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   **Pločasti izmjenjivači** su vrlo raširen tip izmjenjivača topline između toplog medija kojem treba hlađenje i hladnog medija koji preuzima toplinu, pogotovo na postrojenjima **ograničenog** prostora, upravo zbog svoje praktične konstrukcije, jednostavnosti u radu i kompaktnosti prilikom ugradnje.

Cjenovno su skuplji u odnosu na [cijevne izmjenjivače](https://en.wikipedia.org/wiki/Shell-and-tube_heat_exchanger), međutim imaju niže troškove održavanja i rezervnih dijelova.

![Screenshot_2024-01-30_at_22.04.17-transformed.png](https://strapi.metrikon.io/uploads/Screenshot_2024_01_30_at_22_04_17_transformed_c61381c8b9.png)
Slika: Pločasti izmjenjivači topline u radu 

Pločasti izmjenjivači topline se koriste preko 100 godina za **optimizaciju procesa** u kemijskoj, prehrambenoj, farmaceutskoj, naftnoj i petrokemijskoj industriji. Prvi zabilježeni **patent** za pločasti izmjenjivač prijavio je njemački izumitelj [Albrecht Dracke](https://trans-motauto.com/sbornik/2015/1/09.USING%20OF%20WASTE%20HEAT%20OF%20INTERNAL%20COMBUSTION%20ENGINES%20AND%20DRAFT%20OF%20EXHAUST%20GAS%20HEAT%20EXCHANGER.pdf) i tako otvorio put  praktičnoj izmjeni topline između dvaju radnih medija.

[Dr. Richard Seligman](https://www.soci.org/about-us/history/notable-scientists-and-inventors/richard-seligman) je prvi započeo **komercijalno** proizvoditi pločaste izmjenjivače 1923. u svojoj kompaniji [_Aluminum Plant and Vessel Company Ltd_ ](https://www.spxflow.com/apv/).

Razvoj pločastih izmjenjivača topline se nastavio, a popularnost među projektantima, tehničarima i inženjerima je stekao zahvaljujući velikoj **toplinskoj efikasnosti**, mogućnosti **povećanja kapaciteta** hlađenja dodavanjem rebrastih ploča i jednostavnosti prilikom rastavljanja i čišćenja.
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Tehničke karakteristike i konstrukcija pločastih izmjenjivača definirane su **Europskom direktivom za opremu pod tlakom PED 2014/68/EU** (Pressure Equipment Directive), te normom [ASME norma Sec VIII Div.1](https://inspectioneering.com/tag/asme+section+viii).

## Što čini pločasti izmjenjivač?
Svaki pločasti izmjenjivač topline mora na vanjskoj strani okvirne ploče obavezno imati nazivnu pločicu.

Na pločici se navode informacija o: vrsti izmjenjivača topline, serijskom broju, dopuštenim tlakovima [bar g],  **dopuštenim temperaturama** [°C], ispitnom tlaku [bar g], volumenu [L],  **dimenzijama kompresije** Lmax. i Lmin. [mm], neto masi, godini proizvodnje.
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Na slici je prikazan tipičan pločasti izmjenjivač sastavljen od okvira i nosača s vodilicama.

![Izmjenjivac.png](https://strapi.metrikon.io/uploads/Izmjenjivac_b3d63dff92.png)
Slika: Dijelovi pločastog izmjenjivača (Izvor: Skenirana slika iz knjige Velimir Ozretić - Brodski Pomoćni Strojevi i Uređaji)

Na **vodilicama** su redom poslagane rebraste ploče u snopu ili tkz. saću.

**Razmak** između dviju ploča je obično od 1,3 do 1,5 mm.

**Rebra** na pločama stvaraju veću rashladnu površinu i time omogućavaju bolju učinkovitost hlađenja jer poboljšavaju [turbulentno strujanje](https://hr.wikipedia.org/wiki/Turbulencija) radnog medija.

Izbor materijala za izradu rebrastih ploča je određen temeljem **specifičnih radnih uvjeta** budućeg korisnika, uključujući tlakove, temperature, radne medije i režime rada.

Rebraste ploče se najčešće izrađuju od nikla, bakra, slitine čelika i aluminija ili čelika i titanija, ovisno o namjeni izmjenjivača.
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Nakon određenog vremena u radu, na površinama rebrastih ploča se počinju stvarati naslage kalcijevog karbonata, kalcijevog sulfata i silikata ili se javlja **korozija**.

[Korozija](https://www.metrikon.io/hr/blog/6-types-of-corrosion-on-metal-materials-and-how-to-recognize-them) je posljedica međudjelovanja materijala rebraste ploče i kemijskog sastava radnog medija.

Nastale **naslage** dodatno usporavaju protok topline i usporavaju turbulentno strujanje što dovodi do smanjenja **efikasnog hlađenja**.

Navedena pojava definira se pojmom **faktor onečišćenja** ili **faktorom zaprljanja** Rf (fouling faktor, m2K/W). [Faktor onečišćenja](https://en.wikipedia.org/wiki/Fouling) zapravo predstavlja **termalni otpor** nastalih naslaga na površini ploče izmjenjivača prema prijenosu topline radnih medija.

