Hi again,

I'm trying to get my head around thermal conductivity (C) vs thermal diffusivity (D). I guess my confusion is whether they are both measurements within a single body/block of material, or whether one is inter-body.

According to Wikipedia, both appear to be intra-body and both include a "speed" so I'm not sure of the difference.

Thank you,

Hans

Say you have a mold material with a low thermal diffusivity (plastic) vs a mold material with high thermal diffusivity (silver). You freeze the same material in the same freezer in both of these molds. Which will be frozen faster? Will it be the one with the high or low thermal diffusivity that freezes faster? I'm having trouble understanding this concept. Thanks for any help

Hi all. I'm working on a research project and need to find these thermal property values. We used a 3D printer to print out a small object and a thermal camera recorded the temperature profile. We also used a drill to drill into the material and recorded how the heat dissipates after the drilling. Is there anyway to use this data to get heat diffusion or conductivity values

I am having trouble locating a citable source for the thermal diffusivity of aluminum metal at room temp. and 100 Celsius. Does anyone know where to find it?

*I've already looked all over my school's databases and I'm still having trouble finding it.

Title says it all. Why would I want one when I've already got an electron microfilter covering the Dall Port?

My friend is building a portable fire pizza oven, I have a basic understanding of thermodynamics but I could need some assistance. My understanding is that we need a material with low thermal diffusivity and high thermal mass, such as clay bricks and concrete, but also having low density. We have been looking into Ultra Light Weight Concrete, perlite and ceramic fibre blanket.

Does anyone have other suggestions? And please correct me if my understanding is incorrect.

Modification of the external surfaces of metal organic frameworks offers a new level of control over their adsorption behavior. We have previously shown that capping of MOFs with ethylenediamine (EDA) can effectively retain small gaseous molecules [Nat. Comm. 2016, 7, 13871] at room temperature. Here, we report a temperature‐induced variation in the capping‐layer gate opening mechanism through a combination of in situ IR experiments and ab initio simulations of the capping layer. We find an atypical acceleration and increase in the loading of weakly adsorbed molecules upon raising the temperature above room temperature. Our findings show the discovery of a novel temperature‐dependent kinetics that goes beyond standard kinetics and suggest a new avenue for tailoring selective adsorption by thermally tuning the surface barrier.

https://ift.tt/2Y8Oyrl

Picture: https://imgur.com/a/AnQEG9N

Hi, I was about to install this sunmaster film today but have a little confusion.

1. Does anyone know if the text comes off in time? With a little work it does rub off but I cant really have text all down the plastic like this in my residential home.

2. I cannot find any instructions online stating if the text should be in or out. No customer service open on weekends.

Also, I made a mistake. I thought I was getting anti condensation / high diffused plastic, but I think not.

From what I'm gathering online, this is less than 20% diffused compared to the "Sunmaster infered thermal anti condensate" is 58% diffused.

Does it make that big a difference that I should wait and get the anti drip diffused film? From what I read diffused is generally better, I also would preferred slightly more privacy, as this sunmaster IV I have is very clear.

I went over the pdf data before I just bought this last week, but now the seller has a totally different product and I cannot confirm what I saw when I ordered it.

This is what I believe I have: https://www.greenhousemegastore.com/content/files/pdf/SUNMASTER-IV-6mil.pdf

This is what I believe I wanted (diffused 58%): https://www.greenhousemegastore.com/content/files/pdf/SUNMASTER-THERMAL-6mil.pdf

Does it really make a difference enough that I should wait to install, buy something different? Otherwise I will be installing tomorrow, really thought I had ordered a diffused film.

thanks

Original post: https://www.reddit.com/r/flashlight/comments/8twjz2/3d_printed_diffuser_for_the_emisar_d4/

A timelapse (~3 minutes): https://gfycat.com/FoolhardyFarDikkops

A shot of the torch body: https://i.imgur.com/MmpMtTL.jpg

View inside the diffuser immediately after taking it off the D4: https://i.imgur.com/72Uud4s.jpg

The opaque white filament seems to do a really good job not absorbing light. The PLA doesn't get soft at all. This is with a 4x Nichia 219 D4 and a freshly charged LG HG2 cell.

