Heat Loss Open Water Tanks

Overview

Engineering reference data for Heat Loss Open Water Tanks in thermodynamics.

Key Formulas

First Law

$\Delta U = Q - W$

Energy is conserved — heat added minus work done.

Ideal Gas Law

$PV = nRT$

Relates pressure, volume, and temperature of an ideal gas.

Heat Transfer

$Q = mc\Delta T$

Sensible heat transfer.

Carnot Efficiency

$\eta = 1 - T_C/T_H$

Maximum efficiency between two temperatures.

Variables

Symbol	Description	Unit
$U$	Internal energy	J
$Q$	Heat	J
$W$	Work	J
$P$	Pressure	Pa
$V$	Volume	m³
$T$	Temperature	K

Heat Loss Data Table

Worked Example Calculation

For an open water tank with:

• Water temperature: 150°F
• Liquid surface area: 10 ft²
• Un-insulated bare steel wall area: 50 ft²

The total heat loss (Q) is calculated as:

1. Surface Heat Loss (Evaporation + Radiation): Using the total surface loss value for 150°F from the table (1040 Btu/ft²·hr): $Q_{\text{surface}} = q_{\text{surface}} \times A_{\text{surface}} = 1040 \frac{\text{Btu}}{\text{ft}^2 \text{hr}} \times 10 \text{ ft}^2 = 10400 \text{ Btu/hr}$

2. Wall Heat Loss (Transmission): Using the bare steel wall loss value for 150°F from the table (180 Btu/ft²·hr): $Q_{\text{walls}} = q_{\text{walls}} \times A_{\text{walls}} = 180 \frac{\text{Btu}}{\text{ft}^2 \text{hr}} \times 50 \text{ ft}^2 = 9000 \text{ Btu/hr}$

3. Total Heat Loss: $Q = Q_{\text{surface}} + Q_{\text{walls}} = 10400 + 9000 = 19400 \text{ Btu/hr}$

Assumptions and Unit Conversions

Important Assumptions: The tabulated values are rough estimates for open tanks in still ambient air at 60°F (15.6°C). Actual losses are highly sensitive to environmental factors including air velocity, turbulence, moisture content, and water agitation. Surface losses, dominated by evaporation, increase dramatically with temperature.

Unit Conversions:

• Temperature: $T(°C) = \frac{5}{9} (T(°F) - 32)$
• Heat Flux: $1 \text{ Btu/(ft}^2\text{·hr)} = 3.1525 \text{ W/m}^2$

Interactive Charts

References

• Original Source