The present invention relates to a solid-state
cooling/heating box. The box of this invention can be used
for storing and/or transporting medicine, drugs, vaccines or
other perishable goods. They can be used in medical and
health care centres for storing/transporting medicines, serum
and other diagnostic materials. It can also be used in
scientific research laboratories for storing desired
materials at prescribed temperature(s), as needed. It is
also useful for storing/transporting vaccine, semen and the
like, useful for animal husbandry. In addition, it can be
used for heating or cooling beverages.
In the overall concept of good health, preventive care has a
major role. From the curing of diseases the attention is now
shifting progressively toward ensuring that every individual
maintains a good health status, so that the quality of life
is improved, and such an approach is economical too. In order
to achieve this goal new methods of health care management
are being formulated. Administering vaccines to prevent
diseases in children is an important component of the
management system. Taking into account the incidence of
diseases and the state of the art in prevention emphasis is
generally on three vaccines : polio vaccine (oral form); the
combined Diphtheria/Pertussis/Tetanus (DPT) (injectable) and
the Measles/Mumps/Rubella vaccine (MMR) (injectable). These
vaccines are biological products and require storage at
prescribed low temperature(s) to maintain their
effectiveness .
In this context a term "Cold Chain" has come into usage. It
is a system of storage and transport of veiccines at low
temperature from the manufacturer to the actual site where
the vaccines are used. The polio vaccine particularly is
degraded if the low temperature conditions are not
maintained. The cold chain equipment usually consists of i)
Cold Box : for the storage and transport cf large quantities
of vaccine; (ii) Vaccine Carrier : to transport small
quantities of vaccine by vehicle, bicycle or even by hand
carrying. The latter equipment is significant in India where
mass health care must reach out to children in rural areas,
some of which cannot be approached by larger vehicles. The
health worker at times has to carry storage unit for the
vaccines. A vaccine carrier with low temperature being
maintained there within, is essential, particularly for the
polio vaccine.
Although several vaccine carriers have been made, so far none
adequately serves the need. Vacuum flasks with ice do not
work well. It is necessary to have a portable, light weight
refrigerator kind of device with a built-in energy source for
driving the system. The standard refrigerator built around a
rotary compressor cannot be effectively scaled down in size
nor can it provide the required efficiency. Thermoelectric
cooling has been proposed to solve the aforesaid problems,
and such proposal and its implementation in various forms
have been found to have considerable potential.
Thermoelectric cooling is based on the Pel:ier effect in
which when a current is passed around a circuit of different
materials, one junction gets heated while the other junction
is cooled. By reversing the direction of current flow the
heating aind cooling of the two junctions is mutually
interchanged.
Solid-state/thermoelectric coolers are small solid-state heat
pumps which transfer thermal energy in accordance with the
laws of thermodynamics. A heat pump comprises of a heat sink
and thermoelectric couples formed by p-and n- type
semiconductor materials sandwiched between ceramic plates.
The heat pump can cool, heat or stabilize temperature based
on the direction of flow of current. Thermoelectric heat
pumps perform the same cooling function as refrigerators
based on vapour compression freon or absorption systems. In
these systems, thermal energy is extracted from a region to
'hereby cool that region and this extracted thermal energy is
passed on to a heat sink region having a higher temperature.
Vapour-cycle devices need moving mechanical parts and a
working fluid for their operation. In contrast,
thermoelectric pumps are totally solid-state and do not have
any moving parts and also no working fluid is necessary.
Tnus, they are CFC-free. Although thermoelectric heat pumps
firive been known, their practical use has been possible only
recently due to the development of semiconductor thermocouple
ni-Ge), Galena
(PbS) {Mecon's earlier Patents No. 174526, 174527, 174528 &
174529} with some dopants could be used as the semiconducting
material.
Each of said first and second sinks may comprise finned heat
exchangers or flat metal plates or water circulating type
through tabes associated with pump(s). The temperature probe
can be located inside the box (e.g. : centre of box).
