New Correlations for Flow and Conjugate Heat Transfer with Surface Radiation Characteristics of a Real-Scale Infrared Suppression System with Conical Funnels

2021 ◽  
Author(s):  
Arnab Mukherjee ◽  
Vikrant Chandrakar ◽  
Jnana Ranjan Senapati
Keyword(s):  
Heat Transfer ◽  
Linear Regression Analysis ◽  
Ambient Air ◽  
Surface Radiation ◽  
Outlet Temperature ◽  
Intake Rate ◽  
Computational Domain ◽  
Exit Temperature ◽  
Real Scale ◽  
Intake Ratio

Abstract The consistent and accurate prediction of fluid flow and heat transfer characteristics in an infrared suppression (IRS) device is challenging due to the complex nature of the flow features. The cool ambient air intake and subsequent mixing of hot exhaust gas from the engine in the cargo/naval ships are done inside the IRS system. The objective is to propose correlations for mass entrainment and outlet temperature of IRS device with conical funnels stacked one above the other. The mass intake rate and funnel exit temperature are determined by a set of relevant operating and geometric parameters, such as Reynolds number, nozzle exhaust temperature, the number of funnels, and funnel overlap. In this study, the funnel walls are conducting with finite wall thickness, and the surface radiation is taken into consideration. Numerical simulations are performed for the real-scale IRS unit by solving the mass, momentum, energy, and radiation equations in the computational domain surrounding the system. Non-linear regression analysis of the data is carried out using the Levenberg and Marquest (L-M) method to achieve an empirical correlation of mass intake ratio and outlet temperature ratio. The proposed correlation for mass intake ratio is valid within ±6%, and that of outlet temperature is valid within ±5% of the numerical data. The valid ranges for correlations are: 6×?10?^5= Nozzle Reynold number 3×?10?^6; 2 = Number of funnel = 5;-0.325 = funnel overlapping height = 0.25;1.33 = Nozzle exit temperature = 2.

scholarly journals Thermal analysis and optimization of L-shape fin heat sink under natural convection using ANOVA and Taguchi

2021 ◽  
pp. 317-317
Author(s):  
Numan Habib ◽  
Muftooh Ur Rehman Siddiqi ◽  
Muhammad Tahir
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Heat Sink ◽  
Transfer Rate ◽  
Flow Behavior ◽  
Three Dimensional ◽  
Ambient Air ◽  
Circuit Board ◽  
Computational Domain ◽  
Sink Size

Advancement in electronic systems resulted in miniaturization and high-power densities. Therefore, the rate of heat generation in circuit board increased dramatically. To overcome the problem of overheating, numerous heat sink designs are proposed including L-shape fins heat sink. The thermo-fluidic flow behavior and temperature difference are analyzed to get better understanding of heat transfer from the sink to ambient air. Governing equations for the model of conjugate heat transfer in three-dimensional environment are solved and discretized across the computational domain. Numerous experiments are carried out to validate the numerical results. The effect of fin numbers, height and heat sink size at three different input power is reported. Furthermore, ANOVA and Taguchi statistical methods are used to predict parameters that affect the heat transfer. The study revealed that fin height affects the heat transfer rate the most, and accounts for 25.3 percent increase in heat transfer rate. Optimization of the heat sink is carried out to ensure better efficiency of the proposed HS. The optimized conditions for the sink are observed to be heat sink size of 90mm, 9 number of fins and 33mm of fin height.

Numerical Study of Natural Convection Heat Transfer Over a Cooling Stage

2017 ◽  
Author(s):  
Mohammad Rejaul Haque ◽  
Amy Rachel Betz
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Numerical Study ◽  
Ambient Air ◽  
Recirculation Region ◽  
Asymmetric Distribution ◽  
Computational Domain ◽  
Cooling Stage

