Investigation on the Radial Heat-Transfer of Pumping Secondary Flow in Semiclosed Rotating Disk Cavity

2020 ◽  
Vol 143 (1) ◽  
Author(s):  
Guohu Luo ◽  
Zhenqiang Yao
Keyword(s):  
Heat Transfer ◽  
Secondary Flow ◽  
Outer Region ◽  
Rotating Disk ◽  
Mean Flow ◽  
Coolant Pump ◽  
Radial Temperature ◽  
Type Flow ◽  
Radial Heat ◽  
Inner Region

Abstract This study investigates the mean flow and radial heat-transfer behaviors in semiclosed rotating disk cavity within the canned reactor coolant pump. The flow in the semiclosed cavity contains the Stewartson type flow at inner region and the Batchelor type flow at outer region. The heat is radially transported from the outer rim of the semiclosed disk cavity to discharge-hole through the nondirect discharge (ND) portion of the superimposed flow from inlet. The effects of rotating Reynolds numbers, cavity aspect ratio and radial location of discharge-hole on the discharge ratio, pumping mass flow rate, local wall shear stress and radial heat-transfer coefficient are examined in the semiclosed rotating cavity flow, respectively. Based on the radial heat transfer behaviors of pumping secondary flow, an equivalent thermal network is proposed and validated by experiments, which can effectively predict the radial temperature distribution from the discharge hole to periphery with the viscous-heating and nonisothermal effects.

Measurement and Analysis of Buoyancy-Induced Heat Transfer in Aero-Engine Compressor Rotors

2020 ◽  
Author(s):  
Richard W. Jackson ◽  
Dario Luberti ◽  
Hui Tang ◽  
Oliver J. Pountney ◽  
James A. Scobie ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Three Dimensional ◽  
Outer Region ◽  
Conjugate Problem ◽  
Radial Temperature ◽  
Nusselt Numbers ◽  
Induced Flow ◽  
Aero Engines ◽  
Inner Region ◽  
Buoyancy Induced Flow

Abstract The flow inside cavities between co-rotating compressor discs of aero-engines is driven by buoyancy, with Grashof numbers exceeding 1013. This phenomenon creates a conjugate problem: the Nusselt numbers depend on the radial temperature distribution of the discs, and the disc temperatures depend on the Nusselt numbers. Furthermore, Coriolis forces in the rotating fluid generate cyclonic and anti-cyclonic circulations inside the cavity. Such flows are three-dimensional, unsteady and unstable, and it is a challenge to compute and measure the heat transfer from the discs to the axial throughflow in the compressor. In this paper, Nusselt numbers are experimentally determined from measurements of steady-state temperatures on the surfaces of both discs in a rotating cavity of the Bath Compressor-Cavity Rig. The data are collected over a range of engine-representative parameters and are the first results from a new experimental facility specifically designed to investigate buoyancy-induced flow. The radial distributions of disc temperature were collected under carefully-controlled thermal boundary conditions appropriate for analysis using a Bayesian model combined with the equations for a circular fin. The Owen-Tang buoyancy model has been used to compare predicted radial distributions of disc temperatures and Nusselt numbers with some of the experimentally determined values, taking account of radiation between the interior surfaces of the cavity. The experiments show that the average Nusselt numbers on the disc increase as the buoyancy forces increase. At high rotational speeds the temperature rise in the core, created by compressibility effects in the air, attenuates the heat transfer and there is a critical rotational Reynolds number for which the Nusselt number is a maximum. In the cavity, there is an inner region dominated by forced convection and an outer region dominated by buoyancy-induced flow. The inner region is a mixing region, in which entrained cold throughflow encounters hot flow from the Ekman layers on the discs. Consequently, the Nusselt numbers on the downstream disc in the inner region tend to be higher than those on the upstream disc.

scholarly journals Effects of the rotation number on flow and heat transfer in contra-rotating disk cavity with superposed flow

2019 ◽  
Vol 11 (10) ◽  
pp. 168781401988104 ◽  
Author(s):  
Shu-xian Chen ◽  
Jing-zhou Zhang
Keyword(s):  
Heat Transfer ◽  
Flow Structure ◽  
Rotation Number ◽  
Tangential Velocity ◽  
Inertial Force ◽  
Rotating Disk ◽  
Rotating Disks ◽  
Radial Temperature ◽  
Disk Rotation ◽  
Type Flow

