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Q  c pm 1 G  1 t   c pm 2 G 2 t   2 t 2  (3.3)
t 
1
1
where, G ,G - a mass flow of fluids, kg ;
1 2 с

c pm 1 , c pm 2 - an average mass isobar heat capacity of fluids in the diapason of

temperatures from t to t  ;

t, t – a temperature of fluids on an entrance of heat exchanger;
1 2
t  , t  – a temperature of fluids on an exit of heat exchanger.
1 2

 Вт 
A value W  c pm  G   is named an aquatic equivalent. Therefore equation of
 К 

thermal balance is possible to write

W t   t
tW   t   W t   t  or 1  2 2 , (3.4)
1 1 1 2 2 2
W t   t 
2 1 1
where, W , W - the equivalents of hot and cold fluids, respectively.
1 2
At the heat exchanger fluids motion changes its temperature and temperatures

difference also. A change of temperatures of fluids is back proportional of it’s an

aquatic equivalents.

Values Δt and k at equation of heat-transfer is possible to consider permanent only

for some component of surface. Therefore equation of heat-transfer can be expression

for a component dF just only differentially

dQ  kdF t (3.5)

A heat transfer which is passed through all of surface

F
Q   kdF  t  kF t  
m (3.6)
0
where - t log mean temperature difference (LMTD).
c

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