CRYOGENIC LIQUID NITROGEN VEHICLES

CRYOGENIC LIQUID NITROGEN VEHICLES
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CHAPTER 1
INTRODUCTION
1.1 INTRODUCTION ZERO EMISSION VEHICLES
In September of 1990, in an effort to improve local air quality, the California
Air Resources Board enacted the Low Emission Vehicle (LEV) program. The LEV
program established several categories of emission standards for cars and light trucks.
The most stringent of these categories was for the zero-emission vehicle (ZEV).
The LEV program requires that, by 2003, each of the seven largest automobile
manufacturers (Chrysler, Ford, General Motors, Honda, Mazda, Nissan and Toyota)
produce and offer for sale ZEVs at a rate equal to 10 % of the automobile sales each
company has in the state, or about 110,000 cars per year. Similar mandates have also
been adopted by New York and Massachusetts.
The impetus for the LEV legislation is the desire to reduce air pollution. In
urban areas of Southern California, vehicles account for over 50% of the air pollution
emitted. In 1995, the South Coast Basin (which includes Los Angeles, Orange, and
parts of San Bernardino and Riverside counties) experienced 98 days in which
the EPA health standard for ground level ozone was exceeded. Ground level
ozone can cause aching lungs, wheezing, coughing and headaches. Serious health
problems can also arise for those people with asthma, emphysema and chronic
bronchitis. Children appear to be at particular risk. A 1984 study conducted at USC
showed that children raised in the South Coast Basin suffered a 10% to 15% decrease
in lung function. The deleterious effects of gasoline and diesel powered vehicles
are not limited to air quality in southern California . In half of the world's cities,
tailpipe emissions are the single largest source of air pollution. Worldwide,
automobiles account for half of the oil consumed and a fifth of the greenhouse gases
emitted. This situation is not expected to improve in the near future, as the number of
cars and light trucks in the world over 500 million is expected to double in the next
thirty years. Most of this growth will occur in developing countries which have little
or no emission controls.

1.2 INTRODUCTION TO CRYOGENIC NITROGEN VEHICLES
The battery powered electric vehicle is the only commercially available
technology that can meet ZEV standards. However, electric vehicles have not sold
well. This is primarily due to their limited range, although anemic performance, slow
recharge and high initial costs are also contributing factors. All of these issues can be
traced directly to the limitations of electrochemical energy storage, particularly lead
acid batteries. Lead acid remains the dominant technology in the electric vehicle
market, but only exhibit energy densities in the range of 30-40W-hr/kg. This
compares with about 3000W-hr/kg for gasoline combusted in an engine running at
28% thermal efficiency. Lead acid batteries can take hours to recharge and must be
replaced every 2–3 years. This raises the specter of increased heavy metal pollution,
were a lead-acid powered electric fleet ever to come to pass.
Even advanced battery systems, such as nickel- metal hydride, zinc-air, and
lithium-ion suffer from slow recharge and high initial cost. Nickel-metal hydride
batteries, often touted as the heir- apparent of lead- acid, still contain a heavy
metal and must realize dramatic reductions in cost in order to be truly competitive.
Lithium - ion batteries, considered by many to be the third generation solution, must
also contend with cost and demonstrate their safety to a wary public. Another energy
storage medium will be required to make ZEVs the non-mandated automobile choice
of the car-buying public. If certain technical challenges can be overcome, that energy
storage medium may well be liquid nitrogen. Since 1993, the University of
Washington has been researching the technical challenges involved in building and
operating a vehicle powered by liquid nitrogen. Issues pertaining to frost-free heat
exchanger performance, cryogenic equipment, cycle analysis, drive train selection
and vehicle configuration are being investigated.
1.3 The COOLN2Car
The COOLN2Car which a converted 1973 Volkswagen and works similar to
that of a steam engine, except for using vaporized cold liquid nitrogen instead of
steam from boiling water. Vapour of the nitrogen actuates the air motor to propel the
car & then escapes out through the tail pipe. As the atmosphere consists of about 78%
of nitrogen, the environmental effects of driving LN2000 vehicles would be

