• The crankshaft , sometimes casually abbreviated to crank, is the part of an engine which translates reciprocating linearpiston motion into rotation. To convert the reciprocating motion into rotation, the crankshaft has "crank throws" or " crankpins", additional bearing surfaces whose axis is offset from that of the crank, to which the "big ends" of the connecting rodsfrom each cylinder attach. It typically connects to a flywheel , to reduce the pulsation characteristic of the four-stroke cycle, and sometimes a torsional orvibrational damper at the opposite end, to reduce the torsion vibrations often caused along the length of the crankshaft by the cylinders farthest from the output end acting on the torsional elasticity of the metal. • http://enggseminartopics.blogspot.com/search/label/Mechanical • http://www.brighthub.com/engineering/mechanical/articles/50414.aspx Chapter 2 Heating Systems Heating systems carry heat from the point of production to the place of use. Heating-system designs are complex with many variations. They are classified by the medium used to carry the heat from the source to the point of use. Steam, hot-water, and for ced-air syst ems are the most common. Hot -wa ter hea tin g is used ext ensive ly. Forced-air hea tin g is used in most semipermanent constructions and in most barracks. Appendix B provides plumbing plans to include a list of heating symbols used on heating-system plans. HOT-WATER HEATING SYSTEMS 2-1. A hot- water heat ing syst em is made up of a heating unit, pipes, and radiators or connectors. Wat er is hea ted at a centra l source, cir cul ated through the system, and returned to the heating unit. Usually a pump (rather than a gravity system) is used to keep the water circu lat ing. The two types of hot-water systems are the one-pipe and the two-pipe. PLANS 2-2. A hot- water heating sys tem may have a separate plan or may be combined with the hot- and cold-water and sewer lines on the plumbing plan. A hot-water-system plan shows the layout of unit s, pipe s, ac ce ssories , an d connections. Figure 2-1 shows a typical system. This figure also shows the location of the boiler, circulating pump, and compression tank. A one- pipe system is shown; however, the hot water will fl ow in two directions (or loops) , each loop containing two radiators. The second radiator in each loop is larger than the first. (Appendix Bprovides heating symbol s that are used on architect's plans.) Figure 2-1. Hot-Water (One-Pipe) Heating-System Plan
• The crankshaft, sometimes casually abbreviated to crank , is the part of an engine which translates reciprocating linear
piston motion into rotation. To convert the reciprocating motion into rotation, the crankshaft has "crank throws" or "crankpins",additional bearing surfaces whose axis is offset from that of the crank, to which the "big ends" of the connecting rods fromeach cylinder attach.
It typically connects to a flywheel, to reduce the pulsation characteristic of the four-stroke cycle, and sometimes a torsional or vibrational damper at the opposite end, to reduce the torsion vibrations often caused along the length of the crankshaft by thecylinders farthest from the output end acting on the torsional elasticity of the metal.
Heating systems carry heat from the point of production to the place of use. Heating-system designs are complex with manyvariations. They are classified by the medium used to carry the heat from the source to the point of use. Steam, hot-water, andforced-air systems are the most common. Hot-water heating is used extensively. Forced-air heating is used in most
semipermanent constructions and in most barracks. Appendix B provides plumbing plans to include a list of heating symbols usedon heating-system plans.
HOT-WATER HEATING SYSTEMS 2-1.A hot-water heating system is made up of aheating unit, pipes, and radiators or connectors.Water is heated at a central source, circulatedthrough the system, and returned to the heatingunit. Usually a pump (rather than a gravity system)is used to keep the water circulating. The twotypes of hot-water systems are the one-pipe andthe two-pipe.
PLANS 2-2. A hot-water heating systemmay have a separate plan or may be combined
with the hot- and cold-water and sewer lines on theplumbing plan. A hot-water-system plan shows thelayout of units, pipes, accessories, andconnections. Figure 2-1 shows a typical system.This figure also shows the location of the boiler,circulating pump, and compression tank. A one-pipe system is shown; however, the hot water willflow in two directions (or loops), each loopcontaining two radiators. The second radiator ineach loop is larger than the first. (Appendix B provides heating symbols that are used onarchitect's plans.)
