DIESEL HEATING AND AIR CONDITIONING
5MARKS
1. Heat-end equipment
Baggage car
Although passengers generally were not allowed access to the baggage car, they were included in
a great number of passenger trains as regular equipment. The baggage car is a car that was
normally placed between the train's motive power and the remainder of the passenger train. The
car's interior is normally wide open and is used to carry passengers' checked baggage. Baggage
cars were also sometimes commissioned by freight companies to haul less-than-carload (LCL)
shipments along passenger routes (Railway Express Agency was one such freight company).
Some baggage cars included restroom facilities for the train crew, so many baggage cars had
doors to access them just like any other passenger car. Baggage cars could be designed to look
like the rest of a passenger train's cars, or they could be repurposed box cars equipped with highspeed trucks and passenger train steam and air connections.
Express car
Express cars carried high value freight in passenger consists. These cars resembled baggage cars,
though in some cases specially equipped box cars or refrigerator cars were used.
Horse car
Main article: Stock car (rail)#Horse cars
Specialized stock cars were used to transport horses and other high value livestock as part of
passenger consists. Similar equipment is used in circus trains to transport their animals.
Prisoner car
In some countries, convicts are transported from court to prison or from prison to another by
railway. In such transportation a specific type of coach, prisoner car, is used. It contains several
cell compartments with minimal interior and commodities, and a separate guard compartment.
Usually the windows are of nontransparent opaque glass to prevent prisoners from seeing outside
and determine where they are, and windows usually also have bars to prevent escapes. Unlike
other passenger cars, prisoner cars do not have doors at the ends of the wagon.
Railway post office
The interior of an RPO on display at the National Railroad Museum in Green Bay,
Wisconsin.Like baggage cars, railway post office (RPO) cars or travelling post offices (TPOs)
were not accessible to paying passengers. These cars' interiors were designed with sorting
facilities that were often seen and used in conventional post offices around the world. The RPO
is where mail was sorted while the train was en route. Because these cars carried mail, which
often included valuables or quantities of cash and checks, the RPO staff (who were employed by
the postal service and not the railroad) were the only train crews allowed to carry guns. The RPO
cars were normally placed in a passenger train between the train's motive power and baggage
cars, further inhibiting their access by passengers.
2. Heavyweight vs. lightweight
A heavyweight car is one that is physically heavier than a lightweight car due to its construction.
While early cars used wood construction, Pullman switched to heavyweight riveted steel
construction in 1910, more or less at the same time as other rail car manufacturers.
Heavyweights are said[by whom?] to offer a more luxurious ride due to their added mass (from the
plate steel construction and concrete floor) and, usually, six-wheeled trucks (bogies). The
stepped roof line of early heavyweights usually consisted of a center sill section (the clerestory)
that ran the length of the car and extended above the roof sides by as much as a foot. This section
of the roof usually had windows or shutters that could be opened for ventilation while the train
was in motion. However, railroad crews and passengers quickly discovered that when these
windows were opened on a passenger train pulled by one or more steam locomotives, smoke and
soot from the locomotives tended to drift in through the windows, especially when the train went
through a tunnel.
In the early 20th century, air conditioning was added to heavyweight cars for the first time. An air
conditioned heavyweight car could be spotted easily since the area where the roof vent windows
existed was now covered, either partially or in full, by the AC duct. As lightweight cars were
introduced, many heavyweight cars were repurposed into maintenance of way service by the
railroads that owned them.
Lightweight passenger cars required developments in steel processing that weren't available until
the 1920s and 1930s. By building passenger cars out of steel instead of wood, the manufacturers
were able to build lighter weight cars with smooth or fluted sides and smooth roof lines.
Steel cars were ushered in at the beginning of the streamline era of the 1930s (although not all
lightweight cars were streamlined) and steel has continued in use ever since then. With the use of
steel for the car sides, railroads were able to offer more innovative passenger car types. It wasn't
until after the first lightweight cars were introduced that railroads began building and using dome
cars because the sides of heavyweight cars weren't strong enough to support the weight of the
dome and its passengers. Lightweight cars also enabled the railroads to operate longer passenger
trains; the reduced car weight meant that more passengers could be carried in a greater number of
cars with the same locomotives. The cost savings in hauling capacity coupled with the increased
car type options led to the quick replacement of heavyweight cars with lightweight cars.
