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STUDY GUIDE · GKU 6

Heat transfer study guide (Mechanical Engineering)

Heat moves in three ways: conduction through solids and still fluids, convection between a surface and a moving fluid, and radiation between surfaces that see each other. The first part teaches each mode from its rate law, builds the general conduction equation, and then uses it for walls, pipes, fins and bodies that heat up or cool down with time; it covers forced and free convection, boiling and condensation, and radiation exchange between real surfaces. The second part, which carries more of the exam weight, applies all of this to heat exchangers: their types, the overall coefficient, and the two ways to size or rate one (LMTD and effectiveness–NTU). The closing sections go beyond the ETEC handout and cover refrigeration, air conditioning and fluid machinery, because the question bank files those course topics here.

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Structured by the official ETEC subject standard for this topic: every listed topic and learning outcome, with formulas, figures and worked examples. The full sections are available to members in the app.

SKU 6.1 · Heat transfer

  1. Modes of heat transfer and their rate laws

    Conduction, convection and radiation: what physically carries the energy in each, and the three rate laws every later section builds on.

  2. The general heat conduction equation

    An energy balance on a small element turns Fourier's law into the equation that governs temperature inside any solid; boundary conditions and heat generation complete the problem.

  3. Steady one-dimensional conduction and thermal resistance

    Plane walls, pipes and spheres as thermal resistances; composite walls in series and parallel; the overall coefficient; contact resistance and the critical radius of insulation.

  4. Extended surfaces (fins)

    Why a fin helps, the fin equation and its solutions, fin efficiency and effectiveness, and when a fin is not worth adding.

  5. Convection fundamentals and external forced flow

    What sets the convection coefficient, the dimensionless groups that organise it, and how to compute h for a flat plate and a cylinder in cross-flow. Impinging jets and packed beds close the section.

  6. Internal forced convection and tube banks

    Flow inside tubes and ducts: the mean temperature, the two wall conditions, laminar and turbulent Nusselt numbers, and flow across banks of tubes.

  7. Natural (free) convection

    Flow driven by buoyancy alone: the Grashof and Rayleigh numbers, correlations for a vertical plate, and when free convection can be ignored next to forced flow.

  8. Boiling and condensation

    Convection with phase change: the pool boiling curve, the critical heat flux and burnout, and film condensation on plates and tubes.

  9. Thermal radiation and the blackbody

    What thermal radiation is, the blackbody laws of Planck, Stefan and Wien, the radiative properties of real surfaces, and the net exchange of a small body with large surroundings.

  10. View factors and radiation exchange between gray surfaces

    How much of what one surface emits reaches another, radiosity, the surface and space resistances of the radiation network, two-surface enclosures and radiation shields.

  11. Transient and two-dimensional conduction

    How bodies heat up and cool down: the Biot and Fourier numbers, lumped capacitance, the one-term solution for thick bodies, the semi-infinite solid, and steady two-dimensional conduction with shape factors.

  12. Applications, sustainability and case studies

    The rate laws at work in real equipment: electronics cooling, insulation and its energy and carbon savings, heat recovery, solar heating, heat pipes and thermal storage, ending with a multi-step design case.

SKU 6.2 · Thermal systems

  1. Types of heat exchangers and the overall coefficient

    How heat exchangers are classified by construction, flow arrangement and duty, and how the overall heat-transfer coefficient U is built from the resistances between the two fluids, including fouling.

  2. Designing a heat exchanger: the LMTD method

    Why the mean temperature difference in an exchanger is logarithmic, how counterflow and parallel flow compare, and the sizing procedure: duty, outlet temperatures, LMTD, correction factor, area.

  3. Rating a heat exchanger: the effectiveness–NTU method

    The effectiveness–NTU method predicts outlet temperatures and heat rate of a given exchanger without trial and error, shows why counterflow wins and where extra area stops paying.

  4. Vapour-compression refrigeration and heat pumps

    The thermodynamics behind every refrigerator, air conditioner and heat pump: the four components, the cycle on the pressure–enthalpy diagram, COP and capacity.

  5. Refrigerants, cycle improvements and multistage systems

    How refrigerants are chosen, and how subcooling, liquid–suction heat exchange, two-stage compression with a flash chamber, cascades and multi-evaporator systems improve on the simple cycle.

  6. Moist air and psychrometric processes

    Humidity ratio, relative humidity, dew point, wet-bulb temperature and enthalpy of moist air, and the air-conditioning processes drawn on the psychrometric chart: heating, cooling, humidifying, dehumidifying, mixing and the cooling coil.

  7. Air-conditioning systems, cooling loads and equipment selection

    The main types of air-conditioning system and their components, how a building cooling and heating load is built up (CLTD/SCL/CLF), the sensible heat factors, and how the load turns into supply air, coil load, tonnage and equipment.

  8. Fluid mechanics for turbomachines: conservation laws, similarity and the Euler equation

    The fluid properties, conservation laws and dimensionless groups that pumps, fans and turbines are built on, and the Euler equation that turns blade velocities into head.

  9. Centrifugal pumps, axial pumps and fans

    How pumps and fans are built and rated, where a pump operates on a pipe system, how to avoid cavitation, and how specific speed picks a centrifugal or an axial machine.

  10. Hydraulic turbines and gas turbines

    Hydropower and the choice between Pelton, Francis and Kaplan turbines, the Pelton wheel analysis, turbine performance, and the gas-turbine (Brayton) plant with regeneration.

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