Experimental Effects of Transverse Oscillations on Free Convection of a Vertical, Finite Plate

1964 ◽  
Vol 86 (2) ◽  
pp. 159-165 ◽  
Author(s):  
V. D. Blankenship ◽  
J. A. Clark
Keyword(s):  
Heat Transfer ◽  
Laminar Flow ◽  
Free Convection ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Experimental Results ◽  
Transverse Oscillation ◽  
Finite Plate ◽  
Analytical Results ◽  
Transverse Oscillations

The effects of transverse oscillation on free convection from a vertical, finite plate is investigated experimentally. This paper supplements an earlier paper wherein analytical results were reported. In that paper it was reported that oscillation slightly decreases the heat-transfer rate for laminar flow. The experimental results are in accord. However, more important is the fact that the oscillation forces the flow to become turbulent whereby large increases in heat-transfer rate are obtained. Experimental results are given for heat-transfer rate, both laminar and turbulent, and transition.

Effects of Oscillation on Free Convection From a Vertical Finite Plate

1964 ◽  
Vol 86 (2) ◽  
pp. 149-158 ◽  
Author(s):  
V. D. Blankenship ◽  
J. A. Clark
Keyword(s):  
Heat Transfer ◽  
Free Convection ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Vibrational Amplitude ◽  
Finite Plate ◽  
Potential Flows ◽  
Steady Heat ◽  
Inertia Forces ◽  
Theoretical Results

The effect of transverse oscillation on free convection from a vertical, finite plate is studied analytically. A second paper will consider the experimental results. Consideration is given to perturbations up to second order for potential flows with small vibrational amplitude and high frequency. Theoretical results are given for velocity, temperature, heat-transfer rate, and shear stress. It is shown that oscillations slightly decrease the steady heat-transfer rate for laminar flow. This reduction is thought to be a result of an interaction between the viscous and inertia forces in the laminar boundary layer which causes a net decrease in the connective flow near the plate.

scholarly journals Assessment of TiO2 Nanoconcentration and Twin Impingement Jet of Heat Transfer Enhancement—A Statistical Approach Using Response Surface Methodology

Energies ◽  
2021 ◽  
Vol 14 (3) ◽  
pp. 595
Author(s):  
Mahir Faris Abdullah ◽  
Rozli Zulkifli ◽  
Hazim Moria ◽  
Asmaa Soheil Najm ◽  
Zambri Harun ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Response Surface Methodology ◽  
Response Surface ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Tio2 Nanoparticle ◽  
Experimental Results ◽  
Improvement Rate ◽  
Design Expert ◽  
Impingement Jet

Impinging jets are considered to be a well-known technique that offers high local heat transfer rates. No correlation could be established in the literature between the significant parameters and the Nusselt number, and investigation of the interactions between the correlated factors has not been conducted before. An experimental analysis based on the twin impingement jet mechanism was achieved to study the heat transfer rate pertaining to the surface plate. In the current paper, four influential parameters were studied: the spacing between nozzles, velocity, concentration of Nano solution coating and nozzle-plate distance, which are considered to be effective parameters for the thermal conductivity and the heat transfer coefficient of TiO2 nanoparticle, an X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) analysis were done, which highlighted the structure and showed that the nanosolution coated the surface homogenously. Moreover, a comparison was done for the experimental results with that of the predicted responses generated by the Design Expert software, Version 7 User’s Guide, USA. A response surface methodology (RSM) was employed to improve a mathematical model by accounting for a D-optimal design. In addition, the analysis of variance (ANOVA) was employed for testing the significance of the models. The maximum Nu of 91.47, where H = S = 1 cm; Reynolds number of 17,000, and TiO2 nanoparticle concentration of 0.5% M. The highest improvement rate in Nusselt was about 26%, achieved with TiO2 Nanoparticle, when S = 3 cm, H = 6 cm and TiO2 nanoparticle = 0.5 M. Furthermore, based on the statistical analysis, the expected values were found to be in satisfactory agreement with that of the empirical data, which was conducted by accounting for the proposed models’ excellent predictability. Multivariate approaches are very useful for researchers, as well as for applications in industrial processes, as they lead to increased efficiency and reduced costs, so the presented results of this work could encourage the overall uses of multivariate methods in these fields. Hypotheses: A comparison was done for the predicted responses generated by the Design Expert software with the experimental results and then studied to verify the following hypotheses: ► Preparation of three concentrations of TiO2 nanosolution was done and studied. ► The heat transfer rate could be increased by surface coating with TiO2 nanoparticle. ► The heat transfer could be improved by the impingement jet technique with suitable adjustments.

