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WorksheetsHeat Transfer Lab Quiz Dec 2025
Total questions: 40
Worksheet time: 24mins
Fourier’s law for one-dimensional steady conduction through a rod is written as qx=−kA(dT/dx) Which statement is correct?
k depends only on geometry.
qx is positive when temperature increases along the x-direction.
The negative sign ensures qx is positive when heat flows from high to low temperature.
A is temperature gradient.
In the steady-state rod experiment the lateral surface is insulated. The usual assumption is:
Significant radial conduction exists.
Heat conduction is one-dimensional along the rod length.
Convection around the rod dominates.
Radiation is dominating.
In the lab rig the heater power is measured using voltmeter and ammeter. If the voltmeter reads V and ammeter reads I, the electrical power supplied is:
V+I
V/I
VI
IV^2
The heat conducted along the metal rod is assumed equal to the heat absorbed by cooling water: Q=m˙Cp(Tout−Tin). If flow is 0.2 L/min, convert to m³/s.
3.33×10−6 m3/s
3.33×10−5 m3/s
2×10−4 m3/s2
2×10−6 m3/s2
Rod: diameter D=0.05m. Water flow = 0.2 L/min, Tin=25∘C, Tout=30∘C. Use ρ=1000 kg/m3, Cp=4180 J/kgK. Compute heat carried by water Q(W).
6.97 W
69.67 W
696.7 W
0.697 W
Which of these most affects measurement accuracy of k in the rod experiment?
Precision of geometric area measurement only.
Accurate measurement of temperature gradient and heat flow.
Color of the rod.
Time of day.
Why do you repeat the rod experiment for different heater outputs?
To cool the rod faster.
To verify linearity and get consistent k values.
To break the insulation.
To change the rod material.
If the lateral insulation is imperfect and a non-negligible radial heat loss exists, the calculated k will be:
Accurate.
Overestimated.
Underestimated.
Zero.
In plotting T vs x for the rod, the slope used to compute dT/dx is normally:
The slope through the maximum number of points.
The first data point only.
The slope of a vertical line.
Always zero.
If the heater electrical power Pelec measured is 75 W and water heat Q computed is 70 W, the small difference usually indicates:
Measurement errors and minor losses (insulation, radiation).
Major energy creation in the rod.
Power is being destroyed.
None of the above.
Thermal resistance for a plane wall of thickness L, thermal conductivity k, and area A is:
kLA
L/(kA)
k/(LA)
LA/k
Thermal contact resistance exists primarily because:
Interfaces are perfectly flat.
Surfaces touch at discrete spots leaving gaps filled with air.
Temperature is constant.
Materials are identical.
Why do we enclose the composite wall assembly in insulation and use a cooling water jacket at the outermost layer?
To create known boundary conditions and minimize radial losses, ensuring 1-D heat flow.
To keep the experiment cold.
To allow radiation to dominate.
To increase contact resistance.
If experimentally measured overall conductance is lower than theoretical ignoring contact resistance, plausible reason is:
Negligible contact resistance.
Significant contact resistance at interfaces.
Perfect contact.
Area was smaller.
A graph of temperature vs distance along the composite wall shows small jumps at interfaces. Those jumps correspond to:
Bulk conduction.
Contact temperature drops due to contact resistance.
Noise only.
Heater malfunction.
For a composite cylinder test with radial heat flow neglected, why is it important that all layers have the same diameter in the manual?
So cross-sectional area remains constant and 1-D axial model is valid.
For aesthetics.
To produce more contact resistance.
To reduce conduction.
The lumped capacitance method is valid when the Biot number Bi=hLc/k satisfies:
Bi>10
Bi<0.1
Bi=1
Bi>0.5
For a sphere of radius R, the characteristic length Lc=V/A equals:
R
R/3
R3
R2
Sphere radius r=0.02 m. Material: steel with ρ=7800 kg/m3, Cp=460 J/kg K, k=45 W/m K. Surrounding air h=10 W/m2K. Compute Bi. Which choice is closest?
