1 / 17

2142-391 Engineering Mechanical Laboratory

Semester 2013-1. 2142-391 Engineering Mechanical Laboratory. Lab 4 (a): Viscosity. Lab 4 (b): Thermocouple. Lecturer: Nopdanai Ajavakom (NAV). Lab 4 (a): Viscosity Measurement.

mayes
Télécharger la présentation

2142-391 Engineering Mechanical Laboratory

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Semester 2013-1 2142-391 Engineering Mechanical Laboratory Lab 4 (a): Viscosity Lab 4 (b): Thermocouple Lecturer: Nopdanai Ajavakom (NAV)

  2. Lab 4 (a): Viscosity Measurement Lubricant= a substance (usually a liquid) introduced between two moving surfaces to reduce the friction and wear between them. Viscosity= one of the most important characteristics of the lubricant

  3. What is viscosity? • Viscosity • the resistance of a fluid to deform under shear stress. • commonly perceived as "thickness” or resistance to flow. • describes a fluid's internal resistance to flow You will learn how to measure the “Viscosity” and compute “Viscosity Index” (the number indicating viscosity-temperature characteristics) How do we measure it?

  4. Measuring Viscosity Liquid which has high viscosity, takes more time to pass the tube. “Thick” (high viscosity) “Light” (low viscosity) Saybolt Viscometer n = f (t) ?

  5. Viscosity vsTemperature 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

  6. Viscosity Index “how less n changes, when T changes” • Indicator for: • One single number n changes much : V.I. is low: n changes little : V.I. is high: better Example: viscosity C VI of A = 32 B VI of B = 51 A VI of C = 73 Temperature

  7. Lab Objectives • To understanding the concept of Viscosity Indexand the basic process of determining it. • To understand the theory underlying the viscosity measurement, and develop some expertise in the measurement of viscosity using Saybolt Viscometer. Measure Viscosity at Find V.I of a lubricant

  8. Lab 4 (b): Calibration ofThermocouple • Temperature • is a thermodynamic property of a body, which is important for analyzing the internal state of the object. • one of the most frequently measured quantities in science and industry. 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. liquid-in-glass thermometer pyrometer RTD: resistance thermometer thermocouple

  9. Thermocouple • is a widely used type of temperature transducer. • relatively cheap, interchangeable, having standard connectors and can measure a wide range of temperature.

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

  11. ThermocoupleType, Range, Sensitivity Constantanis a 55% copper and 45% nickel alloy. Chromelis a 90 % nickel and 10 % chromium alloy. Alumelis a 95% nickel, 2% manganese, 2% aluminium and 1% silicon alloy.

  12. Calibration • is a comparison between measurements – one of known magnitude or correctness made or set with one device and another measurement made in as similar a way as possible with a second device. • The device with the known or assigned correctness is called the standard. The second device is the unit under test, test instrument, etc.

  13. Lab Objectives • To understand the theory of the thermoelectric temperature measurement, especially thermocouples and develop some expertise in the measurement of temperature with thermocouples. • To understand 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.

  14. Calibration Graph EMF (mV) from voltmeter Type J ∆V ∆T Temperature (from a reliable source) ∆V / ∆T = sensitivity (V/ºC)

  15. Thermocouple • low cost • less likely to be broken • wide temperature range • short response time • Repeatability and acuracy • Sensitivity is low • Known temperature reference • nonlinearity

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

More Related