Hot answers tagged

43

A refrigerator is basically a heat pump designed to achieve a temperature close to 0 °C. There are a couple of problems here: Most refrigerators are way too weak to effectively tackle the heat output of modern PCs. It will not magically make your PC 6 °C - instead the PC will de-cool all your groceries. Condensation. Computers and electronics do not like ...


21

For a large and/or high speed fan, there are several mechanical disadvantages, for example The outer ring is highly stressed and therefore heavy. It may also need a heavy containment system to avoid collateral damage if it breaks. For example in a large turbofan jet engine, a mechanical failure caused by a crack near the hub of the fan usually only releases ...


18

We do. It's just an up-sized (i.e. more powerful) version of a refrigerator known as an air conditioning unit. Essentially all server rooms and most spaces where PCs are located (speaking for the U.S., at least) are air conditioned. Server rooms almost universally have dedicated HVAC systems and they will indeed be designed to keep the room at a more-or-less ...


12

refrigerator boxes tend to generate condensate There are specifications for acceptable relative humidity (RH) for servers. Air conditioning in server rooms will maintain RH within the allowed limits as well as maintaining temperature limits. You can't risk having condensation forming on electrical wiring or circuit boards as it will disrupt operation. ...


10

Here's a webpage from a random guy who put a light bulb in his refrigerator to see what would happen, and took careful data to monitor it. Results: The next experiment was to put a 60-watt incandescent light bulb inside the fridge. ... Over the next 55 minutes, I saw the temperature in the fridge slowly creep up, while the fridge's compressor ran ...


9

The concept of what you're doing is sound, and as Russell McMahon notes the efficiency gains could be significant enough to justify the change. I'd strongly suggest that you consider adding a ramp to the back edge as well. Drag force is very sensitive to the downstream (rear) end of a body as well You get some positive pressure at the front of the vehicle, ...


8

You need to consider the density of the air, which varies with temperature and air pressure. At 15 degrees Celsius, at sea level, the density of air is 1.225 ${kg}/{m^3}$. The table here gives air densities at 5 degree intervals. Now density is mass divided by volume, ${\rho} = m/v$ Hence, to get the volume flow rate (in ${m}^3/s$), for a know mass flow ...


8

Silica gel is the standard for most purposes. It's the desiccant you find inside those paper sachets packed with new electronic equipment. It consists of tiny beads of silicon dioxide that are nanometres across (so that a little material has a lot of surface area), and although it's called a gel, the material itself is hard at room temperature and pressure....


7

This phenomenon is known as cavitation for pumping liquids - i.e. for anything that can change phase. If you are pumping gas, then the scenario really does come from choked flow. Let's say you've got a compressor and you're running it as a vacuum pump to evacuate a tank - at some point the tank's pressure on the inside is so low, you can't pump any more ...


7

Are you bound to the shape/configuration of part you constructed in your question? If not, a simple 3-way pneumatic solenoid valve would make this very simple and leak proof(relatively speaking). They are inexpensive too.(eBay) You would have an input and the valve will allow flow through one outlet and then energize the solenoid and you will get flow ...


7

The common pipe threads that are used in buildings for water and gas are tapered threads. The thread is cut on the cone rather than cylinder. In the US, these threads are called National Pipe Thread Tapered (or NPTT1, or simply NPT). They don't seal metal-to-metal. Thread seal tape is wound onto the male thread before it's screwed in. When the tapered ...


7

Fans like the one on the right exist. These where first invented as rim-driven thrusters (rim driven is your search term, not centerless) for marine applications. The rim is the rotor of the electric motor driving the fans, the shroud around the rim contains the stator. With the amount of research I'm willing to do right now, I found no definitive statement ...


6

In the Fluid Dynamics community about 40 years ago, the group was primarily divided into experimentalists and theorists. However, at that time CFD was quite new, had to be run on expensive supercomputers, and untrusted. It was quite common that a theorist or experimentalist would at best discount the results of the CFD, while others may totally disregard ...


6

You are describing a very interesting engineering problem. The requirement of a turbine is to convert fluid-energy into mechanical energy over a range conditions. Since the flow around the airfoils is governed by the (elliptic) Navier-Stockes-Equations, an easy answer to your question is not possible in general. Only in certain edge cases it is possible ...


6

Quick and dirty CFD simulation of your problem using ANSYS Fluent 14.5: I used a 2D duct, 8" x 4" with a 45-degree angle going from the inlet pipes to the main chamber. Assuming 3 liters per hour flow through a half-inch diameter pipe gave me an inlet velocity of 6.6 mm/s. Air enters from the left and exits through the right. Inlet and outlet were set to ...