negligible virtually. The heat exchanger of the vehicle pulls liquid nitrogen from an
insulated fuel tank (cryogenic) through a series of aluminium tubing coils & specially
designed pipes. The heat exchanger is like the radiator of the car, instead of using air
to cool water; here the air is used to boil liquid nitrogen to nitrogen gas for the further
processing’s.
1.4 OBJECTIVES
The primary objective is to introduce cryogenic liquid nitrogen vehicles with
following features
 The cryogenic nitrogen vehicles are work on the basis of frost free heat
exchanger and exhaust is nitrogen gases so there is no pollution.
 Disposing/recycling of Liquid Nitrogen tanks can be done with lesser
pollution than the batteries.
 They are unconstrained by the degradation problems associated with the
battery systems.
1.5APPROACH
This seminar deals with such a futuristic vision which the frost free
heat exchanger for cryogenic automotive propulsion. The COOLN2 concept car the
name symbolizes the nitrogen as fuel for the cryogenic automotive propulsion system,
and the replacement of conventional fuels like petrol, diesel and other petroleum by
products. It is a significant step towards a new kind of automobile that is substantially
friendlier to the environment and provides consumers positive benefits in driving
dynamics, safety and freedom of individual expression”.
1.6 REPORT OUTLINE
The chapter bifurcation in brief is as follows. Initially, Chapter 2 deals with
background information on the approaches and studies which are related to the
cryogenic liquid nitrogen vehicles. It also includes an exhaustive literature review.
Chapter 3 discusses deeply about liquid nitrogen formation process, cryogenic
automotive propulsion it gave a clear idea about working of nitrogen powered car and
ambient air heat exchanger development system. In chapter 4 discusses about

principle of operation, analysis of cooln2 car performance and various cycles of
process. Finally, the report concludes with Chapter 5 which highlights the main
contributions of this seminar, outlines potential direction for further work and
commercialization of nitrogen powered vehicle.

CHAPTER 2
LITERATURE REVIEW
2.1 INTRODUCTION
The purpose of this chapter is to provide a literature survey of past research
effort such as journals or articles related to liquid nitrogen propulsion system and to
study the new inventions related to this topic. Moreover, review of other relevant
research studies are made to provide more information in order to understand more on
this research.
2.2 JOURNAL STUDIES ON CRYOGENIC LIQUID NITROGEN VEHICLES
2.2.1 Cryogenic liquid nitrogen vehicles by K. J. Yogesh
As a result of widely increasing air pollution throughout the world & vehicle
emissions having a major contribution towards the same, it makes its very essential to
engineer or design an alternative to the present traditional gasoline vehicles. Liquid
nitrogen fueled vehicles can act as an excellent alternative for the same. Liquefied N2
at cryogenic temperatures can replace conventional fuels in cryogenic heat engines
used as a propellant. The ambient temperature of the surrounding vaporizes the liquid
form of N2 under pressure & leads to the formation of compressed N2 gas. This gas
actuates a pneumatic motor. A combination of multiple reheat open Rankine cycle &
closed Brayton cycle are involved in the process to make use of liquid N2 as a non-
polluting fuel. A system of such a kind will also be able to refuel itself in a matter of
time comparable to that of traditional engines, unlike the electrically charged ones.
2.2.2 Cryogenic liquid nitrogen vehicles by Sharvin Ghodekar
On account of rising air pollution throughout the world and the automobile
emissions being the largest contributor to the same, there is an immediate need to
provide some alternative means of transport to the current conventional gasoline
vehicles. Liquefied nitrogen cooled up to cryogenic temperatures and used as a
propellant in cryogenic heat engine can be one of the future trends. Heat from
atmosphere vaporizes liquid nitrogen under pressure and produces compressed
nitrogen gas. This gas draws a pneumatic motor with nitrogen gas as exhaust. To use

liquid nitrogen as a non-polluting fuel, a multiple reheat open Rankin and a closed
Brayton cycle are used. A zero emission vehicle utilizing such a propulsion system
would have an energy storage reservoir that can be refilled in a matter of minutes and
a range comparable to that of a conventional automobile.
2.2.3 Liquid nitrogen vehicles by Balaguru Sethuraman
Our paper examines the capability of several energy conversion processes to
provide sufficient energy in a world where the non-renewable resource is getting
depleted. Moreover pollution caused by them is increasing at a rapid rate. One such
efficient and non-polluting means of running the vehicles is the use of liquid nitrogen.
To use liquid nitrogen as a non-polluting fuel, a multiple reheat open Rankine and a
closed Brayton cycle are used. Cryogenic can be defined as the branch of the physics
that deals with the production of and study of effects and very low temperature
Cryogenic heat engine which uses very cold substances to produce useful energy. A
unique feature of a cryogenic heat engine is that it operates in an environment at the
peak temperature of the power cycle, thus there is always some heat input to the
working fluid during the expansion process.
2.2.4 Liquid nitrogen propulsion systems for automotive applications
by Thomas B. North
A dual, double-acting propulsion system is analyzed to determine how
efficiently it can convert the potential energy available from liquid nitrogen into
useful work. The two double- acting pistons (high- and low-pressure) were analyzed
by using a Matlab-Simulink computer simulation to determine their respective
mechanical efficiencies. The flow circuit for the entire system was analyzed by using
flow circuit analysis software to determine pressure losses throughout the system at
the required mass flow rates. The results of the piston simulation indicate that the two
pistons analyzed are very efficient at transferring energy into useful work. The flow
circuit analysis shows that the system can adequately maintain the mass flow rate
requirements of the pistons but also identifies components that have a significant
impact on the performance of the system. The results of the analysis indicate that the
nitrogen propulsion system meets the intended goals of its designers

