Abstract:
Pressure-compensating emitter. The emitter includes an inlet connected to a source of pressurized water and an orifice in fluid communication with the inlet and extending into a channel including a raised land surrounding an outlet. A compliant membrane is positioned above the land in the chamber wherein pressurized water will cause the membrane to deform into contact with the land to alter flow through the outlet so as to provide a constant flow rate. Parameters of the emitter are selected so that the emitter has a large operating range and an activation pressure of 0.15 bar or below.

Description:
[0001]    This application claims priority to provisional application Ser. No. 62/258,067 filed on Nov. 20, 2015, the contents of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This invention relates to irrigation emitters and more particularly to an irrigation emitter providing pressure compensation so that flow rate remains substantially constant as input pressure varies. 
         [0003]    Drip irrigation systems are used to deliver water and/or nutrients directly to the root zone of a plant. In use, an online emitter is inserted into the water lateral lines. The emitter thus acts as a point source for water. Because water is delivered in a controlled way, it is possible to irrigate with substantially less water as compared to conventional water delivery systems including sprinklers and flooding methods. Drip irrigation systems also experience less water percolation, surface run off or evaporation, all saving water. Other advantages are fewer weeds as water is applied only to regions where it is required. Less fertilizer is used as a result of the targeted watering and higher yields result from the better soil moisture levels. 
         [0004]    As water in drip irrigation systems travels through a pipe network including a sub main and lateral pipes from a water source out to a field, there is a continuous pressure loss due to frictional forces that develop between the pipe and flowing water. Other factors such as elevation can also result in water pressure variation. If non-pressure compensating emitters are used, the emitters subject to higher pressures will emit more water, leading to an uneven water distribution in the field. Plants closer to the water and pumping source get more water than the ones farther away. It is desirable that all emitters have uniform water flow rates along the lateral lines. 
         [0005]    Pressure-compensating emitters have been developed that emit constant flow rate of water despite a fluctuation in input water pressure. Such pressure-compensating emitters thus enable longer lateral pipes to be used so that a larger area can be irrigated with the drip irrigation system. 
         [0006]    Existing pressure-compensating emitters have a relatively high activation pressure and a limited operating range. Activation pressure is defined as the pressure above which an emitter begins pressure compensation. Because pumping power in an irrigation system is a function of the water pressure and its flow rate, a high activation pressure means higher power requirements leading to higher incurred costs in power systems, pumps and the need for thicker pipes. 
         [0007]    Many of the currently manufactured pressure-compensating emitters are derivatives of a dripper patented in 1949 as U.S. Pat. No. 2,460,647. The Jain Irrigation Company is a major current-day pressure-compensating emitter manufacturer. Typical Jain Irrigation emitters have an activation pressure of 1.0 bar and an operating range of 3 bars in an 8 liter/hour dripper. 
         [0008]    An object of the present invention is a pressure-compensating emitter that has a low activation pressure of around 0.15 bar and large operating range beyond 4 bars to ensure uniform water distribution on a large field. Another object of the invention is an iterative design procedure for designing pressure-compensating emitters with low activation pressure and larger operating range. 
       SUMMARY OF THE INVENTION 
       [0009]    The pressure-compensating emitter according to the invention includes an inlet connected to a source of pressurized water and an orifice in fluid communication with the inlet and extending into a channel including a raised land surrounding an outlet. A compliant membrane is positioned above the land in the chamber wherein the pressurized water will cause the membrane to deform into contact with the land to alter flow through the outlet. The dimensions of the orifice, land diameter, channel dimensions and outlet diameter along with membrane characteristics are selected to provide substantially constant flow for varying water pressure with an activation pressure of 0.15 bar or below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0010]      FIG. 1 a    is a perspective view of a typical prior art pressure-compensating emitter. 
           [0011]      FIG. 1 b    is a cross-sectional view of the emitter of  FIG. 1   a.    
           [0012]      FIG. 2  is a cross-sectional view of an emitter as modeled for emitter analysis. 
           [0013]      FIG. 3  is a plan view of a prior art Jain Irrigation emitter. 
           [0014]      FIG. 4  is a cross-sectional view of section AA of  FIG. 3 . 
           [0015]      FIG. 5  is a cross sectional view along section BB of  FIG. 3 . 
           [0016]      FIG. 6  is a plan view of an embodiment of an emitter disclosed herein for a flow rate of 8.2 lph. 
           [0017]      FIG. 7  is a cross-sectional view along section AA of  FIG. 6 . 
           [0018]      FIG. 8  is a cross-sectional view along section BB of  FIG. 6 . 
           [0019]      FIG. 9  is a representative graph of flow rate against pressure. 
           [0020]      FIG. 10  is a flow diagram showing the iteration process for designing the low activation pressure, large operating range pressure-compensating emitter of the invention. 
           [0021]      FIG. 11 a    is a cross-sectional view of an emitter of an embodiment of the invention showing bending of the flexible membrane under initial loading. 
