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Finned Tube Heat Exchanger
2
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(Mechanical)
(OP)
20 Jan 22 12:26Hello everyone, hope You all are staying safe in these challenging times.I'm designing fin-tube heat exchanger (water-air). I have all the calculations needed, heat exchanger is manufactured & tested and works great, but as a curious person I'm still wondering about some theoretical aspects. I currently don't have any collegues in mechanical department, so I really appreciate any discussion on the subject. I'm still very fresh engineer, so correct me if I'm wrong anywhere along the way.To visualize the case a little better, here is a simplified drawing of heat exchanger:Knowing the coolant flow for the cooling loop and the size of the Inlet/Outlet coolant connections, we can find the velocity of fluid using: Q = V/t = A*v = (πdv)/4If coolant connections sizes are the same, in&out velocity of fluid will also be the same. (Flow in = Flow out = constant)What about the velocity of fluid inside the tubes? Will the flow inside single fin-tube be "Q/number of tubes"? (Q: system flow)If (1) is the correct assumption, then more fin tubes inside heat exchanger = lower fluid velocity inside single fin-tube = larger cooling capacity, but higher outlet temperature of the coolant.I'm calculating Reynolds Number by multiplying "Mass Flow unit Area" with fin-tube diameter and dividing the product with "Dynamic Exhaust Viscosity @ Mean Temperature". [Re=(G*d)/μ]. My superior says that Reynolds number should be below 12000, but he doesn't really know how to support this statement with scientific knowledge. Is there any way to establish the limits for Reynolds number? Or is there some kind of rule of thumb? I've only learned that for a flow inside a pipe to be laminar, the Reynolds number should be kept under 2000, but that's simplification I remember from uni.Is there any critical velocity for the fluid flow? I remember I've read somewhere that it's usually kept under 3 m/s, as a rule of thumb. However, I don't know more. The only reason I can think of is that the force of moving fluid on the structure (walls) shouldn't exceed certain value.Anyway, I think that's it for now. If any additional questions will pop in my head, I'll surely update.I appreciate every single input. Thanks in advance!
(Materials)
20 Jan 22 14:26Are the tubes all plumbed in parallel, series, of a combination?High velocity promotes mixing and speeds heat transfer.But high V also increases pressure drop (pumping losses) and can promote erosion in susceptible materials (usually softer ones like Cu or Al).
= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed
(Mechanical)
(OP)
21 Jan 22 09:18Hi Ed and thanks for the answer.
Tubes are in parallel.
Is there any way to determine critical in/out velocity?
What about the statements (1) and (2) I made above? Can You either confirm or deny?
(Materials)
21 Jan 22 14:29You know the total flow and the total ID area of the tubes so you can figure out the average velocity.Unless the total ID area of the tubes is less than your inlet you will have significant variation in flow from one tube to the next.While the flow velocity does impact heat transfer there isn't a step function in the range of 1.5 m/s - 4 m/s, it is fairly proportional.Some materials can tolerate 30 m/s (most SS), others begin to have erosion issues above 2 m/s (Cu).
= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed
(Mechanical)
22 Jan 22 07:15The fact that the inlet and outlet are offset from each other would contribute to the flow being evenly distributed between the fins. If the inlet and outlet were directly opposite each other then you would be more likely to have more flow through one side of the heat exchanger than the other.Then you said something interesting that is a common misconception with heat exchangers. You said something about lower velocity causing improved heat transfer because the inlet and outlet temperature are more different. This is not an indication of heat transfer efficiency. If your outlet temperature is much lower or higher than your inlet temperature it could actually be an indication of poor heat transfer. It means that the delta T between the heating fluid and cooling fluid closer to outlet is becoming less and less and that means that heat transfer is becoming worse the closer your getting to the outlet. It means that the flowrate of the fluid that you are heating or cooling is too low.This is a good example of where an increase of the air flowrate would improve the heat transfer. If you increase the air flowrate to a point where the outlet air temperature is about 40 degrees celsius you would improve the overall heat transfer by a lot. You could probably drop your inlet temperature of the fluid into the heat exchanger and by extension the overall system temperature of whatever you are cooling. Obviously this is not always a good thing, but it is food for though nevertheless.