So We've been working in EES for some time and I can't seem to find how to transfer (kW/m^2)/(W/m^2*C) in order to get to Celsius or Kelvin for DeltaT

$UnitSystem SI K kJ bar deg mass Function stephanboiling(FluidType$, F$, Theta, P, q_dot_s)

"Properties at saturation"
T_sat=t_sat(F$,P=P)	"Saturation temperature"
DELTAh_l=enthalpy_vaporization(F$,T=T_sat)	"Latent Heat"
 
Rho_l=density(F$,T=T_sat,x=0)	"Saturated liquid density"
Rho_v=density(F$,T=T_sat,x=1)	"Saturated vapor density"
Cp_l=specheat(F$,T=T_sat,x=0)	"Specific heat of saturated liquid"
K_l=conductivity(F$,T=T_sat,x=0)	"Saturated liquid conductivity"
Nu_l=kinematicviscosity(F$,T=T_sat,x=0)	"Saturated liquid kinematic viscosity"
a_l=K_l/(Rho_l*Cp_l*convert(kJ/kg-K, J/kg-K))	"Saturated liquid thermal diffusivity"
Sigma=surfacetension(F$, T=T_sat)	"Saturated liquid surface tension"
 
D_d=0.0208*Theta*sqrt(Sigma/g#/(Rho_l-Rho_v))	"Bubble departure diameter (Fritz)"
 
X_1=(q_dot_s*convert(kW/m^2, W/m^2)*D_d)/(K_l*T_sat)
X_2=(a_l^2*Rho_l)/(Sigma*D_d)
X_3=(Cp_l*convert(kJ/kg-K, J/kg-K)*T_sat*D_d^2)/(a_l^2)
X_4=(DELTAh_l*convert(kJ/kg, J/kg)*D_d^2)/(a_l^2)
X_5=Rho_v/Rho_l
X_6=Nu_l/a_l
X_13=(Rho_l-Rho_v)/Rho_l
 
If (FluidType$='water') Then 
 
"Exponents"
n_1=0.673; n_2=0; n_3=1.26; n_4=-1.58
n_5=0; n_6=0; n_13=5.22
 
"Constant"
C=0.246e+07
 
Endif
 
If (FluidType$='Hydrocarbon') Then 
 
"Exponents"
n_1=0.67; n_2=0; n_3=0; n_4=0.248
n_5=0.335; n_6=0; n_13=-4.33
 
"Constant"
C=0.0546
 
Endif
 
"Nusselt number"
Nu#_Dc=C*(X_1^n_1)*(X_2^n_2)*(X_3^n_3)*(X_4^n_4)*(X_5^n_5)*(X_6^n_6)*(X_13^n_13)
 
"Convection coefficient"
stephanboiling=(Nu#_Dc*K_l/D_d)*convert(W/m^2-K, kW/m^2-K)
 
End 
 
FluidType$='Hydrocarbon'
F$='Ethanol'
Theta=35
P=1.013 [bar]
q_dot_s=20 [kW/m^2] 
 
Alpha_nb=stephanboiling(FluidType$, F$, Theta, P, q_dot_s)
 
DELTAT=q_dot_s/Alpha_nb 

https://preview.redd.it/krn79cs8gwc81.png?width=596&format=png&auto=webp&s=469f66768008ed9213725bf6db5bcd233fec4339

Also the program is trying to help me but I dont really get it what conversion should I do in order to get DeltaT in Kelvin or Celsius

Metal and wood conduct heat at two different rates, but do gases behave the same? If there is a difference, would the effect be noticeable by touch?

Happy Solstice!

In honor of Winter Solstice for the northern hemisphere, I've made an updated list of popular lights. Today is the day you're most likely to need a flashlight if you live north of the Equator.

There is no best flashlight, so this is an amalgamation of what enthusiasts have been buying and recommending to others lately along with the author's arbitrary preferences and biases. To search more lights by their attributes, try http://flashlights.parametrek.com/index.html

Where possible, official manufacturer URLs are linked here. Sometimes the manufacturer offers good deals through direct orders, sometimes vendors have the best prices. There are coupon codes available that apply to many of the lights listed.

Some people have asked if they can give me kickbacks or gratuities for maintaining the list. I have two options for that now: I'm hosting a version of this list on my own site with affiliate links, and I've set up a tip jar. Please don't feel obligated to use either.

