Heat and Mass Transfer MCQs 2026

Shell-and-tube heat exchanger baffles serve to

1. A block all flow completely ✓
2. B reduce heat transfer area intentionally as primary purpose ✓
3. C increase shell-side turbulence and heat transfer ✓
4. D measure viscosity only ✓

Parallel flow heat exchanger LMTD is

1. A always larger than counterflow LMTD always ✓
2. B zero always ✓
3. C generally smaller than counterflow for same inlet outlet states ✓
4. D independent of inlet outlet temperatures ✓

Heat exchanger effectiveness ε is defined as

1. A LMTD divided by UA as effectiveness definition ✓
2. B UA divided by C_min alone always as effectiveness ✓
3. C actual heat transfer divided by maximum possible heat transfer ✓
4. D pressure drop ratio as effectiveness ✓

Fourier number Fo is

1. A α t / L² ✓
2. B h L / k which is Bi labeled as Fo ✓
3. C k / h L as Fo ✓
4. D ρ v L / μ which is Re as Fo ✓

Heisler charts are used for

1. A transient heat conduction in solids with convection boundary ✓
2. B fatigue S-N curves ✓
3. C steam tables only as Heisler charts purpose ✓
4. D Mohr circle ✓

Transient conduction in semi-infinite solid with sudden surface temperature uses

1. A error function solution ✓
2. B Euler buckling formula ✓
3. C Mohr circle ✓
4. D Rankine formula ✓

Chilton-Colburn j-factor relates

1. A stress and strain ✓
2. B pressure and velocity as j-factor primary ✓
3. C heat and mass transfer coefficients dimensionlessly ✓
4. D entropy and enthalpy as j-factor ✓

Evaporation rate from liquid surface increases with

1. A higher air velocity and lower ambient vapor concentration ✓
2. B lower temperature difference always reducing driving force as increase always ✓
3. C zero concentration difference always beneficial ✓
4. D infinite humidity always beneficial ✓

Lewis number Le is ratio of

1. A mass to thermal diffusivity as Le definition if reversed ✓
2. B Re to Pr as Le ✓
3. C thermal diffusivity to mass diffusivity ✓
4. D Nu to Sh always as Le ✓

Schmidt number Sc equals

1. A ν / D ✓
2. B D / ν as Sc ✓
3. C α / k as Sc ✓
4. D h / k as Sc ✓

Sherwood number Sh is analogous to

1. A Reynolds only as Sherwood analog alone ✓
2. B Euler number as Sherwood analog ✓
3. C Weber number as Sherwood analog ✓
4. D Nusselt number for mass transfer ✓

Mass diffusivity D has units similar to

1. A dynamic viscosity μ only as D units similarity context ✓
2. B thermal diffusivity α ✓
3. C thermal conductivity k only ✓
4. D heat transfer coefficient h only ✓

Fick's first law of diffusion states mass flux is proportional to

1. A negative concentration gradient ✓
2. B positive concentration gradient only always ✓
3. C temperature gradient only as Fick first law ✓
4. D pressure gradient only as Fick first law ✓

Wien's displacement law states λ_max T equals

1. A σ T⁴ as Wien law ✓
2. B k ΔT as Wien law ✓
3. C h L/k as Wien law ✓
4. D constant approximately 2898 μm·K ✓

Kirchhoff's law for radiation at thermal equilibrium relates

1. A reflectivity and transmissivity only always as Kirchhoff primary alone ✓
2. B h and k always ✓
3. C emissivity and absorptivity for a surface ✓
4. D Nu and Re always ✓

Stefan-Boltzmann constant σ appears in

1. A Fourier conduction law only ✓
2. B radiation heat transfer calculations ✓
3. C Newton viscosity law only ✓
4. D Hooke law only ✓

Natural convection heat transfer depends strongly on

1. A only forced velocity always required for natural convection primary ✓
2. B Mach number primarily for natural convection ✓
3. C Froude number primarily for natural convection ✓
4. D Grashof and Prandtl numbers ✓

Grashof number in natural convection is analogous to

1. A Prandtl number as Gr analog ✓
2. B Nusselt number as Gr analog ✓
3. C Reynolds number with buoyancy driving force replacing inertia ✓
4. D Peclet number as Gr analog ✓

Greenhouse effect analogy in heat transfer refers to

1. A Fick law only as greenhouse analogy primary ✓
2. B transparent cover transmitting shortwave and blocking longwave radiation ✓
3. C Darcy law only ✓
4. D Hooke law only ✓

Solar collector efficiency involves

1. A absorbed radiation minus losses by convection and radiation ✓
2. B only Fourier conduction in insulation as sole efficiency factor alone ✓
3. C only bolt preload ✓
4. D only torsion in shaft ✓