The turbulent fluid flow and convective heat transfer in counter-rotating disk cavity with central axial air inflow and radial air outflow are numerically studied based on the finite volume method. Efforts are focused upon the influence of the rotation number Rt on the flow structure, cooling performance, sealing effect, and surface tangential friction characteristics in the cavity. The stagnation point where the radial outward flow along the upstream disk driven by the rotation force meets the radial outward flow along downstream disk driven by the combination of rotation force and inflow inertial force moves from upstream disk wall to the shroud with increasing Rt. At the Rt far smaller than 1, the fluids in the core region between two disks rotate with the upstream disk like a rigid body, and the tangential velocity of the rotating core decreases with the increase of the disk cavity radius, which is different from the Batchelor-type flow. At the Rt larger than 1, the fluids on the upstream disk side rotate like the Batchelor-type flow, while the sandwich rotation disappears in the fluid on the downstream disk side. The temperature on the upstream disk wall increases and then decreases with increasing values of Rt, and the critical value of Rt for the change of temperature variation is assessed to be at about Rt = 0.69. The temperature and radial temperature gradient of the downstream disk wall decrease with increasing Rt. With increasing Rt by increasing the disk rotation rate, the pressures near the downstream disk decrease, while the frictional moments on rotating disks increase. Due to the effect of flow structure, the frictional moment on the upstream disk is smaller than that on the downstream disk.

The Highly Turbulent Flow and Heat Transfer in Semi-Closed Rotating Disc Cavity

2019 ◽  
Author(s):  
Guohu Luo ◽  
Zhenqiang Yao ◽  
Shengde Wang ◽  
Hong Shen
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Aspect Ratio ◽  
Turbulent Flow ◽  
Prediction Models ◽  
Rotating Disk ◽  
Radial Temperature ◽  
Flow And Heat Transfer ◽  
Radial Heat ◽  
Radial Outflow

Abstract The highly turbulent flow and heat-transfer in a semi-closed rotating disk cavity is numerically simulated based on a hybrid RANS/LES turbulence model. The superimposed radial outflow, which enters into the cavity from the inlet and exits the cavity from the discharge holes, results in the three flow region formed in the disk cavity. The effects of rotating Reynolds’ number and cavity aspect ratio on the pumping mass flow, local momentum coefficient as well as radial heat-transfer coefficient are fully examined. And the corresponding correlations are established with respect to rotating Reynolds’ number and aspect ratio. It is revealed that the radial heat-transfer from the periphery of the cavity to discharge hole is highly correlated to the secondary flow pumped by the rotating disk. Based on those prediction models, an equivalent thermal network for the radial heat-transfer is proposed, which can efficiently predict the radial temperature distribution in the semi-closed disk cavity, and estimate the effects of viscous-heating as well as temperature-viscosity correction.

Large Eddy Simulation of Flow and Heat Transfer in a Staggered 45° Ribbed Duct

2004 ◽  
Author(s):  
Samer Abdel-Wahab ◽  
Danesh K. Tafti
Keyword(s):  
Heat Transfer ◽  
Large Eddy Simulation ◽  
Secondary Flow ◽  
Mean Flow ◽  
Cross Sectional ◽  
Heat Transfer Augmentation ◽  
Eddy Simulation ◽  
Flow And Heat Transfer ◽  
Large Eddy ◽  
Rib Vortex

Results from large eddy simulation (LES) of fully developed flow in a staggered 45° ribbed duct are presented with rib pitch-to-height ratio P/e = 10 and a rib height to hydraulic diameter ratio e/Dh = 0.1. The nominal Reynolds number based on bulk velocity is 47,300. Mean flow and turbulent quantities, together with heat transfer and friction augmentation results are presented. The flow is characterized by a helical vortex behind each rib and a complementary cross-sectional secondary flow, both of which result from the angle of the rib with respect to the mean flow. Averaged velocity profiles at the duct center show excellent agreement with experiments and heat transfer predictions agree well with experiments. Turbulent kinetic energy, shear stress, and heat transfer augmentation ratios show a strong correlation to the rib vortex and the secondary flow. Overall, heat transfer is augmented by a factor of 2.3 compared with a smooth duct and matches experimental data within 2%.

