100 MCQ's Heat Transfer Dive into the world of Heat Transfer with this fun and educational 100 MCQ Quiz!Test your knowledge of conduction, convection, radiation, and heat exchangers — the core topics that power every thermal system. Perfect for mechanical engineering students to strengthen fundamentals, prepare for exams, or just challenge their thermal logic in an interactive way. 1 / 100 Radiation heat transfer dominates at High temperature Low temperature Medium temperature Zero temperature difference At high temperatures, radiative effects become more significant than conduction or convection. 2 / 100 When two surfaces have same temperature and emissivity, the net radiation between them is Zero Maximum Minimum Constant No temperature difference means no net heat exchange. 3 / 100 The ratio of radiative heat flux from a surface to that from a black body at same temperature is Emissivity Absorptivity Reflectivity Shape factor Emissivity represents actual radiation relative to black body. 4 / 100 Radiation shields are used to Enhance reflection Reduce heat transfer Increase emissivity Increase temperature Shields minimize radiation exchange by lowering view factor. 5 / 100 According to Wien’s law, the product of wavelength and temperature is Zero Inversely proportional Directly proportional Constant λmaxT=Constant 6 / 100 The wavelength corresponding to maximum emissive power is given by Newton’s Law Kirchhoff’s Law Wien’s Law Fourier’s Law Wien’s law relates temperature and wavelength of peak emission. 7 / 100 A grey body is one which Reflects all incident radiation Absorbs all radiation Does not emit any radiation Has emissivity less than one but constant Grey body emits a fixed fraction of black body radiation at all wavelengths. 8 / 100 The radiation emitted per unit area of a black body is proportional to Square of temperature Temperature difference Inverse of temperature Fourth power of absolute temperature 9 / 100 The emissivity of polished surfaces is generally Low High Equal to one Constant Smooth and shiny surfaces reflect more and emit less heat. 10 / 100 Radiation heat transfer does not require Solid body Liquid Gas Any medium Radiation can occur in vacuum, unlike conduction or convection. 11 / 100 The net radiation heat exchange between two bodies depends on Their temperatures and emissivity's Their densities Only surface area Only distance Heat exchange rate is determined by temperature difference and surface properties. 12 / 100 The shape factor is also known as View factor Radiation angle Transmission ratio Reflectivity It defines the fraction of radiation leaving one surface that strikes another. 13 / 100 Kirchhoff’s law of radiation states that Emissivity is always zero Good absorbers are good emitters Good conductors are bad emitters Radiation is independent of temperature Absorptivity equals emissivity for a body in thermal equilibrium. 14 / 100 The Stefan–Boltzmann constant value is approximately 1.23 × 10⁻⁶ W/m²·K 5.67 × 10⁻⁸ W/m²·K⁴ 6.62 × 10⁻³ J/m²·K 9.81 × 10⁻⁵ W/m²·K² It’s the proportionality constant in Stefan–Boltzmann law. 15 / 100 Stefan–Boltzmann law gives the relation between Emissive power and temperature Conductivity and area Convection coefficient and velocity Pressure and density It states that total emissive power ∝ T⁴. 16 / 100 The emissivity of a perfect black body is 0 0.5 0.9 1 A black body has maximum emissivity value of one. 17 / 100 A perfect black body absorbs No radiation Only visible light Only infrared rays All incident radiation A black body absorbs 100% of the radiation falling on it. 18 / 100 The unit of emissive power is W/m³ W/m² W/m·K J/m²·s It measures energy emitted per unit area per second. 19 / 100 The speed of thermal radiation is equal to Depends on temperature Twice the speed of light Speed of sound Speed of light Radiation energy travels at the same speed as light in vacuum. 20 / 100 Thermal radiation is the transmission of heat through Electromagnetic waves Conduction Convection Physical contact Radiation transfers heat without any medium via electromagnetic waves. 21 / 100 In a double-pipe heat exchanger, heat transfer is mainly by Conduction and convection Only conduction Only radiation Convection and radiation Heat passes through pipe walls by conduction and by convection in fluids. 22 / 100 The effectiveness of a parallel flow heat exchanger is always Zero Equal to counter flow More than counter flow Less than counter flow Counter flow allows larger temperature difference and higher effectiveness. 23 / 100 Increasing flow velocity in a heat exchanger Has no effect Increases fouling Increases heat transfer coefficient Decreases heat transfer coefficient Higher velocity improves turbulence, enhancing convection. 24 / 100 The ratio of actual heat transfer to maximum possible heat transfer is Effectiveness Efficiency Conductivity Capacity ratio It measures actual exchanger performance relative to ideal. 