Quang Ninh University of Industry, Quang Ninh, Vietnam:

Giang Quoc Khanh, Candidate of Engineering Sciences

NUST MISIS, Moscow, Russia:
A. E. Krivenko, Associate Professor, Candidate of Engineering Sciences, krivenko.ae@misis.ru

Gorbachev Kuzbass State Technical University’s Division in Prokopyevsk, Prokopyevsk, Russia:
E. Yu. Pudov, Director, Candidate of Engineering Sciences
E. G. Kuzin, Associate Professor

Operation of hydraulic excavators in open pit mines in tropical countries shows that one of the critical factors of their reliability, endurance and efficiency is the temperature of power fluid. In operation the power fluid temperature is governed by the balance between heat liberation in the hydraulic system and heat transfer to the ambient environment. The process of the power fluid cooling is attended by all components of the hydraulic system but the main part belongs to a cooler. Hydraulic excavators are most often equipped with air-cooling systems represented by worms of oval tubes. Heat rejection in a cooler is a multi-factor process dependent on physical, mechanical and thermodynamic properties of heat sources, ambient temperature of the cooler design variables. The authors’ model of the heat rejection process makes it possible to estimate the heat rejection capacity of the cooler in a wide range of the power fluid temperature with regard to the change in its specific heat and thermal conductivity as functions of the ambient temperature. The calculation of the heat rejection takes into account the design variables of the cooler. Furthermore, thanks to the thermodynamic similarity criteria included, the model possesses flexibility and scalability. The calculations show that for the power fluid temperature in the range of 60–70 °C, the heat rejection efficiency of a standard cooler is 2–2.5 times lower in the hot season than in the season with moderate air temperatures. Later on, the experimental data obtained using infrared thermography can help adjust the computational model and improve the calculation efficiency. The modeling data enable accurate determination of temperature balance in hydraulics of hydraulic excavators.

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