Prljavština nataložena na površini ploče se ponaša kao [izolator](https://hr.wikipedia.org/wiki/Izolator) i smanjuje izmjenu topline čime se direktno smanjuje efikasnost izmjenjivača.

![shutterstock_1090010837-768x576.jpg.webp](https://strapi.metrikon.io/uploads/shutterstock_1090010837_768x576_jpg_ca5a43314e.webp)
Slika: Ploče izmjenjivača sa naslagama prljavštine ([Izvor](https://www.merusonline.com/heat-exchanger-cleaning/))

Najčešći tip onečišćenja je [taloženje](https://hr.wikipedia.org/wiki/Talo%C5%BEenje) krutih tvari iz tekućine na površinu za prijenos topline. Ostale vrste zaprljanja površine uključuju **kemijsko onečišćenje** (npr. korozija) i **biološko obraštanje** uzrokovano rastom [algi](https://en.wikipedia.org/wiki/Algae).

Faktor onečišćenja površine najviše ovisi o **kemijskim i fizikalnim karakteristikama** radnog medija, o brzini protjecanja radnog medija te o vrsti materijala za izradu ploče.

**Brzina protjecanja** od 0.9 m/s ili manja dovodi do bržeg zaprljanja površine ploče.

**Potisna i okvirna ploča** pritišću rebraste ploče u snopu, a čitav snop je stegnut parovima [priteznih vijaka za prednapinjanje](https://zir.nsk.hr/islandora/object/politehnikapu:269/datastream/PDF/view).

Najčešće konstrukcija pločastog izmjenjivača ima najmanje 4 [para vijaka](https://hr.wikipedia.org/wiki/Vij%C4%8Dani_spoj) za prednapinjanje.

Istjecanje medija sprječavaju **brtve** na rubovima rebrastih ploča i omogućavaju alternativni prolaz radnog medija.

Brtve su potrošni dijelovi osjetljivi na kemijsko, termičko i mehaničko oštećenje.

**Izbor materijala** za izradu brtvi je također ovisan o specificiranim tlakovima, temperaturama te svojstvima radnih medija.
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**Brtve** se dijele u dvije skupine: a) [elastomer brtve](https://repozitorij.hzn.hr/norm/HRN+EN+681-4%3A2003%2FA2%3A2007) sa 2 ili 4 oka, pričvršćuju se na površinu ploče uprešavanjem ili pomoću specijalnog ljepila, ovisno o proizvođaču izmjenjivača

b) [tvrde brtve](https://hr.wikipedia.org/wiki/Profilna_brtva) izrađene od [mineralnih vlakana](https://www.arsopi-thermal.pt/media/filer_public/29/8c/298cc053-0693-493c-a5f3-b9f3927c912b/chemicalcatalog_web_mkt102en02.pdf) koje se neizostavno pričvršćuju ljepilom.

**Elastomer brtve** tijekom vremena zastarijevaju i postaju [krhke](https://www.iso.org/standard/72774.html).

Tvrde brtve nemaju svojstvo **kompenziranja** promjena u svojoj strukturi nastalih uslijed **promjene temperaturnog opterećenja** npr. prilikom pokretanja iz hladnog stanja, što može dovesti do propuštanja radnog medija.

Na vijek trajanja brtvi utječe **način** korištenja izmjenjivača.

U slučaju nepravilnog korištenja neminovno će doći do skraćenog vijeka trajanja a time i do većih **troškova održavanja** jer će ih korisnik prije vremena morati mijenjati.

Ako se brtve u potpunosti zamjenjuju, potrebna **dimenzija kompresije L** je jednaka vrijednosti Lmax. otisnutoj na nazivnoj pločici.

![Group 9 (1).png](https://strapi.metrikon.io/uploads/Group_9_1_90e33e62ad.png)
Slika: Bočni prikaz pločastog izmjenjivača topline sa naznačenom dimenzijom kompresije L (prilagođeno prema [Izvor](https://www.separationequipment.com/tl6-plate-heat-exchanger.html))

Kada su ploče izmjenjivača topline samo očišćene a brtve nisu zamijenjene, tada je potrebno [izmjeriti](https://hr.wikipedia.org/wiki/Mjerenje) i zapisati  postojeću dimenzija kompresije L prije otvaranja pločastog izmjenjivača topline te pritegnuti snop na zapisanu vrijednost L.

Ako imamo slučaj **promjene broja ploča** u snopu izmjenjivača topline, bilo da dodajemo nove ploče ili smanjujemo broj postojećih, nova Lmax. dimenzija kompresije treba biti dogovorena i potvrđena sa originalnim proizvođačem izmjenjivača (OEM).

Tada je potrebno ažurirati podatke, izraditi i postaviti **novu** natpisnu pločicu sa novom vrijednosti Lmax.

Tijekom montaže pločasti izmjenjivač topline treba ugraditi prema uputama **proizvođača** na način da se kasnije **izbjegne** prenošenje sila velikog intenziteta, velikih momenata ili povećanih vibracija preko cijevi i spojeva sa izmjenjivačem.