The spacer block can be mounted in said wall by means of a
mounting plate. The first sink can be attached to said
spacer block by means of an assembly of a spring, washers and
screws.
An epoxy seal is preferably provided between the
"hermoelectric module and the wall of the compartment.
The box and said lid and also the partition between the
compartments in case two or more compartments are provided
may be made of metal or plastic or any suitable material
Depending on the anticipated use; and of double walled
construction and the space between the walls filled with
polyurethane foam or any other good thermal insulating
material. A gasket can be provided in said box to sealingly
engage said lid. Latches are preferably provided on the box
to engage the lid in a secure manner.
The present invention has the following advantages :
- High performance with low power consumption;
- Provision of hot and cold switch for heating or cooling the
box; - Adjustable temperature controller (thermostatic
controller) to adjust maximum-minimum temperature;
Light weight & portable
Only one moving part, namely, 'the fan' which is located
outside the cooling/heating compartment
Environmentally friendly - No compressor
No CFC gas
- Operation in any orientation;
- Operation in Zero gravity;
- No acoustical noise;
- Maintenance-free
Trie invention will now be described with reference to
preferred embodiments shown in the accompanying drawings,
wherein :
Fig. 1 shows an isometric exploded view of the elements of a
ccoling/heating box according to the present invention;
Fig. 2 shows an isometric view of the box according to the
invention;
F.i.o.3 shows a single chamber box without the other elements
shown in Fig. 1;
Fig.4 shows a double chamber box without the elements shown
in Fig.l;
Figs. 5 and 6 show sectional views of the box of Fig.2; and
Fig.7 shows an isometric view of the spacer block.
Fig.8 is a typical circuit diagram for explaining the
operation of the temperature controller connected with the
particular embodiment of the solid state cooling/heating box
according to this invention.
The box according to the present invention can be used for
cooling or heating, depending on the direction of current
flow. In the following description, the system is described
in the cooling mode, i.e., for cooling the interior of the
box. When the box is used in the heating mode, the terms
'cold sink' and 'heat sink' are to be read as 'heat sink' and
'cold sink' respectively, which would be obvious to a person
skilled in the art.
In one embodiment of the present invention, shown in Figs. 1
to 3, the solid state cooling/heating box comprises a box [1]
provided with a lid [2]. The lid and the box are of double
walled construction made of suitable material, either
metallic or non-metallic and the space between the walls is
filled with thermal insulating material [13] such as
polyurethane foam. A sealing gasket [6] is provided on the
open top side of the box [1] and the lid sealingly engages
with the open top side of the box [1]. Latches [23] can be
provided on the box for tightly securing the lid to the box.
A cold sink [7] with one side exposed to the interior of the
box [1] is mounted on a wall of the box [1]. A partition made
of thermal insulating material [5] having an opening [9] is
provided in the wall of the box [1] adjacent to the cold sink
[7j. A thermo-electric module [11] is mounted on a spacer
block [10] which is in alignment with the opening [9] in the
partition [5]. A heat sink [8] is provided adjacent to the
thermo electric module [11] and is exposed to the outside of
the box through an opening [12] in one side of the box [1]. A
fan [14] is mounted directly to the heat sink [8] to provide
forced air convection to the heat sink [8] if and when
required. The fan can also be mounted separately (if & when
required).
As can be seen from Fig.2, the thermoelectric module and
spacer block [10] are mounted on a side wall of the box [1].
The use of a spacer block [10] ensures maximum heat transfer
while at the same time separating the heat sink side of the
system from the cold sink side of the system. The spacer
block [10] is mounted between the cold face of the
thermoelectric module [11] and the cold plate or cold side of
the cold sink [7]. The cold sink [7] which is preferably a
finned heat exchanger or a flat metal plate is separated from
the spacer block [10] and thermo-electric module [11] by the
heat insulating partition [5]. The heat sink [8] which is
also preferably a finned heat exchanger or a flat metal plate
is mounted on the other side of the thermo-electric module
[11] remote from the cold sink [7].