3.Automotive Service Excellence
National Institute for Automotive Service Excellence (ASE) is a professional certification group that
certifies professionals in the automotive repair and service industry. It is an independent, non-profit
organization created in 1972[1] in response to consumers needing to distinguish between incompetent
and competent automotive technicians.[2] The organization aims to improve the quality of vehicle repair
and service through the testing and certification of repair and service professionals.
ASE Certification
ASE offers certification tests for automotive professionals at 750 locations around the country
administered by ACT, Inc. These involve several exams, the passing of which, added with two
years of relevant hands-on work experience, will merit certification.[3] Some forms of formal
training will also satisfy part of the 2 year work experience requirement. A re-certification track
is also offered for those who have had previous certification. An ASE certificate serves as proof
of one's competence and effectiveness. Upon certification, the certified applicant will also
receive an ASE shoulder insignia, wallet I.D. card and a wall certificate suitable for framing.
ASE certification is usually required (not by law but by employers) for those interested in
pursuing a career in automotive mechanic/auto mechanic or automotive technician service. Some
municipalities require ASE certification in order to be licensed for motor vehicle repairs, such as
Broward[4] and Miami-Dade[5] Counties.
Testing was previously done twice a year for the written version. All ASE tests are now
computer based and are administered at monitored testing centers. The tests are now offered
more frequently and at more locations.
Additionally ASE certification is not just for technicians anymore and apply to all manner of
jobs relating to the Automotive Industry. And also it is useful in entering in to reputed
Automotive Industries
20MARKS
1.HVDC converter station
An HVDC converter station (or simply converter station) is a specialised type of substation
which forms the terminal equipment for a high-voltage direct current transmission line.[1] It
converts direct current to alternating current or the reverse. Besides the converter itself, the
station usually contains:





three-phase alternating current switch gear
transformers
capacitors or synchronous condensers for reactive power
filters for harmonic suppression, and
direct current switch gear
Components
Converter.
The converter is usually installed in a building called the valve hall. Early HVDC
systems used mercury-arc valves, but since the mid 1970s, solid state devices such as
thyristors are used. Converters using thyristors or mercury-arc valves are known as
line commutated converters. In thyristor-based converters, many thyristors are
connected in series to form a thyristor valve and each converter normally consists of
six or twelve thyristor valves. The thyristor valves are usually grouped in pairs or
groups of four and can stand on insulators on the floor or hang from insulators from
the ceiling.
Line commutated converters require voltage from the AC network for commutation, but since
the late 1990s, voltage sourced converters have started to be used for HVDC. Voltage sourced
converters use insulated-gate bipolar transistors instead of thyristors and can provide power to a
deenergized AC system.
Almost all converters used for HVDC are intrinsically able to operate with power conversion in
either direction. Power conversion from AC to DC is known as rectification and conversion from
DC to AC is known as inversion.
DC equipment
The direct current equipment often includes a coil (called a reactor) that adds inductance in
series with the DC line to help smooth the direct current. The inductance typically amounts to
between 0.1 H and 1 H. The smoothing reactor can have either an air-core or an iron-core. Ironcore coils look like oil-filled high voltage transformers. Air-core smoothing coils resemble, but
are considerably larger than, carrier frequency choke coils in high voltage transmission lines and
are supported by insulators. Air coils have the advantage of generating less acoustical noise than
iron-core coils, they eliminate the potential environmental hazard of spilled oil, and they do not
saturate under transient high current fault conditions. This part of the plant will also contain
instruments for measurement of direct current and voltage.
Special direct current filters are used to eliminate high frequency interference. Such filters are
required if the transmission line will use Power line communication techniques for
communication and control, or if the overhead line will run through populated areas. These
filters can be passive LC filters or active filters, consisting of an amplifier coupled through
transformers and protection capacitors, which gives a signal out of phase to the interference
signal on the line, thereby cancelling it. Such a system was used on the Baltic Cable HVDC
project.
Converter transformer
The converter transformers step up the voltage of the AC supply network. By using a star-delta
(US: wye-delta) connection, the converter can operate with 12 pulses in each cycle of the AC
supply, which eliminates numerous harmonic current components. The insulation of the
transformer windings must be specially designed to withstand a large DC potential to earth.
Converter transformers can be built as large as 300 MVA as a single unit. It is impractical to
transport larger transformers so when larger ratings are required, several individual transformers
are connected together. Either two three-phase units or three single-phase units can be used. With
the latter variant only one type of transformer is used, making the supply of a spare transformer
more economical.
