AU2004212549A1 - Improved (shower drain) heat exchanger - Google Patents

Description

COMPLETE SPECIFICATION STANDARD PATENT IMPROVED (SHOWER DRAIN) HEAT EXCHANGER.

The following statement is a full description of this invention, including the best method of performing it known to me.

IMPROVED (SHOWER DRAIN) HEAT EXCHANGER This invention relates to improvements in devices for heat exchange between two fluid streams.

This invention is a type of helical coil heat exchanger. A particular application is that of recovering waste energy from a shower drain and using that energy to pre-heat the cold feed water to the shower or hot water system. Existing heat exchangers have limitations in this application and there is a need for an improved device as energy demand and costs rise. This invention provides the public with a useful choice.

A shower drain heat exchanger was developed by Vasile, et al., United States patent 4,619,311, October 28, 1986. This device consisted of a large copper pipe around which is wrapped small diameter copper pipe. It can only be used in the vertical position as it relies on the waste water from the shower flowing down the inside of the large copper tube as a spread out, thin film. The cold feed water flows upwards in a counter flow arrangement through the external small diameter copper pipe. The small diameter copper pipe has only point contact with the outside of the copper tube. Heat flow is restricted between the fluid streams due to the small contact area.

An improved helical coil heat exchanger is described by Manning, et al. in United States Patent 6,076,597, June 20, 2000. In the Manning helical heat exchanger, the helical coils are contained in the annulus between the inner and outer shells. The fluid streams are only separated by one tubing wall. In the event of tube failure the two fluids can mix. In a shower drain application this would result in unacceptable mixing of the waste water with the potable cold feed water. Also the internal coil connections are made through special fittings in the end plates of the exchangers. In the event of fouling or blockage it would take considerable time to dismantle and clean or unblock the Manning exchanger.

The improved (shower drain) heat exchanger overcomes these problems.

Drawings: Figure 1: Elevation, external coil option Figure 2: End elevation, external coil option Figure 3: View A-A, external coil option Figure 4: Elevation, jacket option Figure 5: End Elevation, jacket option Figure 6: View B-B, jacket option Figure 7: Elevation, preferred embodiment.

The improved shower drain) heat exchanger comprises a large diameter metal tube which forms the shell Into this shell there have been formed one or more helical grooves. The helical grooves start close to one end and travel around and along, finishing close to the other end. An internal tube (13) with end cap (13A) are normally inserted into the device. Over the outside of the shell either one or more small diameter metal pipe(s) (12) are helically wound into the helical grooves or a jacket (18) is fitted over the helical grooving. Either the ends of the small diameter pipe form the inlet (15) and outlet connection (16) for the first fluid or the jacket connections form the inlet (15) and outlet connection (16) for the first fluid.

The first fluid enters via connection (15) and travels in a helical path leaving via outlet connection (16) The second fluid enters the device via end connection (17) and travels through the helical annulus formed by the outer shell (11) and the inner tube (13) in a counter flow direction to the first fluid before leaving via the end connection Heat transfer takes place through the shell and also via the external tubing if fitted.

Manufacture The device can be manufactured in a variety of materials to suit different applications. The shell (11) is made from annealed large diameter metal tubing. This tubing, cut to length and be-burred is slid over a special former. The former is made from heavy wall chord and has the helical form required machined into it. The helical form may be one, two or more grooves in parallel. The grooving is gradually led in at one end and led out at the other end of the former. The top and bottom edges of the grooves are radiused and the grooves have a smooth finish. The former is split but joined together for tube forming. There are O rings in both ends of the former These seal the internal ends of the large tube to the former. A connection in one end of the former leads to a small hole in the bottom of one groove. This connection allows air to escape during forming and also reverse pressure to be applied to release the formed tube/shell off the former. Once the tubing is in place over the former an honed hydraulic cylinder is slid over both the tube and the former. The internal ends of this cylinder also have O rings fitted and these seal over the ends of the tube to be formed. Hydraulic pressure is applied through connections in the hydraulic cylinder compressing or hydroforming the tube onto the former. The pressure is then released. An internal pressure pulse applied to release the tube/shell from the former. The hydraulic cylinder is then withdrawn. The two halves of the former are unscrewed out from either end of the completed shell (11).

The internal tube (13) cut to length has an end cap (13A) fitted to it and is then inserted into the shell The end cap stops the tube from entering past the start of the helical grooving. One or more tubing coil(s) (12) is (are) then fitted snugly in the external grooves (Figure one) or a jacket (18) is then fitted to complete the device (Figure 4).

Features The device can be orientated and used in any angle from the vertical to the horizontal.There is radial clearance between the inner tube (13) and the inside of helical grooving in the shell (11).

This enables the the inner cylinder to be easily withdrawn if required.The choice of an external coil enables the fluid streams to be twice removed from each other. This minimises the possibility of cross contamination in the case of tube failure.

The external coil or jacket connections are simple and easily accessible compared to the Manning Helical coil design.

The contact area between the external coil (12) which fits snugly into the helical grooves in the shell(11) is greater than the point contact than the Vasile drain heat exchanger. The improved (shower drain) heat exchanger has a greater surface area for a given diameter and length than Vasile's device. This is due to the extended surface created by forming the helical grooves in the improved device. The dimensions of the device and the pitch, number and profile of the helical grooves can be varied. This enables fluid velocities and pressure drops through the spiral paths to be optimised for any given fluid flow. It also enables the heat transfer rates and heat exchanger efficiency to be optimised for different fluids and flows.

