scholarly journals Experimental and Numerical Investigation of the Thermal Transition Area at the Heated Bottom-Wall of a Horizontal Rectangular Channel

2020 ◽  
Vol 328 ◽  
pp. 02022
Author(s):  
Jaroslav Pulec ◽  
Jan Novosád ◽  
Václav Vinš ◽  
Petra Dančová
Keyword(s):  
Heated Surface ◽  
Rectangular Channel ◽  
Bottom Wall ◽  
Real Problem ◽  
Flow Conditions ◽  
Flow And Heat Transfer ◽  
Transition Area ◽  
Ongoing Work ◽  
Longitudinal Coordinate ◽  
Isothermal Water

This article represents a part of an ongoing work on the preparation of an experimental rectangular channel for the PIV and LIF measurements of vortex structures and temperature field in a non-isothermal water flow. The main aim of the current study is to develop a sufficiently accurate simplified numerical model of the real problem. The basic requirements for thermal properties of heated bottom-wall are specified. In the computational model, there are several simplifications such as 2D case and a constant temperature of a heated surface along the longitudinal coordinate. Results of the numerical simulation of the fluid flow and heat transfer are verified on the experimental data obtained in a laboratory channel with the same geometry and similar flow conditions. The presented results helped to define additional requirements on the design of a new experimental channel intended for investigation of the flow instabilities in a non-isothermal liquid flow.

Numerical Simulation of Heat Transfer Mechanisms in Spray Cooling

2010 ◽  
Author(s):  
Eelco Gehring ◽  
Mario F. Trujillo
Keyword(s):  
Heat Transfer ◽  
Heated Surface ◽  
Spray Cooling ◽  
Impingement Zone ◽  
Ongoing Work ◽  
Efficient Suppression ◽  
A Cell ◽  
Cooling Behavior ◽  
Free Surface Capturing ◽  
The Impact

A primary mechanism of heat transfer in spray cooling is the impingement of numerous droplets onto a heated surface. This mechanism is isolated in the present and ongoing work by numerically simulating the impact of a single train of FC-72 droplets employing an implicit free surface capturing methodology. The droplet frequency and velocity ranges from 2000–4000 Hz, and 0.5–2 m/s, respectively, with a fixed drop size of 239 μm. This gives a corresponding Weber and Reynolds range of 10–170 and 330–1300, respectively. Results show that the impingement zone is largely free of phase change effects due to the efficient suppression of the local temperature field well below the saturated value. Due in part to the relatively high value of the Prandtl number and the compression of the boundary layer from the impingement flow, a cell size on the order of 1 μm is necessary to adequately capture the heat transfer dynamics. It is shown that the cooling behavior increases in relation to increasing frequency and impact velocity, but is most sensitive to velocity. In fact, for sufficiently low velocities the calculations show that the momentum imparted on the film is insufficient to maintain a near stationary liquid crown. The consequence is a noticeable penalty on the cooling behavior.

Numerical Simulation of Flow and Heat Transfer in Rectangular Channel With Different Aspect Ratios

2016 ◽  
Author(s):  
Liu Wenhua ◽  
Mo Yang ◽  
Li Ling ◽  
Qiao Liang ◽  
Yuwen Zhang
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Aspect Ratio ◽  
Characteristic Length ◽  
Rectangular Channel ◽  
Equivalent Diameter ◽  
Correction Coefficient ◽  
Corner Region ◽  
Flow And Heat Transfer ◽  
Aspect Ratios

Turbulent flow and heat transfer in rectangular channel has an important significance in engineering. Conventional approach to caculate Nusselt number of rectangular channel approximately is to take the equivalent diameter as the characteristic length and use the classic circular channel turbulent heat transfer coefficient correlations. However, under these conditions, the caculation error of Nusselt number can reach to 14% and thus this approach can not substantially describe the variation of Nusselt number of rectangular cross-sections with different aspect ratios. Therefore, caculation by using equivalent diameter as the characteristic length in classic experiment formula needs to be corrected. Seven groups of rectangular channel models with different aspect ratios have been studied numerically in this paper. By using standard turbulence model, the flow and heat transfer law of air with varing properties has been studied in 4 different sets of conditions in Reynolds number. The simulation and experimental results are in good agreement. The simulation results show that with the increase of aspect ratio, the cross-sectional average Nusselt number increased, Nusselt number of circumferential wall distributed more evenly and the difference between the infinite plate channel and square channel went up to 25%. The effects of corner region and long\short sides on heat transfer have also been investigated in this paper. Results show that in rectangular channel, heat transfer in corner region is significantly weaker than it in other region. With the increase of aspect ratio, effect on the long side of heat transfer of the short side is gradually reduced, and then eventually eliminates completely in the infinite flat place. Based on the studies above, correction coefficient for rectangular channels with different aspect ratios has been proposed in this paper and the accuracy of the correction coefficient has been varified by numerical simulations. This can reflect the variation of Nusselt number under different aspect ratios more effectively and thus has current significance for project to calculate Nusselt number of heat transfer in rectangular channel.

