Study On Convection Heat Transfer And Flow Characteristics Of Drag Reducing Working Medium In Gas Extraction Pump

Gas extraction is an important way to prevent gas disasters.As an essential power source in the system,gas extraction pump has the characteristics of safety and reliability,but it also has obvious shortcomings: low efficiency,high energy consumption and serious waste of resources.Based on drag reduction gas extraction pump energy saving system of the fully enclosed the success of industrial experiments,improved the operation efficiency of gas extraction pump,the energy saving effect is remarkable,but with the increase of energy-saving system is running long,drag reduction agent within the pump fluid temperature is high,the energy saving rate to drop,affect the system stable running,and drag reduction agent in the realization of heat transfer deterioration phenomenon often appear when turbulent drag reduction,using the commonly used pipe type of tube and shell heat exchanger,heat transfer effect is poorer.Therefore,it is of great significance to study the convective heat transfer characteristics and flow characteristics of drag reducing working medium in different types of pipes.By building an experimental system for convection heat transfer and flow characteristics,the convection heat transfer and flow characteristics of drag reducing working medium in different types of pipes were studied.The comprehensive performance index was used to evaluate the experimental results,and the optimal pipe type with comprehensive performance was selected as the basis for the design and selection of heat transfer equipment in the energy saving system.The main work of this paper is as follows:(1)Study on non-Newtonian rheological properties of dry-reducing working medium with different concentrations.The rheological properties of dry-reducing working medium of gas extraction pump with different concentrations were studied by rheometer.The results show that the viscosity of dry-reducing working medium does not change with time at a single shear rate and has good stability.The viscosity of drag reducing medium increases with the increase of concentration and decreases with the increase of shear rate,showing obvious shear thinning phenomenon.The flow index decreased with the increase of concentration and basically increased with the increase of liquid temperature of working medium.The consistency coefficient increased with the increase of concentration and decreased with the increase of liquid temperature.The study of rheological properties provides a basis for the calculation of Reynolds number.(2)Experimental study on convection heat transfer and flow characteristics of drag reducing working medium in gas extraction pump.The experimental system of convective heat transfer and flow characteristics was established to study the convective heat transfer and flow characteristics of drag reducing working medium in straight pipe,bellows with different parameters and spiral grooved tubes.The results show that the convective heat transfer and flow characteristics of bellows and spiral grooved tubes are obviously higher than those of straight pipe.Within the experimental range,the smaller the wave distance,the better the convective heat transfer coefficient,the larger the pressure drop per pipe length and the flow resistance coefficient.The greater the wave height,the greater the pressure drop and flow resistance coefficient per tube length,but the best convective heat transfer coefficient is when the wave height is 1mm.With the increase of screw pitch,the pressure drop per pipe length and flow resistance coefficient also increase,and the convective heat transfer coefficient only decreases with the increase of screw pitch at high Reynolds number(Re>10000).With the increase of groove depth,the pressure drop per pipe length and the flow resistance coefficient increased first and then decreased,but the convective heat transfer coefficient was the best when the groove depth was 0.75 mm.(3)Build a comprehensive performance index to evaluate the convective heat transfer and flow characteristics.In order to find the balance point between heat transfer enhancement and flow resistance increase,the comprehensive performance index of convective heat transfer and flow was introduced to evaluate the comprehensive performance of the test tube.The results show that the comprehensive performance index of the four tubes is greater than 1,indicating that the heat transfer enhancement characteristic is stronger than the flow resistance increment characteristic.The composite performance index of two tubes shows negative value,which indicates that they have strong heat transfer enhancement and flow drag reduction characteristics at low Reynolds number.Compared with the comprehensive performance index within the experimental range,it is found that the spiral groove with pitch of 4mm and groove depth of 1mm is the best,so it can be used as the basis for the design and selection of heat exchange equipment in the energy saving system.There are 42 figures,5 tables and 77 references in this paper.