Science articles

In this article, another attempt is made to carry out an objective, without distortion and emotional coloring, comparison of the two most famous types of heat exchangers - plate and shell-and-tube.

Over the past decade, thanks to massive, and often biased, advertising of plate devices, among employees working in the field of heat engineering, including communal, a false opinion has formed about the absolute superiority of plate heat exchangers over shell and tube exchangers. However, this should not be surprising, since the advertising campaign of plate devices was carried out according to all the rules of exposure - it was vast, constant and either unproven at the spell level (for example, there were articles titled “Plate heat exchangers - there is no alternative”), or pseudo-proof, calculated in this case for a lack of highly specialized knowledge among specialists in heat engineering of a wide profile.

Listing the advantages of plate apparatuses, their apologists, as a rule, distinguish the following advantages: light weight, small overall volume, thin-walled heat transferring plates and a high heat transfer coefficient, increased service life, and ease of maintenance. They prefer to keep silent about the price, because it, as a rule, is several times higher than the price of shell-and-tube apparatuses (hereinafter, we will talk about collapsible plate heat exchangers, since non-separable in the conditions of the CIS, as a rule, they prefer not to use it and, except Moreover, having a lower cost, at the same time they lose a number of advantages of collapsible devices - approx.

Legend number 1 - light weight

The thesis about the insignificant weight of plate heat exchangers was formed at the beginning of the 90s of the last century, when West European companies, having entered the CIS market, massively ran into shell-and-tube apparatuses used in the communal services of the Soviet Union and developed more than half a century ago. It was a sin not to use such a trump card. But at present it seems simply dishonorable to continue exploiting this legend (after all, it cannot be seriously assumed that absolutely all representatives of suppliers of plate heat exchangers do not at all follow the events taking place in the corresponding segment of the scientific and technical market). And currently there are shell-and-tube heat exchangers of the SATEKS company on the market [1],

As an example, we give specific data for one of the facilities, for the assembly of which proposals were made for West European plate heat exchangers and TTAI apparatuses of the Heat Transfer enterprise.

To heat the water in the pool, a heat exchanger was required. The customer, choosing the most setting option, supplied the initial data to various suppliers (in both cases, titanium was provided): it was required to heat sea water with a flow rate of 9.4 t / h from 4 ° C to 27 ° C with fresh water with a flow rate of 10.8 t / h and temperature at the inlet to the heat exchanger 70 ° C. The plate heat exchanger proposed to solve this problem had a dry weight of 120 kg, and the TTAI heat exchanger had a weight of 5 kg. Comments are probably unnecessary.

Thus, it becomes apparent that the low weight of the plate apparatus compared to shell and tube is no more than a legend.

Legend number 2 - small overall volume

By advertising the advantages of plate heat exchangers, they almost always emphasize their merit as a small overall volume, which allows to drastically save the space needed to accommodate the heat exchange equipment and release them for other purposes. For large cities, where every square meter of office or retail space in the city center costs a lot of money, this is really an important quality. But does the word “plate-like” always provide an advantage in this indicator in comparison with the word “shell-and-tube”? Or it would be more honest to write "a modern lamellar compared to an obsolete, shell-and-tube, without centuries ago." It seems that the latter formulation would be much more accurate. However, the reader can judge for himself on the basis of the data below.

It is required to carry out 2-stage heating of hot water supply water, while the consumption of heated water is 8.4 t / h, the temperature of the heated water (sequentially in steps) is 5 ° C, 43 ° C and 55 ° C. The following parameters were set for the heating medium: flow rate through the 2nd and 1st stages, 5.6 t / h and 15.2 t / h, respectively, and the temperature of the heating medium at the entrance to the 2nd and 1st stages, respectively - 70 ° C and 52 ° C.

To solve this problem, a plate heat exchanger of one of the Western European companies was proposed, having an overall volume of 0.19 m3. Solving the same problem (with the same pressure loss) using TTAI heat exchangers required the use of an apparatus with an overall volume of 0.03 m3 for the 1st stage, and 0.007 m3 for the 2nd stage. As you can see, the total overall volume of the two TTAI devices is 5.1 times less than the overall volume of one plate apparatus. Attention should be paid to the fact that in this case a obviously non-winning comparison was made for TTAI devices, since 2-stage heating can be structurally performed in one plate device, but at the moment it requires two TTAI devices (a modification is being developed, allowing to carry out 2-stage heating in one housing of the TTAI heat exchanger). In those cases where 2-stage heating is not required, the gain in overall volume in the case of using shell-and-tube heat exchangers TTAI reaches 10 or more times. And at the same time, one must also take into account that devices of the TTAI type are often more conveniently assembled indoors, which also creates a gain in production areas.

