Views: 27 Author: Site Editor Publish Time: 2024-08-23 Origin: Site
In many industries, especially HVAC, maintaining precise temperature control is crucial for smooth operations. This is where heat exchangers step in. They are the unsung heroes that facilitate setting of various fluids to the desired temperature levels.
Heat exchangers transfer thermal energy between different fluids, making sure that they are separated during the process. The separation is important so that the fluids don’t get mixed or contaminated. This helps in maintaining their characteristics and properties.
Imagine an industrial operation where hot water must warm another fluid without touching each other. The heat exchanger is used to efficiently transfer heat from the hot water to the other fluid.
In this article, we will further discuss concepts like: what is a heat exchanger, the different types of heat exchanger, what type of heat exchangers are suitable for HVAC systems, and how to choose the right one.
A heat exchanger is a mechanical component used to transfer heat from a fluid (liquid, gas, or vapor) to another fluid without direct contact with each other. Its main function is to increase or reduce the temperature of fluids.
The basic structure of a heat exchanger comprises two channels separated by a barrier (which can be a solid wall, tube, or plate). As the hot fluid is passed through a channel, it changes the temperature of the cooler fluid, thus achieving your desired temperature. This is very essential in multi-zone heat pumps, where different parts of a building require varying temperature levels.
Even though there are various types of heat exchanger, they perform the same function. However, they have unique features, advantages, and applications. Let’s look at them below:
The sheet and tube heat exchanger is the most common type of heat exchanger because of its versatility across many industries. It consists of a series of tubes placed inside a cylindrical shell. One of the fluids is transmitted within the tubes while the other fluid flows inside the shell. This heat exchanger is most common in HVAC systems, oil, gas, power plants, food & beverage, and chemical industries.
Some shell and tube heat exchanger are made with high-efficiency finned tubes, and the heat exchange area is 3.7 times more than a normal tube. The compact spiral structure of the coil ensures that the refrigerant can accurately exchange heat and that the water flow rate is uniform. This type of heat exchanger is known for high heat exchange efficiency, portability, resistance to clog, strong anti-freezing ability, and suitability for most single heat units.
There are 2 major shell and tube heat exchanger:
• Single Tube Heat Exchanger: Consists of a single tube passing inside the shell. One fluid is transmitted through the tube, the other fluid is transferred in the free part of the shell.
• Double Tube Heat Exchanger: Consists of two tubes passing inside the shell. One tube carries a particular fluid, while the other carries another fluid.
This type of heat exchanger involves passing fluid into a series of tubes, and pumping gas or air around the tubes to cool the fluid down. Sometimes, finned-tube heat exchangers are enclosed in duct work. Other times, they are fully exposed with air passing over them.
The efficiency of this heat exchanger comes from the added fins (extended surface) that protrude into the gas or air flow, which allow more heat exchange.
Finned-tube heat exchangers are normally used for heat recovery in applications that exhaust hot gasses. The heat in the gas is transferred into a liquid, and then the heated liquid is used in operations that often use more energy to heat up. Some of the common applications are HVAC systems, radiators, and aerospace industry.
This heat exchanger is also called a “tube-in-tube” heat exchanger. It consists of two pipes – one larger pipe and a smaller one, where one is built inside the other. While one fluid is transferred through the larger pipe, the other fluid is carried in the smaller pipe.
It has a compact design, which makes it ideal for applications with limited installation space. The two fluids are inserted inside each other, making it easy to clean and maintain.
Double pipe heat exchangers are highly revered for their ability to handle fluids of high pressure and temperature. Thus, they are often used in applications where extreme conditions are required, such as chemical processing plants, laboratory equipment, and small-scale industrial operations.
This heat exchanger involves passing of fluids through a series of plates that are compacted together side-by-side. It consists of multiple thin plates with alternating channels that gives a large space for heat exchange. The corrugated patterns improve heat transfer between the fluids on both sides of the plates.
At SPRSUN, our plate heat exchanger is made of 316 ultra-low carbon stainless steel plates, which are vacuum welded. Water and refrigerant flow in the thin sheets, with sufficient contact and high heat exchange efficiency.
This heat exchanger type is highly revered for its compact structure, small cooling water volume, high heat exchange efficiency, and strong corrosion resistance, making it ideal for units that require higher heating and cooling power, such as HVAC systems, refrigeration, chemical processing, food & beverage, and power plants.
The condenser is a heat exchange device that takes hot gas or vapor and cools it until it reaches the point of condensation. It employs the two-phase heat transfer mechanism, which involves one fluid undergoing a change during the transfer process. This results in changing the gas or vapor to liquid.
At SPRSUN, our condenser heat exchange is composed of a water tank and a copper tube. The copper tube is wound into a coil shape. The coils are replaced with 316L stainless steel coils, which have high heat exchange and are difficult to scale or corrode.
