New Project 2015
General problem description
The problem we will work on will be an assessment of the relative values of both existing transport
refrigeration systems and a new system. The systems to be assessed are:
1. Standard mechanical systems (Diesel/HCFC)-Thermo-king and Carrier systems for Tractor trailer
and trucks
2. Liquid Nitrogen Systems (LIN)-Direct and indirect systems
3. Liquid Natural Gas Systems for Tractor trailer and trucks operating in conjuction with each of the
above
The values to be assessed are:



Economic
Efficiency
Carbon reduction
Use system referred to in (1) above as the basis for comparison.
Operating conditions









In all cases LNG is used to operate the vehicle.
Refrigerated produce (fruit) maintained at 380F.
Ambient temperature 800F
Vehicle walls and floor preconditioned to 380F at start up
Produce at 380F at start up
Cargo stored on standard wooden pallets 3 ½ x 4 (each pallet is stacked with 3’ of cargo and
stacked 2 high)
Truck size 18lx82
Trailer size 48lx82
Three trip conditions
o Trip one - 400 miles with one stop for refueling (engine off and door closed) for tractortrailer. All cargo unloaded at final stop.
o Trip two -80 miles with 4 stops 45 minutes (engine off and rear door open) for tractortrailer. 25% of cargo unloaded at each stop.
o Trip three - 80 miles with 4 stops 45 minutes (engine off and rear door open) for truck. 25%
of cargo unloaded at each stop.
Functional description of each system
Mechanical system
Select a system as described by one of the above manufacturers; one for a tractor trailer and one for a
truck. The mechanical system will operate in following manner:


Mechanical system alone - System operates continually
Mechanical system with LNG system – operating with engine on.
LIN systems
Consider an indirect system – LIN in liquid state passing over cold plate. Fans circulating air across plate
and then throughout the cargo volume
Consider a direct system – LIN in liquid state injected directly into the cargo area.


Each system will operate continually when required
LIN system in line with LNG system. LNG system will be prime. LIN will operate only when
engine off or when LNG system cannot cool adequately.
LNG system
LNG is prime with engine on in all cases when configured for cooling.
Attachment 1
Attached is description of the LNG cooled tractor trailer system. A key feature is the
two heat exchanger cooling system.
 Liquid natural gas (LNG) to Glycol (salt solution) heat exchanger. Glycol freezes
at -32C.
 Piping from heat exchanger over a fluid connector (must be specified and put in
place) for glycol transfer into trailer interior. Select pipe insulation which will
maintain minimum temperature losses over distance. Trailer is 53 feet long.
Interior heat exchanger (glycol to air) would be placed in center ceiling of
container (approximately 35 feet from front.
 Assume electric pump will circulate glycol through system when system on.
 Mechanical system will be standard Carrier trailer system. Again look at
catalogue specifications.
 Assume there will be a sharing as there was in last year’s project.
 Assume trailer container meets insulation specifications for refrigerated product
K>=4
 Assume cost of system $8,000. Operating costs $0 (no fuel; no service).
 Mechanical system cost $20,000, diesel consumption 8 l/hr;maintenance and
service about $5,000 per year
Attachment 2
Assumption
Impact
Reasoning
For the first driving phase, the truck’s
cargo is cooled entirely by the LNG
system (if supported by calculation
later)
The mechanical system
energy requirements
only begin after the door
is first opened; a
significant amount of
energy is saved
The truck is assumed to
be pre-cooled as it is,
and the LNG
consumption is only
given
The mechanical system begins
cooling only after the temperature
has fallen out of spec after the first
stop 38 OF for the fridge)
Minimize energy
consumption via the
mechanical system
More realistic
application of the
mechanical system.
Also, the fact that it will
minimize energy
consumption was a
reason in making this
assumption
Assumption
Impact
Reasoning
The cargo was pre-cooled to the
specified temperatures 38 OF for the
fridge)
Simplifies the process
and minimizes energy
requirements of the
mechanical system
Instructions per
sponsor
LNG is always on when truck is
running
Minimizes energy
requirements of the
mechanical system
Maximizes use of the
LNG system (whose
sole purpose is to
reduce the use of the
mechanical system)
Both mechanical heat exchangers
have constant cooling loads equal to
the maximum ambient heat
experienced by each compartment
with the door closed. The ambient
heat was calculated based on full
exposure to ambient on each
compartment except for the partition,
which bleeds heat into the freezer.
Calculated heat gains for
compartment is 1135 W (based on
26K difference) for the fridge
Simplifies the
calculations made for
transient air
temperature within the
freezer.
With these values the
mechanical system
should be barely able to
sustain the specified
temperatures and thus
require more use of the
LNG system
Walls maintain constant temperature
(within each compartment
Simplifies the
process/reduces
calculations
Instructions per
sponsor
Pallets are 40” x 48”
Volume occupation of
the produce within the
trailer
Standard size of pallets
Pallets are pushed against the wall
farthest from the trailer door and
span the length of the compartment
Simplifies area
exposure for
temperature
calculations
Instructions per
sponsor
The temperatures of the cargo are
non-changing
Simplifies heat profiles
With the heat capacities
being at least 3 times
that of air, we assume
the temperature of each
cargo will not change
drastically
Assumption
Impact
Reasoning
The fridge air temperature remains
constant (assuming our controller for
the LNG can ensure this)
Simplifies term
dependence
From calculations so
far, the temperature of
the fridge will not
change drastically from
the opening and closing
of the door
pallets are removed instantaneously
(fork lifts)
Removes transient
calculations
Instructions per
sponsor
All heat exchangers within the trailer
are 100% efficient
Simplification
Expectations are that
the heat exchangers
should not vary greatly
from 100% /
instructions per sponsor
Start-up after each stop is ignored;
the glycol flow initiation is
instantaneous
Removes transient
calculations
Assumption that the
transient time of
operation will be
insignificantly small
relative to the overall
operation time
Opening and closing the door is
instantaneous
Removes transient
calculations
Again, assumption that
the time to open and
close the door are small
relative to overall
operation
The fridge door is perfectly sealed in
that they possess the same
insulation as the rest of the trailer
when closed
Simplifies the ambient
heat gain
Assumption that
existent leaks will be
relatively insignificant
When the door is opened, the extra
heat transfer is treated as solely
conduction; the “thickness” of the air
boundary layer is 0.051m (2”)
Affects temperature
gain of the freezer air
Instructions per
sponsor / two inches
was arbitrarily seen as
reasonable in the
thickness of the rest of
the trailer walls, so the
same thickness was
applied here
Average speed of travel is 55 mph
for long trip 30 mph for short trip
Fuel consumption of
LNG
Made based on
highway speeds with
many stops (stoplights,
stop signs, turns, etc.)
Attachment 3-European performance test for Direct Injection LIN


