Two-Phase Flow With Phase Change in Porous Channels

2015 ◽  
Vol 7 (2) ◽  
Author(s):  
Gaurav Tomar
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Phase Change ◽  
Heat Pipes ◽  
Porous Channel ◽  
Two Phase ◽  
Vapor Interface ◽  
Interface Location ◽  
Heat Loads ◽  
Liquid Vapor

Phase change heat transfer in porous media finds applications in various geological flows and modern heat pipes. We present a study to show the effect of phase change on heat transfer in a porous channel. We show that the ratio of Jakob numbers based on wall superheat and inlet fluid subcooling governs the liquid–vapor interface location in the porous channel and below a critical value of the ratio, the liquid penetrates all the way to the extent of the channel in the flow direction. In such cases, the Nusselt number is higher due to the proximity of the liquid–vapor interface to the heat loads. For higher heat loads or lower subcooling of the liquid, the liquid–vapor interface is pushed toward the inlet, and heat transfer occurs through a wider vapor region thus resulting in a lower Nusselt number. This study is relevant in the designing of efficient two-phase heat exchangers such as capillary suction based heat pipes where a prior estimation of the interface location for the maximum heat load is required to ensure that the liquid–vapor interface is always inside the porous block for its operation.

Prediction of the Transport Phenomena in the Micro Capillary Tube of a CPL System

2003 ◽  
Author(s):  
Kyoungwoo Park ◽  
Kwan-Soo Lee
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Capillary Tube ◽  
Transport Phenomena ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Two Phase ◽  
Vapor Interface ◽  
Meniscus Region ◽  
Liquid Vapor

A mathematical model is presented to predict the two-phase transport phenomena of the evaporating extended meniscus region in a micro capillary tube which approximates the evaporator of the CPL system. The behavior of a liquid-vapor interface can be estimated by using the augmented Laplace-Young equation. The governing equations for transport fields of liquid and vapor phases can be obtained by adopting the different physical approaches for the meniscus and thin film regions. In this model, the variation of vapor pressure and the disjoining pressure effect are included and the friction force at the liquid-vapor interface is also considered. The results show that the local heat transfer coefficient has an extremely large value in the thin film region. However, the amount of heat transfer rate, of the meniscus region is larger than that of the thin film region. It is also found that the length of the extended meniscus region is affected by the heat flux, the tube radius and the dispersion constant.

Steady State Numerical Modeling of Non-Conventional Loop Heat Pipes (LHPs)

2012 ◽  
Author(s):  
Karthik S. Remella ◽  
Frank M. Gerner ◽  
Ahmed Shuja ◽  
Praveen Medis
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Single Phase ◽  
Heat Pipes ◽  
Working Fluid ◽  
Vapor Interface ◽  
Loop Heat Pipes ◽  
Led Array ◽  
Fill Volume ◽  
Liquid Vapor

Loop heat pipes (LHPs) transport energy from an evaporator to a condenser in the form of latent heat. In conventional LHPs, the vapor pressure is significantly higher than the liquid pressure across the liquid-vapor interface due to the small pores and the corresponding capillary forces in the wick. This large pressure difference transports the single phase vapor after evaporation from the evaporator to the condenser and once the vapor is condensed, a single phase liquid from the condenser back to the evaporator. This current work involves the development of a steady state design model of the LHP system consisting of a planar evaporator package and a finned copper tube loop, which serves as an air-cooled condenser. Although evaporation due to the heat transfer creates the pressure in the vapor which drives the flow, contrasting to the conventional loop heat pipes, the pressure drop across the liquid-vapor interface is much smaller. A positive hydrostatic head is applied to the liquid above the wick and there is entrainment of liquid from the wick in the evaporator. Therefore, the fluid flow leaving the evaporator package is a two-phase flow, assumed to be saturated liquid and saturated vapor in equilibrium. The primary objective of this non-conventional LHP device is to remove the thermal energy dissipated from a Light Emitting Diode (LED) array. A major portion of this energy causes evaporation of the working fluid within the wick. The remaining energy reheats the liquid in both the liquid return line and within the evaporator package. The evaporator package is modeled as a one-dimensional thermal resistance network and these resistances are empirically determined from experiments. It is found that the convective heat transfer co-efficient of air plays a pivotal role in the heat dissipation and hence, is empirically determined in this work. This value is fairly agreeable with the Nusselt number correlation on the air side developed by Hahne et al. [1]. A mass balance relates the fill volume with the length of the condenser. The temperatures within the LHP are predicted by applying the principle of conservation of energy over the evaporator, the condenser and the sub-cooler sections of the heat exchanger loop. Finally, this LHP model predicts an approximate fill volume necessary for the LHP to operate properly.

