Conduction lab report - heat transfer PDF

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COURSE TITLE: HEAT TRANSFER (EE3388) LAB REPORT TITLE: THE STUDY OF FOURIER’S LAW FOR LINEAR CONDUCTION OF HEAT ALONG A HOMOGENEOUS BAR

NAME: KUGANESH A/L GUNASEHER STUDENT ID: 00003219 COURSE: BME LECTURE: IR. ABDUL MUNIRABDUL KARIM

INTRODUCTION: Thermal conduction is the mode of heat transfer, which occurs in a material by virtue of a temperature gradient. A strong is selected for sheer conduction display as both liquids and gasses display unnecessary heat transfer of convection. In practical situation, heat conduction occurs in three dimensions, a complexity which often requires computation to analyse. In the laboratory, a single dimensional approach is required to demonstrate the basic law that relates rate of heat flow to temperature gradient and area. The Heat Conduction Trainer (Model: CHT-195) used single-dimensional strategy to bring learners to the heat transfer method. The sample modules are fitted with a range of detectors of temperature. To preserve the constant temperature gradient, cooling air to be provided from a conventional laboratory pump is fed into the heat sink reservoir. Due to three dimensional heat transfer, the experiment modules are intended to minimize mistakes. Without understanding of radiation or convection heat transfer, the fundamental concepts of conduction can be trained. The linear test piece is supplied with interchangeable samples of conduction to demonstrate the effort of conductivity. GENERAL DESCRIPTION: The heat conduction trainer is used to introduce learners to the concept of the heat transfer process using the heat conduction technique. The trainer comprises of a material with varying thermal conductivity, a heat source and a heat sink. They are made of stainless steel, aluminium and brass. Temperatures are evaluated using k-type thermocouples at separate places along the material length to simulate the heat transfer process. The flow of water at the heat sink is regulated by a valve and the flow rate can be tuned using a flow meter. Temperature measurements can be noted using the i3 DAQ software supplied in conjunction with the trainer.

Experimental Capabilities 

To study the steady state heat conduction process.



To determine the thermal conductivity of different elements.

Unit construction

1. Heater 2. Heat source 3. Material

4. Heat sink 5. Control Panel 6. Flow Meter

SUMMARY OF THEORY If the temperature varies with location in some stationary medium be it a solid or a fluid then a “temperature gradient” is said to exist in that medium. Energy in transit due to such a temperature gradient is conduction heat transfer. The degree of temperature variation within a conduction medium is quantified using the mathematical tools of vector calculus; in particular, the magnitude of the temperature gradient is found from the derivative of temperature with respect to distance, and the gradient points in the direction of steepest temperature increase. In this laboratory exercise, you will study conduction heat transfer in details, exploring the relationship between heat flux and temperature gradient, geometrical effects, composite structures, and interfacial resistance. The mode of conduction heat transfer differs from radiation, where the heat transfer rate depends on the fourth- power temperature difference, and it differs from convection, where at least one heat transfer medium is in motion. As you consider conduction heat transfer in this laboratory, you may find it useful to contrast conduction with the other modes of heat transfer. You may also find it useful to contrast conduction with the other modes of heat transfer. You may also find it useful to draw analogy between the conduction of heat and that of electricity. You should use this laboratory exercise to develop a feel for the physics of conduction heat transfer as well as sense of its practical application. This mode of heat transfer is extremely important in industry, with application in automotive systems, aerospace system, chemical and material processing, electronics cooling, space conditioning and environmental control, and medicine. Fourier’s Law The fundamental relation between the heat flux, q’’, and the temperature gradient, ΔT, for conduction heat transfer in an isotropic medium is q’’ = - KΔT Where k(W/(m.K)) is an important property of the material called the thermal conductivity. This relationship is based on observations and as such we refer to it as “phenomological”; it is named Fourier’s Law.

