Heat exchanger with helically coiled conduct in casing

A compact highly efficient heat exchanger is used to utilize waste heat from a motor vehicle engine cooling system to heat a source of water for use with a shower or the like in a recreational environment. The heat exchanger comprises a hollow cylinder having a cylindrical wall to define an annular space therebetween. Within the annular space is located a neatly fitting helical tubular coil with spaced helixes to define a helical pathway between adjacent coil helixes working fluid passes through the tubular coil and process fluid passes through the helical pathway to effect heat exchange between the working and process fluids.

This invention is concerned with an improved heat exchanger for fluids and 
in particular to a compact unit designed to accommodate relatively low 
volumes of fluid at relatively low temperatures. 
Most heat exchangers are designed on the basis of: 
the temperature of the working fluid; 
the desired temperature of the process fluid; 
the relative volumes of the process and working fluids; and, 
a relative volumetric flow rates of the process and working fluids. 
In the context of the present invention "working fluid" means that fluid 
which is utilized to heat or cool a "process fluid" in order that the 
"process fluid" may be used for a particular process. For example, in a 
motor vehicle engine cooling system, air passing through the radiator is 
the working fluid and the recirculating liquid coolant is the process 
fluid, used to cool the motor vehicle engine. 
There are many parameters and variables to consider in the design of a heat 
exchange device and this results in widely differing shapes, sizes and 
constructional features if efficiency is to be optimized. Such heat 
exchange devices may vary from a simple conductive tubular metal coil 
located within a container of fluid (such as that described in my 
copending application No. 88767/82) to a highly complex plate or tube type 
heat exchanger of the type employed in many chemical industries. 
It is an aim of the present invention to provide a compact but relatively 
efficient heat exchanger operable for relatively low temperatures and low 
pressure and flow rates. 
According to the invention there is provided a heat exchanger comprising: 
an elongate hollow jacket having an outer wall, an inner wall spaced from 
said outer wall and end walls defining an annular interior space 
therewithin; 
a substantially helical tubular coil located within said annular interior 
space, said tubular coil having an axially outer surface adjacent an inner 
surface of said outer wall and an axially inner surface adjacent an outer 
surface of said inner wall to define a substantially helical pathway 
between adjacent helixes of said coil, 
inlet and outlet ports communicating with the interior of said tubular 
coil; and 
inlet and outlet ports communicating with said helical space. 
The respective inlet and outlet ports may be located towards the opposed 
ends of the jacket and may be located in the jacket wall, but preferably 
in the opposed end walls of the jacket. Alternatively one or more ports 
may be located in the jacket wall and/or one or more may be located in the 
or each end wall of the jacket. 
Most preferably the inlet and outlet ports are located in the opposed 
jacket end walls. 
The hollow jacket may be of any suitable cross sectional shape but 
preferably it is circular thus defining a cylindrical jacket wall. 
The hollow jacket may be formed from any suitable material by any suitable 
means and is preferably capable of withstanding heat and internal 
pressurization. 
The jacket is suitably formed by a pressure moulding process such as die 
casting with zinc or a suitable metal alloy or by injection moulding with 
a plastics material such as polypropylene, nylon, polycarbonate, polyester 
or like polymeric materials, copolymeric plastics, the plastics material 
preferably including a fibrous reinforcing material such as glass fibres. 
The jacket may be formed with a body portion and one or more separate end 
walls but most preferably is formed from a pair of substantially identical 
portions each having a cylindrical wall and an integrally formed end wall. 
The helical tubular coil is suitably comprised of a heat conductive 
material such as copper or aluminium and it may have a smooth or finned 
inner and/or outer surface.

In FIG. 1 the device comprises an annular cylindrical jacket 1 having an 
inner wall 2 and an outer wall 3 defining therebetween an annular space 4. 
Located within annular space 4 is a helical coil 5 fabricated from copper 
tubing. The diameter of the copper tubing is chosen to be a neat fit 
within the annular space 4 to define a helical space or pathway 6 between 
adjacent helixes of the coil 5. Opposed ends 7,8 of the copper coil 
protrude through the end walls 9,10 of the jacket 1 and are sealed in 
fluid tight engagement therewith in any suitable manner. 
