Washing Machine Working Principle

Washing Machines

In our modern-day lives, we use several technological marvels to keep up with the escalating pace of this ever-growing world. Some of them have become so common in our daily use that we hardly ever wonder how these technologies work at their core. One such example is the washing machine that we use to clean our dirty laundry. Just add some water to the washing drum, a few scoops of detergent, turn few nobs, and we have a clean laundry after few minutes. Fairly simple right? It may come as a surprise to you that although washing machines were available since the 19th century, it was not until 2018 that the scientists were able to demystify the working principle of a washing machine. There is a complex interplay of mechanical and chemical actions that makes the cleaning possible inside the washer. Before we understand the working of a washing machine, let’s first try to understand the role of detergent in the cleaning process.

The Role of Detergents in Washing clothes

In chemistry, detergents are known as surfactants, short for surface-active agents. The molecules of detergents can attach themselves to two different types of substances that don’t generally interact with each other, e.g., oil and water. Usually, one end of the surfactant molecule is hydrophobic (water-repellent), and the other is hydrophilic (water-attracting). When the detergent is dissolved in water, its molecules arrange themselves in spherical structures called micelles. The hydrophobic tails of these micelles attach themselves to the dirt or grease molecules, while the hydrophilic heads attach to the water molecules. The general understanding would be that the rotation action of the washing machine would cause this surfactant solution to flow through the fabric and pick up all the dirt molecules hiding in the cracks, which can be removed by the flush of water; however, recent studies have found something different. Fabrics are made of yarn, which in turn is made of interlocked fibers. Although surfactant solution can easily pass through the spaces between the cross-sewed yarns (inter yarn spaces), it can not pass through the yarn itself specifically the spaces between the interlocked fibers (Intra yarn spaces). In general, the ratio of detergent solution that can penetrate through the intra-yarn spaces is only 0.1 percent to the one which cleans the dirt stuck in the inter-yarn strands. Mathematically, this would take several hours to clean the dirt stuck between the intra-yarn pores; however, in reality, it only takes a few minutes to get the dirt out from the intra-yarn pores in a washing machine. The scientific community address this inconsistency as a “stagnant core problem.” This is where the rinse cycle of a washing machine comes into play.

Working Principle of a Washing Machine

Superficially, washing clothes is a pretty straightforward process. Technically, this process is addressed as something called agitation. It is a process of improving the liquid’s chemical or physical action by employing a forced circulatory or any other periodic motion (just like stirring). In a washing machine, agitation causes the clothes to move back and forth inside the washing drum that contains water mixed with detergent, rubbing against each other to remove stains. As discussed earlier in this topic, this process is only efficient in cleaning the inter-yarn spaces and not the intra-yarn pores. Further cleaning is done by something called diffusiophoresis. It is the spontaneous motion of colloidal particles or molecules in a fluid induced by a concentration gradient of a different substance. The rinsing action of the washing machine clears off the dirt-containing micelles, creating a gradient of chemical concentration around the micelles that are holding on to the dirt molecules stuck inside the intra-yarn pores. Moreover, the electric field developed by incorporating the anionic surfactants also aids the removal of the dirt.¬†

Components of a Washing Machine

  • An inner drum: This is where we put the laundry. One can notice that this drum rotates a bit when you touch it, and there are a lot of holes punched into it. These holes allow the water to come in and wash the clothes.
  • Paddles: These are ridges that lie on the edge of the drum and help move your laundry around while being washed.
  • Agitator: It is a paddle, more common in top-load machines, in the middle that helps turn the clothes around in the soapy water.
  • The outer drum: This drum is not visible when you look inside the washer, but there is another drum that holds the water while the inner drum or agitator rotates. This part is completely water-tight to prevent your machine from leakage.
  • Thermostat and heating element: These control the temperature of the water and heats the water to the specified temperature.
  • Pump: This removes the water from the drum after the wash.
  • Programmer: This controls the washing machine through all the steps from washing to rinsing and spin-drying.
  • Pipes and valves: These allow the water in and out of the washer.

Types of Washing Machines

Top-Loading Washing Machines

Top Loading Washing Machines

Top-loading washing machines are generally considered standard washing machines. The most prominent feature of these washing machines is the verticle axis washer that places the clothes in a vertically mounted perforated basket that is contained within a water-retaining tub. A finned water-pumping agitator is placed in the center of the bottom of the basket. The laundry is loaded through the top of the machine, which is usually, but not always, covered with a hinged door. During the wash cycle, the moment of the agitator causes a circulatory motion of water, producing a centrifugal force that pushes water outward between the paddles towards the edge of the tub. The water then moves outward, up the sides of the basket, towards the center, and then down towards the agitator to repeat the process in a circulation pattern similar to the shape of a torus. The agitator direction is periodically reversed because continuous motion in one direction would just lead to the water spinning around the basket with the agitator, rather than the water being pumped in the torus-shaped motion. Some washers supplement the water-pumping action of the agitator with a large rotating screw on the shaft above the agitator to help move water downwards in the center of the basket.