Thoughtful inspection of Fourier’s Law can tell you a lot about conduction heat transfer. Namely, the conductive heat flux is a vector and hence it has a magnitude and direction. The magnitude of the conductive heat flux is proportional to the temperature gradient, and its

direction is coincident with the temperature gradient. Since the temperature gradient is in the direction of maximum temperature change, the heat flux is in the direction of maximum temperature change; i.e., it is perpendicular to the isotherm. The minus sign means the conduction heat flux is in the direction of decreasing temperature.

Many engineers regard Fourier’s Law as defining the thermal conductivity; this is a healthy point of view that you may find useful. In Cartesian (x, y, z) and cylindrical (r, Φ, z) coordinates, Fourier’s Law can be expressed as below.

Cartesian: q” = iqx” + jqy” + kqz” = - kΔT = -k (I

∂T ∂X

+j

∂T ∂y

+k

∂T ) ∂z

Cylindrical: q” = irqr” + iϕqϕ” + izqz” = -kΔT = -k (ir

∂T ∂r

+ iϕ

1 r

∂T ∂φ

+ iz

∂T ) ∂Z

PROCEDURE 1. The main switch is decided off at the beginning. The aluminum conductor portion is then inserted between the hot source and hot sinks and is set together. 2. The temperature sensor is set on the test module and connected to the sensor panel (confirms that the thermocouple fills the appropriate thermocouple port). 3. Open the water supply system and make sure the water flows from the free end of the water pipe. 4. Power and main switch on, ensures that the USB cable is connected to the computer. 5. Turn on the heater and keep the water temperature. 6. The heater is rated at 1 kW and reads the total power of the electric meter in the control panel. 7. Allow enough time to reach a stable position before registering the temperature. 8. Input Power Reading Q from Power Meter (Take Net Energy Value). 9. Temperature, T and distance, drawn by x. Calculate the thermal conductivity of the test part.

10. Change the different middle parts I. Remove the heat source tank from it and remove the internal hot water. II. Remove the thermocouple port and thermocouple from the material. III. Put a new ingredient in the radiator and send the heat source tank back to its root position. IV. Thermocouple port is reconnected to the right place. Inject water into the water source tank. 11. Repeat 1-9 steps for different materials.

RESULTS AND DISCUSSIONS

Material

Heater Power, Q (watts)

T1 (℃)

T2 (℃)

T3 (℃)

T4 (℃)

T5 (℃)

T6 (℃)

T7 (℃)

T8 (℃)

25mm

75mm

125m m

175m m

225m m

275m m

325m m

375m m

Aluminiu m

900

36.14

35.59

32.30

31.36

29.48

29.42

28.94

31.20

Stainless Steel

900

40.92

32.52

26.23

26.58

26.45

26.43

24.69

32.95

Brass

3000

41.02

37.54

33.64

32.17

30.51

28.03

28.59

29.81

Aluminium

Temperature (℃) vs Distance (m) 40

Temperature (°C)

35 30

m=

f(x) = − 18.58 x + 35.51

m=−18.583

25 20 15 10 5 0 0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

Distance (m)

( final reading – initial reading ) q= time

q=

216.5−216.2 20 60

( )

q=0.9

Q=0.9 X 1000 W =900W

∆T q=−kA ∆x

∆T ∆x

k=

−q ∆T A ∆x

k=

−( 900 ) 2 π ( 0.06 ) ( −18.583 )

k =4282.3 W /mK

Stainless Steel

Temperature (℃) vs Distance (m) 45 40

Temperature (°C)

35 f(x) = − 22.49 x + 34.09

30

m=

25 20

∆T ∆x

m=−22.493

15 10 5 0 0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

Distance (m)

q=

( f inal reading – initial reading ) time

q=

216.2−215.9 20 60

( )

q=0.9

Q=0.9 X 1000 W =900W

∆T q=−kA ∆x

k=

−q ∆T A ∆x

k=

−( 900 ) 2 π ( 0.06 ) ( −22.493 )

k =3537.9W /mK

Brass

Temperature (℃) vs Distance (m) 45 40

Temperature (°C)

35

f(x) = − 33.74 x + 39.41

30

m=

25 20

m=−33.74

15 10 5 0 0

∆T ∆x

0.05

0.1

0.15

0.2

0.25

0.3

0.35

Distance (m)

