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jolli1 [7]
3 years ago
7

Determine the COP of a refrigerator that removes heat from the food compartment at a rate of 5060 kJ/h for each kW of power it c

onsumes. Also, determine the rate of heat rejection to the outside air.
Engineering
1 answer:
Olin [163]3 years ago
6 0

Answer:

COP_{R} = 1.406, \dot Q_{H} = 2.406 W

Explanation:

The COP of a refrigerator is modelled after this expression:

COP_{R} = \frac{\dot Q_{L}}{\dot W} \\COP_{R} = \frac{(5060 \frac{kJ}{h})(\frac{1 h}{3600 s})}{1 kW}\\COP_{R} = 1.406

The rate of heat rejection to the outside air is:

\dot Q_{H} = \dot Q_{L} + \dot W\\\dot Q_{H} = (5060 \frac{kJ}{h} )\cdot (\frac{1}{3600 s} ) + 1 kW\\\dot Q_{H} = 2.406 kW

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A polyethylene rod exactly 10 inches long with a cross-sectional area of 0.04 in2 is used to suspend a weight of 358 lbs-f (poun
Nadya [2.5K]

Answer:

Final length of the rod = 13.90 in

Explanation:

Cross Sectional Area of the polythene rod, A = 0.04 in²

Original length of the polythene rod, l = 10 inches

Tensile modulus for the polymer, E = 25,000 psi

Viscosity, \eta = 1*10^{9} psi -sec

Weight = 358 lbs - f

time, t = 1 hr = 3600 sec

Stress is given by:

\sigma = \frac{Force}{Area} \\\sigma = \frac{358}{0.04} \\\sigma = 8950 psi

Based on Maxwell's equation, the strain is given by:

strain = \sigma ( \frac{1}{E} + \frac{t}{\eta} )\\Strain = 8950 ( \frac{1}{25000} + \frac{3600}{10^{9} } )\\Strain = 0.39022

Strain = Extension/(original Length)

0.39022 = Extension/10

Extension = 0.39022 * 10

Extension = 3.9022 in

Extension = Final length - Original length

3.9022 =  Final length - 10

Final length = 10 + 3.9022

Final length = 13.9022 in

Final length = 13.90 in

7 0
3 years ago
Typically each development platform consists of the following components, except:Select one:a.Operating systemb.System softwarec
damaskus [11]

Typically each development platform consists of the following components except compilers and assemblers

  • The platform development simply means the development of the fundamental software which is vital in making hardware work.

  • Operating system: This refers to the low-level software that communicates with the hardware so that other programs can be able to run.

  • System software: This is the software that's designed in order to provide a platform for the other software. Examples include search engines, Microsoft Windows, etc.

  • Compilers and assemblers: Compliers are sued in converting source code to a machine-level language. Assembler is used in converting assembly code to machine code.

  • Hardware platform: This is a set of hardware where the software applications are run.

In conclusion, the correct option is Compilers and assemblers.

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4 0
2 years ago
Whenever you are around construction sites, you should ?
AlexFokin [52]

Here are 8 construction site safety tips:

Use caution when climbing on and off equipment.

Stay away from operating machinery.

Use caution around fall hazards.

Use the proper ladder height.

Keep an updated first aid kit.

Never use damaged equipment.

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4 0
3 years ago
A stainless steel (AISI 304) tube used to transport a chilled pharmaceutical has an inner diameter of 36 mm and a wall thickness
Bingel [31]

Answer:

a) heat gain per unit tube length = \frac{23-6}{1.35} = 12.6W/m

b) heat gain per unit tube length = \frac{23-6}{2.20} = 7.7W/m

Explanation:

Assumptions:

  1. Constant properties
  2. Steady state conditions
  3. Negligible effect of radiation
  4. Negligible constant resistance between tube and insulation
  5. one dimensional radial conduction

a) What is the heat gain per unit tube length

R_{conv,i}'=\frac{1}{2\pi r_1h_i}

d_1=36mm Therefore r_1=\frac{d_1}{2} =36/2=18mm=18*10^{-3}

r_2=2mm=2*10^{-3}m

k_{st}=14.2W/m.k

h_o=6W/m^2

h_i=400W/m^2

R_{conv,i}'=\frac{1}{2\pi * 1.8*10^{-3}*400}= 0.221m.K/W

R_{cond,st}'=\frac{ln(r_2/r_1)}{2\pi k_{st}} =\frac{ln(20/18)}{2\pi *14.2} =1.18*10^{-3}m.K/W

R_{conv,o}'=\frac{1}{2\pi r_2h_0}=\frac{1}{2\pi *2*10^{-3}*6}=1.33m.K/W

R_{tot}'=R_{conv,i}'+R_{cond,st}'+R_{conv,o}'=0.221+(1.18*10^{-3})+1.33=1.35m.K/W

heat gain per unit tube length = \frac{23-6}{1.35} = 12.6W/m

b) What is the heat gain per unit length if a 10-mm-thick layer of calcium silicate insulation (k_ins = 0.050 W/m.K) is applied to the tube

r_3=r_1+r_2+10mm=30mm=0.03m

R_{conv,i}' and R_{cond,st}' are the same, but R_{conv,o}' changes.

Therefore:

R_{conv,o}'=\frac{1}{2\pi r_3h_0} = \frac{1}{2\pi *0.03*6}=0.88m.K/W

R_{conv,ins}'=\frac{ln(r_3/r_)}{2\pi k_{ins}} =\frac{ln(30/20)}{2\pi *0.05} =1.29m.K/W

The total resistance R_{tot}'=R_{conv,i}'+R_{cond,st}'+R_{conv,ins}'+R_{conv,o}'=0.221+(1.18*10^{-3})+1.29+0.88=2.20m.K/W

heat gain per unit tube length = \frac{23-6}{2.20} = 7.7W/m

8 0
3 years ago
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sasho [114]

Answer: the answer for the question is a

Explanation:

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