A thermostatic controller [15] is mounted on the outer side
of the wall of box [1]. This thermostatic controller [15] is
connected to the thermoelectric module [11], fan [14] and to
a DC power supply (not shown) which is connected to the
fan[14] and to the thermoelectric module [11] through wires.
If the box is built for reversible i.e. both heating and
cooling duties then a polarity reversing switch is interposed
between the DC power supply and the thermoelectric module. A
temperature probe (not shown) is connected to the
thermostatic controller. The probe is exposed to the interior
of the box [1]. On sensing the temperature inside the box [1]
as being less than a preset value, the probe activates the
thermostatic controller [15]. The thermostatic controller in
turn steps down the current when the temperature inside the
box reaches the desired temperature, and maintains it at that
temperature. When the temperature inside the box rises above
a preset value, the thermostatic controller steps up the
current until the interior of the box is again cooled to the
desired temperature.
The thermo-electric module is a solid-state noise-and
vibration-free semiconductor device. It comprises two ceramic
plates with silver-like semiconductor pellets sandwiched and
aligned between the two plates. These semiconductor pellets
are aligned electrically in series and thermally in parallel,
thereby making a series of 'P1 and 'N' junctions that create
cooling effect when electrons flow from the P junction to the
N junction. By reversing the direction of current to the
thermoelectric module, electrons can flow from the N junction
zc the P junction, thereby resulting in heating effect.
j
When a DC current is applied to the thermo-electric module
[11], heat from the cold sink [7] is absorbed on the cold-
side ceramic plate of the module, passes through the
semiconductor pellets and is dissipated to the hot side
ceramic plate. The heat sink [8] is attached to the hot side
ceramic plate. As a result heat is dissipated from the
thermoelectric module [11] to the heat sink [8] and from the
hot side of the heat sink to the surrounding environment
through the opening [12] in the box [1].
It is preferable to apply a heat-conducting paste or thermal
grease to the interfaces between cold sink [7] & spacer block
[10], spacer block [10] & the thermoelectric module [11], and
also thermo-electric module [11] & the heat sink [8] to
minimize thermal resistance. A fan [14] is sometimes required
on the hot side of the heat sink. It can be mounted directly
to the heat sink or can be provided separately depending upon
the configuration of fan. It provides convection air to
dissipate heat on the hot side of the heat sink. Under
certain conditions, free convection may provide adequate
cooling of the heat sink and the fan may not be required.
The thermo-electric module [11] is assembled between the heat
sink [8] and the cold sink [7], preferably with a heat
insulating seal between the two sinks. The partition [5]
(Fig.l) and thermal insulation [17] (Fig.5) serve this
purpose. Since the element matrix within t.ie thermoelectric
module [11] is an open DC circuit, and a temperature gradient
is often present, care should be taken to minimize gas flow
which may contain water that can condense. The thermal
insulating partition [5] is a part of a series of matching
components designed to work together as a complete
thermoelectric system. It is provided by inserting sections
of closed cell foam about the cavity and sealing with a non-
corrosive sealant material or an epoxy coating.
From Figs. 5 and 6, it can be seen that in a wall [16] of the
box [1], che spacer block [10] is fitted with a closed cell
thermal insulation [17] on a mounting plate "18]. The cold
sink [7] is fitted in the interior of the box [1] to one side
of the spacer block by means of an assembly comprising of
washers, spring and screws as indicated at [19]. To the other
side of the spacer block [10] is fitted the thermoelectric
module [11]. The thermoelectric module [11] is sealed to the
vail [16] by means of an epoxy seal [20]. Heat sink [8] is
attached to the thermoelectric module [11]. A fan [14] is
provided for providing convention air current to cool the hot
.' ide of the heat sink.
f ig.4 shows an alternative embodiment having two compartments
[,'i] and [4] formed by a partition [22] provided within the
boX [1]. In compartment [3], the cold sink [7] of Fig.l is
exposed to the interior of the compartment while heat sink
is of Fig.l is exposed to the exterior of the box [1].