There is a global supply chain disruption as 2021 comes to an end, so some popular lights are temporarily or permanently unavailable. In many cases, this list reflects current availability.

The Quick List

If you're not interested in flashlights as a hobby, you should probably just get one of these

All of the lights in this section come with a rechargeable battery and have a charger built in to the light. The battery will be a standard size you can buy online from third parties, and the charger will use USB as its power source, though some options do use a special cable. Aside from the A4, all have very good color quality compared to the average LED flashlight, improving your ability to see details. In this section, I've linked good places to buy the lights rather than the manufacturer.

This section is strongly influenced by what is available for purchase within the US. Changes from last time reflect current availability and may be updated before the next list as that changes.

• Wurkkos FC11 - a general-use light for $30. USB-C charging, and it now has proper C-to-C support. There's a strong magnet in the tailcap, and a pocket clip for carry. A 25mm (1 inch) diameter and 120mm (4.7 inches) long is suitable f

I made a post a few weeks back showing the total amount of Wind Tunnel and CFD time allowed for each team to design the aerodynamics on their new 2022 cars under the sliding scale ATR.

I did some research looking at the dates that teams stated in interviews that they switched full development to ‘22, monitoring updates on the cars and listening to a few podcasts on the subject. From that, I’ve estimated the percentage each team might have used during each period to figure out how much time they have actually spent testing Aero components. This is split into runs in the wind tunnel and Restricted Aerodynamic Test Geometry (RATG)

You can see that Haas could have almost twice as much development time as Red Bull to build their car. Alfa Romeo and Williams have around 1000 more runs in the Wind Tunnel than Mercedes. While Ferrari has about 30% more testing allowance than the front 2.

Does all this mean that the grid pecking order will be flipped? Of course not. The big teams have built up massive advantages in terms of facilities, personnel, processes and analysis tools. It’s telling that they are expected to be over twice as efficient with their testing time over those at the back of the grid.

It should however mean that field spread and dominance aren’t a major concern in this regulation change.

In reality, the belief that field spread and domination occur out of every regulation change is a bit of a myth. It’s a bit of a mixed bag and the aero changes most similar to this one in 2009 produced about the closest field spreads F1 has ever had, under 2s from top to bottom in qualifying and all teams scoring at least a 7th place finish on the season. Others spread things out a little bit more. Then there is 2014 when Mercedes spent so much more on their PU that their dominance is still being felt 8 years later. However, most of the reasons why the top teams were ab

Image for reddit's preview thingy but also it looks nice

Introduction

Originally, I wanted to get this guide out before Harrow Prime’s release with The New War, but opted to go more in-depth than initially planned completely overboard, and ended up taking a break from writing it when U31 dropped. Since then I've worked on it gradually, and now here it is! - all 11 pages of it (what have I done).

One particular introductory note - Harrow is often referred to as a "selfish support"; he needs to chain enemies and score kills himself to keep his kit running, and to provide his health/energy restoration. If there aren't enough enemies around, be it from 'competition' with allies or low spawn rates in general, it can become a struggle to do so. While this can definitely be an issue at times, it varies significantly between different mission types and squads, and is generally less of an issue than it's made out to be.

Don't let it deter you from what Harrow has to offer! :)

Don't let the length of this guide deter you either - I've gone a touch overboard in the depth department here, but what his abilities do and how to use them is covered in the first 2 sections. The rest is all about build options, weapon choices, and additional guidance. Feel free to use this guide more like a guide book, and just look at the sections you're interested in.

The first section is a primer, for those that don’t know anything about (or are not familiar with) Harrow’s abilities.

Primer

Passive - doubled overshields cap (+1200 up to +2400), and 100% full energy at the start of missions (as of U31).

Starting off with his third ability, Thurible, his energy source. Casting it once begins channeling energy (at a base 15% conversion rate) into a charge. Casting it a second time (or running out of energy) turns the charge into a buff for 35s, shown in the UI. When Harrow scores kills, the displayed value is restored as energy to Harrow and nearby allies within 20m, which is shown by a ring of energy around Harrow. Headshot kills restore 4x the energy.

