TEKNIK MESIN
FAKULTAS TEKNOLOGI INDUSTRI
UNIVERSITAS MERCU BUANA
MODUL KE DUA BELAS
HEAT TRANSFER
NANANG RUHYAT
KOMPRESI UAP
Siklus Kompresi Uap
Siklus kompresi uap merupakan salah satu siklus yang digunakan dalam proses
pendinginan, siklus kompresi uap memerlukan beberapa komponen utama agar siklus ini
dapat bekerja dengan baik seperti kompresor, kondensor, katup ekspansi, dan evaporator.
Adapun proses ideal yang terjadi pada siklus kompresi uap adalah proses kompresi,
kondensasi, proses ekspansi dan proses evaporasi, dan proses ini dapat digambarkan
sebagai berikut :
( Stoecker, W.F and jones, J.W. 1989 . Refrigerasi dan Pengkondisian Udara, edisi ke2.Alih bahasa Ir.Supratman Hara.Jakarta : Erlangga )
P
4
1
3
2
H
Gambar 1 Diagram PH Sistem Kompresi Uap
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mº
= Laju aliran massa refrigerant ( kg/s).
h3 – h2 = Kerja kompresi (kj/kg).
3–4
Proses Kondensasi
Tahap ini terjadi di dalam kondensor, dimana panas dari refrigerant yang berfasa uap dari
kompresor dibuang ke lingkungan sehingga refrigerant tersebut mengalami kondensasi.
Pada tahap ini terjadi perubahan fasa dari dari fasa uap superheat menjadi fasa cair jenuh,
pada fasa cair jenuh ini tekanan dan temperaturnya masih tinggi. Besarnya kalor yang
dilepaskan di kondensor adalah :
qc = h3 – h4……………………….………( 3)
Dimana :
4–1
qc
= Kalor yang dilepas di kondensor (kj/kg)
h3
= Entalpi refrigerant yang keluar dari kompresor (kj/kg)
h4
= Entalpi refrigerant cair jenuh (kj/kg)
Proses Ekspansi
Tahap ini terjadi di katup ekspansi dimana refrigerant diturunkan tekanannya yang diikuti
dengan turunnya temperatur isentalphi.
Combustion or burning is a complex sequence of chemical reactions between a fuel
and an oxidant accompanied by the production of heat or both heat and light in the form
of either a glow or flames.
In a complete combustion reaction, a compound reacts with an oxidizing element, and
the products are compounds of each element in the fuel with the oxidizing element. For
example:
A simpler example can be seen in the combustion of hydrogen and oxygen, which is a
commonly used reaction in rocket engines:
The result is simply water vapor.
In the large majority of the real world uses of combustion, the oxygen (O2) oxidant is
obtained from the ambient air and the resultant flue gas from the combustion will
contain nitrogen:
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Incomplete
Incomplete combustion happens when there isn't enought oxygen for combustion to occur
completely. The reactant will burn in oxygen, but will produce numerous products. When a
hydrocarbon burns in air, the reaction will yield carbon dioxide, water, carbon monoxide, and
various other compounds such as nitrogen oxides. Incomplete combustion is much more
common and will produce large amounts of byproducts, and in the case of burning fuel in
automobiles, these byproducts can be quite unhealthy and damaging to the environment.
Quality of combustion can be improved by design of combustion devices, such as burners
and internal combustion engines. Further improvements are achievable by catalytic afterburning devices (such as catalytic converters). Such devices are required by environmental
legislation for cars in most countries, and may be necessary in large combustion devices,
such as thermal power plants, to reach legal emission standards.
Smouldering
Smouldering combustion is a flameless form of combustion, deriving its heat from
heterogeneous reactions occurring on the surface of a solid fuel when heated in an
oxidizing environment. The fundamental difference between smouldering and flaming
combustion is that in smouldering, the oxidation of the reactant species occurs on the
surface of the solid rather than in the gas phase. The characteristic temperature and heat
released during smouldering are low compared to those in the flaming combustion of a solid.
Typical values in smouldering are around 600 °C for the peak temperature and 5 kJ/g-O2 for
the heat released; typical values during flaming are around 1500 °C and 13 kJ/g-O2
respectively. These characteristics cause smoulder to propagate at low velocities, typically
around 0.1 mm/s, which is about two orders of magnitude lower than the velocity of flame
spread over a solid. In spite of its weak combustion characteristics, smouldering is a
significant fire hazard.
Generally, the chemical equation for burning a hydrocarbon (such as octane) in oxygen is as
follows:
For example, the burning of propane is: The simple word equation for the combustion
of a hydrocarbon in oxygen is: If the combustion takes place using air as the oxygen
source, the corresponding equations are:
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