Nanoscience is the study of molecules and molecular structures, called nanostructures, having one or more dimensions less than about 100 nanometers. One nanometer is one-billionth of a meter: 1 nm = 10-9 m. To grasp this level of smallness, a stack of 10 hydrogen atoms would have a height of 1 nm, while a human hair has a diameter of about 50,000 nm. Nanotechnology is the engineering of nanostructures into useful products. At the nanotechnology scale, behavior may differ from our macroscopic expectations. For example, the averaging used to assign property values at a point in the continuum model may no longer apply owing to the interactions among the atoms under consideration. Also, at these scales, the nature of physical phenomena such as current flow may depend explicitly on the physical size of devices. After many years of fruitful research, nanotechnology is now poised to provide new products with a broad range of uses, including implantable chemotherapy devices, biosensors for glucose detection in diabetics, novel electronic devices, new energy conversion technologies, and smart materials as, for example, fabrics that allow water vapor to escape while keeping liquid water out.
Nanoscale Machines on the Move
Engineers working in the field of nanotechnology, the engineering of molecular-sized devices, look forward to the time when practical nanoscale machines can be fabricated that are capable of movement, sensing and responding to stimuli such as light and sound, delivering medication within the body, performing computations, and numerous other functions that promote human well-being. For inspiration, engineers study biological nanoscale machines in living things that perform functions such as creating and repairing cells, circulating oxygen, and digesting food. These studies have yielded positive results. Molecules mimicking the function of mechanical devices have been fabricated, including gears, rotors, ratchets, brakes, switches, and abacus-like structures. A particular success is the development of molecular motors that convert light to rotary or linear motion. According to researchers, Although devices produced thus far are rudimentary, they do demonstrate the feasibility of constructing nanomachines.
Fig. Molecular Motor
Drafting occurs when two or more moving vehicles or individuals align closely to reduce the overall effect of drag. Drafting is seen in competitive events such as auto racing, bicycle racing, speed-skating, and running.
Studies show that air flow over a single vehicle or individual in motion is characterized by a high-pressure region in front and a low-pressure region behind. The difference between these pressures creates a force, called drag, impeding motion. During drafting, as seen in the sketch below, a second vehicle or individual is closely aligned with another, and air flows over the pair nearly as if they were a single entity, thereby altering the pressure between them and reducing the drag each experiences. While race-car drivers use drafting to increase speed, non–motor sport competitors usually aim to reduce demands on their bodies while maintaining the same speed.
The energy required by animals to sustain life is derived from oxidation of ingested food. We often speak of food being burned in the body. This is an appropriate expression because experiments show that when food is burned with oxygen, approximately the same energy is released as when the food is oxidized in the body. Such an experimental device is the well-insulated, constant-volume calorimeter shown in Fig. below.
A carefully weighed food sample is placed in the chamber of the calorimeter together with oxygen (O2). The entire chamber is submerged in the calorimeter’s water bath. The chamber contents are then electrically ignited, fully oxidizing the food sample. The energy released during the reaction within the chamber results in an increase in calorimeter temperature. Using the measured temperature rise, the energy released can be calculated from an energy balance for the calorimeter as the system. This is reported as the calorie value of the food sample, usually in terms of kilo-calorie (kcal), which is the “Calorie” seen on food labels.
All activities in nature involve some interaction between energy and matter; thus it is hard to imagine an area that does not relate to thermal‑fluid sciences in some manner. Therefore, developing a good understanding of basic principles of thermal‑fluid sciences has long been an essential part of engineering education.
Thermal‑fluid sciences are commonly encountered in many engineering systems and other aspects of life, and one does not need to go very far to see some application areas of them. In fact, one does not need to go anywhere. The heart is constantly pumping blood to all parts of the human body, various energy conversions occur in trillions of body cells, and the body heat generated is constantly rejected to the environment. Human comfort is closely tied to the rate of this metabolic heat rejection. We try to control this heat transfer rate by adjusting our clothing to the environmental conditions. Also, any defect in the heart and the circulatory system is a major cause for alarm.
Other applications of thermal‑fluid sciences are right where one lives. An ordinary house is, in some respects, an exhibition hall filled with wonders of thermal‑fluid sciences. Many ordinary household utensils and appliances are designed, in whole or in part, by using the principles of thermal‑fluid sciences. Some examples include the electric or gas range, heating and air‑conditioning systems, refrigerator, humidifier, pressure cooker, water heater, shower, iron, plumbing and sprinkling systems, and even the computer, TV, and DVD player.