Converter transformers operate with high flux Power Steps In the Four Steps of the Converter
per cycle, and so produce more acoustic noise than normal three-phase power transformers. This
effect should be considered in the siting of an HVDC converter station. Noise-reducing
enclosures may be applied.
Reactive Power
When line commutated converters are used, the converter station will require between 40% and
60% of its power rating as reactive power. This can be provided by banks of switched capacitors
or by synchronous condensers, or if a suitable power generating station is located close to the
static inverter plant, the generators in the power station. The demand for reactive power can be
reduced if the converter transformers have on-load tap changers with a sufficient range of taps
for AC voltage control. Some of the reactive power requirement can be supplied in the harmonic
filter components.
Voltage sourced converters can generate or absorb reactive as well as real power, and additional
reactive power equipment is generally not needed.
Harmonic filters
Harmonic filters are necessary for the elimination of the harmonic waves and for the production
of the reactive power at line commutated converter stations. At plants with six pulse line
commutated converters, complex harmonic filters are necessary because there are odd numbered
harmonics of the orders
and
produced on the AC side and even harmonics of
order
on the DC side. At 12 pulse converter stations, only harmonic voltages or currents of
the order
and
(on the AC side) or
(on the DC side) result. Filters are
tuned to the expected harmonic frequencies and consist of series combinations of capacitors and
inductors.
Voltage sourced converters generally produce lower intensity harmonics than line commutated
converters. As a result, harmonic filters are generally smaller or may be omitted altogether.
Beside the harmonic filters, equipment is also provided to eliminate spurious signals in the
frequency range of power-line carrier equipment in the range of 30 kHz to 500 kHz. These filters
are usually near the alternating current terminal of the static inverter transformer. They consist of
a coil which passes the load current, with a parallel capacitor to form a resonant circuit.
In special cases, it may be possible to use exclusively machines for generating the reactive
power. This is realized at the terminal of HVDC Volgograd-Donbass situated on Volga
Hydroelectric Station.
AC switchgear
The three-phase alternating current switch gear of a converter station is similar to that of an AC
substation. It will contain circuit breakers for overcurrent protection of the converter
transformers, isolating switches, grounding switches, and instrument transformers for control,
measurement and protection. The station will also have lightning arresters for protection of the
AC equipment from lightning surges on the AC system.
2. VFD types and ratings
Generic topologies
Topology of VSI drive
Topology of CSI drive
Six-step drive waveforms
Topology of direct matrix converter
AC drives can be classified according to the following generic topologies:[c][41][42]






Voltage-source inverter (VSI) drive topologies (see image): In a VSI drive, the DC
output of the diode-bridge converter stores energy in the capacitor bus to supply stiff
voltage input to the inverter. The vast majority of drives are VSI type with PWM voltage
output.[d]
Current-source inverter (CSI) drive topologies (see image): In a CSI drive, the DC
output of the SCR-bridge converter stores energy in series-reactor connection to supply
stiff current input to the inverter. CSI drives can be operated with either PWM or six-step
waveform output.
Six-step[e] inverter drive topologies (see image):[43] Now largely obsolete, six-step
drives can be either VSI or CSI type and are also referred to as variable-voltage inverter
drives, pulse-amplitude modulation (PAM) drives,[44] square-wave drives or D.C.
chopper inverter drives.[45] In a six-step drive, the DC output of the SCR-bridge converter
is smoothed via capacitor bus and series-reactor connection to supply via Darlington Pair
or IGBT inverter quasi-sinusoidal, six-step voltage or current input to an induction
motor.[46]
Load commutated inverter (LCI) drive topologies: In a LCI drive, a special CSI case,
the DC output of the SCR-bridge converter stores energy via DC link inductor circuit to
supply stiff quasi-sinusoidal six-step current output of a second SCR-bridge's inverter and
an over-excited synchronous machine.
Cycloconverter or matrix converter (MC) topologies (see image): Cycloconverters
and MCs are AC-AC converters that have no intermediate DC link for energy storage. A
cycloconverter operates as a three-phase current source via three anti-parallel connected
SCR-bridges in six-pulse configuration, each cycloconverter phase acting selectively to
convert fixed line frequency AC voltage to an alternating voltage at a variable load
frequency. MC drives are IGBT-based.
