What is a Surface Condenser : Construction and Its Working

Generally, every large-scale industry consists of a power plant like a heat engine. The basic components of a power plant are boiler, turbine, condensers, cooling tower, etc, where each component has its individual functionality. A condenser is a unit that condenses steam to water at a pressure less than atmospheric pressure (its function is to provide continuous cooling to the power plant). The condenser is classified into two types, like based on there flow of direction (parallel flow, cross flow, and counter flow) and based on cooling action (Jet type & Surface condenser or non-mixing type). This article gives an overview of the surface condensers.

What is Surface Condenser?

Definition: Surface condensers are mainly used in large power plants and refrigeration systems. The main purpose is to condense the exhausted steam in order to obtain high efficiency and convert the steam into impurity-free water which can be used in a steam generator or steam boiler. It is also called as indirect contact or non-mixed type condenser. One of the advantages of the surface condensers is that they are used in an area where the usage of water is less like the ship, installation of land.

Components of Surface Condenser

The condenser is provided with a horizontal cast-iron of cylindrical-shaped vessel, water tubes where water flows,  and exhaust steam inlet that allows the steam inflow into the cylinder, a baffle, 2 vertical tube plates that are present on either side of the condenser. The design is made in such a way that, it prevents the water leakage from entering into the center space of the condenser.

A cooling inlet which is present at the bottom of the vessel allows the cooling water to inflow, the water tube passes water horizontally through the main condensing space, whose direction of movement of water inside the tube is represented as arrows. The water outlet is provided on the top right of the vessel to allow the impure water to outflow from the condenser, a steam inlet provided at the top of the vessel forces the steam to pass downwards over the tubes. The cooling water flows in one direction in the lower half of the tubes and moves in the opposite direction in the upper half of the tubes.

Working of Surface Condenser

The surface condenser can condense the steam in two ways.

• Firstly by allowing cooling water to flow over the series of tubes and allowing steam to pass over tubes.
• Secondly by allowing steam to pass over a series of tubes and water to flow outside the tubes.

The cooling water from the cooling water inlet is filled inside the tubes and the exhaust steam from exhaust steam inlet enters into the cylinder surrounding, thereby rejecting the heat and condenses the steam into the water which is collected at the bottom of the condenser and the impure water is sent out from the water outlet. This is how a condenser works.

Surface Condenser Efficiency

It is defined as the ratio of temperature rise of cooling water inside the condenser to the difference between vacuum temperature and cooling water inlet temperature.

η _condenser = temperature raise of cooling water inside the condenser (∆T)  / (vacuum temperature and cooling water inlet temperature) ………..(1)

The following are the parameters to be maintained for obtaining better efficiency of surface condenser they are,

Cooling water temperature = 32⁰ C

The outlet temperature of cooling water = 40⁰ C

Vacuum gauge pressure = 0.92 kg/m²

For calculating the vacuum temperature, we should calculate absolute pressure.

Where

absolute pressure P_a = atmospheric pressure – Vacuum gauge pressure P_r…..(2)

We know that atmospheric pressure = 1.0322 kg and vacuum gauge pressure = 0.92

Therefore, on substituting in above equation 2 we get

Absolute pressure P_a = 1.0322 – 0.92 =0.1122……….(3)

From the standard temperature table, we can observe that at P_a = 0.1122 the vacuum temperature to be maintained inside the condenser is 48⁰ C to achieve better efficiency.

η _condenser  = [( 40⁰ – 32⁰ ) / ( 48⁰ – 32⁰ ) ]* 100 = 50 % …….4

Hence the surface condenser achieves 50% of efficiency based on the above parameters.

Surface Condenser Types

Surface condenser are classified into 4 types they are

Down Flow Type

In downflow type condenser, the exhausted steam flows from the top of the condenser shell to the bottom of the condenser over the water tubes (where the water over tubes are passed twice). The cold water flows downwards and later on flows in the upper direction, resulting in the maximum transfer of heat.

Central Flow Type

It is an advanced version of the downflow type, where it consists of a steam of passages surrounding the shell. The main function of this is to pump the air away from the center portion of the condenser. The condensed air moves toward the center portion of the condenser and the exhausted steam move towards the center portion to reduce the under-cooling property.

Evaporative Type

In this type of condenser, the steam which is to be condensed in passed over a series of tubes and sprayed with cooling water so that they are under controlled temperature. The flow of exhausted steam not only increases the evaporation of cooling water but also increases condensate steam.

Difference between Jet and Surface Condenser

The difference between jet and surface condenser is

Advantages

The following are the advantages of surface condenser

• Its vacuum efficiency is high
• They are mainly used in large plants area
• It uses low-quality water
• It also uses impure water for cooling purpose
• The pressure ratio & steam are directly proportional.

Disadvantages

The following are the disadvantages of surface condenser

• Water required is in the large amount
• Complex in construction
• High maintenance
• It occupies a large area.

Applications

The following are the applications of surface condenser

• Refrigeration of vacuum
• Evaporation of vacuum
• Systems like Desalination

FAQs

1). Why it is called surface condenser?

It is called the surface condenser because the exhausted steam and cooling water does not mix up.

2). What is the difference between jet condenser and surface condenser?

In a jet condenser, the exhausted steam and cooling water do mix up, whereas in a surface condenser the exhausted steam and cooling water do not mix up.

3). Does condenser reject heat?

Yes, condenser rejects heat.

4). Will an engine run with a bad condenser?

Yes, a bad condenser can run an engine, but this may lead to severe damage.

5). What is the efficiency of the surface condenser?

The efficiency of surface condensers is 50%.

A condenser is a unit that condenses steam to water at less pressure than atmospheric pressure. They are classified into 2 types, like based on their flow of direction and based on cooling action. A Surface condenser or non-mixing type is a sub-classification of a cooling action condenser. This article discusses an overview of the surface condenser where its main function is not to mix exhausted steam and cooling water compared to another condenser. These kinds of condensers are mainly used in an area where there is less requirement of water quantity, for example: in a ship, based on certain parameters like Cooling water temperature, outlet temperature of cooling water, vacuum gauge pressure, absolute temperature, its efficiency can be calculated.