Purpose. To establish the influence of drilling fluid circulation rate onto the contact temperature during the rotation drilling using an impregnated diamond drill bit; to verify the mathematical model of the diamond drill bit heating process in the course of boreholes drilling. Methodology. Bench experiments and theoretical analysis using methods of mathematical modeling. Findings. In the course of the bench experiments the data of influence of the drilling fluid circulation rate on the contact temperature during drilling of granite rock with a 59-mm diameter drill bit were obtained. A relevant mathematical model of the drill bit heating under the variable rate of drilling fluid was represented on the basis of a system of the heat transfer differential equations. A comparative analysis of experimental and predicted data was carried out, and its findings positively confirm the reliability of the mathematical modeling of heat transfer processes in the downhole during bore-hole drilling. Originality. The methodology of experimental measuring of the contact temperature during the bench experiment borehole drilling using resistance sensors was proposed herein. New experimental data was obtained which allowed establishing a correlation between the contact temperature and the rate of drilling fluid in the downhole area. The proposed mathematical model of the process is found to be adequate; it allows predicting the temperature mode on the working face of borehole in the course of drilling. The findings of the research make it possible to substantiate the effect of the diamond core drilling performance gaining due to transition from the fixed time operation parameters to the variable ones. Practical value. The regularities of action of the drilling fluid circulation rate on the contact temperature of the "tool - working face" system in the course of borehole drilling were established. The performed research confirmed the possibility of managing the thermal mode of drilling by variation of the drilling fluid circulation rate. The diamond core drilling performance gains, therefore, are possible to achieve by way of increasing the thermal stimulation of the mining rock. The developed mathematical model allows forecasting the contact temperature in the course of borehole drilling for various values of the drilling fluid circulation rates. Using of this model makes it possible to define the permissible diminishing of the drilling fluid circulation rate in order to prevent any abnormal thermophysical wear of the drill bit.

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