AU2004200182A1 - Packed plates heat transfer device - Google Patents

Description

AUSTRALIA

Patents Act 1990 Complete Specification Standard Patent PACKED PLATES HEAT TRANSFER DEVICE The invention is described in the following statement PACKED PLATES HEAT TRANSFER DEVICE Heat transfer devices are used to transfer the heat from one fluid to another. They are also known as heat exchangers, condensers, evaporators, regenerators and coolers etc.

They are widely used in a variety of application in power production, waste heat recovery, oil rigs and chemical process industry. The design of heat exchanger involves heat transfer rate calculation and the pumping power requirements. There have been proposed numerous constructions of the heat transfer devices and exchangers. There are many types of heat transfer devices and many ways to categorise and classified them. Shell and tube heat exchangers are the most common type heat transfer device in the engineering industry. They are robust and versatile but provides relatively poor performance due to smaller surfaces densities (surface density usually 200 m 2 /m 3 low heat transfer coefficient and also need more space than compact type heat exchangers.

The compact heat exchangers on the other hand have more heat transfer area per unit volume and used in applications were size and weight of the heat exchangers is an important design constraints. The compact heat exchangers including the plate fin heat exchangers and gasketed plate heat exchangers, though compact but also have some limitations. Plate fin heat exchangers usually have limited fluid compatibility and limited fin efficiency. On the other hand gasket plate heat exchangers have significant limitation on temperature, pressure and fluid compatibility. Further the passages are not well suited to gaseous, viscous or two phase fluids. Another category of compact heat exchangers is the printed circuit heat exchangers. The name is given due to the chemical etching of flow passages, similar to the electronic printed circuit board. The printed circuit heat exchangers do not have the limitation of fluid compatibility, temperature and pressure. They have high surface densities comparable to plate fin heat exchangers (typically of 1000-5000 m 2 /m These heat exchangers also have some drawbacks including higher pumping losses, fouling and manufacturing complexities. For higher flow rates the grooves or the flow passages on the plates require higher plate thickness, adding to the cost of material and manufacturing. Further zigzag channel passages incur higher pumping losses. All these add to the higher capital and operating cost.

Main objectives of the present invention are to provide a highly efficient heat transfer device and minimize the weight and size of the device. The provided packed plates heat transfer device may be classified under the compact heat exchangers family and it offers some better features as compared to the printed circuit heat exchangers. The design and construction details of the provided heat exchangers are shown in the Figure 1 to Figure 9. This device has following main parts.

1. Flat straight plates 2. Stripes and flow guides 3. Headers Flat straight plates The Figure 1 shows the plates and stripes in the three dimensional view. These are simple straight metal plates without any corrugations or channels. The plates are long and can have a triangular shape at each end to attach headers. Other end shapes can also be used for the same purpose or the plate may be just the rectangular or square shape. The triangular shapes at the end of the plate help provide near counter current flow and thus higher log mean temperature difference. Further it also facilitate the attachment of headers at the end of the stack of the plates as shown in Figure 9 and a better space fit, since the device is better aligned in the direction of the flow. The thickness of these plate can be varied (usually between 0.02 mm to 10 mm or even more) depending on the duty of the device i.e. operating temperature and pressure. The shape and size of these plates can also be changed to suit a particular space and size requirement. These plates can have very small round shape or any other shape projections as shown in the Figure 3. The density of these projections i.e. number of projections per unit area is dependent on the thickness of the plate. These projections help maintaining a constant gap between the two plates, provide strength to the plate, promote turbulence and support the neighboring plate. Further in larger plates, flow guides may also be attached to guide the flow as shown in Figure 4. The cross sectional views of the stack of plates and stripes at A A and B B are shown in Figure 6 and Figure 7 respectively.

Stripes Two different shapes of the metal stripes for triangular shape plates are shown in Figure The shape of these stripes can be different for other plate shapes. The metal stripes may be cut to size from the sheet metal in desired shape and thickness. These stripes are cut to the size as per the shape of the edges of the plates described above in Figure 1, or can be manufacture by any other method. The width of these stripes is very small as compared to their length so as to provide maximum possible area for the fluid on the plate. The usual width may be typically 0.5 mm to 20 mm or more depending up on the pressure and temperature inside chambers formed between the plates and type of the fluid. The width can be determined on the basis of operating pressure. These stripes when placed on the plates, match the edges of the plates and flushed with the edges as shown in the three-dimensional drawing in Figure 2. The thickness of these stripes determines the gap between the two successive plates. For example if the thickness is 0.1 mm the gap between the two successive plates is 0.1 mm. The gap between these plates depends on the fluid properties, flow rate and the requirements of heat transfer duty of the device. Similar stripes of different shapes (such as latter I, S. L, Z etc.) and very small width may be used as a flow guide to direct and deflect the flow as shown in Figure 4. These flow guides can also help to maintain constant gap between the plates and support the plates.

