Heat and Mass Transfer MCQs 2026

Greenhouse effect analogy in heat transfer refers to

1. AFick law only as greenhouse analogy primary✓
2. Btransparent cover transmitting shortwave and blocking longwave radiation✓
3. CDarcy law only✓
4. DHooke law only✓

Solar collector efficiency involves

1. Aabsorbed radiation minus losses by convection and radiation✓
2. Bonly Fourier conduction in insulation as sole efficiency factor alone✓
3. Conly bolt preload✓
4. Donly torsion in shaft✓

Cooling tower performance depends on

1. Aonly conduction through concrete shell as performance primary alone✓
2. Bonly nuclear fission✓
3. Cevaporative heat and mass transfer between water and air✓
4. Donly beam bending✓

Distillation column separation relies on

1. Adifference in volatility causing mass transfer between phases✓
2. Bonly conduction through metal tray as separation mechanism primary alone✓
3. Conly radiation between trays✓
4. Donly centrifugal force as distillation mechanism✓

Adsorption mass transfer at surface differs from absorption by

1. Aboth identical always✓
2. Baccumulation on surface vs penetration into bulk phase✓
3. Cadsorption always in bulk only✓
4. Dabsorption always surface only reversed always✓

Knudsen number important in mass transfer indicates

1. Atransition between continuum and molecular flow regimes✓
2. Bturbulent vs laminar heat transfer only as Knudsen meaning alone always✓
3. Celastic vs plastic stress only✓
4. Dsubsonic vs supersonic only as Knudsen✓

Dryer design uses

1. Aonly Rankine cycle analysis as dryer design primary tool alone✓
2. Bheat and mass transfer to remove moisture from solids✓
3. Conly Mohr circle✓
4. Donly belt friction✓

Humidification involves simultaneous

1. Aheat and mass transfer at air-water interface✓
2. Bonly conduction in steel wall as humidification primary✓
3. Conly torsion in shaft✓
4. Donly buckling in column✓

Mass convection over flat plate analog to heat transfer uses

1. Aonly Darcy law as mass convection model primary✓
2. Bonly Euler column formula✓
3. Conly Mohr circle✓
4. Dsimilar boundary layer equations with concentration instead of temperature✓

Recovery factor relates

1. Afin efficiency labeled as recovery factor✓
2. Bheat exchanger effectiveness labeled as recovery factor✓
3. Cbolt tightening factor labeled as recovery factor✓
4. Dactual recovery of kinetic energy to total enthalpy in boundary layer✓

Stagnation temperature in high-speed flow includes

1. Aonly radiation temperature as stagnation T components alone✓
2. Bonly wet bulb✓
3. Cstatic temperature plus kinetic energy contribution converted to enthalpy✓
4. Donly dew point as stagnation T✓

Gray body reflects radiation such that for opaque surface

1. Aε + k = 1 mixing emissivity and conductivity✓
2. Bh + k = 1✓
3. CNu + Pr = 1✓
4. Dα + ρ = 1✓

Radiation shield between two surfaces reduces

1. Aconduction through vacuum always increases as shield effect primary✓
2. Bmass diffusivity always increases as shield effect✓
3. CReynolds number always increases as shield effect✓
4. Dnet radiant heat exchange✓

Nucleate boiling heat flux increases rapidly with

1. Adecreasing wall temperature below saturation as increase flux always✓
2. Bsuperheat ΔT_excess✓
3. Czero pressure always beneficial alone✓
4. Dinfinite thermal conductivity of vapor alone✓

Pool boiling critical heat flux (CHF) marks

1. Aonset of conduction only as CHF✓
2. Bstart of freezing✓
3. Ctransition from efficient nucleate boiling to film boiling regime✓
4. Dlaminar flow inception as CHF✓

Dropwise condensation compared to filmwise generally gives

1. Alower coefficient always✓
2. Bsame coefficient always✓
3. Chigher heat transfer coefficient✓
4. Dzero heat transfer✓

Condensation heat transfer on vertical plate often uses

1. AFourier law alone without convection as condensation model primary✓
2. BNusselt film condensation theory✓
3. CDarcy law✓
4. DBernoulli only as condensation✓

Shell-and-tube heat exchanger baffles serve to

1. Ablock all flow completely✓
2. Breduce heat transfer area intentionally as primary purpose✓
3. Cincrease shell-side turbulence and heat transfer✓
4. Dmeasure viscosity only✓

Parallel flow heat exchanger LMTD is

1. Aalways larger than counterflow LMTD always✓
2. Bzero always✓
3. Cgenerally smaller than counterflow for same inlet outlet states✓
4. Dindependent of inlet outlet temperatures✓