Doubly fed slip[f] recovery system topologies: A doubly fed slip recovery system feeds
rectified slip power to a smoothing reactor to supply power to the AC supply network via
an inverter, the speed of the motor being controlled by adjusting the DC current.
Control platforms
See also: Dqo transformation and Alpha–beta transformation
Most drives use one or more of the following control platforms:[41][47]



PWM V/Hz scalar control
PWM field-oriented control (FOC) or vector control
Direct torque control (DTC).
Load torque and power characteristics
Variable frequency drives are also categorized by the following load torque and power
characteristics:



Variable torque, such as in centrifugal fan, pump and blower applications
Constant torque, such as in conveyor and displacement pump applications
Constant power, such as in machine tool and traction applications.
Available power ratings
VFDs are available with voltage and current ratings covering a wide range of single-phase and
multi-phase AC motors. Low voltage (LV) drives are designed to operate at output voltages
equal to or less than 690 V. While motor-application LV drives are available in ratings of up to
the order of 5 or 6 MW,[48] economic considerations typically favor medium voltage (MV) drives
with much lower power ratings. Different MV drive topologies (see Table 2) are configured in
accordance with the voltage/current-combination ratings used in different drive controllers'
switching devices[49] such that any given voltage rating is greater than or equal to one to the
following standard nominal motor voltage ratings: generally either 2.3/4.16 kV (60 Hz) or
3.3/6.6 kV (50 Hz), with one thyristor manufacturer rated for up to 12 kV switching. In some
applications a step up transformer is placed between a LV drive and a MV motor load. MV
drives are typically rated for motor applications greater than between about 375 kW (500 hp) and
750 kW (1000 hp). MV drives have historically required considerably more application design
effort than required for LV drive applications.[50][51] The power rating of MV drives can reach
100 MW, a range of different drive topologies being involved for different rating, performance,
power quality and reliability requirements.[52][53][54]
Drives by machines & detailed topologies
It is lastly useful to relate VFDs in terms of the following two classifications:


In terms of various AC machines as shown in Table 1 below[55][56]
In terms of various detailed AC-AC converter topologies shown in Tables 2 and 3 below.
3.System description and operation
VFD system
A variable frequency drive is a device used in a drive system consisting of the following three
main sub-systems: AC motor, main drive controller assembly, and drive operator interface.[5][4]
AC Motor
The AC electric motor used in a VFD system is usually a three-phase induction motor. Some
types of single-phase motors can be used, but three-phase motors are usually preferred. Various
types of synchronous motors offer advantages in some situations, but three phase induction
motors are suitable for most purposes and are generally the most economical choice. Motors that
are designed for fixed-speed operation are often used. Elevated voltage stresses imposed on
induction motors that are supplied by VFDs require that such motors be designed for definitepurpose inverter-fed duty in accordance to such requirements as Part 31 of NEMA Standard MG1.[6]
Controller
The variable frequency drive controller is a solid state power electronics conversion system
consisting of three distinct sub-systems: a rectifier bridge converter, a direct current (DC) link,
and an inverter. Voltage-source inverter (VSI) drives (see 'Generic topologies' sub-section
below) are by far the most common type of drives. Most drives are AC-AC drives in that they
convert AC line input to AC inverter output. However, in some applications such as common DC
bus or solar applications, drives are configured as DC-AC drives. The most basic rectifier
converter for the VSI drive is configured as a three-phase, six-pulse, full-wave diode bridge. In a
VSI drive, the DC link consists of a capacitor which smooths out the converter's DC output
ripple and provides a stiff input to the inverter. This filtered DC voltage is converted to quasisinusoidal AC voltage output using the inverter's active switching elements. VSI drives provide
higher power factor and lower harmonic distortion than phase-controlled current-source inverter
(CSI) and load-commutated inverter (LCI) drives (see 'Generic topologies' sub-section below).