Large scale applications
On a larger scale, thermal‑fluid sciences play a major part in the design and analysis of automotive engines, rockets, jet engines, and conventional or nuclear power plants, solar collectors, the transportation of water, crude oil, and natural gas, the water distribution systems in cities, and the design of vehicles from ordinary cars to airplanes (Fig. 1–2). The energy‑efficient home that you may be living in, for example, is designed on the basis of minimizing heat loss in winter and heat gain in summer. The size, location, and the power input of the fan of your computer is also selected after a thermodynamic, heat transfer, and fluid flow analysis of the computer.
- Fundamentals of Thermal-Fluid Sciences by Yunus A. Cengel
Ball and Detent A simple mechanical arrangement used to hold a moving part in a temporarily fixed position relative to another part. The ball slides within a bored cylinder, against the pressure of a spring, which pushes the ball against the detent, a hole of smaller diameter than the ball. When the hole is in line with the cylinder, the ball falls partially into the hole under spring pressure, holding the parts at that position. Additional force will push the ball back into its cylinder, compressing the spring, and allowing the parts to move.
Bearing The part of a machine within which a rotating or sliding shaft is held. In some bearing types, balls or rollers are used between the bearing surfaces to reduce rolling friction.
Bell crank A pivoting double lever used to change the direction of applied motion.
Boss A cylindrical projection, as on a casting or a forging. Usually provides a contact surface around a hole.
Broach To finish the inside of a hole to a shape other than round, as in a keyway. The tool for the process, which has serrated edges and is pushed or pulled through the hole to produce the required shape.
Burnish To smooth or polish by a rolling or sliding tool under pressure.
Bushing A smooth walled bearing (AKA a plain bearing). Also, a tool guide in a jig or fixture.
Cam A mechanical device consisting of an eccentric or multiply curved wheel mounted on a rotating shaft, used to produce variable or reciprocating motion in another engaged or contacted part (cam follower). Also, Camshaft.
Casting Any object made by pouring molten metal into a mold.
Chamfer A flat surface made by cutting off the edge or corner of an object (bevel).
Clevis A U-shaped piece with holes into which a link is inserted and through which a pin or bolt is run. It is used as a fastening device which allows rotational motion.
Collar A cylindrical feature on a part fitted on a shaft used to prevent sliding (axial) movement.
Collet A cone-shaped sleeve used for holding circular or rodlike pieces in a lathe or other machine.
Core To form the hollow part of a casting, using a solid form placed in the mold The solid form used in the coring process, often made of wood, sand, or metal.
Counterbore A cylindrical flat-bottomed hole, which enlarges the diameter of an existing pilot hole. The process used to create that feature.
Countersink A conical depression added to an existing hole to accommodate and the conic head of a fastener recessing it below the surface of a face.
Coupling A device used to connect two shafts together at their ends for the purpose of transmitting power. May be used to account for minor misalignment or for mitigating shock loads.
Die One of a pair of hardened metal plates or impressing or forming desired shape. Also, a tool for cutting external threads.
Face To machine a flat surface perpendicular to the axis of rotation of a piece.
Fillet A rounded surface filling the internal angle between two intersection surfaces. Also Rounds
Fit The class of contact between two machined surfaces, based upon their respective specified size tolerances (clearance, transitional, interference)
Fixture A device used to hold a workpiece while manufacturing operations are performed upon that workpiece.
Flange (see bushing example) A projecting rim or edge for fastening, stiffening or positioning.
Gage A device used for determining the accuracy of specified manufactured parts by direct comparison..
Gage blocks Precision machined steel blocks having two flat, parallel surfaces whose separation distance is fabricated to a guaranteed accuracy of a few millionths of an inch;
Gear Hobbing A special form of manufacturing that cuts gear tooth geometries. It is the major industrial process for cutting involute form spur gears of.
Geneva Cam A device to turn constant rotational motion into intermittent rotational motion.
Gusset (plate) A triangular metal piece used to strengthen a joint.
Hasp A metal fastener with a slotted, hinged part that fits over a loop and is secured by a pin, bolt, or padlock.
Idler A mechanism used to regulate the tension in belt or chain. Or, a gear used between a driver and follower gear to maintain the direction of rotation.