Cooling tower performance depends on

1. A only conduction through concrete shell as performance primary alone ✓
2. B only nuclear fission ✓
3. C evaporative heat and mass transfer between water and air ✓
4. D only beam bending ✓

Distillation column separation relies on

1. A difference in volatility causing mass transfer between phases ✓
2. B only conduction through metal tray as separation mechanism primary alone ✓
3. C only radiation between trays ✓
4. D only centrifugal force as distillation mechanism ✓

Adsorption mass transfer at surface differs from absorption by

1. A both identical always ✓
2. B accumulation on surface vs penetration into bulk phase ✓
3. C adsorption always in bulk only ✓
4. D absorption always surface only reversed always ✓

Knudsen number important in mass transfer indicates

1. A transition between continuum and molecular flow regimes ✓
2. B turbulent vs laminar heat transfer only as Knudsen meaning alone always ✓
3. C elastic vs plastic stress only ✓
4. D subsonic vs supersonic only as Knudsen ✓

Dryer design uses

1. A only Rankine cycle analysis as dryer design primary tool alone ✓
2. B heat and mass transfer to remove moisture from solids ✓
3. C only Mohr circle ✓
4. D only belt friction ✓

Humidification involves simultaneous

1. A heat and mass transfer at air-water interface ✓
2. B only conduction in steel wall as humidification primary ✓
3. C only torsion in shaft ✓
4. D only buckling in column ✓

Mass convection over flat plate analog to heat transfer uses

1. A only Darcy law as mass convection model primary ✓
2. B only Euler column formula ✓
3. C only Mohr circle ✓
4. D similar boundary layer equations with concentration instead of temperature ✓

Recovery factor relates

1. A fin efficiency labeled as recovery factor ✓
2. B heat exchanger effectiveness labeled as recovery factor ✓
3. C bolt tightening factor labeled as recovery factor ✓
4. D actual recovery of kinetic energy to total enthalpy in boundary layer ✓

Stagnation temperature in high-speed flow includes

1. A only radiation temperature as stagnation T components alone ✓
2. B only wet bulb ✓
3. C static temperature plus kinetic energy contribution converted to enthalpy ✓
4. D only dew point as stagnation T ✓

Gray body reflects radiation such that for opaque surface

1. A ε + k = 1 mixing emissivity and conductivity ✓
2. B h + k = 1 ✓
3. C Nu + Pr = 1 ✓
4. D α + ρ = 1 ✓

Radiation shield between two surfaces reduces

1. A conduction through vacuum always increases as shield effect primary ✓
2. B mass diffusivity always increases as shield effect ✓
3. C Reynolds number always increases as shield effect ✓
4. D net radiant heat exchange ✓

Nucleate boiling heat flux increases rapidly with

1. A decreasing wall temperature below saturation as increase flux always ✓
2. B superheat ΔT_excess ✓
3. C zero pressure always beneficial alone ✓
4. D infinite thermal conductivity of vapor alone ✓

Pool boiling critical heat flux (CHF) marks

1. A onset of conduction only as CHF ✓
2. B start of freezing ✓
3. C transition from efficient nucleate boiling to film boiling regime ✓
4. D laminar flow inception as CHF ✓

Dropwise condensation compared to filmwise generally gives

1. A lower coefficient always ✓
2. B same coefficient always ✓
3. C higher heat transfer coefficient ✓
4. D zero heat transfer ✓

Condensation heat transfer on vertical plate often uses

1. A Fourier law alone without convection as condensation model primary ✓
2. B Nusselt film condensation theory ✓
3. C Darcy law ✓
4. D Bernoulli only as condensation ✓

Fourier's law of heat conduction states that heat flux is proportional to

1. A positive temperature gradient only always ✓
2. B pressure gradient ✓
3. C negative temperature gradient ✓
4. D velocity gradient ✓

Thermal conductivity k has SI units

1. A J/kg ✓
2. B W/(m·K) ✓
3. C Pa·s ✓
4. D W/m² ✓

Steady one-dimensional conduction through plane wall is

1. A Q = h A ΔT only without conduction path ✓
2. B Q = σ A ΔT/L ✓
3. C Q = m cp ΔT only as conduction through wall ✓
4. D Q = k A ΔT / L ✓

Thermal resistance of conduction layer is

1. A k A / L ✓
2. B L / (k A) ✓
3. C h A only ✓
4. D 1/(h A) which is convection resistance ✓

Composite wall in series has total thermal resistance

1. A product of resistances ✓
2. B always zero ✓
3. C equal to smallest layer only ✓
4. D sum of individual layer resistances ✓

Newton's law of cooling for convection is

1. A q″ = k dT/dx only always as convection law ✓
2. B q″ = σ T⁴ only as convection ✓
3. C q″ = h (T_s − T_∞) ✓
4. D q″ = D dC/dx only as convection ✓

