scholarly journals Optimization of thermo-hydraulic characteristics of solar cavity receiver under concentrated heat flux

2019 ◽  
Vol 103 (1) ◽  
pp. 003685041987590
Author(s):  
Yun Hao ◽  
Yueshe Wang
Keyword(s):  
Heat Flux ◽  
Heating Surface ◽  
Flow Distribution ◽  
Working Fluid ◽  
Stable Operation ◽  
Hydraulic Characteristics ◽  
Spot Center ◽  
Research Findings ◽  
High Temperature Steam ◽  
Better Than

It is important to study the effects of heat flux on the thermo-hydraulic characteristics in a solar cavity receiver because of the non-uniform radiation flux temporally and spatially. In this article, we presented a mathematical model of thermo-hydraulic characteristics of a solar cavity receiver, considering the effect of heat flux distribution on the energy transfer (radiation–conduction–convection). Using the model, the thermo-hydraulic characteristics under high concentrated heat flux were studied and then optimized the characteristics from two aspects: tube diameter (22, 27, 32, and 38 mm) and connection structure of the heating surface (H-type, central inlet/outlet, and vertical U-type). It was found that flow distribution changed smoothly at the diameter of 27 mm with the increase of the heat flux; when the diameter of tubes at the certain distance (1.6 σHF) from the spot center was replaced by 38 mm, the thermo-hydraulic characteristics were improved. For the evaporating surfaces, the thermo-hydraulic characteristics of working fluid (water) with the central inlet/outlet connection structure were better than those of the H-type connection structure. For the surperheated surfaces, the vertical U-type connection structure was applied to obtain the high temperature steam. These research findings are helpful for the safe and stable operation of the whole solar power system.

Experimental Study on the Critical Heat Flux of Nanofluid Flow Boiling Under Different Conditions

2018 ◽  
Author(s):  
Y. Wang ◽  
K. H. Deng ◽  
J. M. Wu ◽  
N. N. Yue ◽  
Y. F. Zan ◽  
...  
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Mass Flux ◽  
Flow Boiling ◽  
Heating Surface ◽  
Vertical Tube ◽  
Working Fluid ◽  
Nanofluid Flow ◽  
Sem Images ◽  
Heat Transfer System

Nanofluid has been attracted great attention since it was proposed as a preeminent working fluid. Flow boiling is familiar in heat transfer system and the critical heat flux is a key parameter for the design of thermal hydraulic. In present work, the critical heat flux of nanofluid flow boiling is experimentally investigated in a vertical tube with the consideration of outlet pressure, mass flux, inlet subcooling, heating length and diameter. The results indicate that the critical heat flux of nanofluid flow boiling is enhanced compared with base fluid and the increasing radio is increased with increasing the mass flux, diameter and pressure, and with decreasing the heating length. In addition, the inlet subcooling and concentrations (0.1vol.%, 0.5vol.%) have almost no significant influence. Furthermore, a new mechanism for the enhancement of nanofluid flow boiling critical heat flux was proposed by the SEM images of nanopariticle deposition on the heating surface.

Use of Liquid Film Evaporation in Biporous Media to Achieve High Heat Flux Over Large Areas

2005 ◽  
Author(s):  
Tadej Semenic ◽  
Ying-Yu Lin ◽  
Ivan Catton
Keyword(s):  
Heat Flux ◽  
Test Chamber ◽  
Heat Removal ◽  
High Heat ◽  
Working Fluid ◽  
Interface Temperature ◽  
High Heat Flux ◽  
Film Evaporation ◽  
Powder Diameter ◽  
Better Than

Boiling characteristics of three biporous and one monoporous sintered wick are tested. The monoporous wick has the same wick thickness as a comparable biporous wick. Diameters of the clusters of the comparable biporous wick are equal to the powder diameter of the monoporous wick. A second biporous wick has the same configuration as the first, but is sintered in a thicker layer. The third biporous wick that is tested has smaller cluster sizes then the first two. All three biporous wicks have clusters sintered from powder with the same size distribution. The results demonstrate the advantages of a biporous capillary structure. All biporous wicks reached higher critical heat flux (CHF) then the monoporous wick. Experiments show that larger clusters are better than smaller. Comparing two different wick thicknesses, we can see that even though there is a dryout region inside the thick wick, it is still able to continuously remove heat at constant superheat. No sudden changes in superheat are seen. This process of heat removal is not possible with the thin wick. The working fluid in all runs is methanol. 4-mm thick wick with powder diameter ranging from 53 to 63 microns and cluster diameter ranging from 500 to 707microns is able to remove 377W/cm2 at temperature difference 110°C. A partial pressure inside the test chamber at this heat flux is 0.68atm and the interface temperature 167°C.

