Effectiveness-NTU Calculator
Analyze heat exchanger performance and design using the effectiveness-NTU method
Heat Exchanger Analysis
Cold Fluid Properties
Hot Fluid Properties
Area of Heat Transfer
Results
Example Calculation
Water-to-Air Heat Exchanger (Counter Flow)
Given:
• Hot water: ṁh = 2 kg/s, cp,h = 4180 J/(kg·K), Th,i = 80°C
• Cold air: ṁc = 1.5 kg/s, cp,c = 1005 J/(kg·K), Tc,i = 20°C
• U = 300 W/(m²·K), A = 10 m²
Solution
Ch = 2 × 4180 = 8360 J/K
Cc = 1.5 × 1005 = 1507.5 J/K
Cmin = 1507.5 J/K, Cr = 1507.5/8360 = 0.18
NTU = (300 × 10)/1507.5 = 1.99
Counter flow effectiveness = 0.86
Heat Exchanger Types
Parallel Flow
Both fluids flow in same direction
Lower effectiveness
Counter Flow
Fluids flow in opposite directions
Highest effectiveness
Cross Flow
Fluids flow perpendicular
Intermediate effectiveness
Shell & Tube
Complex multi-pass design
Compact, efficient
Key Principles
Effectiveness
ε = q / qmax
NTU
NTU = UA / Cmin
Heat Capacity Ratio
Cr = Cmin / Cmax
Range
0 < ε < 1
Understanding the Effectiveness-NTU Method
What is the Effectiveness-NTU Method?
The effectiveness-NTU method is a heat exchanger analysis technique preferred when outlet temperatures are unknown. It relates actual heat transfer to the maximum possible heat transfer through dimensionless parameters.
Key Advantages
- •Direct solution without iteration
- •Suitable for performance analysis
- •Works with unknown outlet temperatures
- •Universal approach for all heat exchanger types
Mathematical Foundation
Effectiveness:
ε = q / qmax
Ratio of actual to maximum heat transfer
Maximum Heat Transfer:
qmax = Cmin(Th,i - Tc,i)
Theoretical maximum based on inlet conditions
Number of Transfer Units:
NTU = UA / Cmin
Dimensionless heat exchanger size parameter
Design vs. Performance Calculations
Design Problem
- • Known: inlet/outlet temperatures, flow rates
- • Calculate: required heat transfer area
- • Process: q → ε → NTU → A
- • Application: sizing new heat exchangers
Performance Calculation
- • Known: inlet temperatures, area, U-value
- • Calculate: outlet temperatures, heat transfer
- • Process: NTU → ε → q → Tout
- • Application: analyzing existing heat exchangers