Hydraulics of KAU drip irrigation system

Abstract

Irrigation advancements within the last decade has been astounding. Drip irrigation is one of the latest innovations for applying water to the field and it represents a definite advancement in irrigation technology. An attempt was made to study the hydraulics of microtube emitters of 1-3 mm size, Black polyethylene tube of 1" was used as main line. In the main line, three laterals of 1/2 diameter were connected. Discharge measurements were taken at different pressure heads.The total energy drop (H) in a microtube emitter is the summation of friction loss (Hf) and minor loss (Hm). There was no empirical equation available for calculating the friction drop from a microtube of size less than 4 mm. With the help of a computer, analysis was made to establish the relationships between pressure head H, length L, diameter D and discharge Q. The empirical equations obtained are 1. Combind flow condition H = 0.01402 Q1.23938/D3.54926 L0.86030 2. Turbulent flow condition H = 0.00764 Q1.82655/D4.61537 L0.77823 3. Flow in transition region H = 0.00817 Q1.56882/D3.83531 L0.83541 4. Laminar flow condition H = 0.00796 Q1.23461/D3.59105 L0.98712 Where Q = discharge, 1/hr L = length of tube, cm D = diameter of tube, mm The minor losses, viz. exit, entry, losses due to fittings and sudden contration can be expressed as a function of velocity head. The minor loss was significant because of the smaller size and short length of the microtube. The numerical solution for minor loss coefficient K was obtained in order to make the power of L unity in the estimating equations for head loss due to friction. The equations obtained are 1. Combind flow Hm = 2.34 V2/2g 2. Turbulent flow Hm = 2.14 V2/2g 3. Flow in transition region Hm = 3.18 V2/2g 4. Laminar flow Hm = 0.84 V2/2g Where V = Velocity, m/s G = acceleration due to gravity, m/s2 The empirical equations for friction drop were developed for different flow condition by fitting multiple log linear regression equations. The equations obtained are 1. Combined flow Hf = 0.00737 Q1.18905/D3.58352 L 2. Turbulent flow Hf = 0.00359 Q1.74866/D4.80544 L 3. Flow in transition region Hf = 0.00397 Q1.46302/D3.74436 L 4. Laminar flow Hf = 0.00743 Q1.22546/D3.58420 Similar to Blasius and general equations, the following equations were developed for friction factor in turbulent and laminar regions. f = 0.248/Re0.25 and f = 67.2/Re where f = friction factor Re = Reynolds number The KAU drip system has an additional component ‘Distributor’. Experiments were conducted to study the effect of distributor on flow rate. It was observed that the discharge rate was higher from the system with distributor than that of microtube having the same length. The frictional losses and the combined loss of minor and distributor for different flow conditions were estimated. Few combinations which satisfy the requirements of discharge, length and pressure head were selected for the design purpose of KAU drip irrigation system. The effect of clogging on discharge rate was studies and it was found that clogging was higher in 1 mm tube than the 2 mm and 3 mm tubes. Experiments were conducted to estimate friction loss in laterals. Hazen – Williams equation was found suitable for turbulent region and not for laminar and transition region. By adopting drip system we can bring more area under cultivation by maximum utilisation of available water. By combining improved agronomic practices along with an efficient drip irrigation system, it is possible to bring about a substantial progress in the farm front.