CHAPTER 3
METHODOLOGY
3.1 LIQUID NITROGEN
Liquid nitrogen is nitrogen in a liquid state at an extremely low temperature. It
is a colorless clear liquid with a density of 0.807 g/ml at its boiling point (−195.79 °C
(77 K; −320 °F)) and a dielectric constant of 1.43.Nitrogen was first liquefied at the
Jagiellonian University on 15 April 1883 by Polish physicists, Zygmunt Wróblewski
and Karol Olszewski. It is produced industrially by fractional distillation of liquid air.
Liquid nitrogen is often referred to by the abbreviation, LN2 or "LIN" or "LN" and
has the UN number 1977. Liquid nitrogen is a diatomic liquid, which means that the
diatomic character of the covalent N bonding in N2 gas is retained after liquefaction.
The temperature of liquid nitrogen can readily be reduced to its freezing point 63 K
(−210 °C; −346 °F) by placing it in a vacuum chamber pumped by a vacuum pump.
Liquid nitrogen's efficiency as a coolant is limited by the fact that it boils
immediately on contact with a warmer object, enveloping the object in insulating
nitrogen gas. This effect, known as the Leidenfrost effect, applies to any liquid in
contact with an object significantly hotter than its boiling point. Faster cooling may
be obtained by plunging an object into a slush of liquid and solid nitrogen rather than
liquid nitrogen alone.
3.2 PROPERTIES OF LIQUID NITROGEN
Liquid nitrogen is inert, colorless, odorless, non-corrosive, nonflammable, and
extremely cold. Nitrogen makes up the major portion of the atmosphere (78.03% by
volume, 75.5% by weight). Nitrogen is inert and will not support combustion;
however, it is not life supporting. Nitrogen is inert except when heated to very high
temperatures where it combines with some of the more active metals, such as lithium
and magnesium, to form nitrides. It will also combine with oxygen to form oxides of
nitrogen and, when combined with hydrogen in the presence of catalysts, will form
ammonia.

Physical Properties
 Molecular Weight: 28.01
 Boiling Point @ 1 atm: -320.5°F (-195.8°C, 77oK)
 Freezing Point @ 1 atm: -346.0°F (-210.0°C, 63oK)
 Critical Temperature: -232.5°F (-146.9°C)
 Critical Pressure: 492.3 psia (33.5 atm)
 Density, Liquid @ BP, 1 atm: 50.45 lb/scf
 Density, Gas @ 68°F (20°C), 1 atm: 0.0725 lb/scf
 Specific Gravity, Gas (air=1) @ 68°F (20°C), 1 atm: 0.967
 Specific Gravity, Liquid (water=1) @ 68°F (20°C), 1 atm: 0.808
 Specific Volume @ 68°F (20°C), 1 atm: 13.80 scf/lb
 Latent Heat of Vaporization: 2399 BTU/lb mole
 Expansion Ratio, Liquid to Gas, BP to 68°F (20°C): 1 to 694
3.3 FORMATION OF LIQUID NITROGEN
Liquid Nitrogen is the cheapest, widely produced and most common
cryogenic liquid. It is mass produced in air liquefaction plants. The liquefaction
process is very simple in it normal, atmospheric air is passed through a dust
precipitator and pre-cooled using conventional refrigeration techniques. It is then
compressed inside large turbo pumps to about 100 atmospheres. Once the air has
reached 100 atmospheres and has been cooled to room temperature it is allowed to
expand rapidly through a nozzle into an insulted chamber. By running several cycles
the temperate of the chamber reaches low enough temperatures the air entering
it starts to liquefy. Liquid nitrogen is removed from the chamber by fractional
distillation and is stored inside well insulated Dewar flasks.
Liquid nitrogen is used in association with cryogenic heat engines. It is an
engine that uses very cold substances to produce useful energy. A unique feature of
an cryogenic heat engine is that it operates in an environment at the peak temperature
of the power cycle, & thereby there is always an heat input to the working fluid
during the expansion process.

