Core annular flow theory as applied to the adiabatic section of heat pipes

2020 ◽  
Vol 32 (8) ◽  
pp. 083607
Author(s):  
Aishwarya Rath ◽  
M. R. Flynn
Keyword(s):  
Annular Flow ◽  
Heat Pipes ◽  
Flow Theory ◽  
Adiabatic Section

Correlations of Critical Froude Number for Annular-Rimming Flow in Rotating Heat Pipes

2001 ◽  
Vol 123 (4) ◽  
pp. 909-913 ◽  
Author(s):  
J. Baker ◽  
T. Oliver ◽  
L. Lin ◽  
R. Ponnapan ◽  
J. Leland
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Annular Flow ◽  
Heat Pipes ◽  
Operating Conditions ◽  
Uniform Thickness ◽  
Heat Transfer Characteristics ◽  
Rimming Flow ◽  
Critical Rotational Speed ◽  
Flow Transitions

The behavior of flow within a rotating finite length cylinder has been investigated. For low rotational speeds, the flow is characterized by a non-uniform thickness i.e., rimming flow. Above a critical rotational speed, the flow transitions to annular flow. Correlations developed from the experimental data are presented for the three regimes: onset of annular flow, complete annular flow, and collapse of annular flow. The correlation for the collapse of annular flow compared well with a previously presented, theoretically developed correlation. Given that the heat transfer characteristics of rotating heat pipes depend upon the film thickness of the fluid charge, the correlations presented here will be valuable in determining regular operating conditions.

scholarly journals Thermodynamic Analysis of the Dryout Limit of Oscillating Heat Pipes

Energies ◽  
2020 ◽  
Vol 13 (23) ◽  
pp. 6346
Author(s):  
Florian Schwarz ◽  
Vladimir Danov ◽  
Alexander Lodermeyer ◽  
Alexander Hensler ◽  
Stefan Becker
Keyword(s):  
Flow Pattern ◽  
Annular Flow ◽  
Analytical Data ◽  
Heat Pipes ◽  
Threshold Value ◽  
Vapor Quality ◽  
Cooling Systems ◽  
Key Factor ◽  
Operating Limits ◽  
Experimental Approaches

The operating limits of oscillating heat pipes (OHP) are crucial for the optimal design of cooling systems. In particular, the dryout limit is a key factor in optimizing the functionality of an OHP. As shown in previous studies, experimental approaches to determine the dryout limit lead to contradictory results. This work proposes a compact theory to predict a dryout threshold that unifies the experimental and analytical data. The theory is based on the influence of vapor quality on the flow pattern. When the vapor quality exceeds a certain limit (x = 0.006), the flow pattern changes from slug flow to annular flow and the heat transfer decreases abruptly. The results indicate a uniform threshold value, which has been validated experimentally and by the literature. With that approach, it becomes possible to design an OHP with an optimized filling ratio and, hence, substantially improve its cooling abilities.

Experimental Research and Simulation in a Thermosyphon

2012 ◽  
Vol 580 ◽  
pp. 441-444
Author(s):  
K.M. Yang ◽  
N.H. Wang ◽  
C.H. Jiang ◽  
L. Cheng
Keyword(s):  
Heat Pipe ◽  
Cfd Simulation ◽  
Thermal Characteristics ◽  
Heat Pipes ◽  
High Heat ◽  
Evaporation And Condensation ◽  
Maximum Value ◽  
High Heat Transfer ◽  
Adiabatic Section ◽  
Very High

Heat pipes are devices capable of very high heat transfer and have been widely used in many thermal management applications. An experimental investigation and CFD simulation of thermal characteristics of heat pipe was presented in this paper. It can be found that UDF in FLUENT can simulate the evaporation and condensation in heat pipe. The pressure difference between evaporation section and condenser ensure the vapor can flow successfully from the evaporation section to condenser. In steady state, the fluctuation of axial velocity is very small in the most area in heat pipe. In general, the magnitudes of velocity vary from 0 to maximum from the end of both evaporation section and condenser, and the maximum value was maintained in the adiabatic section.

