# Calculation Method Of Heat Exchanger

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.

1. Heat load, Theta and LMTD calculation Where: 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