Figure 3.1: Liquid nitrogen formation process
3.4 CRYOGENIC AUTOMOTIVE PROPULSION
The cryogenic automobile is a zero-emission vehicle. It operates on the
thermodynamic potential between the ambient atmosphere and a reservoir of liquid
nitrogen. One way to utilize that potential is through an open Rankine cycle. The
liquid nitrogen is drawn from a tank, pumped up to the system pressure, then
vaporized and superheated in a two-stage heat exchange system. The resulting high
pressure, near ambient temperature gas is injected into a quasi-isothermal expander
which produces the system's motive work. The spent, low pressure gas is exhausted
back to the atmosphere. Because a zero emission vehicle is required to produce no
smog-forming tailpipe or evaporative pollutants, and because nitrogen gas is its only
emission, the cryogenic automobile meets California's ZEV guidelines. Although the
concept of a nitrogen powered automobile has been studied in the past, there are two
key technologies that have yet to be demonstrated: the quasi-isothermal expander and
a frost-free liquid nitrogen heat exchange system. There are many thermodynamic
cycles available for utilizing the thermal potential of liquid nitrogen. These range
from the Brayton cycle, to using two and even three-fluid topping cycles, to
employing a hydrocarbon fueled boiler for superheating beyond atmospheric
temperatures. The easiest to implement, however, and the one chosen for this study, is

shown in Figure 3.2 This system uses an open Rankine cycle. It begins with a tank of
liquid nitrogen stored at 77 K and 1 bar. The nitrogen is pumped, as a liquid, to the
system's working pressure. This high pressure liquid flows into the economizer. The
economizer is a shell-and-tube heat exchanger where the shell- side fluid is the
exhaust from the expander. While this step is not necessary from an energy point of
view, it does have the advantage of providing a frost-free pre-heat to the incoming
liquid.
Figure 3.2: Liquid nitrogen propulsion system.
Once through the economizer, the vaporized nitrogen enters the heat
exchanger, which has a multi-element, tube-in- cross flow configuration. The exterior
fluid is the ambient atmosphere, which is drawn through the core of the heat
exchanger either by the motion of the vehicle or by a fan, depending on the operating
regime. This heat exchanger must be able to operate across most of the spectrum of
environmental and operating conditions without suffering the adverse effects of frost
buildup. Upon leaving the heat exchanger, the working fluid is a high pressure, near-
ambient temperature gas. It is injected into the expander which provides all of the
motive work for the system. This can be either a positive displacement or turbine

engine. Following expansion, the low-pressure exhaust is warm enough to be used in
an economizer, where it preheats the incoming liquid, before finally being vented to
the atmosphere.
3.5 NITROGEN POWERED CAR
A test vehicle has been purchased to serve both as a proof-of-concept and
as a rolling test-bed for further system refinements. The vehicle itself is a 1984
Rumman-Olson Kubvan, pictured in Figure 3.3. To emphasize the near-term potential
of this project, it has been christened the LN2000.
Figure 3.3: 1984 Grumman-Olson Kubvan.
This particular vehicle was originally electric, operating on a pack of 14 lead
acid batteries which weighed over 450 kg. The running gear for this vehicle is from a
right-hand drive 1984 Volkswagen Rabbit. The construction is welded frame with
riveted body panels and is made entirely of aluminum.
The Kubvan was selected as a test-bed for several reasons. The volume
available is well suited to the placement of the necessary equipment. The simplicity
of its construction –flat sheet-metal body panels, aluminum frame, and open interior –
is conducive to making modifications. Also, because it was originally designed to
be electric, it operates with very few "hotel" functions such as air conditioning and
rear window defrosting.

City
Cycle
Highway
Cycle
Straight
and
Level*
Avg. Mass
Flow (g/s)
81 204 256
Max. Mass
Flow (g/s)
297 298 256
Consumption
(kg/km)
9.5 10.0 10.8
Avg. Power
(kW)
4.0 10.7 13.0
Max. Power
(kW)
13.0 13.0 13.0
Table3.1: Performance of the open Rankine cycle.
The Kubvan performance using the prototype LN2 propulsion system has been
calculated and is given in Table 3.1. This employs an EPA approved Federal Urban
Driving Schedule. Velocity dependent rolling resistance and aerodynamic drag were
calculated, and correlated reasonably well with coast down tests made with the
vehicle. The equipment layout is shown in Figure 3.4 Most of the cryogenic plumbing
is stainless steel, but the components attached to the economizer are aluminum. Low
pressure plumbing utilizes large diameter rubber hose where possible.
Figure 3.4: Schematic of vehicle equipment layout.