( final reading – initial reading ) q= time Q=3 X 1000 W =3000 W

q=

215.9−214.9 20 60

( )

q=3

0.4

q=−kA

∆T ∆x

k=

−q ∆T A ∆x

k=

−( 3000 ) π ( 0.062 ) ( −33.74 )

k =7861.8W /mK

COURSE TITLE: HEAT TRANSFER (EE3388) LAB REPORT TITLE: CONVECTION HEAT TRANSFER TRAINER

NAME: KUGANESH A/L GUNASEHER STUDENT ID: 00011847 COURSE: BME

LECTURE: IR. ABDUL MUNIRABDUL KARIM

INTRODUCTION

The Heat Convection Trainer (Model: TERA-CT) is used to introduce learners to the heat transfer method through natural and forced convection. Convection is a heat transfer by the mass movement of a liquid, such as air or water, when the heated fluid is induced to move away from the heat source, carrying energy with it. GENERAL DESCRIPTION The Heat Convection Trainer (Model: TERA-CT-115) is used to introduce learners to the concept of natural and compelled convection heat transfer. The trainer comprises of heating elements of distinct forms. The air blew from fan via ducting will extract the heat from heater elements and will bring it to exhaust of the system. The trainer contains three different heating elements. These heaters have the shape of round, fin and flat plate. The axial fan is located at one end ducting. The temperatures are measured by using k-type thermocouples at four different locations to stimulate the heat transfer process. Air velocity meter is fixed at the ducting to measure the velocity of air passing through the ducting. The temperature readings can be observed using the i3 DAQ software provided together with trainer.

Experiment Capabilities: •

To study the temperature distribution along the length of a vertical pipe in natural and forced convection.

•

To calculate Nu and Pr numbers in natural and forced convection

•

To determine the surface heat transfer coefficient for a vertical tube losing heat by natural and forced convection.

UNIT CONSTRUCTION

SUMMARY OF THEORY Introduction – Convection Heat Transfer The term convection refers to heat transfer that will occur between a surface and a moving or stationary fluid when they are at different temperature as shown in Figure 4.1. This mode of heat transfer comprises of two mechanisms. In addition to energy transfer due to random molecular motion (conduction), energy is also transferred by the bulk, or macroscopic motion of the fluid. This fluid motion is associated with the fact that, at any instant, large numbers of molecules are moving collectively or as aggregates. Such motion, in the presence of a temperature gradient, contributes to heat transfer. Because the molecules in the aggregate retain their random motion, the molecules and by the bulk motion of the fluid. It is customary to use the term convection when referring to this cumulative transport, and the term advection when referring to transport due to bulk fluid motion.

Figure 4.1: Convection from a surface to moving fluid

You learned in the fluids course that, with fluid flow over surface, viscous effects are important in the hydrodynamic (velocity) boundary layer and, for a Newtonian fluid, the frictional shear stresses are proportional to the velocity gradient. In the treatment of convection in the heat transfer course, you have been exposed to the concept of thermal boundary layer, the region that experience a temperature distribution from that of the free steam ∞ T to the surface s T (refer to Figure 11.2).

Figure 4.2: Hydrodynamic and thermal boundary development in convection heat transfer

Appreciation of boundary layer phenomena is essential to understanding of convection heat transfer. It is for this reason that the discipline of fluid mechanics plays a vital role in our analysis of convection mechanism.

It is important to emphasize that convection heat transfer may be classified according to the nature of the flow. We speak of forced convection when the flow is caused by external means, such as a fan, a pump, or atmospheric winds. In contrasts, for free (or natural) convection, the flow is induced by buoyancy forces, which arise from density differences caused by temperature variations in the fluid. We speak also of external and internal flow. As you learned in fluid mechanics course, external flow is associated with immersed bodies for situations such as flow over plates, cylinders and foils. In internal flow, the flow is constrained by the tube or duct surface. You saw that the corresponding hydrodynamic boundary layer phenomena are quite distinctive.