Nusselt number Nu is defined as

1. A h L / k ✓
2. B k / h L ✓
3. C ρ v L / μ which is Reynolds ✓
4. D μ cp / k which is Prandtl ✓

Prandtl number Pr equals

1. A α / ν ✓
2. B ν / α or μ cp / k ✓
3. C h L / k which is Nusselt ✓
4. D g β ΔT L³/ν² which is Grashof ✓

Reynolds number in forced convection characterizes

1. A radiation to conduction ratio ✓
2. B ratio of inertial to viscous forces ✓
3. C mass diffusivity to thermal diffusivity as Re ✓
4. D surface tension effects only always as Re ✓

Stefan-Boltzmann law for gray surface gives emitted power per area as

1. A ε σ T⁴ ✓
2. B σ T only linear ✓
3. C k ΔT only ✓
4. D h ΔT only as radiation law ✓

Emissivity ε of real surface is

1. A always equal to 1 for all materials ✓
2. B ratio of surface emissive power to blackbody emissive power at same T ✓
3. C ratio of absorptivity to reflectivity always as definition of ε alone ✓
4. D always zero for metals ✓

View factor F_12 between two surfaces represents

1. A conductive heat flux fraction ✓
2. B convective coefficient ratio ✓
3. C mass transfer coefficient ✓
4. D fraction of radiation leaving surface 1 intercepted by surface 2 ✓

Radiation heat exchange between large parallel gray plates includes factor

1. A 1/(1/ε1 + 1/ε2 − 1) multiplying σ A (T1⁴ − T2⁴) ✓
2. B h ΔT only ✓
3. C k/L only ✓
4. D D/L only as radiation exchange ✓

Fin effectiveness increases with

1. A higher convection coefficient and higher fin thermal conductivity ✓
2. B lower k always beneficial ✓
3. C zero surface area always beneficial ✓
4. D infinite length always without diminishing returns ✓

Fin efficiency compares

1. A actual heat transferred by fin to heat if entire fin at base temperature ✓
2. B fin cost to weight only ✓
3. C Reynolds to Prandtl only without fin context ✓
4. D LMTD to NTU only as fin efficiency ✓

Infinite fin heat transfer rate for uniform h and k is

1. A Q = h A only without fin geometry ✓
2. B Q = k A/L only as infinite fin ✓
3. C Q = √(h P k A_c) (T_b − T_∞) ✓
4. D Q = σ T⁴ only as fin law ✓

Biot number Bi is defined as

1. A k / h L_c ✓
2. B h L_c / k ✓
3. C h L / ρ v cp ✓
4. D D / ν as Bi ✓

Lumped capacitance method valid when Bi is

1. A less than about 0.1 ✓
2. B greater than 10 always as lumped criterion ✓
3. C equal to Reynolds number ✓
4. D infinite always required ✓

LMTD for counter-flow heat exchanger uses

1. A arithmetic mean always without log as LMTD ✓
2. B maximum difference only always as LMTD ✓
3. C minimum difference only always as LMTD ✓
4. D log mean of hot and cold end temperature differences ✓

NTU method in heat exchangers relates

1. A only pressure drop in pipes alone as NTU method scope ✓
2. B only radiation view factors ✓
3. C size (UA) and heat capacity rates to effectiveness ✓
4. D only Fick diffusion only as NTU ✓

Overall heat transfer coefficient U in plane wall includes

1. A only radiation always alone without convection conduction ✓
2. B conduction and convection resistances in series ✓
3. C only mass transfer coefficient ✓
4. D only Darcy friction factor ✓

Critical radius of insulation for cylinder occurs when

1. A Bi = 0 always as critical radius condition ✓
2. B Bi = 1 for cylinder definition r_c = k/h ✓
3. C Re = 2300 always ✓
4. D Pr = 0.7 always as critical radius ✓

Electrical analogy for conduction uses

1. A pressure as heat flow always in analogy ✓
2. B velocity as temperature ✓
3. C temperature difference as driving force and heat flow as current ✓
4. D mass flux as voltage ✓

Contact resistance between two solids increases with

1. A perfectly smooth surfaces always as increase contact R always ✓
2. B higher pressure always increases contact R ✓
3. C higher k always increases contact R ✓
4. D surface roughness and lower contact pressure ✓

Heat pipe transfers heat effectively by

1. A solid conduction only through vacuum as heat pipe mechanism ✓
2. B evaporation and condensation of working fluid in closed cycle ✓
3. C radiation only through vacuum as primary mechanism alone ✓
4. D forced air only without phase change as heat pipe ✓

Thermal boundary layer thickness grows along flat plate because

1. A radiation only at leading edge as sole cause ✓
2. B phase change only ✓
3. C mass diffusion only as thermal BL growth cause alone ✓
4. D momentum and thermal diffusion from wall ✓