**Dobra praksa** je da ovlašteni predstavnik proizvođača ili dobavljača bude prisutan tijekom montaže pločastog izmjenjivača i puštanja u rad te **potvrdi ispravnost ugradnje** primopredajnim zapisnikom.
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Ako ne želite imati probleme sa začepljenjem pločastog izmjenjivača topline ili njegovih priključnih cijevi tijekom prvog puštanja u rad, obavezno montirajte filter ili premosnu cijev za prvo ispiranje sveukupnog sustava cijevi.

Filter ili premosnu cijev treba ukloniti nakon što pločasti izmjenjivač postigne stabilne radne parametre.

## Kako funkcionira pločasti izmjenjivač topline?

**Oko ili otvor** na svakom kutu rebraste ploče omogućavaju **istovremeno** ulazak 2 radna medija različitih temperatura koji potom ulaze u rebra tj. **uske kanale** na površini ploča.
Kanali **usmjeravaju** tok rednog medija.

Brtve na rubovima ploča su montirane tako da radni medij prolazi **alternativnim** putem, medij **“A“** ulazi putem neparnih prolaza dok medij **“B“** ulazi između parnih prolaza.
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Na slici je prikazan način funkcioniranja klasičnog pločastog izmjenjivača.

![izmjenjivac-2.jpeg](https://strapi.metrikon.io/uploads/izmjenjivac_2_63b018f906.jpeg)
Slika: Funkcioniranje pločastog izmjenjivača (Izvor: Skenirana slika iz knjige Velimir Ozretić - Brodski Pomoćni Strojevi i Uređaji)

**Dijagram protjecanja** radnih medija na sljedećoj slici pokazuje da hladni medij (plavi) i topli medij (crveni) naizmjenično protječu površinama ploča.

Hladni i topli medij su u potpunosti **odvojeni** jedan od drugoga pločama izmjenjivača.

Brtve na rubovima ploča osiguravaju da se u potpunosti izbjegne **miješanje** radnih medija.

![plate-heat-exchanger-flow-path-1.jpeg](https://strapi.metrikon.io/uploads/plate_heat_exchanger_flow_path_1_03cffe1b5e.jpeg)
Slika: Dijagram tijeka hladnog i toplog radnog medija u pločastom izmjenjivaču ([Izvor](https://savree.com/en/encyclopedia))

**Održavanje i rješavanje kvarova**

Pločasti izmjenjivači topline bi uvijek trebali biti u **funkcionalnom** stanju. Tako će se izbjeći pojava prerane preuranjena **istrošenost** specifičnih dijelova pločastog izmjenjivača topline zbog nepovoljnih uvjeta okoline.

[Kvaliteta](https://hr.wikipedia.org/wiki/Kvaliteta) održavanja pločastog izmjenjivača izravno utječe na učestalost pojave kvarova.

Obavezne aktivnosti [održavanja](https://www.alfalaval.com/service-and-support/product-services/plate-heat-exchanger-services/service-company/efficiency-and-performance/) i praćenja rada obuhvaćaju:

- Redoviti **vizualni pregledi** pločastoga izmjenjivača topline tijekom rada, provjera ima li propuštanja, javlja li se kondenzirani radni medij na okvirnoj i/ili potisnoj ploči te pojave isparavanja
- **Praćenje** tlakova i temperatura
- Provjera koristi li se **ispravan** radni medij,
- Redovito uzimanje **uzoraka** radnog medija i slanje na laboratorijsku analizu
- Rad unutar **minimalnih i maksimalnih radnih parametara** navedenih na natpisnoj pločici, u listi podataka, u tehnološkom priručniku i u standardnim operativnim procedurama
- Izbjegavanje **naglih promjena** tlakova i temperatura u radu
- Plansko čišćenje izmjenjivača izvana sa [visokotlačnim peračem](https://en.wikipedia.org/wiki/K%C3%A4rcher) (miniwash)
- Plansko [čišćenje](https://www.youtube.com/watch?v=nC8Spxv5GE4) "na mjestu" kada kroz izmjenjivač topline umjesto tekućeg medija [protječe](https://vimeo.com/486410465) kemikalija za čišćenje. [Otopina kemikalija](https://en.wikipedia.org/wiki/Cleaning_agent) otapa naslage i tako ih uklanja sa rebraste površine, što je dodatno pojačano turbulentnim strujanjem.
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Kemikalije za čišćenje moraju biti **kompatibilne** sa materijalom rebrastih ploča i sa materijalom brtvi da se izbjegne oštećenje i nagrizanje.
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Otopina kemikalija treba sadržavati maksimalno 5% volumnog udjela [lužine](https://hr.wikipedia.org/wiki/Lu%C5%BEine) ili 0.5% masenog udjela [kiseline](https://hr.wikipedia.org/wiki/Kiseline) pri maksimalnoj temperaturi 70°C prilikom ispiranja.