Jig A special device used to guide a cutting tool (drill jig) or to hold material in the correct position for cutting or fitting together (as in welding or brazing)
Journal The part of a shaft that rotates within a bearing
Kerf A channel or groove cut by a saw or other tool.
Key (Woodruff key shown) A small block or wedge inserted between a shaft and hub to prevent circumferential movement.
Keyseat A slot or groove cut in a shaft to fit a key. Key rests in a Keyseat.
Keyway A slot cut into a hub to fit a key. A key slide in a keyway. See Broach.
Knurl To roughen a turned surface, as in a handle or a knob.
Lug Projection on (typically) a cast or forged part to provide support or allow mounting or the attachment of another component.
Neck To cut a groove around a shaft, usually toward the end or at a change in diameter. A portion of reduced diameter between the ends of a shaft.
Pad A rectangular or irregular projection, as on a casting or a forging. Usually provides a contact surface around a set of holes.
Pawl A device used to prevent a toothed wheel (ratchet) from rotating backwards, or a device that stops, locks, or releases a mechanism.
Pillow Block A bearing housing which typically mounts to a single planar face. May be split or unsplit to accommodate insertion /removal of the bearing.
Pinion A plain gear, often the smallest gear in a gearset, often the driving gear. May be used in conjunction with a gear rack
Planetary Gears A gearset characterized by one or more planet gear(s) rotating around a sun gear. Epicyclic gearing systems include an outer ring gear (known as an annulus) with the planetary system.
Ratchet A mechanical device used to permit motion in one direction only.
Relief A groove or cut on a part used to facilitate machining.
Retaining Ring A tool steel ring used in conjunction with a shaft groove or internal groove to located or control position of a component.
Rocker Arm A pivoted arm-like lever used to transfer the application direction of a linear force.
Scotch Yoke Mechanism used to convert rotational motion to linear motion.
Sheave A grooved wheel used to accommodate a belt for the transmission of power. Sometimes referred to as a pulley sheave.
Shim A thin strip of metal inserted between two surfaces to adjust for fit.
Shoulder A plane surface on a shaft, normal to the axis, produced by a change in diameter.
Spline A cylindrical pattern of keyways. May be external (L) or internal (R)
Spotface a round machine surface around a hole on a casting or forging, usually to provide a contact surface for a fastener or other mating component.
Standoffs A mounting designed to position objects a predetermined distance above or away from the surface upon which they are mounted.
Tap To cut internal machine threads in a hole, the tool used to create that feature.
Undercut A cut having inward sloping sides, to cut leaving an overhanging edge
Yoke A clamp or vise that holds a machine part in place or controls its movement or that holds two such parts together. A crosshead of relatively thick cross section, that secures two or more components so that they move together.
Turbo selection isn’t what it used to be. Once upon a time, self-proclaimed engineers were content to build an engine that produced massive power at high rpm, but drove like a dog at anything but. However, once hot-rodders figured out that anybody could bolt a junk turbo to any engine and make power, focus shifted from top-end force to overall driveability. With a little bit of extra work, anyone with a seventh-grade education can one-up the experts of yore and pick the perfect turbo for any application.
- Assess your budget. Building a turbocharged engine isn’t about just bolting a giant huffer to the exhaust manifolds and calling it a day. The turbo might only cost you $500, but a good install doesn’t stop there. Turbochargers make power as a function of the engine’s original horsepower and torque, so building an engine to make more power before bolting the turbo onto it will likely yield benefits that compensating with huge boost won’t.
- Determine the required airflow in cubic feet of air per minute. Boost doesn’t make power, it just shoves more air through your engine. Because engines typically operate an air/fuel ratio of about 14 parts air to 1 part fuel, and because gasoline contains a certain amount of energy (about 114,000 British Thermal Units per gallon), you can make a direct correlation between airflow in cfm and horsepower. That ratio is about 150 cfm to 100 horsepower. As an example, let’s put together a 900 horsepower Chevrolet 350: For this application, you’ll need about 1,350 cfm of air.
- Calculate your engine’s non-turbo airflow in cfm. There are three ways to do this: You can either use an online cfm-to-horsepower calculator that takes engine displacement, efficiency and rpm into account, and you can extrapolate from the engine’s stock horsepower; or you can take the engine to a dyno room and check it. For our example engine, we’ll say that (in non-turbo form) it produces 300 horsepower at 5,500 rpm, at an 80 percent volumetric efficiency. The online calculator gives us 446 cfm airflow, and using the 150-cfm/100-horsepower ratio gives us 450 cfm.
