Convective Heat Transfer of Unchoked and Choked Gas Flow in Micro-Tubes

2014 ◽  
Author(s):  
Chungpyo Hong ◽  
Yutaka Asako
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Turbulent Flow ◽  
Wall Temperature ◽  
Gas Flow ◽  
Stagnation Pressure ◽  
Bulk Temperature ◽  
Stagnation Temperature ◽  
Computational Domain ◽  
Downstream Region

Heat transfer characteristics of unchoked and choked gas flows in micro-tubes with constant wall temperature were numerically investigated both laminar and turbulent flow cases. The numerical methodology is based on the Arbitrary-Lagrangian-Eulerian (ALE) method. The Lam-Bremhorst Low-Reynolds number turbulence model was used for turbulent flow. The compressible momentum and energy equations with the assumption of the ideal gas were solved. The computational domain should be extended to the downstream region of the hemisphere from micro-tube outlet. The back pressure was given to the outside of the downstream region. The stagnation temperature is fixed at 300K and the computations were done for the wall temperature which ranges from 305K to 350K. The tube diameter ranges from 50 to 250 μm and tube aspect ratio is 200. The stagnation pressure is chosen in such a way that the flow at micro-tube exit is enough to be fully under-expanded. By increasing the stagnation pressure, the internal flow in the micro-tube is choked and the flow at the micro-tube outlet is under-expanded. Although the velocity remains constant, the mass flow rate (Reynolds number) increases. The results in a wide range of Reynolds number and Mach number were obtained. The bulk temperature based on the static temperature and the total temperature are compared with those of the incompressible flow. A correlation for the prediction of the heat transfer rate of the unchoked and choked gas flow in micro-tubes is proposed.

Numerical Simulation on Heat Transfer Characteristics of Turbulent Gas Flow in Micro-Tubes

2011 ◽  
Author(s):  
Kyohei Isobe ◽  
Chungpyo Hong ◽  
Yutaka Asako ◽  
Ichiro Ueno
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Wall Temperature ◽  
Gas Flow ◽  
Tube Diameter ◽  
Turbulence Energy ◽  
Stagnation Temperature ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Turbulent Gas Flow

Numerical simulations were performed to obtain for heat transfer characteristics of turbulent gas flow in micro-tubes with constant wall temperature. The numerical methodology was based on Arbitrary-Lagrangian-Eulerinan (ALE) method to solve compressible momentum and energy equations. The Lam-Bremhorst Low-Reynolds number turbulence model was employed to evaluate eddy viscosity coefficient and turbulence energy. The tube diameter ranges from 100 μm to 400 μm and the aspect ratio of the tube diameter and the length is fixed at 200. The stagnation temperature is fixed at 300 K and the computations were done for wall temperature, which ranges from 305 K to 350 K. The stagnation pressure was chosen in such a way that the flow is in turbulent flow regime. The obtained Reynolds number ranges widely up to 10081 and the Mach number at the outlet ranges from 0.1 to 0.9. The heat transfer rates obtained by the present study are higher than those of the incompressible flow. This is due to the additional heat transfer near the micro-tube outlet caused by the energy conversion into kinetic energy.

Total Temperature Measurements of Gaseous Flow at Micro-Tube Outlet

2009 ◽  
Author(s):  
Takaharu Yamamoto ◽  
Chungpyo Hong ◽  
Yutaka Asako ◽  
Koichi Suzuki
Keyword(s):  
Heat Transfer ◽  
Wall Temperature ◽  
Gas Flow ◽  
Atmospheric Condition ◽  
Stagnation Temperature ◽  
Constant Wall Temperature ◽  
Gaseous Flow ◽  
Circulating Water ◽  
Total Temperature ◽  
Exit Mach Number

This paper presents experimental results on heat transfer characteristics of gaseous flow in a micro-tube with constant wall temperature. The experiment was performed for nitrogen gas flow through a micro-tube with 166 micro meters in diameter and 50mm in length. The wall temperature was maintained at 305K, 310K, 330K and 350K by circulating water around the micro-tube, respectively. The stagnation pressure is chosen in such a way that the exit Mach number ranges from 0.1 to 1.0. The outlet pressure was fixed at the atmospheric condition. The total temperature at the outlet, the inlet stagnation temperature, the mass flow rate, and the inlet pressure were measured. The numerical computations based on the Aribitary - Langrangian - Eulerian (ALE) method were also performed for the same cases of the experiment for validation of numerical computation. The both results are in excellent agreement. The total temperatures obtained by the present study are slightly higher than those of the incompressible flow. This is due to the additional heat transfer near the micro-tube outlet caused by the temperature decrease due to the energy conversion into the kinetic energy. A quantitative correlation for the prediction of the heat transfer rate of the gaseous flow in a micro-tube was proposed.

