The operating principles of a marine heat exchanger are the same as a cooler designed for fresh water use, the main consideration for the designer however is that the marine heat exchanger must be resilient to erosion or corrosion caused by sea water.
There are other factors which need to be taken in to consideration when a marine heat exchanger is being designed. One is the velocity, if it is too low then there is a risk that sand and other particles will block the tubes.
If it is too fast on the other hand then those same particles can rapidly erode the tube plate and tubes. Additional protection can be provided by installing a sacrificial anode which Thermex can include upon request. This will be installed in to the threaded hole normally used for a drain plug and is in direct contact with the sea water flow. The suitability of a fluid with a heat exchanger will depend on the type of heat exchanger being used and the materials which are available.
For more corrosive fluids such as chlorinated salt water, refrigerants and acids other materials such as Stainless Steel and Titanium will need to be used instead. Temperature cross over is a term used to describe the scenario where the temperatures of both circuits in a liquid cooled heat exchanger begin to cross over.
This can be an important factor in a heat exchanger design as the efficiency of a cooler will be significantly reduced when the temperatures cross over. In many cases a plate heat exchanger is the best option for applications where temperature cross over can't be avoided.
The table above demonstrates that the cooling water outlet temperature is slightly higher than the outlet temperature of the oil. One simple way to combat this and increase the efficiency of the oil cooler is to increase the flow rate of the coolant. A Heat Exchanger Pass refers to the movement of a fluid from one end of the heat exchanger to the other.
The images below will help to demonstrate this;. Heat exchanger efficiency can be defined in many ways, in terms of thermal performance there are several key factors to consider;. Temperature differential - As discussed in point 3 temperature cross-over the difference between the hot fluid and coolant is very important when designing a heat exchanger.
The coolant always needs to be at a lower temperature than the hot fluid. Lower coolant temperatures will take more heat out of the hot fluid than warmer coolant temperatures. If you had a glass of drinking water at room temperature for example, it is much more effective to cool it down using ice rather than just cool water, the same principle applies to heat exchangers.
Flow rate - Another important factor is the flows of the fluids in both the primary and the secondary side of the heat exchanger. A greater flow rate will increase the capability of the exchanger to transfer the heat, but a greater flow rate also means greater mass, which can make it more difficult for the energy to be removed as well as increasing velocity and pressure loss. Installation - The heat exchanger should always be installed based on a manufacturers' guidelines.
View Larger Image. What is a furnace heat exchanger? How does a furnace heat exchanger work? How can you keep your heat exchanger working safely? First, make sure to schedule a furnace tune-up every year.
Inspecting your heat exchanger is one of the most important tasks that we perform during a tune-up. The design of the plate and frame heat exchanger creates a large heat transfer area, high turbulence, and high fouling resistance. The overall heat transfer coefficient and efficiency are higher compared to tubular heat exchangers.
However, the high-pressure drop is encountered by the fluids due to high wall shear stress that makes pumping costs expensive. It is also not advisable to be used if the fluids have high-temperature differences.
Plate fin heat exchangers are valued for their compactness, the ratio of the heat transfer area to heat exchanger volume. Hence, they consume small floor spaces and are lightweight.
This type of heat exchanger is used in aerospace, cryogenic air separation, and refrigeration. Direct Contact Heat Exchangers do not involve a conductive partition and rely on direct contact for the heat exchange to take place. They are suitable for two immiscible fluids, or if one of the fluids will undergo a phase change. They are cheaper due to their simpler design.
It is commonly used in seawater desalination, refrigeration systems, and waste heat recovery systems. Examples of direct contact heat exchangers are direct contact condensers, natural draft cooling towers, driers, and steam injection. These are also known as regenerators or capacitive heat exchangers. Regenerative heat exchangers are types of heat exchanger equipment that utilizes a heat storage medium that is made to contact with the hot and cold fluids.
The two fluids are usually gases. They are used in power plants, glass and steel making, and heat recovery systems. However, there is potential contamination since the same medium is used to interact with the hot and cold fluids. Operation of static regenerators is semi-batch since the flow of the fluids is intermittent. To achieve a continuous operation, two channels must be used. Thermodynamics of Heat Exchangers.
A typical shell and tube exchanger can have tubes running from one side to another; or bend inside to follow a U-shaped path. The most simple design in the construction of shell and tube exchanger; is the one with tubes welded to the shell. It is most economical and allows the movement of fluid from one side to another side of the shell. Moreover it allows for the manual cleaning of the tubes internal along with normal chemical cleaning procedures.
The two fluids flow in tubes and the surrounding shell; with heat flowing from medium in tubes to that in shell or vice versa. The inlet and outlet points for shell medium is called; inlet and outlet nozzles for the shell. On another hand the inlet and outlet points for tubes are called front and rear header respectively.
The tubes used in its construction must be thermal conductive with the ability to withstand thermal stress; due to varying temperature across the width of the tube surface. Moreover the tube must withstand the thermal expansion with change in temperature. Furthermore the tube must be strong, corrosion resistant and compatible with fluid medium. The material of these tubes should be such that it does not react with these fluids under normal condition.
A heat exchanger works on the simple principle of second law of thermodynamics; the heat flow from a body to another in respect of their temperature difference.
The heat under natural state will move from a hot body to a cooler one. In shell and tube type heat exchanger the cooling medium; whether water, steam, ethanol or polypropylene glycol is passed through the tubes within the shell structure.
On other hand the medium to be cooled around these tubes within shell structure. In most scenario the cooling medium say sea water enters from the bottom or rear header based on design; to leave from top or front header passing through aluminum brass tubes. Similarly the cooling medium say lub oil enters through the inlet nozzle to leave via exit passing through baffles within shell structure.
These baffles helps improve the efficiency by creating turbulence in the flow avoiding creation of hot and cold pockets within the medium. It also can have either concurrent, counter concurrent or cross flow arrangement based on design and requirement. The temperature of the output fluid medium is controlled using a bypass valve; increasing or decreasing flow of the cooling medium.
Similarly to protect the fluid medium from intermixing due to leakage; the pressure of cooling medium is kept lower than that of the fluid medium to be cooled.
This allows the fluid such as lub oil from being contaminated even in event of any leakage. A plate type heat exchanger transfer heat from one medium to another with the help of identical thin plates; made of titanium or stainless steel.
They are held together with the help a fine clearance maintained by the gasket material of rubber and asbestos fiber. They are much compact and have an added advantage of variable capacity.
0コメント