Figure 2-1. Hot-Water (One-Pipe) Heating-System Plan
2-3. A one-pipe system is thesimplest type of hot-water system and is adequate for very small installations(Figure 2-2). Hot water circulates through one set of pipes through each radiator.As a result, the water reaching the last radiator is
cooler than the water in thefirst radiator. To obtain thesame amount of heat from allthe radiators, each radiator must be larger than the one
before.
Figure 2-2. One-Pipe Hot-Water Heating System
TWO-PIPE SYSTEM
2-4. In a two-pipe system thehot water goes from theheating unit to each radiator by way of the main,connected by Ts and elbows(Figure 2-3). The cooler water leaving the radiatorsreturns to the heater throughseparate return piping.
Figure 2-3. Two-Pipe Hot-Water Heating System
STEAM-HEATING SYSTEMS 2-5. A steam-heating system consists of a boiler that heats the water, producing thesteam; radiators in which the steam turns back to water (condenses), giving heat; and connecting pipes that carry the steam fromthe boiler to the radiators and returns the water to the boiler. This system includes either an air valve or other means of removingair from the system. The two types of steam-heating systems are the one-pipe and the two-pipe, which are classified as—
• High-pressure. A high-pressure system operates above 15-psi gauge.
• Low-pressure. A low-pressure system operates from 0- to 15-psi gauge.
• Vapor. A vapor system operates under both low-pressure and vacuum conditions.
• Vacuum. A vacuum system operates under low-pressure and vacuum conditions with a vacuum pump.
2-6. The one-pipe system uses asingle main and riser to carrysteam to radiators or other heatingunits and to return condensedsteam (condensate) to the unit.This system is best for smallinstallations where low cost andeasy operation are important.Each radiator or other heating unitis equipped with an air valve,controlled by heat (thermostatic),as shown in Figure 2-4. Larger air valves are installed at the end of steam mains. These valves
should be the vacuum-type with asmall check valve to keep air fromflowing back into the system whenheat input is reduced. Theconnection to the unit may haveshutoff (angle) valves. Since therestricted opening causes arepeated banging sound (water hammer), these valves cannot bepartly closed for heat input control.
Figure 2-4. Radiator Connections for a One-Pipe SteamSystem
2-7. The two-pipe system hastwo sets of mains and risers: oneset distributes steam to theheating unit and the other returns condensate to the boiler.Figure 2-5 shows a two-pipesteam system. This system
operates under high- or low-pressure, vapor, or vacuumconditions, and with either upflowor downflow distribution. Thissystem allows adjustment of steam flow to individual heatingunits. It uses smaller pipes thanthe one-pipe system. A two-pipeupflow vapor system, which canoperate over a range of pressures, is shown in Figure 2-6.
Figure 2-5. Two-Pipe Steam Heating System (Upflowor Downflow)
Figure 2-6. Two-Pipe Upflow Vapor System
FORCED-AIR HEATING SYSTEMS
2-8. A forced-air upflow heatingsystem distributes heated air through a duct system (Figure 2-7). The air is usually heated by agas-fired or oil-fired furnace. Thissystem consists of a furnace, abonnet, warm-air supply ductsand registers, return cold-air registers and ducts, and a fan or blower forced-air circulation.Figure 2-8 shows a downflowfurnace with a crawl space ductsystem and a crawl spaceplenum system.
2-9. In a forced-air heating-system plan, solid linesindicate warm-air ducts; cold-air return ducts are indicatedby dashed lines (Figure 2-9).
(Appendix B gives the mostcommon heating symbols usedon plans.) All duct sizes givethe horizontal or widthdimensions first. (Depth, thesecond dimension, is notshown on a plan drawing.) Usethe plan to determine thelocation and sizes of warm-air registers needed. When ceilingregisters (diffusers) are used,the neck dimensions are given.When wall or baseboardregisters are used, facedimensions are given. Look in
the notes on a plan for theheight of the wall registersabove the finished floor line.
