Apa saja aplikasi proses termodinamika isobarik dan isotermal dalam kehidupan sehari-hari?

? asked 2 years agoWas originally asked on Yahoo Answers Indonesia

msalnya kan proses termodinamika adiabatik yg trjd sehri hari tuh ada pada mesin motor yg...... trs contoh proses termodinamika isobarik dalam kehidupan sehari-hari dan contoh proses termodinamika isotermal sehari hari itu pada apa?? please tolongin gw :__(

Isobarik --> Memasak air tanpa tertutup wadah dan semua proses pemanasan pada umumnya. Semisal memanaskan udara pada wadah terbuka atau dapat terekspansi secara bebas. Aplikasi umum di Industri apa pada penukar panas (heat exchanger). Penukar panas memanaskan fluida pada tekanan konstan. Contohnya boiler(ketel uap) di PLTU, air dipanaskan hingga menguap pada tekanan konstan. 

Pendinginan yang dilakukan kulkas juga berlangsung secara isotermal. Udara di kabin didinginkan dengan cara "relatif" tidak mengubah tekanan. Contoh lain pendinginan udara oleh AC, dan lainnya. 

Isotermal --> Umumnya berkaitan dengan perubahan fasa. Semisal pencairan dan penguapan. Contoh lain ada pada Mesin(engine) dengan daur Stirling atau daur(siklus) Ericsson. Atau proses kompresi pada siklus kriogenik. Kompresi dilakukan bertingkat dengan melakukan pendinginan, sehingga temperatur terjaga konstan. 

Proses kompresi atau ekspansi umumnya tidak isotermal, hanya jika dilakukan secara lambat, bisa dianggap isotermal. Semisal "memompa"(mengkompresi) ban sepeda secara pelan-pelan.

BAB II

Prinsip Kerja Mesin Pendingin

A. Sistem Pendinginan Absorbsi

Sejarah mesin pendingin absorbsi dimulai pada abad ke-19 mendahului

jenis kompresi uap dan telah mengalami masa kejayaannya sendiri.

pendinginan absorbsi mirip dengan siklus pendinginan kompresi uap.

utama kedua siklus tersebut adalah gaya yang menyebabkan terjadinya perbedaan

tekanan antara tekanan penguapan dan tekanan kondensasi serta cara perpindahan

uap dari wilayah bertekanan rendah ke wilayah bertekanan tinggi.

Pada sistem pendingin kompresi uap digunakan kompresor, sedangkan

pada sistem pendingin absorbsi digunakan absorber dan generator.

bertekanan rendah diserap di absorber, tekanan ditingkatkan dengan pompa dan

pemberian panas di generator sehingga absorber dan generator dapat

menggantikan fungsi kompresor secara mutlak.  Untuk melakukan proses

kompresi tersebut, sistem pendingin kompresi uap memerlukan masukan kerja

mekanik sedangkan sistem pendingin absorbsi memerlukan masukan energi

panas.  Oleh sebab itu, siklus kompresi uap sering disebut sebagai siklus yang

digerakkan dengan kerja (WORK-OPERATED) dan siklus absorbsi disebut sebagai

siklus yang digerakkan dengan panas (HEAT OPERATED

menunjukkan persamaan dan perbedaan antara siklus kompresi uap dengan siklus

absorbsi.

Pada tahun 1901 , Italia penemu Luigi Bezzera datang dengan solusi yang bisa diterapkan . Pavoni diproduksi mesin-mesin espresso pertama pada tahun 1905 .