This heat exchanger type is efficient in removing latent heat, especially in refrigeration & air conditioning systems, power plants for condensing steam from turbines, distillation & refinement processing, and chemical processing.
These heat exchangers are the opposite of condensers. They change fluids from liquid to gas/vapor. The point at which the liquid transforms to gas is called vaporization. It offers efficient heat absorption, crucial for cooling processes and handling various fluids & temperature ranges.
Evaporators and boilers are used in refrigeration systems for cooling, HVAC systems for air conditioning, distillation & refinement processing, and chemical processes for concentrating solutions.
This type of heat exchanger works by using the surrounding air to cool and condense the fluids that are transferred. The fluids are stored in heat conducting finned tubes and electric cooling fans are used to dispense sufficient air.
Air cooled heat exchangers are often used in applications that involve limited access to cold water. Also, they are used when the outlet temperature is at least 20⁰C more than the ambient temperature. They are commonly found in chemical plants & refineries, petrochemical manufacturing plants, natural gas processing plants, compressor stations, and nuclear power plants.
A fan cooled heat exchanger is similar to air cooled heat exchanger. But it relies on forced air rather than natural convection. Basically, it uses fans to move air when cooling fluids. No water required, making it suitable for dry environments and it can be used in confined spaces where natural convection is inadequate.
Fan cooled heat exchangers are efficient in cooling even in high temperature environments and can be used in applications like automotive radiators, HVAC systems for cooling, and industrial machinery cooling.
An adiabatic wheel heat exchanger uses a rotating wheel, typically made of a heat-absorbing material to transfer heat between two fluids. The wheel alternates between the hot and cold air fluids, absorbing heat from one and releasing it to the other.
This heat exchanger has a compact design with a large surface area that can handle large air volumes. It has high efficiency in heat recovery and is used for applications like HVAC systems, industrial ventilation, chemical & petrochemical processing, petroleum refineries, food processing & pasteurization, power generation, cryogenics, and aerospace.
For types of heating systems that demand heat transmission to viscous or sticky materials, the Scraped Surface Heat Exchanger is the best option. It is specially designed to remove sticky materials by using rotating blades, which guarantees uniform heat transfer throughout the heating system.
The blades turn the fluids in the same direction around the exchanger, as they enter through one side and exit via the other. The sticky materials are pushed into a cylinder at the bottom. This ensures quality and uniformity in the industrial process.
Common applications of scraped surface heat exchangers are food, pharmaceutical, crystalizing & phase changing products (like sugar concentrates), and products that are sticky (like toothpaste).
Water cooled heat exchangers remove unwanted heat from a process by moving it to water, thereby keeping it at an ambient temperature. As opposed to the air cooled heat exchanger, this type of heat exchanger offers different levels of cooling. It is not limited to the ambient temperature of the environment.
Water cooled heat exchangers are very reliable at transmitting and removing unwanted heat. Hence, why they are often used across many industrial operations, such as steam condensing, marine applications for engine cooling, power plants for cooling turbine exhaust, and oil & gas.
This type of heat exchanger has a similar structure as Plate Heat Exchanger. However, the corrugated metal plates are brazed together and fully sealed using a process called fusion bonding. The plates form alternating channels for fluids, which helps to increase the heat transfer efficiency.
Brazed plate heat exchangers are designed to be compact and lightweight, making them 90% smaller than other plate type heat exchangers. Thus, they are a great option for small spaces with high pressures and temperatures. These heat exchangers are largely used in refrigeration & HVAC systems, renewable energy systems like solar thermal & geothermal, and boiler separation plates.
Sometimes called Dimple Plate Heat Exchanger, it is designed with two thin metal plates that are welded together at intervals, creating pillow-like structures. The space between the plates enables the seamless flow of fluid, thereby providing a large surface area for heat transfer.
As the metal plates are welded tightly, the risk of fluid leak is eliminated, making it a cost-effective option for various industries like food & beverage, chemical processing, and renewable energy systems.
This exchanger serves as a waste heat recovery system, absorbing heat energy from exhaust gasses (diesel, hydrogen, gas, or biogas-powered engine) and transferring them to a water circuit. The recovered heat can be used for preheating combustion air, generating steam, or other heating applications.
Exhaust gas heat exchangers are often used in bakeries, industrial furnaces, hardening plants, and processing plants. These types of heat exchangers help to lower fuel consumption and can be easily integrated into existing systems with minimal modifications. They are also used in hazardous applications to reduce the exhaust temperature released into the environment.
This heat exchanger uses a rotating matrix to alternate the flow of hot and cold fluids through a single tube at regular intervals. It stores the heat from the hot fluid in a thermal tank before transmitting it to the cold fluid.
