Once this project is off the ground, and can be kept in stock for anyone who wants to buy, I will look at doing another design.have you thought about doing something similar for mATX aswell?
and my reply:How exactly was CFD utilized? Was it for rooting out eddies or is there some clever forced convection that isn't apparent in the renders? I'm an aerospace engineer, but most of the CFD I've done has dealt with significantly faster air, so you've got me curious.
Are you designing both heatsinks from scratch? Heatpipes, solid, or another technology? I think the biggest issue you'll see there is the interface between heatpipes and fins. That's why it took noctua so long to come out with the CHROMAX coolers. The paintjob messed with the solder job. And it will be incredibly difficult to simulate the heat transfer capabilities of such a system without knowing how good the manufacturer you use is at soldering them.
The top and bottom panels will be the most expensive part of the case to manufacture. It looks like those will have to be milled instead of stamped, which is $$$. You might want to start optimizing for cost before you finalize your CFD optimization. That same cross section on a flat plane would be an order of magnitude cheaper.
I use a raijintek morpheus GPU cooler in an inverted but otherwise conventional case. It can cool my 1080 passively without throttling (barely) but fans at 300 rpm drop temps a solid 20C. I'm very curious to see how your cooler compares to it. (Hint hint I can help)
Since one of the goals of this is full passivity(Is that a word?) you should definitely make SFX-L PSU compatibility more of a surefire idea since there are fully passive PSUs in that size.
I really appreciate that you're trying to make waves in the SFF market with something that isn't merely a box that holds smaller boxes. Do you have any idea how much it's going to cost with and without the coolers? Oversized coolers are kind of my jam...
------------Rooting out eddies and stagnant air was a huge part of it for the passive cooling mode. Forced convection was a bigger part of the semi-passive mode, with a focus on keeping turbulence (and therefore noise) to a minimum.> Was it for rooting out eddies or is there some clever forced convection that isn't apparent in the renders?
It's also currently being used to optimize some of the heatsink parameters (fin spacing, thickness, and geometry). I haven't shown any of this yet but it's important to get this right. Enough fin density to maximize thermal performance in passive and semi passive modes, while making sure that I don't have dead air in low flow situations (~5 CFM).
I'm planning to lock down some parameters that I want for the heat sink, and then turning over the design, engineering, and manufacturing to a company specializing in computer heat sinks. I'm planning to go with a copper block, sintered copper heat pipes, and zippered aluminum fins. I'm still not sure what this will end up costing, but it will probably be similar in price to a liquid cooling loop...> Are you designing both heatsinks from scratch? Heatpipes, solid, or another technology? I think the biggest issue you'll see there is the interface between heatpipes and fins. That's why it took noctua so long to come out with the CHROMAX coolers. The paintjob messed with the solder job.
Yeah, it's the part that most worries me, as the central rectangle is the final load bearing component right now. If this turns out to be prohibitively expensive, I will have to modify the design for more "traditional" feet. I will have to see what they quote me, and then alter the design if needed.> The top and bottom panels will be the most expensive part of the case to manufacture. It looks like those will have to be milled instead of stamped, which is $$$.
If I have a small focus group seeded with prototypes, I'll reach out> I'm very curious to see how your cooler compares to it. (Hint hint I can help)
SFX-L support is there. It might make cable management a bit tight, but there should be enough room if it's a fully modular power supply. I may change the central spine a bit to give a few more mm of clearance for cable management> you should definitely make SFX-L PSU compatibility more of a surefire idea
I'm aiming for under $300 without the heat sinks, and hopefully less than $150 on the two custom heat sinks... (Very tentative prices, so we'll see).> Do you have any idea how much it's going to cost with and without the coolers?
Thank you! this is a passion project, and I hope that I'm able to give the community something special.> I really appreciate that you're trying to make waves in the SFF market
And my reply:+1
Also aerospace guy here, curious as well about what role CFD played in the design. Was it optimized for a very specific set of fan and heatsinks and expansion cards?
My sorta pet peeve is seeing folks put together some flashy rainbow graphics for "CFD anaylzed" or "FEA evaluated" or whatever, when it's clear that it was pretty much just a perfunctory effort to make something sound sciency and cool.
Like, understanding the external loads on a part and what dynamic response it needs is hard. Sizing a simple part for those loads is not. I'm very unimpressed when I see a 'finite element analysis' of some aftermarket car part where they just applied a static unidirectional load to it and screenshotted it. Like yeah, cool, you analyzed this strut bar for 200 lbf static compression. How much load does it actually see in the vehicle? What is it's dynamic response? Have you done instrumented testing or modelled the rest of the system? They never have, it's just the basic FEA analysis in their CAD. It looks cool but it doesn't provide any more fidelity than just doing basic hand calcs.
