Home appliances exist to make life more convenient, so we often take them for granted. But do you ever wonder what’s really going on inside your coffee maker or your refrigerator? In this presentation on how home appliances work ? we crack open common household devices and take a look at how they function.
The refrigerator is one of those miracles of modern living that totally changes life. Prior to refrigeration, the only way to preserve meat was to salt it, and iced beverages in the summer were a real luxury.
Without refrigeration, we'd be throwing out our leftovers instead of saving them for another meal
There are five basic parts to any refrigerator (or air-conditioning system):
Heat-exchanging pipes - serpentine or coiled set of pipes outside the unit
Heat-exchanging pipes - serpentine or coiled set of pipes inside the unit
Refrigerant - liquid that evaporates inside the refrigerator to create the cold temperatures Many industrial installations use pure ammonia as the refrigerant. Pure ammonia evaporates at -27 degrees Fahrenheit (-32 degrees Celsius).
The basic mechanism of a refrigerator works like this:
The compressor compresses the refrigerant gas. This raises the refrigerant's pressure and temperature (orange), so the heat-exchanging coils outside the refrigerator allow the refrigerant to dissipate the heat of pressurization.
As it cools, the refrigerant condenses into liquid form (purple) and flows through the expansion valve.
When it flows through the expansion valve, the liquid refrigerant is allowed to move from a high-pressure zone to a low-pressure zone, so it expands and evaporates (light blue). In evaporating, it absorbs heat, making it cold.
The coils inside the refrigerator allow the refrigerant to absorb heat, making the inside of the refrigerator cold. The cycle then repeats.
"instant cold packs" that looks like a plastic bag filled with liquid. You hit it, shake it up and it gets extremely cold. The liquid inside the cold pack is water . In the water is another plastic bag or tube containing ammonium-nitrate fertilizer . When you hit the cold pack, it breaks the tube so that the water mixes with the fertilizer. This mixture creates an endothermic reaction -- it absorbs heat. The temperature of the solution falls to about 35 F for 10 to 15 minutes.
When the temperature outside begins to climb, many people seek the cool comfort of indoor air conditioning. Like water towers and power lines, air conditioners are one of those things that we see every day but seldom pay much attention to.
An air conditioner is basically a refrigerator without the insulated box. It uses the evaporation of a refrigerant , like Freon, to provide cooling. The mechanics of the Freon evaporation cycle are the same in a refrigerator as in an air conditioner.
COFFEE MAKER We will look inside a typical drip coffee maker so you can understand exactly what is happening when you make coffee .
A modern drip coffee maker is a surprisingly simple device. Manufacturers have had 25 years to hone their designs, so these coffee makers are pretty straightforward once you open them up. The warming plate Where the hot water drips into the ground coffee
If you take off the top of the coffee maker, you find three things:
1) There is a little bucket that holds the water when you pour it into the pot at the start of the coffee-making cycle (on the right in the picture above). There is a hole in the bottom of the bucket, and its role will become obvious in a moment.
2) There is a black tube that carries the hot water to the drip area.
3) There is the drip area (on the left-hand side of this picture). Water arrives here from the black hot-water tube and simply falls through the holes into the coffee grounds.
INSIDE THE COFFEE MAKER The view inside the bottom of the coffee maker The depression on the right-hand side of this figure is the bottom of the bucket. The orange tube in the center is the hot-water tube (it connects to the black tube that we saw in the previous picture). The other orange tube picks up cold water from the hole in the bucket
You can see the connection between the heating element and the warming plate. The heating element presses directly against the underside of the warming plate, and a white, heat-conductive grease makes sure that the heat transfers efficiently to the plate .
The coffee maker heating element and warming plate
The coffee maker's switch turns power to the heating element on and off. To keep the heating element from overheating, there are three solid-state temperature sensors, as shown here: The coffee maker heating element by itself
Simple solid-state temperature sensors cut off the current when things get too hot.
