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Term 2009-1 2142-391 Engineering Mechanical Laboratory Lab 9(a): Viscosity Lab 9 (b): Thermocouple Lab 9 (a): Viscosity Measurement Lubricant is a substance (usually a liquid) introduced between two moving surfaces to reduce the friction and wear between them. “Viscosity” is one of the most important characteristics of the lubricant and it should be match with the mechanism requirement. You will learn how to measure the “Viscosity” and “Viscosity Index” (the number indicating viscosity-temperature characteristics) What is viscosity? the resistance of a fluid to deform under shear stress. It is commonly perceived as "thickness", or resistance to flow. Viscosity describes a fluid's internal resistance to flow and may be thought of as a measure of fluid friction. How do we measure it? Liquid with high viscosity, takes more time to pass the tube. Principle concept of Saybolt Viscometer Measuring Viscosity Liquid which has high viscosity, takes more time to pass the tube. “Thick” (high viscosity) “Light” (low viscosity) Saybolt Viscometer B= f (t) ? n At (Strock, Centistroke) t Objective To determine a viscosity and viscosity index (VI) of lubricating oil by Saybolt viscometer Viscosity and Temperature Viscosity is one of most important property of lubricant, while temperature is the most important factor affecting viscosity. The fluid usually becomes less viscous, when temperature arises. Thus the viscosity of a lubricant can be matched to the mechanism’s requirement only if the lubricant’s viscosity temperature characteristics are known over the considerable temperature range. One way to evaluating Viscosity-temperature characteristics is Dean and Davis’s VI (“Viscosity Index”) method Dean and Davis’s V.I. (Viscosity Index) • Indicator for: “how much n changes, when T changes” • One single number viscosity B In the sense that n changes much : V.I. is low n changes little : V.I. is high C VI of A = 32 A VI of B = 51 VI of C = 73 Temperature Lab Objectives To gain some understanding on the theory underlying the viscosity measurement, and develop some expertise in the measurement of viscosity using Saybolt Viscometer. Measure Viscosity T 100o F T 210o F To gain an understanding on the concept of Viscosity Index and basic process of determining it. Find V.I of a lubricant T 100o F T 210o F C F 32 5 9 Saybolt Viscometer • To measure viscosity at specific temperature. • To find V.I. Saybolt Viscometer T 100 F o T 210o F Lab 9(b) : Calibration of Thermocouple Temperature is a thermodynamic property of a body. It is one of the most frequently measured quantities in science and industry. Its measurement is vital for analyzing the internal state of the object. Since it is not possible to measure a temperature change directly, “changes of other properties” (that can be observed easily) are used as indicators of temperatures. Sensor liquid-in-glass thermometer pyrometer Transducer RTD: resistance thermometer thermocouple Thermocouple Thermocouple is a widely used type of temperature transducer. They are cheap, interchangeable, having standard connectors and can measure a wide range of temperature. measuring junction Two wires of dissimilar metals, connected at both ends to form a circuit. T Tmeas Tref (change in voltage) electromotive force (emf) reference junction thermocouple In this experiment, we will study the relation of T and the emf same temp. Thermocouple Usage Law of intermediate metals Thermocouple Type E Chromel - Constantan -270 to 1000’C 60.9 uV/’C J Iron & Constantan -210 to 1200’C 51.7 uV/’C K Chromel & Alumel -270 to 1350’C 40.6 uV/’C T Copper & Constantan -270 to 400’C 40.6 uV/’C R Platinum & -50 to 1750’C 87%Platinum 90% Platinum & 10% -50 to 1750’C Rhodium 94% Platinum & 6% -50 to 1750’C Rhodium 6 uV/’C S B 6 uV/’C 6 uV/’C Pro and Cons • • • • • low cost Less likely to be broken wide temperature range short response time Repeatability and acurracy • Sensitivity is low • Accuracy • Known temperature reference • nonlinearity Lab Objectives To gain some understanding on the theory underlying the thermoelectric temperature measurement, especially thermocouples and develop some expertise in the measurement of temperature with thermocouples. To gain an understanding on the concept of calibration and basic process of calibrating an instrument. Specifically, to realize the purposes of calibration, why an instrument should be calibrated before use.