Mach Number on Outlet Plane of a Straight Micro-Tube

2013 ◽  
Author(s):  
Y. Asako ◽  
D. Kawashima ◽  
T. Yamada ◽  
C. Hong
Keyword(s):  
Mach Number ◽  
Turbulent Flow ◽  
Gas Flow ◽  
Flow Characteristics ◽  
Ideal Gas ◽  
Computational Domain ◽  
Arbitrary Lagrangian Eulerian ◽  
Downstream Region ◽  
Laminar And Turbulent Flow ◽  
Energy Equations

The Mach number and pressure on the outlet plane of a straight micro-tube were investigated numerically for both laminar and turbulent flow cases. The numerical methodology is based on the Arbitrary-Lagrangian-Eulerian (ALE) method. The LB1 turbulence model was used for the turbulent flow case. The compressible momentum and energy equations with the assumption of the ideal gas were solved. The computational domain is extended to the downstream region from the micro-tube outlet. The back pressure was given to the outside of the downstream region. The computations were performed for a tube whose diameter ranges from 50 to 500 μm. The average Mach number on the outlet plane of the fully under-expanded flow depends on the tube diameter and ranges from 1.16 to 1.25. The flow characteristics of the under-expanded gas flow in a straight micro-tube were revealed.

Total Temperature Measurements of Gaseous Flow at Micro-Tube Outlet: Cooled From the Wall

2009 ◽  
Author(s):  
Takaharu Yamamoto ◽  
Chungpyo Hong ◽  
Yutaka Asako ◽  
Koichi Suzuki
Keyword(s):  
Wall Temperature ◽  
Gas Flow ◽  
Atmospheric Condition ◽  
Bulk Temperature ◽  
Inlet Temperature ◽  
Stagnation Temperature ◽  
Constant Wall Temperature ◽  
Gaseous Flow ◽  
Total Temperature ◽  
Exit Mach Number

This paper presents experimental results on heat transfer characteristics of gaseous flow in a micro-tube with constant wall temperature whose wall temperature is lower than the inlet temperature (cooled case). The experiment was performed for nitrogen gas flow through a micro-tube with 163.4 micro meters in diameter and 50 mm in length. The gas was heated at the inlet of the micro-tube to Tin = 315K, 335K and 355K. The wall temperature was maintained at 305K which was lower than the inlet temperature by circulating water around the micro-tube. The stagnation pressure was chosen in such a way that the exit Mach number ranges from 0.1 to 0.9. The outlet pressure was fixed at the atmospheric condition. The total temperature at the outlet, the inlet stagnation temperature, the mass flow rate, and the inlet pressure were measured. The numerical computations based on the aribitary-Langrangian-Eulerian (ALE) method were also performed for the same conditions of the experiment. The total and bulk temperature obtained by the present study are compared with those of the numerical cases and also compared with temperatures of the incompressible flow. The results have similar trends.

Convective Heat Transfer of Turbulent Gas Flow in Micro-Tubes With Constant Wall Temperature (Cooled Case)

2012 ◽  
Author(s):  
Kyohei Isobe ◽  
Chungpyo Hong ◽  
Yutaka Asako ◽  
Ichiro Ueno
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Wall Temperature ◽  
Gas Flow ◽  
Tube Diameter ◽  
Heat Transfer Characteristics ◽  
Constant Wall Temperature ◽  
Transfer Characteristics ◽  
Turbulent Gas Flow ◽  
Heated Case

Numerical computations were performed to obtain for heat transfer characteristics of turbulent gas flow in micro-tubes with constant wall temperature whose temperature is lower than the inlet temperature (cooled case). The numerical methodology was based on Arbitrary-Lagrangian-Eulerinan (ALE) method to solve compressible momentum and energy equations. The Lam-Bremhorst Low-Reynolds number turbulence model was employed to evaluate eddy viscosity coefficient and turbulence energy. The tube diameter ranges from 100 μm to 400 μm and the aspect ratio of the tube diameter and the length is fixed at 200. The stagnation temperature was fixed at 300 K and the computations were done for wall temperature, which ranged from 250 K to 295 K. The stagnation pressure was chosen in such a way that the flow is in turbulent flow regime. The results in wide range of Reynolds number and Mach number were obtained. The bulk temperature based on the static temperature and the total temperature of the cooled case are compared with those of heated case and also with temperatures of the incompressible flow. The result shows that different heat transfer characteristics are obtained for each cooled and heated case. A correlation for the prediction of the heat transfer rate of the turbulent gas flow in a micro-tube is proposed.