A particular preferred manner of sealing is illustrated wherein the ends 
7,8 of the coil protrude through screw threaded sockets 11,12 formed in 
the end walls 9,10 respectively. Screw threaded spigots 13,14 in sockets 
11,12 to clamp therebetween an "o" ring 15 of rubber, plastics or the like 
to form a fluid tight seal between the outer wall of the tube and the 
socket and spigot assembly. 
Similar spigot assemblies 17,18 are provided in sockets 11a,12a to 
communicate with the helical pathway 6. If required spigots 17,18 may be 
formed integrally with the end walls 9,10 and any one or all of the 
spigots 13,14 and 17,18 may include barbed flanges 19 as shown on spigots 
17,18 to enable attachment of a flexible hose by means of a hose clamp or 
the like or they may include a threaded connection 19a as shown on spigots 
13,14. 
The jacket 1 is preferably formed from injection moulded plastics and may 
be formed from two substantially identical mouldings connected at the mid 
point of the jacket by bolted or screwed flanges 20. Alternatively and/or 
in addition the walls 2 and 3 may be formed with complementary ramped 
surfaces 2a,3a which may be glued or welded to ensure a fluid tight seal 
therebetween. 
The jacket 1 may have formed integrally therewith a suitable mounting 
bracket 21 if required. 
It will be seen that the present invention provides a simple and 
inexpensive form of heat exchanger which facilitates a particularly easy 
assembly. After formation of the coil on a suitable mandrel or the like 
the mating jacket halves are simply pushed together over the coil with the 
free ends of the coil protruding through the spigots 13,14. The flanges 19 
and complementary ramped surfaces, 2a,3a are pre-glued and the assembly is 
firmly clamped together by bolts screws or rivets through the mating 
flanges 20. 
When assembled, inner walls 2 and end walls 9,10 define a hollow space 22 
within the central region of the jacket 1. 
FIG. 2 illustrates an alternative embodiment of the device shown in FIG. 1. 
The jacket 1 comprises a hollow cylindrical body having an outer wall 3 and 
end walls 9,10. The jacket is comprised of a pair of substantially 
identical mouldings joined at flanges 20 by a plurality of nuts and bolts 
spaced around the flanges 20. A fluid tight seal is effected between the 
flanges 20 by a resilient rubber or plastics "o" ring 23 clamped 
therebetween. 
Within jacket 1 is located a helically wound tubular highly thermally 
conductive copper coil 5 which is wound about a hollow highly thermally 
conductive copper tube 24 closed at both ends 25. In a similar fashion to 
the embodiment of FIG. 1 the copper coil 5 is a neat sliding fit between 
the inner surface of wall 3 and the outer surface 2 of tube 24 to define a 
helical pathway between adjacent helixes of coil 5. 
The opposed free ends 7,8 of coil 5 are sealingly engaged in spigots 13,14 
respectively located in screw threaded sockets 11,12 and fluid tight 
sealing is effected by a rubber or plastics "o" ring 15 clamped between 
the ends of the spigots, their respective sockets and a respective end of 
coil 5. 
Additional spigots 17,18 located in respective screw threaded sockets 11a, 
11b communicate with a plenum 26 at each end of the hollow interior of 
jacket 1 between end walls 9,10 and a respective adjacent closed end 25 of 
tube 24. Each plenum 26 communicates with the opposed ends of the helical 
pathway a formed between adjacent helixes of coil 5. 
The spigots 13,13a and 14,14a may have threaded connections 19a as shown on 
spigots 13,14 or barbed hose connections 19 as shown on spigots 13a,14a. 
On the exterior of jacket 1, integrally formed mounting brackets 21 are 
provided for attachment of the heat exchanger to a suitable mounting 
surface. Preferably the heat exchanger is mountable within the engine 
compartment of a motor vehicle. 
In use, the threaded spigots 13,14 are connected into the cooling fluid 
circuit of a motor vehicle. This connection may be effected by severing a 
hose in the vehicle heater circuit and connecting to the free ends of the 
hose mating threaded socket fittings for connection to the threaded 
spigots 19a. 