A Study on Flow Boiling in Microchannel With Piranha Pin Fin

2015 ◽  
Author(s):  
X. Yu ◽  
C. Woodcock ◽  
Y. Wang ◽  
J. Plawsky ◽  
Y. Peles
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Fluid Flow ◽  
Pressure Drop ◽  
Heat Transfer Performance ◽  
Flow Boiling ◽  
Transfer Performance ◽  
Flow Conditions ◽  
Pin Fin ◽  
Flow And Heat Transfer

In this paper we reported an advanced structure, the Piranha Pin Fin (PPF), for microchannel flow boiling. Fluid flow and heat transfer performance were evaluated in detail with HFE7000 as working fluid. Surface temperature, pressure drop, heat transfer coefficient and critical heat flux (CHF) were experimentally obtained and discussed. Furthermore, microchannels with different PPF geometrical configurations were investigated. At the same time, tests for different flow conditions were conducted and analyzed. It turned out that microchannel with PPF can realize high-heat flux dissipation with reasonable pressure drop. Both flow conditions and PPF configuration played important roles for both fluid flow and heat transfer performance. This study provided useful reference for further PPF design in microchannel for flow boiling.

Investigation of Airflow and Temperature Distribution in the Freezer Cabinet of a Domestic No-Frost Refrigerator

2009 ◽  
Author(s):  
Melike Nikbay ◽  
M. Berkay Acikgoz ◽  
Husnu Kerpicci
Keyword(s):  
Energy Consumption ◽  
Temperature Distribution ◽  
Uniform Temperature ◽  
Flow Conditions ◽  
Piv Measurements ◽  
Factors Affecting ◽  
Flow And Heat Transfer ◽  
Cfd Analyses ◽  
Off Time ◽  
Laminar Flow Conditions

Uniformity of temperature distribution in a loaded freezer cabinet is one of the most important factors affecting energy consumption of a refrigerator. Present study focuses on the airflow behavior and the temperature distribution inside the freezer compartment of a domestic no-frost refrigerator. Energy consumption increases in a freezer cabinet if the temperature difference between the warmest load package and average of all packages is high. The objective is to reduce the energy consumption by providing a uniform temperature distribution and also to keep the food fresh for a longer time. In this study, the air flow and heat transfer during on-time and off-time periods inside the freezer compartment is modeled by considering turbulent and laminar flow conditions in 3D transient CFD analyses. The initial and boundary conditions are provided from temperature controlled room and PIV measurements. The CFD analyses obtained are verified by experimental measurements.

Computation of Flow and Heat Transfer in Rotating Rectangular Channels (AR=4:1) With Pin-Fins by a Reynolds Stress Turbulence Model

2006 ◽  
Vol 129 (6) ◽  
pp. 685-696 ◽  
Author(s):  
Guoguang Su ◽  
Hamn-Ching Chen ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Rotation Number ◽  
Rectangular Channel ◽  
Density Ratio ◽  
Three Dimensional ◽  
Diameter Ratio ◽  
Mean Velocity ◽  
Flow And Heat Transfer ◽  
Pin Fins

Computations with multi-block chimera grids were performed to study the three-dimensional turbulent flow and heat transfer in a rotating rectangular channel with staggered arrays of pin-fins. The channel aspect ratio (AR) is 4:1, the pin length to diameter ratio (H∕D) is 2.0, and the pin spacing to diameter ratio is 2.0 in both the stream-wise (S1∕D) and span-wise (S2∕D) directions. A total of six calculations have been performed with various combinations of rotation number, Reynolds number, and coolant-to-wall density ratio. The rotation number and inlet coolant-to-wall density ratio varied from 0.0 to 0.28 and from 0.122 to 0.20, respectively, while the Reynolds number varied from 10,000 to 100,000. For the rotating cases, the rectangular channel was oriented at 150deg with respect to the plane of rotation to be consistent with the configuration of the gas turbine blade. A Reynolds-averaged Navier-Stokes (RANS) method was employed in conjunction with a near-wall second-moment turbulence closure for detailed predictions of mean velocity, mean temperature, and heat transfer coefficient distributions.

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