- Plansko **podmazivanje** navoja na vijcima za pritezanje i provjera dotegnutosti svih matica

- Redovito bojanje okvirne i potisne ploče nanošenjem novog zaštitnog premaza

Kada se pločasti izmjenjivač topline stavlja izvan pogona na duži period, mora u potpunosti biti **ispražnjen** i **rasterećen** od tlaka radnog medija.

Potom ga treba temeljito **očistiti, konzervirati** i prikladno pohraniti idućeg puštanja u rad.

Plansko održavanje se uglavnom sastoji od redovitog [čišćenja](https://www.youtube.com/watch?v=1AYWVZ1FhM8&pp=ygUocGxhdGUgaGVhdCBleGNoYW5nZXIgY2xlYW5pbmcgYWxmYSBsYXZhbA%3D%3D) rebrastih ploča pomoću visokotlačnog perača sa obiju strana.
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**Interval čišćenja** se određuje praćenjem stanja izmjenjivača, tj. praćenjem [temperature](https://hr.wikipedia.org/wiki/Temperatura) radnih medija na manometrima ugrađenim na ulaznim i izlaznim cjevovodima ili praćenjem razlike tlakova na [diferencijalnom manometru](https://ba.gvda-instrument.com/info/what-is-a-differential-pressure-gauge-and-its-84033727.html).

Što je **manja** razlika temperature na ulazu i izlazu, to je izmjenjivač prljaviji i učinkovitost hlađenja je manja jer je smanjen prijenos topline.

Na pločama izmjenjivača se najčešće talože **naslage** blata, mulja, pijeska ili algi. Obraštanje algi je čest slučaj kod brodskih izmjenjivača koji hlade slatku vodu pomoću morske vode.

Izmjenjivači za hlađenje **vodom** su podložniji nastanku naslaga blata dok su izmjenjivači za hlađenje **ulja za podmazivanje** ili goriva podložni nastanku naslaga [koksa](https://hr.wikipedia.org/wiki/Motorno_ulje).

**Rastavljanje** pločastog izmjenjivača se izvodi tako da se prvo zatvore svi ventili dovoda i odvoda dvaju radnih medija i da se izmjenjivač dobro ohladi.

Potom treba **odzračiti i drenirati** izmjenjivač, očistiti i podmazati nosače i vodilice te podmazati navoje i matice priteznih vijaka.

Ako su matice **zapekle ili korodirale** upotrijebite [WD 40](https://wd40.hr/vijestiindustrija/sto-znaci-naziv-wd-40) ili kemijsko sredstvo slične namjene.

Izmjerite i zabilježite **duljinu između okvirne i potisne ploče** na vrhu i na dnu s obje strane tj. dimenziju kompresije L. Biti će potrebna 4 mjerenja duljine, po dvije za svaku stranu, pri vrhu i pri dnu.

Potom **otpustite** matice priteznih vijaka, gornji lijevi i donji desni ili obratno, bitno je da se otpuštanje izvodi na kontra stranama.
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Uklonite pritezne vijke i okvirnu ploču pa krenite redom s vodilica skidati rebraste ploče i **obilježite** ih brojevima jednu za drugom radi istog redoslijeda prilikom montaže.

Zasebno operite svaku ploču s obje strane pomoću [vodenog mlaza pod tlakom](https://www.youtube.com/watch?v=rhz0b6W8r8s) i očiste mekanom četkom.

Ne smiju se koristiti [ručne žičane četke](http://www.zima.si/hr/vodic-po-produktima/1336-alati-za-pripremu-povrsine/428-rucne-zicane-cetke/) od čeličnih vlakana jer će oštetiti površinu ploče. Ako su prisutni debeli slojevi naslaga, ploče je potrebno uroniti u adekvatnu kemijsku kupku.

Detaljno pregledajte sve brtve na svim pločama u potrazi za **oštećenjima**.

Pregledajte jesu li sve ploče dobro očišćene. Montirajte ih na nosače slaganjem na vodilice tako da **posljednja skinuta ploča ide prva** i tako redom sve do montaže potisne ploče.

Montirajte pritezne vijke i lagano dotežite matice suprotno postavljenih vijaka, potom [pritegnite](https://www.metrikon.io/hr/blog/10-tips-for-using-a-torque-wrench-correctly) do kraja.

Ponovno pričvršćivanje steznih dijelova pločastog izmjenjivača topline se može izvršiti samo u stanju kada je izmjenjivač u potpunosti **ispražnjen** i nema tlaka radnog medija jer u suprotnom dimenzija kompresije Lmin. može biti manja.

Kažemo da pločasti izmjenjivač mora biti rasterećen.

Provjerite jesu li rebraste ploče odgovarajuće pritisnute između okvirne i potisne ploče tako da ponovno izmjerite udaljenost **L** među njima na više strana, na isti način kao što ste napravili prije rastavljanja.
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Kada je sve **ispravno** postavljeno, rebraste ploče bočno izgledaju kao saće.

**Najčešći kvarovi pločastih** izmjenjivača su **propuštanje** radnog medija prema van ili prema unutra zbog oštećenih brtvi, **previsoke temperature** radnih medija, neodgovarajuća pritegnutost vijaka ili nastanak **pukotina** na pločama zbog [korozije](https://www.metrikon.io/hr/blog/6-types-of-corrosion-on-metal-materials-and-how-to-recognize-them).