1.48×10⁻³
1.48×10⁻¹
1.48
14.8
In the Stefan-Boltzmann based experiment (E3) the disc is coated with lampblack (ε≈0.95). Why would you coat the sphere/disc in transient radiative experiments?
To approximate black-body emission and maximize radiative exchange predictability.
To make it shiny.
To insulate it.
To reduce mass.
1. Which parameter is increased by adding fins to a heated surface?
Temperature difference
Convection coefficient
Effective surface area
Thermal conductivity
The efficiency of a fin is defined as:
Maximum rate of heat transfer from the fin
Ratio of actual to maximum possible heat transfer rate
Conductivity of the fin material
Area of fin surface
For free convection from a horizontal cylinder, which dimensionless number is used to characterize heat transfer?
Reynolds number
Grashof number
Nusselt number
Prandtl number
1. In a straight circular tube, how is the flow classified when the Reynolds number is below 2,300?
Transitional
Turbulent
Laminar
Fully developed
Which instrument is used to measure the volume flow rate through the pipe in the experimental setup?
Rotameter
Pitot tube
Orifice meter
Thermocouple
Why is rock-wool insulation used over the heated portion of the pipe?
Minimize axial conduction loss
Maximize convective loss
Minimize radial conduction losses
Increase heat flux
For laminar flow, if h=3.3 W/m²K, D=0.036 m, and k=0.026856 W/mK, find Nu at the exit section.
2.23
3.66
4.47
6.79
For turbulent flow: Dittus-Boelter correlation for Nu if Re=2930, Pr=0.692. What is Nu?
9.06
11.78
3.29
6.79
In the context of heat transfer experiments, which dimensionless number compares buoyancy to viscous force in a fluid?
Prandtl number
Nusselt number
Grashof number
Reynolds number
For an ideal gas, the coefficient of thermal expansion (β) is given by:
β=1/T
β=p/T
T/p
β=T2/p
If Gr/Re >> 1 in a system, which type of convection can be neglected?
Forced convection
Natural convection
Radiation
Conductive heat transfer
In the described experiment, how is the vertical hollow cylinder heated?
By steam externally
Electric heater inside
Solar irradiation
Hot air from outside
Given surface area As=0.0688 m², voltage = 62 V, current = 0.33 A, calculate average heat flux input qs.
185 W/m²
297 W/m²
109 W/m²
67 W/m²
For location X = 0.028 m, given qconv=187.96 W/m² and TS1=55.5∘C, ambient temperature T=32.2∘C, calculate hx1 (local heat transfer coefficient):
4.32 W/m²K
2.55 W/m²K
8.07 W/m²K
12.10 W/m²K
What is the main objective of the double pipe heat exchanger experiment?
To measure wall emissivity
To evaluate performance under parallel and counter flow arrangements
To estimate viscosity
To study free convection from a cylinder
Which type of flow arrangement allows for the cold fluid to potentially exit at a temperature higher than the hot fluid’s exit temperature?
Parallel flow
Counter flow
Cross flow
Regenerative flow
What instrument is used to measure the flow rate in the heat exchanger apparatus?
Rotameter
Stopwatch and volumetric collection
Thermocouple
Manometer
How is steady-state ensured during the experiment?
By recording data rapidly while temperatures still change
By waiting until inlet and outlet temperatures remain constant
By maintaining constant ambient temperature only
By keeping flow rates at a minimum
Ignoring fouling and tube wall resistance, what is the overall heat transfer coefficient equation for the heat exchanger?
U1=1/hi+1/ho
U=hi+ho
U=hiho
U=1/(hi−ho)
The heat transferred is given by Q=UAΔTm. What does ΔTm represent?
Arithmetic mean temperature difference
Logarithmic mean temperature difference (LMTD)
Exit temperature
Inlet temperature
