HMT lab manual - Complete Lab Report for Heat and Mass transfer subject PDF

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Complete Lab Report for Heat and Mass transfer subject...

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HEAT AND MASS TRANSFER

Experiment no 1: Investigation of Fourier’s law for linear conduction in one dimension along a single bar.

      

Objective Apparatus Theory Procedure Observation & Calculations Graphs Comments

HEAT AND MASS TRANSFER

Experiment no 1: Investigation of Fourier’s law for linear conduction in one dimension along a single bar.

Apparatus: Heat Conduction Apparatus.

Theory: Definition: The law of heat conduction, also known as Fourier's law, states that: “Flow of heat per unit area is proportional to the temperature difference per unit length.”

Key points:  

More is the area exposed → More will be the heat transferred More is the temperature difference → More will be the heat transfer

Formula: dT Q´ =−k A dx

( )



Where k is known as Thermal conductivity.



Q is Heat flow through a body per unit time



A is Surface area of heat flow



dt is Temperature difference



dx is Thickness of the body in the direction of flow.

HEAT AND MASS TRANSFER

Properties of ‘K’ 

It is a material property and a function of temperature.



It may be different in different orientations.

Here, (-) sign is added because the gradient of temperature (dT/dx) is negative i.e. decreases with distance.

Example: The same amount of hot coffee cools faster in a bigger cup than a small one.

Applications: 1. Electric fuse cutoff 2. Electric heater 3. Burning of wood on coal 4. Carbonization of coal 5. Thermometer- Yes, mercury acts as a thermometric liquid and good conductor of heat among liquids 6. Melting of iron in blast furnace 7. Fission reactions in nuclear fuel rods of nuclear reactors. 8. Electrical wiring in housing 9. Electric discharge machining in manufacturing 10. Plastics are bad conductors of heat. That is why we use them as handles for many appliances.

Material used: A circular bar made up of Brass is used for this experiment.

Properties of Brass: Brass is an alloy of copper and zinc, in proportions which can be varied to achieve varying mechanical and electrical properties.

HEAT AND MASS TRANSFER

HEAT AND MASS TRANSFER

Procedure: 1) First of all place the bar into the small container of the apparatus. 2) Connect all nine temperature sensors carefully. 3) Make sure all the sensors are connected properly. 4) Fill water into the small water container. 5) Switch on the apparatus and apply power to the heater through the control unit. 6) Wait for 10-15 minutes. 7) Note the readings for T1 to T9. 8) Repeat the experiment for different values of power.

HEAT AND MASS TRANSFER

Observations and Calculations:

Sr #

Heat supplied (watts)

T1 o C

T2 o C

T3 o C

1 2 3

Calculations: Power = Q = 10 Watts Diameter =25 mm Length of material = 30mm Material type = Brass k dT 44.5 −53.1 =−286.6 = −3 m dx 30 × 10 K ( dTdx )= mm ´ Q =−KA=constant dT dx

( )

−KA=

10 −286.6

KA=0.034

W −1 Km m

T3 o C

T4 o C

T5 o C

T6 o C

T7 o C

T8 o C

T9 o C

HEAT AND MASS TRANSFER 25 ×10−3 ¿ ¿ π ¿ 4 0.034 K= ¿

2

Graph: Graph between the temperature difference and length of the bar is given below.

Graph between K and heat supplied

HEAT AND MASS TRANSFER

Comments: We perform the experiment study and observe the heat transfer rate through a circular bar of Brass and verify Fourier’s Law of heat conduction. Make sure the temperature sensors work properly.

HEAT AND MASS TRANSFER

Experiment no 2: Study the conduction of heat along a composite bar and calculate overall Heat Transfer Coefficient.

 Objective

HEAT AND MASS TRANSFER

 Apparatus  Theory  Procedure  Observation & Calculations  Graphs  Comments

HEAT AND MASS TRANSFER

Experiment no 2: Study the conduction of heat along a composite bar and calculate overall Heat Transfer Coefficient.

Apparatus: Heat Conduction Apparatus.

Theory: Definition: The law of heat conduction, also known as Fourier's law, states that: “Flow of heat per unit area is proportional to the temperature difference per unit length.”

