Question

Fluids

Q1- What is the difference between precision and accuracy? Can a measurement be very precise but inaccurate? Explain. Q2- What is specific gravity? How is it related to density? What is cavitation? What causes it? Q3- For the setup shown in Figure, what is the the pressure P^ if the specific gravity of oil is 0.82? Open 4m 320 mm

Answer 1

ANSWER:
Given that ne → į measured value Accuracy the gives the close neis of the actual value. to >> precession measuring means closeness of the different relles the same quantity under similar conditions » can be very precise but not accurate The measurement and vice versa . 1 - Specific Gravity: It is defined and the ratio of density of a substance to the density of standard substance at a specified temperature : Generally for liquids, writer is taken as a standard fluid . Its density is 1000 kg/m3 at uc. specific Gravity : she fliquid PH₂O Discussion! : By looking at the value of specific gravity one can judge

whether the density of liquid is less than or greater than water. I liquids having specific gravity less than lane lighter than water . 2. liquids having specific gravity greater than I are heavier than water Cavitation: Cavitation as the formation and collapsing of cavities of bubbles in a liquid mostly developed in the areas which have relatively low pressure around the pump impeller. It occurs in the absence of the net positive Suction head the pump. It's the formation of bubbles in the liquid flowing in any hydraulic turbine. It occurs when the vapour pressure goes beyond the static pressure of the liquid. In some engineering constežti, Cavitation is a significant cause of wear. what causes it? for the maintenance of the impeller pump cavitation, the difficult .past comes to the fact that cavitation is not

caused by a single factor. There are many factors which contribute to the formation of cavitation Rapid dropping in the pressure at the suctions nogale. The fluid pressure at the suction pump needs to the above the liquid vapor pressure. However, when the vapour pressure becomes very low at the nozzle, vapori zation takes place leading to the formation of an unlimited number of gas bubbles. In the process cavitation takes place un unerled flow conditions: Sometimes obstructions in the valves and shop elbows do occur. when this happens especially in the suctors piping and other fittings, there to an increase in the frictional pressure loss. This leads to an increase in the possibility of great reduction of the pressure of the Suction pump which will eventually lead to puorip impeller cavitation, Un even increase of the pumped liquid temperatura At certain times the temperature at of the liquid can une venly .In the process, the liquid vapor pressure Promeans

1. This leads to the operating pressure falling be low the rapor pressure limit, thus, the formation of bubbles and what follows is pump impeller cavitation. High fluid velocity at the suctions pump: when the liquid flow rates rise at the pump suction than at the designed case, frictional pressure drop level rises with the increasing flow rate. This love is the pressure increases the chances for cavitation to occur at the suction pump. Cavitation can be caused by a number of bactors. It is advisable to prevent pump Pompeller cavitation which occurs as a result of vez porization. ro 3r . Patm. 320mm

specific gravity of oila mercury. Soil = 0.82 mercury = 13.6 PA - pressure of Air (Inside ). fat the outlet, pata will act as it is opentootemaphores s point to have water at some level P, = P21 (point & a have. Hg at some level - Pq =P3, This we can conclude that (P = P2 = P3] Thus taking bcoz oo t6 are extreme points JCPA + Pop & Po upto pt. c. (Paton + PHq cup to point (.) PA --0-82 x 1000 x 9.81% 3 +1000X9.81 14m3 ) : 101325 (Pa) +13=6X1000X9.81% 0:32 formula o fight - Bil - Sony Say He Serge Coq ti datoreipheric pressure Pectory 101325 kpq? th 101315 Pa ) V =101325 + 13.6 9810X632-8200 X 9.81x3 - 9810

Pa = 110075.52 pucal, PA = 110.075 kPa. PA, Vaccum = PA - Palma = 110,075 -101.325 = 8.75 kpa . PA = 110.07kpal IPA Vaccum= 875 kPa)