Heat exchanger effectiveness ε is defined as

1. ALMTD divided by UA as effectiveness definition✓
2. BUA divided by C_min alone always as effectiveness✓
3. Cactual heat transfer divided by maximum possible heat transfer✓
4. Dpressure drop ratio as effectiveness✓

Fourier number Fo is

1. Aα t / L²✓
2. Bh L / k which is Bi labeled as Fo✓
3. Ck / h L as Fo✓
4. Dρ v L / μ which is Re as Fo✓

Heisler charts are used for

1. Atransient heat conduction in solids with convection boundary✓
2. Bfatigue S-N curves✓
3. Csteam tables only as Heisler charts purpose✓
4. DMohr circle✓

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

1. Aerror function solution✓
2. BEuler buckling formula✓
3. CMohr circle✓
4. DRankine formula✓

Chilton-Colburn j-factor relates

1. Astress and strain✓
2. Bpressure and velocity as j-factor primary✓
3. Cheat and mass transfer coefficients dimensionlessly✓
4. Dentropy and enthalpy as j-factor✓

Evaporation rate from liquid surface increases with

1. Ahigher air velocity and lower ambient vapor concentration✓
2. Blower temperature difference always reducing driving force as increase always✓
3. Czero concentration difference always beneficial✓
4. Dinfinite humidity always beneficial✓

Lewis number Le is ratio of

1. Amass to thermal diffusivity as Le definition if reversed✓
2. BRe to Pr as Le✓
3. Cthermal diffusivity to mass diffusivity✓
4. DNu to Sh always as Le✓

Schmidt number Sc equals

1. Aν / D✓
2. BD / ν as Sc✓
3. Cα / k as Sc✓
4. Dh / k as Sc✓

Sherwood number Sh is analogous to

1. AReynolds only as Sherwood analog alone✓
2. BEuler number as Sherwood analog✓
3. CWeber number as Sherwood analog✓
4. DNusselt number for mass transfer✓

Mass diffusivity D has units similar to

1. Adynamic viscosity μ only as D units similarity context✓
2. Bthermal diffusivity α✓
3. Cthermal conductivity k only✓
4. Dheat transfer coefficient h only✓

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

1. Anegative concentration gradient✓
2. Bpositive concentration gradient only always✓
3. Ctemperature gradient only as Fick first law✓
4. Dpressure gradient only as Fick first law✓

Wien's displacement law states λ_max T equals

1. Aσ T⁴ as Wien law✓
2. Bk ΔT as Wien law✓
3. Ch L/k as Wien law✓
4. Dconstant approximately 2898 μm·K✓

Kirchhoff's law for radiation at thermal equilibrium relates

1. Areflectivity and transmissivity only always as Kirchhoff primary alone✓
2. Bh and k always✓
3. Cemissivity and absorptivity for a surface✓
4. DNu and Re always✓

Stefan-Boltzmann constant σ appears in

1. AFourier conduction law only✓
2. Bradiation heat transfer calculations✓
3. CNewton viscosity law only✓
4. DHooke law only✓

Grashof number in natural convection is analogous to

1. APrandtl number as Gr analog✓
2. BNusselt number as Gr analog✓
3. CReynolds number with buoyancy driving force replacing inertia✓
4. DPeclet number as Gr analog✓

Natural convection heat transfer depends strongly on

1. Aonly forced velocity always required for natural convection primary✓
2. BMach number primarily for natural convection✓
3. CFroude number primarily for natural convection✓
4. DGrashof and Prandtl numbers✓

Electrical analogy for conduction uses

1. Apressure as heat flow always in analogy✓
2. Bvelocity as temperature✓
3. Ctemperature difference as driving force and heat flow as current✓
4. Dmass flux as voltage✓

Critical radius of insulation for cylinder occurs when

1. ABi = 0 always as critical radius condition✓
2. BBi = 1 for cylinder definition r_c = k/h✓
3. CRe = 2300 always✓
4. DPr = 0.7 always as critical radius✓

Overall heat transfer coefficient U in plane wall includes

1. Aonly radiation always alone without convection conduction✓
2. Bconduction and convection resistances in series✓
3. Conly mass transfer coefficient✓
4. Donly Darcy friction factor✓

NTU method in heat exchangers relates

1. Aonly pressure drop in pipes alone as NTU method scope✓
2. Bonly radiation view factors✓
3. Csize (UA) and heat capacity rates to effectiveness✓
4. Donly Fick diffusion only as NTU✓

LMTD for counter-flow heat exchanger uses

1. Aarithmetic mean always without log as LMTD✓
2. Bmaximum difference only always as LMTD✓
3. Cminimum difference only always as LMTD✓
4. Dlog mean of hot and cold end temperature differences✓

