My undergrad thesis requires EES to solve the design of the heat exchanger I’m working on. I’ve already calculated the heat needed in the room I’m heating and now I just need to check if the gases passing through the piping are enough to provide it, but it seems I’ve made some mistakes with the lower and upper boundaries of the mean logarithmic temperature in the flow. Anyone has any advice for this values constrains?

Say I have a power supply or circuit board I want to air cool. Pretending that the surface is a flat plate, is it better to have a fan at the leading edge pushing air across the plate or at the trailing edge pulling air across the plate?

Assume it's the same fan in either situation, set up in it's optimal direction. Will there be a noticable thermal difference? Are there other factors to consider when making a design choice between the two?

Thanks for the help!

Diagram provided in comments:

I am designing a heater made from a powered heating element that will be welded into a long copper heater. Nitrogen gas of a known temperature will be flowed over the heater at a known volumetric flow rate. I am trying to figure out how to calculate the heat transfer of this model, specifically, how long I need to make the copper heater so the exit gas will achieve a desired temperature.

The copper heater will be placed inside a quartz dewar vessel (very well insulated) so we can assume negligible heat loss through the walls.

I have knowledge in Thermodynamics, Thermal System Design, and Fluid Mechanics... but I can't seem to find an equation that adequately describes this situation. If anyone can point me in the right direction to figure this out I would be very grateful!

I'm a first year Mech Eng student and am studying for exams.

I thought heat would transfer by forced convection as the fluid is being pumped through the system but some of the material we have been given states to assume it is natural. Why do they do this? Is it actually natural and I'm mistaken or is it just easier to calculate the heat transfer rate?

Here's a long and very specific question, but I think it's a very interesting one. I'd very much appreciate some discussion:

I'm reading this paper on ancient Roman baths, which discusses using solar radiation to heat a room via an enormous south-facing opening (a glassless window). The author claims that with a hypocaust (floor/wall heating), you could keep the floor and the walls at around 100F, providing radiant heating which would keep bathers comfortable, even when the outside temperature dropped to 30F.

I'm not convinced, and neither is this author, who wrote a response saying "You botched the convection calculations, it would be horribly cold without glass in those windows." Here's a diagram of the room. The window is facing south(east). The first author claims that the "stack effect" (the natural convection shown in the diagram) would only occur in conditions of little or no wind. Higher wind pressure would instead cause a slower flow of air through the room, either through the doors or through the oculus in the ceiling.

This seems absurd to me. I don't see how any amount of wind could reduce heat transfer. The author of the response paper agrees, saying:

>The net result would be to set the 52.5 x 105 BTU/hr heat loss calculated above as a minimum value and in windy situations to expect this loss to be even greater with the concomitant effect of an even faster lowering of the bath temperature, more quickly chilling the nude bather.

Is this the whole story? Could the first author have gotten his facts so wrong? His paper is much longer and more thoroughly researched than the response, so I have a hard time believing that he botched the analysis in such a crucial way. Thoughts?

Hi r/cooking!

I am in a situation where I am looking to make a pork shoulder dish for 15-20 people. Where I am living right now the ONLY oven I have access to is an industrial level forced convection oven.

I know that oven roasted pork is cheating. I also know that cooking in a forced convection oven is different than using a regular home oven. My questions to r/cooking are twofold:

1. How do cooking temperatures and time differ when using a forced convection oven? I imagine I will be cooking the shoulder for at least 6-8 hours so would a general rule of "take 15 minutes off the normal cooking time" not work?

2. Second if anyone has any awesome pork shoulder recipes let me know.

Thank you so much!

P.S. mods if this is in the wrong place please let me know and I'll move it or something.

Hello! I'm writing a MATLAB script to calculate the average heat transfer coefficient (Hc) for a hot metal slab under forced convection however I'm running into some difficulties and my Hc value is coming out very low (around 4). Could someone please has a look through my script and outline any problems?

I think the problem is to do with the division characteristic length at the end of the script, usually this is a decimal which increases the Hc value. However my hot metal slab is large 11mx1.8mx0.25m so my characteristic length is large as well.

I found a correlation for cuboids in a free stream here http://www.mhtlab.uwaterloo.ca/pdf_papers/mhtl01-3.pdf however I think a simple average over a horizontal flat surface could surfice.

Link to script: https://www.dropbox.com/s/guwi2m8s4tuzjce/ConvectiveCoeficientForced.m?dl=0

Any help is really appreciated, thanks!

I am designing a small system that attempts to transport air via forced convection.