Design of a Microfin Array Heat Sink Using Flow-Induced Vibration to Enhance the Heat Transfer Rate in the Laminar Flow Regime

2001 ◽  
Author(s):  
Jeung Sang Go ◽  
Geunbae Lim ◽  
Hayong Yun ◽  
Sung Jin Kim ◽  
Inseob Song
Keyword(s):  
Heat Transfer ◽  
Laminar Flow ◽  
Heat Transfer Enhancement ◽  
Flow Regime ◽  
Heat Transfer Rate ◽  
Heat Sink ◽  
Transfer Rate ◽  
Transfer Enhancement ◽  
Air Velocity ◽  
Flow Induced Vibration

Abstract This paper presented design guideline of the microfin array heat sink using flow-induced vibration to increase the heat transfer rate in the laminar flow regime. Effect of the flow-induced vibration of a microfin array on heat transfer enhancement was investigated experimentally by comparing the thermal resistances of the microfin array heat sink and those of a plain-wall heat sink. At the air velocities of 4.4m/s and 5.5 m/s, an increase of 5.5% and 11.5% in the heat transfer rate was obtained, respectively. The microfin flow sensor also characterized the flow-induced vibration of the microfin. It was determined that the microfin vibrates with the fundamental natural frequency regardless of the air velocity. It was also shown that the vibrating displacement of the microfin is increased with increasing air velocity and then saturated over a certain value of air velocity. Based on the numerical analysis of the temperature distribution resulted from microfin vibration and experimental results, a simple heat transfer model (heat pumping model) was proposed to understand the heat transfer mechanism of a microfin array heat sink. Under the geometric and structural constraints, the maximum heat transfer enhancement was obtained at the intersection of the minimum thickness of the microfin and constraint of the bending angle.

The impacts of non-uniform magnetic field on free convection heat transfer of a magnetizable micropolar nanofluid

2019 ◽  
Vol 29 (10) ◽  
pp. 3685-3706
Author(s):  
Zafar Namazian ◽  
S.A.M. Mehryan
Keyword(s):  
Heat Transfer ◽  
Free Convection ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Volume Fraction ◽  
Convection Heat Transfer ◽  
Content Type ◽  
Viscosity Parameter ◽  
Micropolar Nanofluid ◽  
Free Convection Heat

Purpose The purpose of this study is to numerically study the heat transfer of free convection of a magnetizable micropolar nanofluid inside a semicircular enclosure. Design/methodology/approach The flow domain is under simultaneous influences of two non-uniform magnetic fields generated by current carrying wires. The directions of the currents are the same. Although the geometry is symmetric, it is physically asymmetric. The impacts of key parameters, including Rayleigh number Ra = 103-106, Hartman number Ha = 0-50, vortex viscosity parameter Δ = 0-4, nanoparticles volume fraction φ = 0-0.04 and magnetic number Mnf = 0-1000, on the macro- and micro-scales flows, temperature and heat transfer rate are studied. Finding The outcomes show that dispersing of the nanoparticles in the host fluid increases the strength of macro- and micro-scale flows. When Mnf = 0, the increment of the vortex viscosity parameter increases the strength of the particles micro-rotations, while this characteristic is decreased by growing Δ for Mnf ≠ 0. The increment of Δ and Ha decreases the rate of heat transfer. The increment of Ha decreases the enhancement percentage of heat transfer rate because of dispersing nanoparticles, known as En parameter. In addition, the value of Δ has no effect on En. Moreover, the average Nusselt number Nuavg and En remain constant by increasing the magnetic number Mnf for different volume fraction values. Originality/value The authors believe that all of the results, both numerical and asymptotic, are original and have not been published elsewhere yet.