Lumped capacitance method valid when Bi is

1. Aless than about 0.1✓
2. Bgreater than 10 always as lumped criterion✓
3. Cequal to Reynolds number✓
4. Dinfinite always required✓

Biot number Bi is defined as

1. Ak / h L_c✓
2. Bh L_c / k✓
3. Ch L / ρ v cp✓
4. DD / ν as Bi✓

Infinite fin heat transfer rate for uniform h and k is

1. AQ = h A only without fin geometry✓
2. BQ = k A/L only as infinite fin✓
3. CQ = √(h P k A_c) (T_b − T_∞)✓
4. DQ = σ T⁴ only as fin law✓

Fin efficiency compares

1. Aactual heat transferred by fin to heat if entire fin at base temperature✓
2. Bfin cost to weight only✓
3. CReynolds to Prandtl only without fin context✓
4. DLMTD to NTU only as fin efficiency✓

Fin effectiveness increases with

1. Ahigher convection coefficient and higher fin thermal conductivity✓
2. Blower k always beneficial✓
3. Czero surface area always beneficial✓
4. Dinfinite length always without diminishing returns✓

Radiation heat exchange between large parallel gray plates includes factor

1. A1/(1/ε1 + 1/ε2 − 1) multiplying σ A (T1⁴ − T2⁴)✓
2. Bh ΔT only✓
3. Ck/L only✓
4. DD/L only as radiation exchange✓

View factor F_12 between two surfaces represents

1. Aconductive heat flux fraction✓
2. Bconvective coefficient ratio✓
3. Cmass transfer coefficient✓
4. Dfraction of radiation leaving surface 1 intercepted by surface 2✓

Emissivity ε of real surface is

1. Aalways equal to 1 for all materials✓
2. Bratio of surface emissive power to blackbody emissive power at same T✓
3. Cratio of absorptivity to reflectivity always as definition of ε alone✓
4. Dalways zero for metals✓

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

1. Aε σ T⁴✓
2. Bσ T only linear✓
3. Ck ΔT only✓
4. Dh ΔT only as radiation law✓

Reynolds number in forced convection characterizes

1. Aradiation to conduction ratio✓
2. Bratio of inertial to viscous forces✓
3. Cmass diffusivity to thermal diffusivity as Re✓
4. Dsurface tension effects only always as Re✓

Prandtl number Pr equals

1. Aα / ν✓
2. Bν / α or μ cp / k✓
3. Ch L / k which is Nusselt✓
4. Dg β ΔT L³/ν² which is Grashof✓

Nusselt number Nu is defined as

1. Ah L / k✓
2. Bk / h L✓
3. Cρ v L / μ which is Reynolds✓
4. Dμ cp / k which is Prandtl✓

Newton's law of cooling for convection is

1. Aq″ = k dT/dx only always as convection law✓
2. Bq″ = σ T⁴ only as convection✓
3. Cq″ = h (T_s − T_∞)✓
4. Dq″ = D dC/dx only as convection✓

Composite wall in series has total thermal resistance

1. Aproduct of resistances✓
2. Balways zero✓
3. Cequal to smallest layer only✓
4. Dsum of individual layer resistances✓

Thermal resistance of conduction layer is

1. Ak A / L✓
2. BL / (k A)✓
3. Ch A only✓
4. D1/(h A) which is convection resistance✓

Steady one-dimensional conduction through plane wall is

1. AQ = h A ΔT only without conduction path✓
2. BQ = σ A ΔT/L✓
3. CQ = m cp ΔT only as conduction through wall✓
4. DQ = k A ΔT / L✓

Thermal conductivity k has SI units

1. AJ/kg✓
2. BW/(m·K)✓
3. CPa·s✓
4. DW/m²✓

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

1. Apositive temperature gradient only always✓
2. Bpressure gradient✓
3. Cnegative temperature gradient✓
4. Dvelocity gradient✓

Contact resistance between two solids increases with

1. Aperfectly smooth surfaces always as increase contact R always✓
2. Bhigher pressure always increases contact R✓
3. Chigher k always increases contact R✓
4. Dsurface roughness and lower contact pressure✓

Heat pipe transfers heat effectively by

1. Asolid conduction only through vacuum as heat pipe mechanism✓
2. Bevaporation and condensation of working fluid in closed cycle✓
3. Cradiation only through vacuum as primary mechanism alone✓
4. Dforced air only without phase change as heat pipe✓

Thermal boundary layer thickness grows along flat plate because

1. Aradiation only at leading edge as sole cause✓
2. Bphase change only✓
3. Cmass diffusion only as thermal BL growth cause alone✓
4. Dmomentum and thermal diffusion from wall✓

