Aim of the Experiment
To determine the overall heat transfer coefficient and effectiveness of a shell and tube heat exchanger using the LMTD and NTU methods, and to compare parallel flow and counter flow configurations.
Apparatus Required
- Shell and tube heat exchanger apparatus
- Hot water generator / heater with temperature controller
- Cold water supply with flow control valves
- Thermometers or PT100 temperature sensors (at least 4 points)
- Flow meters (rotameters) for hot and cold fluid
- Stopwatch and measuring cylinder
Theory
A shell and tube heat exchanger consists of a bundle of tubes enclosed within a cylindrical shell. One fluid flows through the tubes (tube-side) while another flows over the tubes inside the shell (shell-side). Heat is transferred through the tube walls.
LMTD Method: Q = U × A × LMTD
Where LMTD = (ΔT₁ − ΔT₂) / ln(ΔT₁/ΔT₂), ΔT₁ and ΔT₂ are temperature differences at each end.
NTU-Effectiveness Method: ε = Q_actual / Q_max, where Q_max = C_min × (T_h,in − T_c,in)
NTU = U × A / C_min; Effectiveness ε relates to NTU and heat capacity ratio Cr = C_min/C_max.
Procedure
- Set up the apparatus in parallel flow configuration. Start the heater and set hot water temperature to approximately 60–70°C.
- Set the cold water flow rate and allow the system to reach steady state (temperatures stabilise).
- Record inlet and outlet temperatures of hot fluid (T_h1, T_h2) and cold fluid (T_c1, T_c2).
- Record the flow rates of both hot and cold fluid (ṁ_h and ṁ_c in kg/s).
- Calculate Q_hot = ṁ_h × Cp × (T_h1 − T_h2) and Q_cold = ṁ_c × Cp × (T_c2 − T_c1).
- Calculate LMTD for parallel flow. Calculate overall heat transfer coefficient U = Q / (A × LMTD).
- Reconfigure to counter flow and repeat all steps.
- Compare U and effectiveness ε for both configurations.
Observation Table
| Parameter | Parallel Flow | Counter Flow |
|---|---|---|
| Hot fluid inlet temp T_h1 (°C) | ||
| Hot fluid outlet temp T_h2 (°C) | ||
| Cold fluid inlet temp T_c1 (°C) | ||
| Cold fluid outlet temp T_c2 (°C) | ||
| Hot fluid flow rate (kg/s) | ||
| Cold fluid flow rate (kg/s) | ||
| LMTD (°C) | ||
| Overall U (W/m²K) | ||
| Effectiveness ε |
Result
Counter flow configuration gives higher LMTD and effectiveness compared to parallel flow at the same operating conditions. The experimental overall heat transfer coefficient U = _______ W/m²K (parallel flow) and _______ W/m²K (counter flow).
Internal Links
Related resources: Heat Transfer Lab Equipment | Double Pipe Heat Exchanger Experiment | Heat Conduction Experiment | Engineering Lab Equipment Guide
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