Emitter Coefficient Research Articles

Investigation of Interlayer Thermal Coupling of Multilayer Insulation in Spacecraft Equipment

In general, for installing multilayer insulation (MLI) blankets on curved spacecraft equipment, creating a pattern that has multiple sectors is necessary because of the impossibility of establishing a single piece of MLI. The sector area of the MLI contains numerous seams and sewing. Therefore, prediction of overall performance or effective emittance is not simply possible, and they need to be tested in some experimental ways. The aim of the current research is to present a methodology for determining the conductivity between layers in both nonsewing and sewing regions of MLI to correctly estimate the effective emittance coefficient and the thermal behavior of MLI. Firstly, by conducting two experimental tests, both sewn and nonsewn square MLIs’ effective emittance coefficients are computed. In the second step, the conductive thermal coupling coefficients of nonsewing and sewing regions are determined as 1.615 and 1.95 W/(m2⋅K) respectively, utilizing experimental data. In the third step, a spherical geometry fuel tank is selected as a case study, and these coefficients are utilized in the simulation process of an MLI tank. Finally, the overall effective emittance coefficient of that tank is determined. The results indicate that the effective emittance is reduced by about 8%.

Localization estimation of two leaks in pipelines through Monte Carlo simulations and hydraulic-spatial constraints

The problem of localizing two leaks using only flow rate and pressure measurements at the boundaries of a pipeline, and under steady-state flow conditions, is ill-posed due to the undetermined nature of the inverse problem, which involves two coupled equations with four unknowns associated with the presence of the leaks: two emitter coefficients and two locations. Therefore, attempting to solve this problem using any method without imposing additional constraints leads to an unbounded solution space, which contains solutions that may be physically meaningless. In this article, we propose a four-algorithm method that incorporates both spatial and hydraulic constraints to filter out physically infeasible solutions. The proposed method is based on Monte Carlo simulations, which use input data from hydraulic instruments installed at the boundaries of the pipeline, as well as random values with predefined probabilities that are bounded by the hydraulic-spatial constraints. The outputs of the method are probability distributions for the four unknowns. To demonstrate the feasibility of the method, results obtained through simulations and experimental testing on a test bed are presented.

Application of Optimization Algorithms for Leakage Identification for Data Sparse Old Town

Numerous cities developed in the 20th century have a Water Distribution Network(WDN) with decade-old pipes. Aging pipelines can leak with lower the water revenue ratio, thus resulting in waste and economic losses. In this study, new methods for localizing leakage in WDNs are proposed and tested. Two meta-heuristic methods based on Harmony Search(HS) and Genetic Algorithm(GA) are developed to detect leakage of WDNs through an evaluation of emitter coefficients. The old town of G-Town in South Korea has a 50-year-old WDN and a low water revenue ratio. High quality field measurements in G-Town allowed detailed testing of optimization methods based on emitter coefficients for leakage detection. As a result, both GA and HS yielded comparable outputs. The HS method performed with slightly better accuracy in minimizing the objective function than GA after about 1,000 iterations. Leakage detection becomes fairly accurate after approximately 30 minutes of optimization and pipe networks with more than 100 pipes and 50 nodes require more iterations and calculation time.

Analysis of Intermittent Water Distribution Networks Using a Dummy Emitter Device at Each Demand Node

The pipe component of a water distribution network (WDN) is sized based on the fixed design demand considering a peak factor and design period. Simulation of the designed network by a hydraulic solver provides nodal pressure head, head loss, velocity, and flow in each pipe as the prime outputs for the design demand, and it can also be used for extended-period simulation for a particular demand pattern over the supply hours. But, in reality, the behavior of the network does not match with such a result in an intermittent water supply (IWS) system due to the fact that all house service connections behave as an uncontrolled orifice. This has made it a challenging task in understanding and in predicting the behavior of the networks by the municipal engineer once the water starts flowing through the house service connections (HSCs). Though the municipal engineer provides the same pipe size for HSCs to all residences, the flow received by each house could vary based on the available pressure head at the ferrule point of the main water supply pipeline. In reality, maintaining constant pressure at each HSC is not feasible due to frictional head loss. Hence, variation in flow at the HSC is inevitable even with a small water supply system. This paper illustrates how to simulate the behavior of an IWS system based on the number of HSCs provided to each pipeline using a hydraulic solver. Hydraulic simulation of the water distribution network that provides IWS to consumers can be implemented easily by adding a fictitious node by assigning an appropriate emitter coefficient to each demand node through a fictitious link having a check valve in it. The method for finding the appropriate value of the emitter coefficient that helps in simulating HSCs is illustrated in the present work.