You can see that a coffee maker is about as simple as an appliance can get. Here's how it works:
When you pour in cold water, it flows from the bucket through the hole in the bottom of the bucket and into the orange tube.
The water then flows through the one-way valve into the aluminum tube in the heating element, and then partially up through the black tube. This all happens naturally because of gravity.
When you turn on the switch, the heating element starts heating the aluminum tube, and eventually the water in the tube boils.
When the water boils, the bubbles rise up in the black tube. What happens next is exactly what happens in a typical aquarium filter: The tube is small enough and the bubbles are big enough that a column of water can ride upward on top of the bubble.
The water flows out the end of the black tube to drip into the coffee.
It has probably washed your clothes hundreds of times, but have you ever wondered what's inside that trusty washing machine?
We'll start by explaining how the washing machine cleans clothes, then we'll take a look at how the machine is put together. We'll look at the plumbing, the drive mechanism and the controls.
INSIDE A WASHING MACHINE If we take a look under the washing machine, you'll see what makes it so heavy Yes, that is in fact a block of concrete in the picture above. The concrete is there to balance the equally heavy electric motor, which drives a very heavy gearbox that is attached to the steel inner tub. There are lots of heavy components in a washing machine.
The washing machine has two steel tubs. The inner tub is the one that holds the clothes. It has an agitator in the middle of it, and the sides are perforated with holes so that when the tub spins, the water can leave.
The outer tub , which seals in all the water, is bolted to the body of the washer. Because the inner tub vibrates and shakes during the wash cycle, it has to be mounted in a way that lets it move around without banging into other parts of the machine.
The inner tub is attached to the gearbox , which is attached to the black metal frame you see in the picture above. This frame holds the motor, gearbox and the concrete weight.
The picture above shows just the black metal frame, without the tub or gearbox. The cable that you see on the left side of the picture is the other end of the same cable that you see on the right side. There are a total of three pulleys , so that if one side of the frame moves up, the other side moves down. This system supports the weight of the heavy components, letting them move in such a way as not to shake the entire machine .
Cable-and-pulley support system
Vibration-damping system A laundry machine has a damping system that uses friction to absorb some of the force from the vibrations.
The plumbing on the washing machine has several jobs:
It fills the washing machine with the correct temperature of water.
It recirculates the wash water from the bottom of the wash tub back to the top (during the wash cycle).
It pumps water out the drain (during the spin cycle).
The washing machine has hookups for two water lines on the back, one for hot water and one for cold. These lines are hooked up to the body of a solenoid valve .
The image above shows the back and front of the solenoid valve. You can see that there are two valves , but they feed into a single hose . So depending on the temperature selected, either the hot valve, the cold valve or both valves will open.
The drive mechanism on a washing machine has two jobs:
To agitate the clothes, moving them back and forth inside the wash tub.
To spin the entire wash tub, forcing the water out.
There is a really cool GEARBOX that handles these two jobs, and it uses the same trick as the pump does. If the motor spins in one direction, the gearbox agitates; if it spins the other way, the gearbox goes into spin cycle.
Controls Cycle switch The controls for this machine were designed before microcontrollers were being used in appliances. In fact, there is not a single resistor or capacitor in the whole machine. Inside the cycle switch
CONTROLS Speed and temperature control switches Water level control switch
When the science of electricity really got going in the mid 1800s, inventors everywhere were clamoring to devise a practical, affordable electrical home lighting device. Englishman Sir Joseph Swan and American Thomas Edison both got it right around the same time (in 1878 and 1879, respectively), and within 25 years, millions of people around the world had installed electrical lighting in their homes. The easy-to-use technology was such an improvement over the old ways that the world never looked back.
Light is a form of energy that can be released by an atom. It is made up of many small particle-like packets that have energy and momentum but no mass. These particles, called light photons , are the most basic units of light.
