Table of Contents
Text content Page a) Objective.................................................................................................2 b) Introduction.............................................................................................2 c) Material & Apparatus..............................................................................3 d) Procedure...............................................................................................3 e) Results & Discussion..............................................................................4 f) Conclusion..............................................................................................5 g) References..............................................................................................5

OBJECTIVE
This experiment was carried out to study the conduction of heat along a composite bar and evaluate the overall heat transfer coefficient.

INTRODUCTION
Conduction is defined as the transfer of energy from more energetic particles to adjacent less energetic particles as a result of interactions between the particles. In solids, conduction is the combined result of molecular vibrations and free electron mobility. Metals typically have high free electron mobility, which explains why they are good conductors.

Conduction can be easily understood if we imagine two blocks, one hot and the other cold. If we put these blocks in contact with one another but insulate them from the surroundings, thermal energy will be transferred from the hot block to the cold block. This mode of heat transfer between the two solid blocks is termed as ‘conduction’.

Figure 1: Schematic of a long cylindrical insulated bar
Provided that the heated, intermediate and cooled sections are clamped tightly together, so that the end faces are in good thermal contact, the three...

...HeatConductionalong a CompositeBar
Objective
To study the conduction of heatalong a compositebar and evaluate the overallheattransfercoefficient.
Theory
Thermal conduction is the mode of heattransfer which occurs in a material by virtue of a temperature gradient within it. A solid is chosen for the demonstration of pure conduction since both liquids and gasses exhibit excessive convective heattransfer. In a practical situation, heatconduction occurs in three detentions, a complexity which often requires extensive 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.
For steady flow along the bar, the heat flow through successive slabs is the same for reasons of continuity. Hence, from Fourier’s law
QA=kHTHS-THIXH=kSTHI-TCIXS=kCTCI-TCSXC (1)
We may write Eq (1) as
QA=U(THS-TCS) (2)
Where,
1Q=XHkH+XSkS+XCkC (3)
U is overallheattransfercoefficient for the composite...

...of a gas takes place with no flow of heat energy either into or out of the gas - the process is said to be isentropic or adiabatic. The isentropic (adiabatic) process can be expressed with the Ideal Gas Law as:
p / ρk = constant
where
k = cp / cv - the ratio of specific heats - the ratio of specific heat at constant pressure - cp - to the specific heat at constant volume - cv
The isentropic or adiabatic process can also be expressed as
pVk= constant
or
p1V1k = p2V2k
The Second law of thermodynamics states that,
where δQ is the amount of energy the system gains by heating, T is the temperature of the system, and dS is the change in entropy. The equal sign will hold for a reversible process. For a reversible isentropic process, there is no transfer of heat energy and therefore the process is also adiabatic. For an irreversible process, the entropy will increase. Hence removal of heat from the system (cooling) is necessary to maintain a constant internal entropy for an irreversible process in order to make it isentropic. Thus an irreversible isentropic process is not adiabatic. For reversible processes, an isentropic transformation is carried out by thermally "insulating" the system from its surroundings. Temperature is the thermodynamic conjugate variable to entropy, thus the conjugate process would be an isothermal process in which...

...Practice Problems Set – 1 MEC301: HeatTransfer
Q.1 The slab shown in the figure is embedded on five sides in insulation materials. The sixth side is exposed to an ambient temperature through a heattransfercoefficient. Heat is generated in the slab at the rate of 1.0 kW/m3. The thermal conductivity of the slab is 0.2 W/m-K. (a) Solve for the temperature distribution in the slab, noting any assumptions you must make. Be careful to clearly identify the boundary conditions. (b) Evaluate T at the front and back faces of the slab. (c) Show that your solution gives the expected heat fluxes at the back and front faces.
Q.2
Compute overallheattransfercoefficient U for the slab shown in the figure.
Given: Ls = 2 mm = 0.002 m Lc = 3 mm = 0.003 m ks = 17 W/m-K kc = 372 W/m-K Q.3 A 4 mm diameter spherical ball at 50oC is covered by a 1 mm thick plastic insulation (k = 0.13 W/m-K). The ball is exposed to a medium at 15oC, with a combined convection and radiation heattransfercoefficient of 20 W/m2-K. Determine if the plastic insulation on the ball will help or hurt heattransfer from the ball. Q.4 Prove that if k varies linearly with T in a slab, and if heattransfer is one-dimensional and steady, then q may...

...16: Heatconduction
Introduction
In this laboratory you will study heat flow across a temperature gradient. By comparing the temperature difference across one material to the temperature difference across a second material of known thermal conductivity, when both are conducting heat at a steady rate, you will be able to calculate the thermal conductivity of the first material. You will then compare the experimental value of the calculated thermal conductivity to the known value for that material. Thermal conductivity is an important concept in the earth sciences, with applications including estimating of cooling rates of magma chambers, geothermal explorations, and estimates of the age of the Earth. It is also important in regard to heat transport in air, to understanding the properties of insulating material (including the walls and windows of your house), and in many other areas. The objective of this laboratory experiment is to apply the concepts of heat flow to measure the thermal conductivity of various materials.
Theory
Temperature is a measure of the kinetic energy of the random motion of molecules with a material. As the temperature of a material increases, the random motion of its molecules increases, and the material absorbs and stores a quantity which we call heat. The material is said to be hotter. Heat, once thought to be a fundamental quantity...

