Study on heat transfer characteristic parameters and cooling effect of cold wall cooling system in coal mines

ABSTRACT

The paper designed a new type of mine cooling method. A small-scale experimental device was used to study the heat transfer characteristic parameters of the water film board of the core component of the method. Combined with the heat transfer model and experimental data, the average thermal conductivity and heat-absorbing efficiency were calculated to 0.0085 W/m·K and 85%. By setting different heat flux values, the roadway temperature dropped by 5.6°C to 22.1°C at a water flow rate of 25 ml/s. The paper also calculated the temperature rise value of a 100-m-long actual roadway after installing the cooling system through numerical simulation.

KEYWORDS:

• Cold wall cooling system
• thermal conductivity
• heat absorption efficiency
• cooling effect
• coal mines

Nomenclature

A	=	area (m2)
cw	=	specific heat capacity of water (J/kg∙°C)
g	=	acceleration of gravity (m/s2)
Hd	=	height of water film board (m)
h	=	convection heat transfer coefficient (W/m2·K)
k	=	thermal conductivity (W/m·K)
kair	=	thermal conductivity of dry air(W/m·K)
L	=	thickness (m)
n	=	number
$\overline{{\mathrm{N}}_{\mathrm{u}\mathrm{L}}}$	=	average Nusselt number
Pr	=	Prandtl number
q	=	thermal power (W)
qs	=	electric power (W)
Q	=	total heat absorbed by water (W)
r	=	radius (m)
RaL	=	Rayleigh number
T	=	absolute temperature (°C)
T∞	=	air temperature (°C)
Ts	=	surface temperature (°C)
Tf	=	temperature of heating film (°C)
ΔT	=	temperature difference (°C)
vw	=	velocity of water (m/s)

Greek letters

α	=	coefficient of thermal diffusion (m2/s)
β	=	coefficient of thermal expansion (K−1)
ν	=	kinematic viscosity (m2/s)
ξ	=	thermoelectric conversion rate
ηs	=	heat absorption efficiency of a single water film board
ηf	=	heat absorption efficiency of the cold wall cooling system
ρ	=	density of dry air (kg/m3)
ρw	=	density of water (kg/m3)

Subscripts

1	=	outside
2	=	inside
a	=	insulation layer
b	=	reflective film
c	=	roadway frame
d	=	water film board
in	=	inward
k	=	the rest
out	=	outward
x	=	x axis
w	=	water

Acknowledgments

The authors are grateful for the support from the Fundamental Research for the Central Universities (grant No. 2018CXNL08).

Correction Statement

This article has been republished with minor changes. These changes do not impact the academic content of the article.

Additional information

Funding

This work was supported by the Fundamental Research Funds for the Central Universities [grant No. 2018CXNL08].