3.5.1 Liquid nitrogen storage tank
The Dewar chosen for this application can hold 80 liters of liquid nitrogen at
24 bars with a daily boil-off rate of ~3%. The primary protection against over
pressure is a relief valve connected to the internal vessel. This valve also serves as the
bleed for the boil off gases, which are vented to the outside by a rubber hose. There
are several other safety devices, providing multi-tiered protection against catastrophic
rupture. The dewar is held in place at five attachment points: one on the roof, the
other four on the floor.
3.5.2 Pressurization system
The pressurization system consists of two high-pressure nitrogen bottles
stored under the rear deck of the Kubvan. The blow down system has the advantage
of mechanical simplicity at the cost of increased weight and volume. Each of the
nitrogen bottles has a mass of 40 kg. The volume of gas required was calculated such
that the pressurant tanks and the Dewar get to within 3 bar of equilibrium just as the
last of the liquid nitrogen is drained out. The pressurant tanks are initially filled to a
starting pressure of about 133 bars. This is regulated down to the system pressure of
24 bars before being injected into the Dewar. The hardware required for filling both
the pressurant bottles and the Dewar is attached to the vehicle.
3.5.3 Economizer
The economizer is actually a pair of shell-and-tube heat exchangers, as shown
in Figure 3.5 These heat exchangers operate in parallel, with the shell-side fluid being
the exhaust from the expander. When operating at maximum mass flow, ~300 g/s, the
economizer is designed to bring the liquid nitrogen to a quality of about 75%. This
represents approximately one quarter of the total enthalpy change the nitrogen will
experience before being injected into the expander. At lower mass flows, the
vaporization will be complete.

Figure.3.5: Economizer units with and without shell.
3.5.4 Ambient air heat exchanger
The ambient air heat exchanger is made up of 45 finned-tube elements. These
elements are manifolded together, as shown in Figure 3.6 to make a staggered array
of tubes in cross flow with the incoming air. Either the motion of the vehicle, or the
two ducted fans located at the back of the van; draw the air through the heat
exchanger. The air inlet consists of a sheet-metal scoop slung underneath the vehicle.
Figure 3.6: Ambient-air heat exchanger assembly.

3.5.5 Expander
The expander chosen for the prototype vehicle is an 11.1 kW, radial piston air
motor made by Cooper Power Tools. This motor, pictured in Fig 3.7 has a cast-iron
block with five 7.5 cm cylinders. Each cylinder holds a steel piston attached to the
single-throw crank shaft by a connecting rod. Lubrication is maintained by splash and
by an oiler located near the gas inlet. The motor is attached to the front- wheel drive,
5-speed manual transmission by a custom-made aluminum gear-box. The output shaft
of the motor drives a 15.24 cm diametric pitch (DP) spur gear. The input shaft to the
clutch assembly has a 7.62 cm. DP spur gear, giving a 1:2 speed ratio through the
gear box. The running gear is from a 1984 Volkswagen Rabbit and is right - hand
drive.
Figure 3.7: Motor and transmission assembly.
3.6 AMBIENT-AIR HEAT EXCHANGER DEVELOPMENT
The goal of this research is to design a heat exchanger that can operate in a
variety of environmental conditions and is structurally robust, while not being
hampered by the buildup of frost. Many approaches have been examined, but in

general, strategies for dealing with frost formation fall into two categories: passive
and active control. Passive control involves either preventing frost formation, or over
sizing the heat exchanger such that frost build up is unimportant on time scales
characteristic of automotive travel. The advantages of passive control are mechanical
simplicity and reliability. One disadvantage is that passive systems are, in general,
less flexible in dealing with off design operation.
Active control of frost formation entails allowing frost to accrete, and then
removing it either thermally or mechanically. The advantage of active systems is that
they are more operationally robust. Performance of an actively controlled heat
exchanger is much less dependent on the ambient or operational conditions since
these systems can be responsive to different frost loading conditions. Disadvantages
include the power consumption and poor long term reliability.
Both options have been examined closely. Of the two, the passive control heat
exchanger was chosen for the LN2000 as the best possible solution to the issue of
frost formation. As of this writing, the ambient air heat exchanger has been built and
pressure tested. The results presented in this chapter are calculated and have not yet
been experimentally verified. Described here it is the theoretical modeling, design,
and fabrication of the ambient air heat exchanger. Future plans include rigorous
testing to verify the calculations and identify possible modifications for a second-
generation heat exchanger.
3.6.1 Design
The operating environment of a typical automobile can be a demanding one.
There are weather conditions such as rain, snow, or extreme heat to contend with.
There are driving conditions such as rough pavement, gravel roads, potholes and
speed-bumps, and there are situations such as stop-and-go traffic, long-distance
highway travel, and cold-starts. Finally, automobiles have to meet rigorous safety,
comfort, and reliability standards if they are to compete in today's marketplace. A
heat exchanger for automotive application has to successfully meet all of these
requirements.

