questions 123 are connected A refrigerated boxcar is being c

questions 1,2,3 are connected

A refrigerated boxcar is being carried at various speeds V as part of a train. It may be assumed that the three sides of the boxcar, with dimensions shown in the figure below, are exposed to air at various temperatures Too(t). At all times, the contents of the car must be maintained at car 16.0°C. During the design of the box car, the electrical engineering team must specify the appropriate gauge of wire, and other components to be used in the boxcar\'s electrical system to ensure compliance of the boxcar\'s design with all applicable codes, to properly size the electric motors used in the car\'s heat pump calculations the expected extreme and nominal heat loss values are required. The boxcar walls are heavily insulated to mitigate heat loss. Use the figures and tables provided to answer the questions. Ignore the underside of the box car, as well as the front/rear faces of the boxcar as it is assumed that over 90% of the heat transfer between the boxcar and surroundings occur on the sides considered. 3.25 m 17.0 m Tropicana O 3.65 m 3132 kg ABS 1070 1.424 0.100 0.066. 10-6 Plastic 105 0.036 0.431, 10-6 Fiber Glass 0.795 1040 Wrought 7854 17.7. 10-6 0.434 60.5 Steel

Given:

kplastic = .1

kglass = .036

ksteel = 60.5

Lplastic = 0.04m

Lglass= 0.14m

Lsteel=0.02m

‘hin = 13.2

‘hout= 70

Total Thermal resistance ,

Rtot= (1/hout) + (Lsteel/ksteel) + (Lglass/kglass) + (Lplastic / kplastic)+(1/ hin)

= (1/70) +(.02/60.5)+(.14/.036)+(.04/.1)+(1/13.2)

= 4.38 m2.k/w(total thermal resistance)

Avg convective heat transfer coefficient, hc = 10.45-v + 10 x v1/2

V= 12 m/s

hc = 10.45-12 + 10 x 121/2

= 33 W/m2.k

Heat Transfer rate , Q=

= x A x T

= Stefan blotzman constant = .0174 Btu/hr-ft2-R

A= surface area total

= 2x 17x 3.65 + 17x 3.25

=179.35 sq.m

=1930.5 sq.feet

T= 120 C

= 513.27 Rankine scale

= 53.330 F

Q = 17241 Btu/hr

We also know that same heat transfer rate, Q = hc x A x (Ts-Ta)

hc= 33 W/m2.k

= 5.81 Btu/hr. ft2.F

17241 = 5.81 x 1930.5 x (Ts – 53.33)

Ts = 53.33 + 1.53

Ts = 54.860 F

= 12.70 C(exterior surface temperature of boxcar)