Numerical study of natural convection phenomenon close to a cooling stage has been investigated in a two dimensionally controlled environment. The study was conducted for ambient air which was kept at constant temperature (22°C) and Prandtl number of this Newtonian fluid was taken as 0.71. The cooling stage was kept at 5°C and height of the stage was considered 0.02 m. The stage was located at the bottom on the computational domain. The center of cooling stage was placed at X = 0.35 m and X = 0.5 m respectively from the left boundary of the domain. Later, computational analysis was performed to solve coupled momentum and energy equations for appropriate boundary conditions. The study was performed for a range of Rayleigh number from 102 to 107. Thermal and hydrodynamic behavior was reported in terms of isotherms, streamlines and average Nusselt number calculation. The position of the stage significantly effects heat transfer and flow fields. Nusselt number was evaluated close to cooling stage. Streamlines resulted huge recirculation region which was symmetric about the vertical mid-centerline of the domain for cooling stage located at X = 0.5 m. The center of core vortices shifted near to the cooling stage as Rayleigh number increases ensuring enhancement of heat transfer. Additionally, increasing Rayleigh number induces significant buoyancy driven flow. The velocity of this driven flow increases towards left and right wall as Rayleigh number increases. Velocity profile was also evaluated due to flow inside the enclosure. A parabolic variation was observed for horizontal velocity component near the isothermal walls and it was found less significant compared to vertical component due to buoyancy driven flow. Moreover, the asymmetric distribution of isotherms created by eccentric position of the stage resulted better enhancement than centric position of the cooling stage. Finally, this results would help the researchers find the optimal position of any sample on a cooling stage subjected to convection phenomenon. This could be significant in the collection of experimental data for condensation and frost formation.

scholarly journals Experimental Determination of Stator Endwall Heat Transfer

1989 ◽  
Author(s):  
Robert J. Boyle ◽  
Louis M. Russell
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Test Section ◽  
Electrical Power ◽  
Exhaust System ◽  
Ambient Air ◽  
Reynolds Numbers ◽  
Inlet Velocity ◽  
Turbine Vane

Local Stanton numbers were experimentally determined for the endwall surface of a turbine vane passage. A six vane linear cascade having vanes with an axial chord of 13.81 cm was used. Results were obtained for Reynolds numbers based on inlet velocity and axial chord between 73,000 and 495,000. The test section was connected to a low pressure exhaust system. Ambient air was drawn into the test section, inlet velocity was controlled up to a maximum of 59.4 m/sec. The effect of the inlet boundary layer thickness on the endwall heat transfer was determined for a range of test section flow rates. The liquid crystal measurement technique was used to measure heat transfer. Endwall heat transfer was determined by applying electrical power to a foil heater attached to the cascade endwall. The temperature at which the liquid crystal exhibited a specific color was known from a calibration test. Lines showing this specific color were isotherms, and because of uniform heat generation they were also lines of nearly constant heat transfer. Endwall static pressures were measured, along with surveys of total pressure and flow angles at the inlet and exit of the cascade.

scholarly journals Fully Coupled Large Eddy Simulation of Conjugate Heat Transfer in a Ribbed Channel with a 0.1 Blockage Ratio

Energies ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 2096
Author(s):  
Joon Ahn ◽  
Jeong Chul Song ◽  
Joon Sik Lee
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Conjugate Heat Transfer ◽  
Heat Transfer Analysis ◽  
Scale Model ◽  
Computational Domain ◽  
Blockage Ratio ◽  
Ribbed Channel ◽  
Large Eddy ◽  
Cooling Passage

Large eddy simulations are performed to analyze the conjugate heat transfer of turbulent flow in a ribbed channel with a heat-conducting solid wall. An immersed boundary method (IBM) is used to determine the effect of heat transfer in the solid region on that in the fluid region in a unitary computational domain. To satisfy the continuity of the heat flux at the solid–fluid interface, effective conductivity is introduced. By applying the IBM, it is possible to fully couple the convection on the fluid side and the conduction inside the solid and use a dynamic subgrid scale model in a Cartesian grid. The blockage ratio (e/H) is set at 0.1, which is typical for gas turbine blades. Through conjugate heat transfer analysis, it is confirmed that the heat transfer peak in front of the rib occurs because of the impinging of the reattached flow and not the influence of the thermal boundary condition. When the rib turbulator acts as a fin, its efficiency and effectiveness are predicted to be 98.9% and 8.32, respectively. When considering conjugate heat transfer, the total heat transfer rate is reduced by 3% compared with that of the isothermal wall. The typical Biot number at the internal cooling passage of a gas turbine is <0.1, and the use of the rib height as the characteristic length better represents the heat transfer of the rib.

scholarly journals Combined Heat Transfer Mechanisms in the Porous Char Layer Formed from the Intumescent Coatings under Fire