scholarly journals Effect of One-Target Focus Type on Hydrodynamic Characteristics of Tower Solar Cavity Receiver

2014 ◽  
Vol 6 ◽  
pp. 615942 ◽  
Author(s):  
Yun Hao ◽  
Kaituo Chen ◽  
Yueshe Wang ◽  
Tian Hu
Keyword(s):  
Heat Flux ◽  
Flow Distribution ◽  
Working Fluid ◽  
Hydrodynamic Characteristics ◽  
Two Phase ◽  
Local Overheating ◽  
Focus Type ◽  
Flow Circulation ◽  
The One ◽  
Thermal Deviation

On account of one-target focus type of the heliostats in the tower solar power technology, the heat transfer was analyzed for the vapor-liquid two-phase or single-phase superheated steam in the parallel heated panel bundles of the solar cavity receiver. A nonlinear mathematical model of the hydrodynamic characteristics in the evaporation panels was developed to obtain the flow rate distribution, thermal deviation, and two-phase flow circulation reliability of the working fluid under the severe nonuniform heat flux from the one-target focus of the heliostats. The simulation results show that for the evaporation panels the flow distribution can synchronize with that of the heat flux at the low heat flux, while for the superheater sections the flow distribution decreases with the increase of heat flux. This desynchrony may give rise to stagnation or backflow of the working fluid and lead to the panels burst or erosion due to the local overheating in some extreme situation.

Numerical Analysis on Heat Transfer and Oxidation Characteristics of High-Temperature Steam Pipes in Supercritical Units

2014 ◽  
Vol 908 ◽  
pp. 81-84
Author(s):  
Pan Pan Sun ◽  
Shu Zhong Wang ◽  
Yan Hui Li ◽  
Xue Dong Li
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Oxide Film ◽  
Flue Gas ◽  
Working Fluid ◽  
Gas Temperature ◽  
Steam Temperature ◽  
Average Temperature ◽  
High Temperature Steam ◽  
Steam Pipes

In this paper, for Super304H steel, the growth law of oxide films and the heat transfer characteristics between the pipe and the working fluid were investigated by using numerical software ANSYS, which simulated comprehensively the effects of pipe size, flow rates of steam, flue gas temperature, and steam temperature on the formation and thickness of the oxide film. A bigger pipe wall thickness, a smaller steam flow rate or a higher flue gas temperature will lead the faster growth of the oxide film thickness, the heat flux density through the wall being smaller and the wall temperature being higher. With increases in steam temperature and thickness of the oxide film, the heat flux through the wall decreases with a small amplitude, and the average temperature of tube walls increases slightly.

scholarly journals Subcooled Flow Boiling Heat Flux Enhancement Using High Porosity Sintered Fiber

2021 ◽  
Vol 11 (13) ◽  
pp. 5883
Author(s):  
Edgar Santiago Galicia ◽  
Yusuke Otomo ◽  
Toshihiko Saiwai ◽  
Kenji Takita ◽  
Kenji Orito ◽  
...  
Keyword(s):  
Heat Flux ◽  
Porous Body ◽  
Flow Boiling ◽  
Heating Surface ◽  
Working Fluid ◽  
High Porosity ◽  
Subcooled Flow Boiling ◽  
Wall Superheat ◽  
Subcooled Flow ◽  
Bare Surface

Passive methods to increase the heat flux on the subcooled flow boiling are extremely needed on modern cooling systems. Many methods, including treated surfaces and extended surfaces, have been investigated. Experimental research to enhance the subcooled flow boiling using high sintered fiber attached to the surface was conducted. One bare surface (0 mm) and four porous thickness (0.2, 0.5, 1.0, 2.0 mm) were compared under three different mass fluxes (200, 400, and 600 kg·m−2·s−1) and three different inlet subcooling temperature (70, 50, 30). Deionized water under atmospheric pressure was used as the working fluid. The results confirmed that the porous body can enhance the heat flux and reduce the wall superheat temperature. However, higher porous thickness presented a reduction in the heat flux in comparison with the bare surface. Bubble formation and pattern flow were recorded using a high-speed camera. The bubble size and formation are generally smaller at higher inlet subcooling temperatures. The enhancement in the heat flux and the reduction on the wall superheat is attributed to the increment on the nucleation sites, the increment on the heating surface area, water supply ability through the porous body, and the vapor trap ability.