3.6.2 Constraints
Along with meeting the necessary design requirements, the automotive heat
exchanger has to also fit within constrained volume and mass envelopes. The LN2000
has a space in back, under the cargo deck, which provides a large volume and allows
easy ducting of ambient air from beneath the vehicle. Furthermore, because the heat
exchanger can be hung directly from the deck, structural modifications are minimal.
The available space constrains the heat exchanger to dimensions of no more than
78 cm x 53 cm x 38 cm. The mass constraint is less well defined, but it does stand to
reason that in an 1100 kg automobile with an 11 kW motor, less mass is better.
3.6.3 Configuration
Figure 3.8: Frost free heat exchanger element.
To prevent frost buildup on sub ambient heat exchangers, the exterior surfaces
must be kept above the freezing point of water. A method for achieving this is shown
in Figure 3.8. The principle is the same as for multi fluid heat exchange systems,
where heat is transferred from source to sink via a number of media operating in
series. In this concept, that series of media is simply the nitrogen gas at different
stages of its thermal history. Figure 3.8 shows only three passes, but it is possible to
use as few as two, or as many as can be fit within the outermost tube. Two concentric
tubes, operating within a bundle in a shell-and-tube heat exchanger, are known as

bayonets. These have been used for years to eliminated stresses due to differential
thermal expansion between the shell and its tube bundle. More recently, a 1995 patent
for a frost-tolerant heat exchanger described much the same idea as that presented
here, but using only two concentric tubes in a variety of configurations.
The choice of three passes was based on two practical considerations. The
first is that using an odd number of internal passages allows the inlet and outlet to be
at opposite ends of the element, greatly simplifying the manifolding. The second is
that going to more internal passages such as five or seven can present problems with
fabrication, cost and mass. This has to be weighed against the fact that more passes
increase the robustness of the system. Robustness insures that frost free performance
can be maintained in lower temperature environments.
Figure 3.9: Temperature profile of frost-free heat exchanger element.
An example of the behavior of the gas as it passes through the heat exchanger
element is given in Figure 3.9. The black arrows represent heat transfer: from the
ambient air to the wall, from the wall to the nitrogen and from each pass to the
previous one. The exterior wall temperature is dependent on the heat transfer
coefficient and fluid temperature in the outermost passage only.
Passive heat exchangers are more tightly coupled to environmental and
operating conditions. In the case of this particular concept, when the outside
temperature is lower than the freezing point of water, frost will form. In fact, frost

will form even when the ambient temperature is above the freezing point of water,
if the temperature difference from the air to the wall is too large .
3.7 ALTERNATIVE HEAT EXCHANGER DESIGN
Till now described a frost-free heat exchange system that relied on keeping
the exterior wall temperature above the freezing point of water. The penalty for this
type of passive heat exchanger is that the ΔT which drives the heat transfer is
necessarily small. To account for this, very large surface areas are required to keep
the size of the heat exchanger reasonable; i.e., 45 finned tubes. An active frost-control
heat exchanger can exploit the large ΔT that occurs between the ambient atmosphere
and a cryogenic fluid to achieve a very compact unit.
A heat exchanger has been developed which uses rotating brushes for active
frost-control. As shown in Figure 3.10, this heat exchanger consists of several multi
pass tubes sandwiched between two sets of concentric rings. The cryogenic fluid
(either liquid or gas) flows through the tubing, running in cross flow with the ambient
air. The rings provide structural support for the tubing, as well as added heat transfer
area.
Threaded through the center of these rings is a shaft, to which are attached
two brushes. The brushes engage the tube/ring structure from either side and rotate,
driven by a motor (not pictured). As they rotate, accumulated frost is scraped free of
the heat transfer surfaces and eventually falls out the bottom of the unit. Each of these
tube/ring structures can serve as a stand-alone unit or they can be stacked together to
form a multi-element heat exchanger. The entire assembly is enclosed in a cylindrical
duct through which the air flows. For multi element designs, only one shaft is needed
to drive the brush assembly for the entire heat exchanger.