Coatings ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 200
Author(s):  
Lingyun Zhang ◽  
Yupeng Hu ◽  
Minghai Li
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Thermal Conduction ◽  
Total Heat ◽  
Surface Radiation ◽  
Total Heat Transfer ◽  
Char Layer ◽  
Competition Result ◽  
Transfer Mechanisms ◽  
Combined Heat Transfer

This study examines the combined heat transfer by thermal conduction, natural convection and surface radiation in the porous char layer that is formed from the intumescent coating under fire. The results show that some factors, such as the Rayleigh number, conductivity ratio, emissivity, radiation–conduction number, void fraction and heating mode have a certain effect on the total heat transfer. In addition, the natural convection of the air in the cavity always inhibits surface radiation among the solid walls and thermal conduction, and the character of the total heat transfer is the competition result of the three heat transfer mechanisms.

scholarly journals Predicting the effect of the rib pitch on thermal performance factor of small channels plate heat exchangers fitted with Y and C shapes obstacles

2021 ◽  
Vol 3 (4) ◽  
Author(s):  
Sirine Chtourou ◽  
Hassene Djemel ◽  
Mohamed Kaffel ◽  
Mounir Baccar
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Computer Aided Design ◽  
Flow Characteristics ◽  
Plate Heat Exchanger ◽  
Geometrical Parameters ◽  
Computational Domain ◽  
Ansys Fluent ◽  
Plate Heat ◽  
Small Channels

AbstractThis study presents a numerical analysis of a laminar counter flow inside small channels plate heat exchanger fitted with Y and C shape obstacles. Using the Computational Fluid Dynamics CFD, an advanced and modern simulation technique, the influence of the geometrical parameters (such as geometry, rib pitch) on the flow characteristics, the thermal and the hydrodynamics performance of the PHE (plate heat exchanger) is investigated numerically. The main goal of this work is to increase the flow turbulence, enhance the heat transfer and the thermal efficiency by inserting new obstacles forms. The computational domain is a conjugate model which is developed by the Computer Aided Design CAD software Solidworks. The results, obtained with Ansys Fluent, show that the presence of the shaped ribs provides enhancement in heat transfer and fluid turbulence. The CFD analysis is validated with the previous study. The non-dimensional factors such as the Nusselt number Nu, the skin friction factor Cf and the thermo-hydraulic performance parameter THPP are predicted with a Reynolds number Re range of 200–800. The temperature and the velocity distribution are presented and analyzed. The Y ribs and the C ribs offer as maximum THPP values respectively about 1.44 and 2.6 times of a smooth duct.

scholarly journals Analysis and Comparison of Some Low-Temperature Heat Sources for Heat Pumps

Energies ◽  
2019 ◽  
Vol 12 (10) ◽  
pp. 1853 ◽  
Author(s):  
Pavel Neuberger ◽  
Radomír Adamovský
Keyword(s):  
Heat Transfer ◽  
Low Temperature ◽  
Heat Source ◽  
Heat Pump ◽  
Heat Exchangers ◽  
Ambient Air ◽  
Heat Transfer Fluid ◽  
Heat Sources ◽  
Ground Heat Exchangers ◽  
Temperature Heat

The efficiency of a heat pump energy system is significantly influenced by its low-temperature heat source. This paper presents the results of operational monitoring, analysis and comparison of heat transfer fluid temperatures, outputs and extracted energies at the most widely used low temperature heat sources within 218 days of a heating period. The monitoring involved horizontal ground heat exchangers (HGHEs) of linear and Slinky type, vertical ground heat exchangers (VGHEs) with single and double U-tube exchanger as well as the ambient air. The results of the verification indicated that it was not possible to specify clearly the most advantageous low-temperature heat source that meets the requirements of the efficiency of the heat pump operation. The highest average heat transfer fluid temperatures were achieved at linear HGHE (8.13 ± 4.50 °C) and double U-tube VGHE (8.13 ± 3.12 °C). The highest average specific heat output 59.97 ± 41.80 W/m2 and specific energy extracted from the ground mass 2723.40 ± 1785.58 kJ/m2·day were recorded at single U-tube VGHE. The lowest thermal resistance value of 0.07 K·m2/W, specifying the efficiency of the heat transfer process between the ground mass and the heat transfer fluid, was monitored at linear HGHE. The use of ambient air as a low-temperature heat pump source was considered to be the least advantageous in terms of its temperature parameters.

Sign in / Sign up

Export Citation Format

Share Document