Numerical Simulation Of Large Pipe Tees Local Resistance Characteristics And Analysis Of Central Heating System With Multi-heat Sources Operation

Central heating system with multi-heat sources can accommodate the demands and changes of large-scale district heating load preferably,and central heating is con-ducive to adopt advanced technology to economize on energy and reduce discharge.Combining the project among enterprises,universities and research institutes with the practice,and based on the engineering practice,The main work of this paper includes:1)For pipe tee local resistance of heating network has significant influence on the hydronic balancing and energy consumption,the velocity and pressure field of pipe tees with diameter greater than or equal to 400 mm were discussed by Fluent.Flow ratio（q）,Reynolds number（Re）,diameter ratio（dλ）and the angle between main branch and side branch（θ）impact on local resistance was analyzed.The results showed that: within the scope of the research,local resistance coefficient of main branch to side branch ζ₀₁ and main branch to straight branch ζ₀₂ were decreased with Re increasing and stabilized when Re was greater than 4.8×105.ζ₀₁ and ζ₀₂ were increased with q increasing,they were in parabolic curve relationship with q when dλ was larger than 0.8,however.ζ₀₁ decreased rapidly with dλ increasing but decreased slowly when dλ was greater than 0.7.Flow characteristics analysis showed that: with θ increasing,the size of the spiral,velocity gradient,streamline curve degree in branch side increased sharply,resulting in ζ₀₁ increased rapidly,the velocity gradient in straight branch increased slightly resulting in ζ₀₂ increased a little.Provided theoretical guidance of tee selection and operation optimization for heating pipelines or networks.2)For the energy efficiency of the heating system,The author of the thesis surveyed and investigated heat source,the level I pipe network and the heat-exchange station of the central heating system,and collected a large number of operating data in 2014-2015.Analyzed the date by using the “Heating System Energy Saving Transformation Technical Specifications”（GB/T 50893-2013）and calculated per unit quantity of heat and per unit heating area energy consumption,boiler efficiency,filling water rate and the hydraulic balance degree.Then,evaluated the caculated results by using above standard.Results showed that,the per unit quantity of heat energy consumption up to standard,the per unit area energy consumption exceed however.power consumption is 3.36kWh/m² and heat consumption is 0.404GJ/m²,the per unit area heating load is 43W/m².The 6# boiler keeps inefficient operation of large flowrate and small temperature difference.The system filling water rate overweight,0.78% more than the above the prescribed standards.about 70% of the 16 analytical heat exchanger station of hydraulic balance is not eligible.3)For the double-heat-source branched network heating system,based on the heat source station heat load demand dynamically,using the method of graph theory,analyzed the influence on pump power consumption with the different heat source distribution.The results show that: 1)When the heat requirement rate is 100%,95% and 90%,the 1st heat station load sharing ratio is 57.6%,42.2% and 42.2% accordingly,the minimum pump power consumption is 1439.26 kW,1247 kW,and 1143 kW.When the heat requirement rate is less than 85%,considering the 1st heat source station’s heating capacity can satisfy user heat load needs,all the heat load can be provided by 1 station,it is more economic;4)Based on literature research and the central heating system project with the running 1# heating source,under building 2# heating source and planning 3# heating source,studies experimental model of network and design experiments preliminarily.