Enthalpy Of Evaporation Of Water In Humidification Calculator

Formula Used:

\[ h_{fg} = \frac{c_p \times Le^{0.67}}{\frac{Y_w - Y_{\infty}}{T_{\infty} - T_w}} \]

Specific Heat of Air (cₚ):

J/kg·K

Lewis Number (Le):

Absolute Humidity of Air(tw) (Yₚ):

Absolute Humidity of Air(atm) (Y∞):

Air Temperature (T∞):

°C

Wet Bulb Temperature (Tₚ):

°C

Enthalpy of Evaporation (hₚ):

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1. What is Enthalpy of Evaporation?

Enthalpy of evaporation is the amount of energy (enthalpy) that must be added to a liquid substance to transform a quantity of that substance into a gas. In humidification processes, it represents the energy required to evaporate water into air.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ h_{fg} = \frac{c_p \times Le^{0.67}}{\frac{Y_w - Y_{\infty}}{T_{\infty} - T_w}} \]

Where:

\( h_{fg} \) — Enthalpy of evaporation (J/kg·K)
\( c_p \) — Specific heat of air (J/kg·K)
\( Le \) — Lewis Number (dimensionless)
\( Y_w \) — Absolute humidity at wet bulb temperature
\( Y_{\infty} \) — Absolute humidity at atmospheric temperature
\( T_{\infty} \) — Air temperature (°C)
\( T_w \) — Wet bulb temperature (°C)

Explanation: This formula calculates the enthalpy required for water evaporation in humidification processes based on psychrometric properties of air.

3. Importance of Enthalpy Calculation

Details: Accurate calculation of evaporation enthalpy is crucial for designing HVAC systems, humidification processes, and understanding heat and mass transfer in air-water systems.

4. Using the Calculator

Tips: Enter all required parameters with appropriate units. Ensure temperature difference (T∞ - Tw) is not zero to avoid division by zero errors.

5. Frequently Asked Questions (FAQ)

Q1: What is the Lewis Number in this context?
A: The Lewis Number is a dimensionless number defined as the ratio of thermal diffusivity to mass diffusivity, representing the relative rates of heat and mass transfer.

Q2: Why is the exponent 0.67 used for Lewis Number?
A: The exponent 0.67 is derived from empirical correlations for heat and mass transfer analogy in air-water systems.

Q3: What are typical values for specific heat of air?
A: Specific heat of air at room temperature is approximately 1005 J/kg·K.

Q4: How does humidity affect evaporation enthalpy?
A: Higher humidity differences (Yw - Y∞) generally result in lower evaporation enthalpy values, as the driving force for evaporation increases.

Q5: What applications use this calculation?
A: This calculation is used in HVAC system design, industrial humidification processes, cooling tower design, and psychrometric analysis.