Key points: 

More is the area exposed → More will be the heat transferred



More is the temperature difference → More will be the heat transfer

Formula: ´ Q dT =−k A dx

( )



Where k is known as Thermal conductivity.



Q is Heat flow through a body per unit time



A is Surface area of heat flow



dt is Temperature difference



dx is Thickness of the body in the direction of flow.

Properties of ‘K’ 

It is a material property and a function of temperature.



It may be different in different orientations.

Here, (-) sign is added because the gradient of temperature (dT/dx) is negative i.e. decreases with distance.

HEAT AND MASS TRANSFER

Example: The same amount of hot coffee cools faster in a bigger cup than a small one.

Applications: 1. Electric fuse cutoff 2. Electric heater 3. Burning of wood on coal 4. Carbonization of coal 5. Thermometer- Yes, mercury acts as a thermometric liquid and good conductor of heat among liquids 6. Melting of iron in blast furnace 7. Fission reactions in nuclear fuel rods of nuclear reactors. 8. Electrical wiring in housing 9. Electric discharge machining in manufacturing 10. Plastics are bad conductors of heat. That is why we use them as handles for many appliances.

Material used: A composite bar made up of Brass and Steel is used for this experiment.

Properties of Brass & Steel: Brass is an alloy of copper and zinc, in proportions which can be varied to achieve varying mechanical and electrical properties. The most important properties of steel are great durability, good tensile and yield strength and good thermal conductivity.

HEAT AND MASS TRANSFER

Procedure: 1) First of all place the circular bar into the small housing of the apparatus. 2) Connect all nine temperature sensors carefully. 3) Make sure all the sensors are connected properly. 4) Fill water into the small water container. 5) Switch on the apparatus and apply power to the heater through the control unit. 6) Wait for 10-15 minutes. 7) Note the readings for T1, T3, T7 & T9 8) Repeat the experiment for different values of power.

Observation & Calculations

Sr #

1 2 3

Heat supplie d (watts)

T1

T3

T7

T9

o

o

o

o

C

C

C

C

HEAT AND MASS TRANSFER

Experiment no 3: To investigate the effect of change in cross-sectional area on the temperature profile along a Thermal Conductor.

 Objective  Apparatus  Theory  Procedure  Observation & Calculations  Graphs  Comments

HEAT AND MASS TRANSFER

Experiment no 3: To investigate the effect of change in cross-sectional area on the temperature profile along a Thermal Conductor.

Apparatus: Linear heat flow apparatus with composite bar.

Theory: Definition: The law of heat conduction, also known as Fourier's law, states that: “Flow of heat per unit area is proportional to the temperature difference per unit length.”

Explanation: In this experiment we will study the effect of area on the rate of heat transfer and verify Fourier’s law.

Key points: 

More is the area exposed → More will be the heat transferred



More is the temperature difference → More will be the heat transfer

Formula: ´ dT Q =−k A dx

( )



Where k is known as Thermal conductivity.



Q is Heat flow through a body per unit time



A is Surface area of heat flow



dt is Temperature difference



dx is Thickness of the body in the direction of flow.

Properties of ‘K’ 

It is a material property and a function of temperature.



It may be different in different orientations.

HEAT AND MASS TRANSFER Here, (-) sign is added because the gradient of temperature (dT/dx) is negative i.e. decreases with distance.

Example: The same amount of hot coffee cools faster in a bigger cup than a small one.

Applications: 1. Insulating 2. Electrical wiring in housing

Material used: A composite bar made up of Brass and Steel having different cross-sectional area is used for this experiment.

Properties of Brass & Steel: Brass is an alloy of copper and zinc, in proportions which can be varied to achieve varying mechanical and electrical properties. The most important properties of steel are great durability, good tensile and yield strength and good thermal conductivity.

Procedure: 1) First of all place the circular bar into the small housing of the apparatus. 2) Connect the temperature sensors carefully. 3) Make sure all the sensors are connected properly. 4) Fill water into the small water container. 5) Switch on the apparatus and apply power to the heater through the control unit. 6) Wait for 10-15 minutes. 7) Note the readings for T1, T2, T3, T7, T8 & T9 8) Repeat the experiment for different values of power.

