HEAT EXCHANGER OF "TUBE-IN-TUBE" TYPE
The invention relates to heat exchanging equipment and is to be used in household and various branches of industry. Background Art At present such heat exchangers are used in industry and household as described in "Directory on plumbing fixture on factories of public service" after N.B.Bahenkov and B.V.Kuznetsov (p.25). Such heat exchangers have a case in the form of cylinder, inside which brass tubes with diameter 16 mm are located between tube boards.. Heat transfer is carried out through walls of brass tubes. For extending of surface of heat transfer the quantity of tubes is increased.
Thereby such heat exchangers are complicated in manufacturing and have big dimensions.
There were attempts to make heat exchangers of "tube-in-tube" type, that were resulted in creation of heat exchangers of big length. Attempts to decrease length of heat exchangers were confined by increasing heating surface due to additional devices (appliances) - ribs which are made in the form of spiral helix. On the one hand, it has not given desired decrease of length, on the other hand, it resulted in complication of design.
Heat exchanging element of "tube-in-tube" type is known (author's license of the USSR #932184), in which the inner tube has a section that changes stepwise in the direction of flow. The outer tube has cross-section that changes stepwise in the direction of flow, and its steps are shifted with respect to steps of inner tube. The latter are provided with grooves on the outlet butt-end. Outer and inner tubes are made in the form of bellows, and grooves - in the form of corrugations. Disadvantage of the known element is as follows: in the structure made of thin- wall tubes the effect from stepwise changing of section is negligible as the result of little difference in diameters; besides improving of heat exchange occurs only in places of step transition. If each element of the outer or inner tubes has significant length, so, in spite of steps a heat preventing boundary layer is formed on its surface, pressure gradient occurs only in transition points from one section to another, that amplifies turbulization and intesifies heat exchange, due to constant section of each tube element.
Heat exchanger of "tube-in-tube" is known (author's license of the USSR #1695119) that contains spiral ribs, located on the inner tube with a gap with respect to
the outer tube; at that the latter has feed and exhaust nipples of intertube medium which are located tangentially; on the surface of ribs from the side of feed nipple shoulder blades are made which adjoin to rib edges and are located with a gap with respect to inner tube. Presence of shoulder blades provides direction of flow of heat carrier to the surface of the inner tube; it increases the heat output, but such design is complicated in manufacturing.
Heat exchanger is known (author's license of the USSR #1511567) that contains outer and inner tubes arranged with variable gap; the latter tube has a round section, and is provided with spiral ribs adjoining to walls of the outer tube; at that, outer tube has a section of elliptical shape of ellipse and is arranged coaxially with the inner tube.
The most close heat exchanger design to this being declared, is the heat exchanger registered by author's license of the USSR #595619. The inner tube is provided with spiral ribs arranged with a gap in the outer tube, that has fittings for heated medium; at that, the gap is of constant size that is less than step of spiral ribs by
1-6 mm; an electric heater is positioned on the inner tube along its axis, fittings are arranged tangentially.
Abovementioned heat exchangers have big weight and length and they are complicated in manufacturing. Thereby at present they are not used in industry and household.
Disclosure of the Invention
The main goal of invention is improvement of the known heat exchanger design that contains two tubes set up one inside another. Effect is achieved due to change of shape of heat exchanger which provides high turbulization of moving flows of heat carrier in the inner tube and of hquid to be heated in intertube space, one towards another. It allows to maintain high productivity as well as simplify the design of the heat exchanger with relatively small weight and length, due to ehmination of additional elements which increase surface of heating. This task posed is solved as follows: the heat exchanger of "tube-in-tube" contains two tube set up with gap between them; fitting of inlet of liquid to be heated is located from the side of heat carrier outlet; fitting of outlet of hquid to be heated is located from the side of heat carrier inlet. The heat exchanger is made in the form of spiral helix.
Such design of the heat exchangers in the form of spiral helix allowed to intensify whirls in each coil of spiral, heat exchange between them has been improved, heat transfer coefficient is increased. Along with preservation of high productivity it allows to shorten the surface of heat exchange i. e. decrease his height by 4-5 times, diameter by 3-4 times, weight by 6-10 times, consumption of heat carrier by 2 times as well as simplify its design in comparison with heat exchangers that are currently used in industry.
Brief Description of the Drawings
Figure 1 shows the schematic of heat exchanger proposed. Figure 2 shows the left side view of figure 1 with the fragmentary inner sight.
Heat exchanger consists of outer tube 1 and inner tube 2 made in the form of spiral helix and set up with the gap between them. On the inner tube 2 fittings 3 and 4 are set up for inlet and outlet of the heat carrier, respectively. On the outer tube 1 fittings 5 and 6 are set up for inlet and outlet of hquid to be heated, respectively. Heat exchanger works like as follows. Heat caπier flows along the inner tube 2 through fitting 3 from the one side and hquid to be heated in the intertube space between tubes 1 and 2 through fitting 5 from the another side are directed simultaneously towards one another.
High grade of turbulization along with whirls in coils of tube helix excludes completely stagnant zones and improves heat transfer. Intensity of heat transfer is increased as well along with flows of heat caπier and hquid to be heated that are directed towards one another, that enables decreasing of heat exchanger surface. This allows to decrease the size of heat exchanger, its weight, consumption of heat carrier, but at the same time preserves high productivity of heat transfer. Such design of heat exchanger provides full utilization of all its surface.
In connection with the feature that heat exchangers described above are not used in domestic industry we include a table of comparative performances of the heat exchanger offered and those of heat exchangers described in "Directory on plumbing fixture on factories of pubhc service" after N.B.Bahenkov and B.V.Kuznetsov (p.25). Principle of heat exchanger's work and heat transfer rate was examined on the model with the diameter of the outer tube 26.75 mm, thickness of the wall 2.75 mm and diameter of the inner tube 16 mm and thickness of the wall 2 mm. Heat transfer rate that has been obtained experimentally is equal:
K = 692 Kcal/m2 gramm*hour.
The heat transfer rate obtained is compared with the rates of existing heat exchangers (see table).
Parameters Type of heat exchanger
3075 #1 Proposed 3077 Proposed
1. Productivity liter/hour 667 667 1667 1667
2. Temperature of heat carrier at °C 100 100 100 100 inlet
3. Temperature of heat carrier at °c 70 40 70 40 outlet
4. Temperature of hquid to be °C 10 10 10 10 heated at inlet
5. Temperature of hquid to be "C 60 60 60 60 heated at outlet
6. Consumption of heat carrier liter/hour 1112 556 2778 1339
7. Weight kg 428 40 677.6 100
8. Length mm 2155 400 2813 1000
9. Diameter mm 916 550 1216 550
The table shows that along with the same productivity 667 liter/hour the offered heat exchanger with length 400 mm and heat exchanger #3075 with length 2,155 mm, consumption of heat carrier decreases by 2 times, weight of heat exchanger decreases by 10 times, length - by 4 times, diameter - by 2 times.
At equal productivity of 1,667 liter/hour of the heat exchanger taken for comparison with the length of 2813 mm and the offered heat exchanger with the length of 1000 mm, consumption of heat carrier decreased by 2 times, weight by 6 times, length by 3 times, diameter by 2 times.
Offered heat exchanger is to be widely used in household, petroleum, food and enrergy industries, especially where its weight and dimensions are limited.