Dittus-Boelter equation estimates Nu for

1. A turbulent flow in smooth tubes ✓
2. B laminar tube flow always as Dittus-Boelter primary regime ✓
3. C natural convection on vertical plate always as Dittus-Boelter primary ✓
4. D radiation between plates always as Dittus-Boelter ✓

For laminar fully developed flow in circular tube with constant heat flux, Nu equals

1. A 0.023 Re^0.8 Pr^n which is turbulent correlation for laminar fully developed ✓
2. B 4.36 ✓
3. C 3.66 for constant wall temperature case confused ✓
4. D 1.0 always ✓

Log-mean temperature difference correction factor F for shells is used when

1. A Bi < 0.1 only as F factor purpose ✓
2. B radiation only as F factor purpose ✓
3. C mass transfer only as F factor purpose ✓
4. D flow arrangement deviates from true counterflow or multipass ✓

Countercurrent flow heat exchanger achieves

1. A always lower effectiveness always compared to parallel ✓
2. B same effectiveness always regardless of arrangement ✓
3. C zero heat transfer ✓
4. D higher effectiveness than parallel flow for same UA generally ✓

Mass transfer coefficient k_m relates

1. A heat flux to temperature difference only as k_m definition ✓
2. B momentum flux to velocity gradient only as k_m ✓
3. C pressure drop to flow rate only as k_m ✓
4. D mass flux to concentration difference ✓

Equimolar counter-diffusion in gases has molar flux proportional to

1. A temperature gradient only as equimolar diffusion driving force alone ✓
2. B pressure squared only alone always ✓
3. C concentration gradient and inversely to thickness ✓
4. D velocity cubed ✓

Molecular diffusion in solids is generally

1. A much slower than in gases ✓
2. B faster than gases always ✓
3. C identical rate always ✓
4. D independent of temperature always ✓

Turbulent eddy diffusivity enhances

1. A only laminar sublayer without effect always ✓
2. B both heat and mass transfer in turbulent flow ✓
3. C only radiation ✓
4. D only conduction in solids as turbulent eddy effect ✓

Peclet number Pe equals

1. A Re × Pr or v L / α ✓
2. B Nu × Pr as Pe always ✓
3. C Gr × Pr which is Rayleigh labeled as Pe ✓
4. D Sh × Sc labeled as Pe ✓

Rayleigh number Ra equals

1. A Re × Pr which is Peclet labeled as Ra ✓
2. B Nu × Pr labeled as Ra ✓
3. C Sh × Sc labeled as Ra ✓
4. D Gr × Pr ✓

Stanton number St relates

1. A only mass diffusivity as St primary alone ✓
2. B only radiation emissivity as St ✓
3. C heat transfer coefficient to flow properties in dimensionless form ✓
4. D only fin efficiency as St ✓

Colburn analogy gives relation between

1. A stress and strain in solids as Colburn analogy scope ✓
2. B entropy and enthalpy as Colburn analogy scope ✓
3. C bolt preload and torque only as Colburn analogy scope ✓
4. D Stanton and friction factor f/2 for similar transfer mechanisms ✓

Thermal diffusivity α equals

1. A ρ cp / k as α definition ✓
2. B k cp / ρ ✓
3. C h / k as α ✓
4. D k / (ρ cp) ✓

Insulation purpose on hot pipe is to

1. A increase heat loss always as insulation purpose ✓
2. B increase pipe stress only as primary purpose ✓
3. C measure flow rate only ✓
4. D reduce heat loss to surroundings ✓

Extended surface (fin) material should have

1. A high thermal conductivity ✓
2. B low conductivity always beneficial for fin material choice ✓
3. C zero conductivity ideally ✓
4. D low density only without conductivity consideration alone always as sole criterion ✓

Adiabatic tip fin boundary condition means

1. A fixed temperature at tip always as adiabatic condition ✓
2. B zero heat flux at tip ✓
3. C infinite convection at tip as adiabatic ✓
4. D constant heat generation at tip as adiabatic ✓

Heat generation in solid modifies conduction equation by adding

1. A only convection term as sole modification always ✓
2. B radiation only as sole modification ✓
3. C q_gen term to energy balance ✓
4. D mass flux only as sole modification in conduction eqn ✓

Two-dimensional conduction shape factor S is used when

1. A only turbulent pipe flow as shape factor use case ✓
2. B only radiation view factors conflated always ✓
3. C analytical series solutions cumbersome for complex geometries ✓
4. D only fatigue analysis ✓

Hydrodynamic and thermal entry lengths in tube flow differ because

1. A Reynolds alone makes them identical always ✓
2. B Prandtl number affects thermal development rate ✓
3. C pressure alone determines both equally ✓
4. D roughness alone determines both equally ✓