Internal Low Reynolds-Number Turbulent and Transitional Gas Flow With Heat Transfer

1966 ◽  
Vol 88 (2) ◽  
pp. 239-245 ◽  
Author(s):  
D. M. McEligot ◽  
L. W. Ormand ◽  
H. C. Perkins
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Gas Flow ◽  
Low Reynolds Number ◽  
Bulk Temperature ◽  
Temperature Ratio ◽  
Heating Rates ◽  
Reynolds Analogy ◽  
Number Range ◽  
Low Reynolds

The results of a semitheoretical and experimental investigation of the heat-transfer and frictional effects in air, nitrogen, and helium in steady flow in the downstream region of round tubes are presented. The constant-properties analysis for low Reynolds-number turbulent flow is evolved from an improved description of the adiabatic velocity profile, without modifying the Reynolds analogy assumption of equal eddy diffusivities. Data cover peak wall-to-bulk temperature ratios from near unity to 4.8 and entering Reynolds numbers from 1450 to 45,000. Low and moderate temperature-ratio data are used to confirm and to extend the analysis, while high temperature-ratio results are utilized for classification of flow regimes at high heating rates in the low Reynolds-number range.

Heat Transfer Characteristics of Compressible Laminar Flow Through Microtubes

2011 ◽  
Vol 134 (1) ◽  
Author(s):  
Chungpyo Hong ◽  
Takaharu Yamamoto ◽  
Yutaka Asako ◽  
Koichi Suzuki
Keyword(s):  
Heat Transfer ◽  
Wall Temperature ◽  
Gas Flow ◽  
Atmospheric Condition ◽  
Stagnation Temperature ◽  
Heat Transfer Characteristics ◽  
Constant Wall Temperature ◽  
Gaseous Flow ◽  
Transfer Characteristics ◽  
Flow Through

This paper describes experimental results on heat transfer characteristics of gaseous flow in a microtube with constant wall temperature. The experiments were performed for nitrogen gas flow through three microtubes of 123 μm, 163 μm, and 243 μm in diameter with 50mm in length, respectively. The wall temperature was maintained at 310 K, 330 K, and 350 K by circulating water around the microtube, respectively. The stagnation pressure is chosen in such a way that the exit Mach number ranges from 0.1 to 1.0. The outlet pressure was fixed at the atmospheric condition. The total temperature at the outlet, the inlet stagnation temperature, the mass flow rate, and the inlet pressure were measured. The numerical computations based on the Arbitrary-Lagrangian-Eulerian (ALE) method were also performed with the same conditions of the experiment for validation of numerical results. Both the results are in excellent agreement. In some cases, the total temperatures obtained by the present experimental study are higher than the wall temperature. This is due to the additional heat transfer from the wall to the gas near the microtube outlet caused by the temperature fall due to the energy conversion into the kinetic energy. A quantitative correlation for the prediction of the heat transfer rate of the gaseous flow in microtubes which had been proposed in our previous study (Hong and Asako, 2007, “Heat Transfer Characteristics of Gaseous Flows in a Microchannel and a Microtube with Constant Wall Temperature,” Numer. Heat Transfer, Part A, 52, pp. 219–238) was validated.

Mach number at outlet plane of a straight micro-tube

2016 ◽  
Vol 230 (19) ◽  
pp. 3420-3430 ◽  
Author(s):  
D Kawashima ◽  
T Yamada ◽  
C Hong ◽  
Y Asako
Keyword(s):  
Mach Number ◽  
Turbulent Flow ◽  
Gas Flow ◽  
Flow Characteristics ◽  
Ideal Gas ◽  
Computational Domain ◽  
Arbitrary Lagrangian Eulerian ◽  
Choked Flow ◽  
Downstream Region ◽  
Energy Equations

The Mach number and pressure at the outlet plane of a straight micro-tube were investigated numerically for both laminar and turbulent flow cases. The numerical methodology is based on the arbitrary Lagrangian-Eulerian method. The LB1 turbulence model was used for the turbulent flow case. The compressible momentum and energy equations with the assumption of the ideal gas were solved. The computational domain is extended to the downstream region from the micro-tube outlet. The back pressure was given to the outside of the downstream region. The computations were performed for a tube whose diameter ranges from 50 to 500 μm. The average Mach number at the outlet plane of the choked flow depends on the tube diameter and ranges from 1.16 to 1.25. The flow characteristics of the under-expanded gas flow in a straight micro-tube were revealed.

