7/23/2019 RMIK_T3

1/3

Romero Moreno Itzel Karina

Tarea No.3

Una rebanada de mantequilla de 34mm de grueso se encuentra inicialmente a 5C. Se

coloca sobre una superficie aislada y expuesta al aire a 30 C. El coeficiente de

transferencia conectia de calor es !."3#$m%&. 'as propiedades de la mantequilla son lassiguientes( &)0.*+%#$m &, calor espec-fico)%%50$&g & y densidad) ++!& g$m3.Calcule

la temperatura *0mm de ba/o de la superficie despus de 30min,*1, *1 30min, %1, %1

30min, 31, 31 30min, 41, 41 30min y 51.

997Kg

m32250

J

Kg K

=8.56108

m2

s

= K

CP=0.192

W

m K

n=

(3410 )m34m

=

24

34=0.71

m= K

h Xi=

0.192 W

mK

7.83W

m2

0.034m

=0.71

t=30min

= t

xi=8.5610

8 m2

s 1800 s

(0.034m)2 =0.13

Y=T

1T

T1T0;T=T

1[Y(T1T0 ) ]

T=30 [.50 (305 )]=17.5

t=60min

7/23/2019 RMIK_T3

2/3

= t

xi=8.5610

8m2

s3600 s

(0.034m)2 =0.27

T=30

[.49

(30

5

)]=17.75

t=90min

= t

xi=8.5610

8 m2

s 5400 s

(0.034m)2 =0.4

T=30 [. 48(305)]=18

t=120min

= t

xi=8.5610

8m2

s7200 s

(0.034m)2 =0.53

T=30 [. 46 (305)]=18.5

t=150min

= t

xi=8.5610

8m2

s9000 s

(0.034 m)2 =0.67

T=30 [. 44 (305 )]=19

t=180min

= t

xi=8.56108 m

2

s 10800 s

(0.034m)2 =0.80

T=30 [. 42(305)]=19.5

t=210min

7/23/2019 RMIK_T3

3/3

= t

xi=8.5610

8 m2

s 12600 s

(0.034m)2 =0.93

T=30

[.39

(30

5

)]=20.25

t=240min

= t

xi=8.5610

8 m2

s 14400 s

(0.034m)2 =1.07

T=30 [.37 (305)]=20.75

t=270min

= t

xi=8.5610

8 m2

s 16200s

(0.034m)2 =1.2

T=30 [.34 (305)]=21.5

t=300min

= t

xi=8.5610

8 m2

s 18000 s

(0.034m)2 =1.33

T=30 [.32 (305)]=22