Next up is his first ability, Condemn. When cast, a wave is sent forward for 20m which expands horizontally as it travels, and chains any enemies it hits in place for 6s. Each enemy chained restores 150 points of Harrow’s shields, building into overshields. Enemies chained

If a gas expands once in contact with a hot surface and the difference in concentration generates a diffusive motion (non-gravitational) would that be a form of convection? Could it be called natural convection even though no gravity is present?

As the gas moves from the high density region to the low density region it would shift the system's center of mass. How would momentum be conserved if no forces were exerted?

Wanted to write the definitive guide to Divine Tribe bubbler options. If anyone has more information to add then just let me know and I can expand the list.

Large Bubblers

A good full size option is the HydraTube. The HydraTube is a great piece to have in any bubbler collection. The HydraTube comes in 14mm for $39 and 18mm for $58. You will need an 18mm to 14mm Reducer to use the 18mm HydraTube if using the INH $8 14mm Glass Tip. INH also sells an $8 18mm Glass Tip that can be used directly with the HydraTube sans reducer/adapter.

I have heard the 18mm HydraTube from INH is thicker, heavier, and larger than the 14mm version but I can't say its DEFINITELY true.

The HydraTube, and its DHGate cousins are probably the largest bubblers on this list.

Some other options for "HydraTube" clones would be the $59 VapeXhale Hydratube 9.8" or this $52.80 VapeXhale Hydratube 7".

_______________________________________________________________________________________________________

Regular Bubblers

First we will start with the OG V4 bubbler which is the [$27 Hubble Bubble](https://ineedhemp.com/product/hubble-bubble-14mm-glass-hy

Hey Reddit. Us again.

Fun weekend, huh? Turns out, the headline "Company dares Sony to sue, folds when threatened with lawsuit" sparked quite the dialogue.

We sure did.

Before unpacking the final chapter in this soon-to-be-greenlit Netflix special, we’d like to set the record straight on a widespread misconception.

This is not the reason Sony threatened us with a lawsuit:

https://preview.redd.it/mmnmwmixpau71.png?width=2538&format=png&auto=webp&s=fb88c662cfc072c110203f440330d35c54539c8e

This is:

https://preview.redd.it/d1nec8cypau71.png?width=2722&format=png&auto=webp&s=b4770d50a119510dfd932c15db62802faa805a54

See, while we appreciate all the armchair legal advice that filtered in over the weekend, the reality of this Darkplates dispute is quite simple:

1. You can’t successfully sue someone over an alleged “design infringement” without a registered design patent.
2. Sony did not have a registered design patent for the PS5’s side panels when we launched Darkplates (or for many, many months following the release).
3. We didn’t think they’d ever get one.
4. They did.
5. Here we are.

So, faced with this registered design patent which, according to Sony, alleges to cover the shape of the PS5’s side panels, we had two options:

1. Spend millions fighting the legitimacy of the design patent claims for many years in court.
2. Start fresh.

Great advice, u/Lazyjellything.

Without further ado, we’d like to introduce you to…

https://i.redd.it/ii2e39p3qau71.gif

Darkplates 2.0

While working through the redesign process over the past few months, we quickly realized that in order to make this thing any less of an abomination, we'd need to either overhaul the faceplates or make our own gaming console. Because our north star is to do whatever KFC isn't doing, we got to work redesigning Darkplates.

By creating a brand new design, Darkplates 2.0 successfully closes the loop on this dispute and neutralizes any future infringement claims from Sony.

More importantly: it makes your PlayStation 5 considerably less ugly.

New shape, new box.

But wait - we did more than

I don't want to step on anybody's toes here, but the amount of non-dad jokes here in this subreddit really annoys me. First of all, dad jokes CAN be NSFW, it clearly says so in the sub rules. Secondly, it doesn't automatically make it a dad joke if it's from a conversation between you and your child. Most importantly, the jokes that your CHILDREN tell YOU are not dad jokes. The point of a dad joke is that it's so cheesy only a dad who's trying to be funny would make such a joke. That's it. They are stupid plays on words, lame puns and so on. There has to be a clever pun or wordplay for it to be considered a dad joke.

Again, to all the fellow dads, I apologise if I'm sounding too harsh. But I just needed to get it off my chest.

A/N Edit 2: In an effort to create continuity.

