A heat exchanger is an energy exchange system (in the form of heat) between a hot and a cold fluid. In practice, all the thermal duty of the hot fluid is transferred to the cold fluid , thereby fulfilling the next energy balance.
The thermal duty of a fluid in liquid state depends on the mass flowrate and the temperature differential between the inlet and outlet sections. In a fluid with a change of phase in saturated conditions, the heat power depends on the mass flowrate and the enthalpy of the phase change, that is determined by the saturation pressure.
The Heat Exchanger Calculator is a program specially designed to predict the performance of the heat exchanger Model Number you choose based on the parameters you input.
This is a calculator for sizing a shell and tube heat exchanger with tube side flow fixed. With shell side and tube side inlet/outlet temperatures fixed, the required shell side flow is calculated corresponding to given tubeside flow. The log mean temperature difference (LMTD) is also reported.
For known shell side and tube side dimensions heat transfer areas and heat transfer coefficients on both sides are calculated. Finally the overall heat transfer coefficient is calculated and reported. If a different value of overall heat transfer coefficient is assumed or desired, then that value should be specified in the end section. The required heat transfer area corresponding to the assumed overall heat transfer coefficient is then reported.
Two formulas can be used to determine the heat load of a heat exchanger:
1. Heat load, Theta and LMTD calculation
P = heat load (btu/h)
m = mass flow rate (lb/h)
cp = specific heat (btu/lb °F)
δt = temperature difference between inlet and outlet on one side (°F)
k = heat transfer coefficient (btu/ft2 h °F)
A = heat transfer area (ft2)
LMTD = log mean temperature difference
T1 = Inlet temperature – hot side
T2 = Outlet temperature – hot side
T3 = Inlet temperature – cold side
T4 = Outlet temperature – cold side
LMTD can be calculated by using the following formula, where ∆T1 = T1–T4 and ∆T2 = T2–T3
2. The heat transfer coefficient and the design margin
The total overall heat transfer coefficient k is defined as:
α1 = The heat transfer coefficient between the warm medium and the heat transfer surface (btu/ft2 h °F)
α2 = The heat transfer coefficient between the heat transfer surface and the cold medium (btu/ft2 h °F)
δ = The thickness of the heat transfer surface (ft)
Rf = The fouling factor (ft2 h °F/btu)
λ = The thermal conductivity of the material separating the medias (btu/ft h °F)
kc = Clean heat transfer coefficient (Rf=0) (btu/ft2 h °F)
k = Design heat transfer coefficient (btu/ft2 h °F)
M = Design Margin (%)
Combination of these two formulas gives: M = kc · Rf
i.e the higher kc value, the lower Rf-value to achieve the same design margin.
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