The concrete slab of a basement is 11 m long, 8 m wide, and 0.20 m thick. During the winter, temperatures are nominally 17°C and 10°C at the top and bottom surfaces, respectively. If the concrete has a thermal conductivity of 1.4 W/m·K, what is the rate of heat loss through the slab? If the basement is heated by a gas furnace operating at an efficiency of ηf = 0.90 and natural gas is priced at Cg = $0.02/MJ, what is the daily cost of the heat loss?

Respuesta :

Answer:

so heat loss =  4312 W

cost of heat loss daily is $8.28 per day

Explanation:

given data

slab length L = 11 m

slab wide W = 8 m

thickness t = 0.20 m

temperature top T1 = 17°C

temperature bottom T2 = 10°C

thermal conductivity k = 1.4 W/m-K

efficiency ηf = 0.90

priced  Cg = $0.02 / MJ

to find out

rate of heat loss and daily cost of the heat loss

solution

we calculate here heat loss by heat transfer

so apply here formula that is

q = (thermal conductivity × area × temperature difference) / thickness

put here all these value we get heat loss

q  = [tex]\frac{k*L*W*(T2-T1)}{t}[/tex]

q  = [tex]\frac{1.4*11*8*(17-10)}{0.2}[/tex]

q = 4312 W

so heat loss =  4312 W

and

cost of the heat loss is express as

cost of heat loss = [tex]\frac{q*Cg}{efficiency}[/tex]

put here all these value

cost of heat loss is = [tex]\frac{4312*0.02*10^6}{0.9}[/tex]  × 24 hr/day × 3600 s/hr

cost of heat loss = 8.279

so cost of heat loss daily is $8.28 per day

The heat loss be "4312 W" and cost will be "$8.28 per day".

Thermal conductivity:

According to the question,

  • Slap length, L = 11 m
  • Wide, W = 8 m
  • Thickness, t = 0.20 m
  • Top temperature, T₁ = 17°C
  • Bottom temperature, T₂ = 10°C
  • Thermal conductivity, k = 1.4 W/m-K
  • Efficiency, nf = 0.90
  • Priced, Cg = $0.02/MJ

We know the relation,

→ [tex]q = \frac{Thermal \ conductivity\times Area\times Temperature \ difference}{Thickness}[/tex]

or,

     [tex]= \frac{k\times L\times W(T_2-T_1)}{t}[/tex]

By substituting the values,

     [tex]= \frac{1.4\times 11\times 8(17-10)}{0.2}[/tex]

     [tex]= 4312 \ W[/tex]

now,

The cost of heat loss be:

= [tex]\frac{q\times C_g}{Efficiency}[/tex]

= [tex]\frac{4312\times 0.02\times 10^6}{0.9}\times 24\times 3600[/tex]

= [tex]8.28 \ per \ day[/tex]

Thus the above response is correct.

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