25 / 100 Fouling in a heat exchanger Decreases heat transfer Increases heat transfer Has no effect Reduces flow resistance Deposits form thermal resistance, lowering efficiency. 26 / 100 For two fluids with equal mass flow rate and specific heat, the temperature change will be Equal Zero Double for cold fluid Half for hot fluid Equal capacities result in equal temperature changes. 27 / 100 Fins are used in heat exchangers to Reduce turbulence Increase thermal resistance Increase heat transfer area Decrease heat transfer rate Fins enlarge the area for better convection heat transfer. 28 / 100 A regenerative heat exchanger works by Changing phase Storing heat temporarily Using cooling water Mixing both fluids It stores heat from hot fluid and releases it to cold fluid alternately 29 / 100 The value of overall heat transfer coefficient is highest for Free convection Radiation Condensation Convection Condensation offers very high film coefficients leading to large U values. 30 / 100 In a shell-and-tube heat exchanger, baffles are used to Support the tubes only Reduce heat transfer Guide fluid in straight path Increase turbulence and heat transfer Baffles improve fluid mixing and enhance heat transfer rates 31 / 100 The overall heat transfer coefficient depends on Individual film coefficients and wall resistance Flow rate only Temperature only Density of fluids U is influenced by convection, conduction, and fouling resistances. 32 / 100 NTU stands for Normal Thermal Unit Number of Transfer Units Nominal Transfer Utility Net Transfer Usage NTU indicates the size and performance capability of a heat exchanger. 33 / 100 The effectiveness of a heat exchanger depends on NTU and capacity ratio Only mass flow rate Only temperature Only material Effectiveness increases with NTU and depends on heat capacity rates of fluids. 34 / 100 In a counter flow heat exchanger, LMTD is Zero Equal to parallel flow Less than parallel flow Greater than parallel flow Counter flow arrangement has higher temperature difference, improving efficiency. 35 / 100 The unit of overall heat transfer coefficient (U) is W/m²·K W/m·K W/m³·K J/m²·s It represents total heat transfer per unit area per unit temperature difference. 36 / 100 The Log Mean Temperature Difference (LMTD) is used to calculate Velocity of fluid Rate of heat transfer Mass flow rate Fluid pressure LMTD represents the average driving temperature difference across the exchanger. 37 / 100 The performance of a heat exchanger is usually measured by Effectiveness Pressure drop Temperature difference Flow velocity Effectiveness shows how well a heat exchanger transfers heat. 38 / 100 In a counter flow heat exchanger, the fluids move In circular paths In opposite directions In the same direction Perpendicular to each other Counter flow gives maximum temperature difference and efficiency. 39 / 100 In a parallel flow heat exchanger, both fluids Flow in opposite directions Remain stationary Flow perpendicular Flow in the same direction In parallel flow, hot and cold fluids move parallel and in the same direction. 40 / 100 The main function of a heat exchanger is to Transfer heat between two fluids Store heat energy Increase pressure of fluid Reduce fluid friction A heat exchanger allows thermal energy transfer without mixing fluids. 41 / 100 In radiation heat transfer, the primary mode of energy transmission is Electromagnetic Waves Molecular Collision Conduction Convection Currents Radiation transmits energy via electromagnetic waves, independent of medium 42 / 100 Surfaces with high absorptivity also have Low Emissivity High Reflectivity High Emissivity Low Reflectivity As per Kirchhoff’s law, good absorbers are good emitters 43 / 100 The total emissive power of a black body at 300 K is proportional to (300)⁴ (300)³ (300)² (300) Emissive power is proportional to the fourth power of absolute temperature 44 / 100 The unit of Stefan–Boltzmann constant is W/m·K W/m²·K J/m³·K W/m²·K⁴ It represents the proportionality constant in the Stefan–Boltzmann equation. 45 / 100 Radiation shape factor between a surface and itself is Zero One Infinity Depends On Area A surface cannot radiate energy to itself, hence its view factor is zero. 46 / 100 The emissivity of polished aluminum is Low High Equal To 1 Greater Than 1 Polished metals reflect most radiation, so emissivity is low. 47 / 100 A surface which absorbs all incident radiation is called Black Body White Body Opaque Body Gray Body A black body absorbs 100% of radiation falling on it. 48 / 100 The net radiation heat exchange between two parallel plates is proportional to T₁ - T₂ T₁² - T₂² T₁³ - T₂³ T₁⁴ - T₂⁴ According to Stefan–Boltzmann law, heat transfer varies with the difference of fourth powers of temperatures. 49 / 100 Radiation exchange between two bodies depends mainly on Density Specific Heat Pressure View Factor The view factor (or shape factor) indicates the fraction of energy leaving one surface that strikes another. 