Oil Reservoir for Heat Exchanger Testing System

[jnelson33]

We have a heat exchanger testing system whose reservoir is a cheap food fryer, with a sheet metal lid that has pipes welded through it for inlet and outlet. The heat exchangers that we test overwhelm the heat output of our fryer, even after applying duct insulation to the tank.

I brought this to the attention of my boss and we've found some options.

The problem is that the beautiful immersion heaters that Watlow and Chromalox have suggested need 220V and are priced near $1000. These are shock factors to my boss as he does not want to pay to have the electrical work done for 220V to be run to that room, in addition to $1000 just seeming ludicrous for a heater. Despite my research into this, his idea is to use cheap immersion heaters (low Watt density) that you can get on Amazon or whatever, along with a hydraulic fluid storage tank.

Before I get too far, let's delve into the operating conditions of the current system:

The system uses a spur gear pump to draw heated oil from the reservoir and circulates it through insulated -10 SAE lines and fittings, along with the heat exchanger of course. The oil is a full synthetic 5W-30 by Quaker State and is circulated at around 22.7 liters per minute, with a system pressure of about 206 kPa which are both set at no-less-than 100ºC. The heat exchanger sits within a wind tunnel where ambient air is blown past it.

Some things I've learned are this; engine oil is truly exceptional at the purpose it is designed for. Engine oil cannot maintain a desirable level of heat once circulated through our current system, despite being powered by a 2500 Watt (what seemed high at the time) food fryer set on maximum, with the insulated lines and reservoir. Engine oil is designed to move heat out of 120+ HP engines, not 3.3 HP engines, ha!

So, you can see why we need a new heater so that we can keep our inlet temperatures controlled for our heat exchanger duty testing. However, I am concerned that a single storage tank would not be sufficient for our needs still, even when using lighter weight oil like 0W-20. From my experience on this old test system that I've been dying to fix, I believe I need one tank that cold oil is dumped into so that it may be heated to the desired temperature before is moved into the next storage tank that also has a heater which maintains the oil at a constant temp +/- some margin.

Does that seem overkill? Watlow and Chromalox's reps seemed to think that their products could do what we needed alone, however, if those are not a possibility for me, then this storage tank made from existing parts seems to be my fate. I want to be damn sure I design something that's more than capable, at the best price of course. I also really want to tie in the current drawn from the heater, to the inlet and outlet temperatures to have a fully automatic system that can turn on and off the heater based on system conditions: Also not in the budget.

Has anyone designed a system tank like this that can share some thoughts on my thoughts?

 

[Compositepro]

Perhaps you can explain what you are trying to accomplish along with your explanation of how you are trying to do it. Oil heat is good for maintaining uniform temperature at low heat loads but is a poor option for transferring large amounts of heat effectively. If you are trying to heat air in a wind tunnel you can get far more heat power from a natural gas or propane heater than an electrical heater. For example, a clothes dryer in your home has more heating power than your 2,500 Watts. You can buy a space heater with over 100,000 BTU/hr. capacity for a few hundred dollars. I do not think you will get much help here because what you are doing has many potential hazards.

 

[jnelson33]

The system's goal is to establish the overall heat transfer coefficient of the heat exchangers that we test. We also do comparative testing that is time based, wherein the heat exchangers are timed to see how long it take to get from a prescribed hot temperature to a prescribed cold temperature.

The heat exchanger is within the wind tunnel, and has room temperature, ambient air being blown across its core to dissipate heat from the hot oil that is running through the heat exchanger. Think of a car's radiator receiving air as it drives forward, and that's the setup for our heat exchangers within the wind tunnel testing chamber.

Engine oil was originally chosen by my boss because it's what would actually be circulated through these products. I think his idea was to make it as realistic as possible, possibly not understanding what that would ultimately entail for a truly reliable testing system.

I am now fully aware that it is not a friendly fluid to deal with when the goal is to transport the oil from the heated source, through lines and into the heat exchanger to be passed back into the heated reservoir again after it's been drastically reduced in temperature. I had a conceptual idea of why oil is good at what it's designed to do, but the real world testing changed that further for me. It's showed me what you've stated, it's a PITA to use in the system we have, with the intentions of use that we have.

Do you believe this post to be better served on the Boiler and Pressure Vessel Forum? All I really want to figure out is if someone has done a storage tank with similar service aspects. Storage of course implies it's not continually circulated, so I get that this Forum may not be the most applicable.

 

[LittleInch]

Looks like overkill to me but a diagram would be nice plus some idea of how big your planned storage tank is compared to the incoming flow rate.

I think you will need something like min 3-5 minutes residence time for the cold oil to not lower the temperature of the hot oil too much when the heaters kick in and eventually you establish some sort of thermal equilibrium whereby the amount of heat "lost" by the oil in the heat exchanger is replaced by the heaters. sounds like your HX is more efficient than you first thought if you're loosing 2.5kW, or did no one do any calculations??

I have to sat that for some sort of presumably industrial testing facility, this set up seems very low tech, unsafe and not what I would expect from someone "testing" something inside a wind tunnel. Care to explain a bit more?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[jnelson33]

+1 for overkill, thank you!

I really do understand that the way that I've typed this seems ridiculous. This is a ridiculous situation that I'm in, as I'm sort of picking up the pieces from an idea that was never fully developed and thought about. I have no idea whether that relates to lack of knowledge on testing systems, or purposeful ignorance to things that needed to be taken care of from the get-go. We are a somewhat new company (10 years old this year) and still very small (6 total people; I am the only ME).