CFD is cool, CFD is hard, and In curious if it's being used in a meaningful way or just as a buzzword for using a fancy tool to do the same calculation you could just do by hand.
What followed was an interesting discussion about Noctua Fans, and how to model these systems correctly...It has been optimized for the very specific heat sink that's being custom designed for this case, in two operating modes - passive (natural convection ~5 CFM) and semi-passive (forced convection, with Noctua Fans such as the NFA14 and NFA12x25, same heat sink ~30CFM).
When these heat sinks are used, they are attached to bare PCBs, that are vertical and centrally mounted in the case, so the PCBs don't play a massive role in the airflow. The heatsinks are closer to the sides of the case, (lining up with the top/bottom vents) quite a distance from the PCBs, and air has an uninterrupted path through the vertically oriented fins, from the bottom of the case to the top.
For Liquid Cooling and "Regular" Air Cooling (compact heat sinks with fans, Off the shelf AIO's / case fans / a typical blower or twin axial GPU) there are far too many variables to do anything meaningful with CFD, so these configurations have not been evaluated (no meaningful data to extract), as they are already known to work in a wide variety of cases and layouts that already exist on the market. (grab parts, slap into case of choice, and see if it posts)
I hope that's the answer you were looking for. I'm a chemical engineer*, so I get what you mean about people throwing around FEA / CFD in marketing materials with no real understanding of what's going on. *(though I've been in healthcare / biotech / product management for quite some time)
I have some CAD drawings of a couple of Noctua fans (NFA14's NFA12x25's and NFA12x15). I reached out directly to Noctua to see if they'd provide me with their own CFD data (can't hurt to ask) and predictably they said no, but suggested that I could model their fans myself and use the RPMs listed on thier website and see if I get expected values for flow.> How do the fans get modelled
Airflow is tested assuming the case sits on a solid surface, with the actual fan CAD models (as accurately as I could get them) rotating at various RPMs to push / pull air through the case. Airflow source isn't defined as the fans. Instead the system is defined as a large cube of air around the case (as the bounding box), which lets me see how the motion of the fans is driving air from the environment into and through the case, including the assumption that the air is being pulled from somewhere outside of said case.> do you just model them as a source of air with a certain mass flow?
I'm focusing on steady state operation by selecting values from a range of fan RPMs, with the assumption / expectation that PWM controlled fans can maintain something relatively close to steady state operation.
Clever! I was wondering if you'd be able to get an accurate enough impeller model to actually use that in the CFD, or if you'd have to settle for just using some mass flow data or airflow vs RPM curves and just model it as a circular opening that the airflow comes out of. Were you able to correlate well to their performance curves? Were there any interesting things you discovered that you didn't expect (swirl angle maybe?)
I believe my models are reasonably accurate, considering the velocities, RPMs, and flow rates we're talking about. I did use digital calipers and try to be as consistent with my measurements as I could. But some of those curves are just difficult to define (especially with swept, curved blades like on the A12x25] which are PAINFULLY difficult to model. I tried to fit curves to the profiles at various points, but that is just an approximation... Until I get the first physical prototype built, It'll be hard to see if what I've measured / simulated correlates to the real world (model, simulate, validate, iterate as best practices go) that "V" will be challenging, but important...> I was wondering if you'd be able to get an accurate enough impeller model to actually use that in the CFD
The other issue in model accuracy is one of material properties. While Noctua uses high quality PBT plastics for most of their lineup, the A12x25 is made of their proprietary Sterrox® Liquid Crystal Polymer, for which there is very little data publicly available, so I can't say the simulation is extremely accurate. It remains to be seen how well my results will correlate to the real world. I'm hoping that at least in the "no fan" simulation there is more accuracy, as it's more critical there. As for semi-passive operation, at low fan speeds (under 1000 RPM) the data should be reasonably accurate.