Figure 3.10: Heat exchanger employing active frost removal.
Joining of the tube/ring structure can be accomplished by spot welding or, for
larger assemblies, by dip brazing in molten salts. The result is a very rigid, yet light
weight structure which easy to manifold. A prototype active control heat exchanger
has been successfully fabricated and tested.

CHAPTER 4
RESULT ANALYSIS AND DISCUSSION
4.1 PRINCIPLE OF OPERATION
The principle of running the LN2000Car is similar to that of a steam engine,
except for the fact that there is no combustion process involved. Instead pressurized
liquid nitrogen at –320oF (-196oC) is used and then vaporized in a heat exchanger by
ambient air. This heat exchanger is like the radiator of a car but instead of using air to
cool water, it uses air to heat and boil liquid nitrogen. The resulting high pressure
nitrogen gas is fed to an engine that operates like a reciprocating steam engine,
converting pressure to mechanical power. The only exhaust is nitrogen, which is
major constituent of our atmosphere. The efficiency of LN2 car: It can travel 15 miles
on a full (48 gallons) of liquid nitrogen going 20 MPH. Its maximum speed is about
35MPH.
4.2 ANALYSIS OF COOLN2 CAR PERFORMANCE
A single-cylinder reciprocating expander running on compressed nitrogen gas
releasing exhaust gas into the atmosphere was considered. As compressed gas was
allowed to flow into the expander’s cylinder, isobaric work was done on the moving
piston by the nitrogen gas. The net isobaric expansion work done during a single
cycle is gauge pressure of the gas multiplied by the volume of the gas that flows into
the cylinder.
The isobaric specific energy is given by,
Wi = (Ph-Pi)V
 Ph-Pi is the difference in absolute pressure between inlet and exhaust (outlet)
gas.
 V -Volume occupied by the compressed gas/unit mass of gas
The inlet Exhaust Pressure ratio P=Ph /Pi
Then the equation become

Wi=Ph (1-P^-1) V/A
The isobaric specific energy become
Wi=R Th (1-P^-1)
 Th refers to the temperature of the high pressure inlet gas.
4.3 OPEN RANKINE CYCLE PROCESS
The processes considered are the expansion of nitrogen gas at 300K and 3.3
MPA to near atmospheric pressure. The first process considered is isothermal
expansion from 3.3 MPA to 120KPA and the work can be easily computed as
Wisothermal = rT ln (P2/P1)
r = 0.2968 (KJ/KgK) for nitrogen gas and T = 300K.
The result for Nitrogen is 291.59 KJ/Kg. Another limiting process is the simple
adiabatic expansion of the gas in which no heat is admitted during. the expansion. The
work is calculated as
Wadiabatic = KrT [1-(P2 / P1) K-1/K] (k-1)
Where T = 300K and K = 1.4, the ratio of specific heats for nitrogen.
The resulting Wadiabatic is 180KJ/Kg of Nitrogen exhausted at 150KPA.
4.4 CLOSED BRAYTON CYCLE
Figure 4.1:Closed brayton cycle cryogenic Heat engine

Operation of liquid-nitrogen fueled, regenerative, closed Brayton cycle, cryogenic
heat engine is illustrated. Taking into consideration the adiabatic expander and
compressor, the specific energy provided by the system is given by,
W = egμ (eewe-wc/ec) ……………….(1)
Here,
μ = AεL/Rt cold(pε-1)] ………….……(2) is the ratio of the working fluid mass
flow rate to the liquid nitrogen vaporization rate.
T coldis the temperature of the heat single.
P is the ratio of the absolute pressures on the high and low pressure sides.
L = liquid nitrogen’s latent heat of vaporization.
R = 8314 J/mol-K universal gas constant
ε = 1-1 /r ; r = working fluid’s ratio of specific heat capacities at constant
pressure and constant volume.
The ideal specific energy provided by an adiabatic expander is
We =RThot (1-p-ε)/[A.ε] ……….(3)
That = temperature of heat source
The ideal work done by an adiabatic compressor per unit mass of gas is
Wc = RTcold (Pε-1)(A.ε) …..…(4)
By combining equations we get
W = egL [eep-ε (Thot / Tcold) - (1/ec)] ……..(5)
The equation (5) considers the energy available from using liquid nitrogen as a
heat sink. The cold nitrogen gas that is produced by vaporizing liquid nitrogen can be
used a heat sink as well.