HEAT AND MASS TRANSFER

Observations and Calculations:

Sr #

Heat supplie d (watts)

1 2 3

T1

T2

T3

T7

T8

T9

o

o

o

o

o

o

C

C

C

C

C

C

HEAT AND MASS TRANSFER

Experiment no 4: Investigation of the temperature profile and determination of rate of transfer resulting from radial disc.

 Objective  Apparatus  Theory  Procedure  Observation & Calculations  Graphs  Comments

HEAT AND MASS TRANSFER

Experiment no 4: To investigate the temperature profile and determination of rate of transfer resulting from radial disc.

Apparatus: Radial Heat Flow Apparatus

Theory: Rate of heat transfer: “The rate of heat flow is the amount of heat that is transferred per unit of time in some material”. For a radial disc, lets consider a radial disc having external radius r o and the temperature at the external surface To. Fr steady state and one dimensional case, we have (in term of polar coordinates for radial disc). dT =0 dθ dT =0 dz dT ≠0 dr '

q =0

Thus, rate of heat transfer becomes, Q ' =−kA

( dTdr )

Integrating the right side, we get, To

ro

Q =−kA ∫ dT ∫ dr .

T1

r1

Since surface area of disc,

A = 2 π rL

HEAT AND MASS TRANSFER

Where L is the length of the disc and r is the radius of the disc at any point. Thus, ´ Q=

2 πkL( T 1−T 0 ) ln

( ) r0 r1

So, Temperature of Profile=

( T 1−T 0) ln

( ) r0 r1

Procedure: 1) First of all place the radial disc into the housing of the apparatus. 2) Connect the temperature sensors carefully. 3) Make sure all the sensors are connected properly. 4) Fill water into the small water container. 5) Switch on the apparatus and apply power to the heater through the control unit. 6) Wait for 10-15 minutes. 7) Note the readings for T1, T2, T3, T4, T5, T6 8) Repeat the experiment for different values of power.

HEAT AND MASS TRANSFER

Observations and Calculations:

Sr. No.

Heat supplied

T1

T2

T3

T4

T5

T6

(oC)

(oC)

(oC)

(oC)

(oC)

(oC)

(watts) 1

5

33.3

33.2

32.7

32.45

32.2

31.4

2

10

35.2

34.5

33.9

33

31.5

30.2

3

15

38.7

36.3

35.1

34.5

33.8

31

Where,

r1 = 4mm, r2 = 14mm, r3 = 24mm, r4 = 34mm, r5 = 44mm, r6 = 54mm

ln ( r 0 /r 1)

Sr

T1-T0

No.

(K)

1-2

0.1

1.25

2-3

0.5

0.53

3-4

0.25

0.34

4-5

0.25

0.25

5-6

0.8

0.20

HEAT AND MASS TRANSFER

Conclusion: The trend followed by the temperature profile differs from that of ideal profile. This is due to:  

Malfunctioning temperature sensors Unstable temperature readings acquisition

HEAT AND MASS TRANSFER

Experiment no 5: To determine the working principle of concentric tubes heat exchanger operating under the condition of parallel flow.

 Objective  Apparatus  Theory  Procedure  Observation & Calculations  Graphs  Comments

HEAT AND MASS TRANSFER

Experiment no 5: To determine the working principle of concentric tubes heat exchanger operating under the condition of parallel flow.

Apparatus: Parallel flow shell and tube type heat exchanger.

Theory:

Heat Exchanger: A heat exchanger is a system used to transfer heat between two or more fluids. Heat exchangers are used in both cooling and heating processes The fluids may be separated by a solid wall to prevent mixing or they may be in direct contact.Heat exchanger is basically a heat exchanger equipment between two fluids with different temperatures and heat. One fluid gives heat, while the other receives heat.