50 / 100 A Gray body is defined as one which Reflects All Radiation Absorbs All Incident Radiation Has Constant Emissivity For All Wavelengths Has Zero Absorptivity Gray bodies have same emissivity for all wavelengths but less than unity. 51 / 100 The radiosity of a surface includes Emitted And Reflected Energy Only Emitted Energy Only Reflected Energy Absorbed Energy Radiosity is the total radiation leaving a surface, both emitted and reflected. 52 / 100 The sun’s radiation reaches the earth mainly by Radiation Convection Conduction Reflection Space has no medium, so radiation is the only mode of heat transfer. 53 / 100 The wavelength corresponding to maximum emissive power is given by Kirchhoff’s Law Newton’s Cooling Law Pascal’s Law Wien’s Law Wien’s law relates peak wavelength to absolute temperature (λₘ·T = constant). 54 / 100 Radiation intensity depends on Specific Heat Temperature And Nature Of Surface Thickness Of Material Velocity Of Fluid Smooth, polished, and lighter surfaces emit less radiation than rough or dark ones. 55 / 100 The absorptivity and emissivity of a body are equal according to Planck’s Law Newton’s Law Kirchhoff’s Law Stefan–Boltzmann Law Kirchhoff’s law states that good absorbers are also good emitters at the same temperature. 56 / 100 A perfect reflector has emissivity equal to 1 0.9 0.5 0 Reflectors emit no radiation; thus, emissivity is zero. 57 / 100 The emissivity of a perfect black body is 1 0 Between 0 And 1 Greater Than 1 A black body emits maximum possible radiation, hence emissivity = 1. 58 / 100 The unit of emissive power is J/kg·K W/m²·K W/m² W/m·K It represents energy emitted per unit area per second. 59 / 100 The energy radiated per unit area is governed by Fourier’s Law Newton’s Law Pascal’s Law Stefan–Boltzmann Law The Stefan–Boltzmann law states that radiated energy is proportional to the fourth power of absolute temperature. 60 / 100 Heat transfer by radiation requires No Medium A Solid Medium A Liquid Medium A Gas Medium Radiation can occur even in a vacuum, unlike conduction and convection. 61 / 100 The local heat transfer coefficient is highest At The Trailing Edge At The Leading Edge Of A Flat Plate Midway Independent Of Position Near the leading edge, temperature gradient is steepest, increasing heat flux. 62 / 100 The boundary layer thickness grows Against Flow Along The Flow Direction On A Plate Independent Of Flow Decreases With Distance As fluid travels, more of it is affected by surface friction, thickening the layer 63 / 100 Dropwise condensation provides Higher Heat Transfer Rate Lower Heat Transfer Same As Film No Transfer Droplets expose more surface area, increasing heat flux. 64 / 100 Film condensation occurs when Vapor Remains Static Boiling Starts Condensate Forms A Continuous Liquid Film Droplets Form On Surface Continuous liquid film creates resistance to heat transfer. 65 / 100 Boiling and condensation are examples of Phase Change Convection Radiation Pure Conduction Steady State Transfer Heat transfer occurs during change of state with latent heat involvement 66 / 100 The film coefficient of heat transfer increases with Fluid Velocity And Turbulence Surface Roughness Alone Temperature Decrease Low Pressure Faster fluid motion improves heat transfer between surface and fluid 67 / 100 The Grashof number relates Heat Transfer To Velocity Reynolds To Prandtl Density To Conductivity Buoyancy To Viscous Forces It determines the significance of natural convection effects 68 / 100 Natural convection strongly depends on Velocity Gradient Temperature Difference And Gravity Pressure Only Density Only Buoyancy due to temperature differences drives motion in natural convection. 69 / 100 In turbulent flow, the heat transfer coefficient is Higher Than Laminar Flow Same As Laminar Lower Zero Mixing in turbulence increases temperature uniformity and enhances heat transfer. 70 / 100 Reynolds number helps determine Type Of Flow Amount Of Heat Transfer Heat Capacity Thermal Conductivity It predicts laminar or turbulent flow regime in a fluid. 71 / 100 When Prandtl number is small, it indicates Low Thermal Diffusivity High Viscosity Poor Conductivity High Thermal Diffusivity The smaller the Pr, the faster heat diffuses compared to momentum. 72 / 100 For gases, the Prandtl number is approximately 0.7 1.5 2.0 10.0 Gases generally have Pr ≈ 0.7 because heat and momentum diffuse similarly. 73 / 100 The Prandtl number is the ratio of Specific Heat To Viscosity Density To Viscosity Momentum Diffusivity To Thermal Diffusivity Thermal Conductivity To Density It shows how momentum and heat spread through a fluid 74 / 100 In laminar flow over a flat plate, Nusselt number depends on Viscosity Alone Reynolds And Prandtl Numbers Only Temperature Plate Length Both flow type and fluid properties influence convective performance. 