Practical Aspects of the Energy Efficiency Evaluation of a Water Distribution Network Using Hydrodynamic Modeling—A Case Study

Water and energy are the main natural resources, and their rational use is the basis for sustainable development. Therefore, the energy efficiency of water supply networks is one of the priorities for the management system of water utilities. Many methods and indicators can be used to assess the energy efficiency of water distribution networks (WDNs), and their choice should be adapted to the characteristics of a WDN. This paper presents an energy audit of WDNs that are supplied from five reservoirs located above the supply area, to which water is supplied from four underground and surface water intakes. In the analysis of the system operation, a hydrodynamic computer model of the water distribution network was used to estimate the operating parameters that are necessary to determine the energy efficiency indicators. A new method for calibrating the emitter coefficient used for water loss modeling is also proposed. The conducted audit showed that more than 70% of the energy supplied to the WDS was “lost”, mainly due to friction (37%) and water losses (27%). Thanks to hydraulic modeling, it was possible to indicate that 34% of the energy lost in the system was related to the use of pressure-reducing valves (PRV), and that only 3% was directly related to friction. In turn, the majority of leaks are attributed to service connections (17.4% vs. 8.8% in the water distribution network).

Effect of variation of empirical exponent coefficient values in water distribution network analysis

The water distribution network supplies water to consumer to fulfill demands at desired pressure. Due to pressure deficient conditions pressure fall below minimum required which ultimately lead to reduction in flow supplied to consumer. The water distribution network is said to be pressure deficient, if the pressure head in each node is less than the required head. Adding artificial element approach for predicting partial flow at demand node in pressure deficient condition is used by many researchers. The objective of study is to investigate effect of variation in empirical exponent coefficient on emitter exponent, pressure and actual demand at demand node. The steady state simulation is carried out for case study network with pressure deficient node as emitter node using Fictitious component free – Pressure Deficient Network Algorithm. The emitter coefficient formula, derived from Wagner’s equation is used for predicting actual demand under pressure deficient condition. The value of emitter coefficient depends on emitter exponent coefficient value, which is calculated using empirical exponent coefficient. The study is carried out for three different values of empirical exponent coefficient 0.5, 1, 1.5, 1.852, 2 and 2.5 respectively. The simulation analysis shows that as empirical exponent increases emitter exponent decreases, pressure decreases and actual demand at nodes increases. This study can be useful in calculating resilience index, which is measure of average efficiency of water distribution network under pressure deficient condition.

Leakage detection in water distribution networks using space search reduction and local fitness in steady-state and EPS (case study: water distribution network of Birjand)

AbstractUsing hydraulic model calibration of a water distribution network is one of the methods that can reduce leak detection costs by identifying areas with high leakage. In the present paper, a new factor called local fitness is used in combination with the search space reduction method to obtain an optimal answer. In this method, a fitness function is calculated for each zone. For each zone, proximity of the pressure and flow rates obtained from the model to the corresponding observational data indicates that the values selected for the nodes of that zone are close to the correct values. In the next steps, using a search space reduction method and performing the optimization process with the local fitness function, the chance of selecting those values is increased. In this study, leakage was assigned to nodes with emitter coefficient. This method was used on the water distribution network of Birjand. Three factors of background leakage, leakage hotspot and apparent losses were considered as unknown parameters. Results of the present method were compared with the results of a genetic algorithm (GA) and the corresponding exact values. Based the results, the present method showed better results in terms of convergence speed and accuracy.

A Proof-of-Concept Study for Hydraulic Model-Based Leakage Detection in Water Pipelines Using Pressure Monitoring Data

