Category: Physics

Electrodialysis

Electrodialysis

Electrodialysis

10/17/25

“How can we use electric potential to desalinate water?”

Saltwater is much more common than freshwater in the world. Consequently, we could greatly increase our water supplies by converting saltwater to freshwater. But traditional reverse osmosis techniques are incredibly energy-intensive. Is there an easier way to desalinate water? Well, we know that salts have an electrostatic charge. So what if we were to place the water stream between a cathode and an anode and insert an alternating series of membranes that only allow cations or anions to pass? Well, this will create streams of purified water, separated from saltwater. This process, called Electrodialysis, is a smart way to desalinate water and make it useful for people. 

Image credit: https://static.wixstatic.com/

Mass Transfer

Mass Transfer

Mass Transfer

10/12/25

“How does mass move from one phase/substance to another?”

Substances in different phases or substances may come into contact with each other. This can cause the mass of a certain substance in one phase or concentration to move to another, such as through diffusion (one substance moving from a single concentration in another to uniform distribution), convection (mass transport by bulk motion of a surrounding fluid), absorption (chemical penetration of one substance into another), or distillation (separation of different components by different boiling points). This Mass Transfer is foundational to understanding how chemical engineering systems operate.

Osmotic Pressure

Osmotic Pressure

Osmotic Pressure

09/30/25

“What’s the pressure needed to stop osmosis?”

Imagine a semi-permeable layer dividing a container of freshwater from a container of saltwater, each with equal volumes. Now imagine that the semi-permeable layer is small enough for water particles to pass through, but not for salt particles. Since there are more water particles on the saltwater side than on the freshwater side, there will be a water particle migration until there’s an equal amount on both sides. This will lead to a pressure differential in the direction of the salt water. The pressure necessary to overcome this imbalance and begin the reverse osmosis process is called the Osmotic Pressure, given by the equation pi = phi * (n/V)RT, where pi is the osmotic pressure, phi is the osmotic coefficient, n is the number of moles in the solute (in this case, salt), V the volume of the solvent, R the universal gas constant, and T the absolute temperature.

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Distillation

Distillation

Distillation

09/29/25

“How can we use boiling to separate two substances mixed together?”

Substances mixed together in a liquid can be difficult to separate. But applying a bit of chemical knowledge can help us. If the two mixtures have significantly different boiling points, then one will vaporize before the other. So what if we were to capture this vapor and condense it into another reservoir to separate the substances? Well, this is the idea behind Distillation. Water treatment systems can apply distillation to separate water from contaminants. If the boiling points between the different substances are less than 100 degrees ˚C apart, then operators must use a special fractional distillation technique.

Henry’s Law

Henry’s Law

Henry’s Law

09/28/25

“What describes the relationship between the amount of gas dissolved in a liquid and the partial pressure above the liquid?”

Pressure forces gas to move. If gas is in a container with a liquid and high pressure is acting on the gas, there is more force to move more of the gas into the liquid. If there is low pressure acting on the liquid, then more of the gas will escape from the liquid. This behavior is described by Henry’s Law, which is described by the formula C = k_H*P, with C being the concentration of the gas dissolved in the liquid (mol/L or mg/L), k_H the Henry’s Law constant (mol/liter-atm or dimensionless), and P the partial pressure of the gas in the air above the liquid (atm). Henry’s Law is a vital part of mass transfer analysis for many applications.

Filter Backwashing

Filter Backwashing

Filter Backwashing

09/25/25

“Why can we clean filters by pumping water backwards?”

Filters collect trapped material over time. Sometimes this piles up so much that it hampers further treatment. To solve this, infrastructure operators can pump water in the other direction to remove water from filtration. This Filter Backwashing is vital for treatment maintenance.

Image credit: https://www.aquabluepools.net/

Gravity Hills

Gravity Hills

Gravity Hills

08/28/25

“Why do objects appear to roll upwards and defy gravity on some hills?”

There are places where nature does not seem to obey the laws of physics. For example, on some hills, objects appear to roll upward instead of downward. There are countless videos on the internet showing the strangeness of these Gravity Hills. But what exactly is happening? Well, it turns out that the slopes of these hills are actually an optical illusion, making downhill look like uphill. These hills usually lack a clear horizon, making it difficult to accurately judge the real direction. Furthermore, a road might be at a slightly different angle than the incline, causing a visual cue mismatch. One example of a gravity hill is in Aragats, Armenia, as seen in the attached picture.

Image credit: https://i.ytimg.com/

Net Positive Suction Head (NPSH)

Net Positive Suction Head (NPSH)

Net Positive Suction Head (NPSH)

08/14/25

“What is the minimum pressure needed to avoid cavitation in pumps?”

If pumps don’t have enough pressure, then water vapor can form in the pumps and cause cavitation in the pump blades. Pumps can prevent this from occurring by maintaining pressure above the vapor pressure. The difference between these quantities is known as the Net Positive Suction Head (NPSH). The NPSH required (NPSH-R) is the pressure at the impeller entrance needed to avoid cavitation, equal to the difference between the stagnation pressure and the vapor pressure at the inlet. The Net Positive Suction Head Available (NPSH A) is the pressure available at the pump inlet above the vapor pressure and losses due to system friction. For functional system operation, NPSH A must be greater than NPSH R.

Static Pressure

Static Pressure

Static Pressure

08/13/25

“What’s the pressure of a fluid’s presence?”

Fluid pressure comes in all kinds of forms. Fluids will exert a pressure from their presence alone called Static Pressure. Air in a balloon is an example of static pressure.