Similariy, in compartment [4], cold sink [7] is exposed to
the interior of the compartment [4] while heat sink is
exposed to the exterior of the box [1]. The arrangement in
the two compartments is thus mirror image of one another and
the arrangement in each compartment is same as that described
with reference to Figs. 1 to 3. Obviously, the two
compartments of box [1] of Fig.4 can be used for storing
different materials at different temperatures.
In both the embodiments, suitable latches [23] (Fig.2) are
provided for keeping the lid [2] in tight sealing
relationship with the box [1]. It would be obvious to a
person skilled in the art to realize that more than two
compartments with similar arrangements can be provided in box
[ 1J •
When the thermostatic controller [15] is activated by the
probe, the cold sink in the interior of the box gets cooled
and through natural convection the air in the interior of the
dox [1] flows over the cold sink [7] and the cold sink
functions just like an evaporator coil in a conventional
(Freon) air conditioner. Passage of cold air to the cold sink
is continued until the interior of the box is. cooled to the
desired temperature. Concurrently with the above the heat
generated on the hot side of the thermoelectric module [11]
passes to the heat sink [8] where the heat is expelled to the
atmosphere outside of the box. Fan [14] may te required to
cool the hot side of the heat sink if cooling of the heat
sink by natural convection is not adequate.
When the desired temperature is reached in any compartment,

the thermostatic controller of that compartment reduces current supplied to the
thermoelectric module of that compartment until the inside
temperature again goes above the desired temperature. When
the temperature inside the box rises, the thermostatic
controller is activated to bring the inside temperature of
that compartment back to the desired temperature.
Similarly, when the articles/materials are required to be
stored hot, the direction of current is reversed so that the
cold sink [7] functions as the heat sink while the heat sink
[8] functions as the cold sink.
The main objective of the circuit shown in figure 8 is to
control the load current (Two stages) with respect to change
of temperature as measured by the "sensor". When the box is
being used as a cooling box, full load current is applied if
the "sensor" indicates a temperature higher than the upper
limit of the specified (temperature) control band. Because
of cooling effect, the temperature is reduced. When the
"sensor" indicates the temperature to be less than or equal
to the lower limit of the specified temperature band, the
applied current is reduced to a lower value which is
preselected at some value between 33%-50% of the full load
current. However, direct supply is available for operation
of D.C. cooling fan.
When the cooling box is initially connected to the power
supply the temperature "sensor", as shown in the circuit
diagram of Fig.8, will indicate a temperature higher than
the upper limit of the control band. Under this condition
the relay RL is energized and full current is applied to the
thermoelectric module. As a result of thermoelectric cooling
the temperature inside the box begins to reduce.
When cooling box temperature is decreasing, then sensor
resistance value is increasing. When the temperature reduces
to a value less than the lower limit of the control band, the
sensor resistance value reduces to a level such that the
reference voltage at an operational amplifier ICI(A)
decreases. The output of amplifier ICI(A) serves as input to
another amplifier ICI(B), which is a comparator to compare
the output of ICI(A) against a fixed voltage reference which
is derived from the high regulated 5V DC power supply through
a voltage divider network as shown. The output of the
amplifier ICI(B) is set at its positive saturation voltage if
the output of the amplifier ICI(A) is greater than the fixed
voltage reference and set at its negative saturation voltage
if the output of the amplifier ICI(A) is less than the fixed
voltage reference.
The output of the amplifier ICI(B) is input to an amplifier
ICI(C) which is a level setting amplifier. This is used for
fine adjustment of the voltage at the output of ICI(C)
corresponding to some voltage at its input.
