## How to calculate a heat exchanger in 10 minutes?

As a customer, how do I know if the proposal of my supplier is close to what my process needs?

Two parameters can be calculated: capacity and heating surface. Below you can find a brief description on how to do this yourself. Be warned that this is a strongly reduced and conservative calculation method, meant to be fast and to dimension approximately. In reality a lot more parameters need to be considered so the exact outcome may be different.

* Capacity P* = Q x Cp x (T2-T1) x rho

With:

P = Capacity in [J/s] of [W]

Q = Flow in [m³/s]

Cp = specific heat [J/kg.K]

T2 – T1 = temp @ inlet heat exchanger – temp @ outlet HE [K]

Rho = density in [kg/m³]

You could check and make the calculations for both hot and cold side, with P1 = P2 as a must.

* Heating surface* = P / (k x dTavg)

(“How many tubes at which length do we need?”)

with ‘k’ thermal heat conductivity coefficient in [W/m².°C]

Some typical values for k: (conservative + estimations!)

Steam – water: 1000

Water – water: 700

Water – oil: 300

Steam – oil: 500

Steam – air: 25 to 150

dTavg = average temperature difference between cold and hot side [°C], see example

* Small example*:

Suppose we want to heat up 5 000 L hot water from 70°C to 90°C in 1u.

In our department we have saturated steam available @ 5 barg (saturation temperature = 159°C)

P = (5 x 1000 x 4,186 x 20)/3600 = 116 kW

dTavg = [(159-70) + (159-90)] / 2 = 79°C

HS = 116 000 / [(1000)*(79)] = *1,47 m²*