Theoretical research of heat exchange between air flow and shaft lining subject to convective heat transfer

2020 ◽  
pp. 151-167
Author(s):  
M. A. Semin ◽  
L. Yu. Levin
Keyword(s):  
Heat Transfer ◽  
Heat Flow ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Transfer Factor ◽  
Air Flow ◽  
Air Interface ◽  
Heat Transfer Factor ◽  
Shaft Lining ◽  
Ventilation Duct

The heat and mass transfer in a mine shaft under construction is researched theoretically under temperature conditions in the shaft lining lower than the temperature of air flow fed in the shaft via a ventilation duct. The research was aimed to ensure stable airing of mine shafts in the period of construction before cutting a shaft-to-shaft connection with artificial freezing of surrounding rock mass. The multi-parametric numerical modeling of nonstationary aeroand thermo-dynamic parameters in a mine shafts was performed using 3D convective heat transfer model in ANSYS. It is found that convective heat can exert considerable influence on the heat and mass exchange in the air space of the shaft when the shaft lining temperature is lower than the temperature of air flow from the ventilation duct at the shaft bottom. Inside the shaft, the back convective flows appear and air circulates in convective cells, which increases air flow rate in the shaft. As a consequence, the heat transfer factor at the shaft lining-air interface is much higher than the calculated factor without regard to the convective heat. The influence of the temperature difference at the air and shaft lining interface and the shaft lining roughness on the average values of the heat transfer factor and heat flow at the shaft lining and air interface is investigated. The empirical formulas are proposed for calculating the heat transfer factor and specific heat flow at the shaft lining and air interface depending on the temperature difference, shaft diameter and roughness of walls of underground openings.

Numerical Study on the Surface Convective Heat Transfer of Mass Concrete Structure

2015 ◽  
Vol 723 ◽  
pp. 992-995
Author(s):  
Biao Li ◽  
Fu Guo Tong ◽  
Chang Liu ◽  
Nian Nian Xi
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Flow Velocity ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Air Flow ◽  
Convective Heat Transfer Coefficient ◽  
Concrete Surface ◽  
Mass Concrete ◽  
Air Flow Velocity

The surface convective heat transfer of mass concrete is an important element of concrete structure temperature effect analysis. Based on coupled Thermal Fluid governing differential equation and finite element method, the paper calculated and analyzed the dependence of the concrete surface convective heat transfer on the air flow velocity and the concrete thermal conductivity coefficient. Results show that the surface convective heat transfer coefficient of concrete is a quadratic polynomial function of the air flow velocity, but influenced much less by the air flow velocity when temperature gradient is dominating in heat transfer. The concrete surface convective heat transfer coefficient increases linearly with the thermal conductivity of concrete increases.

Numerical and Experimental Study of Flow and Convective Heat Transfer on a Rotor of a Discoidal Machine with Eccentric Impinging Jet

2019 ◽  
pp. 1-29
Author(s):  
Chadia Haidar ◽  
Rachid Boutarfa ◽  
Mohamed Sennoune ◽  
Souad Harmand
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Steady State ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Air Flow ◽  
Impinging Jet ◽  
Rotating Disk ◽  
Reynolds Numbers ◽  
Air Jet

This work focuses on the numerical and experimental study of convective heat transfer in a rotor of a discoidal the machine with an eccentric impinging jet. Convective heat transfers are determined experimentally in steady state on the surface of a single rotating disk. The experimental technique is based on the use of infrared thermography to access surface temperature measurement, and on the numerical resolution of the energy equation in steady-state, to evaluate local convective coefficients. The results from the numerical simulation are compared with heat transfer experiments for rotational Reynolds numbers between 2.38×105 and 5.44×105 and for the jet's Reynolds numbers ranging from 16.5×103 to 49.6 ×103. A good agreement between the two approaches was obtained in the case of a single rotating disk, which confirms us in the choice of our numerical model. On the other hand, a numerical study of the flow and convective heat transfer in the case of an unconfined rotor-stator system with an eccentric air jet impinging and for a dimensionless spacing G=0.02, was carried out. The results obtained revealed the presence of different heat transfer zones dominated either by rotation only, by the air flow only or by the dynamics of the rotation flow superimposed on that of the air flow. Critical radii on the rotor surface have been identified

An experimental investigation in forced convective heat transfer and friction factor of air flow over aligned round and flattened tube banks

2019 ◽  
Vol 48 (6) ◽  
pp. 2350-2369 ◽  
Author(s):  
Ataalah Hussain Jassim ◽  
Tahseen Ahmad Tahseen ◽  
Ahmed Waheed Mustafa ◽  
Md Mustafizur Rahman ◽  
Mahadzir Ishak
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Convective Heat Transfer ◽  
Friction Factor ◽  
Convective Heat ◽  
Air Flow ◽  
Forced Convective Heat Transfer ◽  
Tube Banks