Study on the effect of the adiabatic section parameters on the performance of pulsating heat pipes

2020 ◽  
Vol 180 ◽  
pp. 115813
Author(s):  
Qingfeng Li ◽  
Chenhao Wang ◽  
Yanan Wang ◽  
Zhengkun Wang ◽  
Hua Li ◽  
...  
Keyword(s):  
Heat Pipes ◽  
Adiabatic Section

scholarly journals Correlations to predict thermal performance affected by working fluid’s properties of vertical and horizontal closed-loop pulsating heat pipe

2016 ◽  
Vol 20 (5) ◽  
pp. 1555-1564
Author(s):  
Phrut Sakulchangsatjatai ◽  
Niti Kammuang-Lue ◽  
Kritsada On-Ai ◽  
Pradit Terdtoon
Keyword(s):  
Heat Pipe ◽  
Thermal Performance ◽  
Closed Loop ◽  
Heat Pipes ◽  
Bond Number ◽  
Working Fluid ◽  
Inlet Temperature ◽  
Pulsating Heat Pipe ◽  
Dimensionless Numbers ◽  
Adiabatic Section

Objectives of this paper are to investigate the effects of dimensionless numbers on the thermal performance, and to establish correlations to predict the thermal performance of the vertical and a horizontal closed-loop pulsating heat pipe. The heat pipes were made of long copper capillary tubes with 26 meandering turns and both the ends were connected together to form a loop. R123, R141b, acetone, ethanol, and water were chosen as variable working fluids with a constant filling ratio of 50% by total volume. The inlet temperature of the heating medium and the adiabatic section temperature were constantly controlled and maintained at 80?C and 50?C, respectively. The thermal performance was represented in terms of the Kutateladze number. It can be concluded that when the Prandtl number of the liquid working fluid, as well as the Karman number, increases, the thermal performance increases. On the other hand, when the Bond number, the Jacob number, and the Aspect ratio increase, the thermal performance decreases. These effects of the dimensionless numbers on the thermal performance are valid for both the heat pipes, except in the case of Bond number which has no effect on the thermal performance as far as the horizontal heat pipe is concerned. Moreover, correlations to predict thermal performance have been successfully established.

On the Test Setting at Condenser in Thermal Performance Tests of Heat Pipes

2017 ◽  
Author(s):  
S.-C. Wong ◽  
Z.-J. Hsu ◽  
L.-C. Hsu
Keyword(s):  
Heat Pipe ◽  
Pipe Wall ◽  
Cooling Water ◽  
Heat Pipes ◽  
Performance Tests ◽  
Test Results ◽  
Performance Measurements ◽  
The Third ◽  
Reliable Performance ◽  
Adiabatic Section

This work compares the heat pipe test results using different test settings at the condenser under an identical evaporator setting and operating temperature of 45°C at the adiabatic section. The first test setting, considered as the standard, adopts a pair of water-cooled cold plates in which the heat pipe condenser is embedded, with a number of thermocouple beads attached to the condenser wall. In the second setting, the condenser resistances are determined based on the wall temperatures measured outside either end of the cold plate. The third setting adopts a water jacket with a number of thermocouples attached to the condenser wall but exposed to the cooling water. These three test settings have been applied in the literature. The second setting fails to count in the thermal resistances across the wick and pipe wall, and thereby seriously under-estimated the condenser resistances. For the third setting, the temperature readings are lowered by the cooling water so that the condenser resistances are greatly over-estimated. However, a fourth setting with the cooling-protected thermocouples yields similar results obtained using the standard setting. These results suggest that thermocouples be suitably arranged to ensure reliable performance measurements for the heat pipe condenser.

Effect of particle size on erosion measurements and predictions in annular flow for an elbow

Wear ◽  
2020 ◽  
pp. 203579
Author(s):  
G. Haider ◽  
M. Othayq ◽  
J. Zhang ◽  
R.E. Vieira ◽  
S.A. Shirazi
Keyword(s):  
Particle Size ◽  
Annular Flow ◽  
Effect Of Particle Size
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