The following link contains a couple of diagrams. One shows a plan view of the system, the other shows a cross-section view of the "fan box".

http://imgur.com/a/BncAM#0

The system needs to circulate air from the smaller box to the larger box, and back again in a loop.

The tubes have an inner diameter of 3 mm. Here's a page with a picture and some additional information: http://www.coleparmer.ca/Product/Tygon_non_DEHP_ND100_65_1_8_X3_16_50/RK-95666-05

Each length of tubing (note that there are 4 lengths) will probably be ~ 35 cm in length. Connections (into the various boxes) will be via luer locks: http://www.coleparmer.com/buy/category/nylon-fittings

Cross section of a luer lock: http://www.freepatentsonline.com/6673059-0-large.jpg

The fans are small 4 cm x 4 cm fans that look kind of like this: http://www.pcsilent.de/ppic-MAXI-Scythe-Mini-Kaze-4cm-fan-2pin-connector-quiet-40mm-fan-hard-drive-chipset-scyminikaze40u.jpg

They will be enclosed in a plastic box that fits snugly around, and will have two luer locks, on both of the 4 cm x 4 cm faces. The fans will be arranged so that they will blow air in a loop (see the bird's eye view picture).

My intuition with this is rather terrible at the moment, so this preliminary design probably has quite a lot of issues with it.

My questions:

1. Will the "fan boxes" actually push air through the tubing? I highly doubt this at the moment because of the large difference in dimension between the inner diameter of the tubing and the fan box (which is even worse really, due to the constraints in inner diameter imposed by the luer lock...so the minimum diameter along the length tube is actually < 3 mm). I personally think the fans won't really push air through the tubing, as much as bounce air around the fan box (little as it is, since the box fits very snugly around the fan box, and is well sealed) but I would appreciate some way of being able to confirm this beyond just an intuitive look.

2. What are some simple mathematical models I should be aware of while designing such a system?

Thanks a lot for your time!

I'm trying to write a paper on impinging jets, but can't find a paper that compares them to normal flat plate convection. Any help pointing me in the right direction would be appreciated.

It confuses me a bit because I only realised recently that there's a surprising amount of difference between American ovens, and ovens elsewhere. I heard recently that the feature that as far as I'm aware is completely standard in UK and Australia, is rare and kinda fancy for US ovens, which is fan force. Except, I was only told this, and I notice that I never hear American's actually use the words 'fan force' but I do hear some say "if you have a convection setting, use that", which sounds kinda like it might be fan force, but perhaps it's something else.

My reading seems to suggest that they are the same but then the naming confuses me because, isn't that not convection? Isn't convection the movement of molecules based on heating? Like if you boil water, the water at the bottom will heat and rise and is it does cool causing it to move to the bottom where it's heated and rises again causing a circular 'convection' current? In an oven it would be air moving around based on this same idea I would have thought. Wouldn't the inclusion of a fan moving the air around because of the mechanical force of the blades acting on the air be something other than convection. This is part of why I wonder if the term isn't referring to what I call the 'fan force' setting after all and it's some other feature.

[](/# MC // section intro)

Welcome to the r/SpaceX Transporter-2 Launch Discussion and Updates Thread!

I'm u/hitura-nobad, your host for this launch.

r/SpaceX Launch Weather Review

(15:10 UTC)

Weather-wise, so far everything looks pretty good, with showers, storms and cloud debris well away from the zone around the pad.

However, on days like these where the main threats are primarily diurnal convection which evolves quickly and unpredictably, we'll only really get a better idea within an hour or two from launch, at least beyond the 45th's mesoscale forecast and 70% GO.

(17:00 UTC)

With less than two hours to go until launch, the weather is still looking pretty good around the pad, better than yesterday so far, with showers and storm cells still keeping generally well clear of the 10 nmi/19 km zone around the pad, and like yesterday, cirrus blowoff from storm anvils to the west causing high-level cloudiness but seemingly well removed from their source such that they should not preculde launch.

(18:30 UTC)

Looks like there's just one modest cell that's the problem, that looks to pass directly over the pad. It should be on track to clear the area by the new scheduled launch time, but there are a few others downstream that may intrude on the party.

(by u/CAM-Gerlach)

[](/# MC // section events)

Timeline

More information about this particular one can be found here: https://www.reuters.com/world/europe/rare-tornado-storms-rip-through-southern-czech-republic-2021-06-24/

The moon has a massive impact on the movement of our oceans. So why not on the magma within the earth? To me the tidal forces from the moon would appear to be more powerful a force than convection currents.

