Definition and formulas
The uniformity coefficient is a coefficient that allows you to express a quality judgment of the system on the basis of the quality of the distribution of the flow rates (and therefore indirectly of the pressures) in a system. There are several expressions that allow you to calculate its value. It is the most important data of a plant because it indicates whether the design quality is acceptable or not.
The uniformity of delivery depends on the distribution of the piezometric loads in the different sections of the network and therefore on the pressure drops that are determined in them, the morphology of the soil, the quality and type of the drippers and consequently the flow-pressure relationship, the number of drippers per plant, the temperature of the circulating water and any obstruction phenomena that occur during operation.
Christiansen coefficient
The UCC uniformity coefficient for drip systems can be calculated using the equation proposed by Christiansen for sprinkler systems and adapted for drip systems (Wu et Al.[1979] ):
in which Qi represents the flow rate delivered by each dripper, Qm the average flow rate and N the total number of drippers present. For UCC values = 100% the plant is excellent, while for UCC values< 90% the implant is not acceptable.
Karmeli and Keller coefficient
Another expression used for the design uniformity coefficient, CU [%], for drip plants is the one proposed by Karmeli and Keller[1975] :
in which CVT is the technological variation coefficient of the devices, n is the number of emitters per plant, Qmin the minimum flow rate deduced from the distribution characteristic curve as a function of the minimum load, Qm the average flow rate of all the dispensers present. In particular, if more emitters are installed per plant, the CVT / n0.5 value represents the technological variation coefficient CVTn relating to the group of n emitters serving each plant. In relation to the values assumed by the CU, an opinion can be expressed on the quality of the plant project, in particular:
- great for CU = 100
- good for 94< CU< 100
- enough for 90< CU< 94
- not acceptable for CU< 90