Transient Pool Boiling Under Self Pressurized Systems

2003 ◽  
Author(s):  
Ahmed ElGafy ◽  
Khalid Lafdi
Keyword(s):  
Heat Flux ◽  
Pool Boiling ◽  
Saturation Temperature ◽  
Heating Surface ◽  
Working Fluid ◽  
Atmospheric Conditions ◽  
Transient Conditions ◽  
System Pressure ◽  
The Mean ◽  
The Heat Transfer Coefficient

An experimental investigation of the transient pool boiling under self-pressurized systems is presented in this work. A vertical cylindrical heating surface of known surface roughness is used. Test runs are carried out on a closed vessel to attain self-pressurized system while water is utilized as the working fluid. Two glass windows are opened in the test vessel to observe the phenomenon. The increasing pressure and the consequent variable difference between the mean heating surface temperature and the saturation temperature corresponding to the system pressure are measured during each of the test runs. The runs cover an input heat flux from (40 × 103 to 80 × 103 W/m2) over a pressure range from the atmospheric to 5.5 bars. For transient conditions, an empirical correlation to relate the heat transfer coefficient to both heat flux and pressure is obtained. Also, a comparative study is performed between the present work and a previous work under steady state atmospheric conditions.

Effect of Liquid Volume on Thermosiphon Loop Performance Using Open Microchannels Manifold for CPU Cooling in Data Center

2017 ◽  
Author(s):  
Aranya Chauhan ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Data Center ◽  
Heat Dissipation ◽  
Heating Surface ◽  
Working Fluid ◽  
Liquid Volume ◽  
Transfer Coefficients ◽  
Unique Challenge ◽  
Maximum Heat

The efficient cooling of servers in data center offers unique challenge to reduce the worldwide energy consumption and fluid inventory. The presented work addresses the great potential of a thermosiphon system using two-phase heat transfer process which improves the efficiency of the system by significantly improving the heat dissipation ability. The latent heat transfer is more effective than sensible heat. However, the system performance is limited by Critical Heat Flux (CHF) and Heat Transfer Coefficients (HTC). An increase in CHF offers wide temperature operating range while HTC defines the efficiency of the process. In the current design of the cooling solution, a manifold with a taper is employed over the heater surface to guide vapor away from the surface along the flow length. The incoming liquid flows over the heating surface unobstructed developing separate liquid-vapor pathways. A 6° taper manifold is analyzed with HFE7000 as the working fluid. The performance of thermosiphon loop is evaluated for three different liquid volumes resulting in three different liquid heads available in the thermosiphon loop. The respective heat flux and HTC are compared. The maximum heat dissipation was observed for 325ml liquid with a microchannel chip resulting in a CHF of 42.1W/cm2 at a wall superheat of 17.8°C. The observed performance data shows that thermosiphon loop is an eligible replacement for conventional single-phase cooling techniques used for CPU cooling in data centers.

Development of Boiling Type Cooling System Using Electrohydrodynamics Effect

2013 ◽  
Vol 135 (9) ◽  
Author(s):  
Ichiro Kano ◽  
Yuta Higuchi ◽  
Tadashi Chika
Keyword(s):  
Heat Flux ◽  
Electric Field ◽  
Critical Heat Flux ◽  
Electric Fields ◽  
Cooling System ◽  
Surface Condition ◽  
Heating Surface ◽  
Nucleate Boiling ◽  
Working Fluid ◽  
High Electric Fields

This paper describes results from an experimental study of the effect of an electric field on nucleate boiling and the critical heat flux (CHF) in pool boiling at atmospheric pressure. A dielectric liquid of HFE-7100 (3 M Co.) was used as working fluid. A heating surface was polished with the surface roughness (Ra) of 0.05 μm. A microsized electrode, in which the slits were provided, was designed in order to generate non uniform high electric fields and to produce electrohydrodynamic (EHD) effects with the application of high voltages. The obtained results confirmed the enhancement of CHF since the EHD effects increased the CHF to 47 W/cm2 at the voltage of −1500 V, which was three times as much as CHF for the free convection boiling. From the observations of the behavior of bubbles over the electrode and of the boiling surface condition, the instability between the liquid and the vapor increased the heat flux, the heat transfer coefficient (HTC), and the CHF. The usual traveling wave on the bubble interface induced by the Kelvin-Helmholtz instability was modified by adding the EHD effects. The ratio of critical heat flux increase with and without the electric field was sufficiently predicted by the frequency ratio of liquid–vapor surface at the gap between the boiling surface and the electrode.

