Lab 3

Question 1

measuring convective heat transfer coefficients

Answer 1

ex. measure the heat transfer rate from an airplane wing with fuel inside

Question 2

parameters: Uinfinity

Answer 2

free stream velocity

Question 3

parameters: L

Answer 3

characteristic wing length

Question 4

parameters: μ

Answer 4

fluid viscosity

Question 5

parameters: p (rho)

Answer 5

density

Question 6

parameter: k

Answer 6

thermal conductivity

Question 7

parameter: Cp

Answer 7

specific heat

Question 8

parameters: relevant temperature

Answer 8

ambient and surface

Question 9

dependeent variable

Answer 9

convective heat transfer coefficanet h-> q

Question 10

reynolds number

Answer 10

Re = pUinfL/u = Uinf L / v = inertial forces/vicous forces

Question 11

critical reynolds number

Answer 11

Re ~5x10^5 for a flat plate

Question 12

transition to turbulent flow

Answer 12

xc/L = Rexc/ReL
ReL > Rexc

Question 13

trip

Answer 13

this influences the flow to transition to turbulent flow

Question 14

momentum (velocity) boundary layer

Answer 14

region of flow characterized buy velocity gradient and shear stress

Question 15

laminar flow over a flat plane

Answer 15

thickness = 5x/sqrt(Rex)

Question 16

turbulent flow over a flat plane

Answer 16

thickness = 0.37xRex^-1/5

Question 17

thermal boundary layer thickness

Answer 17

flow characterized by temperature gradient and heat flux

Question 18

prandtl number

Answer 18

viscosity/thermal diffusivity
pr&raquo_space; 1 thicker momentum BL
pr ~ 1 about equal (gas)
Pr &laquo_space;thicker thermal BL

Question 19

nusselt number

Answer 19

Nu = hL/kf

Question 20

laminar flow subject to constant surface temperature

Answer 20

Nux = hx/k = 0.322Re^1/2Pr^1/3

Question 21

laminar flow subject to constant surface temperature with average boundary layer results

Answer 21

Nu = 0.664 Re^1/2Pr^1/3

Question 22

laminar flow subject to constant surface temperature for constant heat flux

Answer 22

Nu = 0.453Re^1/2Pr^1/3
pr>0.6

Question 23

how to measure thermal boundary layer

Answer 23

vertical thermal couple

Question 24

how to measure velocity boudnary layer

Answer 24

preston probe

Question 25

bernoulli’s equation to get velocity measurment

Answer 25

ptotal = pu^2/2 + pstatic
pu^2/2 = pdynamic
u = velocity

Question 26

Local heat transfer coefficient measurement

Answer 26

htop = hbottom = h (symetric consfiguration)

Question 27

heat disipated by two heaters

Answer 27

qheater = V^2front/Rfront + V^2back/Rback

Question 28

local convection heat flux leaving top and bottom surface

Answer 28

q’’ = qheater /2LW

Question 29

local convection heat flux leaving top and bottom surface + radiation