1. 2142-391 Engineering Mechanical Laboratory Term 2009-1 Lab 9 (b): Thermocouple Lab 9(a): Viscosity

2. 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)

3. What is viscosity? Saybolt Viscometer Liquid with high viscosity, takes more time to pass the tube. 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.resistancefluidshear stressfriction How do we measure it? Principle concept of

4. Measuring Viscosity Saybolt Viscometer  = f (t) ? “Thick” (high viscosity) “Light” (low viscosity) Liquid which has high viscosity, takes more time to pass the tube. Objective To determine a viscosity and viscosity index (VI) of lubricating oil by Saybolt viscometer

5. Viscosity and Temperature Viscosity is one of most important property of lubricant, while temperature is the most important factor affecting viscosity. 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. Dean and Davis’s VI (“Viscosity Index”) method The fluid usually becomes less viscous, when temperature arises. One way to evaluating Viscosity-temperature characteristics is

6. Dean and Davis’s V.I. (Viscosity Index) Indicator for: “how much  changes, when T changes” One single number Temperature viscosity A C B VI of B = 51 VI of C = 73 VI of A = 32 In the sense that  changes much : V.I. is low  changes little : V.I. is high

7. Lab Objectives To gain an understanding on the concept of Viscosity Index and basic process of determining it. 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 Find V.I of a lubricant

8. Saybolt Viscometer To measure viscosity at specific temperature. To find V.I. Saybolt Viscometer

9. Lab 9(b) : Calibration of Thermocouple Temperature is a thermodynamic property of a body. 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. RTD: resistance thermometer thermocouple pyrometer liquid-in-glass thermometer 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. Sensor Transducer

10. 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. Two wires of dissimilar metals, connected at both ends to form a circuit. thermocouple wire A wire B reference junction measuring junction electromotive force (emf) (change in voltage) In this experiment, we will study the relation of  T and the emf

11. same temp.Law of intermediate metals Thermocouple Usage

12. 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 & 87%Platinum -50 to 1750’C 6 uV/’C S 90% Platinum & 10% Rhodium -50 to 1750’C 6 uV/’C B 94% Platinum & 6% Rhodium -50 to 1750’C 6 uV/’C

13. 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

15. Lab Objectives 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. 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.