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Lab1REVB.docx

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INTRODUCTION ................................................................................................................. 2 OBJECTIVES ...................................................................................................................... 2 NOMENCLATURE .............................................................................................................. 2 THEORY ..................................................................................................
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    I  NTRODUCTION  ................................................................................................................. 2 O BJECTIVES  ...................................................................................................................... 2  N OMENCLATURE  .............................................................................................................. 2 T HEORY  ............................................................................................................................ 3 A PPARATUS  ...................................................................................................................... 6 P ROCEDURE  ...................................................................................................................... 7 R  ESULTS  ........................................................................................................................... 8 D ISCUSSION  .................................................................................................................... 16 C ONCLUSION  .................................................................................................................. 17 R  EFERENCES  ................................................................................................................... 18   Appendix 1: Sample of calculations  2 I  NTRODUCTION   Using pumps is common in many industries. The understanding of pump characteristics is important for selecting them and analysing their states. In this laboratory, it was used the series/parallel pumps apparatus for taking the characteristic values from one single pump and constructing their curves. The similarity equation will  be applied for predicting curves at not tested speeds. Then, for a parallel pump system, the collected values will be compared to theoretical expected values. O BJECTIVES   a.   Construct pump characteristics curves for one pump at operating speeds of 1200, 1600 and 2000 rpm  b.   Construct pump characteristics curves for one pump at speeds of 1400 and 1800 using similarity equations c.   Compare experimental and theoretical operational values of two pumps in  parallel  N OMENCLATURE   ω = Angular velocity η = Efficiency    P= Pressure variation H= Head in meters H s = Pressure/Head in the suction of the pump H d = Pressure/Head in the discharge of the pump  N = Pump speed in rpm M = Mass Power_out = Energy to the fluid Power_in= Power delivered by motor Q = Flow rate T = Torque  3 T HEORY   a)   Pump curves The performance of a centrifugal pump is shown by performance curves which are: head, power consumption, efficiency and NPSH. They are constructed by testing the  pump at various speeds and flow rates, and measuring the pressure. ISO 9906 Annex A explains how pump curves have to be designed (GRUNDFOS Pump Handbook, 2004, 9). Fig.1: Typical pump curves. Reproduced from: The centrifugal pump The construction of the following curves is the objective in this laboratory: i)   Head curves This curve shows the head which the pump is able to perform at a given flow. Usually head is showed in meters [m] and flow in liter/second [l/s] or meter cubic/second [m 3 /s]. The advantage of using the unit [m] for measuring head is that the curve flow-head is not affected by the type of the fluid which could be pumped (GRUNDFOS Pump Handbook, 2004, 9). In laboratory, the head was measured in [m] of water and flow in [l/s] ii)   Efficiency curves The efficiency is the relation between power out (utilised power) and  power in (supplied power). The following expressions are useful to calculated the efficiency  4    ** sup  T Q P  P  P   plied utilised     It used following expressions to calculate the efficiency with the collected data in the laboratory: i)    P in [Pa]=  H*density of water*gravity=(H d -H s )*1000*9.81 ii)   Q in [m 3 /seg] iii)   T in [N.m]= distance of arm [m] * Balance Mass[kg]* gravity = 0.235 * M*9.81 iv)   ω in [rad/s] = 2*π*N/60   b)   Affinity laws Affinity (similarity) laws are obtained by using dimensional analysis. These laws allow that certain changes in the pump parameters (flow, geometry or speed) can be  predicted when one of them is changed. In the laboratory, the parameter that was changed is the rotational speed (N). For this condition similarity laws are: i)   For Flow rate:           ii)   For Head:             iii)   For Efficiency: η A   = η B  Where A is the pump whose data is known and B is the pump whose data is unknown (only it is known the rotational speed) c)   Parallel pumps A parallel operation of pumps means that two or perhaps more pumps are operating at the same time with a common outlet. The main requirement is all of them must have the same discharge pressure; otherwise, the pump with low pressure would be stalled and damaged.
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