Evaporation of Single Drops of n-Pentane/n-Hexane Mixtures in Water

1992 ◽  
Vol 114 (4) ◽  
pp. 965-971 ◽  
Author(s):  
H. Shimaoka ◽  
Y. H. Mori
Keyword(s):  
Heat Transfer ◽  
Temperature Difference ◽  
Vapor Bubble ◽  
Experimental Results ◽  
Rise Velocity ◽  
Heat Transfer Characteristics ◽  
Two Phase ◽  
Transfer Characteristics ◽  
Preceding Work ◽  
Liquid Vapor

The evaporation of isolated drops (2.1−3.0 mm diameter) of nonazeotropic n-pentane/n-hexane mixtures in the medium of water was observed under pressures of 0.11−0.46 MPa and temperature differences up to 27 K. The mole fractions of n-pentane, x, in the mixtures were set at 0.9, 0.5, 0.1, and 0, to be completed by the condition x = 1 set in a preceding work (Shimaoka and Mori, 1990). Experimental results are presented in terms of the instantaneous rise velocity of, and an expression of instantaneous heat transfer to, each drop evaporating and thereby transforming into a liquid/vapor two-phase bubble and finally into a vapor bubble. The dependencies of the heat transfer characteristics on the pressure, the temperature difference, and x are discussed.

Phase Change Process Inside a Small-radii Cylinder Subjected to Cyclic Convective Boundary Conditions: a Numerical Study

2021 ◽  
Author(s):  
Yousef Kanani ◽  
Avijit Karmakar ◽  
Sumanta Acharya
Keyword(s):  
Heat Transfer ◽  
Surface Temperature ◽  
Phase Change ◽  
Phase Change Materials ◽  
Numerical Study ◽  
Convective Boundary Condition ◽  
Freezing Process ◽  
Fourier Number ◽  
Two Phase ◽  
Convective Boundary

Abstract We numerically investigate the melting and solidi?cation behavior of phase change materials encapsulated in a small-radii cylinder subjected to a cyclic convective boundary condition (square wave). Initially, we explore the effect of the Stefan and Biot numbers on the non-dimensionalized time required (i.e. reference Fourier number Tref ) for a PCM initially held at Tcold to melt and reach the cross?ow temperature Thot. The increase in either Stefan or Biot number decreases Tref and can be predicted accurately using a correlation developed in this work. The variations of the PCM melt fraction, surface temperature, and heat transfer rate as a function of Fourier number are reported and analyzed for the above process. We further study the effect of the cyclic Fourier number on the periodic melting and freezing process. The melting or freezing front initiates at the outer periphery of the PCM and propagates towards the center. At higher frequencies, multiple two-phase interfaces are generated (propagating inward), and higher overall heat transfer is achieved as the surface temperature oscillates in the vicinity of the melting temperature, which increases the effective temperature difference driving the convective heat transfer.

scholarly journals An investigation on effect of EDL on heat transfer of micro heat pipe with square and triangular cross section

2020 ◽  
Vol 21 (3) ◽  
pp. 309
Author(s):  
Maryam Fallah Abbasi ◽  
Hossein Shokouhmand ◽  
Morteza Khayat
Keyword(s):  
Heat Transfer ◽  
Heat Pipe ◽  
Double Layer ◽  
Electric Double Layer ◽  
Heat Pipes ◽  
The Body ◽  
Working Fluid ◽  
Two Phase ◽  
Micro Heat Pipe ◽  
Micro Heat Pipes