 Calculations for: K  0.4 W / m 2  deg , temperature in trailer
Tin  20 C , outside temperature Tout  30 C , trailer total surface
area F  155 m 2 .

 The heat influx into trailer through its heat insulation is:
Qin  K  F  T  0.4 155  50  3100 W .
 The heat influx to liquid nitrogen in the pipe, supplying it into trailer,
is: Qtu = 133 W.
 So, the total heat, which is to be absorbed by our system, is:
Q  Qin  Qtu  3100 W  133 W  3233 W .
 1 gram of liquid nitrogen absorbs during vaporization q 1  190 J ; 1
gram of generated vapor, under condition that it is heated in trailer
to temperature by 10 degree less than Tin , absorbs q2  174 J . So 1
gram of liquid nitrogen absorbs totally in the trailer
q  q1  q2  190  174  364 J .
 The total liquid nitrogen consumption is:
G  Q / q  3233 / 364  8.88 g / s  32 kg / hour .
 The following table shows time of operation of different systems
depending on the amount of liquid nitrogen stored in the system
vessel (or vessels):

Volume of nitrogen, l 650 1000 1300
Mass of nitrogen, kg 520
800
1040
Time of operation, h
25
32
16

 These results were obtained under condition, that heat influx into
trailer from its surrounding, during filling the system vessels with
liquid nitrogen, was taken into account.
 And we remind that consumption of liquid nitrogen is equal to 32
kg/h.



 Calculations for: K  0.36 W / m 2  deg , the other of initial data
being the same.
 This time the table of results is as follows:

Volume of nitrogen, l 650 1000 1300
Mass of nitrogen, kg 520
800
1040
Time of operation, h
27
35
17

 The consumption of liquid nitrogen this time is equal to 29 kg/h.

Attachment 4 LNG Truck configuration with mechanical system
Attachment 5 LNG Truck configuration with LIN system
Attachment 6 LNG tractor-trailer configuration with mechanical system