Introduction

This report

discusses the heat transfer between a Forced Convection Heat Transfer apparatus

and its surroundings, complete with calculations using the steady-flow energy

equation. Once a value for the heat transfer is obtained, the importance of the

right-hand values in the steady-flow energy equation will be considered and

evaluated.

The

experiment was performed to analyse the heat transfer between the apparatus and

its surroundings. It was important to analyse this in

order to see how efficient the system is whilst it is in use.

The

following table details the aims of this experiment and how I plan on achieving

them:

Aims

Objectives

To estimate the heat transfer between a Forced Convection Heat Transfer system and its surroundings.

·

Measure values

for terms in the steady-flow energy equation.

·

Calculate each

term of the steady flow energy equation.

·

Rearrange the

steady-flow energy equation in order to calculate the value for “Qin”.

·

Substitute my

values for each term into the equation.

To examine the relative importance of the right-hand

terms of the steady-flow energy equation.

·

Examine each

term individually in order to compare them to each other.

·

Discuss what

each value contributes to the overall equation.

I predict that the value of Q? will be a negative value as I

believe that there will be some heat loss to the surroundings, as there is no

such thing as a perfect system.

Background Theory

There are several fundamental rules regarding the

thermodynamic behaviour of materials that have been established over the years

as a result of many years of analysis of thermodynamic experiments carried out

by both scientists and engineers alike. These rules are known as the “Laws of

Thermodynamics”.

The first law of thermodynamics directly applies to this

experiment and is known as the “Conservation of Energy”. The law states that the total energy of an isolated

system is constant; meaning energy can change state, but cannot be created

nor destroyed.

There are two flow processes: non-flow and steady-flow. This

report will focus on the use of the law regarding steady-flow processes only.

Steady-flow processes involve mass flow across their boundaries (unlike

non-flow processes), where work is required to push the mass into or out of the

control volume. This work is known as the flow work or flow energy and is

necessary for maintaining a continuous flow through a control volume. It is

important to note that in steady-flow systems, the mass flow of a fluid at any

section is the same as in any other section.

Thermodynamic systems

are categorised as being open, closed or isolated. The system that will be used

in the experiment is an open system, meaning it is able to exchange energy and

matter with its surroundings. A closed system exchanges energy but not matter

with its surroundings; and an isolated system does not exchange either with its

surroundings. However, in reality, there is no such thing as a perfectly

isolated system as all systems transfer energy to their surroundings through

loss of heat energy, regardless of how well insulated they are.

Methods and procedures

In order to complete the experiment, the following equipment

will be needed:

·

Forced Convection Heat Transfer apparatus

·

Measuring tape

·

Vernier calliper

The following details the

recommended experimental procedure:

1. Turn on the power switch on the instrument panel.

2. Record the ambient temperature indicated on the

temperature indicator. (Assume this to be the ambient air temperature at the fan

inlet.)

3. Turn on the fan by pressing the GREEN button on the

instrument panel for the fan.

4. Turn on the heater by pressing the GREEN button on the

instrument panel for the heater.

5. Adjust the power control until the ammeter on the

instrument panel reads “4 Amperes”.

6. Record the corresponding voltage value indicated by the

voltmeter on the instrument panel.

7. Turn the thermocouple selector to position 7 which

indicates the discharged air temperature at the pipe outlet.

8. Whilst waiting for the temperature to stabilise, record

other measurements needed using the equipment provided.

9. Once the temperature has stabilised, record its final

value.

10. Finally, record the value of the water column on the

Orifice Plate Pressure Drop Manometer.

Once the experiment is complete, turn off the heater first

and allow the airflow to continue for a while before turning off the fan.

Analysis and Discussion

From my calculations, I obtained a value of -1362.5J for

. As the value is a negative value, this

indicates to me that there is some heat lost to the apparatus’s surroundings. I

am not surprised at this because as discussed earlier, there is no such thing

as a perfectly isolated system.

In order to analyse the importance of the right-hand terms of

the equation, we must first understand the value of each term. The right-hand

terms of the steady-flow energy equation are as follows:

The first term,

is

the difference in the specified enthalpy of the fluid at the air inlet and

outlet. In terms of this experiment, this value is 40.7kJ/kg.

The second term,

is

the difference in velocity of the air at the inlet and outlet (where each value

is squared) halved. This value of is 314.36m/s.

The third term,

is

the value of gravity multiplied by the difference in height of the air inlet

and outlet. In terms of this experiment, this value is 8.76.

From what the values contribute to the equation, for this

system, I would rank the terms in this order (most important to least

important):

I have ranked them in this order as I believe that velocity is a

large contributing factor to the efficiency of a thermodynamic system because

the system must be able to cope with a high velocity of a fluid and must be

able to run effectively. ENTHALPY. I ranked the height

term last as I do not think that this is a significant contributing factor to

the equation. I inputted various numbers of a large range into the equation to

see how it would affect the outcome, but even with a large number (e.g. 1000),

there was not a huge difference.

Conclusions

In conclusion, from carrying out the experiment and the

required calculations, I

obtained a value of -1362.5J for

,

meaning that there was heat lost to the surroundings, just as I expected there

would be. From using the steady-flow energy equation and analysing my results, I

was then able to examine the importance of the right-hand terms of the

equation.

I believe that the experiment was successful as my results were

as I predicted and I met all of my aims and objectives that were set out at the

beginning of this report. I also completed thorough research into the

background theory of the equation which contributed to my overall understanding

of the topic.