Buoyancy-Induced Convection in Metal Foam and Finned Metal Foam Heat Sinks©

2000 ◽  
Author(s):  
A. Bhattacharya ◽  
Roop L. Mahajan
Keyword(s):  
Heat Transfer ◽  
Porous Medium ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Metal Foam ◽  
Metal Foams ◽  
Experimental Results ◽  
Heat Sinks ◽  
Normal Metal ◽  
Optimum Number

Abstract In this paper, we present our recent experimental results on buoyancy induced convection in metal foams of different pore densities (corresponding to 5, 10, 20 and 40 pores per inch) and porosities (0.89–0.96). The results show that compared to a hot surface facing up, the heat transfer coefficients in these heat sinks are 5 to 6 times higher. However, when compared to commercially available heat sinks of similar dimensions, the enhancement is found to be marginal. The experimental results also show that for a given pore size, the heat transfer rate increases with porosity suggesting the dominant role played by conduction in enhancing heat transfer. On the other hand, if the porosity is held constant, the heat transfer rate is found to be lower at higher pore densities. This can be attributed to the higher permeability with the larger pores, which allows higher entrainment of air through the porous medium. An empirical correlation, developed for the estimation of Nusselt number in terms of Rayleigh and Darcy numbers, is found to be in good agreement with the experimental data with a maximum error of 10%. We also report our results on novel finned metal foam heat sinks© in natural convection. Experiments were conducted on aluminum foams of 90% porosity with 5 and 20 PPI (pores per inch) with one, two, and four aluminum fins inserted in the foam. All these heat sinks were fabricated in-house. The results show that the finned metal foam heat sinks© are superior in thermal performance compared to the normal metal foam and conventional finned heat sinks. The heat transfer increases with increase in the number of fins. However, the relative enhancement is found to decrease with each additional fin. The indication is that there exists an optimum number of fins beyond which the enhancement in heat transfer due to increased surface area is offset by the retarding effect of overlapping thermal boundary layers. Similar to normal metal foams, the 5 PPI samples are found to give higher values of the heat transfer coefficient compared to the 20 PPI samples due to higher permeability of the porous medium. Future work is planned to arrive at the optimal heat sink configuration for even larger enhancement in heat transfer.

Experimental Study on Flow Visualizing and Heat Transfer Characteristic of Pulsating Heat Pipe

2007 ◽  
Author(s):  
Li Jia ◽  
Dayan Yin
Keyword(s):  
Heat Transfer ◽  
Heat Pipe ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Flow Patterns ◽  
Bulk Flow ◽  
Experimental Results ◽  
Pulsating Heat Pipe ◽  
Transition Flow ◽  
Fill Ratio

The flow of looped pulsating heat pipe was studied by a visualizing experiment, and the PHP is made of high quality glass capillary tube. Under different fill ratio, heat transfer rate and many other influence factors, the flow patterns were observed in the start-up, transition and stable stage. The experimental results indicate that bulk flow, transition flow and annular flow are the major flow patterns in PHP. Under different fill ratios and heat transfer rate, the flow pattern in PHP is transferred form bulk flow to semi-annual flow and annual flow, and the performance of heat transfer is improved. In the experiment, nuclear boiling, the convergence and break up of liquid-plug and vapor-slug were observed. The influence characterization has been done for the variation of fill ration, heat transfer rate, non-condensable gas and inclination angle. The experimental results indicate that the total heat resistant of PHP is increased with fill ratio, and heat transfer rate achieves optimum at filling rate 50%; the heat resistance is decreased with heat transfer rate, and non-condensable gas also has significant influence on it. The temperature of tubes in heating, condensing and observe sections were recorded, The fluctuation of heat pipe wall temperature was analysed, and the phenomena of suddently increase or decrease of temperature, the unregular fluctuation of temperature were analyzed. Otherwise the response time under different conditions was also analyzed.

