Unit 42 Heat Transfer and Combustion



Unit 42:

Heat Transfer and Combustion

 

Unit code:
K/601/1443

QCF level:
5


Credit value:
15






Aim

This unit will develop learners’ understanding of heat transfer principles and empirical relationships enabling them to solve practical problems involving heat transfer, combustion and the specification of practical engineering equipment.

Unit abstract

This unit will build on learners’ knowledge of the theory and associated formulae for heat transfer by conduction, convection and radiation. Learners will also analyse the materials used for lagging and their economic effects.

Learners will then study the applications of dimensional analysis, a more detailed treatment of heat transfer mechanisms and the determination of heat transfer coefficients. The unit goes on to look at the specification and performance of heat transfer equipment and learners are then introduced to the chemistry of the combustion process and analysis of the products of combustion.

Learning outcomes

On successful completion of this unit a learner will:

1     Understand heat transfer rates for composite systems

2     Understand heat transfer mechanisms and coefficients

3     Be able to evaluate heat transfer equipment

4       Be able to analyse the combustion processes.


Unit content

1      Understand heat transfer rates for composite systems

Interfaces: conduction (Fourier’s law, thermal conductivity, thermal resistance, temperature gradient, composite plane walls and thick cylinders); convection (description of forced and natural convection, convective heat transfer coefficient, film and overall coefficient)

Radiation: nature of radiation; Stefan-Boltzman law; black and grey body radiation; emissivity; absorptivity; correction for overall heat transfer coefficient

Lagging: material types; conductivity; energy costs; economic lagging


2      Understand heat transfer mechanisms and coefficients

Dimensional analysis: dimensionless groups; Reynolds, Nusselt, Prandtl, Stanton, Grashof numbers

Heat transfer mechanism: description of flow in tubes, ducts and across surfaces; boundary layer; laminar and turbulent; forced and natural convection; fluid properties; flow parameters; boiling and condensation

Determine heat transfer coefficients: Dittus-Boelter equation for forced convection in circular ducts and tubes, for various fluids, tube dimensions and flow parameters; use of charts and data for fluid properties


3      Be able to evaluate heat transfer equipment

Recuperators: concentric tube (parallel and counter flow, cross flow, shell and tube, plate, extended surface)

Heat transfer performance: steady state performance; overall heat transfer coefficient; log mean temperature difference (LMTD); effectiveness; pressure drop; fouling factors

Fluids: water; oil; air; refrigerants; steam

Applications: specification of suitable recuperator and fluids for given applications such as oil cooling and heat recovery; calculation of heat transfer rates given fluid and recuperator data

4      Be able to analyse the combustion processes

Combustion chemistry: composition of air and hydrocarbon fuels; combustion equations; stoichiometric and actual air:fuel ratios; mixture strength; excess air

Energy of combustion: calorific values; higher and lower; thermal and boiler efficiency; practical determination of calorific value of various solid, liquid and gaseous fuels

Products of combustion: instrumentation for flue gas and exhaust products; volumetric analysis; variation of proportions of products dependent on air:fuel ratio and combustion quality

Learning outcomes and assessment criteria



Learning outcomes
Assessment criteria for pass

On successful completion of
The learner can:

this unit a learner will:







LO1 Understand heat transfer
1.1
apply Fourier’s law and the Newton rate equation to

rates for composite systems

composite solids and fluid/solid interfaces


1.2
calculate heat transfer rates for combined modes



including radiation


1.3
evaluate lagging for optimum performance





LO2 Understand heat transfer
2.1
apply dimensional analysis to energy and mass

mechanisms and coefficients

transfer relationships


2.2
evaluate heat transfer mechanisms


2.3
determine heat transfer coefficients using



experimental and tabulated data





LO3 Be able to evaluate heat
3.1
evaluate various types and layout of recuperators

transfer equipment
3.2
estimate heat transfer performance




3.3
specify recuperator type, size and fluids for given



applications





LO4 Be able to analyse the
4.1
derive combustion equations

combustion processes
4.2
determine calorific value




4.3
analyse products of combustion.





Guidance

Links

This unit can be linked with Unit 41: Fluid Mechanics or Unit 61: Engineering Thermodynamics.


Essential requirements

Centres will need to provide access to laboratory facilities suitable for the analysis of flow, heat exchange performance and products of combustion.

Employer engagement and vocational contexts


Liaison with industry can help centres provide access to relevant industrial facilities and related plant. Where possible work-based experience should be used to provide practical examples of heat transfer rates and mechanisms.

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