THE MECHANISM OF RAISING AND QUANTIFICATION OF SPECIFIC HEAT FLUX AT BOILING OF NANOFLUIDS IN FREE CONVECTION CONDITIONS

2017 ◽  
pp. 25-34
Author(s):  
V.N. Moraru
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Capacity ◽  
Specific Heat ◽  
Chemical Properties ◽  
Heating Surface ◽  
Physical Models ◽  
Superheated Liquid ◽  
Two Phase ◽  
Boiling Process

The results of our work and a number of foreign studies indicate that the sharp increase in the heat transfer parameters (specific heat flux q and heat transfer coefficient _) at the boiling of nanofluids as compared to the base liquid (water) is due not only and not so much to the increase of the thermal conductivity of the nanofluids, but an intensification of the boiling process caused by a change in the state of the heating surface, its topological and chemical properties (porosity, roughness, wettability). The latter leads to a change in the internal characteristics of the boiling process and the average temperature of the superheated liquid layer. This circumstance makes it possible, on the basis of physical models of the liquids boiling and taking into account the parameters of the surface state (temperature, pressure) and properties of the coolant (the density and heat capacity of the liquid, the specific heat of vaporization and the heat capacity of the vapor), and also the internal characteristics of the boiling of liquids, to calculate the value of specific heat flux q. In this paper, the difference in the mechanisms of heat transfer during the boiling of single-phase (water) and two-phase nanofluids has been studied and a quantitative estimate of the q values for the boiling of the nanofluid is carried out based on the internal characteristics of the boiling process. The satisfactory agreement of the calculated values with the experimental data is a confirmation that the key factor in the growth of the heat transfer intensity at the boiling of nanofluids is indeed a change in the nature and microrelief of the heating surface. Bibl. 20, Fig. 9, Tab. 2.

scholarly journals Parametric CFD Thermal Performance Analysis of Full, Medium, Half and Short Length Dimple Solar Air Tube

2021 ◽  
Vol 13 (11) ◽  
pp. 6462
Author(s):  
Mir Waqas Alam ◽  
Basma Souayeh
Keyword(s):  
Thermal Performance ◽  
Energy Transport ◽  
Hydraulic Performance ◽  
Short Length ◽  
Working Fluid ◽  
Solar Air Heater ◽  
Hydraulic Characteristics ◽  
Height Ratio ◽  
Pitch Ratio ◽  
Full Medium

In the present decade, research regarding solar thermal air heaters (SAHs) has noticed a continuous progression in thermo-hydraulic performance augmentation approaches. There now exists a wide variety of thermo-hydraulic performance augmentation approaches and researchers have designated various structures. Nevertheless, there seems to be no generalization to any of the approaches employed. The present numerical investigation reports on the thermo-hydraulic characteristics and thermal performance for flow through a varied length (full, medium, half, and short length) dimple solar air heater (SAH) tube. The study highlights recent developments on enhanced tubes to augment heat transfer in SAH. The influence of different length ratio, dimple height ratio (H), and pitch ratio (s) on thermo-hydraulic characteristics have been investigated in the Reynolds number (Re) range from 5000 to 25,000. Air is used as the working fluid. The commercial software ANSYS Fluent is used for simulation. The shear stress transport (SST) model is used as the turbulence model. Thermal energy transport coefficient is increased in the full-length dimple tube (FLDT), compared to the medium-length dimple tube (MLDT), half-length dimple tube (HLDT) and short-length dimple tube (SLDT). Similarly, the pitch ratio (s) has more influence on Nusselt number (Nu) compared to the dimple height ratio (H). The friction factor decreases with an increase in pitch ratio. Nu increases and f decreases with increasing Re for all combinations of H and s. Low s and higher H yields high enhancement of HT and PD. Integration of artificial roughness on the tube increases the values of Nu and f by 5.12 times and 77.23 times for H = 0.07, s = 1.0 at Re value of 5000 and 25,000, respectively, in regard to the plain tube. For all the tested cases, the thermo-hydraulic performances (η) are greater than unity.

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