Piezoelectric Actuating Sprayed Phase-Change Cooling Technique for VLSI Chips

2005 ◽  
Author(s):  
Yu-Lin Huang ◽  
Shuo-Hung Chang ◽  
Chin-Horng Wang ◽  
Chiung-I Lee
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Flow Rate ◽  
Transfer Rate ◽  
Copper Surface ◽  
Experimental Results ◽  
Maximum Heat ◽  
Pzt Actuator ◽  
Wide Range ◽  
Cooling Technique

To develop high performance cooling systems for high heat generation electronic devices, such as CPU, the spray cooling technique using piezoelectric (PZT) actuator in vacuum with its experimental results will be described. The water droplets were ejected through an circular orifice array membrane vibrating at high frequency bending mode which was excited by a ring-shape PZT actuator. Two parts of experiment has been conducted that including the driving conditions for PZT and the heat transfer of the micro scale water droplet. Furthermore, the maximum heat transfer rate has been evaluated at different ambient pressure. The cooling capability at a wide range of operation conditions was measured. The experimental results indicate that the stability of the spray flow rate will affect the heat transfer rate dramatically. In our experiment, the water was used as the coolant and 30 μm diameter orifice array. At a flow rate of 1.2 ml/min will remove the heat over 50.3 W/cm2, and the copper surface would be 123.18°C. When vacuum technique is used to reduce the operation pressure to 21.33 kPa, the copper surface temperature can decrease to 85.78°C at 50.3 W/cm2 heat flux. The described cooling technique demonstrates competitive potential for next generation cooling for CPU applications.

Experimental Research on Heat Transfer Characteristics of Pulsating Heat Pipe

2008 ◽  
Author(s):  
Li Jia ◽  
Yan Li
Keyword(s):  
Heat Transfer ◽  
Heat Pipe ◽  
Heat Transfer Rate ◽  
Experimental Research ◽  
Transfer Rate ◽  
Experimental Results ◽  
Pulsating Heat Pipe ◽  
Heat Transfer Characteristics ◽  
Fill Ratio ◽  
Transfer Characteristics

Experimental research was conducted to understand heat transfer characteristics of pulsating heat pipe in this paper. The PHP is made of high quality glass capillary tube. The heat transfer rate and many other influence factors, the flow patterns were observed in the start-up, transition and stable stage under different fill ratio. The effects of heating position on heat transfer were discussed. The experimental results indicate that no annular flow appeares in top heating condition. The flow pattern in PHP is transferred form bulk flow to semi-annual flow and annual flow, and the performance of heat transfer is improved for down heating case under different fill ratios and heat transfer rate. The experimental results show that the total heat resistant of PHP is increased with fill ratio, and heat transfer rate achieves optimum at filling rate 50%. But for pulsating heat pipe with changing diameters the thermal resistance is higher than that with uniform diameters.

Heat or Mass Transfer in Laminar Flow in Conduits With Constriction

1973 ◽  
Vol 95 (3) ◽  
pp. 352-356 ◽  
Author(s):  
J. C. F. Chow ◽  
K. Soda
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Laminar Flow ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Bulk Temperature ◽  
Fluid Temperature ◽  
Entry Length ◽  
Moderate Reynolds Number ◽  
Length Changes

Analytical solutions are obtained on the effects of boundary constriction on heat or mass transfer at the entrance region in a well-developed steady laminar flow in symmetric and axisymmetric conduits subjected to uniform wall temperature or mass concentration. The solutions are limited to the fluids of constant properties with negligible viscous dissipation, moderate Reynolds number, and large Peclet or Schmidt number, and the spread of the wall constriction is large compared to the mean width or radius of the conduits. It is found that both the bulk temperature and heat transfer rate at the wall are oscillatory in nature, and their amplitudes decrease drastically as the fluid moves away from the entrance. Near thermal entry length, the bulk fluid temperature approaches its mean value with vanishing oscillation, but the heat transfer rate at the wall stays oscillatory in nature due to the irregularity of the wall. The thermal entry length changes very little from the corresponding straight-wall conduits. These results are also true for the mass transfer.

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