Mesin ini juga bertenaga uap . Namun, uap tidak datang ke dalam kontak dengan kopi . Sebaliknya , tekanan uap pada bagian atas boiler memaksa air di bagian bawah boiler melalui kopi bubuk . Kopi diselenggarakan dalam kelompok yang terdiri dari portafilter , filter keranjang logam dan removable kuningan gunung , dan kepala brew di mana portafilter menempel . Pipa dan kelompok yang dirancang untuk bertindak sebagai radiator panas , sehingga suhu air bertekanan turun dari 250 ° F ( 120 ° C ) dalam boiler dengan suhu menyeduh benar pada grouphead tersebut . Prinsip ini bir masih digunakan dalam kompor mochapots . Karena air bertekanan , kopi bisa menjadi tanah halus daripada di bir pourover teratur, mengurangi siklus pembuatan bir minimum dari sekitar 4 menit 30 detik. Mesin espresso dan penggiling kopi yang menyertainya menjadi perlengkapan standar untuk membuat kopi di Italia , Perancis Selatan , Spanyol dan Amerika Latin . Di bagian lain dunia, diikuti imigran Italia yang mempopulerkannya di setiap negara mereka menetap .

Namun teknologi bergerak, dan metode ini tidak lagi dianggap sebagai khusus espresso , meskipun mochapots dan bir ditekan uap lainnya terus dipasarkan di bawah nama . Pada 1920-an melalui tahun

1940-an , insinyur Italia bereksperimen dengan perangkat memompa untuk meningkatkan tekanan pembuatan bir . Yang praktis pertama dikembangkan oleh Cremonesi pada tahun 1938 dan diproduksi oleh Achille Gaggia pada tahun 1946 . Dulu tangan piston bertenaga . Pada mesin jenis ini , tekanan steam dalam boiler memaksa air ke dalam silinder , tetapi kemudian bertekanan lebih lanjut dengan piston musim semi bertenaga sekitar 8 sampai 9 bar ( 120-135 PSI ) , atau 8 sampai 9 kali tekanan yang telah dikembangkan oleh mesin uap. Musim semi yang kekuatan piston dikompresi oleh tuas dipaksa turun oleh barista ( Italia untuk barkeep ) - orang yang membuat kopi . Seperti dengan mesin generasi tua , kelompok-kelompok tuas dirancang untuk mendinginkan air dari boiler suhu pembuatan bir .

Heat Exchanger Machines How They Work» Coffeetime Contents Page » Equipment » Heat Exchanger Machines How They Work

The Heat Exchanger Espresso Machine - Demystified

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In this article I want to explain how the Heat Exchanger type of espresso machine actually works. This type of machine is really very simple, although often people seem to believe it’s much more complicated than it is, especially the mystical “heat exchanger”. As usual on Coffeetime, we like to keep it simple:

Let’s first start with an explanation of the “Heat Exchanger (HX)”, a very fancy term for a copper tube that passes through hot water. In the picture below, we have built one, and as the cold water flows through the copper tube, immersed in a container of hot water, it gets heated up.

So the HX is really very simple and it is probably clear that the temperature of hot water exiting the heat exchanger depends on a number of things

How hot the water in the container (boiler) is The surface area of the copper tube (or to put it simply, how long it is) The temperature of the water when it enters the copper tube How fast the water flows

The espresso machine designers will have to consider these factors in designing a machine that is able to produce enough hot water, without it being too hot and to minimise the requirements of a cooling flush. Now we have the “complexities of the very simple device that is the “Heat Exchanger” out of the way, lets move on to a simplified diagram of the insides of a real espresso machine

The diagram has been divided into 3 coloured sections for clarity (click to enlarge).

Yellow Section

This section is what could be termed the cool side of the machine; it will contain the cold water tank (or possibly mains water inlet on a plumbed machine). Its task is to provide water at the correct pressure to the rest of the espresso machine. The pump can be either a Vibration pump, or in the case of a machine like my Izzo Alex, a rotary pump. Its sole purpose is to pump water at high pressure (9 or 10 bar).

Note: Vibration pumps are unregulated and deliver water at a pressure of 15 bar (much too high for espresso). Rotary pumps have their own internal pressure regulation and can be regulated to deliver water directly at 9 bar.

