scholarly journals Experimental Investigation of Heat Transfer Enhancement by Pulsating Flow in a Minichannel

2021 ◽  
Vol 2116 (1) ◽  
pp. 012031
Author(s):  
P Kumavat ◽  
S M O’Shaughnessy
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Enhancement ◽  
Flow Rate ◽  
Wall Temperature ◽  
High Performance ◽  
Amplitude Ratio ◽  
Constant Heat Flux ◽  
Pulsating Flow ◽  
Transfer Enhancement

Abstract The increasing power density requirements of next generation high performance electronic devices has resulted in ever-increasing heat flux densities which necessitates the evolution of new liquid-based heat exchange technologies. Pulsating flow in single-phase cooling systems is viewed as a potential solution. In this study, an experimental analysis of thermally developed pulsating flow in a rectangular minichannel is conducted. The channel test setup involves a heated bottom section approximated as a constant heat flux boundary. Asymmetric sinusoidal pulsating flows with a fixed flow rate amplitude ratio of 0.9 and Womersley numbers (Wo) of 0.51 and 1.6 are investigated. The wall temperature profiles are recorded using infrared thermography. It is observed that the transverse wall temperature profile is influenced by the sudden velocity variations of such characteristic waveforms. A heat transfer enhancement of 6% was determined for asymmetric flow pulsations of Wo > 1 over the steady flow with a potential augmentation for higher flow rate amplitudes.

Numerical Study of the Effects of Different Buoyancy Models on Supercritical Flow and Heat Transfer

2013 ◽  
Author(s):  
X. Y. Xu ◽  
T. Ma ◽  
M. Zeng ◽  
Q. W. Wang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Enhancement ◽  
Wall Temperature ◽  
Mass Flux ◽  
Wall Heat Flux ◽  
Turbulent Heat ◽  
Transfer Enhancement ◽  
Temperature Prediction ◽  
Flow And Heat Transfer

Due to the dramatic changes in physical properties, the flow and heat transfer in supercritical fluid are significantly affected by buoyancy effects, especially when the ratio of inlet mass flux and wall heat flux is relatively small. In this study, the heat transfer of supercritical water in uniformly heated vertical tube is numerically investigated with different buoyancy models which are based on different calculation methods of the turbulent heat flux. The applicabilities of these buoyancy models are analyzed both in heat transfer enhancement and deterioration conditions. The simulation results show that these buoyancy models make few differences and give good wall temperature prediction in heat transfer enhancement condition when the ratio of inlet mass flux and wall heat flux is very small. With the increase of wall heat flux, the accuracy of wall temperature prediction reduces, and the differences between these buoyancy models become larger. No buoyancy model can currently make accurate wall temperature prediction in deterioration condition in this study.

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.

Roles of Nanofluids, Temperature of Base Fluids, and Pressure Gradient on Heat Transfer Enhancement From a Cylinder: Uniformly Heated/Heat Flux

2019 ◽  
Vol 141 (6) ◽  
Author(s):  
Dilip K. Maiti ◽  
Swati Sharma
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Gradient ◽  
Heat Transfer Enhancement ◽  
Thermal Conditions ◽  
Constant Heat Flux ◽  
Inlet Temperature ◽  
Water Mixture ◽  
Transfer Enhancement ◽  
Different Temperatures

Heat transfer from a cylinder of square cross section (either dissipating constant heat flux (qW) or maintaining at a constant temperature (TW)) placed near a plane wall under the incidence of nonuniform linear/nonlinear velocity profile is studied numerically (finite volume method (FVM), quadratic upstream interpolation for convective kinematics (QUICK), and SIMPLE). The conventional fluids are chosen as water, and ethylene glycol–water mixture. The nanoparticles are selected as Al2O3 and CuO. Roles of pressure gradient P (at the inlet), temperature of base fluids, thermal conditions (TW or qW), and nanofluids' parameters (nanoparticle concentrations (ϕ), diameter, materials, and base fluids) on the heat transfer (Nusselt number (Nu¯M)) of the cylinder are investigated here. Nu¯M enhancement from the cylinder together with its drag coefficient reduction/increment due to addition of nanomaterials in both fluids at two different temperatures is assessed under the Couette flow. Classical fluid dynamics relationship among Nu¯M, Reynolds number (Re), and Prandtl number is discussed through Colburn j–factor, and hence the utility of proposed correlation between j–factor and Re toward engineering problems is also explored. The graphical observations of dependency of Nu¯M on the aforesaid parameters are reconfirmed by proposed functional forms of Nu¯M=Nu¯M(P), Nu¯M=Nu¯M(ϕ) and hence Nu¯M=Nu¯M(P,ϕ). An effort is made to examine the effectiveness of the aforementioned parameters on the heat transfer enhancement rate.

scholarly journals Heat transfer enhancement during condensation of water steam on inclined pipe

2021 ◽  
Vol 2039 (1) ◽  
pp. 012031
Author(s):  
S Z Sapozhnikov ◽  
V Yu Mityakov ◽  
A V Mityakov ◽  
A Yu Babich ◽  
E R Zainullina
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Enhancement ◽  
Unit Area ◽  
Experimental Results ◽  
Transfer Enhancement ◽  
Water Steam ◽  
Saturated Water ◽  
Informative Content ◽  
Inclined Pipe

Abstract This paper presents experimental study of heat transfer during film condensation of saturated water steam on the outer surface of the inclined pipe by gradient heatmetry. Heat flux per unit area was measured by gradient heat flux sensors made of a single-crystal bismuth. The experimental results are presented in the graphs of heat flux per unit area dependence on time and azimuthal angle. The highest average heat transfer coefficient during condensation of α = 6.94 kW/(m2 • K) was observed when the pipe was inclined at the angle of ψ = 20 °. This value exceeds one obtained on a vertical pipe by 14.9 %. Heat transfer enhancement during condensation of saturated water steam on inclined pipe is associated with changes in condensate film flow. Another part of experiments was made by simultaneously using of gradient heatmetry and condensate flow visualization. Experimental results confirmed the applicability and high informative content of proposed comprehensive method. Comprehensive study of heat transfer during condensation confirmed that heat flux per unit area pulsations may be explained by the formation of individual drops, their coalescence, and drainage from the sensor surface.

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