2142-391 Engineering Mechanical Laboratory

Term 2009-1

Lab 9 (b): Thermocouple

Lab 9(a): Viscosity

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?

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.

How do we measure it?

Principle concept of

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

(Strock, Centistroke)B

Att

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 evaluatingViscosity-temperaturecharacteristics is

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

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 100oT F 210oT F

100oT F 210oT F

Saybolt Viscometer

• To measure viscosity at specific temperature.

• To find V.I. 100oT F 210oT F

32

5 9

C F

Saybolt Viscometer

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

pyrometerliquid-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

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

meas refT T T

electromotive force (emf)

(change in voltage)

In this experiment, we will study the relation of T and the emf

same temp. Law of intermediate metals

Thermocouple Usage

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

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 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.