The water is drawn from the cold water tank, into the vibration pump, and through a device called an OPV (pressure release valve) which lowers it’s pressure. You will notice that this OPV has a tube leading back to the cold water tank, because to regulate water pressure down to 9 or 10 bar, it has to allow some of the water back to the tank rather than into the machine (see OPV article for more information on how the OPV works).

The water now passes from the OPV to the rest of the machine; this water can now only exert a maximum static pressure of 9 or 10 bar. It next comes to something called an “Autofill Solenoid”. The “Autofill Solenoid” has two positions:

Water is directed to the E61 group (via the HX) for making coffee (normally in this position)

Water is directed into the main boiler to refill e.g. after steaming, or using hot water.

The function of this solenoid, as you may have guessed, is simply to ensure the main boiler can fill when needed, without pushing water through the E61 group.

Our water leaves the yellow section, able to exert a maximum static pressure of 9 or 10 bar, fine for making coffee and at a high enough pressure to fill our boiler (which is usually kept at around 1.3 bar).

Red Section

This can be termed the hot side of the machine, it’s where the water gets heated, steam is produced and everything is prepared for coffee making.

The main component of this section is the Boiler, as you can see it is full of hot water and steam. It can do this because the boiler is like a pressure cooker and inside it’s at a higher pressure than atmospheric. In fact the boiler is usually at around 1.2 bar. This means we have water at around 124C (yes hotter than boiling which is 100C) and an area of steam above the hot water. The boiler is maintained at this pressure by the little pressurestat which switches the heating element on/off as required to maintain 1.2 bar. These pressurestats are usually adjustable, via an adjuster on top (using a screwdriver.).

When we open the steam tap, steam comes out and the pressure in the boiler drops, this causes the water to instantly boil, producing more steam…very simple

When we open the hot water tap, steam pressure forces the water out

The autofill probe is just in the water, but when the water level drops as in steaming or drawing hot water, it senses this drop in level and tells the Control Board (brain). The brain then switches on the pump and sets the autofill solenoid to the fill the boiler position. Once the water level reaches the probe, the pump switches off and the autofill solenoid goes back to the making coffee position.

You can clearly see the HX tube within the boiler and this works no differently to the simple diagram given earlier.

Tan (or Coffee Coloured) Section

This is the business end of the machine, the part you normally see and interact with. All the previous wizardry was to deliver hot water at about 93-96C and 9 bar (140 psi) to this part of the machine for making coffee. Move lever up, pump starts, water passes through HX into group at 9 bar, into portafilter and through coffee….mmmm espresso!

The only slight complexity here is shown in the area marked by the green dashed line. The E61 thermosyphon (link). This is a simple passive circuit that allows convection currents to

circulate through the E61 group to keep it hot (this increases temperature stability during the shot). You can read much more about it in the E61 thermosyphon article.

Lastly the poor old control board…well it’s box of electronics and controls the pump, water level, autofill solenoids and even has a protective circuit that prevents the heating element coming on if the boiler needs filling. It does a few other fancy functions at switch on, but it’s really a simple device. They are sometimes called level controllers and are usually made by Giemme or Gicar for prosumer machines. They are not meant to be user serviceable and if they go wrong are usually replaced. However often a fault is a simple transformer that runs one of the solenoids and these can sometimes be purchased cheaply for a few pounds and replaced using a soldering iron.

How it Work

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The special patent for the steam thermoregulation of the group unit, which enables to obtain Coffee always at the same serving temperature, has given a high quality level that can be distinguished from all the other products on the market.

 Electronic espresso coffee machine with automatic and proportioned dose setting   Electronic temperature probe for the thermoregulation controlled by microprocessor   Electronic control

panel and display : adjustement and control of all working parameters of the   machine and self-diagnosis system  Automatic filler up of the boiler   Electric cup warmer   Cups counter for all dispensing units and doses   External or built-in pump   Safety thermostat which can be reset   All controls and electrovalves of the dispensing units at low tension (24V)   Available in different colours : stainless-steel , oxinox, gold and copper