Light bulbs have a very simple structure. At the base, they have two metal contacts, which connect to the ends of an electrical circuit. The metal contacts are attached to two stiff wires, which are attached to a thin metal filament. The filament sits in the middle of the bulb, held up by a glass mount. The wires and the filament are housed in a glass bulb, which is filled with an inert gas, such as argon.
When the bulb is hooked up to a power supply, an electric current flows from one contact to the other, through the wires and the filament. Electric current in a solid conductor is the mass movement of free electrons (electrons that are not tightly bound to an atom) from a negatively charged area to a positively charged area.
As the electrons zip along through the filament, they are constantly bumping into the atoms that make up the filament. The energy of each impact vibrates an atom -- in other words, the current heats the atoms up. A thinner conductor heats up more easily than a thicker conductor because it is more resistant to the movement of electrons.
Bound electrons in the vibrating atoms may be boosted temporarily to a higher energy level. When they fall back to their normal levels, the electrons release the extra energy in the form of photons. Metal atoms release mostly infrared light photons, which are invisible to the human eye. But if they are heated to a high enough level -- around 4,000 degrees Fahrenheit (2,200 degrees C) in the case of a light bulb -- they will emit a good deal of visible light .
The filament in a light bulb is made of a long, incredibly thin length of tungsten metal. In a typical 60-watt bulb, the tungsten filament is about 6.5 feet (2 meters) long but only one-hundredth of an inch thick. The tungsten is arranged in a double coil in order to fit it all in a small space. That is, the filament is wound up to make one coil, and then this coil is wound to make a larger coil. In a 60-watt bulb, the coil is less than an inch long.
Tungsten is used in nearly all incandescent light bulbs because it is an ideal filament material. In the next section, we'll find out why this is, and we'll examine the role of the glass bulb and inert gas.
In this article, we'll find out how fluorescent lamps emit such a bright glow without getting scalding hot like an ordinary light bulb. We'll also find out why fluorescent lamps are more efficient than incandescent lighting, and see how this technology is used in other sorts of lamps .
The central element in a fluorescent lamp is a sealed glass tube . The tube contains a small bit of mercury and an inert gas, typically argon , kept under very low pressure. The tube also contains a phosphor powder , coated along the inside of the glass. The tube has two electrodes , one at each end, which are wired to an electrical circuit. The electrical circuit, which we'll examine later, is hooked up to an alternating current (AC) supply
To send a current through gas in a tube, then, a fluorescent light needs to have two things:
Free electrons and ions
A difference in charge between the two ends of the tube (a voltage)
Generally, there are few ions and free electrons in a gas, because all of the atoms naturally maintain a neutral charge. Consequently, it is difficult to conduct an electrical current through most gases. When you turn on a fluorescent lamp, the first thing it needs to do is introduce many new free electrons from both electrodes.
Start it Up The classic fluorescent lamp design, which has fallen mostly by the wayside, used a special starter switch mechanism to light up the tube. You can see how this system works in the diagram below. When the lamp first turns on, the path of least resistance is through the bypass circuit, and across the starter switch . In this circuit, the current passes through the electrodes on both ends of the tube. These electrodes are simple filaments , like you would find in an incandescent light bulb. When the current runs through the bypass circuit, electricity heats up the filaments. This boils off electrons from the metal surface, sending them into the gas tube, ionizing the gas.
In a gas discharge, such as a fluorescent lamp, current causes resistance to decrease. This is because as more electrons and ions flow through a particular area, they bump into more atoms, which frees up electrons, creating more charged particles. In this way, current will climb on its own in a gas discharge, as long as there is adequate voltage (and household AC current has a lot of voltage). If the current in a fluorescent light isn't controlled, it can blow out the various electrical components
A ballast can only slow down changes in current -- it can't stop them. But the alternating current powering a fluorescent light is constantly reversing itself, so the ballast only has to inhibit increasing current in a particular direction for a short amount of time.
Rapid start and starter switch fluorescent bulbs have two pins that slide against two contact points in an electrical circuit.
The ballast, starter switch and fluorescent bulb are all wired together in a simple circuit .