It is estimated that about 20% of treated drinking water is lost through distribution pipeline leakages in the United States. Pipeline leakage detection is a top priority for water utilities across the globe as leaks increase operational energy consumption and could also develop into potentially catastrophic water main breaks, if left unaddressed. Leakage detection is a laborious task often limited by the financial and human resources that utilities can afford. Many conventional leak detection techniques also only offer a snapshot indication of leakage presence. Furthermore, the reliability of many leakage detection techniques on plastic pipelines that are increasingly preferred for drinking water applications is questionable. As part of a smart water utility framework, this paper proposes and validates a hydraulic model-based technique for detecting and assessing the severity of leakages in buried water pipelines through monitoring of pressure from across the water distribution system (WDS). The envisioned smart water utility framework entails the capabilities to collect water consumption data from a limited number of WDS nodes and pressure data from a limited number of pressure monitoring stations placed across the WDS. A popular benchmark WDS is initially modified by inducing leakages through addition of orifice nodes. The leakage severity is controlled using emitter coefficients of the orifice nodes. WDS pressure data for various sets of demands is subsequently gathered from locations where pressure monitoring stations are to be placed in that modified distribution network. An evolutionary optimization algorithm is subsequently used to predict the emitter coefficients so as to determine the leakage severities based on the hydraulic dependency of the monitored pressure data on various sets of nodal demands. Artificial neural networks (ANNs) are employed to mimic the popular hydraulic solver EPANET 2.2 for high computational efficiency. The goals of this study are to: (1) validate the proof of concept of the proposed modeling approach for detecting and assessing the severity of leakages and (2) evaluate the sensitivity of the prediction accuracy to number of pressure monitoring stations and number of demand nodes at which consumption data is gathered and used. This study offers new value to prioritize pipes for rehabilitation by predicting leakages through a hydraulic model-based approach.

Data-Driven Leak Localization in Urban Water Distribution Networks Using Big Data for Random Forest Classifier

In the present paper, a Random Forest classifier is used to detect leak locations on two different sized water distribution networks with sparse sensor placement. A great number of leak scenarios were simulated with Monte Carlo determined leak parameters (leak location and emitter coefficient). In order to account for demand variations that occur on a daily basis and to obtain a larger dataset, scenarios were simulated with random base demand increments or reductions for each network node. Classifier accuracy was assessed for different sensor layouts and numbers of sensors. Multiple prediction models were constructed for differently sized leakage and demand range variations in order to investigate model accuracy under various conditions. Results indicate that the prediction model provides the greatest accuracy for the largest leaks, with the smallest variation in base demand (62% accuracy for greater- and 82% for smaller-sized networks, for the largest considered leak size and a base demand variation of ±2.5%). However, even for small leaks and the greatest base demand variations, the prediction model provided considerable accuracy, especially when localizing the sources of leaks when the true leak node and neighbor nodes were considered (for a smaller-sized network and a base demand of variation ±20% the model accuracy increased from 44% to 89% when top five nodes with greatest probability were considered, and for a greater-sized network with a base demand variation of ±10% the accuracy increased from 36% to 77%).

A Study on the Delineation of Flushing Sections and Simulation Method to Verify Appropriate Flushing Velocity for Applying Flushing

Recently, water supply networks have experienced deterioration because of various factors, which result in the accumulation of a large amount of scale on the inside surface of pipes. The scale may enter houses when a surge occurs owing to abrupt velocity or flow direction change in pipes, and eventually, water quality accident such as red-water can occur. The scale should be removed by applying pipe-cleaning practices, such as flushing, to prevent this type of accident. Currently, most studies have suggested only the desirable flow velocity to remove the scale through flushing. In our opinion, it will be more critical to develop a method for determining whether it would be possible to achieve the desired flow velocity. Hence, we developed a method to delineate a flushing section and modify a water supply network in considering the minor loss on the hydrant using the head loss-flow rate curve for the hydrant. Next, we simulated a flow condition using the emitter coefficient to achieve the desired flow velocity for flushing each section. The proposed method was applied to a part of the water supply network of a city in Korea. From the results, the pressure head at the primary water source point of the network was sufficient such that each flushing section experienced the desired flow velocity to complete the flushing process. We lowered the pressure head by 20 m at the primary water source point and simulated a flow condition for insufficient pressure head. Under these conditions, some of the flushing sections could not experience the desired flow velocity, and hence, the scale could not be removed as desired. In this case, we believe that the utility authority should decide whether flushing is still a suitable option for cleaning the pipe, or whether other cleaning methods should be considered.