...Forced and free convection Laboratory
Introduction
Convection, along with conduction and radiation is one of the three ways in which heat is transferred. In convection, heat can be exchanged from one fluid to another. In this experiment, a heated plate is in contact with air inside a rectangular cross section duct. The air is heated by conduction from the heated plate. The density of the air decreases as it is heated and this makes the warm air rise. Colder air, which in turn is less dense, then replaces the warmer air, which has risen. The plate then heats this colder air, which will eventually rise to be replaced by colder less dense air. This is known as free convection. However in forced convection, the flow of air is not due to small currents set up by natural convection. Forced convection is due to a large interfering flow of air such as a fan.
Aims and objectives
The aim of this laboratory experiment it to find the convection heattransfercoefficient of a flow of air that is flowing over a heated plate at a known speed. The convection heattransfercoefficient can be determined using the values of temperatures recorded, the area of the heated plate and finally the energy converted into heat.
The main objective of this laboratory is to prove the theory of forced convection is...

...Conduction Through A Thick-Walled Tube
This problem is important in the process industries, but we do need to make the distinction between thick and thin walled pipes. In general thin walled pipes can be considered by the previous analysis – but assuming that the pipe wall is effectively unwrapped so that it looks like a flat plate, with the process fluid on one side and the ambient condition on the other. The situation for thick pipes is, however, more complex.
[pic]
The figure shown above represents the condition in a thick walled pipe. The area for heat flow is proportional to the radius – as may be seen, the area at the outside wall of the pipe is much greater than the middle. As a result the temperature gradient is inversely proportional to the radius.
The heat flow ‘per unit length of pipe’ at any radius r, is
[pic]
cf. [pic]
Note: Area,[pic]
Note there is no length of pipe (l) in this equation as we choose to deal with loss per unit length of pipe instead – later we shall introduce the length again, to calculate the total heat loss.
Integration the above equation between r1 and r2 gives
[pic]
or
[pic]
Which, if we define rm as a logarithmic mean radius then
[pic]
[pic]
In Coulson and Richardson Vol 1 it is said that for thin walled pipes it is sufficient to use the arithmetic mean radius ra giving:
[pic] (Used for thin cylinder)
Compare this equation with the...

...Basrah
Third year 32 Lectures
Lectures of HeatTransferHeatTransfer Rate Processes
Mode Conduction Convection Radiation Transfer Mechanism Diffusion of energy due to random molecular motion Diffusion of energy due to random molecular motion plus bulk motion Energy transfer by electromagnetic waves Rate of heattransfer (W)
q = - kA
dT dx
q = h A(Ts-T∞) q = σ ε A(Ts4-Tsur4)
By Mr. Amjed Ahmed Ali
Syllabus of HeatTransfer (English),
(2 hours/ week, Applied 2 hours /week) 1.Heattransfer by conduction, convection and radiation 2.One-dimensional steady state conduction 3.Systems with conduction-convection 4.Radial systems(cylinder and sphere) 4. Overallheattransfercoefficient 5. Critical thickness of the insulator 6. Heat source systems 7. Extended Surface (Fins) 8. Resistance to heat contact 9. Unsteady state conduction • Complete heat capacity system • Limited conditions of convection • Application and Hessler's diagrams 11. Multi-dimensions systems 12. Principles of heattransfer by convection 13. Boundary layer for laminar and turbulent flow 14. Thermal boundary layer for laminar and...

...Mechanisms of HeatTransfer
Prepared by: Ms. Ana Antoniette C. Illahi
1
Conduction
• conduction (or heatconduction) is the transfer of thermal energy between regions of matter due to a temperature gradient. Heat spontaneously flows from a region of higher temperature to a region of lower temperature, and reduces temperature differences over time, approaching thermal equilibrium.
Prepared by: Ms. Ana Antoniette C. Illahi
2
(Heat Current in Conduction)
• • • • • • • • H - Heat Current dQ – Quantity of Heat dt – Time dQ/dt – the rate of heat flows A – Cross sectional area (TH - TC) – Temperature difference L – Length k – constant (thermal conductivity)
Prepared by: Ms. Ana Antoniette C. Illahi
H = dQ/dt = kA (TH - TC)/L
3
Conduction
H = dQ/dt = -kA (dT/ dx) H = A(TH - TC) / R R = L/ k R – thermal resistance
Prepared by: Ms. Ana Antoniette C. Illahi 4
Thermal Conductivities k (W/m oC)
Metals Aluminum Brass Copper Lead Mercury Silver Steel 205.0 109.0 385.0 34.7 8.3 406.0 50.2
Prepared by: Ms. Ana Antoniette C. Illahi 5
Solids (representative values) Brick. Insulating 0.15 Brick. red 0.6
Concrete 0.8
Cork Felt Fiberglass Glass Ice Rock wool Styrofoam Wood
0.04 0.04 0.04 0.8 1.6 0.04 0.01 0.12-0.04
Prepared by: Ms. Ana Antoniette C....

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