           [0022]      FIG. 11 b    is a cross-sectional view of an embodiment of the invention illustrating the membrane shearing into the channel. 
           [0023]      FIG. 11 c    is a graph of flow rate versus inlet pressure. 
           [0024]      FIG. 11 d    is a graph of loss coefficient versus inlet pressure. 
           [0025]      FIG. 12  is a graph of flow rate versus pressure for emitters having nominal 8.2 lph, 4.2 lph and 3.2 lph. 
           [0026]      FIG. 13  is a plan view of an embodiment of an emitter disclosed herein for a nominal flow rate of 4.2 lph. 
           [0027]      FIG. 14  is a cross-sectional view along section AA of  FIG. 13 . 
           [0028]      FIG. 15  is a cross-sectional view along section BB of  FIG. 13 . 
           [0029]      FIG. 16  is a plan view of an embodiment of an emitter having a nominal flow rate of 3.2 lph. 
           [0030]      FIG. 17  is a cross-sectional view along section AA of  FIG. 16 . 
           [0031]      FIG. 18  is a cross-sectional view along section BB of  FIG. 16 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0032]    The pressure-compensating emitters of the invention utilize the same principles exhibited by other current pressure-compensating emitters. A compliant diaphragm sits on top of a pressure chamber and the flow path deforms under pressure and changes the cross section and length of the flow path resulting in approximate linear increases in resistances for increases in pressure resulting in a constant flow rate over a fluctuation and/or variation in pressure. 
         [0033]    With reference first to  FIGS. 1 a  and 1 b   , a typical emitter  10  includes an orifice  12 , land  14 , a channel  16 , an outlet  18  and a chamber  20 . As will be seen, the dimensions of these features affect activation pressure. The emitter  10  typically consists of tubular structures made from hard plastic usually injection molded. The compliant membrane within it deforms and leads to pressure-compensating behavior.  FIGS. 1 a  and 1 b    illustrate the parameters that influence the emitter  10  performance. The parameters of interest with respect to the membrane are its material properties, thickness and diameter. Parameters of interest with regard to the rigid emitter body are the orifice dimensions, the land diameter, channel dimensions, maximum height of deflection of the unstressed membrane, and outlet diameter. 
         [0034]      FIG. 2  depicts the cross section of the emitter as it was modeled. Fluid flows into the emitter  10  at an inlet pressure, P 1 . The fluid then flows into the chamber  20  under the membrane through an orifice  12  which leads to a pressure loss of ½ PV2κ. The fluid in the chamber at pressure P 2  flows out of the emitter to the outside through the outlet hole  18 . 
         [0035]    To achieve the objective of low activation pressure and large operating range, the emitter of the invention is designed with an analysis of the fluid-structure interaction within a commonly used 8 l/hr. dripper and optimizes the parameters using a genetic algorithm. The fluid-structure interaction is modeled in “A Mathematical Model for Pressure Compensating Emitters,” proceedings of the 2015 IDETC ASME 2015 International Design Engineering Technical Conference, Aug. 2, 2015, Boston, Mass. The contents of this reference by two of the inventors herein is incorporated herein by reference in its entirety. This paper presents a mathematical model investigating the physics behind pressure-compensating drip irrigation emitters and explains the relationship between pressure, structural deformation and fluid flow within a pressure-compensating emitter. The paper presents a parametric study to understand the effects of geometric and material properties with regard to activation pressure and pressure-compensating behavior. 
         [0036]      FIGS. 3, 4 and 5  are directed to existing pressure-compensating emitters from the Jain Irrigation Company. The relevant dimensions are noted on the figures. 
         [0037]      FIGS. 6, 7 and 8  show details of the pressure-compensating emitter disclosed herein that achieves the low activation pressure of 0.15 bar or below and with an operating range beyond 4 bar. The circled dimensions on  FIGS. 6, 7 and 8  highlight differences with respect to the Jain irrigation emitter shown in  FIGS. 3, 4 and 5 . Note in particular the orifice  12  in an embodiment of the present invention has a diameter of 1.25 mm as compared to a 1.07 mm diameter in the prior art. The outlet  18  according to an embodiment of the present invention has a diameter of approximately 1.28 millimeters as compared with a diameter of 1.89 millimeters in the prior art device. Also note that the membrane sits above the land by an amount of 0.7 mm in the emitter of the invention as compared to a dimension of 0.5 mm in the prior art device. The dimensions in  FIGS. 6, 7 and 8  are entirely exemplary. As will be discussed further hereinbelow, a methodology is disclosed for performing a parameter study for other designs that meet the required specifications. 
         [0038]    To achieve the objective of low activation pressure and larger operating range, the publication above incorporated by reference analyzes the fluid-structure interaction within a commonly used 8 l/hr. dripper and optimizes the parameter using a genetic algorithm. The analysis has been performed in MATLAB. It is important to note that the most relevant performance metric for an emitter is a flow rate versus pressure graph such as the representative graph shown in  FIG. 9  and illustrating the pressure-compensating region. 
