Tham khảo tài liệu 'developments in heat transfer part 16', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 590 Developments in Heat Transfer The temperature of intake air due to its passage through an underground opening gradually increases due to depth and the length of air travel through underground opening. The main cause of heat transfer to air flow in underground atmosphere is due to thermal properties of virgin rock known as geothermal gradient. Other sources of heat to the air in underground atmosphere are air auto-compression diesel emission explosive detonation human metabolism and influx of thermal water. 2. Mathematical model of heat transfer The total variation of temperature in an underground environment Attotai can be calculated by including the variation of temperature from air auto-compression Ata thermal properties of rock Atr heat emission from diesel equipments Atd heat due to breaking of rocks with the use of explosives Ate human metabolism Ath and thermal water Atw as outlined in equation 1 AtM Afa Atr Afd Ate Ath Atw 1 With increasing mining depths the influence of the thermal properties of the rock mass becomes more important Navarro et al 2008 . Based on equation 1 the total underground atmosphere temperature T2 will be expressed by equation 2 as a function of surface temperature ts or underground opening initial temperature T1. T2 - ts total or T2 - T1 2 Surface air temperature It is well known that the surface air temperature varies with the seasons and is subjected to regional variations according to local weather conditions so that the temperature variation is influenced by the ventilation current temperature in underground openings. Fig. 2. Typical surface air dry temperature in Neves Corvo and San Rafael mines Figure 2 indicates that average monthly surface temperature in Neves Corvo mine was maximum C in July minimum C in January and mean being C and in San Rafel Thermal State and Human Comfort in Underground Mining 591 mines was maximum temperature was C in November minimum 4 C in July and mean being C. Surface