A Study of Convective Heat Transfer in a Model Rotor–Stator Disk Cavity

2001 ◽  
Vol 123 (3) ◽  
pp. 621-632 ◽  
Author(s):  
R. P. Roy ◽  
G. Xu ◽  
J. Feng
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Air Flow ◽  
Disk Surface ◽  
Core Region ◽  
Air Flow Rate ◽  
The Core ◽  
Rotor Disk ◽  
Secondary Air

In this study, the fluid (air) temperature field and the convective heat flux distribution on the rotor disk surface were measured and computed in a model rotor–stator disk cavity. Both mainstream flow and secondary air flow were provided. The radial distribution of convective heat transfer coefficient on the rotor disk surface, which was calculated as the ratio of the local heat flux and the local temperature difference across the thermal boundary layer on the disk, is also reported. In the experiments, the disk rotational Reynolds number, Reϕ, ranged from 4.65×105 to 8.6×105, and the nondimensional secondary air flow rate, cw, ranged from 1504 to 7520. The secondary air was supplied at the cavity hub. All experiments were carried out at the same mainstream air flow rate, Rem=5.0×105. The cavity fluid temperature distribution was measured by traversing miniature thermocouples, and the rotor disk surface temperature and heat flux were measured by a quasi-steady thermochromic liquid crystal technique in conjunction with resistance temperature detectors embedded in the disk. The measurements are compared with predictions from the commercial CFD code Fluent. The Fluent simulations were performed in the rotationally symmetric mode using a two-zone description of the flow field and the RNG k-ε model of turbulence. The convective heat transfer coefficient distribution on the rotor disk surface exhibited the influence of the source region and the core region of air flow in the cavity. In the source region, which is radially inboard, the convective heat transfer was dominated by the secondary air flow rate. In the core region, which is radially outboard, the heat transfer was dominated by the rotational motion of the fluid relative to the rotor disk. An empirical correlation for the local Nusselt number on the rotor disk surface is suggested for the core region.

Experimental Studies on Energy and Exergy Analysis of a Single-Pass Parallel Flow Solar Air Heater

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
G. Raam Dheep ◽  
A. Sreekumar
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Air Temperature ◽  
Flow Rate ◽  
Temperature Difference ◽  
Air Flow ◽  
Experimental Studies ◽  
Solar Air Heater ◽  
Energy And Exergy

Solar air heaters (SAHs) are the simplest form of nonconcentrating thermal collectors. SAHs utilize solar thermal energy to increase the temperature of air for thermal applications of less than 80 °C. The energy efficiency of SAHs is significantly low due to poor convective heat transfer between the absorber and the air medium. In this present study, it is aimed to increase the convective heat transfer by modifying the absorber and the type of air flow inside the duct. Experimental studies were performed to study about the energy and exergy efficiencies of SAH with the absorber of longitudinal circular fins. The thermal analysis of the SAH is evaluated for five mass flow rates of 30, 45, 60, 75, and 90 kg/h m2 flowing inside the duct of thickness 100 mm. The impact of the flow rate on the absorber and air temperature, temperature difference (ΔT), energy and exergy efficiencies, irreversibility, improvement potential, sustainability, and CO2 reduction potential is studied. The experimental results show that the first and second laws of thermodynamic efficiency increase from 44.13% to 56.98% and from 24.98% to 36.62% by increasing the flow rate from 30 to 90 kg/h m2. The results conclude that the air flow duration inside the duct plays an important role in efficiency of the solar air heater. Therefore, lower flow rate is preferred to achieve maximum outlet air temperature and temperature difference.

scholarly journals Numerical modelling of convective heat transport by air flow in permafrost-affected talus slopes

2016 ◽  
Author(s):  
Jonas Wicky ◽  
Christian Hauck
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Thermal Regime ◽  
Air Flow ◽  
Cooling Capacity ◽  
High Porosity ◽  
Frozen Ground ◽  
Talus Slope ◽  
Talus Slopes

Abstract. Talus slopes are a widespread geomorphic phenomenon in the Alps. Due to their high porosity a gravity-driven internal air circulation can be established which is forced by the gradient between outside (air) and internal (talus) temperature. The thermal regime is different from the surrounding environment often leading to cold microclimates and permafrost occurrences. So far this phenomenon has mainly been analysed by field studies and only few explicit modelling studies of this phenomenon exist. Numerical simulations of permafrost sometimes use parameterizations for the effects of convection, but mostly neglect the influence of convective heat transfer in air on the thermal regime. On the contrary, in civil engineering many studies were carried out to investigate the thermal behaviour of blocky layers and to improve their passive cooling capacity. The present study further develops and applies these concepts to model heat transfer in air flow in a natural scale talus slope. Modelling results show that convective heat transfer has the potential to develop a temperature difference between the lower and the upper part from about 0.7 °C (boundary closed to the atmosphere) to 2.5 °C (boundary open to the atmosphere). A seasonally alternating chimney-effect type circulation develops. Modelling results also show that this convective heat transfer leads to a cold reservoir in the lower part of the talus slope which can be crucial for maintaining the frozen ground conditions under climate change.

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