Improvement of solar flat‐plate collector performance by optimum tilt angle and minimizing top heat loss coefficient using particle swarm optimization

AbstractIn this paper, the efficient amounts of radiation received by a flat‐plate collector and top heat loss coefficient along with affecting parameters are investigated using measured data in different climates of Iran. Coded program in MATLAB software is then distributed to calculate the optimum tilt angle for extracting the highest solar radiation in different months of the year for five cities of Iran with different geographic latitudes. An optimal annual slope is obtained for maximum utilization and for conditions where the collector can only be adjusted at an angle during the year. Using an interpolation, an equation has been derived for obtaining the optimal tilt angle of collector for areas with latitude between 27° and 37°. Inasmuch as the top heat loss coefficient is required for evaluating the thermal performance of solar collectors, the value for different temperatures is obtained at ambient temperature up to 200°C for the absorber plate. Effects of key parameters such as collector slope, number of covers, wind speed, emittance coefficient of adsorption plate, and cover spacing on top heat loss coefficient are investigated. In the end, the particle swarm optimization (PSO) method is employed to minimize the top heat loss coefficient. The minimum amount of top heat loss coefficient is obtained with the amount of 0.99 W/m2K.

Analysis of water distribution network under pressure-deficient conditions through emitter setting

Abstract. Pressure-driven analysis (PDA) of water distribution networks necessitates an assessment of the supplying capacity of a network within the minimum and required pressure ranges. Pressure-deficient conditions happen due to the uncertainty of nodal demands, failure of electromechanical components, diversion of water, aging of pipes, permanent increase in the demand at certain supply nodes, fire demand, etc. As the demand-driven analysis (DDA) solves the governing equations without any bound on pressure head, it fails to replicate the real scenario, particularly when the network experiences pressure-deficient situations. Numerous researchers formulated different head–discharge relations and used them iteratively with demand-driven software, while some other approaches solve them by incorporating this relation within the analysis algorithms. Several attempts have been made by adding fictitious network elements like reservoirs, check valves (CVs), flow control valves (FCVs), emitters, dummy nodes and pipes of negligible length (i.e., negligible pressure loss) to assess the supplying capability of a network under pressure-deficient conditions using demand-driven simulation software. This paper illustrates a simple way of assessing the supplying capacity of demand nodes (DNs) under pressure-deficient conditions by assigning the respective emitter coefficient only for those nodes facing a pressure-deficit condition. The proposed method is tested with three benchmark networks, and it is able to simulate the network without addition of any fictitious network elements or changing the source code of the software like EPANET. Though the proposed approach is an iterative one, the computational burden of adding artificial elements in the other methods is avoided and is hence useful for analyzing large networks.

Experimental analysis of pressure-discharge relationship in a private water supply tank

AbstractIn Mediterranean countries, users are often equipped with private tanks, which provide a temporary water storage capacity, able to compensate service interruptions due to either scarcity or irregularity of water supply. In the presence of private water storage, water supply is no longer linked to users' consumption and network-operating conditions can be off-design, therefore specific models have to be introduced in simulation models of water distribution networks. Here, a new mathematical model is proposed that is able to reproduce a tank's emptying/filling cycles. Specifically, by means of experimental analysis, a hyperbolic tangent law was tested to reproduce the filling process for private tanks. The flow rate is calculated by means of the classical Torricelli law, in which the float valve emitter coefficient and the valve area are calculated using a function that takes into account the water level within the private tank. The comparison obtained through the mathematical model and those observed from experiments confirmed the ability of the model to predict the flow rate balance within private tanks. The results show that the model is suitable for any length of float valve branch. The mathematical system can be easily used in a transient model to correctly estimate the supplied demand.

Pressure-Discharge Law of Local Tanks Connected to a Water Distribution Network: Experimental and Mathematical Results

In many Mediterranean countries, users store water resources in private tanks, which are typically located on rooftops. These local reservoirs are generally connected directly to the water distribution network (WDN). This installation scheme causes a disconnection of the WDN from the users, and thus, the users’ water supply is no longer linked to their consumption, which changes the network operating conditions from the designed conditions. For WDNs characterized by the presence of several private tanks, specific models have to be developed to correctly simulate the operation of the WDN while accounting for reservoirs located between the hydraulic network and users. Some mathematical models that are able to reproduce the tank emptying/filling cycles have already been developed, which combine a tank continuity equation with a float valve emitter law. In the present work, a new emitter law is proposed that improves the predictability of actual models. The new formulation takes into account the variation of the emitter coefficient and of the discharge area during the phases of the filling process of private tanks. Specifically, hyperbolic tangent laws were adopted. A comparison between the proposed mathematical model and the experimental data demonstrated the ability of the new law to estimate the flow discharging into private tanks independently of the float valve branch and of the pressure in the network. The developed model can easily be implemented in hydrodynamic models to take private tanks into account.