(Chemical)
22 Jan 22 13:29Hi,
A great resource about heat exchanger available using your favorite search engine is Wolverine engineering data book 2
Good luck
Pierre
(Mechanical)
22 Jan 22 17:22Possible source for Wolverine book:Walt
(Mechanical)
1 Feb 22 13:39As mentioned, turbulent flow is used in heat exchangers to promote heat transfer. The standard flow profile of laminar flow (which I assume you're familiar with if you remember the Re for transition is ~2000) has low velocity at the wall, which can lead to the fluid building an "insulative layer" on the wall of the tube and not transferring temperature to the entire column of flow in the tube.
1. What about the velocity of fluid inside the tubes? Will the flow inside single fin-tube be "Q/number of tubes"? (Q: system flow)
2. If (1) is the correct assumption, then more fin tubes inside heat exchanger = lower fluid velocity inside single fin-tube = larger cooling capacity, but higher outlet temperature of the coolant.
3. I'm calculating Reynolds Number by multiplying "Mass Flow unit Area" with fin-tube diameter and dividing the product with "Dynamic Exhaust Viscosity @ Mean Temperature". [Re=(Gn*d)/μE_Mean]. My superior says that Reynolds number should be below 12000, but he doesn't really know how to support this statement with scientific knowledge. Is there any way to establish the limits for Reynolds number? Or is there some kind of rule of thumb? I've only learned that for a flow inside a pipe to be laminar, the Reynolds number should be kept under 2000, but that's simplification I remember from uni.
4. Is there any critical velocity for the fluid flow? I remember I've read somewhere that it's usually kept under 3 m/s, as a rule of thumb. However, I don't know more. The only reason I can think of is that the force of moving fluid on the structure (walls) shouldn't exceed certain value.
(Mechanical)
(OP)
2 Feb 22 08:31Pierre, Walt - Thank You for the book, I've started to read it to get a better understanding of concepts within heat transfer. Great read so far!
Rputvin - Thank You for your throughout answer with explainations. I really appreciate it.
(Mechanical)
2 Feb 22 14:17Vfresh, just to give you a little more to chew on - this is a section of the input screen for a coil selection software. It gives you an idea of some of the design variables that influence performance. If you can get your hands on selection software and a crash course in using it they can be somewhat illuminating to mess around with and try and understand why different input changes influence the performance (and you don't need to do the math yourself every time)If you go deeper down the rabbit hole on these units be aware that everyone uses a lot of different terminology. For instance the coil snip is in "heating" even though the project is working to cool a process because of how this company arranges the terminology for their product, and the item is a "water coil" despite being rated and used for a wide array of fluids. Inlet/outlet, entering/leaving, heating/cooling, supply/return, etc can all flip depending on the framing of the conversation. The same product is called something different, sometimes incorrectly, by every customer, vendor, and colleague; Dry Cooler, Radiator, Fin-Fan Unit, Fluid Cooler, "Chiller", Air Cooled Heat Exchanger, Heat Exchanger, Water Coil, Aerial Cooler, I'm probably forgetting 10 more I've heard.
(Aerospace)
Link to gtboiler
2 Feb 22 18:16@StrongThat link was a waste of time; the download only contains the ToC and cover page, a total of 7 pages.It appears to be something that requires payment from a legitimate vendor like https://www.wieland-thermalsolutions.com/en/engine...
TTFN (ta ta for now)
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What is a fin tube heat exchanger? Heat exchangers heat or cool buildings, improve the efficiency of engines and machines. Refrigerators and air conditioners use heat exchangers to cool elements; radiators use them to warm environments. It’s all about controlling heat energy — either removing it or adding it, depending on the goal and function.
At Energy Transfer, we manufacture fin tubes, as well as enhanced surface and formed and dimpled tubes, for tube fin and tubular heat exchangers. We sell both to original equipment manufacturers as well as people looking to repair existing heat exchangers.
When it comes to building or repairing a tube fin or tubular heat exchanger, how do you determine which tube is right for your heat exchanger? Which one will provide the best thermal solution? What do you need to know to ensure superior heat transfer capability?