Regardless of the particular nature of the convection heat transfer process, the appropriate rate equation, known as Newton’s law cooling is of the form

In this case heat transfer is positive to the surface. The choice of equation (1) or (2) is normally made in the context of a particular problem as appropriate.

It is

important to note that the convection coefficient depends on conditions in the boundary layer, which is influenced by surface geometry, the nature of fluid motion, and assortment of fluid thermodynamic and transport properties. Any study of convection ultimately reduces to a study of the means by which h may be determined. One of the means to estimate the value of h under turbulent flow conditions will carried out in the present experiment.

EXPERIMENTAL PROCEDURE 1.The convection heat exchanger 240 is connected to the VAC single-phase power supply and the main switch in the control panel is turned on. The digital meter displays the start up time of a few seconds before the experiment. 2. Make sure the anemometer is installed correctly in the pipeline. 3. The fan is enabled, allowing the air to run for a few minutes in the pipeline. 4. Insert the tube with the plate heater and keep the temperature without heat. 5. Notice and record the temperature and readings of the thermometer in I3 DAQ software. 6. Use the energy supplied to monitor the power of the heater. 7. Start the heater using a heater switch in the control panel and wait for the constant status to reach constant. Temperature and speed are recorded in the form provided. 8. After the experiment is completed, turn off the heater, cool the unit for 2-3 minutes and then turn off the fan. 9. Repeat steps 4-8 with other heaters.

Shut-Down Procedures 1.Turn off the system using the buttons in the control panel. 2. Remove the heater and arrange the space provided at the bottom of the rig.

RESULTS AND DISCUSSION Flow case

Rod Heater

Fin Heater

Flat Plate Heater

Heater surface area (m2)

0.09048

0.09

0.018

Free stream velocity (U)

1.524

2.083

1.473

2.235

1.524

2.286

Type of speed

Low

High

Low

High

Low

High

T1 T2 Tm Ts

29.6 44.0 36.8 47.6

26.6 36.4 31.5 42

37.5 42.8 40.15 63

29.1 31.2 30.15 57

37.9 38.4 38.15 50

30.2 32.4 31.3 43

Density, p (kg/m3) at Tm

1.138

1.158

1.126

1.163

1.133

1.158

1007

1007

1007

1007

1007

1007

Kinematic

1.671x10-

1.620

1.703

1.609

1.684

Viscocity, v at Tm

5

x10-5

x10-5

x10-5

x10-5

0.02638

0.02603

0.02675

0.02598

0.02651

0.02595

Mass Flow rate, ṁ

0.0250

0.0254

0.0247

0.0255

0.0248

0.0254

Initial energy (kWh)

5431

5476

5350

5397

5505

5546

Final energy (kWh)

5449

5493

5368

5418

5521

5562

Heat absorbed, Q (watts)

216

204

216

252

192

192

Heat transfer coefficient, ĥ

221.04

227.35

104.47

88.91

201.45

204.03

0.12

0.12

0.12

0.12

0.12

0.12

10944

11288

10739

11366

10859

11288

1005.48

1045.09

468.65

410.66

911.88

943.49

0.7261

0.7278

0.7250

0.7280

0.7259

0.7277

34.47

35.36

33.93

35.56

34.25

35.37

Specific Heat Capacity, Cp(j/kg.C) at Tm

Thermal conductivity, k (W/m.K) at Tm

Hydraulic Diameter, DH Reynolds Number, Re

1.620 x10-5

Nusselt Number from experiment, (Nuexp) Prandtl Number from experiment, Prexp Nusselt Number from Correlation, Nucor

CALCULATION

Find T m T m=

29.6℃ +44.0 ℃ =36.8 ℃ 2

ρ−1.147 36.8−35 = 1.127−1.147 40 −35

Density , ρ

C p −1007 36.8−35 = 1007−1007 40 −35

Specific Heat Capacity , C p

ρ=1.138

C p =1.138

−5

36.8−35 v−1.655 ×10 = −5 −5 40 −35 1.702 ×10 −1.655 × 10

Kinematic Viscocit y , v

T h ermal Conductivity , k

Mass flow rate , m ´

36.8−35 k −0.02625 =...