Effects of antireflection layers on the optical and thermal stability properties of a spectrally selective CrAlN–CrAlON based tandem absorber

Spectrally selective CrAlN–CrAlON based tandem absorber was deposited by magnetron sputtering and the effects of antireflection layers on the optical and thermal stability properties of tandem absorber were investigated. The thickness of the individual component layers was optimized by matrix method to achieve high solar absorptance and low thermal emittance. TEM, XRD and XPS results confirmed the microstructure of the nanocomposite CrAlN and CrAlON coatings was consisted of nanocrystalline CrN embedded in amorphous matrix of AlN or Al2O3. The optimized CrAlN/CrAlON/Al2O3 tandem absorber exhibited a high absorptance of 0.984 and a low emittance of 0.07 at 82°C. The high absorptance value of this CrAlN–CrAlON based tandem can be partially attributed to the nanocomposite structure of the CrAlN and CrAlON coatings. Accelerated aging tests indicated that the CrAlN/CrAlON/Al2O3 tandem absorbers had high thermal stability in air up to 550°C for 100h with high solar selectivity of 11.5. However, for CrAlN/CrAlON/Si3N4 tandem absorber, the emittance coefficient increased drastically above 500°C which can be attributed to the increased surface roughness and oxidation of Si3N4 antireflection layer. The CrAlN/CrAlON/Al2O3 tandem absorber with high thermal stability has great potential for application in high temperature solar selective field.

Model Calibration and Leakage Assessment Applied to a Real Water Distribution Network

The use of water distribution network models depends highly on the confidence that the operators have on them. Models generated automatically from the Geographical Information System using the hydraulic equations integrated in a simulation model [7] are available in most of the water utilities. Once the first simulation results are compared with the available measurements, calibration is required [6]. This paper presents the process of adjusting the original network model of a village called Sant Joan de Vilatorrada network to fit the simulation results with the measurements. The adjustments in the model range from the macroalibration level to the microcalibration level [3]. The macrocalibration process is based on the analysis done by the engineers, and the conclusions are formalised for future use in other networks. Microcalibration is centred in setting the emitter coefficients using Genetic Algorithm optimisation. The results of the work include an adjusted model for decision taking, an assessment of the background leakage and a methodology to be applied in other parts of the network.

Uncertainty Assessment of Measurement in Variation Coefficient of Drip Irrigation Emitters Flow Rate

A comparison analysis on the uncertainty of the emitter coefficient of flow rate variation method for two emitter test devices is presented. The effect and adaptability of two Type A uncertainty methods, traditional and maximum entropy, are discussed for the manual and automatic emitter test devices. Several conclusions from the analysis and test date are: the automatic device has a higher accuracy than manual device and it is suggested that the automatic device be used; Type B standard uncertainty, which is not based on a series of test data, has less proportion in combined standard uncertainty than Type A standard uncertainty; the expanded uncertainty of the maximum entropy method in manual and automatic devices are 13% and 16% higher than that of conventional method in manual and automatic devices, respectively; the distribution density functions and the skewness coefficient of maximum entropy method are more accurate fitting than the conventional method, and the minimum number of tests for the maximum entropy method is two times the required number for the conventional method.

Hydraulic design procedure for drip irrigation submain unit based on relative flow difference

The combined effects of hydraulic variation and manufacturing variation on the relative flow difference in drip emitters were analyzed for a drip irrigation submain unit. Emitter manufacturing variation is a random variable and follows a normal distribution, which can be expressed by emitter coefficient of manufacturing variation (v) and a random variable (u) following a standardized normal distribution. Emitter flow rate equation can be expressed by two parts: (1) emitter discharge coefficient (k) and discharge exponent (x) determine the flow rate (khx) from an emitter at pressure head (h) and (2) the unknown random term (uvkhx), taking into account emitter manufacturing variation. Next, the formula for relative flow difference in a drip irrigation submain unit is derived based on (1) hydraulic variations due to head loss and elevation differences and (2) emitter manufacturing variation. A new hydraulic design procedure for drip irrigation submain unit is proposed based on the formula.