The output of the amplifier ICI(C) is input to another
amplifier ICI(D, which is a voltage amplifier that amplifies
the output voltage of the amplifier ICI(C). The output of
the amplifier ICI(D) is applied to transistors Ql and Q2,
which serve as high gain current amplifier that boosts the
current to a level required to energize the relay and serves
as a driver for the relay (RL).
When the reference voltage at the amplifier ICI(A) reduces to
a value corresponding to the lower limit of the temperature
control zone, the output of the amplifier ICI(D) reduces to a
level that causes transistor Q2 to switch off. This results
in the relay RL becoming de-energized and the current applied
to the LOAD (i.e. thermoelectric module) is reduced to the
lower value.
Operational amplifier ICI(A) is high input instrumentation
amplifier to sense the change of sensor output and,
accordingly, provides a variable stable voltage output.
Operational amplifier ICI(B) is a comparator to measure the
change of voltage output of ICI(A) with respect to a fixed
high stable reference voltage. The amplifier ICI(B) is also
having an active feedback loop to provide a high stability of
the comparator.
Operational amplifier ICI(C) is a level setting amplifier,
whereas operational amplifier ICI(D) is a voltage amplifier
to drive the transistor.
Transistors Ql, Q2 comprise a high gain current amplifier to
drive the relay RL.
The contact of the relay RL is being used for change over the
load current. The entire circuit is driven by regulated
power supply with 5 volts DC.

9. RL (Relay) imported - Electronic PCB mounting Relay 12
volts/10 amp/200R/S/C.
(Electromagnetic).
10. Sensor - NTC Type imported (Thermistor) 1KR
As can be seen from the preceding description, a portable
refrigerator is realised. It can be used for
storing/transporting vaccines. The system is effective in
both dry and humid summer seasons as well e.s in cold season.
The system can be operated through electrical mains power
using rectifier system and also be operated by means of
external batteries. Suitable electronic charging system can
be provided for charging the batteries with the help of
automobile dynamo.
The cooling/heating box of the present invention has the
following special features :
a) CFC free - so environment friendly;
b) No compressor - so noise and vibration - free;
c) Rugged and reliable design;
d) Easy handling;
e) Tight sealing lid for better efficiency; and
f) It can be used as a cooling box as well as a hot box.
Although the invention has been described with reference to
preferred embodiments, it is not limited to these
embodiments. The invention extends to all embodiments of the
invention as claimed.
WE CLAIM :
1. A solid state cooling/heating box comprising :
a box [1] provided with a lid [2] and at least one
compartment inside the box;
a first sink [7] provided in the interior of said
compartment and mounted on a wall of said compartment
forming an exterior wall of said box, one of the sides of
the first sink being exposed to the interior of the
compartment;
at least one spacer block [10] having one face attached to
the other side of said first sink [7], with heat
conducting paste, said spacer block being mounted in said
wall;
at least one thermoelectric module [11] having one side
attached to the other face of said spacer block with heat
conducting paste and another side attached to one side of
a second sink [8] with heat conducting paste mounted in
said wall, the other side of said second sink being
exposed to the exterior of said box; and a d.c. power
supply connected to said thermoelectric module [11] for
providing electrical energy to said thermoelectric module
[11], to a temperature probe exposed to the interior
of said compartment through a thermostatic controller (15) mounted on the exterior
wall of said box.