- Divide your required airflow by your engine’s stock airflow to determine the required boost pressure ratio (the ratio of boost pressure to atmospheric pressure, which is about 14.7 psi). For the example engine, you arrive at a pressure ratio of exactly 3.00. Here’s a bit of trickery, though: Dividing desired horsepower by non-turbo horsepower will give you the same pressure ratio figure as going through this long-form cfm-to-horsepower-to-pressure ratio calculation. You only went this far to understand the factors that you’ll be dealing with in turbo selection from here on.
- Look through a manufacturer’s selection of “turbo maps.” A turbo map is a graph that indexes airflow to pressure ratio, and gives a visual representation of turbo efficiency at a given pressure ratio and cfm. You’ll see pressure ratio on the vertical axis and the airflow on the horizontal axis. A compressor map looks something like an elongated bulls-eye: the center of that bull’s eye is the compressor’s maximum efficiency range, which is where it makes boost without producing excess heat.
- Compare your engine’s required pressure ratio and airflow in cfm to various compressor maps and find one that puts your target airflow/pressure point in the center-to-upper-right-hand corner of the compressor’s maximum efficiency range (the center of the bulls-eye). Many times you’ll find airflow expressed in the metric “m3/s,” or meters cubed per second. To convert cfm to m3/s, multiply cfm by 0.00047. For our example engine, we’ll need to find a turbo that supplies full efficiency at a 3.00 pressure ratio at 0.6345 m3/s flow. Again, find a compressor where that point falls in the center-to-upper-right-hand corner of the turbo’s maximum efficiency range.
- Repeat Steps 2 through 7, using the engine’s peak torque rpm. The Chevy 350 in our example makes its peak torque at 2,000 rpm, where (according to the stock dyno graph) it makes 140 horsepower. Apply the 150-cfm/100-horsepower rule and you’ll find that this engine uses 210 cfm at that rpm. Multiply that airflow by the required pressure ratio (3.00) and you have your low-end boost response requirement. In addition to producing a 3.00 pressure ratio at 1,350 cfm (0.6345 m3/s), it should produce that same 3.00 PR at 630 cfm (0.2961).
- Search and search some more until you find a turbo that’s completely spooled up (producing a 3.00 PR, in this case) at your torque-peak airflow and maintains that PR through the engine’s horsepower-peak airflow. You’ll often find that, for larger engines like our 350, such turbos do not exist. No turbo out there will provide those PR and flow numbers over such a wide spectrum of airflow.
- Re-calculate for a multiple-turbo setup. If you can’t find a turbo to fit, divide your airflow figures by the number of turbos you want to use. Two turbos flow twice as much air as one, and smaller turbos have a wider efficiency range relative to absolute airflow than smaller ones. So, for our example 350, divide 1,350 cfm (0.6345 m3/s) and 630 cfm (0.2961) by two; now you need a pair of turbos that will provide a 3.00 PR at 675 cfm (0.3172 m3/s) to 315 cfm (0.1480 m3/s). That’s a spread of only 360 cfm for the little twin-turbo setup, versus 720 cfm for the single, big turbo setup — a much more achievable goal for any compressor.
- If you got all disappointed when you got to Step 7 and found out that you’d have to do everything over again, then find a turbo that fit both requirements, then don’t feel bad. Some of the biggest names in the business don’t bother calculating the airflow spread from peak torque to peak horsepower. However, this little oversight just isn’t cool for modern turbo-engine builders. The modern turbo engineer understands that quality turbo selection is about performance throughout the engine’s entire operating range, not just at peak horsepower. Turbo lag is so 1980s.
- When you do turbocharge your vehicle, make sure to support it with other modifications, as the turbo will probably make other parts of your car break.
- It would be a good idea to install forged pistons, increase injector capacity, a higher flowing fuel pump, a new exhaust system, head studs, and forged connecting rods.
- Installing a turbocharger yourself, and making it live, is a very difficult and in depth project. If you’re a beginning mechanic, it is not recommended that you try this unless you have someone experienced helping you.
- The increased power of your vehicle can also make other parts of your car break. It could snap your axles, bend your drive shaft, break the rear end in a RWD car, and even bend your car from the increased torque. Be sure to upgrade the other parts of your car at the same time as you install the turbocharger, or else you could end up with a powerful car sitting in the driveway because there’s no way to put the power down.