6

The yellow curve corresponds to a fan that will provide mostly a set pressure differential, say, keeping fumes from escaping a tank through elsewhere than dedicated vents. If there is a circumstance that reduces the pressure differential, it will speed up and increase the flow, to compensate. The blue curve is a fan that doesn't expect any significant ...


5

HVAC-Systems usually give a Volume-Flow-Rate, hence $m^3/s$. If you need Mass-Flow-Rate ($kg/s$) you simply need to multiply with the density ($\rho$) of the fluid. The density can be calculated using the ideal gas law (see 1): $$ \rho_s = \frac{p_s}{R T_s}$$ Please observe that you need static values for the pressure ($p_s$, see 2) and temperature ($T_s$, ...


5

What you want is called a heat exchanger. Imagine two long air tubes with a thin wall between them. The air exiting the house travels in one tube, and entering air in the other, but in opposite directions. Over the length of the tubes, heat transfers thru the thin wall. Ideally, by the time the house air gets to the far end where the outside air comes in,...


5

The fundamental problem is that hot air must leave the room and cold air must enter it, both at the same time through the same single opening. The conflicting forces will mostly cancel each other out, resulting in very little actual exchange of air. What you really need is old technology. Double hung windows are what our ancestors used. The bottom sash ...


5

In addition to tapered threads for creating seals, there are Compression Fittings which use a matching male and female mating low angle taper to create a sealing surface. When properly torqued, they rely on elastic deformation to "squish" the mating surfaces together to create a seal. These are re-usable. Crush washers are used in a similar fashion to ...


5

The short answer is that they don't. Choking is not a bad thing. For a gas flow regulator, it's actually a good thing, because under choking conditions, the mass-flow rate is no longer dependent on the downstream pressure. The mass-flow rate is still dependent on the upstream pressure and the size of the aperture connecting the high and low-pressure sides. ...


5

The capacity of an evaporative cooler depends on the relative humidity. The lowest theoretical temperature that the cooler can reach is the wet bulb temperature. The wikipedia article has some discussion on the design and shows how it works with psychometric charts. For the design you'd look at a 'typical' hot day, compare wet bulb to dry bulb for that day ...


5

Normally fans are not custom built by a company that does not build fans. The concept of a centrifugal fan is not particularly complicated, but it is difficult to achieve target flow rate, pressure, and efficiency if your company does not do it on a daily basis. If you are not able to purchase a fan, another option is to copy someone else's simple straight ...


5

They've been doing that with computers for 30+ years. Back when computers were the size of refrigerators. They use to get a regular air conditioner. Build a platform for the computer to stand on. A hole in the center of the platform. Then duct the air conditioner to the bottom of the platform. Forced air rose through the computer. For your needs - can ...


4

CFD I ran this situation through a couple of simple 2D CFD models. As you can see from the pictures below, one way to keep debris from gathering in this area is to increase the velocity of wind in the corner. To do this, you need to place an obstacle that will direct the wind into the corner. Original Situation: Obstacle Added: Even with this, there will ...


4

It's a trade-off between the simplicity of the sensor and how comprehensive the reported data is. The locked rotor sensor only reports whether or not the motor is spinning, not how fast it's spinning or how much resistance is on the fan. It is a very simple signal though, it's either on or off. On the other hand, the tachometer signal is a bit more ...


4

You need to push air through the turbine at 11 m/s, or just above. That's what the rated windspeed means: it's the lowest windspeed at which the turbine hits rated power, at standard atmospheric pressure. The volume of air you need is determined by the area of the rotor. Let's say it's $\alpha m^2$. So you know you need to push through $11\alpha m^3/s$. So ...


4

Constant entropy doesn't mean constant temperature, the gas flow through nozzle is subject to change in pressure and velocity (continuity equation) due to the variation in cross section, and being compressible the change in pressure will be reflected as change in temperature and density. That being said, since the flow is isentropic and there will be no ...


4

The sun is heating mode. When the room temperature reaches the set temperature, the air conditioner stops operating until the temperature falls below the set temperature and the starts operating again. When in heating mode, the air conditioner does not cool. This setting is used during cold weather periods, such as in winter. The snowflake is cooling mode. ...


4

A truck speeding down a highway creates an envelope stream of high pressure air surrounding it. This is basically a wake, composed of layers of high pressure shockwaves, created when the front of the truck, hood and cabin penetrate the still air and push it open. This shockwave moves with the truck and after turning into a small turbulent tail at the ...


Only top voted, non community-wiki answers of a minimum length are eligible