An Analytical Model of External Streaming and Heat Transfer for a Levitated Flattened Liquid Drop

2007 ◽  
Author(s):  
Sungho Lee ◽  
S. S. Sadhal ◽  
Alexei Ye. Rednikov
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Acoustic Field ◽  
Thermophysical Properties ◽  
Liquid Drop ◽  
Thermocapillary Flow ◽  
Heat Transfer Analysis ◽  
Thermal Stimulus ◽  
Steady Streaming ◽  
Stokes Layer

We present here the heat transfer and fluid flow analysis of an acoustically levitated flattened disk-shaped liquid drop. This work arises due to an interest in the non-contact measurement of the thermophysical properties of liquids. Such techniques have application to liquids in the undercooled state, i.e., the situation when a liquid stays in a fluidic state even when the temperature falls below the normal freezing point. This can happen when, for example, a liquid sample is held in a levitated state. Since such states are easily disrupted by measurement probes, non-contact methods are needed. We have employed a technique involving the use of acoustically levitated samples of the liquid. A thermal stimulus in the form of laser-heating causes thermocapillary motion with flow characteristics depending on the thermophysical properties of the liquid. In a gravity field, buoyancy is disruptive to this thermocapillary flow, masking it with the dominant natural convection. As one approach to minimizing the effects of buoyancy, the drop was flattened (by intense acoustic pressure) in the form of a horizontal disk, about 0.5 mm thick. As a result, with very little gravitational potential, with most of the buoyant flow suppressed, thermocapillary flow remained the dominant form of fluid motion within the drop. This flow field is visualizable and subsequent analysis for the inverse problem of the thermal property can be conducted. This calls for numerical calculations involving a heat transfer model for the flattened drop. With the presence of an acoustic field, the heat-transfer analysis requires information about the corresponding Biot number. In the presence of a high-frequency acoustic field, the steady streaming originates in a thin shear-wave layer, known as the Stokes layer, at a surface of the drop. The streaming develops into the main fluid, and is referred to as the outer streaming. Since the Stokes layer is asymptotically thin in comparison to the length scale of the problem, the outer streaming formally appears to be caused by an effective slip velocity at the boundary. The presence of the thin Stokes layer, and the slip condition at the interface, changes the character of the heat transfer mechanism which is inherently different from the traditional boundary layer. The current analysis consists of a detailed semi-analytical calculation of the flow field and the heat transfer characteristics of a levitated drop in the presence of an acoustic field.

An Analytical Model of External Streaming and Heat Transfer for a Levitated Flattened Liquid Drop

2008 ◽  
Vol 130 (9) ◽  
Author(s):  
Sungho Lee ◽  
S. S. Sadhal ◽  
Alexei Ye. Rednikov
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Acoustic Field ◽  
Thermophysical Properties ◽  
Liquid Drop ◽  
Thermocapillary Flow ◽  
Heat Transfer Analysis ◽  
Thermal Stimulus ◽  
Steady Streaming ◽  
Stokes Layer

We present here the heat-transfer and fluid flow analysis of an acoustically levitated flattened disk-shaped liquid drop. The interest in this work arises from the noncontact measurement of the thermophysical properties of liquids. Such techniques have application to liquids in the undercooled state, i.e., the situation when a liquid stays in a fluidic state even when the temperature falls below the normal freezing point. This can happen when, for example, a liquid sample is held in a levitated state. Since such states are easily disrupted by measurement probes, noncontact methods are needed. We have employed a technique involving the use of acoustically levitated samples of the liquid. A thermal stimulus in the form of laser heating causes thermocapillary motion with flow characteristics depending on the thermophysical properties of the liquid. In a gravity field, buoyancy is disruptive to this thermocapillary flow, masking it with the dominant natural convection. As one approach to minimizing the effects of buoyancy, the drop was flattened (by intense acoustic pressure) in the form of a horizontal disk, about 0.5mm thick. As a result, with very little gravitational potential, and with most of the buoyant flow suppressed, thermocapillary flow remained the dominant form of fluid motion within the drop. This flow field is visualizable and subsequent analysis for the inverse problem of the thermal property can be conducted. This calls for numerical calculations involving a heat-transfer model for the flattened drop. With the presence of an acoustic field, the heat-transfer analysis requires information about the corresponding Biot number. In the presence of a high-frequency acoustic field, the steady streaming originates in a thin shear-wave layer, known as the Stokes layer, at a surface of the drop. The streaming develops into the main fluid, and is referred to as the outer streaming. Since the Stokes layer is asymptotically thin in comparison to the length scale of the problem, the outer streaming can be formally described by an effective slip velocity at the boundary. The presence of the thin Stokes layer, and the slip condition at the interface, changes the character of the heat-transfer mechanism, which is inherently different from the traditional boundary layer. The current analysis consists of a detailed semianalytical calculation of the flow field and the heat-transfer characteristics of a levitated drop in the presence of an acoustic field.