More recently, it was possible to allocate an additional 63 m2 of retail space in one of the largest shopping centers in Kiev only due to the transition to TTAI heat exchangers from previously planned to install plate devices.

The extremely small overall volume of TTAI devices, i.e., their pseudo-uniformity, opens up unexpected opportunities for radical savings in production space when creating individual heating units (ITP). The use of TTAI devices made it possible to apply a fundamentally new ideology for creating ITP, the so-called "Tablet" ITP. Such ITPs generally do not occupy space in the plan, but are distributed over the building envelope. Such an ideology is by definition unavailable when using even the most modern plate heat exchangers.

The presented digital and visual data confirm that the small overall volume of the plate apparatus also belongs to the area of ​​legends, albeit beautiful.

Legend No. 3 - thin-walled heat transfer plates and high heat transfer coefficient

Describing the positive consumer properties of plate devices, they almost always note their higher heat transfer coefficient, justifying this with developed turbulization of the flow and the thinness of the heat transfer plates.

Here we are generally faced with a substitution of concepts. Indeed, what does the consumer care about, due to which the object he needs (in this case, the heat exchanger) has certain outstanding properties. After all, buying a car, we are not interested, for example, in the compression ratio of the working mixture in the engine cylinder. It is important for us that the engine has the required power, consumes less fuel, is more environmentally friendly, etc., etc. And due to what this was achieved, we are not interested. Why impose information on the consumer of heat exchangers about how to achieve such small mass-dimensional characteristics of plate heat exchangers? Is it possible to create pseudo-scientific substantiation of the inaccessibility of these devices by other types of heat exchangers?

However, since the topic is identified and actively played out, there is a need to carry out its substantive analysis. So, the main technical (we emphasize again - not consumer) indicator is the heat transfer coefficient. A comparative analysis of this indicator for modern plate apparatuses and modern shell-and-tube apparatuses produced by various manufacturers (except for TTAI apparatuses) no longer gives rise to excessively optimistic estimates of the corresponding values ​​for plate apparatuses [6]. They, as a rule, have more plate devices, but not enough to give it such a great sound. But if we compare this indicator of plate heat exchangers with TTAI heat exchangers, then the situation completely changes to the opposite - the heat transfer coefficients of the plate apparatuses are significantly less than the corresponding values ​​of the TTAI apparatuses. To fill this statement with specifics, we give as an example the heat transfer coefficients characterizing the heat exchangers for the first case described in this article - with heating of sea water). The proposed plate heat exchanger had a value of 5854 W / (m2.oC), and the TTAI apparatus had a value of 8397 W / (m2.oC). Exceeding almost 1.5 times in TTAI devices leaves no moral right to speak of higher heat transfer coefficients of plate heat exchangers. characterizing heat exchangers for the first case described in this article - with heating of sea water). The proposed plate heat exchanger had a value of 5854 W / (m2.oC), and the TTAI apparatus had a value of 8397 W / (m2.oC). Exceeding almost 1.5 times in TTAI devices leaves no moral right to speak of higher heat transfer coefficients of plate heat exchangers. characterizing heat exchangers for the first case described in this article - with heating of sea water). The proposed plate heat exchanger had a value of 5854 W / (m2.oC), and the TTAI apparatus had a value of 8397 W / (m2.oC). Exceeding almost 1.5 times in TTAI devices leaves no moral right to speak of higher heat transfer coefficients of plate heat exchangers.

As for the discussion about the high degree of turbulization and the small thickness of the plates, it is very obvious the artificial reception of a set of positive qualities. Firstly, these are even more highly specialized issues than even the heat transfer coefficient, and therefore should not go to the consumer level. Secondly, specialists know that today turbulization methods for pipes are not worse developed, but even better than for plates. Therefore, in particular, in TTAI heat exchangers optimal flow turbulization is carried out, not inferior to turbulization in modern plate apparatuses.

Talking about the extremely small thickness of the plates (by the way, almost no effect on the heat transfer coefficient in the absolute majority of cases), reaching 0.5 mm and even, in the limit, 0.4 mm [7], immediately mentioning rather high pressures working environments (at 1.6 MPa) does not even seem professional enough. After all, it is known that a cylindrical shell is better able to withstand excessive pressures than a flat wall. Indeed, for more than 10 years, TTAI devices have been produced with tubes having a wall thickness of 0.3 mm. Obviously, this is less than 0.5 mm and even less than 0.4 mm.