The drive controller can also be configured as a phase converter having single-phase converter
input and three-phase inverter output.[7]
Controller advances have exploited dramatic increases in the voltage and current ratings and
switching frequency of solid state power devices over the past six decades. Introduced in 1983,[8]
the insulated-gate bipolar transistor (IGBT) has in the past two decades come to dominate VFDs
as an inverter switching device.[9][10][11]
In variable-torque applications suited for Volts per Hertz (V/Hz) drive control, AC motor
characteristics require that the voltage magnitude of the inverter's output to the motor be adjusted
to match the required load torque in a linear V/Hz relationship. For example, for 460 volt, 60 Hz
motors this linear V/Hz relationship is 460/60 = 7.67 V/Hz. While suitable in wide ranging
applications, V/Hz control is sub-optimal in high performance applications involving low speed
or demanding, dynamic speed regulation, positioning and reversing load requirements. Some
V/Hz control drives can also operate in quadratic V/Hz mode or can even be programmed to suit
special multi-point V/Hz paths.[12][13]
The two other drive control platforms, vector control and direct torque control (DTC), adjust the
motor voltage magnitude, angle from reference and frequency[14] such as to precisely control the
motor's magnetic flux and mechanical torque.
Although space vector pulse-width modulation (SVPWM) is becoming increasingly popular,[15]
sinusoidal PWM (SPWM) is the most straightforward method used to vary drives' motor voltage
(or current) and frequency. With SPWM control (see Fig. 1), quasi-sinusoidal, variable-pulsewidth output is constructed from intersections of a saw-toothed carrier frequency signal with a
modulating sinusoidal signal which is variable in operating frequency as well as in voltage (or
current).[16][9][17]
Operation of the motors above rated nameplate speed (base speed) is possible, but is limited to
conditions that do not require more power than the nameplate rating of the motor. This is
sometimes called "field weakening" and, for AC motors, means operating at less than rated V/Hz
and above rated nameplate speed. Permanent magnet synchronous motors have quite limited
field weakening speed range due to the constant magnet flux linkage. Wound rotor synchronous
motors and induction motors have much wider speed range. For example, a 100 hp, 460 V,
60 Hz, 1775 RPM (4 pole) induction motor supplied with 460 V, 75 Hz (6.134 V/Hz), would be
limited to 60/75 = 80% torque at 125% speed (2218.75 RPM) = 100% power.[18] At higher
speeds the induction motor torque has to be limited further due to the lowering of the breakaway
torque[a] of the motor. Thus rated power can be typically produced only up to 130...150% of the
rated nameplate speed. Wound rotor synchronous motors can be run at even higher speeds. In
rolling mill drives often 200...300% of the base speed is used. The mechanical strength of the
rotor limits the maximum speed of the motor.
Fig. 1: SPWM carrier-sine input & 2-level PWM output
An embedded microprocessor governs the overall operation of the VFD controller. Basic
programming of the microprocessor is provided as user inaccessible firmware. User
programming of display, variable and function block parameters is provided to control, protect
and monitor the VFD, motor and driven equipment.[9][19]
The basic drive controller can be configured to selectively include such optional power
components and accessories as follows:



Connected upstream of converter - circuit breaker or fuses, isolation contactor, EMC filter, line
reactor, passive filter
Connected to DC link - braking chopper, braking resistor
Connected downstream of inverter - output reactor, sine wave filter, dV/dt filter.[b][21]
Operator interface
The operator interface provides a means for an operator to start and stop the motor and adjust the
operating speed. Additional operator control functions might include reversing, and switching
between manual speed adjustment and automatic control from an external process control signal.
The operator interface often includes an alphanumeric display and/or indication lights and meters
to provide information about the operation of the drive. An operator interface keypad and display
unit is often provided on the front of the VFD controller as shown in the photograph above. The
keypad display can often be cable-connected and mounted a short distance from the VFD
controller. Most are also provided with input and output (I/O) terminals for connecting
pushbuttons, switches and other operator interface devices or control signals. A serial
communications port is also often available to allow the VFD to be configured, adjusted,
monitored and controlled using a computer.[9][22][23]
Drive operation
Electric motor speed-torque chart
Referring to the accompanying chart, drive applications can be categorized as single-quadrant,
two-quadrant or four-quadrant; the chart's four quadrants are defined as follows:[24][25][26]




Quadrant I - Driving or motoring[27], forward accelerating quadrant with positive speed and
torque
Quadrant II - Generating or braking, forward braking-decelerating quadrant with positive speed
and negative torque
Quadrant III - Driving or motoring, reverse accelerating quadrant with negative speed and
torque
Quadrant IV - Generating or braking, reverse braking-decelerating quadrant with negative speed
and positive torque.
Most applications involve single-quadrant loads operating in quadrant I, such as in variabletorque (e.g. centrifugal pumps or fans) and certain constant-torque (e.g. extruders) loads.