         [0039]    The steps undertaken in the analyses are summarized below. Details may be found in the incorporated paper. To obtain a flow versus pressure graph the analysis determines the flow rate at each pressure point. The steps in the algorithm are shown in the flow chart of  FIG. 10 . 
         [0040]    The first step in the procedure is to define the geometry of an emitter including the geometry of the solid portion and the compliant membrane. Next, in step  2 , an estimate is made of the pressure loading for a specific inlet pressure. This loading is then used in a step  3  to calculate the compliant diaphragm deflection while interacting with the solid, non-compliant section of the emitter. As discussed in the incorporated paper, the deflection is split into two sections, namely, bending deflection up to the channel and shearing deflection into the channel. The bending deflection is calculated using small deflection formulae and linear superpositioning followed by conversion into a larger deflection using Timoshenko correction factors. Once the membrane or diaphragm touches the land, a circular line force is induced preventing the diaphragm from deflecting any further. Any further deformation will occur in the channel  16  when the diaphragm shears into it. 
         [0041]    The next step, step  4 , is to calculate the fluid flow characteristics and, in particular, flow rates. Based on pressure loading and deflection of the diaphragm, a flow path is formed. Using the D′Arcy Weishbach equation coupled with Colebrook equations and mass continuity, loss coefficients and flow rates can be calculated. The next step, step  5 , is to recalculate the pressure loading based on the flow rates calculated previously. Steps  3 - 5  are iterated until the flow rates calculated match the flow rates from the previous iteration to within 1%. Steps  2 - 5  are repeated for different inlet pressures in order to obtain a flow rate versus pressure graph for a pressure range of 0-4 bar. 
         [0042]    After performing the genetic algorithm, experimental pieces were manufactured typically using rapid prototyping production techniques such as 3D printing and CNC milling. Hydraulic performance tests on experimental pieces were performed to obtain their flow rate against pressure graph for different geometries. The analytical model may be validated by comparing and analyzing the results obtained in the above steps. Correction factors can be added if needed. Optimization is performed on the current geometry to obtain other geometries that would meet the design requirements of being pressure-compensating with a low activation pressure and large range. 
         [0043]    As stated earlier, the design process has been used to design an 8.2 l/hr emitter having an activation pressure of 0.15 bar and an operating range beyond 4 bar. This is in contrast to the Jain irrigation dripper at 8 l/hr. with an activation pressure of 1.0 bar and an operating range of 3 bar. 
         [0044]    The pressure-compensating emitter of this embodiment of the invention has a flow rate of approximately 8.2 l/hr, large operating range of 0-4 bar and low activation pressure of 0.15 bar. Hydraulic performance tests have shown the emitter of the invention to have a low flow exponent, consistency, high uniformity and good anti-clogging performance. The major improvements of the emitter of the invention are an increased range of operating pressure and, most importantly, lower activation pressure. 
         [0045]    With reference now to  FIGS. 11 a - d   , one can see that there are two main flow regimes affecting pressure, namely, flow through the orifice  12  and then through the channel  16 .  FIG. 11 a    shows bending of the flexible membrane under initial loading. The primary flow restriction is caused by k orifice  illustrated by a resistor symbol. Loss coefficient versus inlet pressure is plotted  225  in the first portion of  FIG. 11   d.    
         [0046]    As shown in  FIG. 11 b   , the flexible membrane shears into the channel  16 . In this regime, flow restriction is caused by the sum of k orifice  and the variable resistance of k channel  that increases with rising inlet pressure as shown in  FIG. 11 d   .  FIG. 11 c    shows flow rate versus inlet pressure for pressure compensating behavior. 
         [0047]    For the two regimes, pressure loss in the orifice affects activation pressure (i.e., if k orifice  is low, activation pressure will be lower) and pressure loss in the channel affects pressure compensating behavior. 
         [0048]      FIG. 12  is another graph of flow rate versus pressure for emitters having nominal flow rates of 8.2, 4.2, and 3.2 liters per hour (lph). Note that the activation pressure is 0.15 bar for the nominal 8.2 lph emitter and an activation pressure of 0.25 bar for the nominal 4.2 and 3.2 lph emitters. 
         [0049]      FIGS. 13, 14 and 15  illustrate an embodiment of the emitter disclosed herein for delivering a nominal 4.2 liters per hour flow rate with an activation pressure of 0.25 bar. The relevant parameter dimensions are shown in the circles in  FIGS. 13, 14 and 15 .  FIGS. 16, 17 and 18  are corresponding figures for an embodiment with a nominal flow rate of 3.2 liters per hour. Again, the relevant parameters are listed in the circles. 
         [0050]    It is recognized that modifications and variations of the invention will be apparent to those of ordinary skill in the art and it is intended that all such modifications and variations be included within the scope of the appended claims.