Variable Venturi Throat Constriction for Precision Liquid Additive Metering
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Solution Overview
Problem
Existing metering devices with reciprocating differential piston pumps face challenges in maintaining precision and efficiency when metering liquid additives above 2% in the main liquid flow, due to increased pressure drop differences between upward and downward strokes, leading to reduced precision and inability to maintain pressure drop over a large range of flow rates.
Innovation Solution
Incorporating a means to vary the constriction of the venturi throat, controlled by a pressure-sensitive mechanism that adjusts the passage cross-section based on pressure drop differences between the pump and the venturi, ensuring better matching of total pressure drops, using a sliding vane or cylindrical rod with a membrane to compare pressures and adjust the venturi constriction accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the metering rate of liquid additive is increased above 2% in the main liquid flow, then the metering capacity is improved, but the precision of metering deteriorates due to increased pressure drop differences between upward and downward strokes
Solution Approach 1:
The venturi throat constriction is made variable through a control means that adjusts the passage cross-section dynamically. When additive metering increases, the control means constricts the venturi throat to increase pressure drop, compensating for the reduced pressure drop difference caused by high metering rates. This dynamic adjustment maintains the pressure conditions necessary for precise metering across varying flow rates.
Solution Approach 2:
A control means senses the pressure drop across the pump and automatically adjusts the venturi throat constriction accordingly. This feedback mechanism detects when pressure drop differences become insufficient at high metering rates and responds by constricting the venturi throat to restore the necessary pressure differential, thereby maintaining metering precision.
2Productivity
If the pressure in the metering system is increased to handle higher flow rates, then the productivity is improved, but the pressure drop difference between upward and downward strokes decreases, worsening the metering precision
Solution Approach 1:
The venturi throat constriction is dynamically adjusted based on system pressure conditions. At higher pressures and flow rates, the control means increases the venturi throat constriction to maintain adequate pressure drop differences, compensating for the compressibility effects that reduce pressure differential at high pressures.
Solution Approach 2:
The physical parameter of venturi throat cross-section is changed in response to pressure variations. When system pressure increases and causes reduced pressure drop differences, the control means modifies the venturi throat parameter (constriction) to restore the necessary pressure differential for accurate metering.
3Adaptability or versatility
If a diversion line with a factor of 10 is used to achieve low additive concentrations (0.03% in total flow), then the metering range is extended, but the pressure drop differences become insufficient, reducing metering effectiveness
Solution Approach 1:
The venturi throat constriction is dynamically controlled to compensate for the reduced pressure drop differences inherent in high-diversion-ratio configurations. By adjusting the venturi throat passage cross-section, the system maintains adequate pressure differential even when the pump handles only a small fraction of the total flow, ensuring reliable metering across the extended range.
4Device complexity
If the venturi throat passage cross-section is kept constant, then the device complexity is minimized, but the pressure drop matching between pump and venturi deteriorates at varying flow rates, reducing energy efficiency
Solution Approach 1:
The venturi throat constriction is made variable through a control means that adjusts the passage cross-section to match pump pressure drop characteristics at different flow rates. This dynamic adjustment optimizes energy efficiency by ensuring that the venturi pressure drop closely matches the pump pressure drop across the operating range, minimizing energy losses.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution improves the metering device's effectiveness by minimizing pressure drop differences, maintaining precision and efficiency even at high additive metering rates (above 0.2% in the main liquid), broadening the operational range and ensuring reliable startup at low flow rates while maintaining precise metering.
Implementation Method 1
the venturi must be provided in order to create a pressure drop, between its inlet and the throat, which is essentially equal to the pressure drop in the pump
Implementation Method 2
a means sensitive to the pressure drop in the pump, which means is able to control the means for constricting the throat of the venturi
Data Source
AI summary
Metering device for introducing a liquid additive into a main liquid flowing along a pipe, includes a pump for withdrawing additive from a container and metering it, this pump including a first inlet for receiving a flow of main liquid which drives the pump, a second inlet for picking up additive and an outlet for the resulting mixture; a Venturi installed in the pipe, and connected in parallel with the pump, the first pump inlet connected by a first line to the Venturi inlet while the outlet connected by a second line to the Venturi throat; a first element for varying the restriction at the Venturi neck, and a second element sensitive to the pressure drop across the pump for controlling the first element to reduce the bore section when the pressure drop across the pump increases, and increase the bore section when the pressure drop across the pump decreases.