Certain applications involve two-quadrant loads operating in quadrant I and II where the speed is
positive but the torque changes polarity as in case of a fan decelerating faster than natural
mechanical losses. Some sources define two-quadrant drives as loads operating in quadrants I
and III where the speed and torque is same (positive or negative) polarity in both directions.
Certain high-performance applications involve four-quadrant loads (Quadrants I to IV) where the
speed and torque can be in any direction such as in hoists, elevators and hilly conveyors.
Regeneration can only occur in the drive's DC link bus when inverter voltage is smaller in
magnitude than the motor back-EMF and inverter voltage and back-EMF are the same
polarity.[28]
In starting a motor, a VFD initially applies a low frequency and voltage, thus avoiding high
inrush current associated with direct on line starting. After the start of the VFD, the applied
frequency and voltage are increased at a controlled rate or ramped up to accelerate the load. This
starting method typically allows a motor to develop 150% of its rated torque while the VFD is
drawing less than 50% of its rated current from the mains in the low speed range. A VFD can be
adjusted to produce a steady 150% starting torque from standstill right up to full speed.[29]
However, motor cooling deteriorates and can result in overheating as speed decreases such that
prolonged low speed motor operation with significant torque is not usually possible without
separately-motorized fan ventilation.
With a VFD, the stopping sequence is just the opposite as the starting sequence. The frequency
and voltage applied to the motor are ramped down at a controlled rate. When the frequency
approaches zero, the motor is shut off. A small amount of braking torque is available to help
decelerate the load a little faster than it would stop if the motor were simply switched off and
allowed to coast. Additional braking torque can be obtained by adding a braking circuit (resistor
controlled by a transistor) to dissipate the braking energy. With a four-quadrant rectifier (activefront-end), the VFD is able to brake the load by applying a reverse torque and injecting the
energy back to the AC line.
4.Thermodynamics
A rigorous treatment of OTEC reveals that a 20 °C temperature difference will provide as much
energy as a hydroelectric plant with 34 m head for the same volume of water flow. The low
temperature difference means that water volumes must be very large to extract useful amounts of
heat. A 100MW power plant would be expected to pump on the order of 12 million gallons
(44,400 metric tonnes) per minute.[27] For comparison, pumps must move a mass of water greater
than the weight of the Battleship Bismark, which weighed 41,700 metric tons, every minute. This
makes pumping a substantial parasitic drain on energy production in OTEC systems, with one
Lockheed design consuming 19.55 MW in pumping costs for every 49.8 MW net electricity
generated. For OTEC schemes using heat exchangers, to handle this volume of water the
exchangers need to be enormous compared to those used in conventional thermal power
generation plants,[28] making them one of the most critical components due to their impact on
overall efficiency. A 100 MW OTEC power plant would require 200 exchangers each larger than
a 20 foot shipping container making them the single most expensive component.[29]
Variation of ocean temperature with depth
The total insolation received by the oceans (covering 70% of the earth's surface, with clearness
index of 0.5 and average energy retention of 15%) is: 5.45×1018 MJ/yr × 0.7 × 0.5 × 0.15 =
2.87×1017 MJ/yr
We can use Lambert's law to quantify the solar energy absorption by water,
where, y is the depth of water, I is intensity and μ is the absorption coefficient. Solving the above
differential equation,
The absorption coefficient μ may range from 0.05 m−1 for very clear fresh water to 0.5 m−1 for
very salty water.
Since the intensity falls exponentially with depth y, heat absorption is concentrated at the top
layers. Typically in the tropics, surface temperature values are in excess of 25 °C (77 °F), while
at 1 kilometer (0.62 mi), the temperature is about 5–10 °C (41–50 °F). The warmer (and hence
lighter) waters at the surface means there are no thermal convection currents. Due to the small
temperature gradients, heat transfer by conduction is too low to equalize the temperatures. The
ocean is thus both a practically infinite heat source and a practically infinite heat sink.
This temperature difference varies with latitude and season, with the maximum in tropical,
subtropical and equatorial waters. Hence the tropics are generally the best OTEC locations.
Open/Claude cycle
In this scheme, warm surface water at around 27 °C (81 °F) enters an evaporator at pressure
slightly below the saturation pressures causing it to vaporize.
Where Hf is enthalpy of liquid water at the inlet temperature, T1.
