Thermal Transport Phenomena in Turbulent Gas Flow Through a Tube at High Temperature Difference and Uniform Wall Temperature

1998 ◽  
Vol 120 (3) ◽  
pp. 784-787 ◽  
Author(s):  
Shuichi Torii ◽  
Wen-Jei Yang
Keyword(s):  
Heat Flux ◽  
High Temperature ◽  
Temperature Difference ◽  
Wall Temperature ◽  
Thermal Transport ◽  
Gas Flow ◽  
Uniform Wall Temperature ◽  
Uniform Wall ◽  
Flow Through ◽  
Turbulent Gas Flow

A numerical study is performed to investigate thermal transport phenomena in turbulent gas flow through a tube heated at high temperature difference and uniform wall temperature. A k-ε turbulence model is employed to determine the turbulent viscosity and the turbulent kinetic energy. The turbulent heat flux is expressed by a Boussinesq approximation in which the eddy diffusivity of the heat is determined by a t2-ε, heat transfer model. The governing boundary layer equations are discretized by means of a control-volume finite difference technique and are numerically solved using a marching procedure. It is disclosed from the study that (i) laminarization takes place in a turbulent gas flow through a pipe with high uniform wall temperature just as it does in a pipe with high unform wall heat flux, and (ii) the flow in a tube heated to high temperature difference and uniform wall temperature is laminarized at a lower heat than that under the uniform heat flux condirion.

Total Temperature Measurement of Turbulent Gas Flow at Microtube Exit

2013 ◽  
Author(s):  
Chungpyo Hong ◽  
Kyohei Isobe ◽  
Yutaka Asako ◽  
Ichiro Ueno
Keyword(s):  
Heat Transfer ◽  
Temperature Measurement ◽  
Wall Temperature ◽  
Gas Flow ◽  
Constant Wall Temperature ◽  
Circulating Water ◽  
Total Temperature ◽  
Flow Through ◽  
Exit Mach Number ◽  
Turbulent Gas Flow

This paper describes experimental results on total temperature measurement to obtain heat transfer characteristics of turbulent gas flow in a microtube with constant wall temperature. The experiments were performed for nitrogen gas flow through a microtube of 354 μm in diameter with 100 mm in length. The wall temperature was maintained at 310 K, 330 K, and 350 K by circulating water around the microtube, respectively. The stagnation pressure was chosen in such a way that the exit Mach number ranges from 0.1 to 1.0. In order to obtain heat transfer rate of turbulent gas flow through a micro-tube, the total temperatures of gas flowing out of a microtube exit were measured with the set of total temperature measurement attached to micro stage with position fine adjustment. The numerical computations based on the Arbitrary - Langrangian - Eulerian (ALE) method were also performed for the turbulent gas flow with the same conditions of the experiments. The results were in excellent agreement.

DSMC Study of Pressure-Driven Slip Flow through Microchannel at Non-Uniform Wall Temperature

2015 ◽  
Vol 31 (3) ◽  
pp. 279-289
Author(s):  
C.-C. Tai ◽  
P.-Y. Tzeng ◽  
C.-Y. Soong
Keyword(s):  
Temperature Gradient ◽  
Wall Temperature ◽  
Gas Flow ◽  
Slip Flow ◽  
Thermal Creep ◽  
Adiabatic Wall ◽  
Uniform Wall Temperature ◽  
Creep Effect ◽  
Uniform Wall ◽  
Pressure Driven

ABSTRACTThe present study is to investigate the pressure-driven gas flow in microchannel at no-uniform wall temperature. DSMC is employed to generate the flow field details which are then used in analysis of the slip flow characteristics. The major concern is the influences of thermal creep effect on the pressure-driven slip flow. Thermal creep is resulted from tangential wall temperature gradient. In this work, two kinds of thermal boundary condition are considered. One is the linearly varied temperature (LVT) applied to both walls, the other is that has the bottom wall at a thermal condition combined LVT and adiabatic (AD) wall, i.e. LVT-AD-LVT condition. The present DSMC results reveal that the fluid slip is weakened (enhanced) in the case with a negative (positive) wall temperature gradient. Relatively, thermal creep effect on fluid slip over the adiabatic wall is more pronounced in the presence of negative wall temperature gradient. The mass flowrate is a strong function of the wall temperature gradient. However, there is only little difference between the mass flowrates predicted under the two kinds of thermal conditions studied in the present work.