**Veliki pad tlaka** je rezultat veće količine naslaga na površinama ploča, dok **savijene** ploče ili prevelike **naslage** nečistoće onemogućavaju dotezanje priteznih vijaka.

Pojava **visokog tlaka** se obavezno treba izbjegavati.

Do pojave visokog tlaka će dovesti pogrešna **dimenzija kompresije** L te problemi u **strujanju** radnih medija ili njihova neodgovarajuća fizikalna i/ili kemijska svojstva.

Izvođenje brzih prespoja poput zamjene armature na cijevima spojenima sa pločastim izmjenjivačem topline ili poremećaji u procesu kao što su ubrzani nastanak [kondenzata](https://hr.wikipedia.org/wiki/Kondenzacija) ili [isparavanje](https://hr.wikipedia.org/wiki/Isparavanje) isto tako dovode do nastanka visokog tlaka radnog medija.
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Cijevni priključci i ostala armatura spojena sa pločastim izmjenjivačem ponekad može biti uzrok kvara jer poteže izmjenjivač u stranu i dovodi do **savijanja** rebrastih ploča.

Događa se u slučajevima kada imamo prevelika **opterećenja** na cijevnom priključku zbog mase cijevi, brtveni prsten je prljav ili nepravilno prianja te prirubnički spoj nije odgovarajuće pritegnut.

Svaki pločasti izmjenjivač mora biti odgovarajuće [uzemljen](https://www.iea.lth.se/publications/ms-theses/Short%20article/5422_Smf.pdf).

[Zavareni spojevi](https://hr.wikipedia.org/wiki/Zavarivanje) na potisnoj i okvirnoj ploči, na nosaču i na vodilicama ne smiju imati pukotina.

U  slučaju nastanka pukotina potrebno je reparaturno zavarivanje pomoću [srebrne elektrode](https://en.wikipedia.org/wiki/Silver_chloride_electrode) sa udjelom minimalno 45% [srebra](https://en.wikipedia.org/wiki/Silver) pri čemu temperatura prilikom zavarivanja ne smije prijeći 650°C.

small_plastinchatyeteploobmennikimin.jpeg

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Pločasti izmjenjivači rješavaju problem izmjene topline u procesnoj industriji na jednostavan način. Upoznajte ih detaljnije!   

**Plate Heat Exchangers** are a widely used type of heat exchanger between the hot fluid that needs cooling and the cold fluid that absorbs the heat, especially in facilities with **limited** space, due to their practical design, operational simplicity, and compact installation.

They are more expensive compared to [shell-and-tube heat exchangers](https://en.wikipedia.org/wiki/Shell-and-tube_heat_exchanger), but they have lower maintenance costs and spare parts expenses.

![Screenshot_2024-01-30_at_22.04.17-transformed.png](https://strapi.metrikon.io/uploads/Screenshot_2024_01_30_at_22_04_17_transformed_c61381c8b9.png)
Image: Plate heat exchangers in operation 

Plate heat exchangers have been used for over 100 years to optimize processes in the chemical, food, pharmaceutical, oil, and petrochemical industries. The first recorded **patent** for a plate heat exchanger was filed by German inventor [Albrecht Dracke](https://trans-motauto.com/sbornik/2015/1/09.USING%20OF%20WASTE%20HEAT%20OF%20INTERNAL%20COMBUSTION%20ENGINES%20AND%20DRAFT%20OF%20EXHAUST%20GAS%20HEAT%20EXCHANGER.pdf), paving the way for practical heat exchange between two working fluids.

[Dr. Richard Seligman](https://www.soci.org/about-us/history/notable-scientists-and-inventors/richard-seligman) was the first to **commercially** produce plate heat exchangers in 1923 in his company [_Aluminum Plant and Vessel Company Ltd_ ](https://www.spxflow.com/apv/).

The development of plate heat exchangers continued, gaining popularity among designers, technicians, and engineers due to their high **thermal efficiency**, the possibility of **increasing cooling capacity** by adding corrugated plates, and simplicity in disassembly and cleaning.

The technical characteristics and construction of plate heat exchangers are defined by the **European Pressure Equipment Directive PED 2014/68/EU**, and the [ASME standard Sec VIII Div.1](https://inspectioneering.com/tag/asme+section+viii).


## What does a plate heat exchanger consist of?
Every plate heat exchanger must have a nameplate on the external side of the frame plate.

The nameplate provides information about: the type of heat exchanger, serial number, permissible pressures [bar g], **permissible temperatures** [°C], test pressure [bar g], volume [L], compression dimensions Lmax. and Lmin. [mm], net mass, and year of manufacture.

The image shows a typical plate heat exchanger assembled from a frame and carrier with guides.

![Izmjenjivac.png](https://strapi.metrikon.io/uploads/Izmjenjivac_b3d63dff92.png)
Image: Parts of a plate heat exchanger (Source: Scanned image from the book Velimir Ozretić - Ship Auxiliary Machinery and Devices)

Corrugated plates are arranged in a bundle or so-called honeycomb on the **guides**.