Return (cold-air) registers are shown recessed into the wall. The face dimensions of the return registers arenoted adjacent to the register symbol.
Figure 2-9. Partial View of a Forced-Air Heating-System Plan
INSTALLATION AND OPERATION 2-10. The bonnet above the heat plant (furnace) collects the heated air for distribution to various rooms. The warm air is distributed from the bonnet through rectangular-shaped supply ducts and registers
(warm-air) into the rooms. The warm-air registers are installed in the ceiling. The air, after circulating through the rooms and losingheat, is returned to the furnace by the return (cold-air) registers and ducts. The return registers are placed in the wall, just belowthe opening; the return air ducts are installed in the crawl space. The warm-air distribution by branch ducts is the same as theexamples shown in Figure 2-9.
2-11. Forced-air systems are laid out so that the warm air from the registers is directed at the cold exterior walls. In somesystems, the warm-air registers are located in exterior walls below windows. The registers for cold-air return are normally installedat baseboard height. Cold air moves to the floor where it is collected by the cold-air registers and returned through ducts to thefurnace for reheating and recirculation. Furnace location is important for proper forced-air heating. This design equalizes ductlengths by centrally locating the furnace room (Figure 2-9) .
Comfort Zone Design 2-12. The comfort zone is a horizontal area between the top of the average person's head andknees. Air blowing from the supply is uncomfortable. To avoid this, registers are placed either above or below the comfort zone-high on the wall or in the baseboard.
Duct Connections 2-13. The main trunkshould run above a central corridor to equalizebranch duct lengths to individual rooms. Figure 2-10 shows common rectangular duct connections.(Figure 2-10. Rectangular Duct Connections)
2-14. Figure 2-10 also shows atypical warm-air bonnet with twomain supply ducts. It shows twopossible elbow connections andtwo duct Ts. The split T is used to
direct the air flow on the warmside of the system. The straight Tmay be used on the cold-air return. Trunk takeoffs are shown.In the double-branch connection,less air is present in the mainduct after some of it has beenchanneled into branch ducts. Thesize of the main duct can then bereduced on the far side of theconnection point. The single-branch connection shows twomethods of reduction. First,reduction in the duct is made atthe connection. Secondly, a
reduction in duct depth is made on the far side of the connection. In both double- and single-branch takeoffs, thebranch connections form a natural air scoop to encourage airflow in the desired direction.
2-15. A boot is one method tochange the shape of a ductwithout changing the equivalentcross section area or constricting the air flow. A boot
fitting from branch to stack, withthe stack terminating at a warm-air register, is shown in Figure 2-11. Table 2-1 gives theequivalent lengths of gravityduct fittings.
Figure 2-11. Duck (Boot) Fittings
Table 2-1. Equivalent Lengths of Gravity Duct Fittings
Warm-Air Boot Name of CombinationEquivalent Number
of 90-Degree Elbows
A45-degree angle bootand 45-degree elbow
1
B 90-degree angle boot 1
C Universal bootand 90-degree elbow 1
D End boot 2
E Offset boot 2 1/2
F 45-degree angle boot 1/2
G Floor register, second story 3
H Offset 3
I Offset 2 1/2
AIR SOURCE HEAT PUMPS An air source heat pump uses outside air as a heat source or heat sink. Acompressor, condenser and refrigerant system is used to absorb heat at one place and release it at another. An air source heatpump works in exactly the same way as a ground source heat pump, only it extracts heat from the air (instead of the ground)outside a building, and uses it to heat water in the building (air-water system), or the air in the building (air-air). The advantage of an air source heat pump over a ground source heat pump is that an air source heat pump requires far less space to install, and noexcavations. This makes air source heat pumps far more suitable for the average urban home.
Outside air , necessarily existing at some temperature above absolute zero, is a heat container. An air-source heat pump moves("pumps") some of this heat to provide hot water or household heating. This can be done in either direction, to cool or heat theinterior of a building.
The main components of an air-source heat pump are made up of three main components - an evaporator coil, a compressor ,and a heat exchanger .
