Konsep dasar hasil belajar termodinamika

KONSEP DASAR

TERMODINAMIKA

THERMO vs. HEAT TRANSFER

• _{Thermodynamics stems from the Greek words}

therme (heat) and dynamis (power or motion), which is most descriptive of the early efforts to convert heat into power. Today thermodynamics is broadly interpreted to include all aspects of energy and energy transformations, including power generation, refrigeration, and

relationships among the properties of matter.

• _{Heat transfers the science that deals with the}

THERMO vs. HEAT TRANSFER (cont)

• _{Thermodynamics membicarakan sistem keseimbangan} (equilibrium), bisa digunakan untuk menaksir besarnya energi yang diperlukan untuk mengubah suatu sistem keseimbangan, tetapi tidak dapat dipakai untuk

menaksir seberapa cepat (laju) perubahan itu terjadi karena selama proses sistem tidak berada dalam

keseimbangan.

• _{Heat Transfer tidak hanya menerangkan bagaimana} energi itu dihantarkan, tetapi juga menaksir laju

APLIKASI

• _{Tubuh manusia}

• _{Meniup kopi panas}

• _{Perkakas elektronik (sirip, heat sink)} • _{Refrigerator (AC, Kulkas)}

• _{Mobil (siklus engine, sirip, radiator)} • _{Pembangkit listrik (turbin, boiler)}

• _{Industri (penyulingan, pendinginan,}

DIMENSI dan SATUAN

• _{Dimensi (M,L,T,θ)}  homogen

• _{Satuan : SI Units (m, s, kg, K)} • _{Kesalahan umum:}

1. Tidak paham

2. Usaha minimal, kurang latihan

3. Tidak terampil melakukan konversi satuan

• _{Trik: perhitungan harus}

SECONDARY UNITS

• _{Secondary units can be formed by}

combinations of primary units. Example:

SISTEM vs. LINGKUNGAN

• _{A system is defined as a quantity of matter or}

a region in space chosen for study.

• _{The mass or region outside the system is}

called the surroundings.

• _{The real or imaginary surface that}

separates the system from its surroundings is called the

OPEN vs. CLOSSED SYSTEMS

• _{Closed system (= control}

mass): Mass can’t cross the boundary, but energy can. • _{Volume of a closed system}

may change.

CLOSSED SYSTEM

OPEN vs. CLOSSED SYSTEMS

• _{Open system (= control volume) is a properly}

selected region in space. It usually encloses a device that involves mass flow such as a

compressor, turbine, or nozzle.

• _{Both mass and energy can cross the boundary}

of a control volume.

• _{The boundaries of a control volume are called}

OPEN SYSTEM

SIFAT-SIFAT SISTEM

• _{Any characteristic of a system is called a property.}

• _{Some familiar properties are pressure P, temperature T,}

volume V, and mass m. The list can be extended to include less familiar ones such as viscosity, thermal conductivity,

modulus of elasticity, thermal expansion coefficient,

electric resistivity, and even velocity and elevation.

• _{Intensive properties are those that are independent of the}

mass of a system, such as temperature, pressure, and density.

• _{Extensive properties are those whose values depend on the}

size—or extent—of the system.

• _{Extensive properties per unit mass are called specific}

SIFAT INTENSIF vs. EKSTENSIF

TUGAS (dikumpul Senin) : Sebuah apel dibelah dua. Buatlah daftar sifat

intensif dan ekstensifnya

SIFAT-SIFAT SISTEM PENTING

• _{Densitas atau massa jenis: masa}

per satuan volume

• _{Volume spesifik, kebalikan dari} densitas: volume per satuan masa (m3/kg)

• _{Densitas relatif atau specific}

gravity: nisbah densitas suatu substansi dengan densitas

substansi standar pada suhu tertentu (biasanya air pada 4oC

ENERGY SISTEM TERMODINAMIKA

• _{BENTUK ENERGI:}

1. Energi Kinetik (KE) 

2. Energi Potensial (PE)  PE = mgh

3. Energi dakhil atau Internal Energy (U)

POSTULAT KEADAAN

• _{All properties (can be measured or calculated)} completely describes the condition, or the state, of the system. At a given state, all the properties of a system have fixed values. If the value of even one property changes, the state will change to a different one.

• _{The number of properties required to fix the state} of a system is given by the state postulate:

PROSES

dan SIKLUS

• _{Any change that a}

system undergoes from one equilibrium state to another is called a

process

• _{The series of states}

through which a system passes during a process is called the path

MACAM-MACAM

PROSES

• _{Proses isotermal: proses pada suhu T konstan.} • _{Proses isobaris: proses pada tekanan P konstan.} • _{Proses isokhoris (isometris): proses pada}

volume spesifik  konstan.