It pays to do your homework. Thoroughly researching a manufacturer’s product offerings and capabilities invariably results in a more suitable fin tube to meet your goals and ambitions.
Energy Transfer manufactures a diverse range of fin tube pipes to serve a variety of heat exchanger needs. All options are on the table. We’re ready to meet any need — turn your vision into a reality of superior performance.
This guide will walk you through the selection process of how to choose the optimal finned tube for your heat exchanger. [/vc_column_text][/vc_column][/vc_row][vc_row][vc_column][vc_column_text]
What is a Fin Tube Heat Exchanger?
[/vc_column_text][vc_empty_space][/vc_column][/vc_row][vc_row][vc_column width=”1/2″][vc_column_text]By definition, a heat exchanger is a device used to transfer thermal energy between two or more fluids — it allows heat from a liquid or gas fluid to pass to a second liquid or gas without the two fluids mixing together or coming into direct contact.
The objective of a heat exchanger may be to recover or reject heat, or to sterilize, pasteurize, fractionalize, distill, crystallize, or control a fluid or process fluid.[/vc_column_text][/vc_column][vc_column width=”1/2″][vc_single_image image=”3487″ img_size=”full” alignment=”center” style=”vc_box_border_circle” border_color=”black”][/vc_column][/vc_row][vc_row][vc_column][vc_empty_space][vc_column_text]Tubular heat exchangers consist of small tubes located within a cylindrical shell. These finned pipes are positioned within a cylinder as a bundle, allowing various gases or liquids to circulate in a process of heat exchange that either warms or cools an element.
One fluid or gas flows through a set of metal tubes while a second fluid or gas passes through a surrounding sealed shell. The fluids can flow in the same direction (a parallel flow) or opposite directions (counterflow or counter-current), or at right angles (crossflow).
To increase heat transfer capabilities, fin tube pipes can either have fins that are applied as a second material (as is the case of applied fin tubes), or raised out of the material of the tube itself (such as low fin, medium-high fin, and high finned tubes).
For tubular heat exchangers where there are no fins but just a smooth tube, the tubes can have enhanced surface or formed dimples to mitigate flow and increase heat exchange capabilities.
Conventional Tube-Fin heat exchangers are most commonly used in gas-to-liquid applications. Round fins on the outside of the tube are used on the gas side of the heat exchanger to increase surface area. The liquid side of the heat exchanger consists of a tube bundle of Finned Tubes supported by a sheet metal frame with common headers on each end of the bundle.[/vc_column_text][vc_empty_space][vc_column_text]
Determining Required Heat Transfer for Finned Tubes
The first step is to determine how much heat transfer is required and how much heat transfer surface you’ll need. This will help decide which type of fin tube pipe is the optimal thermal solution, including necessary fin surface requirements and the ideal material. What fin tube geometry is required in order to accomplish your vision?
You also should determine the necessary rate of flow, which will affect the required diameter of the fin tube. This is affected by tube size.
How much pressure drop is needed?
What size of hydraulic diameter is required?
What is the flow length of each fluid side of the heat exchanger?
What is the minimum free flow area?
What do you need in the frontal area?
What is the flow length of each fluid side of the heat exchanger?
Heat transfer can be improved by increasing the number of tubes or by increasing the length of the finned tubes.
These factors are all measured by heat transfer calculation software that boils down the necessary physics of the tube through well defined computed science. You can then determine if you’ll need a smooth tube, a formed and dimpled tube, or a finned tube to achieve the required heat exchange capabilities. [/vc_column_text][vc_empty_space][vc_single_image image=”3490″ img_size=”full” alignment=”center” style=”vc_box_shadow_circle”][vc_empty_space][/vc_column][/vc_row][vc_row][vc_column][vc_column_text]
How to Optimize Heat Transfer Performance
The potential heat transfer you can achieve is baked into the thermal properties of the fin pipes themselves. The amount of heat transfer can be controlled through surface dimension: fin count, the length of tube, and enhanced or formed and dimpled tube shapes.
Heat transfer is also affected by the thermal conductivity of the metals used to make the fin tubes. Copper fin tubes, for example, are nearly twice as conductive as aluminum fin tubes, and nearly 6 times the thermal conductivity of steel fin tubes. Copper finned tubes are more than 25 times the conductivity of stainless steel finned tubes.