• a heat exchanger, over which outside air is blown, to extract the heat from the air
• a compressor, which acts like a refrigerator but in reverse and raises the temperature from the outside air
• a way to transfer the heat into a hot water tank or heating system, such as radiators or under-floor heating tubes
Heating and cooling is accomplished by moving a refrigerant through the heat pump's various indoor and outdoor coils andcomponents. A compressor , condenser , expansion valve and evaporator are used to change states of the refrigerant from a liquid to hot gas and from a gas to a cold liquid. The refrigerant is used to heat or cool coils in a building or room and fans pull the roomair over the coils. An external outdoor heat exchanger is used to heat or cool the refrigerant. This use of outside air has led to theterm "Air Source" Heat Pump. The overall operation uses the concepts described in classic vapor compression refrigeration.
When the liquid refrigerant at a low temperature passes through the outdoor evaporator coils, the temperature of the outsideair causes the liquid to boil. This change of state from liquid to a vapor requires a considerable amount of energy or "latent heat"which is provided by outside air passing over the coils.
This vapor is then drawn into the compressor where the temperature of the vapor is boosted to well over 100 degrees Celsius. At this point we have used heat from the outside air to change the liquid refrigerant to a gas and added an amount of compression"work" to raise the temperature of the vapor. The vapor now enters the condenser heat exchanger coils where it begins to transfer heat to the air being drawn across the coils. As the vapor cools, it condenses back to a liquid and in so doing releases andtransfers considerable latent heat to the air passing over the condenser unit coils. We have used the heat energy of outside air tochange the phase of the refrigerant and then released this heat for heating, a typical heat pump operation.
At this stage we now have a very cold liquid refrigerant compressed to a high pressure. The refrigerant is next passed throughan expansion valve which turns it back to a low pressure cold liquid ready to re-enter the evaporator to begin a new cycle.
The heat pump can also operate in a cooling mode where the cold refrigerant is moved through the indoor coils to cool the roomair.
The evaporator coil is fitted to the outside of an external wall. Here it absorbs heat from the outside air. The compressor pushes the refridgerant gas through the system compressing it until it is at the desired temperature (typically up to 35-40 degreesCelcius). The hot refridgerant then passes through the heat exchanger where the heat from the refridgerant is transferred to water or air.
In the schematic above the evaporator coil is labelled as outdoor coil , and the heat exchanger is the indoor coil since thesystem illustrated is an air-air heating system. Note that the operation of a heat pump can be reversed and used to cooldown the air in a building by radiating it outside - behaving in exactly the same way as a refridgerator:
Efficiency The 'efficiency' of air source heat pumps is measured by the Coefficient of performance (COP). Insimple terms, a COP of 3 means the heat pump produces 3 units of heat energy for every 1 unit of electricity it consumes. In mildweather, the COP of an air source heat pump can be up to 4. However, on a very cold winter day, it takes more work to move thesame amount of heat indoors than on a mild day. The heat pump's performance is limited by the Carnot cycle and will approach1.0 as the outdoor-to-indoor temperature difference increases at around −18 °C (0 °F) outdoor temperature for air source heatpumps. However, heat pump construction methods that enable use of carbon dioxide refrigerant extend the figure downward to -30°C (-22 °F). A Geothermal heat pump will have less change in COP as the ground temperature from which they extract heat is
more constant than outdoor air temperature.
Seasonally adjusted heating and cooling efficiencies are given by the heating seasonal performance factor (HSPF) and seasonal energy efficiency ratio (SEER) respectively.
Advantages
• Typically draws approximately 1/3 to 1/4 of the electricity of a standard resistance heater for the same amount of heating,reducing utility bills.[1] This typical efficiency compares to 70-95% for a fossil fuel-powered boiler [citation needed ].
• Few moving parts, reducing maintenance requirements. However, it should be ensured that the outdoor heat exchanger andfan is kept free from leaves and debris. Morover, it must be borne in mind that a heat pump will have significantly more movingparts than an equivalent electric resistance heater or fuel burning heater.