The gap between two plates is usually between 1.3 and 1.5 mm.

The **corrugations** on the plates create a larger cooling surface, improving the efficiency of cooling by enhancing [turbulent flow](https://en.wikipedia.org/wiki/Turbulence) of the working fluid.

The choice of materials for making corrugated plates is determined by the **specific operating conditions** of the future user, including pressures, temperatures, working fluids, and operating modes.
\
Corrugated plates are most commonly made of nickel, copper, steel and aluminum alloy, or steel and titanium, depending on the purpose of the exchanger.
\
After a certain period of operation, deposits of calcium carbonate, calcium sulfate, and silicates, or **corrosion**, begin to form on the surfaces of the corrugated plates.

[Corrosion](https://www.metrikon.io/en/blog/6-types-of-corrosion-on-metal-materials-and-how-to-recognize-them) is a consequence of the interaction between the material of the corrugated plate and the chemical composition of the working fluid.

The formed **deposits** further slow down heat transfer and impede turbulent flow, leading to a reduction in **effective cooling**.

This phenomenon is defined by the term **fouling factor** or fouling factor Rf (m2K/W). [Fouling factor](https://en.wikipedia.org/wiki/Fouling) represents the **thermal resistance** of deposits on the surface of the heat exchanger plate to the transfer of heat from the working fluids.

Dirt deposited on the surface of the plate acts as an [insulator](https://en.wikipedia.org/wiki/Insulator) and reduces heat exchange, directly decreasing the efficiency of the exchanger.

![shutterstock_1090010837-768x576.jpg.webp](https://strapi.metrikon.io/uploads/shutterstock_1090010837_768x576_jpg_ca5a43314e.webp)
Image: Plates of the heat exchanger with deposits of dirt ([Source](https://www.merusonline.com/heat-exchanger-cleaning/))

The most common type of fouling is the deposition of solid substances from the liquid onto the heat exchange surface. Other types of surface fouling include **chemical fouling** (e.g., corrosion) and **biological fouling** caused by the growth of [algae](https://en.wikipedia.org/wiki/Algae).

The fouling factor on the surface depends primarily on the chemical and physical characteristics of the working fluid, the flow velocity of the working fluid, and the type of material used for the plate construction.

**A flow velocity** of 0.9 m/s or lower leads to faster fouling of the plate surface.

**The pressure plate and frame plate** press the corrugated plates into a bundle, and the entire bundle is tightened by [pairs of preload bolts](https://zir.nsk.hr/islandora/object/politehnikapu:269/datastream/PDF/view).

Typically, the construction of a plate heat exchanger includes a minimum of 4 [pairs of bolts](https://en.wikipedia.org/wiki/Bolted_joint) for pre-tensioning.

Media leakage is prevented by **gaskets** on the edges of the corrugated plates, allowing an alternative passage of the working fluid.

Gaskets are consumable parts sensitive to chemical, thermal, and mechanical damage.

**The choice of materials** for making gaskets also depends on specified pressures, temperatures, and the properties of working fluids.
\
**Gaskets** are divided into two groups: a) elastomeric gaskets with 2 or 4 eyes, attached to the plate surface by embedding or using special adhesive, depending on the heat exchanger manufacturer.

b) [hard gaskets](https://hr.wikipedia.org/wiki/Profilna_brtva) made of [mineral fibers](https://www.arsopi-thermal.pt/media/filer_public/29/8c/298cc053-0693-493c-a5f3-b9f3927c912b/chemicalcatalog_web_mkt102en02.pdf) that are invariably attached with adhesive.

**Elastomeric gaskets** age over time and become [brittle](https://www.iso.org/standard/72774.html).

Hard gaskets do not have the property of **compensating** for changes in their structure due to **changes in temperature** loading, for example, during startup from a cold state, which can lead to leakage of the working fluid.

The service life of gaskets is **influenced** by the usage mode of the heat exchanger.

In the case of improper use, a shortened service life is inevitable, leading to higher **maintenance costs** as the user needs to replace them prematurely.

When gaskets are completely replaced, the required **compression dimension L** is equal to the value Lmax. imprinted on the nameplate.

![Group 9 (1).png](https://strapi.metrikon.io/uploads/Group_9_1_90e33e62ad.png)
Image: Side view of a plate heat exchanger with the indicated compression dimension L (adapted from  [Source](https://www.separationequipment.com/tl6-plate-heat-exchanger.html))

When the plates of the heat exchanger are only cleaned, and the gaskets are not replaced, it is necessary to [measure](https://en.wikipedia.org/wiki/Measurement) and record the existing compression dimension L before opening the plate heat exchanger and tighten the bundle to the recorded value L.

If there is a case of **changing the number of plates** in the heat exchanger bundle, whether adding new plates or reducing the number of existing ones, the new Lmax. compression dimension must be agreed upon and confirmed with the original equipment manufacturer (OEM).

Then it is necessary to update the data, create and install a **new** nameplate with the new value of Lmax.

