FLOW PATTERN IDENTIFICATION WITH BOTH WALL TEMPERATURE DISTRIBUTIONS AND HEAT TRANSFER CHARACTERISTICS DURING REFRIGERANT EVAPORATION IN SPIRALLY GROOVED TUBE

Equipment ◽  
2006 ◽  
Author(s):  
S. Momoki ◽  
S. Higashiiue ◽  
T. Shigechi ◽  
T. Yamaguchi ◽  
H. Mori
Keyword(s):  
Heat Transfer ◽  
Flow Pattern ◽  
Wall Temperature ◽  
Pattern Identification ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Temperature Distributions ◽  
Grooved Tube ◽  
Flow Pattern Identification

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.

Investigation of Buoyancy Effects on Heat Transfer Characteristics of Supercritical Carbon Dioxide in Heating Mode

2015 ◽  
Vol 1 (3) ◽  
Author(s):  
Sandeep R. Pidaparti ◽  
Jacob A. McFarland ◽  
Mark M. Mikhaeil ◽  
Mark H. Anderson ◽  
Devesh Ranjan
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Shear Stress ◽  
Wall Temperature ◽  
Reynolds Numbers ◽  
Turbulent Shear ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Turbulent Shear Stress ◽  
Heating Mode

Experiments were performed to investigate the effects of buoyancy on heat transfer characteristics of supercritical carbon dioxide in heating mode. Turbulent flows with Reynolds numbers up to 60,000, at operating pressures of 7.5, 8.1, and 10.2 MPa, were tested in a round tube. Local heat transfer coefficients were obtained from measured wall temperatures over a large set of experimental parameters that varied inlet temperature from 20 to 55°C, mass flux from 150 to 350  kg/m2s, and a maximum heat flux of 65  kW/m2. Horizontal, upward, and downward flows were tested to investigate the unusual heat transfer characteristics due to the effect of buoyancy and flow acceleration caused by large variation in density. In the case of upward flow, severe localized deterioration in heat transfer was observed due to reduction in the turbulent shear stress and is characterized by a sharp increase in wall temperature. In the case of downward flow, turbulent shear stress is enhanced by buoyancy forces, leading to an enhancement in heat transfer. In the case of horizontal flow, flow stratification occurred, leading to a circumferential variation in wall temperature. Thermocouples mounted 180° apart on the tube revealed that the wall temperatures on the top side are significantly higher than the bottom side of the tube. Buoyancy factor calculations for all the test cases indicated that buoyancy effects cannot be ignored even for horizontal flow at Reynolds numbers as high as 20,000. Experimentally determined Nusselt numbers are compared to existing correlations available in the literature. Existing correlations predicted the experimental data within ±30%, with maximum deviation around the pseudocritical point.

Experimental Study on Condensation Heat Transfer and Flow Modes of R245fa on Enhanced Surface Tubes

2015 ◽  
Vol 23 (02) ◽  
pp. 1550014 ◽  
Author(s):  
Daisuke Jige ◽  
Tomonobu Matsuno ◽  
Norihiro Inoue
Keyword(s):  
Heat Transfer ◽  
Saturation Temperature ◽  
Condensation Heat Transfer ◽  
Flow Mode ◽  
Heat Transfer Characteristics ◽  
Enhanced Heat Transfer ◽  
Finned Tubes ◽  
Transfer Characteristics ◽  
Grooved Tube ◽  
Enhanced Surface

The present study experimentally investigated the condensation heat transfer characteristics and condensate flow mode of R245fa on horizontal low-finned and microscopic-grooved tubes. Five low-finned tubes and a microscopic-grooved tube with tube diameters at the fin tip of approximately 19 mm were used. Experiments were conducted at a saturation temperature of 40°C. The fundamental heat transfer characteristics of the low-finned and microscopic-grooved tubes were experimentally investigated to clarify the flow modes of the condensate and the efficacy of the enhanced heat transfer.

On the Mathematical Modeling of Heat Transfer Characteristics of Turbulent Flames in Industrial Furnaces

2002 ◽  
Author(s):  
Essam E. Khalil
Keyword(s):  
Mathematical Modeling ◽  
Heat Transfer ◽  
Flow Pattern ◽  
Three Dimensional ◽  
Flow Regimes ◽  
Wall Heat Transfer ◽  
Governing Equations ◽  
Heat Transfer Characteristics ◽  
Combustion Chambers ◽  
Transfer Characteristics

The recent advances in numerical methods and the vast development of computers had directed the designers to better development and modifications to air flow pattern and heat transfer in combustion chambers. Extensive efforts are exerted to adequately predict the air velocity and turbulence intensity distributions in the combustor zones and to reduce the emitted pollution and noise abatement to ultimately produce quite and energy efficient combustor systems. The present work fosters mathematical modeling techniques to primarily predict what happens in three-dimensional combustion chambers simulating boiler furnaces, areo engines in terms of flow regimes and interactions. The present work also demonstrates the effect of chamber design and operational parameters on performance, wall heat transfer under various operating parameters. The governing equations of mass, momentum and energy are commonly expressed in a preset form with source terms to represent pressure gradients, turbulence and viscous action. The physical and chemical characteristics of the air and fuel are obtained from tabulated data in the literature. The flow regimes and heat transfer play an important role in the efficiency and utilization of energy. The results are obtained in this work with the aid of the three-dimensional program 3DCOMB; applied to axisymmetrical and three-dimensional complex geometry with and without swirl with liquid or gaseous fuels. The present numerical grid arrangements cover the combustion chamber in the X, R or Y and Z coordinates directions. The numerical residual in the governing equations is typically less than 0.001%. The obtained results include velocity vectors, turbulence intensities and wall heat transfer distributions in combusors. Examples of large industrial furnaces are shown and are in good agreement with available measurements in the open literature. One may conclude that flow patterns, turbulence and heat transfer in combustors are strongly affected by the inlet swirl, inlet momentum ratios, combustor geometry. Both micro and macro mixing levels are influential. The present modeling capabilities can adequately predict the local flow pattern and heat transfer characteristics in Complex combustors. Proper representation of the heat transfer and radiation flux is important in adequate predictions of large furnace performance.

A Parametric Experimental Study on the Heat Transfer Characteristics of Supercritical Kerosene in Active Cooling Channels of Scramjets

2013 ◽  
Vol 774-776 ◽  
pp. 252-257
Author(s):  
Ning Wang ◽  
Jin Zhou ◽  
Yu Pan ◽  
Hui Wang
Keyword(s):  
Heat Transfer ◽  
Wall Temperature ◽  
Sharp Increase ◽  
Film Boiling ◽  
Transfer Enhancement ◽  
Heat Transfer Characteristics ◽  
Heat Transfer Deterioration ◽  
Cooling Channels ◽  
Transfer Characteristics ◽  
The Heat Transfer Coefficient

Heat transfer characteristics of China RP-3 kerosene under supercritical state were experimentally investigated. Results showed that at sub-critical pressures, heat transfer deterioration happens, and the wall temperature rises from approximately 350°C to 750°C. This is thought to be resulted from film boiling when kerosene begins to transfer from liquid to gas. At supercritical pressures, heat transfer enhancement was observed. And it is mainly caused by the sharp increase of specific heat of kerosene when the wall temperature is approaching the critical temperature of kerosene. The heat transfer coefficient doesnt increase with velocity for kerosene, because the thermal properties and residence time of kerosene have changed when velocity is changed.

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