This temporarily superheated water undergoes volume boiling as opposed to pool boiling in
conventional boilers where the heating surface is in contact. Thus the water partially flashes to
steam with two-phase equilibrium prevailing. Suppose that the pressure inside the evaporator is
maintained at the saturation pressure, T2.
Here, x2 is the fraction of water by mass that vaporizes. The warm water mass flow rate per unit
turbine mass flow rate is 1/x2.
The low pressure in the evaporator is maintained by a vacuum pump that also removes the
dissolved non-condensable gases from the evaporator. The evaporator now contains a mixture of
water and steam of very low vapor quality (steam content). The steam is separated from the
water as saturated vapor. The remaining water is saturated and is discharged to the ocean in the
open cycle. The steam is a low pressure/high specific volume working fluid. It expands in a
special low pressure turbine.
Here, Hg corresponds to T2. For an ideal isentropic (reversible adiabatic) turbine,
The above equation corresponds to the temperature at the exhaust of the turbine, T5. x5,s is the
mass fraction of vapor at state 5.
The enthalpy at T5 is,
This enthalpy is lower. The adiabatic reversible turbine work = H3-H5,s .
Actual turbine work WT = (H3-H5,s) x polytropic efficiency
The condenser temperature and pressure are lower. Since the turbine exhaust is to be discharged
back into the ocean, a direct contact condenser is used to mix the exhaust with cold water, which
results in a near-saturated water. That water is now discharged back to the ocean.
H6=Hf, at T5. T7 is the temperature of the exhaust mixed with cold sea water, as the vapour
content now is negligible,
The temperature differences between stages include that between warm surface water and
working steam, that between exhaust steam and cooling water, and that between cooling water
reaching the condenser and deep water. These represent external irreversibilities that reduce the
overall temperature difference.
The cold water flow rate per unit turbine mass flow rate,
Turbine mass flow rate,
Warm water mass flow rate,
Cold water mass flow rate
Closed Anderson cycle
Developed starting in the 1960s by J. Hilbert Anderson of Sea Solar Power, Inc. In this cycle, QH
is the heat transferred in the evaporator from the warm sea water to the working fluid. The
working fluid exits the evaporator as a gas near its dew point.
The high-pressure, high-temperature gas then is expanded in the turbine to yield turbine work,
WT. The working fluid is slightly superheated at the turbine exit and the turbine typically has an
efficiency of 90% based on reversible, adiabatic expansion.
From the turbine exit, the working fluid enters the condenser where it rejects heat, -QC, to the
cold sea water. The condensate is then compressed to the highest pressure in the cycle, requiring
condensate pump work, WC. Thus, the Anderson closed cycle is a Rankine-type cycle similar to
the conventional power plant steam cycle except that in the Anderson cycle the working fluid is
never superheated more than a few degrees Fahrenheit. Owing to viscous effects, working fluid
pressure drops in both the evaporator and the condenser. This pressure drop, which depends on
the types of heat exchangers used, must be considered in final design calculations but is ignored
here to simplify the analysis. Thus, the parasitic condensate pump work, WC, computed here will
be lower than if the heat exchanger pressure drop was included. The major additional parasitic
energy requirements in the OTEC plant are the cold water pump work, WCT, and the warm water
pump work, WHT. Denoting all other parasitic energy requirements by WA, the net work from the
OTEC plant, WNP is
The thermodynamic cycle undergone by the working fluid can be analyzed without detailed
consideration of the parasitic energy requirements. From the first law of thermodynamics, the
energy balance for the working fluid as the system is
where WN = WT + WC is the net work for the thermodynamic cycle. For the idealized case in
which there is no working fluid pressure drop in the heat exchangers,
and
so that the net thermodynamic cycle work becomes
Subcooled liquid enters the evaporator. Due to the heat exchange with warm sea water,
evaporation takes place and usually superheated vapor leaves the evaporator. This vapor drives
the turbine and the 2-phase mixture enters the condenser. Usually, the subcooled liquid leaves
the condenser and finally, this liquid is pumped to the evaporator completing a cycle.
Environmental impact
Carbon dioxide dissolved in deep cold and high pressure layers is brought up to the surface and
released as the water warms.[citation needed]
Mixing of deep ocean water with shallower water brings up nutrients and makes them available
to shallow water life. This may be an advantage for aquaculture of commercially important
species, but may also unbalance the ecological system around the power plant.