Research On Discharge Coefficient Of Orifice Plate Flow Sensor Under Specific Installation Conditions

With the expansion of the scale of heating in northern China,the flow of heat source exports is increasing.The issue of heat trade settlement of the corresponding large diameter pipelines is becoming more and more serious.The heat meter is composed of three parts of the flow sensor,the matched temperature sensor and the heat integral calculation display,the flow meter uses orifice flow sensor.At present,the pipe diameter of the hot water pipeline is more than DN1000,the appliccation range of the orifice flowmeter specified in the GB2624 specification is DN50^DN1000,only in this scope can it ensure its measurement characteristics,and the international standard ISO5167 is also the same.As the field calibration of the large diameter orifice flowmeter above DN1000 is almost impossible,the large diameter orifice flowmeter is selected as the research object.In this paper,numerical simulation is used to simulate the flow field of orifice flow sensor and its measuring section under the specific installation conditions of the weld and the front elbow.,and the influence of the C value of the outflow coefficient is analyzed,a certain reference is provided for the installation and use of the meter.The Fluent software is used to carry out the standard mode of the design working condition?common flow?of the without oblique orifice flowmeter,and the reliability of the numerical simulation is verified by comparing the C value of the simulation result with the design condition.The above physical models are used to simulate the flow of multiple flows between?5160t/h,8029t/h?under design conditions,the deviation between outflow coefficient C value and outflow coefficient C₀ value of common flow?design condition?varies between?0.28%,-0.29%?,the C₀ value of outflow coefficient corresponding to the common flow?design condition?is applicable to the whole range of orifice flow sensor.The orifice flowmeter with oblique angle is not only smaller than the orifice flowmeter without oblique angle,but the quality requirements of the orifice plate with oblique angle are relatively low,it has better superiority at this time.When the front weld of the orifice plate is located upstream of the front pressure outlet,The length between the weld and the hole plate is 1300 mm,,the deviation coefficient C of outflow coefficient is 0.40%,which has relatively little influence on flow measurement.When the front end of the orifice plate is located downstream of the front pressure outlet,The length between the weld and the hole plate are 100 mm,700mm and 1000 mmrespectively,the deviation of outflow coefficient C is 1.16%,0.64%and 0.60%respectively.When the front weld is located in the front vortex area,The length between the weld and the hole plate is 400 mm,the flow occurs in the wall separation area,the deviation of the outflow coefficient C value is 3.73%,it is obviously increased.The length between the weld and the hole plate is from 100 mm to1300mm,the outflow coefficient and deviation increase first and then decrease,the appearance of weld on the front of the orifice leads to a positive deviation of the outflow coefficient C value,which makes the flow measurement smaller.The single elbow and the plane double elbow are located upstream of the orifice plate,according to the requirements of GB2624 and ISO5167,straight pipe section of large diameter orifice flowmeter is set,at this point the deviation of the C value of the outflow coefficient is 0.96%and 2.96%,the measurement of flow rate is small.it is not consistent with the uncertainty of 0.5%in GB2624 and ISO5167,it is verified that GB2624 and ISO5167 stipulate that the length of straight pipe after small diameter elbow can not meet the requirement of large diameter.The length of straight pipe after single elbow is changed from 15 D to 22.5D,the deviation is changed from 1.67%to0.79%;the length of straight pipe after the plane double elbow is changed from 16 D to22D,the deviation is 3.48%to 2.96%,the plane double elbow has a more severe disturbance to the downstream flow field.