Regenerative heat exchangers are best suited for gas to gas heat exchange where the fluids don’t have to be fully separated. They are commonly found in operations that involve increasing the efficiency of high pressure boilers and industrial furnaces, as well as chemical applications.
This type of heat exchanger involves two fluids flowing perpendicularly to each other. One fluid is transferred through tubes or plates, while the other is transmitted across them, allowing for efficient heat transfer between both fluids.
Cross flow heat exchangers are popularly used in automotive radiators, industrial cooling processes, and air conditioning & refrigeration systems.
For this type of heat exchanger, both fluids enter the heat exchanger at the same end and move in the same direction. The transfer of heat happens as the fluids move parallel to each other. It is suitable for applications with moderate heat transfer requirements, such as HVAC systems, simple industrial processes, and small-scale heating & cooling systems.
This type of heat exchanger involves the fluids entering the heat exchanger from opposite ends and flowing in opposite directions. The counter flow heat exchanger is designed to enable maximum temperature gradient between the fluids, thereby improving heat transfer efficiency.
Its uses can be found in power plants for steam generation, refrigeration systems for efficient cooling, and chemical processing for heating & cooling.
The different types of heat exchangers explained above perform the same function and can be confusing to differentiate sometimes. But a way to differentiate them is to identify their flow arrangement. There are 3 main flow arrangements, which are:
• Parallel Flow Arrangement: The hot and cold fluids are poured into the exchanger in a parallel flow and they exit together the same way. The parallel flow arrangement is mostly seen in shell and tube heat exchangers and double pipe heat exchangers.
• Counter Flow Arrangement: The hot and cold fluids are poured into the exchanger at opposite ends, move in opposite ends, and exit the exchanger at opposite ends. This flow arrangement is common in shell and tube heat exchangers, high-efficiency plate heat exchangers, and double pipe heat exchangers.
• Cross Flow Arrangement: The hot and cold fluids flow perpendicular to each other. While one fluid is transferred inside the tubes or plates, the other fluid flows across the tubes or plates. This flow arrangement is popular in air cooled heat exchangers and condensers.
Amongst the various heat pump exchangers discussed above, there are 3 specific ones that are most suitable for HVAC systems.
• Shell and Tube Heat Exchanger: Has the capability to handle a wide range of operations, including small residential buildings to large industrial applications. Shell and tube heat exchangers structure and large surface area for heat transfer ensures reliability and optimal performance over a long time.
• Plate Heat Exchanger: This heat pump heat exchanger is greatly revered thanks to its compact design and capacity to handle varying temperatures. The plate heat exchanger is ideal for HVAC applications where space is limited and high efficiency is required.
• Finned-Tube Heat Exchanger: This heat exchanger increases the heat transfer surface area through fins, making it great for air-to-liquid heat transfer. Finned-tube heat exchangers are normally used in heat pump systems like the heat pump R290 to improve heat exchange between air and water.
These are the factors you should keep in mind when choosing the right heat exchanger for HVAC systems:
• Fluid Type, Stream, and Properties: The specific type of fluid (whether liquid, air, or gas), as well as the fluid stream (whether high pressure or low pressure) should influence the heat exchanger you choose. Also, you should select a heat exchanger that can withstand the fluid properties, such as the temperature, acidity, and alkalinity of the fluids.
• The Desired Thermal Output: The amount of heat transferred between fluids and the corresponding temperature change at the end of the heat transfer process should also be considered. Choose a heat exchanger that can efficiently achieve your desired heat exchange between both fluids.
• Size Limitation: It is paramount to pick the right size of heat exchanger. It is advisable to choose a heat exchanger that has a little more space for fluid expansion and smooth flow, rather than choosing one that tightens the fluid flow.
• Costs: Consider the total costs of the heat exchanger. This includes not only the initial cost, but the installation, operational, and maintenance costs. Going ahead to choose less-expensive heat exchangers because of budget constraints might result in shorter lifespan and possible damage to other components in your HVAC system.
• Design Optimization: You can also select a preferred heat exchanger based on your custom needs. Discuss with your supplier for a uniquely designed heat pump heat exchanger with construction patterns that suit your application. Crucial elements to discuss are the fluid types, thermal efficiency, sizing, costs, maintenance, and durability.
Source：SPRSUN Heat Pump
At SPRSUN, our goal is to provide you with high quality heat pumps. As a leading professional heat pump manufacturer, we offer the best HVAC systems using the best heat exchangers. In our inverter heating and cooling heat pump systems, we utilize Plate Heat Exchangers for optimal performance. For heat pump systems within 15HP that are specifically engineered for hot water applications, we employ Shell and Tube Heat Exchangers to ensure efficiency and reliability.
We offer all-round heat pump services. For inquiries on other heat pump needs, you can contact us here to discuss with our experts.