FLOW FIELD AND HEAT TRANSFER ANALYSIS IN AMON/MMH BIPROPELLANT ROCKET ENGINE

2017 ◽  
Vol 16 (3) ◽  
pp. 263-280 ◽  
Author(s):  
Yu Daimon ◽  
Hideyo Negishi ◽  
Hiroumi Tani ◽  
Yoshiki Matsuura ◽  
Shigeyasu Iihara ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Rocket Engine ◽  
Heat Transfer Analysis

Computational Investigation of Flow and Heat Transfer Characteristics of Impingement Cooling Channel

2013 ◽  
Author(s):  
B. V. N. Ramakumar ◽  
D. S. Joshi ◽  
Murari Sridhar ◽  
Jong S. Liu ◽  
Daniel C. Crites
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Heat Transfer Analysis ◽  
Computational Investigation ◽  
Heat Transfer Characteristics ◽  
Transfer Coefficients ◽  
Impingement Cooling ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
High Heat Transfer

Impingement cooling offers very high heat transfer coefficients. Flow field, involved in impingement cooling is dominated by stagnation zone, transition zone and developing zone. Understanding of complex flow phenomenon and its effects on heat transfer characteristics is useful for efficient designing of impingement channels. Computational fluid dynamics (CFD) has emerged as a powerful tool for the analysis of flow and heat transfer systems. Honeywell has been investigating the use of CFD to determine the characteristics of various complex turbine blade cooling heat transfer augmentation methods such as impingement. The objective of this study is to develop CFD methodology which is suitable for computational investigation of flow and heat transfer analysis of impingement cooling through validation. Single row of circular jets impinging on concave (curved) surface has been considered for this study. The validation was accomplished with the test results of Bunker and Metzger [10] and with the correlations of Chupp et al. [7]. The parameters which are varied in this study include jet Reynolds number (Re2B = 6750–10200), target plate distance to jet diameter ratio (Z/d = 3 and 4), and target surface sharpness (i.e. radius ratio, r* = 0.2, 0.4 and 1) the simulations are performed under steady state conditions. Predicted results are compared for local endwall heat transfer results along the curve length of the mid span target wall. Flow field results obtained at different locations are presented to understand the heat transfer behavior.

Simulation of Acoustic Enhancement of Heat Transfer in a Droplet Heat Exchanger

2007 ◽  
Author(s):  
Melaku Habte ◽  
Savas Yavuzkurt
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Acoustic Field ◽  
High Intensity ◽  
Acoustic Fields ◽  
Single Droplet ◽  
Enhancement Of Heat Transfer ◽  
Nusselt Numbers ◽  
2D Simulation ◽  
Simulation Results