Dittus-Boelter equation estimates Nu for

1. Aturbulent flow in smooth tubes✓
2. Blaminar tube flow always as Dittus-Boelter primary regime✓
3. Cnatural convection on vertical plate always as Dittus-Boelter primary✓
4. Dradiation between plates always as Dittus-Boelter✓

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

1. A0.023 Re^0.8 Pr^n which is turbulent correlation for laminar fully developed✓
2. B4.36✓
3. C3.66 for constant wall temperature case confused✓
4. D1.0 always✓

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

1. ABi < 0.1 only as F factor purpose✓
2. Bradiation only as F factor purpose✓
3. Cmass transfer only as F factor purpose✓
4. Dflow arrangement deviates from true counterflow or multipass✓

Countercurrent flow heat exchanger achieves

1. Aalways lower effectiveness always compared to parallel✓
2. Bsame effectiveness always regardless of arrangement✓
3. Czero heat transfer✓
4. Dhigher effectiveness than parallel flow for same UA generally✓

Mass transfer coefficient k_m relates

1. Aheat flux to temperature difference only as k_m definition✓
2. Bmomentum flux to velocity gradient only as k_m✓
3. Cpressure drop to flow rate only as k_m✓
4. Dmass flux to concentration difference✓

Equimolar counter-diffusion in gases has molar flux proportional to

1. Atemperature gradient only as equimolar diffusion driving force alone✓
2. Bpressure squared only alone always✓
3. Cconcentration gradient and inversely to thickness✓
4. Dvelocity cubed✓

Molecular diffusion in solids is generally

1. Amuch slower than in gases✓
2. Bfaster than gases always✓
3. Cidentical rate always✓
4. Dindependent of temperature always✓

Turbulent eddy diffusivity enhances

1. Aonly laminar sublayer without effect always✓
2. Bboth heat and mass transfer in turbulent flow✓
3. Conly radiation✓
4. Donly conduction in solids as turbulent eddy effect✓

Peclet number Pe equals

1. ARe × Pr or v L / α✓
2. BNu × Pr as Pe always✓
3. CGr × Pr which is Rayleigh labeled as Pe✓
4. DSh × Sc labeled as Pe✓

Rayleigh number Ra equals

1. ARe × Pr which is Peclet labeled as Ra✓
2. BNu × Pr labeled as Ra✓
3. CSh × Sc labeled as Ra✓
4. DGr × Pr✓

Stanton number St relates

1. Aonly mass diffusivity as St primary alone✓
2. Bonly radiation emissivity as St✓
3. Cheat transfer coefficient to flow properties in dimensionless form✓
4. Donly fin efficiency as St✓

Colburn analogy gives relation between

1. Astress and strain in solids as Colburn analogy scope✓
2. Bentropy and enthalpy as Colburn analogy scope✓
3. Cbolt preload and torque only as Colburn analogy scope✓
4. DStanton and friction factor f/2 for similar transfer mechanisms✓

Thermal diffusivity α equals

1. Aρ cp / k as α definition✓
2. Bk cp / ρ✓
3. Ch / k as α✓
4. Dk / (ρ cp)✓

Insulation purpose on hot pipe is to

1. Aincrease heat loss always as insulation purpose✓
2. Bincrease pipe stress only as primary purpose✓
3. Cmeasure flow rate only✓
4. Dreduce heat loss to surroundings✓

Extended surface (fin) material should have

1. Ahigh thermal conductivity✓
2. Blow conductivity always beneficial for fin material choice✓
3. Czero conductivity ideally✓
4. Dlow density only without conductivity consideration alone always as sole criterion✓

Adiabatic tip fin boundary condition means

1. Afixed temperature at tip always as adiabatic condition✓
2. Bzero heat flux at tip✓
3. Cinfinite convection at tip as adiabatic✓
4. Dconstant heat generation at tip as adiabatic✓

Heat generation in solid modifies conduction equation by adding

1. Aonly convection term as sole modification always✓
2. Bradiation only as sole modification✓
3. Cq_gen term to energy balance✓
4. Dmass flux only as sole modification in conduction eqn✓

Two-dimensional conduction shape factor S is used when

1. Aonly turbulent pipe flow as shape factor use case✓
2. Bonly radiation view factors conflated always✓
3. Canalytical series solutions cumbersome for complex geometries✓
4. Donly fatigue analysis✓

Hydrodynamic and thermal entry lengths in tube flow differ because

1. AReynolds alone makes them identical always✓
2. BPrandtl number affects thermal development rate✓
3. Cpressure alone determines both equally✓
4. Droughness alone determines both equally✓