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3.2 A bases of thermal calculation of heat exchangers
Heat exchangers transfer heat from one working fluid to another. For instance,

steam generators, feedwater heaters, reheaters and condensers are all examples of heat
exchangers found in nuclear power systems.

The heat transfer rate across a heat exchanger is usually expressed in the form

I
Q =kFΔT m , (3.1)

I
where: Q = heat transfer rate;
k = overall heat transfer coefficient;

F = heat exchanger area;

ΔT m = average temperature difference between the fluids.

The overall heat transfer coefficient is a function of the flow geometry, fluid

properties and material composition of the heat exchanger. The average temperature

difference between the fluids is in general a function of the fluid properties and flow

geometry as well. Heat exchanger design requires consideration of each of these factors.

The main goal of a heat exchanger thermal calculation is definition of its area. When

area of heat exchanger is known, in that case the goal of calculation is determine

eventual temperatures of fluids.

The bases of calculation equations of a heat exchanger are thermal balance equation

and heat-transfer equation.

Equation of heat-transfer is written

Q  kF t  t 2  kF t (3.2)
1
where Q - a heat transfer rate;

k - a average of heat-transfer coefficient;

F- an area of floor of heat exchange ;

t , t - temperatures of hot and cold fluids work.
1 2
If to ignore thermal energy looses, equation of thermal balance is written as a

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