In the middle of the morning convection and bored out of my mind (Forced to watch it with my pimi family.” I’m so sick of hearing “We are just so close the end” cult speak. This saying has been around since 1914..it’s fucking insanity

Latest observation

Wednesday, 30 June — 11:00 PM Atlantic Standard Time (EDT; 03:00 UTC)

Latest updates

Wednesday, 30 June — 11:00 PM AST (03:00 UTC) | Discussion by /u/giantspeck

The fifth tropical cyclone of the 2021 Atlantic season has formed

Convection surrounding an area of low pressure situated approximately 1,500 kilometers (900 miles) to the east-southeast of the Windward Islands has become markedly more defined over the past several hours. Animated infrared imagery depicts a pronounced band of deep convection wrapping into the better defined, albeit elongated low-level center from the west. Strong divergence aloft, particularly to the south of the surface low, is helping to establish a rather robust equatorward outflow, as evidenced by water vapor imagery.

Satellite imagery analysis, combined with recent scatterometer data, has helped to confirm that the disturbance has developed into a full-fledged tropical depression. Intensity estimates indicate that while the cyclone is more organized than it was six hours ago, it is still producing maximum one-minute sustained winds around 55 kilometers per hour (30 knots). The depression continues to move rather quickly toward the west-northwest under the steering influence of the Bermuda High to the north.

Forecast discussion

Wednesday, 30 June — 11:00 PM AST (03:00 UTC) | Discussion by /u/giantspeck

The depression is likely to reach tropical storm strength overnight

The depression is moving through a favorable environment characterized by weak northerly shear (5 to 10 knots), abundant mid-level moisture, a warm sea-surface (27 to 28°C) with ample ocean heat content, and strong divergence aloft. While this is expected to allow the depression to further develop, its strengthening is likely to be severely tempered by the cyclone's rapid westward movement. Climatologically spe

In my part of Europe, most homes are heated by running warm water through (floor/wall) radiators.

In the US, air seems to be the norm? Is it because of cooling? Though I also see a LOT of A/C window units. Do those buildings have water-based heating? Are there other reasons for going with air over water?

To clarify, I didn't mean steam-based heating, but a closed water loop through a radiator.

hi- stumbled upon these guys: http://www.healthyrips.com/ https://www.youtube.com/watch?v=8vp5-Bt8znQ

they also designed a clone like a few similar convectors in the market and sell it at 149$ (will pick up a Fenix for 75$ over this any day)

anyone have some more info? thanks.

Why You Should Marble Your Marshmallows:

These are cinnamon marshmallows, marbled with dark chocolate and salted almond butter:

tl;dr: Swirling fat-based add-ins into marshmallow batter causes interposition between the gelatinous marshmallow matrix. The result are multitudes of discrete layers of add-ins (in this case, chocolate and almond butter) and marshmallow. The interruption of a continuous marshmallow structure results in a drastically different texture and eating experience. The best way I can describe it is a "soft bite"/"soft chew". Think "cotton candy, but a bit firmer". (I won't claim it's a "superior" change, just a different one. Everyone's got their preferences!)

Here's an unmarbled 'mallow (same recipe): It has a continuous gelatin matrix, so it exhibits that springy, chewy quality you associate with a marshmallows. Compare with the marbled one: It has far less spring and give to it in the marbled section due to the solidity of the reformed chocolate and the almond butter.

Think of the difference between brioche and puff pastry/millefeuilles. Brioche has a continuous gluten network, and it's soft, springy, and fluffy. The puff pastry in a millefeuille has all those layers of wafer-thin pastry, and the resultant texture is flaky. (I know this isn't an entirely accurate comparison, but I think it serves well enough.) It's that disruption of that gelatin matrix that results in the unique texture exhibited by these marshmallows. If I knew more of materials science, I'd try to use terms like "shearing force" and "layered materials", but I didn't study engineering in college.

(Quick edit: if you're the visual type, and would like to see the process behind making these, I made a relatively short vid on it:) Hope it's helpful!

RECIPE

450g sugar

250g corn syrup

80g water

25g gelatin + 100g cold water

3g salt

1tsp Saigon cinnamon

7.5mL vanilla extract

150g 72% dark chocolate, finely chopped and divided

125g almond butter*

*I used my own almond butter for this recipe. To make the almond butter, roast 785g almonds at 350F/176C (convection) for 8-10 minutes. Grind with 10g salt into a butter. For best results, use a melanger to grind it down even smoother.