Numerical Investigation of Mixed Convective Flow Through a Vertical Duct With a Backward-Facing Step Using Nanofluids

2010 ◽  
Author(s):  
A. A. Al-aswadi ◽  
H. A. Mohammed ◽  
N. H. Shuaib
Keyword(s):  
Wall Temperature ◽  
Volume Fraction ◽  
Heated Wall ◽  
Recirculation Region ◽  
Fluid Temperature ◽  
Backward Facing Step ◽  
Uniform Wall Temperature ◽  
Uniform Wall ◽  
Flow Through ◽  
Vertical Duct

Laminar mixed convective buoyancy assisting flow through a two-dimensional vertical duct with a backward-facing step using nanofluids as a medium is numerically simulated using finite volume technique. Different types of nanoparticles with 5% volume fraction are used. The wall downstream of the step was maintained at a uniform wall temperature, while the straight wall that forms the other side of the duct was maintained at constant temperature equivalent to the inlet fluid temperature. The wall upstream of the step and the backward-facing step were considered as adiabatic surfaces. The duct has a step height of 4.9 mm and an expansion ratio of 1.942, while the total length in the downstream of the step is 0.5 m. The Reynolds number was in the range of 0 ≲ Re ≤ 100. The downstream wall was fixed to be at uniform wall temperature of 20 °C higher than the inlet flow temperature. A recirculation region was developed straight behind the backward facing step which was appeared between the edge of the step and few millimeters before the corner which connect the step and the downstream wall. In the few millimeters gap a U-turn flow was developed opposite to the recirculation flow which mixed with the unrecirculated flow and travels along the channel. It is inferred that diamond nanofluid has the highest velocity in the vicinity to the heated wall.

Heat Transfer Characteristics of Turbulent Gas Flow Through Micro-Tubes

2010 ◽  
Author(s):  
Chungpyo Hong ◽  
Yuki Uchida ◽  
Takaharu Yamamoto ◽  
Yutaka Asako ◽  
Koichi Suzuki
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Wall Temperature ◽  
Transfer Rate ◽  
Gas Flow ◽  
Gas Flows ◽  
Heat Transfer Characteristics ◽  
Total Temperature ◽  
Flow Through ◽  
Turbulent Gas Flow

This paper presents experimental results on heat transfer characteristics of turbulent gas flows though a micro-tube with constant wall temperature. The experiments were performed for nitrogen gas flows through a micro-tube with 242μm in diameter and 50 mm in length. The wall temperature was maintained at 5K, 20K and 30K higher than the inlet temperature by circulating water around the micro-tube, respectively. In order to measure heat transfer rate of gas flow through a micro-tube, the total temperature at a micro-tube exit was measured. The stagnation pressure was chosen in such a way that the Reynolds number ranges from 3000 to 12000. 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 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. A correlation for the prediction of the heat transfer rate of the turbulent gas flow through a micro-tube was proposed.

CFD-Aided Simulation of Frost Growth Inside a Narrow Duct With Uniform Wall Temperature Variation

2014 ◽  
Author(s):  
Masoud Darbandi ◽  
Ehsan Asgari ◽  
Morteza Hajikaram ◽  
Gerry E. Schneider
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Growth Rate ◽  
Temperature Variation ◽  
Wall Temperature ◽  
Uniform Wall Temperature ◽  
Boundary Location ◽  
Uniform Wall ◽  
Semi Empirical ◽  
Frost Growth

In this paper, we study the frost formation and growth at the walls of a duct with uniform wall temperature variation. The simulation is performed for laminar flow regime considering suitable semi-empirical models incorporated with computational fluid dynamics (CFD) method. The frost growth is considered to be normal to the duct surface. Since the duct aspect ratio is high, we perform our simulations in two-dimensional zones. To simulate the frost layer properly, we solve both the energy and mass balance equations implementing some semi-empirical correlations on the frost side. At this stage, we suitably predict the required heat flux value at the solid boundary and the heat transfer coefficient, which are required to be used in the CFD calculations in the next stage. So, next is to use the CFD tool to calculate the required heat transfer parameters at the air side. Since the frost growth is performed locally along the wall, the achieved frost growth rate can be applied at any specific location independently. We also investigate the effects of various environmental parameters on the frost growth rate. The current achieved results are verified by comparing them with previous available experimental data. After verification the numerical algorithm, we investigate the frost growth in a duct with uniform wall temperature variation. We assume that the variation of temperature would be gradually and uniform with time. We eventually present the effects of different parameters affecting the frost growth along the duct surface. One significant contribution of this work is to address the effects of inlet boundary location on the frost growth. In this regard, the inlet boundary is placed initially at real entrance and then at a location far upstream of the real entrance. We evaluate the effect of this boundary location on frost thickness. The use of CFD is unavoidable in this study because we need its capability to compute the required wall heat flux condition, which is an input to our semi-empirical analysis in this problem with an unsteady thermal boundary condition situation, in which the wall temperature continuously varies with time. It should be noted that, our chosen empirical method estimate the wall heat flux based on the Nusselt number value. Therefore, CFD largely helps to correct the actual heat flux at the airside. Another contribution of this work is to study frost formation in confined flow cases, in which the flow is developing both hydrodynamically and thermally. Evidently this is in contrast to the frost growth over a simple flat plate like geometry.

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