• As an electric system, no flammable or potentially asphyxiating fuel is used at the point of heating, reducing the potentialdanger to users, and removing the need to obtain gas or fuel supplies (except for electricity).
• The same system may be used for air conditioning in summer, as well as a heating system in winter.
• lower running costs, the compressor being the thing that uses most power - when in comparison with traditional electricalresistance heaters.[citation needed ].
DisadvantagesThe following disadvantages are associated with all air source heat pump designs:
• Air source heat pumps require electricity for operation. Electricity generation accounts for a significant amount of emissionspollutants and greenhouse gases.
• External space needs to be found for the outside condenser unit which can be somewhat noisy [citation needed ] and possibly
unsightly.• The cost of installation is high (though less than a Ground Source heat pump because a ground source heat pump requiresinstallation of a ground loop).The following disadvantages are associated with units charged with HFC refrigerants:
• Usually marketed as low energy or a sustainable technology, the HFCs have the potential to contribute to globalwarming[citation needed ]. The effect the refrigerant could have is measured in global warming potential (GWP) and ozone depletion potential (ODP).
• Air source heat pumps lose their efficiency as external temperatures fall. In colder climates the system needs to be installedwith an auxiliary source of heat to providing heat at low temperatures or if the heat pump should require repair.
• The COP is reduced when heat pumps are used to reach over 55°C for heating domestic water or in conventional central heating systems using radiators to distribute heat (instead of an underfloor heating array).
• Retrofit is difficult when used with conventional heating systems using radiators or radiant panels. The lower Heat Pumpoutput temperatures would mean radiators would have to be increased in size or a low temperature underfloor heating system beinstalled instead.
Coefficient of Performance Heat pumps are measured by their coefficient of performance (CoP). The CoP for air source heat pumps is very similar to that for ground source heat pumps at approximately 2-3. With a CoP for instance of 3, 3 unitsof heat are produced for every 1 unit of electricity consumed. (The two free units of heating were extracted from the outside air).Even with ambient air temperatures of -10 to -15 degrees Celcius, an air source heat pump can extract useful heat (i.e. > 1 unit of heat generated per unit of electricity consumed).
What Is a Catalytic Converter?
The catalytic converter is a device located in the exhaust system of all modern motor vehicles. It is an important device in the exhaust
gas de-pollution process, which reduces harmful environmental exhaust emissions of motor vehicle’s combustion cycle by-products.Its function is to chemically change harmful pollutants that the engine has combusted in the process of its various starting, driving,power and idle conditions.
What Are The Pollutants?
These pollutants include carbon monoxide, hydrocarbons, nitrous oxides, etc. A catalytic converter chemically changes these intoharmless substances like carbon dioxide, nitrogen and water vapour.
How Are Harmful Exhaust Pollutants Eliminated?
The catalytic converter uses an inside structure called a substrate. This is a ceramic or stainless steel monolith block that is coveredwith precious metals such as platinum, palladium and rhodium. The monolithic block consists of many fine channels, which are coveredby a coarse washcoat above which the catalytically effective precious metal layer is placed. It is these elements, which cause thechemical change.
Catalytic Converter Longevity In Service
For a catalytic converter to last in normal vehicle service operation, it is essential the engine, its ignition system, fuel system, andemission devices must all operate within manufacturer specifications properly, consistently, efficiently and correctly at all times.
If the catalytic converter you replaced or are about to replace was damaged or destroyed by the melting of the ceramic monolithicstructure or the metallic substrate, it means that excessive amounts of liquid fuel particles reached the catalytic converter substrate.When this occurs, it raises temperatures, causing the substrate to exceed its fusion point of around 1,500 degrees Fahrenheit, thusharming the substrate.
In such instances, THE INSTALLER MUST FIRST LOCATE AND CORRECT THE CAUSE OF THE MONOLITHIC OR SUBSTRATEMELTING AND IN PARTICULAR ENSURE THAT ALL THE ENGINE, IGNITION, FUEL AND EMISSION SYSTEM/S AND ORDEVICES ARE OPERATING correctly before replacing or renewing the catalytic converter.