Directions

Grease a 20x20cm / 8x8in pan with nonsti

So hear me out here (and yes as my username implies I am an actual career food scientist) but wouldn’t a rotisserie not do too much in a pellet grill (assuming your pellet grill acts as a forced convection oven like my GMG?)

In principle, a rotisserie helps with even cooking by moving your meat around direct heat. The same cooking should occur if you move your heat around your meat, like you would in a forced convection oven.

The only advantage I can think of would be using gravity to prevent your juices from dripping out with the constant rotation. One of my buddies swears by the “constantly flip your burgers” theory, and he makes really good burgers.

Anyways just wanted to throw that out there. I’ve used my GMG DB Prime a million times with no problems, so there’s no going prime plus now.

Phil

Water:

Distillate: User cleans the minerals from their system for a brief period, making them immune to Electric attacks for 3 turns.

Rip Current: User runs a convection current through their body, cleansing them and their teammates of status effects for 3 turns.

Geyser: User summons a powerful geyser to blast the foe from the ground; can hit during semi-invulnerable turns of Bounce, Fly and Sky Drop.

Oxidize: Super-effective against Steel types.

Fountain Jump: User uses jets of water to launch into the air, then strikes on the second turn.

Arctic Water: User unleashes a powerful blast of frigid water at the target that has a 10% chance to freeze target on impact; signature move of Suicune.

Fire:

Hot Spot: Summons a bubble of magma under the battlefield. If the user is hit with a Ground type move within two turns, the spot explodes and deals damage to the opponent.

Flame Sword: User creates a blade of infrared energized air and strikes the opponent with it. Variation of Leaf Blade.

Flame Shield: User summons a burning aura that protects the user and absorbs power from enemy special attacks, boosting the user's own Sp Attack by 25% on being hit.

Ash Cloud: User releases a plume of smoke and hot rocks at the opposing team, dealing damage and reducing accuracy by one stage.

Ember Shower: User surrounds itself in a cloud of scalding embers and dives into the target, partially damaging itself and potentially burning the target; more powerful version of Flare Blitz; signature move of Moltres.

Ground:

Quicksand: The opponent is sucked into a pool of quicksand, reducing speed by two stages.

Seismic Wave: The user charges energy on the first turn, then unleashes a giant rippling shock wave through the earth. Can hit on the semi-invulnerable turns of Dig and Dive.

Sandblast: User shoots a high power stream of sand at the opponent, dealing damage and reducing the opponent's special defense by one stage.

Undermine: Removes the earth from under the battlefield's surface. If the opposing Pokemon uses a Physical move within two turns, the ground collapses, damaging the opponent.

Dust Devil: User creates a small tornado of sand and dust that has a 20% chance of confusing the target; this move is guaranteed to hit during a Sandstorm, and can also hit Flying types; less powerful variation of Hurricane.

Land Storm: User summons a mighty cyclone of earth that strikes all Pokemon on the opposing side, erasing their defense stat modifiers but forcing the us

Latest observation

Friday, 18 June — 1:00 PM Central Daylight Time (CDT; 18:00 UTC)

Latest news

Friday, 18 June — 1:00 PM CDT (18:00 UTC) | Discussion by /u/giantspeck

A tropical storm could develop over the northern Gulf of Mexico later this evening

A broad area of low pressure situated over the northern Gulf of Mexico continues to gradually organize this afternoon. Animated infrared imagery depicts deeper convection which remains confined to the east of the disturbance's low-level center by strong westerly shear. A recent U.S. Air Force Hurricane Hunters aerial reconnaissance mission was able to identify the disturbance's center of circulation, but found that it was actually located farther east than expected.

Intensity estimates derived from satellite imagery analysis and aerial reconnaissance data indicate that the disturbance is producing maximum one-minute sustained winds near 35 knots (40 miles per hour), though these winds are confined to the stronger thunderstorms east of the low-level center. While this disturbance is producing tropical storm-force winds, it lacks a sufficiently organized structure for the National Hurricane Center to justify upgrading it to a tropical storm.

Forecast discussion

Friday, 18 June — 1:00 PM CDT (18:00 UTC) | Discussion by /u/giantspeck

Strong winds, heavy rainfall, and dangerous storm surge are expected to impact the central Gulf Coast this weekend

The disturbance continues to move northward through a weakness in the subtropical ridge created by an approaching upper-level trough over Texas. This trough continues to impart strong westerly shear to the Gulf of Mexico, which is preventing the disturbance from consolidating its deep convection close