Material corrosiveness or acidity is also a determining factor in material selection, depending on the nature of the gas or fluid that will flow through the heat exchanger.
When choosing materials, you naturally face 2 concerns:
Availability of Materials
Cost of Materials
Is the material going to be readily available or will it take time to get? How will this affect manufacturing deadlines?
What is the cost of each material? These are precious materials with an inherent value based on fair market prices. Copper fin pipe will generally cost more than aluminum, but it maintains the best heat transfer among common alloys. Copper’s chemical properties are ideal for many heat exchanger applications — it’s easily formed and can be readily enhanced for heat exchanges.
Ask yourself:
Are the desired heat exchange properties and corrosion advantages worth the cost?
Can the materials be accessed within an acceptable time frame?
Thermal solution advantages must be weighed against cost and material procurement concerns to determine the best path forward.[/vc_column_text][vc_empty_space][vc_single_image image=”3494″ img_size=”full” alignment=”center” style=”vc_box_border_circle” border_color=”black”][vc_empty_space][vc_column_text]
Proactive Material Procurement in the Age of COVID-19
The cost of materials is naturally affected by the metals market — which can ebb and flow even in normal times. But in the headwinds of COVID-19, it’s a perfect storm.
The pandemic has had a radical impact on the tube mill industry and its ability to respond to demand. Many mills have limited production of certain materials; some mills have stopped production completely.
To navigate these challenges, we’ve had to be more thorough in our planning of material procurement. We need to think further ahead and be more proactive in future planning needs.
To optimally meet material needs as we accommodate the challenges of today’s “new normal,” flattening demand is essential.
Anything you can do to ensure consistency and avoid spikes or drops in demand will result in a smoother procurement process. Fluctuations in demand prove challenging, but consistency can be planned and optimally accommodated. This will result in a smoother, streamlined manufacturing process that’s more predictable with fewer hiccups.
By planning for consistency, you’ll stay ahead of demand — and maintain an even flow of the fin tubes you need.[/vc_column_text][vc_empty_space][vc_column_text]
Our Unsurpassed Variety in Fin Tube Potential
There is a wide range of fin tubes, enhanced surface tubes, and formed and dimpled tubes available to accommodate an eclectic array of challenges and functions.
Energy Transfer just happens to have some of the largest varieties of finned tubes on the market. And because of our versatile market position, we can accommodate nearly every style of heat exchanger design and fin tube application you can come up with.
To optimize the heat transfer capabilities of your heat exchanger, take some time to learn what we have available. Take a close look at our product pages, our sales brochure, and the engineering dimensions outlined in detail. [/vc_column_text][vc_row_inner][vc_column_inner width=”1/2″][vc_single_image image=”3495″ img_size=”full” alignment=”center”][/vc_column_inner][vc_column_inner width=”1/2″][vc_column_text]After all, creativity is largely fueled by option availability. You can either look at the different finned tube products we have available and pick one — or you can learn about our capabilities and come up with your own configuration based on existing products.
Having that information will streamline the selection process for which products will work best. It will also give you a rich understanding of our full potential — and help to leverage the advantages of Energy Transfer’s superior performance.[/vc_column_text][/vc_column_inner][/vc_row_inner][/vc_column][/vc_row][vc_row][vc_column][vc_column_text]Once you’ve taken a detailed look at what finned tubes we have available, talk to one of our sales engineers to see what’s truly possible.
The beauty of variety is unleashed potential. That’s the advantage of working with a highly qualified company with a rich diversity in product offerings. Energy Transfer has the tooling, mechanical engineers, and development teams ready on hand to make your vision a reality — whatever form that might take.[/vc_column_text][vc_empty_space][vc_separator color=”black” border_width=”3″][vc_empty_space][vc_column_text]
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Want to build a seamless fin tube? Our FREE GUIDE tells you everything you need to know. Download yours today![/vc_column_text][vc_empty_space][/vc_column][/vc_row][vc_row][vc_column][vc_column_text] [/vc_column_text][/vc_column][/vc_row]
Want more information on Industrial Finned Tube Heat Exchanger? Feel free to contact us.