Chiller Technical Information　2-2. Liquid-cooled heat exchanger (liquid to liquid)

This section describes the structure and characteristics of liquid-cooled heat exchangers (liquid to liquid).

Roles and applications of liquid-cooled heat exchangers

A heat exchanger is a device that transfers thermal energy from a hot fluid to a cold fluid. It is used for heating and cooling by efficiently exchanging heat energy using fluids such as liquids and gases. It is used in a wide range of applications such as the production process of industrial products and air conditioning of buildings.

Types of liquid-cooled heat exchangers

A liquid-cooled heat exchanger is a heat exchanger designed to efficiently exchange heat without having to mix the fluids of 2 systems. There are many types of heat exchangers for liquid-to-liquid heat exchange, but the following heat exchangers which have extensive operating track records are introduced here: (1) blazing plate heat exchangers, (2) gasket plate heat exchangers, (3) shell and tube (multi-tube) heat exchangers, (4) throw-in heat exchangers, and (5) jacket tanks.

1. Blazing plate heat exchanger（Water cooling chillers　PCU-SL/PCU-R Series）
2. Gasket plate heat exchanger
3. Shell & tube heat exchanger
4. Throw-in heat exchanger
5. Jacket tank

*For more details on the cooling water used for liquid cooling, go to “3-1. Types and Characteristics of Cooling Water”

(1) Blazing plate heat exchanger

・Setup and structure

As shown in Figure 1 below, the structure consists of laminated electrical heating plates which are sealed by soldering the recesses (brazing). Copper is often used as a brazing material from a cost and workability perspective. If hygiene specifications are required in the food, pharmaceutical, semiconductor and other industries, nickel brazing, stainless steel brazing, etc., can also be selected.
The structure allows a high-temperature and low-temperature liquid to flow alternately in the gaps between the plates, which allows heat to be exchanged efficiently, thereby keeping the heat exchanger compact for the amount of heat exchanged. It is advantageous to use the “countercurrent” circulating the high temperature liquid and low temperature liquid in opposite directions as the heat exchange efficiency as shown in Figure 2 below.

・Features

○Relatively compact for its heat duty.
○Cost is relatively low.
○Since the flow path cannot be broken down narrowly, clogging of solids may occur.

(2) Gasket plate heat exchanger

・Setup and structure

The structure is the same as a blazing heat exchanger in that the plates are laminated and two kinds of fluids flow in an alternate manner, but the plates are separated by rubber gaskets in this case. By removing the tightening bolts that fasten the securing plates at both ends, it is possible to maintain the plates and gaskets, and also increase the cooling capacity by adding a number of plates. As a result, the heat exchanger is slightly larger in size than a brazing heat exchanger, so the maintenance space also needs to be considered during installation.

・Features

○Slightly larger than the brazing type, but is relatively small for its heat duty.
○Plate can be disassembled for maintenance.
○Gasket material can be changed according to the specifications.

(3) Shell & tube heat exchanger

・Setup and structure

A shell and tube (multi-tube) heat exchanger is a heat exchanger with a tube (heat transfer tube) stowed in a shell (body) as shown in Figure 5 and 6 below.
In order to obtain the same heat transfer area, the size is larger compared to a plate heat exchanger. As a result, the shell (body) has a wide flow path and the tube (heat transfer tube) splits into multiple branches, allowing the pressure loss of the fluid to be reduced for high viscosity fluids in the design too. For this reason, it is used in hydraulic-related equipment and chemical plants etc. where high viscosity oils are handled.
It can be used for all kinds of applications from low temperature to high temperature, low pressure to high pressure, and for heating, cooling, evaporation and condensation.
Maintenance is also easy because the structure is simple and can be disassembled (depending on the type of equipment).

・Features

○Size is larger compared to the plate type.
○The pressure loss of the fluid can be designed as small so that high viscosity fluids can also be used.
○Can be disassembled for maintenance.
○Can be designed to withstand high pressures.

(4) Throw-in heat exchanger

・Setup and structure

Cooling is performed by immersing a tubular or plate-shaped heat exchanger into a tank with the liquid to be cooled. Although the advantage is that there is no need for a circulation circuit of the liquid to be cooled, countermeasures such as the installation of an agitator for the cooling target etc. are required to improve the cooling efficiency.

・Features

○Implementation is relatively easy.
○Shape and heat transfer area can be designed according to the tank size and shape.
○Agitators etc. are required to improve heat transfer efficiency.
○Difficult to predict the amount of heat exchanged as it is difficult to quantify the stirring extent.
○Condensation occurs when the cooling water temperature is low, so contamination of the liquid to be cooled is a concern.

(5) Jacket tank

・Setup and structure

As shown in Figure 11, the tank has a double structure consisting of an inner tank and jacket to cool, heat, and keep the contents placed in the inner tank warm. By circulating cooling water and hot water in the jacket, the raw materials placed in the inner tank are heated.
Generally, the structure is made of stainless steel and is easy to clean, so it is often used in the manufacturing process of foods and pharmaceutical products. Compared to a circulating heat exchanger, the heat transfer area is smaller and unevenness in the temperature is likely to occur. In such cases, the inner tank is stirred with an agitator to improve the heat transfer efficiency and equalize the temperature in the tank.

・Features

○Suitable for sanitary use as cleaning is easy.
○Agitators etc. are required to improve heat transfer efficiency.
○Difficult to predict the amount of heat exchanged as it is difficult to quantify the stirring extent.

Previous item: 2-1. Air-cooled heat exchanger (liquid to gas)
Next item: 2-3. Direct cooling by chiller