Preferred Embodiment The following is a description of one preferred form of the invention given by way of example, with reference to the accompanying drawing figure 7.

The preferred embodiment of this device is as a shower drain heat exchanger This shell (11) of this device is made annealed copper tube. The external coil (12) from small diameter copper tube and the inner tube and cap from UPVC plastic These materials are suitable for use with sewage, potable water and have good corrosion resistance although other materials can be used such as stainless steel.

A removable end (10) is fitted to the device and near this an inlet branch connection (17) is fitted to the shell. An eccentric reducer is fitted to the other end to form outlet connection (14) During operation the shower drain waste fluid enters the device via inlet connection (17) it then passes into the helical annulus formed by the outer shell (11) and the inner cylinder It then leaves via exit connection (14).

The cold water feed enters the device via inlet connection It travels in a counter flow direction to the shower drain water and leaves via exit connection (16).

Small radial clearance gaps between the outside diameter of the inner tube (13) and the bottom surface of the helical grooving in the shell (11) allow some shower drain water to pass longitudinally along these gaps as well as along the helical path.

Energy is transferred from the shower drain water to the cold feed water via the shell (11) and the helical coil (12).

The dimensions of the device, the pitch, the number of parallel helical paths, the depth and the shape of the helical cross section can be altered to suit varying fluids and flows. This enables the fluid velocities and overall pressure drops through the spiral paths can to be optimised for any given fluid flow.

The small radial clearance gaps between the copper shell and the inner tube enables the shower drain water to circulate not only spirally but simultaneously longitudinally. This mixed-directional flow of the shower drain water creates turbulence. The smooth surface of the copper pipe and the plastic inner tube enables higher design velocities to be used for a given head loss. The turbulent flow and high velocities used in the device leads to good heat transfer rates. An advantage of the radial clearance gaps is to enable the inner cylinder to be easily withdrawn for cleaning of the device.

An advantage of the removable end cap (10) is that the device can be easily cleaned in situ without having to remove pipe work connections. For cleaning, the end cap (10) is removed. The inner cylinder (13) is withdrawn and the inside of the shell (11) is then accessible for cleaning. After cleaning the inner cylinder (13) is reinstalled and the end cap (10) reattached and the device can be returned to service.

An advantage of the UPVC inner plastic tube and plumbing grade/thin wall copper is their light weight. These contribute to a lightweight device which is easy to carry and install.

The device is self draining on the drain side and has only a small volume of water in the outer spiral coil.

The lightweight design and low water volume holding capacity contribute to the low thermal inertia of the device.

The low thermal inertia coupled with the counter flow arrangement enable good thermal response in cyclical operation.

This thermal response and the good overall heat transfer coefficients achieved improve the cyclical efficiency of the exchanger.

Cyclical efficiency is important because of the intermittent use of the device in a shower drain application.

Because it uses commercially available pipe and fittings and fabrication is simple the cost of the device can be kept low.

This device can be orientated and used in any angle from the horizontal to the vertical.

When it is installed in or near the vertical position the inner cylinder can be removed as centrifugal force holds the drain water in the spiral path.

With the inner cylinder removed there is no chance of blockage and the device is self cleaning. The potable water in the outer spiral coil is twice removed from sewage in the drainage channel. This minimizes any possibility of cross contamination in the event of damage to, or failure of the copper tubing.

Claims (4)

1. A new form of heat exchanger for heat exchange between two fluids comprising: a large diameter metal shell into which there have been formed one or more helical grooves, the shell having an inlet end and an outlet end, through which the first fluid flows in a helical path; an internal tube complete with end cap inserted into the shell, around and along which the first fluid flows in a helical path; one or more small diameter metal pipe(s) helically wound into the external helical grooves on the shell, each having inlet and outlet ends, through the second fluid flows in a helical path either parallel or in counter flow to the first fluid.

2. A new form of heat exchanger for heat exchange between two fluids comprising: a large diameter metal shell into which there have been formed one or more helical grooves, the shell having an inlet end and an outlet end through which the first fluid flows in a helical path; an internal tube complete with end cap inserted into the shell, around and along which the first fluid flows in a helical path; an external jacket fitted over the helical grooves on the shell and sealed at each end to the shell, having an inlet connection and an outlet connection through which the second fluid flows in a helical path either parallel or in counter flow to the first fluid.

3. The heat exchanger of claim 1 or 2 used in a vertical or near vertical position where the internal tube and end cap are removed, the first fluid continuing to flow through the shell in a helical path as it held in the helical grooves by centrifugal force.

4. A new form of shower drain heat exchanger for heat exchange between the warm waste fluid from a shower drain and the cold feed to the shower or hot water cylinder comprising; a large diameter metal shell, preferably copper, into which has been formed helical grooving and to one end of which has been attached a removable end cap; A side inlet branch connection fitted to the shell adjacent the removable end cap and an eccentric reducer fitted to the the other end of the shell forming the outlet connection through which the shower drain waste flows; an internal UPVC or other suitable material tube and end cap, around and along which the shower drain water flows in a helical path; -8- one or more small diameter metal, preferably copper, pipe(s) helically wound into the external helical grooves on the shell, each having inlet and outlet ends, through the second fluid flows in a helical path either parallel or in counter flow to the first fluid. Terence William Newlands Samuel John Newlands