Concepts
Evaluation of natural v. forced convection efficacy
natural convection << forced convection
See notes
What is a 1-2 H.E?
Delta Tlm for 2-4 counter-current flow H.E where
Th,in = 250[F] Th,out = 153[F]
Tc,in = 92[F] Tc,out = 187[F]
What is 55.8[F]?
flow type with higher convection coefficient values
hturbulent >> hlaminar
The companies participating in the Monday tour
Three types of boiling
Nucleate boiling
Transition boiling
Film boiling
Visual of plug flow
See notes
radiative q between two directly radiating disks of D=22[in] separated by 5[in]
T1=115[F] emissivity1=0.89
T2=83[F] emissivity2=0.56
Boltzmann constant= 0.1624e-8 [Btu/(ft^2 h R^4)]
q12 = 87.9[Btu/h]
emissivity equation
what is emissivity power/emissivity power of a blackbody
The location of the fluid with a higher h in a finned heat exchanger.
where is inside the tubes? This is because the fins add a higher external surface area for the fluid with lower convection coefficient
The biggest challenge of operating a plate type heat exchanger
what are leaks? This is because the seal is provided by gaskets and not solid tubes
Temperature diagram for a 2-4 counter-current where
Ttube, in = 377[F]
Ttube,out = 200[F]
Tshell,in = 160[F]
Tshell,out = 275[F]
see diagram
q/L for a pipe with a surface temp. of 176[F], outer radius of 1.35[in] with air moving across its normally its surface at 70[ft/s], 110[F] and atmospheric pressure
viscosity of air = 0.021[cP]
density of air = 0.0613[lbm/ft^3]
thermal conductivity of air= 0.081[Btu/(h ft F)
What is 45.03 [Btu/(h ft)]?
Driving concept of the NTU method
what is thermal momentum (mass flowrate*Cp)
The factor accounts for there being two phases in two phase flow
What is void fraction?
what is an ideal emitter and absorber; not a physical reality but used as a normalizer to a perfect scenario
P, T, density and velocity relationships between points A and B for compressible and incompressible flow
incompressible: Pa>Pb, Ta=Tb, density-a=density-b, velocity-a=velocity-b
compressible: Pa>Pb, Ta>Tb, density-a<density-b, velocity-a<velocity-b
# of Heat Exchanger Tubes required given:
q = 1.6e6 [Btu/h] U=63 [Btu/(F h ft^2)]
di = 3 [in] L = 8[ft] 1-1 counter-current
cw: in = 87[F] out = 120[F]
engine oil: in = 243[F] out = 185[F]
What are 37 tubes?
Nh equation for NTU method
(Tc,o-Tc,i)/LMTD = UA/(mCp)
(1) Maximize heat transfer within the footprint
(2) Minimize pressure drop within the HE (decreased tube diameter leads to increased pressure drop and higher pump costs
Three ways qualities of radiation in object interactions and what it means (words or picture)
absorptivity (radiation taken in and increases T)
reflectivity (radiation bounces off with little to no absorption)
transmissivity (radiation passing through object possibly depositing energy)
DOUBLE JEOPARDY
Graph with q" v. Ts-Tliquid and show the 4 distinct boiling regions with sketches of each.See Graphs 500
DOUBLE JEOPARDY
Using the Lockhart-Martinelli Method for delta P(two-phase) over 347[ft] of 4[in] inner diameter pipe where:
Vapor Liquid
density [lbm/ft^3] 2.43 29.49
viscosity [cP] 1.021*10^-2 5.365*10^-2
surface tension [dyne/cm] 4.62
mass flowrate [lbm/h] 165,000 490,000
what is 8.783*10^-10 [psi]
Definition of each term of the equation for heat transfer by radiation between two bodies
what are:
q1-2 = heat transfer by radiation between two bodies
sigma = botlzmann constant
A = area between two bodies
(cursive)F1-2 = empirical correlation geometric correlation factor
T1 & T2 = absolute temperatures of the surfaces
A method of increasing Fg within a particular design
what is increasing the number of tubes (example in notes