75 / 100 The Nusselt number represents the ratio of Convective To Conductive Heat Transfer Viscous To Buoyant Forces Conductive To Convective Kinetic To Potential Energy It indicates the effectiveness of convection compared to conduction. 76 / 100 Free (natural) convection occurs due to Chemical Reaction Radiation External Mechanical Devices Density Differences Caused By Temperature Variation Buoyancy forces move the fluid in natural convection. 77 / 100 Forced convection occurs when Fluid Motion Is Induced By External Means Fluid Is Stationary Buoyancy Acts Alone Conduction Is Dominant Fans, pumps, or blowers drive the flow in forced convection. 78 / 100 The unit of heat transfer coefficient is W/m·K J/kg·K W/m²·K J/m·s·K It defines the amount of heat transferred per square meter per degree temperature difference. 79 / 100 Newton’s law of cooling relates heat transfer rate with Temperature Difference Heat Capacity Specific Heat Density The rate of convective heat transfer is proportional to the temperature difference between surface and fluid. 80 / 100 Convection is the mode of heat transfer that occurs through solid medium stationary fluid moving fluid radiation Convection happens when fluid particles move and carry heat energy with them. 81 / 100 The concept of thermal circuit is similar to Fluid mechanics Structural analysis Electrical circuit Magnetic field Like voltage and current, temperature and heat flow obey similar resistance principles. 82 / 100 When thermal contact resistance increases, overall heat transfer rate Becomes zero Remains same Increases Decreases Higher resistance limits heat flow at the interface. 83 / 100 The heat flow through a cylinder is proportional to ln(r₂ / r₁) (r₂ - r₁) 1 / (r₂ - r₁) r₂² - r₁² Logarithmic relation appears in cylindrical conduction formula. 84 / 100 For a plane wall, heat transfer per unit area is k (ΔT / L) kL / ΔT L / (kΔT) ΔT / kL Derived from Fourier’s law for one-dimensional steady conduction. 85 / 100 Steady-state conduction assumes Constant temperature at every point over time Constant heat source Variable conductivity Zero temperature gradient Heat flow and temperature profile remain unchanged with time. 86 / 100 For good insulating materials, thermal diffusivity should be High Zero Low Infinite Low diffusivity means slower heat penetration. 87 / 100 The unit of thermal diffusivity is W/m·K J/kg·K W/m² m²/s It shows area per time, representing how fast temperature changes. 88 / 100 Thermal diffusivity is defined as Cp / ρ k·ρ·Cp ρ·Cp / k k / (ρ·Cp) It indicates how quickly heat spreads through a material. 89 / 100 If the thickness of a wall is doubled, the heat transfer rate becomes Half Double Same Four times Heat transfer is inversely proportional to thickness. 90 / 100 In a composite wall with layers in series, total thermal resistance is Difference of resistances Sum of individual resistances Product of resistances Average of resistances Resistances in series add up to give total opposition to heat flow. 91 / 100 The thermal resistance of a slab is given by L / (kA) kA / L 1 / (kA) A / L Higher thickness or lower conductivity increases resistance. 92 / 100 In one-dimensional steady-state conduction, the temperature distribution is Linear Parabolic Cubic Random Temperature decreases uniformly across the slab. 93 / 100 In a composite wall, the heat flow rate is Different for each layer Highest in the outer layer Depends only on material Same through all layers Under steady conditions, heat rate remains constant through each layer. 94 / 100 Metals are good conductors because They have crystalline structure They have free electrons They have low density They have high specific heat Free electrons carry energy rapidly through metals. 95 / 100 A perfect thermal insulator has Zero thermal conductivity High specific heat Infinite density High emissivity It doesn’t allow heat transfer by conduction. 96 / 100 The rate of heat conduction depends on Only the material used Only the temperature difference Only the thickness Area, temperature difference, material, and thickness Greater area and temperature difference increase heat flow. 97 / 100 In steady-state conduction, the temperature Does not change with time Increases linearly with time Decreases exponentially Varies irregularly In steady state, temperature remains constant over time. 98 / 100 The SI unit of thermal conductivity is J/m·s W/m·K J/kg·K W/m²·K It measures watts of heat conducted per meter per kelvin. 99 / 100 Thermal conductivity represents The heat stored in a material The resistance to heat flow The energy absorbed by radiation The ability of a material to conduct heat It defines how easily heat passes through a material. 100 / 100 The rate of heat transfer through a solid is governed by Fourier’s Law Newton’s Law of Cooling Pascal’s Law Stefan–Boltzmann Law Fourier’s Law states that heat flow is proportional to temperature gradient and area. 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