Heat Exchanger Simulator
LMTD • NTU • Parallel • Counter • Cross Flow — Simulate • Explore • Practice • Quiz
Heat Exchanger Design — LMTD & NTU Methods Explained
A heat exchanger is a device that transfers thermal energy between two or more fluids at different temperatures without mixing them. Heat exchangers are fundamental components in power plants, chemical processing, HVAC systems, automotive radiators, and refrigeration cycles. The two primary methods for analysing heat exchanger performance are the LMTD (Log Mean Temperature Difference) method and the NTU-Effectiveness method. Understanding both approaches is essential for any thermal engineer designing or evaluating heat transfer equipment.
In a typical shell-and-tube heat exchanger, one fluid flows through a bundle of tubes while the other flows over the tubes inside the shell. The heat transfer rate depends on the overall heat transfer coefficient (U), the surface area (A), and the temperature driving force. The flow arrangement — parallel flow, counter flow, or cross flow — significantly affects the temperature distribution and overall effectiveness of the exchanger.
The LMTD Method for Heat Exchanger Analysis
The LMTD method is used when all four terminal temperatures (hot inlet, hot outlet, cold inlet, cold outlet) are known or can be determined from an energy balance. The log mean temperature difference is calculated as LMTD = (ΔT1 − ΔT2) / ln(ΔT1 / ΔT2). For counter-flow exchangers, ΔT1 = Th,in − Tc,out and ΔT2 = Th,out − Tc,in. The heat transfer rate is Q = U × A × LMTD. Counter-flow configurations always produce a higher LMTD than parallel-flow for the same operating conditions, making them more efficient.
The NTU-Effectiveness Method
The NTU method is preferred when outlet temperatures are unknown. NTU (Number of Transfer Units) is defined as NTU = UA / Cmin, where Cmin is the smaller of the two heat capacity rates (Ch = ṁhCp,h and Cc = ṁcCp,c). The effectiveness ε = Q / Qmax represents the fraction of maximum possible heat transfer actually achieved. For a counter-flow exchanger, the effectiveness relationship is ε = [1 − exp(−NTU(1−Cr))] / [1 − Cr·exp(−NTU(1−Cr))], where Cr = Cmin/Cmax.
Who Uses This Simulator?
This heat exchanger simulator is designed for mechanical engineering students, thermal design engineers, chemical engineering trainees, HVAC professionals, and instructors teaching heat transfer and thermodynamics. It provides a visual, interactive approach to understanding heat exchanger behaviour without needing laboratory equipment or specialised software.
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