I didn't want to bore y'all with the origins of the test system in the first post, plus it would've been a long post.

I'll try to be brief. I was part time at the company back when my boss (software engineering background) set up the first test system. There was no wind tunnel; there was not even half of the instrumentation that we have now. There was a fan, a very incapable heater and some automotive instrumentation connected to a computer, this was all set on a table. I have zero clues on what was planned there; maybe it was just more proof of concept? I think we might've purchased the food fryer that we use now when this old system was around. The food fryer seemed capable on the old system because that first fan barely moved air, and since it wasn’t in a wind tunnel, most of it probably passed around.

When I started full-time, as a newly graduated ME, I knew that my boss wanted to upgrade the system. Fortunately for us my boss's cousin was laid-off from Cummins and came to work for us for a few months. My boss thought it must've been a better idea to have himself and his cousin undertake it, being that his cousin was technically a more experienced ME. I still provided them with all of my NASA wind tunnel lab literature from school to design the tunnel. The problem is that I was not really involved with much else other than building the system after it was planned. I highly doubt that the heat exchangers we wanted to test were looked at for things like, heat extraction capabilities. Like I said, lack of knowledge, or blind ignorance, I'm just trying to fix this.

So, since the system has been built, I've encountered several issues that, to me, wouldn't have been there if due diligence was carried out. This oil heating issue is one of the last issues I am fighting (I mean that) to solve. I’m more experienced as a worker now and have realized that I had fallen victim to obeying boss’ orders while not thinking about the holes in the plan; soldier obeying orders. But after realizing how bad the system is after using it, realizing stuff that I would’ve looked at wasn’t looked at, and now calling for action, there’s pride at stake now. The coveted idea fell apart slightly, and I think that’s somewhat hard for him to swallow: The hired ME knows more in this field. That’s also why I am here posting: I am still pretty new in the working world and want to bounce my ideas off of other people who have experience. I can’t do that here, and I need to basically have proof to help with gaining trust. Yes, office politics exist even at small companies…

After the few posts here, I can already basically surmise that I need to ditch the large storage tank idea for the primary heating. If anything, I can have a tank with an assisting heater, but then use a primary process circulation heater to heat the oil right before it goes into the heat exchanger itself. From the products that Watlow and Chromolox offer, they say they should be able to accomplish that on their own without a heated tank assisting them at all; for parts that can cost near $2000, it would have to be certainty. My boss keeps jumping on this decision to speed it up, and keeps trying to show me water heater elements on Amazon to put in a hydraulic fluid tank, just basically a larger version of what we have now, with more elements, but no calculations have been done, like I have carried out to determine that we need one of these process circulation heaters if we want to use oil.

After seeing some of these challenges we’ve encountered, I think moving away from oil would be the best option for cash conservation. I hope I haven’t bored y’all, but this is my scenario :/

 

[Compositepro]

I'm still trying to understand what you want to accomplish. It seems that you are testing an oil to air heat exchanger that you manufacture. Do you want to determine the heat transfer efficacy of your exchanger? In that case, using hot oil and a wind tunnel makes sense. What do you propose as an alternative?
Water heater elements are the least costly heaters you can buy but you cannot use them at rated power in oil. Water has about the best heat transfer of any liquid and these heaters have a high watt density (Watts/cm[sup]2[/sup]). You will char the oil. You can run the 240V heaters on 120V and use more heaters. In the end getting packaged heating units from Chomalox will be cheaper than all the time you will spend trying to figure things out. Although, for the good of your career, you do need to eventually figure these things out. Chomalox and their competition have very good educational material in their catalogs and handbooks. You should thoroughly read this before you do anything else. You can learn from others' mistakes or from your own. The first option is less expensive, but sometimes not as much fun.

 

[jnelson33]

Compsitepro, among other automotive racing products, we sell third party heat exchangers and have developed our own line of heat exchangers to compete with those products. We partnered with an existing company. All of these heat exchangers are stacked plate, cross-flow (with fins), air-to-oil style exchangers (think automobile radiator). My boss' idea was to match the core dimensions of our highest selling exchangers, but make a more efficient one. The wind tunnel system tests the exchangers (one at a time) to compare their thermal extraction abilities to one another. The end goal is to be able to display comparative data on the website to show our customers how much more, or how much less heat a similarly sized heat exchanger can remove from a system so that they can make the purchase they want based on data. I plan to expand on that more, but I have to get the test system capable first.

Myself, through thorough research understand all of the nuances associated with the different heat element types, conveying that to my boss is a different story. He insists that things that I have researched, for which I have concluded that they cannot work for us, should work for us. This is my battle. I know that the Chromalox and Watlow heaters are the quickest and most applicable solution if we want to continue using engine oil to test in our system. The work I'd have to complete with assembling a custom heater system is going to outweigh just buying a calibrated, insulated, properly designed part. I think we can all agree on that because we understand how annoying setting up your own test system is, and thus why test equipment is expensive, especially if it has to be safe.

 

[LittleInch]

Sounds like you getting first hand experience of the potential downsides of working in a small company run by an egomaniac who believes all his own ideas are the best thing ever and he can shave $'s from a project with a bit of googling on amazon.

Sounds like a smaller version of Tesla!

So do you need anything more from us here?

If not be sure to let us have pictures of the fire that will engulf the test area

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[LittleInch]

If you want to see a picture of this, then the OP had another post which shows it in its glory..

J Nelson - in future if you have different, but related posts going just link them together.

https://www.eng-tips.com/viewthread.cfm?qid=439699

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.