Overall Heat Transfer Coefficient For Unfinned Tube Calculator

Overall Heat Transfer Coefficient Formula:

\[ U_d = \frac{1}{\left(\frac{1}{h_{outside}}\right) + R_o + \frac{d_o \cdot \ln\left(\frac{d_o}{d_i}\right)}{2k} + \frac{R_i \cdot A_o}{A_i} + \frac{A_o}{h_{inside} \cdot A_i}} \]

External Convection Heat Transfer Coefficient:

W/m²·K

Fouling Factor on Outside of Tube:

m²·K/W

Outside Tube Diameter:

Inside Tube Diameter:

Thermal Conductivity:

W/m·K

Fouling Factor on Inside of Tube:

m²·K/W

Outside Tube Surface Area:

m²

Inside Tube Surface Area:

m²

Inside Convection Heat Transfer Coefficient:

W/m²·K

Overall Heat Transfer Coefficient after Fouling:

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is the Overall Heat Transfer Coefficient?

The Overall Heat Transfer Coefficient after Fouling represents the combined thermal resistance of a heat exchanger system, accounting for convection coefficients, conduction through tube walls, and fouling factors on both inside and outside surfaces of the tubes.

2. How Does the Calculator Work?

The calculator uses the comprehensive heat transfer formula:

\[ U_d = \frac{1}{\left(\frac{1}{h_{outside}}\right) + R_o + \frac{d_o \cdot \ln\left(\frac{d_o}{d_i}\right)}{2k} + \frac{R_i \cdot A_o}{A_i} + \frac{A_o}{h_{inside} \cdot A_i}} \]

Where:

\( h_{outside} \) — External convection heat transfer coefficient (W/m²·K)
\( R_o \) — Fouling factor on outside of tube (m²·K/W)
\( d_o \) — Outside tube diameter (m)
\( d_i \) — Inside tube diameter (m)
\( k \) — Thermal conductivity of tube material (W/m·K)
\( R_i \) — Fouling factor on inside of tube (m²·K/W)
\( A_o \) — Outside tube surface area (m²)
\( A_i \) — Inside tube surface area (m²)
\( h_{inside} \) — Inside convection heat transfer coefficient (W/m²·K)

Explanation: The formula accounts for all thermal resistances in series, including convection, conduction, and fouling effects on both sides of the heat exchanger tube.

3. Importance of Overall Heat Transfer Coefficient

Details: Accurate calculation of the overall heat transfer coefficient is crucial for designing efficient heat exchangers, predicting performance under fouling conditions, and determining maintenance schedules for cleaning operations.

4. Using the Calculator

Tips: Enter all required parameters with appropriate units. Ensure all values are positive and physically meaningful. The calculator handles the complex logarithmic and fractional calculations automatically.

5. Frequently Asked Questions (FAQ)

Q1: What is the significance of fouling factors?
A: Fouling factors account for the additional thermal resistance caused by the buildup of deposits on heat transfer surfaces, which significantly reduces heat exchanger efficiency over time.

Q2: How does tube diameter affect heat transfer?
A: Larger diameter differences between inside and outside affect the conduction resistance through the tube wall, as captured by the logarithmic mean term in the formula.

Q3: Why are both inside and outside surface areas needed?
A: The formula normalizes all resistances to a common basis, requiring area ratios to properly account for different heat transfer areas on each side of the tube.

Q4: What are typical values for convection coefficients?
A: Convection coefficients vary widely: 5-25 W/m²·K for natural convection, 50-1000 W/m²·K for forced convection liquids, and 10-100 W/m²·K for gases.

Q5: How often should fouling factors be updated?
A: Fouling factors should be based on operational experience and may need adjustment as fouling characteristics change with operating conditions and time.