Applications: The applications of heat exchangers are countless. Some are given below,  Refrigeration systems  Electricity and power generation  Chillers  Compressor cooling  Chemical and Petro-chemical plants  Air conditioning systems

HEAT AND MASS TRANSFER

Classification of Heat Exchangers: Heat exchangers are mainly classified based on their flow. They are mainly classified in four categories. 1. Parallel flow heat exchangers 2. Counter flow heat exchangers 3. Cross flow heat exchangers 4. Shell and tube type heat exchangers

Parallel flow: In the parallel-flow arrangement, the hot and cold fluids enter at the same end, flow in the same direction, and leave at the same end.

Shell and tube heat exchanger: Shell and tube heat exchangers consist of series of tubes. One set of these tubes contains the fluid that must be either heated or cooled. The second fluid runs over the tubes that are being heated or cooled so that it can either provide the heat or absorb the heat required. A set of tubes is called the tube bundle A double pipe heat exchanger can be operated in parallel flow mode. Similarly a shell and tube heat exchanger can be operated in approximately parallel flow by having both fluids enter at one end and exit at the other end. With parallel flow the temperature difference between the two fluids is large at the entrance end, but it becomes small at the exit end as the two fluid temperatures approach each other. The overall measure of heat transfer driving force, the log mean temperature difference is greater for counter flow, so the heat exchanger surface area requirement will be larger than for a counter flow heat exchanger with the same inlet and outlet temperatures for the hot and the cold fluid.

HEAT AND MASS TRANSFER

Procedure: 1) First of all setup the apparatus and make sure the dials are showing exact values. 2) Switch on the apparatus and apply power to the heater through the control unit. 3) Make sure all the sensors are connected properly. 4) Wait for 10-15 minutes. 5) Note the readings for Vc , Vh , Tc (mean) , Tc (out) , Th (in) , Th (mean) , Th (out) 6) Repeat the experiment for different values of power.

Calculations: As we know,

Q=UA ∆ T

For the parallel flow heat exchangers, heat transfer is given by dq=−m h c h d T h=m c c c d T c

The heat transfer is also given as, dq =U ( T h−T c) dA

−dq d Th = mh c h

HEAT AND MASS TRANSFER

Observations & Calculations:

Area=0.67m2

HEAT AND MASS TRANSFER

Conclusion: The experiment shows that as the water flows from the inlet towards the outlet, the cold water gains heat from hot water, If enough time or length is supplied to the water to flow both the lines of hot and cold water should meet at a point but this doesn’t happen because the exchanger cannot be 100 percentage efficient.

HEAT AND MASS TRANSFER

Experiment no 6: To determine the working principle of concentric tubes heat exchanger operating under the condition of counter flow.

 Objective  Apparatus  Theory  Procedure  Observation & Calculations  Graphs  Comments

HEAT AND MASS TRANSFER

Experiment no 6: To determine the working principle of concentric tubes heat exchanger operating under the condition of counter flow.

Apparatus: Counter flow shell and tube type heat exchanger

Theory: Heat Exchanger: A heat exchanger is a system used to transfer heat between two or more fluids. Heat exchangers are used in both cooling and heating processes The fluids may be separated by a solid wall to prevent mixing or they may be in direct contact. Heat exchanger is basically a heat exchanger equipment between two fluids with different temperatures and heat. One fluid gives heat, while the other receives heat.

Applications: The applications of heat exchangers are countless. Some are given below,  Refrigeration systems  Electricity and power generation  Chillers  Compressor cooling  Chemical and Petro-chemical plants  Air conditioning systems

HEAT AND MASS TRANSFER

Counter flow: A counter flow or counter-current shell and tube heat exchanger’s construction is in many ways identical to that of a parallel flow shell and tube heat exchanger. “The main difference is that the tube side fluid enters the exchanger at the opposite end of the shell side fluid. This results in the two fluids running against each other rather than in the same direction”. The counter flow pattern is the most common in shell and tube heat exchangers, primarily because it’s the most efficient. This flow pattern allows for the greatest temperature change between fluids. Additionally, unlike in parallel flow exchangers, the cold-fluid can reach the hottest temperature of the hot-fluid since it exits at the end where the hot-fluid enters.

Why Counter flow heat exchanger is more efficient? The exchanger is performing at its best when the outlet temperatures are equal. Counter flow heat exchangers are inherently more...