I do not have enough data to recreate / simulate the properties of Sterrox or guess at how they'll affect things like Swirl Angle. The best I can do is assume a high quality PBT. I specifically chose not to simply increase stiffness of the PBT model and call it a good approximation, because that's just a stab in the dark. Better to simulate for "high quality PBT" which at least resembles a real world material, and is used in the other fans. (for those of you on the sidelines reading this, material properties are not as simple as "increase this one thing" and call it good -- each variable you change will have a ripple effect on other properties of a material, so changing one thing immediately changes other things and assuming that changing one property won't mess with another is just a great way to create an imaginary material that doesn't act like anything real)
As Noctua states:
Source: NFA12x25 Design Document, Courtesy of Noctua -- that entire document is a fascinating read for anyone who's an engineer. It's a brilliant take on integrating materials engineering into design... and it's given me a new respect for Noctua, even though I already loved them.Sterrox® is Noctua’s own customised type of fibre-glass reinforced LCP that has been specifically fine-tuned for use in next-generation fan designs such as the NF-A12x25. Its extreme tensile strength, exceptionally low thermal expansion coefficient, high environmental inertia and excellent dimensional stability have made it possible to reduce impeller creep phenomena to levels that were previously unthinkable.
In addition to permitting fan designs with much lower tip clearances, Sterrox® provides a second key advantage in having an elasticity modulus and damping properties that are ideal for reducing resonance and vibration phenomena in advanced fan blade designs such as the NF-A12x25. In particular, the use of Sterrox® allows the suppression of a phenomenon called blade surface mode vibration
So far the model seems to generate something similar to the P/F curve that Noctua published for the A12x25. Not exact, since there isn't enough information on what procedures were used to generate these curves, but as close as I could get with what I was given, and some reasonable assumptions about how to go about measuring this (fan in tube with a manometer), and hopefully that assumption hasn't introduced major errors... I couldn't get Noctua to comment on their methods.> Were you able to correlate well to their performance curves?
Thank you! I’ll certainly keep this in mind and may reach out to Loque and Thorzone for some more adviceI don't have too much knowledge about doing extrusion/CNC cases myself, but I would point you towards the Ghost, Mjolnir, and Circle One as those are the closest to what you're doing. If you're committed to this method of construction, I wouldn't expect it to come out any less costly than those cases.
One general tip for CNC is that more holes = more machine time = higher cost, so anything you can do to reduce the total number of machined holes will help to keep costs under control.
Thanks for sharing your insights about the CFD. You're doing something really special.Yes, I will be sharing some of the results of the CFD studies later on . I'm still running the current set of studies on the heat sink design. They should complete in a week's time. (my poor 4790k has been toiling away at it for a while now).
If you're curious I'll jump into a bunch of detail on how these studies have informed the design thus far: (wall of text for all you enthusiasts)
The first thing I learned during the CFD studies informed the top and bottom panel design. To elaborate: whenever there is flow of a fluid past a surface (like air past aluminum), there is drag because of the boundary layer, leading to some amount of stagnant air. This results in a pressure drop which reduces flow velocity. So the reason you see such massive openings on the top and bottom is because in a passive cooling configuration, very slow convection can be significantly "stopped up" by a series of small holes. For example, a case which has an array of small holes in the top panel (with, let's say 50% open area) has 13.5 METERS of total perimeter (adding all the holes). That is a lot of surface against which there will be stagnated flow *in a passive cooling setup*. It's fine in active cooling because you use a fan to overcome the resistance, but you still pay with a pressure drop (blow on one side of the holes, and you'll feel significantly less force on the other side. Repeat this with a single big hole that achieves 50% OA and you'll incur less pressure drop due to a smaller boundary perimeter.
So, the reason for those huge slots on the end plates is to minimize air resistance for all flow configurations. In passive cooling, it lets warm air escape with minimal resistance, and prevents stagnation that would effectively hotbox the PC. In active cooling configurations, the lower resistance leads to less fan noise, as you can achieve good flow at significantly lower fan RPMs (fan airspeed velocity is highest at the furthest ⅓ of the fan blade, so having a rectangle covering the hub leads to minimal losses). This highly effective airflow configuration when combined with the semi passive heatsink which has widely spaced fins for easy airflow (for similar reasons), cuts down significantly on air resistance, boosting cooling capacity, but keep noise *very* low.
Airflow also drove the choice of going with a Sandwich layout. One of the things you learn in fluid dynamics is that changing the direction of fluid flow by 90º leads to a *roughly* 30% pressure drop. Lower pressure = less airflow. To compensate, you need to generate higher "initial" pressure (meaning higher fan RPM / noise). While this case is big enough to contain a "traditional" PC layout (T shaped, no riser) the heat sink geometry required for passive cooling would be significantly more challenging (See the 2019 Mac Pro Thermal Design, and layout to get an idea of what this would look like). In an SFF case, due to the Power Supply being in the way, a 90º Turn (and the accompanying pressure drop) would be unavoidable, leading to cooling inefficiencies. By contrast, a Sandwich layout (pioneered by the Dan A4), with all components vertical, would preserve a linear airflow path in a small form factor, and allow for a sane design and easy mounting of large heatsinks to both the CPU and GPU.