Flow and Thermal Fields in a Pendant Droplet Moving on Lyophobic Surface

2010 ◽  
Author(s):  
Basant Singh Sikarwar ◽  
K. Muralidhar ◽  
Sameer Khandekar
Keyword(s):  
Heat Transfer ◽  
Contact Angle ◽  
Reynolds Number ◽  
Shear Stress ◽  
Heat Transfer Coefficient ◽  
Wall Shear Stress ◽  
Transfer Coefficient ◽  
Maximum Shear Stress ◽  
Computational Domain ◽  
Wall Shear

Clusters of liquid drops growing and moving on physically or chemically textured lyophobic surfaces are encountered in drop-wise mode of vapor condensation. As opposed to film-wise condensation, drops permit a large heat transfer coefficient and are hence attractive. However, the temporal sustainability of drop formation on a surface is a challenging task, primarily because the sliding drops eventually leach away the lyophobicity promoter layer. Assuming that there is no chemical reaction between the promoter and the condensing liquid, the wall shear stress (viscous resistance) is the prime parameter for controlling physical leaching. The dynamic shape of individual droplets, as they form and roll/slide on such surfaces, determines the effective shear interaction at the wall. Given a shear stress distribution of an individual droplet, the net effect of droplet ensemble can be determined using the time averaged population density during condensation. In this paper, we solve the Navier-Stokes and the energy equation in three-dimensions on an unstructured tetrahedral grid representing the computational domain corresponding to an isolated pendant droplet sliding on a lyophobic substrate. We correlate the droplet Reynolds number (Re = 10–500, based on droplet hydraulic diameter), contact angle and shape of droplet with wall shear stress and heat transfer coefficient. The simulations presented here are for Prandtl Number (Pr) = 5.8. We see that, both Poiseuille number (Po) and Nusselt number (Nu), increase with increasing the droplet Reynolds number. The maximum shear stress as well as heat transfer occurs at the droplet corners. For a given droplet volume, increasing contact angle decreases the transport coefficients.

A Method of Solving Three Temperature Problem of Turbine With Adiabatic Wall Temperature

2021 ◽  
Author(s):  
Zeyu Wu ◽  
Xiang Luo ◽  
Jianqin Zhu ◽  
Zhe Zhang ◽  
Jiahua Liu
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Reynolds Number ◽  
Wall Temperature ◽  
Reference Temperature ◽  
Inlet Temperature ◽  
Adiabatic Wall ◽  
Rotating Cavity ◽  
Temperature Problem ◽  
Turbulence Parameters

Abstract The aeroengine turbine cavity with pre-swirl structure makes the turbine component obtain better cooling effect, but the complex design of inlet and outlet makes it difficult to determine the heat transfer reference temperature of turbine disk. For the pre-swirl structure with two air intakes, the driving temperature difference of heat transfer between disk and cooling air cannot be determined either in theory or in test, which is usually called three-temperature problem. In this paper, the three-temperature problem of a rotating cavity with two cross inlets are studied by means of experiment and numerical simulation. By substituting the adiabatic wall temperature for the inlet temperature and summarizing its variation law, the problem of selecting the reference temperature of the multi-inlet cavity can be solved. The results show that the distribution of the adiabatic wall temperature is divided into the high jet area and the low inflow area, which are mainly affected by the turbulence parameters λT, the rotating Reynolds number Reω, the high inlet temperature Tf,H* and the low radius inlet temperature Tf,L* of the inflow, while the partition position rd can be considered only related to the turbulence parameters λT and the rotating Reynolds number Reω of the inflow. In this paper, based on the analysis of the numerical simulation results, the calculation formulas of the partition position rd and the adiabatic wall temperature distribution are obtained. The results show that the method of experiment combined with adiabatic wall temperature zone simulation can effectively solve the three-temperature problem of rotating cavity.

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