Flexible hoses may then be connected to the barbed spigots 17,18. One of 
the flexible hoses is connected to a source of fluid e.g. water to be 
heated. The source may take the form of a container of water or the hose 
may be connected to a reticulated supply of water under pressure such as a 
faucet in a recreational vehicle park. 
The other hose may be connected to a shower hose or other suitable fitting 
to control the flow of water. 
The vehicle engine is started and the engine coolant is recirculated 
through coil 5. The source of water to be heated is allowed to pass 
through the helical passage 6, preferably in a countercurrent direction, 
whereupon the water is heated for use in a shower, for washing clothes, 
dishes, etc. 
The temperature of the heated water may be regulated by adjusting the 
idling speed of the vehicle. engine and/or by adjusting the flow rate 
through passage 6. Flow rate may be conveniently controlled by a valve 
associated with the inlet or outlet hose. 
The working fluid i.e. engine coolant, may be circulated via passage 6 but 
preferably is circulated via coil 5 as the working fluid pressures are 
likely to be considerably higher than the process fluid i.e. water being 
heated. 
By means of this construction the copper coil is capable of utilizing a 
working fluid at relatively high temperatures and pressures in conjunction 
with a process fluid at relatively low temperatures and pressures. 
The device according to the present invention is particularly suitable for 
utilizing waste motor vehicle engine heat by using the recirculating 
coolant as a working fluid at temperatures between say 40 degrees 
centigrade to 120 degrees centigrade and at pressures between 5 psi and 15 
psi. 
To demonstrate the efficacy of the heat exchange device according to the 
invention and the following tables show performance criteria using 
different motor vehicle engines operating different speed ranges and 
utilizing differing process fluid flow rates. 
EXAMPLE 1 
TABLE 1 
______________________________________ 
Process Process 
Process Fluid Fluid 
Fluid Inlet Temp. 
Outlet Temperature 
Engine 
Flow Rate Deg. Temp. Deg. 
Rise 
RPM Liter/min. 
Centgrd. Centgrd. Deg. Centgrd. 
______________________________________ 
500 3 28.5 53 24.5 
500 6 28.5 42 17.5 
1500 1.5 28.5 71 42.5 
1500 3 28.5 63 34.5 
1500 6 28.5 49 20.5 
______________________________________ 
EXAMPLE 2 
TABLE 2 
______________________________________ 
Process Process 
Process Fluid Fluid 
Fluid Inlet Temp. 
Outlet Temperature 
Engine 
Flow Rate Deg. Temp. Deg. 
Rise 
RPM Liter/min. 
Centgrd. Centgrd. Deg. Centgrd. 
______________________________________ 
750 1.5 28.5 70 41.5 
750 3 28.5 58.5 30.0 
750 6 28.5 48 19.5 
1500 1.5 28.5 77 48.5 
1500 3 28.5 66 37.5 
1500 6 28.5 55 26.5 
______________________________________ 
In both Examples 1 and 2 the same heat exchange device was employed. 
The heat exchanger employed in the examples possessed the general 
configuration as illustrated in FIG. 2 having the following relevant 
dimensions: 
Jacket: 
Internal length: 23.8 cm 
Internal diameter: 6.8 cm 
Copper Coil: 
Length: 238 cm 
Diameter: 3/8 inch (nominal O.D.) 
Wall Thickness: 18 gauge 
Internal Cylinder: 
Diameter: 4.8 cm 
Length: 20.5 cm 
Upon assembly all joints in the jacket including the threaded connections 
between the spigots and the body were coated with a curable epoxy resin 
composition to ensure a fluid tight connection. 
The device may include a flow control means whereby the temperature of the 
process fluid is governed by its rate of flow through the heat exchange 
device. For greatest efficiency the working fluid flows countercurrent 
relative to the process fluid. 
In a further embodiment of the invention the apparatus may have associated 
therewith an electric pump or the like to pump the process fluid 
therethrough. The pump may be separate or formed integrally with the 
device and may be attached at one end of the jacket or located within the 
central aperture 22 of the annular jacket in FIG. 1. 
It will be readily apparent to a skilled addressee that many variations and 
modifications to the present invention will be possible without departing 
from the spirit and scope thereof.