During the installation of the plate heat exchanger, it should be installed according to the instructions of the **manufacturer** in a way that **avoids** transferring forces of high intensity, large moments, or increased vibrations over pipes and connections with the exchanger.

**Good practice** is to have an authorized representative of the manufacturer or supplier present during the installation of the plate heat exchanger and commissioning to **confirm the correctness of the installation** with a handover protocol.

If you want to avoid problems with clogging the plate heat exchanger or its connecting pipes during the initial commissioning, be sure to install a filter or bypass pipe for the first flushing of the entire pipe system.

The filter or bypass pipe should be removed after the plate heat exchanger reaches stable operating parameters.

## How does a plate heat exchanger work?

**An eye or opening** at each corner of the corrugated plate allows **simultaneous** entry of 2 working fluids of different <u>temperatures</u>, which then enter the corrugations, i.e., **narrow channels** on the surface of the plates.

The channels **direct** the flow of the working fluid.

The channels **direct** the flow of the working fluid. Gaskets on the edges of the plates are mounted so that the working fluid passes through an **alternative** path. Fluid **"A"** enters through odd passages, while fluid **"B"** enters between even passages.

The image illustrates the operation of a classic plate heat exchanger.

![izmjenjivac-2.jpeg](https://strapi.metrikon.io/uploads/izmjenjivac_2_63b018f906.jpeg)
Image: Operation of a plate heat exchanger (Source: Scanned image from the book Velimir Ozretić - Marine Auxiliary Machinery and Devices)

The **flow diagram** of working fluids in the next image shows that the cold fluid (blue) and the hot fluid (red) alternately flow through the surfaces of the plates.

Cold and hot fluids are completely **separated** from each other on the plates of the heat exchanger.

Gaskets on the edges of the plates ensure that there is no **mixing** of fluids.

![plate-heat-exchanger-flow-path-1.jpeg](https://strapi.metrikon.io/uploads/plate_heat_exchanger_flow_path_1_03cffe1b5e.jpeg)
Image: Flow diagram of cold and hot working fluids in a plate heat exchanger ([Source](https://savree.com/en/encyclopedia))

**Maintenance and troubleshooting**

Plate heat exchangers should always be in a **functional** state to avoid premature **wear** of specific parts due to unfavorable environmental conditions.

The [quality](https://en.wikipedia.org/wiki/Quality_(business)) of maintenance directly affects the frequency of failures.

Mandatory [maintenance](https://www.alfalaval.com/service-and-support/product-services/plate-heat-exchanger-services/service-company/efficiency-and-performance/) and monitoring activities include:

- Regular **visual inspections** of the plate heat exchanger during operation, checking for leaks, condensation of the working fluid on the frame and/or pressure plate, and signs of evaporation.
- **Monitoring** of pressures and temperatures.
- Verification of the use of the **correct** working fluid.
- Regular sampling of the working fluid and sending it for laboratory analysis.
- Operation within **minimum and maximum operating parameters** specified on the nameplate, in the data sheet, in the technological manual, and in standard operating procedures.
- Avoiding **sudden changes** in pressures and temperatures during operation.
- Planned cleaning of the exchanger from the outside with a [high-pressure washer](https://en.wikipedia.org/wiki/Pressure_washing) (miniwash).
- Planned [cleaning](https://www.youtube.com/watch?v=nC8Spxv5GE4) "in place" when instead of a fluid, cleaning chemicals [flow through](https://vimeo.com/486410465) the heat exchanger. [The solution](https://en.wikipedia.org/wiki/Cleaning_agent) dissolves deposits and removes them from the corrugated surface, further enhanced by turbulent flow.

Cleaning chemicals must be **compatible** with the material of the corrugated plates and the gasket material to avoid damage and corrosion.

The cleaning solution should contain a maximum of 5% by volume of [caustic soda](https://en.wikipedia.org/wiki/Caustic_soda) or 0.5% by mass of [acid](https://en.wikipedia.org/wiki/Acid) at a maximum temperature of 70°C during rinsing.

- Planned **lubrication** of the threads on the tightening bolts and checking the tightness of all nuts.

- Regular painting of the frame and pressure plates by applying a new protective coating.

When a plate heat exchanger is taken out of operation for an extended period, it must be completely **drained** and **depressurized** from the working fluid.

It should then be thoroughly **cleaned, preserved**, and properly stored for the next commissioning.

Planned maintenance mainly consists of regular [cleaning](https://www.youtube.com/watch?v=1AYWZ1FhM8&pp=ygUocGxhdGUgaGVhdCBleGNoYW5nZXIgY2xlYW5pbmcgYWxmYSBsYXZhbA%3D%3D) of the corrugated plates using a high-pressure washer from both sides.

The **cleaning interval** is determined by monitoring the condition of the exchanger, i.e., by monitoring the [temperature](https://en.wikipedia.org/wiki/Temperature) of the working fluids on the pressure gauges installed on the inlet and outlet pipelines or by monitoring the pressure difference on a [differential pressure gauge](https://ba.gvda-instrument.com/info/what-is-a-differential-pressure-gauge-and-its-84033727.html).