Thus, it becomes clear that the opinion of a high heat transfer coefficient of plate heat exchangers and of extremely small plate thicknesses most likely was consciously formed as a scientific and technical legend.

Legend No. 4 - Longer Life

Significant advantages of plate heat exchangers include their increased service life. As an argument, we mainly use references to the fact that, firstly, the plates are made of special stainless steel, so that they do not corrode, and secondly, the plates have an appropriate profile that turbulates the flow, which prevents the formation of deposits, and, thirdly, the devices are equipped with rubber gaskets made of EPDM rubber, capable of withstanding sufficiently high temperatures [8]. But the Heat Transfer Enterprise, as noted above, has been producing TTAI shell-and-tube heat exchangers for more than 10 years, in which, firstly, the tubes are also made of stainless steel, exactly the same grades as the plates in the plate apparatuses, and secondly , the tubes have a special profile, providing the same turbulization effect and preventing the formation of deposits and, thirdly, silicone rubber identical in composition, operable in the same temperature range, is used for compaction. Information on this has been given for many years at numerous exhibitions, seminars, conferences, etc., where representatives of Heat Transfer LLC take part, and is also published in scientific and technical periodicals [9, 10, 11].

Consequently, the actively disseminated information about the increased service life of plate apparatuses as compared to shell-and-tube apparatuses is also nothing more than a legend.

Epilogue

The above and a number of unnamed, less popular legends actively promoted over the past decade have created a myth about the outstanding properties of foreign plate heat exchangers, which has generated, on the one hand, the opinion that it is only necessary to use such devices, and, on the other hand, which has brought about a boom in the organization of assembly or even almost full-scale production of such devices. In fact, these are really highly efficient and high-quality heat exchangers, but they are not a panacea. In some cases, their use is justified and today is the most optimal. But in most cases, they have a worthy alternative and even more, often modern shell-and-tube apparatuses, surpass modern plate heat exchangers throughout the entire range of consumer properties.

Having reliable information on the state of affairs in this area, I would like to emphasize that if over the past decade at least 10% of the funds that went to Western European companies in payment for lamellar apparatuses were addressed to firms working in this direction and using the backlog of Soviet scientific research of the defense complex, then perhaps that myth would not have been born, the debunking of which the present article is devoted to and today high-performance lamellar would have been applied, and not her highly efficient shell-and-tube apparatus of domestic development. However, not everything is lost.

Literature

1. “On the issue of choosing the type of water-to-water heaters for heat supply systems,” V. Permyakov et al., “Industrial Energy”, M., 2000, No. 4, pp. 37–44.
2. “The results of tests of head samples of water-to-water heaters for heat supply systems,” Baluev B.F. et al., Proceedings of NPO CKTI, St. Petersburg, 2002, pp. 163-175.
3. “OPTO heat exchangers for heat and hot water supply systems,” V. Permyakov et al., Proceedings of NPO CKTI, St. Petersburg, 2002, pp. 147-162.
4. “Thin-walled shell-and-tube apparatuses”, Baron V. G., “Ventilation, heating, conditioning (AVOK)”, Moscow, 2000, No. 3, pp. 62–64.
5. “Thin-walled heat exchangers intensified (TTAI). General analysis of the situation ”, Baron V. G.,“ Energy Saving ”, Donetsk, 2002, No. 7, pp. 20-22.
6. “On some problems of creating highly efficient tubular heat exchangers”, G. Dreitzer, Proceedings of the international symposium on heat and mass transfer, Minsk, 2004.
7. “Alfa Laval Plate Heat Exchangers. Is there a limit to perfection? ”,“ Heat-efficient technologies, ”St. Petersburg, 2003, No. 1, pp. 40–44.
8. “Some issues of designing automated heating units”, V. Baranov, “Heat-energy-efficient technologies”, St. Petersburg, 2002, No. 2, pp. 44–47.
9. “Shell-and-tube heat exchangers of the late twentieth century”, Baron V. G., “Alternative and renewable energy sources”, Odessa, 2000, No. 2 (5), pp. 34–36.
10. “Heat exchangers of the TTAI type and specific features of individual heat points”, Baron V. G., “News of heat supply”, M., 2000, October, pp. 24–27.
11. “Thin-walled heat-exchangers intensified apparatuses are an alternative to plate heat exchangers”, Baron V. G., “Heat-energy-efficient technologies”, St. Petersburg, 2003, No. 4, pp. 52–55.
12. “Unusual features of the usual shell-and-tube heat exchangers”, Baron V. G., “Refrigeration business”, Moscow, 1999, No. 6, pp. 27–29.

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