• _{Proses adiabatik: proses di mana tidak terjadi}

pertukaran kalor dengan lingkungan.

• _{Proses isentropik: proses pada entropi S}

STEADY-FLOW PROCESS

• _{The terms steady and uniform are used}

frequently in engineering, and thus it is

important to have a clear understanding of their meanings.

• _{The term steady implies no change with time.} • _{The opposite of steady is unsteady, or}

transient.

• _{The term uniform, however, implies no change}

PROSES dan

SIKLUS

• _{A system undergoes a cycle if it returns to its}

initial state at the end of the process.

Siklus dengan 2 lintasan

TEKANAN

• _{Tekanan (P) : gaya (F) per satuan luas (A).}

• _{Satuan tekanan adalah pascal (Pa) = N/m}2.

• _{Untuk benda padat gaya per luas satuan tidak disebut}

tekanan, tetapi tegangan (stress).

• _{Untuk fluida diam, tekanan adalah sama ke segala arah.} • _{Tekanan di dalam fluida meningkat sesuai dengan}

kedalamannya akibat berat fluida (pengaruh gravitasi) sehingga fluida pada bagian bawah menanggung beban yang lebih besar daripada fluida di bagian atas.

• _{Tetapi tekanan tidak bervariasi pada arah horisontal.} • _{Tekanan gas di dalam tangki dapat dianggap seragam}

TEKANAN: UKUR, ATM, VAKUM

• _{Tekanan aktual pada posisi tertentu disebut tekanan}

absolut dan diukur secara relatif terhadap tekanan vakum, yaitu tekanan nol mutlak.

• _{Kebanyakan pengukur tekanan dikalibrasi untuk}

membaca nol di atmosfer (tekanan atmosfer lokal).

• _{Perbedaan tekanan absolut dan tekanan atmosfer}

disebut tekanan ukur (pressure gage).

• _{Tekanan di bawah tekanan atmosfer disebut tekanan}

vakum (vacuum pressure) dan diukur dengan pengukur vakum yang menunjukkan perbedaan antara tekanan atmosfer dan tekanan absolut.

TEKANAN UKUR,

PENGUKUR TEKANAN

PRESSURE GAGE

MANOMETER

PRINSIP MANOMETER

Perhatikan gambar:

• _Seimbang F = 0

• _{P1 = P2}

• _{A P1 = A Patm + W}

di mana W = m g =

 V g =  A h g

• _{P1 = Patm +}  h g

EXAMPLE : Manometer

A manometer is used to measure the pressure in a tank. The fluid used has a specific gravity of 0.85, and the manometer column

height is 55 cm, as shown in Figure. If the local

EXAMPLE: MULTIFLUID MANOMETER

Water in a tank is pressurized by air, and the pressure is measured by a multifluid manometer (see Figure). The tank is located on a mountain at an altitude of 1400 m where the atmospheric pressure is 85.6 kPa. Determine the air

pressure in the tank if h₁ = 0.1 m, h₂

= 0.2 m, and h₃ = 0.35 m. Take the densities of water, oil, and mercury to be 1000 kg/m3, 850 kg/m3, and

APLIKASI MANOMETER

pressure drop across a flow section or a flow device by a differential

BAROMETER Torricelli

EXAMPLE3: BAROMETER

• _{Determine the atmospheric pressure at a}

location where the barometric reading is 740 mm Hg and the gravitational acceleration is g 9.81 m/s2. Assume the temperature of

mercury to be 10oC, at which its density is

TEKANAN ATMOSFER

ELEVASI

(m) TEKANAN (kPa) TEKANAN (mmHg)

0 (sea level) 101.325 760.00

1000 89.88 674.15

2000 79.50 596.30

5000 54.05 405.41

10,000 26.5 198.77

20,000 5.53 41.48

TEMPERATURE

• _{Thermodinamika}  SUHU MUTLAK

• _{Satuan kelvin (K) untuk SI}

• _{Satuan renkine (R) untuk USCS}

EXAMPLE4: TEMPERATURE

• _{During a heating process, the temperature of a}

PR:

• _{Soal No: 1-6C, 1-7C, 1-15C, 1-16C, 1-17C,}

1-20C, 1-21C, 1-22C, 1-23C, 1-24C, 1-29, 1-31, 1-34C, 1-35C, 1-36C, 1-39C, 1-40, 1-42, 1-43,

1-44, 1-45, 1-48, 1-51, 1-53, 1-55, 1-57, 1-59,

1-61, 1-62, 1-63, 1-65, 1-66, 1-73, 1-85, 1-88,

1-101, 1-103, 1-105, 1-106, 1-108, 1-120,

1-121, 1-122, 1-123, 1-125.

• _{Kelompok THERMO}