2. A solid-state cooling/heating box as claimed in claim 1,
wherein :
said box has more than one compartments [3, 4] each having a wall forming an exterior
wall of the box;
a said first sink [7] being mounted in the interior of
respective compartment on the side wall of the
compartment;
said first sink having said one side exposed to the
interior of the respective compartment and said other
side attached to said one face of a said respective
spacer block [10] with heat conducting paste mounted in
said respective wall;
a respective said thermoelectric module [11] having said
one side attached to the other face of the respective
spacer block [10] with heat conducting paste and said
other side attached to said one side of respective second
sink [8] with heat conducting paste, the other side of
said respective second sink being exposed to the exterior
of said box;
a respective said thermostatic controller [15] being
mounted on the exterior of said wall of the respective
compartment and connected to a respective thermoelectric
module [11] and to a respective temperature probe exposed
to the interior of the respective compartment; and
said d.c. power supply being connected to each
thermoelectric module [11] temperature probe and fan [14]
separate
through£_thermostatic controllers [15] .
3. A solid-state cooling/heating box as claimed in claim 1
or 2, wherein a fan [14] is provided for directing a
convection air current over said second side of said
second sink [8], said fan being connected to said d.c.
power supply and to the thermostatic controller.
4. A solid-state cooling/heating box as claimed in claim 3,
wherein said fan is mounted on said second sink.
5. A solid-state cooling/heating box as claimed in any of
claims 1 to 4, wherein said thermoelectric module
comprises a pair of ceramic plates between which silver-
like semiconductor pellets are sandwiched, said pellets
being aligned electrically in series sometime series and
parallel and thermally in parallel, to provide a series
of 'P' and 'N' junctions when a current is passed through
the circuit.
6. A solid-state cooling/heating box as claimed in any of
claims 1 to 5, wherein each of said first and second
sinks comprises finned heat exchangers or flat metal
plates or liquid circulating through tubes
associated with pump(s).
7. A solid-state cooling/heating box as claimed in any of
claims 1 to 6, wherein said temperature probe is located
inside box [1] as for example centre of the box.
8. A solid-state cooling/heating box as claimed in any of
claims 1 to 7, wherein said box and said lid are made of
steel or other suitable material in double walled
construction with the space between walls filled with
thermal insulating material such as polyurethane foam
[13].
9. A solid-state cooling/heating box as claimed in any of
claims 1 to 8, wherein a sealing gasket [6] is provided
on said box [1] to sealingly engage said lid.
10. A solid-state cooling/heating box as claimed in any of
claims 1 to 9, wherein latches are provided on the box to
engage the lid in a securely tight manner.
11. A solid-state cooling/heating box as claimed in any of
claims 1 to 10, wherein said spacer block [10] is mounted
in said wall by means of a mounting plate [18].
12. A solid-state cooling/heating box as claimed in any of
claims 1 to 11, wherein said first sink [7] is attached
to said spacer block [10] by means of an assembly [19] of
a spring, washers and screws.
13. A solid-state cooling/heating box as claimed in any of
claims 1 to 12, wherein an epoxy insulating seal [20] is
provided between the thermoelectric module [11] and the
wall [16] of the compartment.
14. A solid-state cooling/heating box as claimed in any of
claims 1 to 13, wherein a heat-conducting paste or
thermal grease is applied at the interface between said
thermoelectric module and the second sink, thermoelectric
module and one side of spacer block, first sink and other
side of spacer block.
15. A solid-state cooling/heating box substantially as herein
described, particularly with reference to the
accompanying drawings.

A solid state cooling/heating box comprising :
a box [1] provided with a lid [2] and at least one
compartment inside the box; a first sink [7] provided in the
interior of said compartment and mounted on a wall of said
compartment forming an exterior wall of said box, one of the
sides of the first sink being exposed to the interior of the
compartment; at least one spacer block [10] having one face
attached to the other side of said first sink [7], with heat
conducting paste, said spacer block being mounted in said
wall; at least one thermoelectric module [11] having one side
attached to the other face of said spacer block with heat
conducting paste and another side attached to one side of a
second sink: [8] with heat conducting paste mounted in said
wall, the other side of said second sink being exposed to the
exterior of said box; and a d.c. power supply connected to
said thermoelectric module [11] for providing electrical
energy to said thermoelectric module [11], and to a
temperature probe exposed to the interior of said
compartment.