Semi-Pressure Driven Analysis와 Harmony Search를 이용한 상수관망 최적 누수탐지 기법 제안

상수도 시스템의 유지관리에 있어 유수율 제고는 필수적이며, 이를 위해서는 능동적인 누수관리가 요구된다. 본 연구에서는 수리해석 시뮬레이션과 최적화 기법을 결합한 최적누수탐지 기법을 새롭게 제안하였다. 상수관망 수리해석 기법으로는 불확실성이 큰 수두와 유출량 관계식 (Head Outflow Relationship, HOR)을 사용하지 않고도 실제적인 누수모의가 가능한 Semi-Pressure Driven Analysis (Semi-PDA) 모형을 적용하였다. 상수도 관망해석 프로그램인 EPANET2의 에미터 (Emitter) 기능을 활용하여 Semi-PDA 모형을 구축하였으며, 에미터 계수의 최적화를 통해 누수위치를 결정하였다. 최적화 기법으로는 국내에서 개발되어 다양한 분야에 적용된 바 있는 화음탐색법을 사용하였다. 제안된 기법을 예제관망에 적용하여 분석한 결과, 누수위치를 효율적으로 탐색하는 것으로 나타났다. 특히 최적화 기법에 있어 화음탐색법과 유전자알고리즘의 결과를 비교하였을 경우 본 연구에서 적용된 화음탐색법이 보다 정확한 결과를 도출하였으며, 실측자료 감소에 따른 누수지점 탐지의 불확실성 증가량이 유전자알고리즘에 비해 적게 나타나는 것을 확인하였다. 따라서 제안된 기법은 기존의 현장 대응의 경험적 누수탐지 기법을 대체할 수 있을 것으로 판단되며, 특히 스마트워터그리드 (Smart Water Grid)와 같은 미래의 능동적 물 관리 환경을 위한 제반기술의 하나로 활용이 가능하다. During maintenance and managing of water distribution systems, reducing water losses is a critical component. To achieve reduction of water losses, active leakage management is required. In this study, we propose optimal leakage detection model, which is the combination of simulation of hydraulic analysis and optimization technique. Through the use of hydraulic analysis method can able to achieve in creating a real-life based Semi-Pressure Driven Analysis (Semi-PDA) model without having to use the highly uncertain Head Outflow Relationship (HOR) is applied. EPANET2 created a model of emitter coefficient's optimization, and it decides leakage location. For optimization technique, Harmony Search (HS) is applied that was developed in Korea and has been used in various cases recently. When we apply proposed method to sample network, it practically searches the leakage location. Especially, in optimization technique, we have a research of comparing the results of Harmony-Search (HS) and Genetic-Algorithm (GA); HS' result is more accurate. Also we verify that increasing of leakage location detection uncertainty by decreasing of number of observed data is less than GA. Therefore, suggested technique can be substituted to existing experiential leakage detection method. Therefore, this basic technology can be used as future proactive water resource management environment like Smart Water Grid.

Application of design theory for restoring the black beach degraded rangeland at the headwater areas of the Qinghai-Tibetan Plateau

Emitter clogging is one of the most important factors that affect the performances on drip irrigation systems. Emitter clogging, which is formed in a short time due to irrigation systems’ running under an inadequate pressure or owing to water quality, not only negatively influences uniformity of water distribution but also causes inadequate irrigation. In this survey, the clogging level determination of the emitters used in drip irrigation systems of some agricultural farms situated in Canakkale and their effects on irrigation performances were observed. The emitters were obtained from different farms in the investigated area, and were tested under the pressures of 50, 100, 150, 200, 250, 300 kPa in hydraulic laboratories. The clogging extend of emitters, flushing of clogging increased pressure and also performance values as coefficient of variation (Cv) under 100 kPa pressure, statistical uniformity (Us), emission uniformity (Eu) and Christiansen’s uniformity coefficient (Cu) were established through the tests. Acquired performance values must be matched with emitter performances that have not been used in irrigation. As a result of the study it was determined that some emitters are plugged on laterals used for 2 or 3 years in consequence of the tests. It as also determined that emitter coefficient of variation varied in the ranges of 0.43 and 0.63, 0.43 and 0.69, 0.48 and 0.58, 0.56 and 0.73 for unused emitters, for one year, for two years and for three years used emitters. Coefficient of variation between emitter flows remained within the limit of 5% in all laterals, except for one of the laterals used for one year. Coefficient of variation of emitters along two of the laterals used two years and all of those used three years remained out of 5% limitation. Similar results to CVm (manufacturing variation coefficient) were determined for performance parameters in respect of statistical uniformity (Us), emission uniformity (Eu) and Christiansen’s uniformity coefficient (Cu). Key words: Drip irrigation, emitter clogging, drip irrigation performance.