#### 5.2.1 HEI Standards

These standards use four basic equations in sizing condensers:

*Mean temperature difference*

The logarithmic mean temperature difference is expressed as follows:

*Coefficient of heat transfer*

The coefficient of heat transfer recommended by HEI is expressed by the heat transfer resistance summation equation:

*The Fourier Equation*

The Fourier equation for unidirectional heat transfer is used to express the rate of heat flow in terms of heat transfer surface area, coefficient of heat transfer and mean temperature difference and is written as follows:

*Heat Balance Equation*

This equation is usually written as:

By suitable manipulation of these equations, a condenser design can be established for a given performance rating, based on eight principal variables, which are:

* 1* Total heat transferred, which is a function of:

- Weight of steam to be considered.
- Enthalpy of steam less enthalpy of condensate.
- Enthalpy loss or gain of drains and make-up.

* 2* Absolute static steam pressure.

* 3* Cooling water flow rate.

* 4* Cooling water inlet temperature.

* 5* Cooling water outlet temperature.

* 6* Cooling water velocity through tubes.

* 7* Effective heat transfer surface, which is a function of:

- Number of tubes.
- Tube length.
- Tube diameter.
- Tube thickness.
- Tube material.
- Number of cooling water passes.

* 8* Service conditions:

- Tube cleanliness.
- Air inleakage.