Hopefully that illuminates how CFD and fluid flow have informed the overall design and airflow considerations made in this case
Also on the topic of heat sink design, Passive heatsinks are a unique beast and the design constraints and conditions are a bit different when compared to "active" (fan-on) heatsinks. This is worth exploring in more detail:
The closer together your fins are, the higher resistance you will have to pushing air through the fin stack. To overcome the resistance to flow, you have to place fans directly on the heat sink (like we see in every CPU cooler), and if fin density goes up enough, you need fans with higher static pressure (like on radiators with dense fins in a liquid cooling loop). Passive heatsinks rely on natural convection, with only the air density difference driving flow. If you pulled the fans off a "normal" heatsink (that has fins close together), it would hurt cooling performance significantly.
To support passive airflow, Your inter-fin distance has to *widen* to prevent stagnation, especially as the heat sink gets larger/longer and the path air has to travel increases (like in a vertical fin stack). In semi-passive mode (with case fans + a heat sink some distance away from the fan), this constraint still applies as even the best fans at lower rpms and far away from the middle of the heat sink are, at best, only pushing 4 inches H2O column of pressure, and the pressure losses are real for any heat sink that's long, or far away from a fan. (Of course, one way around this is massively boost fan RPM! if you use 10k RPM server blower fans, then you can get away with "traditional" heatsinks like they do in 1U and 2U server chassis, with linear airflow front>>back, but now have a screaming banshee in a box...)
So, what if you took an off the shelf "fan-on" heat sink like the NH-U12S, and remove every 3 out of 4 fins, and slap that into a CPU? You have lots of fin spacing, so air will flow nicely through it. However, you've just removed a bunch of mass, and walked into some overheating issues as the *overall mass of the system is too low*. Therefore you must increase the thermal mass of the fins by making them thicker and larger to keep chip temps under control. This is the defining difference between a semi-passive / passive, vs an active heat sink.
Here’s a perfect example of everything I've talked about - a passive/semi passive vs active heat sink designed by a company regarded as one of the best in the business: Noctua.
Noctua NH D14 Active cooler - notice how thin and closely spaced the fins are
Noctua Passive CPU cooler - notice how thick and widely spaced the fins are. It can dissipate 180W in “semi passive” mode.
*both* are valid heat sink designs, but with different applications and tradeoffs in mind, and both are designed by Noctua - a company that *really* knows their stuff when it comes to cooling computers. The stark differences in design are due to the considerations I’ve outlined above.
In the WinterCase, the SPK heat sinks will actually extend from top to bottom leaving space for the 4 140x25mm fans. While the heat sinks handle passive cooling, they can also be used for extremely quiet semi-passive cooling (driven by the case fans). With wide fin spacing, you can achieve lots of flow *and run the fans extremely slow/quiet* and still move lots of air through the heat sink, enabling very quiet high end builds. While it sounds too good to be true, there is a tradeoff - passive heatsinks take up significantly more space than their densely packed active counterparts.
Thank you for the kind offer. Once prototyping is completed, I will take you up on that. Manufacturing is a bit outside my comfort zone, so having someone to point me in the right direction, and answer questions will be incredibly helpfulI have contact with some factories. Let me know if you need help or consultation. I'm willing to help.
Correct!That blade sweep, the narrow triangles on the blades, the shape of the noise isolation bumpers on the corners, it's gotta be the Noctua A12x25
That is the plan right now. If Extrusion ends up not being very cost effective (due to expected volumes) that part will need to change, as it would otherwise require 5-axis milling on a 2 cm billet, which gets very expensive in terms of materials and machining time. There's also the issue of economies of scale when it comes to extrusion. That part, and the part 2 pieces to the right are actually the same extrusion piece, but with different types of post processing on them, to try and further leverage scaling after the initial costs of having to create an extrusion plate.One question: for volume production, how do you plan to manufacture the part top left in the picture? Extrusion & CnC?
Sounds like a good plan.That is the plan right now. If Extrusion ends up not being very cost effective (due to expected volumes) that part will need to change, as it would otherwise require 5-axis milling on a 2 cm billet, which gets very expensive in terms of materials and machining time. There's also the issue of economies of scale when it comes to extrusion. That part, and the part 2 pieces to the right are actually the same extrusion piece, but with different types of post processing on them, to try and further leverage scaling after the initial costs of having to create an extrusion plate.
Naturally, If we move to 100% CNC machined, these pieces will have to change, and that'll depend on the cost analysis, as we do some checks before production.