Electronic industries have always been trying to improve the efficiency of electronic devices with small dimensions through thermal management of this equipment, thus increasing the use of small thermal sinks. In this study micro heat pipes with triangular and square cross sections have been manufactured and tested. One of the main objectives is to obtain an understanding of micro heat pipes and their role in energy transmission with electrical double layer (EDL). Micro heat pipes are highly efficient heat transfer devices, which use the continuous evaporation/condensation of a suitable working fluid for two-phase heat transport in a closed system. Since the latent heat of vaporization is very large, heat pipes transport heat at small temperature difference, with high rates. Because of variety of advantage features these devices have found a number of applications both in space and terrestrial technologies. The theory of operation micro heat pipes with EDL is described and the micro heat pipe has been studied. The temperature distribution have achieved through five thermocouples installed on the body. Water and different solution mixture of water and ethanol have used to investigate effect of the electric double layer heat transfer. It was noticed that the electric double layer of ionized fluid has caused reduction of heat transfer.

Numerical simulation of water/alumina nanofluid mixed convection in square lid-driven cavity

2019 ◽  
Vol 30 (5) ◽  
pp. 2781-2807
Author(s):  
Davood Toghraie ◽  
Ehsan Shirani
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Mixed Convection ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Richardson Number ◽  
Hartmann Number ◽  
Two Phase ◽  
Content Type ◽  
Driven Cavity

Purpose The purpose of this paper is to investigate the mixed convection of a two-phase water–aluminum oxide nanofluid in a cavity under a uniform magnetic field. Design/methodology/approach The upper wall of the cavity is cold and the lower wall is warm. The effects of different values of Richardson number, Hartmann number, cavitation length and solid nanoparticles concentration on the flow and temperature field and heat transfer rate were evaluated. In this paper, the heat flux was assumed to be constant of 10 (W/m2) and the Reynolds number was assumed to be constant of 300 and the Hartmann number and the volume fraction of solid nanoparticles varied from 0 to 60 and 0 to 0.06, respectively. The Richardson number was considered to be 0.1, 1 and 5. Aspect ratios were 1, 1.5 and 2. Findings Comparison of the results of this paper with the results of the numerical and experimental studies of other researchers showed a good correlation. The results were presented in the form of velocity and temperature profiles, stream and isotherm lines and Nusselt numbers. The results showed that by increasing the Hartmann number, the heat transfer rate decreases. An increase from 0 to 20 in Hartmann number results in a 20 per cent decrease in Nusselt numbers, and by increasing the Hartmann number from 20 to 40, a 16 per cent decrease is observed in Nusselt number. Accordingly, it is inferred that by increasing the Hartmann number, the reduction in the Nusselt number is decreased. As the Richardson number increased, the heat transfer rate and, consequently, the Nusselt number increased. Therefore, an increase in the Richardson number results in an increase of the Nusselt number, that is, an increase in Richardson number from 0.1 to 1 and from 1 to 5 results in 37 and 47 per cent increase in Nusselt number, respectively. Originality/value Even though there have been numerous investigations conducted on convection in cavities under various configurations and boundary conditions, relatively few studies are conducted for the case of nanofluid mixed convection in square lid-driven cavity under the effect of magnetic field using two-phase model.

Computation of flow and heat transfer in horizontal gas–solid flows through an adiabatic pipe

2020 ◽  
pp. 095440622093631
Author(s):  
Brundaban Patro ◽  
Kiran K Kupireddi ◽  
Jaya K Devanuri
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Nusselt Number ◽  
Pressure Drop ◽  
Solid Loading ◽  
Gas Velocity ◽  
Two Phase ◽  
Flow And Heat Transfer ◽  
Loading Ratio ◽  
Solid Temperature

The current paper deals with the studies of heat transfer and pressure drop through a horizontal, adiabatic pipe, having gas–solid flows. The inlet air temperature is 443 K, whereas the inlet solid temperature is 308 K. The numerical results are compared with the benchmark experimental data and are agreed satisfactorily. The influences of solid loading ratio, solid diameter and gas velocity on Nusselt number and pressure drop have been studied. The Nusselt number decreases and the pressure drop increases with an increase in the solid diameter. The Nusselt number decreases with an increase in the solid loading ratio at a lower solid diameter of 100 µm. However, at a higher value of solid diameter of 200 µm, the Nusselt number first decreases up to a specific solid loading ratio, and after that, it increases. The pressure drop results show different behaviours with the solid loading ratio. Both the Nusselt number and pressure drop increase with the gas velocity. Finally, a correlation is generated to calculate the two-phase Nusselt number.

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