Headers The main function of theses headers is to distribute the flow evenly all over the plates and they should be big enough to hold sufficient amount of fluid. The construction of header for this device is very simple. It has a nozzle shape construction and a tube attached to it as shown in Figure 4. The headers may be of different shapes and sizes depending on the requirements. A triangular header is shown in Figure 4. The headers for this heat transfer device are attached generally to the ends of the plates but can be attached to any side edge of the stack of the plates to form the inlet and outlet ports. The attachment of these headers determines the flow arrangement in the device i.e. parallel flow, counter flow or the cross flow. The headers may be of any shape and size depending on the requirements. In general triangular, circular, semicircular, rectangular, elliptical shapes may be used.

Any material can be used for making the plates, stripes and headers. Many variation of metals and combinations of these metals and alloys including austensilic steel, duplex steel, 316 stainless steel, 304 stainless steel, nickel alloys, titanium alloys, copper, brass etc. may be used for making the plates, headers, stripes and flow guides for this heat transfer device. The plates and stripes can be joined together by diffusion bonding, welding, brazing or any other method. Similarly the headers can be attached to the stack of plates and stripes by welding, fusion bonding, brazing or any other suitable joining method. The device can also be manufactured by any other suitable method in one piece or in a number of pieces joined together. A complete assembly of this device is shown in Figure The working of this device is very simple. Refer to Figure 1 to Figure 9, the hot fluid (fluidl1) enters from the header provide at the end of the stack of the plates, flows between the gaps of the two adjacent plates, where this hot fluid transfer its heat to the cold fluid (fluid 2) flowing on the other side of the plate between the gaps. The hot fluid comes out from the other end header. Similarly cold fluid enters the device from the end header flows in between the plate gaps, absorbs the heat from the hot fluid and comes out from the other end header. In this arrangement the hot and cold fluids glide over the two consecutive plate surfaces. In parallel flow arrangement both hot and cold fluid enter the device from the same end but from different headers and both fluid come out from the other end headers. There can be many variations of flow arrangements in this device including counter current, parallel flow, cross flow or flows at different angles. A number of inlet and outlet headers may be attached to the edges of the device to supply or take out fluid at different conditions.

Advantages The provided device has the following advantages 1. Better heats transfer characteristics as compared to other available heat exchangers because of the shape of the channel cross section and higher heat transfer surface to volume ratio.

2. Since the flow passages are straight, the pressure drop is smaller than the other compact heat exchangers so less pumping power required.

3. The cross sectional geometry of flow passages makes the analytical prediction of heat transfer performance simpler and more accurate 4. Weight and volume is up to 50% less than the existing teat transfer devices.

Low capital and operating cost as well as low maintenance cost 6. Extreme temperature (up to 800 Celsius) and pressure (up to 5 Mpa) limits.

7. This device is compatible with a range of corrosive resistance materials.

8. This device is safer than shell and tube type heat exchangers, which are prone to tube vibration and tube rupture etc.

9. Simple fabrication and manufacturing

Claims (5)

1. A heat transfer device comprising closely packed parallel metal plates with or without projection on them, with or without flow guides, allowing the heat transfer between the two fluids, in a compact closely packed device, with the flow cross section is a very wide and very thin, a thin layer of the hot and the cold fluids glide over the plate surfaces, the plates are separated by stripes of metal, these metal stripes and the plates are stacked together and joined by welding, diffusion bonding, brazing or any other joining process, the plates with built-in stripes manufactured by any methods, the headers on the stack of plates is attached by welding, diffusion bonding, brazing or by any other methods, these headers form the inlet and outlet ports for the hot and cold fluids, any pair of headers can form inlet and out let for hot or cold fluids, the device has two sections, one for hot fluid and another for cold fluid.

2. A heat transfer device as claimed in claim 1 above, in which the plates are flat and may or may not have small projections are provided on the metal plates surfaces, the projections working as support to the successive plates, keeping the gap between the plates constant through out the surface, to promote turbulence, if flow guides are provided, they also functioning same as the projections as well as flow guides.

3. A heat transfer device as claimed in claim 1 above, in which the plates are flat and may or may not have flow guides provided on the plate surfaces, the flow guide working as support to the successive plates, keeping the gap between the plates constant, to guide the flow on the plate surfaces.

4. A heat transfer device as claimed in claim 1 above, in which headers or ports are attached to the edges of the device or at any point in the flow passages to supply and take out the fluids.

5. The heat transfer device of any one of claims 1 to 4 where in the plate surfaces are flat and hot and cold fluids glide in between the plate surfaces to assist heat transfer between the two fluids. operable as heat exchanger, effluent exchangers, reactor, chillers, condenser, regenerator, economizer, heater, cooler, absorption cycle including the means to regulate temperature, pressure and flow rate. Jay K. Mukhraiya 30 Sept. 2002