Enhancement of heat transfer from a droplet exposed to acoustic fields is investigated. Investigation is part of a research project in enhancing the heat transfer in direct contact heat exchangers. Adding high intensity sound to Droplet Heat Exchanger (DHX) design produces relative gas motion around droplets otherwise entrained in the main flow field. Particles do not get fully entrained in the high frequency acoustic field giving rise to relative velocity. This enhances the heat transfer from droplets. Further benefits could be obtained by acoustic agglomeration of small droplets. DHXs have high contact area, no interface losses, low pressure drop and superior heat transfer characteristics compared to standard heat exchangers. With further enhancement of heat transfer by high intensity acoustic field application makes DHXs very attractive in many industrial applications such as droplet/particle reactors, humidifiers, gas scrubbers as well as ground based power generating gas turbines. In this paper, results of simulations of a single droplet exposed to acoustic fields of a range of sound intensity level (SPL) and frequency are presented. Spherical droplets are exposed to high intensity acoustic fields up to 175 dB with frequencies 25–2000Hz. Droplet size considered here is 100μm. Three dimensional (3-D) simulation of an oscillating flow field around a spherical droplet are carried out using FLUENT code. First, simulation results of space-averaged Nusselt numbers for steady flow around a single droplet are compared with available experimental data. Results were within 1–5% of each other. Simulations with acoustic field with and without steady velocity component were carried out and the results were compared with previous two dimensional studies as well as experimental and correlations of the same phenomena. The current simulation results are on average 22% higher than the 2D simulation results indicating the 3D nature of the flow. Space and time-averaged Nusselt numbers were more than 400% higher than the ones obtained without the acoustic field for acoustic Reynolds number 100 and frequency 50Hz and 30% higher than 2D simulation results. Finally, entrainment of droplets in the oscillating flow field was also considered. The result showed insignificant reduction (< 1%) in heat transfer rate compared to the case with no entrainment at all ranges of frequency (50–2000Hz).

Flow field and heat transfer analysis of local structure for regenerative cooling panel

2012 ◽  
Vol 21 (2) ◽  
pp. 172-178 ◽  
Author(s):  
Yu Feng ◽  
Hongyan Huang ◽  
Tao Li ◽  
Duo Zhang ◽  
Zhongqi Wang
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Local Structure ◽  
Heat Transfer Analysis ◽  
Regenerative Cooling

Numerical Heat Transfer and Entropy Analysis on Liquid Slip Flows Through Parallel-Plate Microchannels

2017 ◽  
Vol 10 (2) ◽  
Author(s):  
Mostafa Shojaeian ◽  
Masoumeh Nedaei ◽  
Mehmet Yildiz ◽  
Ali Koşar
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Nusselt Number ◽  
Entropy Generation ◽  
Thermophysical Properties ◽  
Parallel Plate ◽  
Flux Ratio ◽  
Heat Transfer Analysis ◽  
Temperature Dependent ◽  
Slip Flows

In this study, two-dimensional (2D) numerical simulations of liquid slip flows in parallel-plate microchannels have been performed to obtain heat transfer characteristics and entropy generation rate under asymmetric heating conditions. Heat transfer analysis has been conducted along with second-law analysis through utilizing temperature-dependent thermophysical properties. The results indicate that temperature-dependent thermophysical properties have a positive effect on convective heat transfer and entropy generation. Nusselt numbers of the upper and lower plates and global entropy generation rates are significantly affected by slip parameter and heat flux ratio. It is shown that Nusselt number of the lower plate may have very large but finite values at a specific heat flux ratio. This finding resembles to analytical solutions, where singularities leading to an infinite Nusselt number exist.

Thermophysical Properties of Two-Phase Refrigerant Based Nanofluids in a Refrigeration Cycle

2016 ◽  
Author(s):  
Bilgehan Tekin ◽  
Almila G. Yazicioglu
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Thermophysical Properties ◽  
Base Fluid ◽  
Two Phase Flow ◽  
Cooling System ◽  
Heat Transfer Analysis ◽  
Refrigeration Cycle ◽  
Phase Flow ◽  
Two Phase

Nanofluids are a class of fluids with nanoparticles suspended in a base fluid. The aim for using nanofluids is often to improve the thermophysical properties of the base fluid so as to enhance the energy transfer efficiency. As the technology develops; the size of devices and systems needs to get smaller to fulfill the engineering requirements and/or to be leading among competitors. The use of nanofluids in heat transfer applications seems to be a viable solution to current heat transfer problems, albeit with certain limitations. As an enhancing factor for the thermal conductivity of the base fluid, nanofluids are considered to be use in cooling system applications. For these applications, the base fluid, the refrigerant, exists as a two-phase liquid-vapor mixture in parts of the refrigeration cycle. To analyze, design and optimize the cycle in such applications, the thermophysical properties of the refrigerant based nanofluids for two-phase flow of refrigerant are needed. There are different models present in the literature derived for the thermophysical properties of nanofluids. However, a majority of the existing models for nanofluid thermophysical properties have been proposed for water- and other liquids-based nanofluids, through theoretical, numerical and experimental research. Therefore, the existing models for determination of the nanofluid thermophysical properties are not applicable for refrigerant based nanofluid applications when the results are compared. Thus, in this work, a new model is derived for the thermal conductivity and viscosity of refrigerant based nanofluids, using existing data from both heat transfer and thermophysical property measurement experiments. The effect of the nanoparticles on heat transfer in two phase flow of the refrigerant is considered by applying the two phase heat transfer correlations in the literature to experimental data. As a result, the thermophysical properties of the known states are determined through known heat transfer performance. Even though the model is developed from the analysis of flow in an evaporator and flow in a single tube with evaporating refrigerant, it is aimed to cover the flows in both evaporator and condenser sections in a vapor compression refrigeration cycle to provide the necessary models for thermophysical properties in heat transfer devices which will allow the design of both cycle and evaporator or condenser in terms of sizing and rating problems by performing heat transfer analysis and/or optimization. The model can also be improved by considering the effects of slip mechanisms that lead to slip velocity between the nanoparticle and base fluid.