1. AI Theory Guest Speaker, Attendance Mandatory (you are here)
2. Intro to Practical Philosophy, General Education
3. And Their Rallying Cry

Edit 1: I think I'll refer to this universe as being part of "The Third War Journals."

I've been reading nothing but HFY for the past week and I felt inspiration calling. Please enjoy and if there are any errors needing squashed, feel free to shine a light.

///

The entrances to the grand auditorium were carefully watched by vigilant guardians. None of the students understood why their devices were being logged and confiscated entering the premises. It was not a regular procedure for the Galactic Military Academy, despite all of its various fields of study.

However, attendance was a pass or fail for three semester’s worth of courses. Not just AI Theory Advanced, not just AI Theory Basic, but also Philosophy and Social Science.

Further still, all faculty offered substantial extra credit. No other event elicited the same response.

It took nearly an entire class period to seat dozens of species, all hopefuls from their respective homeworlds. Carnivores, herbivores, the rare omnivores. Bipedal, tripedal, quadrupedal, multi-tentacled. A newly installed section of the audience was even devoted to aquatic species, both those able to wear environmental suits or the open ocean and freshwater chambers integrated within the academy’s campus that allowed for free swimming across the grounds.

Lights began to dim. Voices hissed and rumbled and cooed into silence.

A figure walked up to the podium. Biped. Four limbs total. Strange. Proportions off compared to virtually all other civilizations present in the galaxy.

“Thank you for your attendance,” a voice rang out. A high pitch voice in the clear common language. There was a curious accent to it that many of the students noted. “A short question and answer will be held after the main lecture.”

A pin could drop as the lights fully cut out, leaving only the Speaker and the vidscreens placed around the ceiling for all to follow along with visual aids.

“Artificial intelligence beyond a certain level of complexity and initiative are restricted if not outright banned. This is a r

Seems like a good electricity conductor is also a good heat conductor, but...

Doesn't electricity (at the atomic level) travel a material by electrons repelling each other, which overpowers their attraction to protons, so one electron will take another's place from atom to atom?

While doesn't heat travel a material by atoms colliding, which transfers their motion energy in a dominoes effect?

After getting into a discussion about the heat sink properties of certain metals, I decided that its rather difficult to have said discussion in the context of material Heat Capacity, Thermal Conductivity and density with 3 varying numbers flying around. For instance, the question arose if diamond would be a good material to build a flashlight with, given it has a thermal conductivity of 1000?.. Well, in order to investigate this I decided I needed a new Thermal Property Constant for each material (TPC for short). I’m sharing this brief work I did here today in hopes that it will make material choice for flashlight housings and heat sinks less obfuscated. Ill explain my constant and why I chose to set it up as such.

The three variables:

Heat Capacity (Hc): the ability of a material to absorb heat energy as a ratio of energy input to temperature change. Units: J/gK (joules per gram Kelvin)

Thermal conductivity (Tc): the ability of a material to transfer heat (ie how fast a material may take the heat away from, say, a PCB). Units: W/mK (Watts per meter Kelvin)

Density (D): how many grams per unit volume a substance has. Note that heat capacity deals with mass, and so our picture can’t be complete without a mass ratio for all materials in the constant.

Thermal Property Constant: The combined 3 property constants for a material; calculated through Tc*D*Hc. Tc is directly related to heat sink ability, higher Tc means a better sink, so it stays on top. Density is directly related to how much of a substance with a specific heat can exist in a unit volume. The higher the density the more heat energy can be stored without reaching high equilibrium, so it stays on top as well. Heat Capacity is directly related to the amount of energy needed in a system to raise the material by 1 kelvin, so it stays on top too. Easy enough, we have a three variable product constant. Let's see what it can tell us about different materials and their sinking ability.

Now, I decided to make two constants and see what the community thinks, because they do yield different results. We’ll call this first one I mentioned TPC1 and this following, TPC2. TPC2 is calculated through Tc*D/Hc. I did this because I am unsure whether a higher Hc is better or worse in the context of a constant volume. Less energy to reach a thermal equilibrium seems bad but here it is anyway.. for other people to ponder! My personal pick is TPC1 for because I'm of the opinion lower Hc is bad in context of a hi

What’s better for what :)

1 First Death's Heralds - 2 Toxic and Unbreaking

______

Red lights flashed on and off along the corridor, telling sergeant Wilkes that it was time to load up for launch again. He walked through the halls of the Queen Anne marine's section with his squad, their heavy armor stomping on the metal floors. "Checkdown, now." The marines went over each other's gear, checking magazines and gas levels. By the time they were finished, the hatch to their boarding torpedo opened and they were ready to launch.