Chaotic Heat Transfer in a Laminar Pulsating Flow With Constant Wall Temperature

2014 ◽  
Author(s):  
Mohammad Karami ◽  
Mojtaba Jarrahi ◽  
Zahra Habibi ◽  
Ebrahim Shirani ◽  
Hassan Peerhossaini
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Secondary Flow ◽  
Wall Temperature ◽  
Pulsating Flow ◽  
Mean Flow ◽  
Transfer Enhancement ◽  
Constant Wall Temperature ◽  
Homoclinic Connections

The correlation between heat transfer enhancement and secondary flow structures in laminar flows through a chaotic heat exchanger is discussed. The geometry consists of three bends; the angle between curvature planes of successive bends is 90°. Numerical simulations are performed for both steady and pulsating flows when the walls are subjected to a constant temperature. The temperature profiles and secondary flow patterns at the exit of bends are compared in order to characterize the flow. Simulations are carried out for the Reynolds numbers range 300≤Re≤800, velocity amplitude ratios (the ratio of the peak oscillatory velocity component to the mean flow velocity) 1≤β≤2.5, and wall temperatures 310 ≤ Tw(K) ≤ 360. The results show that in the steady flow, heat transfer enhancement occurs with increasing Reynolds number and wall temperature. However, heating homogenization becomes almost independent of Reynolds number when homoclinic connections exist in the flow. Moreover, at high values of wall temperature, heat transfer enhancement is greater than mixing improvement due to the presence of homoclinic connections. In the pulsating flow, Nusselt number improves with β, and β≥2 is a sufficient condition for heat transfer enhancement. The formation and development of homoclinic connections are correlated with the heating homogenization.

Effect of Heat Source Geometry on the Transient Heat Transfer During Melting Process of a PCM

2016 ◽  
Author(s):  
Mohammad Bashar ◽  
Kamran Siddiqui
Keyword(s):  
Heat Transfer ◽  
Heat Source ◽  
Convective Heat Transfer Coefficient ◽  
Outer Region ◽  
Melting Process ◽  
Melting Rate ◽  
Transfer Coefficients ◽  
Heat Transfer Behavior ◽  
Transfer Behavior ◽  
Inner Region

Thermal energy storage (TES) systems using phase change materials (PCMs) are used in various engineering applications. TES is a means by which heat is ‘hold’ for a certain period of time for use at a later time. We report an experimental study which was conducted to investigate the melting process and associated heat transfer in a rectangular chamber with a cylindrical u-shaped heat source imbedded inside the PCM. The results showed that geometry and orientation of the heat source immensely influenced the heat transfer behavior during solid-liquid phase transition. The heat transfer behavior, interface movement and the heat transfer coefficients differed both axially and vertically inside the chamber as well as with the melting rate. The local convective heat transfer coefficient, hlocal in the inner region, enclosed by the U-tube, was observed to increase at a higher rate than the outer region. Stronger convective flow and a lower viscosity owing to higher temperature in the inner region is believed to have caused faster melting in this region. The melting rate was also found comparatively higher until approximately two-third of the PCM volume was melted before the rate declined.

Analyses on Effect of Helix Angle on the Continuous Helical Baffles Heat Exchanger

2014 ◽  
Vol 1008-1009 ◽  
pp. 901-905
Author(s):  
Jia Zhu Zou ◽  
Feng Wei Yuan ◽  
Liang Bin Hu
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Heat Exchanger ◽  
Cross Section ◽  
Outer Region ◽  
Tangential Velocity ◽  
Helix Angle ◽  
Heat Transfer Characteristics ◽  
Shell Side ◽  
Inner Region

A numerical simulation for heat exchanger with continuous helical baffles was carried out. The study focuses on the effects of helix angle on heat transfer characteristics. The results show that both the shell-side heat transfer coefficient and pressure drop decrease with the increase of the helix angle at certain mass flow rate. The latter decreases more quickly than the former. The tangential velocity distribution on shell-side cross section is more uniform with continuous helical baffles than with segmental baffles. The axial velocity at certain radial position decreases as the helix angle increases in the inner region near the central dummy tube, whereas it increases as the helix angle increases in the outer region near the shell. The heat exchange quantity distribution in tubes at different radial positions is more uniform at larger helix angel.

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