The smaller the temperature difference at the inlet and outlet, the dirtier the exchanger, and the lower the heat transfer efficiency.

Plate surfaces commonly accumulate **deposits** of sludge, mud, sand, or algae. Algae growth is a common occurrence in ship heat exchangers that cool fresh water using seawater.

Exchangers cooling **water** are more susceptible to sludge deposits, while those cooling **lubricating oil** or fuel are prone to [coke](https://en.wikipedia.org/wiki/Motor_oil) deposits.

**Disassembling** a plate heat exchanger is done by first closing all supply and discharge valves of the two working fluids and allowing the exchanger to cool thoroughly.

Then, the exchanger must be **vented and drained**, cleaned, and lubricated for the supports and guides, as well as lubricating the threads and nuts of the tightening bolts.
\
If the nuts are **stuck or corroded**, use [WD 40](https://wd40.hr/vijestiindustrija/sto-znaci-naziv-wd-40) or a similar-purpose chemical.
\
Measure and record the **distance between the pressure plate and the frame plate** at the top and bottom on both sides, i.e., the compression dimension L. Four length measurements will be needed, two for each side, at the top and bottom.

Then, **release** the nuts of the tightening bolts, upper left and lower right, or vice versa. It is important that the release is performed on opposite sides.

Remove the tightening bolts and the frame plate, then proceed sequentially to remove the corrugated plates and **label** them with numbers one after the other for the same order during assembly.

Wash each plate thoroughly on both sides using a [water jet under pressure](https://www.youtube.com/watch?v=rhz0b6W8r8s) and clean with a soft brush.
[Wire brushes](http://www.zima.si/hr/vodic-po-produktima/1336-alati-za-pripremu-povrsine/428-rucne-zicane-cetke/) made of steel fibers should not be used because they will damage the plate surface. If there are thick deposits, the plates need to be immersed in an appropriate chemical bath.

Inspect all gaskets on all plates for **damage**.

Check if all plates are well cleaned. Mount them on the supports by stacking them on the guides so that the **last plate removed goes first**, and so on until mounting the pressure plate.

Install the tightening bolts and gently tighten the nuts of the opposite positioned bolts, then [tighten](https://www.metrikon.io/en/blog/10-tips-for-using-a-torque-wrench-correctly) to the end.

Re-fastening the clamping parts of the plate heat exchanger can only be done when the exchanger is completely **emptied** and there is no pressure from the working fluid, as otherwise, the compression dimension Lmin. may be smaller.

It is said that the plate heat exchanger must be unloaded.

Check if the corrugated plates are adequately pressed between the frame and the pressure plate by re-measuring the distance **L** between them on several sides, the same way as before disassembly.

When everything is correctly set up, the corrugated plates look like a honeycomb from the side.

The most common failures of plate heat exchangers are **leakage** of the working fluid outward or inward due to damaged gaskets, **excessively high temperatures** of the working fluids, improper tightening of bolts, or the occurrence of **cracks** on the plates due to [corrosion](https://www.metrikon.io/en/blog/6-types-of-corrosion-on-metal-materials-and-how-to-recognize-them).

A **large pressure drop** results from a higher amount of deposits on the plate surfaces, while **bent plates** or excessive **deposits** of impurities prevent tightening of the tightening bolts.

The occurrence of **high pressure** must be avoided.

High pressure will result from incorrect **compression dimension** L and problems in the **flow** of working fluids or their inappropriate physical and/or chemical properties.

Fast connections such as replacing fittings on pipes connected to the plate heat exchanger or disruptions in the process, such as accelerated formation of [condensate](https://en.wikipedia.org/wiki/Condensation) or [evaporation](https://en.wikipedia.org/wiki/Evaporation), also lead to the occurrence of high pressure in the working fluid.

Pipe connections and other fittings connected to the plate heat exchanger can sometimes cause malfunctions because they pull the exchanger sideways and lead to the **bending** of the corrugated plates.

This happens in cases where there is too much **load** on the pipe connection due to the pipe's mass, the sealing ring is dirty or does not fit properly, and the flange connection is not properly [tightened](https://www.metrikon.io/en/blog/10-tips-for-using-a-torque-wrench-correctly).

Every plate heat exchanger must be properly [grounded](https://www.iea.lth.se/publications/ms-theses/Short%20article/5422_Smf.pdf).

[Welded joints](https://en.wikipedia.org/wiki/Welding) on the pressure and frame plates, on the support, and on the guides must not have cracks.

In case of cracks, repair welding is necessary using [silver electrodes](https://en.wikipedia.org/wiki/Silver_chloride_electrode) with a minimum 45% [silver](https://en.wikipedia.org/wiki/Silver) content, and the temperature during welding must not exceed 650°C.

Plate heat exchangers solve the heat exchange problem in the process industry in a simple way. Get to know them more closely!

Maintenance and Malfunctions of Plate Heat Exchangers for Laymen

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Održavanje i kvarovi pločastih izmjenjivača topline za laike

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30. siječnja 2024.

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