The mission was to take down a lone warship in orbit of a habitable world. The navy would normally batter it into dust, but the size of the ship and it's apparent armament was legendary in scale and would likely destroy half the fleet before it can be taken down. Noted as a starmaster in Hikor records, it was a mainstay of Hikor naval supremacy. The last system they went into briefly was hosting a war fleet far bigger than the British 2nd fleet, including reinforcing ships still en route. The admiral was not keep to face down twelve starmasters, but taking one would send a nice message and is useful for the engineers on Luna.

A swarm of torpedoes were launched, Wilkes' included. External cameras showed two much larger torpedoes going towards the middle of the ship. How they were able to maintain stealth was beyond him, but Wilkes expected their payload to be a frightening mix of steel and death.

Right before impact, external lights on the Hikor ship turned on, making the vessel very visible but also the torpedoes. It was too late to strike them down though as they made impact and burrowed into the starmaster.

The front of the torpedo blew open and the Death's Heralds flooded the area with gas, obscuring everything in toxic smoke. He heard other torpedoes still making their way in, and to the left he could hear thunderous bangs already, accompanied by small shockwaves through the air. "We go right, don't want to end up downfield from the business end of a hellshroud."

The halls were bigger on the starmaster, even more so along the main corridors, wide and tall enough to fit a tank comfortably. As they made their way down their hall, they could see abandoned carts, some still with warm handprints from recent use. "The crew is fleeing, probably waiting for the cavalry to get here to save their asses from u

I have seen some texts mention axial heat dispersion as being different to axial heat conduction, in that dispersion is typically 'undesirable' heat transfer. What is the difference between the two?

For example, here is an energy balance to a fluid:

https://imgur.com/gallery/N0LinL9

I guess the first term on the right is the axial heat dispersion term? Why is there a need to define heat dispersion as being different from heat conduction?

Hi guys!

I discovered this subreddit few days ago and I'm already hooked! I'm looking to buy a flashlight to use as an EDC, both outdoors and indoors.

Some features I'd like:

• 18650, 21700, 26650 batteries. I don't want to use a bunch of AA/AAAs. I would prefer 18650 since that's what I also use for my vaporizer and I could use the same batteries for both.
• USB-C charging would be nice but I'm really torn on this one. I already have a battery bank that would go great with a rechargeable flashlight, but on the other hand, like I've already read here, it's another possible point of failure. I could buy the XTAR MC1 for like 4$ but it's another gadget I'd have to bring with me..
• Sub-lumen/variable output: I could also use my flashlight when working on my PC builds and I definitely don't need 1000 lumens for that.
• A battery check would be also useful, I wouldn't wanna risk finding myself with a dead battery.
• Shouldn't be too big. The bigger it is, the less likely I'd bring it with me.
• Strobing for self defense? Could it actually work?

Also I don't mind a hard to learn firmware/UI, but I also don't want to spend minutes messing around with the settings in case of an emergency.

Flashlights I had in mind:

• D4V2 (40€): this would be an instant buy if it had USB-C charging. I'm also off-put by the easy thermal throttling, what's the point in all that light output if it can only be sustained for a few seconds? Is it a valid concern?
• Wurkkos FC12 (28€): I found this one reading a bunch of recommendations for the FC11 and since it's below my budget I thought the FC12 would be better. It should have a lower lumen rating than the D4V2 but it should be able to sustain it for much longer. Would be great if it was a little bit shorter.
• IF25/IF25A (both 33€~): I think it can use both 18650 and 21700..? Not sure what would be the difference in using one or the other (output intensity/runtime I guess?). Also, harder to find cheap chargers for 21700 (for example the MC1 doesn't support them), but on the other hand it has USB-C charging.

I also wouldn't mind being able to turn my flashlight into some kind of lamp with a diffuser; I read that you can do that with an addon for the D4V2 but I'm not sure if I can do the same with the other flashlights.

Thoughts? Relevant flashlights that I'm missing?

Thank you!