5 CONCLUSIONS
The cryogenic automobile is a potential contender in the ZEV market,
provided certain key technologies are demonstrated. One of these technologies is the
development of an all - weather heat exchange system. A heat exchanger that
works well in a If more & more of such kinds of vehicles (ZEV) are put into use, the
cleaner the air will becomes marching the society towards an healthier environment,
provided the liquefaction is driven by a non polluting energy source such as solar,
wind, tidal energy. In addition to the environmental impact of these vehicles,
refueling using current technology takes only a few minutes. As there is always a
scope of improvement in all the fields, the safety of the vehicle needs to be improved
from many points of view. Pressure relief valves need to be incorporated in all
apparatus subjected to cryogenic temperatures. Over-pressurization may arise due to
vaporization of nitrogen & the danger it poses to the surrounding is already explained,
making safety issues a major concern to focus upon. More information regarding the
safety concerns are given in various books on cryogenics.
6 SCOPE OF FUTURE WORK
6.1 FUTURE OF CRYOGENIC VEHICLES
There is research going on to design a more efficient motor that could achieve
top speeds of 60 m.p.h. and two to three miles per gallon in an optimally designed
vehicle. This would enable the LN2000, using a 100-gallon tank, to match the average
range for gas-powered vehicles of 250 miles between fill-ups. As large as the 100-
gallon tank sounds, it would still weigh less and take up less space than the batteries
used in electric cars. The liquid nitrogen vehicle also has the potential to be more
economical to operate than electric vehicles, according to the UW researchers.
Assuming a 10-cent-per-gallon price for mass-produced liquid nitrogen, they predict
the LN2000 would cost about 4 cents per mile to drive compared with an estimated 7
cents-per-mile cost of driving electric cars (including the cost of battery replacement
every two to three years Another advantage for liquid nitrogen cars is that they don't
require a new infrastructure for mass utilization. Today's filling stations can easily be
converted to dispense liquid nitrogen instead of gasoline. And users will be able to fill

up in minutes rather than the 4-6 hours required to fully recharge an electric car
battery. In the present scenario, the more such vehicles are used, the cleaner the air
will become. And an added advantage would be if the liquefaction process is driven
by non-polluting energy sources such as solar energy, wind energy, tidal energy. Even
if the liquid nitrogen manufacturing plant is powered by fossil fuels, the exhaust from
these plants would be trapped for use as the feedstock for the liquid nitrogen, so no
pollutants would be released into the atmosphere. In addition to the environmental
impact of these vehicles, refueling using current technology can take only a few
minutes, which is very similar to current gas refueling times.
6.2 THREATS FOR OTHERS
6.2.1 For electric cars
The cost of production of 1 gallon of liquid nitrogen costs approx about Rs. 2/-
(4 cents) whereas an electric car requires 7 cents. Refilling of the tank requires just
10-15 min, while an electric car requires an considerable amount. Extremely non
pollutant whereas, lead-acid batteries used in electric cars pose threats in increasing
metal pollution.
6.2.2 For hydrogen car
More over nitrogen is safer than hydrogen since this is less combustible than
hydrogen and the liquefaction process is simple rather than hydrogen. The engine
design is simple and the availability is more

7 REFERENCES
1. Dooley,J.L., and Hammond,R.P., “The Cryogenic Nitrogen Automotive
Engine”
2. Websites of the University of Washington and University of North Texas
3. Saunders, E.A.D., “Heat Exchangers :Selection Design and Construction”
4. “Liquid nitrogen vehicle” www.wikipedia.org/wiki/ Liquid nitrogen vehicle
5. C. Knowlen, A.T. Mattick, A.P. Bruckner and A. Hertzberg, "High
Efficiency Conversion Systems for Liquid Nitrogen Automobiles", Society of
Automotive Engineers Inc, 1988.
6. Cryogenic liquid nitrogen vehicles by K. J. Yoges, Sharvin Ghodekar
7. “The UW's Revolutionary, Liquid Nitrogen Automobile Could Put Electric
Cars Out in the Cold”, Greg Orwig
8. International Journal of Scientific and Research Publications | IJSRP
www.ijsrp.org
9. “Quasi Iso-thermal Expansion Engines for Liquid Nitrogen Automotive
Propulsion”, Williams, J.,Mattick, A.T. Deparis, H.,SAE 972649, 1997
10. Research paper on “Liquid Nitrogen as a Non-Polluting Vehicle Fuel” by
Mitty C. Plummer, Carlos A. Ordonez and Richard F. Reidy, university of
North Texas. The University of Washington’s Liquid Nitrogen Propelled
Automobile

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