Advantages of Top-Loading Washing Machines
  • The position of the loading inlet on top allows an easy operation for the user who need not bend to load the laundry.
  • Some Top-Loading washing machines even allow adding additional laundry¬†clothes after the initiation of the wash cycle.
  • Top loading washing machines are usually less prone to water leakage.
  • Top-loading washers require low maintenance, and may not need a regular “freshening” cycle to clean door seals and bellows.
  • Top-loading washers are usually less expensive than their alternatives.
Disadvantages of Top-Loading Washing Machines
  • In comparison to other types, top-loading washing machines are not considered efficient in cleaning.
  • Due to the higher involvement of mechanical transmission, top-loading machines are generally noisier than other types.
  • More water can remain in the wet load after the spin cycle, which may increase the drying time.

Front-Loading Washing Machines

Front Loading Washing Machines

Front-loading washing machines are considered more fancy and efficient than top-loading washing machines. The general layout of a front-loading washing machine usually has a horizontal axis washing drum, and loading is done through a door present on the front side of the machine. A transparent window is frequently, but not always, present at the entrance. The cylinder’s back-and-forth rotation as well as gravity provides agitation. The laundry is raised up, and then it is lowered by the paddles on the inside wall of the drum. This motion flexes the fabric’s weave, forcing water and detergent solution through a load of clothing. Because the wash action does not require the clothing to be freely suspended in water, only enough water is needed to moisten the fabric. Front-loaders normally use less soap because less water is needed, and the tumbling action’s repetitive falling and folding action can easily produce large quantities of foam or suds. A Front-loader washing machine makes use of water’s surface tension and capillary action to regulate the water use inside the drum. A front-loader washer fills to the same low water level every time, but a large pile of dry laundry, standing in the water, absorbs moisture and causes the water level to decrease. The washer then refills to keep the water level at the same level as before. As it takes time for this water absorption to occur with a motionless pile of fabric, nearly all front-loaders begin the washing process by slowly plunging the laundry under the stream of water to rapidly saturate the clothes with water.

Advantages of Front-Loading Washing Machines
  • The dimensions of front loading washing machines are usually smaller in comparison to the top-loading washing machines, which makes them a preferable choice when space is concerned.
  • The front-loading washing machines are considered more efficient in cleaning than the top-loading washing machines.
  • The front-loading washing machines use less energy since it requires less water than the other alternatives.
  • The high spin speed of front loading washing machines extracts more moisture from wet loads, which means you can cut down on drying time.
Disadvantages of Front Loading Washing Machines
  • With the advancement of technology and ease of access, the front-loading machines come with a higher price assigned to them.
  • The washing time is usually 20-30% longer than the standard top-loading washing machines.
  • Because of its design, water can get trapped inside, causing musty odors to form in the washtub and the detergent dispenser.

Hybrid Designs

There are several variations in the design of the washing machine, which are fundamentally based on the hybridization of the above-mentioned types. The most featured difference it has from the other two types is the incorporation of impellers instead of agitators. Impellers have an almost similar function to that of agitators except that they do not have the center post, extending up in the middle of the wash tub basket. The loading area in these types of washing machines is mostly present at the top. These machines are narrower but usually taller than front-loaders and usually have a lower capacity. They are intended for use where only a narrow space is available, and hence, they are popular in Asian countries, where population and living area are a concern. In principle, these devices are suitable for overnight washing (the combined cycle is significantly longer), but their ability for cleaning large batches of laundry is severely limited. Since a combo washer-dryer must not only dry the fabric but also the wash chamber and the drying process consumes significantly more energy than using two separate machines.

Precautions while using Washing Machines

  • The machine should be turned off before cleaning and maintenance.
  • It is important to check the pockets of clothes before putting them into the washing drum as hard objects such as coins, safety pins, nails, screws, or stones can cause extensive damage to the machine.
  • It is important to place the washing machine on a leveled surface as the turbulence caused by the high spinning motion of the drum can cause it to wobble a lot. Also, for the same reason, it is advised to place the machine a few inches away from the surrounding walls.
  • Do not overload the washing drum than its specified capacity.
  • It is advised to always wash clothes in small loads with less detergent. The use of excess detergent would not only damage the clothes and the water pipes, but heavy loads can cause leakage, which in turn can also cause severe damage to the motor of the washing machine.
  • In a fully automatic machine, there will be an in-built dryer. It is important to remove the lint from the dryer after every cycle. The lint can clog the filter and restrict the airflow, which can lead to overheating of the dryer. This overheating can shrink delicate clothes.
  • One of the most important steps is to thoroughly understand the settings and operating functions of the washing machine. The lack of proper understanding of the appliance can lead to energy and time wastage along with the damage caused to the clothes and the machine.

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