Abstract
M.Ing.
Gold ore deposits are depleted near the surface of the earth and the remaining deposits are located at great depths of over 3000m. Geothermal energy will cause the ventilation air temperature to increase above 50°C, and therefore it must be cooled to an effective working temperature. The cost of providing acceptable air temperatures to the workers in the mine plays an important role in the feasibility of whether to proceed with a mining project. At present the air in South African gold mines is cooled by a number of processes including bulk air coolers and direct contact spray chambers. In all of the above mentioned processes large quantities of water need to be pumped into the mine where it is used as the cooling fluid to reduce the air temperature. One of the recent developments for cooling the ventilation air uses ice, produced on surface in large quantities and transported underground in conventional plastic piping. It is regarded as the most effective system for creating chilled cooling water. To create an even more effective process, the properties of a new coolant will be investigated. In the new process, ice is transported into the mine and then mixed with a brine solution. The presence of the salt in the brine creates a freezing point depression and an endothermic chemical reaction causing the temperature of the mixture to decrease well below zero degrees Celsius. This chilled brine solution will be used instead of water to decrease the temperature of the ventilation air. The aim of the project is to conduct an analytical and experimental evaluation by using ice and brine as the coolant. In the experimental investigation the coolant is pumped over a flat, multi-plate heat transfer surface where the air flow is maintained at a constant rate. This simplifies the mathematical modeling and gives useful relationships between the experimental results and the theoretical results.