Hot answers tagged

43 votes

Why not put servers in a refrigerator?

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 ...
user avatar
  • 431
21 votes
Accepted

Benefit of removing the center "engine hub" inside a fan

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 ...
user avatar
  • 12.5k
18 votes
Accepted

Why not put servers in a refrigerator?

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.,...
user avatar
  • 296
12 votes

Why not put servers in a refrigerator?

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 ...
user avatar
11 votes

Why not put servers in a refrigerator?

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 ...
user avatar
9 votes
Accepted

How would adding a wind deflector in front of roof-mounted solar panels affect drag on an RV?

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 ...
user avatar
  • 1,966
8 votes

Converting air flow rate between kg/s and m^3/s

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 ...
user avatar
  • 9,462
8 votes

Is there a more active passive technique for removing humidity from the air besides salt blocks?

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 ...
user avatar
  • 3,701
7 votes

How do I calculate the max flow rate for a pump with no power restrictions?

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 ...
user avatar
  • 5,303
7 votes
Accepted

Airflow selection mechanism

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 ...
user avatar
  • 1,578
7 votes

How metal fittings seal connection without rubber gaskets?

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 ...
user avatar
  • 1,045
7 votes

Benefit of removing the center "engine hub" inside a fan

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 ...
user avatar
  • 4,618
6 votes

How are wind tunnel models used when designing supersonic aircraft?

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 ...
user avatar
  • 493
6 votes

efficiency and flow separation

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 ...
user avatar
  • 1,202
6 votes
Accepted

How can I create uniform laminar flow in a short duct?

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 ...
user avatar
  • 2,989
6 votes
Accepted

Fan performance curve

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 ...
user avatar
  • 6,123
5 votes

Converting air flow rate between kg/s and m^3/s

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 ...
user avatar
  • 1,202
5 votes
Accepted

How to minimize heat loss in an air extractor?

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 ...
user avatar
  • 11.2k
5 votes

How does one create a draft in a room (with a single window)?

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,...
user avatar
5 votes

How metal fittings seal connection without rubber gaskets?

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 ...
user avatar
  • 1,578
5 votes
Accepted

How do gas flow regulators avoid choking?

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 ...
user avatar
5 votes
Accepted

How much does an evaporative cooler cool down a room

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 ...
user avatar
  • 377
5 votes
Accepted

How do I choose a blower design for an induced draft brick kiln?

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, ...
user avatar
  • 7,469
5 votes

Why not put servers in a refrigerator?

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. ...
user avatar
  • 51
4 votes

Foiling vortex traps around buildings

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 ...
user avatar
  • 10.6k
4 votes

Fan Sensors (Tachometer vs Locked Rotor)

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 ...
user avatar
  • 2,989
4 votes

What is the power and max flow rate required to rotate a 300 W wind turbine?

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 ...
user avatar
  • 3,701
4 votes
Accepted

Shouldn't enthalpies be equal in isentropic process?

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 ...
user avatar
  • 2,149
4 votes
Accepted

What's the difference between aircon modes Auto, Sun, Snowflake?

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....
user avatar
  • 9,462
4 votes
Accepted

Passing by a semi truck on a highway

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 ...
user avatar
  • 21k

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