Unit 42 Heat Transfer and Combustion

Unit 42:

Heat Transfer and Combustion


Unit code:

QCF level:

Credit value:


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
apply Fourier’s law and the Newton rate equation to

rates for composite systems

composite solids and fluid/solid interfaces

calculate heat transfer rates for combined modes

including radiation

evaluate lagging for optimum performance

LO2 Understand heat transfer
apply dimensional analysis to energy and mass

mechanisms and coefficients

transfer relationships

evaluate heat transfer mechanisms

determine heat transfer coefficients using

experimental and tabulated data

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

transfer equipment
estimate heat transfer performance

specify recuperator type, size and fluids for given


LO4 Be able to analyse the
derive combustion equations

combustion processes
determine calorific value

analyse products of combustion.



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.