cm, 1.5cm, 2.0 cm, 2.5 cm, 3.0 cm, 3.5 cm and 4.0 cm respectively.

scholarly journals AVERAGE HEAT TRANSFER OF TUBES IN DOWNWARD FOAM FLOW

2003 ◽  
Vol 2 (1) ◽  
Author(s):  
J. Gylys ◽  
M. Jakubcionis ◽  
S. Sinkunas ◽  
T. Zdankus
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Liquid Velocity ◽  
Tube Bundle ◽  
Stable Foam ◽  
Foam Flow ◽  
Horizontal Tubes ◽  
Tube Position ◽  
Foam Generator

The model of heat exchanger was investigated experimentally. This model consists of three vertical lines of horizontal tubes with five tubes in each. Tubes were arranged in a staggered order. Heat transfer of staggered bundle of tubes to downward static stable foam flow was investigated experimentally. Heat transfer dependence on specific gas and liquid velocity was determined. Dependence of volumetric void fraction of foam on heat transfer was investigated also. Heat transfer rate dependence on tube position in the line of tube bundle was investigated experimentally. It was established that heat transfer rate highly depends on tube position in the line. Influence of tube position on heat transfer from tube bundle in upward foam flow was compared. Heat transfer dependence on tube position in the bundle was investigated experimentally also. Influence of wall of foam generator on heat transfer to sideline of tubes was established. Experimental results of heat transfer of bundle of tubes to downward static stable foam flow were generalized using dependence between Nusselt and Reynolds numbers.

Effect of tilt angle on the multi-pipe channel with sinusoidal/curved walls – numerical modelling based on finite volume method

2019 ◽  
Vol 29 (5) ◽  
pp. 1590-1605 ◽  
Author(s):  
Payam Hooshmand ◽  
Mohammad Bahrami ◽  
Navid Bagheri ◽  
Meysam Jamshidian ◽  
Emad Hasani Malekshah
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Heat Transfer Rate ◽  
Entropy Generation ◽  
Transfer Rate ◽  
Pure Water ◽  
Cuo Nanoparticles ◽  
Operating Conditions ◽  
Cold Temperatures ◽  
Content Type

Purpose This paper aims to investigate the two-dimensional numerical modeling of fluid flow and heat transfer in a fluid channel. Design/methodology/approach The channel is filled with the CuO-water nanofluid. The KKL model is used to estimate the dynamic viscosity and considering Brownian motion. On the other hand, the influence of CuO nanoparticles’ shapes on the heat transfer rate is taken account in the simulations. The channel is included with several active pipes with hot and cold temperatures. Furthermore, the external curved and sinusoidal walls have cold and hot temperatures, respectively. Findings Three different tilt angles are considered with similar boundary and operating conditions. The Rayleigh numbers, solid volume fraction of CuO nanoparticles in the pure water and the tilt angles are the governing parameters. Different cases studies, such as streamlines, heat transfer rate, local and total entropy generation and heatlines, are analysed under influences of these governing parameters. Originality/value The originality of this work is investigation of fluid flow, heat transfer and entropy generation within a nanofluid filled channel using FVM.

scholarly journals Analytical Performance Analysis of Cross Flow Louvered Fin Automobile Radiator

2018 ◽  
Vol 172 ◽  
pp. 02003
Author(s):  
R Badgujar Pankaj ◽  
S Rangarajan ◽  
S. R Nagaraja
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Cross Flow ◽  
Maximum Deviation ◽  
Side Pressure ◽  
Proposed Model ◽  
Louvered Fin ◽  
Louvered Fins

The objective of the present paper is to propose an analytical model for calculating performance parameter of a radiator having rectangular tube with louvered fins. The theoretical effectiveness, heat transfer rate, outlet temperatures of both air and coolant are determined using effectiveness-NTU method. The coolant and air side pressure drop is also calculated. The proposed procedure is validated with experimetal results available in the literature and the GT model. It is found that the maximum deviation in the heat transfer rate calculated from proposed model is 10.97%, the coolant and air outlet temperatures is 2.75% and variation in pressure drop is about 3.29%.

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

2020 ◽  
Vol 13 (2) ◽  
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.

Nonlinear Dynamic Analysis of the Local Heat Transfer Rate in Three-Phase Reactors

2004 ◽  
Vol 2 (1) ◽  
Author(s):  
Wei Chen ◽  
Atsushi Tsutsumi ◽  
Yoshiki Shigaki ◽  
Kentaro Otawara
Keyword(s):  
Heat Transfer ◽  
Dynamic Analysis ◽  
Heat Transfer Rate ◽  
Nonlinear Dynamic ◽  
Transfer Rate ◽  
Nonlinear Dynamic Analysis ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Operating Conditions ◽  
Three Phase

In this present work, nonlinear dynamic analysis was performed to the fluctuation signals of the local heat transfer rate measured in three-phase reactors of different scales to characterize the dynamics of three-phase reactors. The results of nonlinear test with surrogate data give evidence of nonlinear determinism in heat transfer rates series. The chaotic nature of the local heat transfer rate was further characterized in terms of the correlation dimension and Kolmogorov entropy. It was found that the correlation dimensions were in the range between 2.0 and 4.0 and Kolmogorov entropies were varied with the change of measurement positions and the operating conditions. With the increase of column scale or the addition of solids, Kolmogorov entropies decrease significantly. The dependence of chaotic parameters on the column scale is considered to be closely related to the different macroscopic flow structures observed in three-phase reactors of different scales.

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