Flow and Heat Transfer Analysis Through a Brake Disc: A CFD Approach

2006 ◽  
Author(s):  
S. Manohar Reddy ◽  
J. M. Mallikarjuna ◽  
V. Ganesan
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Heat Dissipation ◽  
Tangential Velocity ◽  
Heat Transfer Analysis ◽  
Brake Disc ◽  
Independence Test ◽  
Flow And Heat Transfer ◽  
Numerical Predictions ◽  
Grid Independence

This paper describes the numerical simulation of the flow and heat transfer around a ventilated brake disc. The aim of this investigation is to provide more insight on ventilated brake disc flow phenomena with a view to improve heat dissipation. Analysis of brake disc has been carried out using FLUENT (CFD code based on the Finite Volume Method). Numerical predictions of the flow and heat transfer are compared with available experimental data in the literature [2]. In the present work validation of numerical results are discussed in two parts. In the first part, the optimum grid was found from the grid independence test and in the second part the effect of turbulence models on flow field development was studied. Three rotors have been considered with each of 36, 40 and 45 number of vanes. Each rotor of two flow passages has been considered for the analysis. An isothermal analysis has been carried out to analyse the heat transfer. From the grid independence test it was found that the grid with 300,000 cells is seems to be the appropriate. SST k-ω turbulence model was able to predict the flow field with an accuracy of 3% and 1% in predicting tangential velocity and radial velocity respectively. From the isothermal rotor analysis it is found that the geometry having 45 vanes dissipates 7.7% and 5% more heat compared to geometries having number of vanes 36 and 40 respectively.

Heat Transfer Analysis of a Wedge Shaped Duct With Pin Fin and Pedestal Arrays: A Comparison Between Numerical and Experimental Results

2004 ◽  
Author(s):  
Antonio Andreini ◽  
Carlo Carcasci ◽  
Andrea Magi
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Gas Turbine ◽  
Turbine Blade ◽  
Experimental Results ◽  
Heat Transfer Analysis ◽  
Bottom Surface ◽  
Mean Flow ◽  
Trailing Edge ◽  
Pin Fin

The use of pin fin arrays in channels is one of the best choices to enhance overall heat transfer in gas turbine trailing edge blade cooling. Furthermore, in this particular application, the use of cross-pins in the trailing edge section of a turbine blade is a good way for supplying structural integrity to the blade itself. In this paper, results of several 3D RANS calculations performed in channels with cross-pins disposition such as in a typical trailing edge of a gas turbine blade are shown. Numerical calculations were compared with experimental results obtained on the same geometries using a transient Thermochromic Liquid Crystals (TLC) based technique. Goals of this comparison are both the evaluation of the accuracy of CFD packages with standard two equation turbulence models in heat transfer problems with complex geometries and the analysis of flow details to complete and support experimental activity. Two computational domains have been considered: they both consist in a wedge shaped channel with a stream-wise normal pin fin or pedestal arrays. The aim of the numerical analysis is the evaluation of convective Heat Transfer Coefficient (HTC) on the planar bottom surface of the wedge-shaped duct: this surface is commonly named “endwall” surface. Detailed analysis of the flow field points out the coexistence of an horse-shoe vortex, a stagnant wake behind the pin and a mean flow acceleration due to convergent shape of the channel. Calculations reveal the presence of a weak jet-like flow field toward endwall surfaces caused by the strong recirculation behind each pin.

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