Cold ioss of supply chilled air for level roadway drifting during mine construction

Chilled air supply with long non-insulated air ducts cooling system is usually used for level roadway drifting during mine construction.The conveying distance is up to 600 m.Due to the large proportion of the cold loss in the long distance transportation,it is a key factor affecting the investment,design and operation management of the cooling system.In order to solve the cold loss calculation problem,the differential equations of temperature fields of air flows inside and outside duct are developed based on heat energy transport and conservation relationship between air flows inside and outside duct and between airflow and the surrounding rock,aiming at the characteristics of heading and ventilation system in horizontal roadway during mine construction.The unstable heat transfer coefficient in the roadway changing with the ventilation duration is analyzed as the spatial distribution function along the length of the roadway.The distribution of the temperature fields inside and outside duct and the cold loss are obtained through numerical calculation.Through theoretical calculation,the operation characteristics of the system are compared when the ventilation duration is 0,30,90,120,and 150 days,the air supply volume is 300,330,and 360 m3/min,and the air inlet temperature is 16,18,and 20 ℃,respectively.The results show that unstable heat transfer coefficient between airflow and surrounding rock decreases with the increase of ventilation time,and basically reaches stability after about 90 days of ventilation.With the increase of ventilation time the air temperature increases significantly inside duct and gradually becomes gentle outside duct along the direction of air flow because of the change of unstable heat transfer coefficient.The cold loss of the system is about 5%-9% of the cooling capacity.It increases by about 5% for every 2 ℃ decrease in the air supply temperature.The cold loss is linearly proportional to the air supply distance.For every 10% increase in ventilation volume,the cold loss decreases by about 4.5%.