Thermodinamika FAKULTAS TEKNOLOGI INDUSTRI UNIVERSITAS MERCU BUANA TEKNIK MESIN FAKULTAS TEKNOLOGI INDUSTRI UNIVERSITAS MERCU BUANA MODUL KETIGA THERMODINAMIKA DASAR NANANG RUHYAT ENTHALPI DAN ENTROPI Entalpi adalah jumlah kalor yang diberikan atau dilepaskan per satuan massa yang ditimbulkan melalui proses dengan tekanan tetap dan meniadakan kerja yang dilakukan. Dalam analisa termodinamika, kombinasi energi dalam (U) dan kerja aliran (pV) atau U + pV sering terjadi, kombinasi ini diberi simbol (H), maka dengan demikian : H = U + Pv bila ditulis per satuan massa akan berbentuk : h = u + pv Tiap besaran pada ruas kanan dari persamaan diatas adalah sifat zat, jadi entalpi merupakan sifat zat. Dari persamaan hukum termodinamika pertama, yaitu : dQ = dU + dW dQ = dU + p.dv karena : d(p.V) = p.dV + V.dp maka : dQ = dU + d(p.V) – V.dp PUSAT PENGEMBANGAN BAHAN AJAR-UMB http://www.mercubuana.ac.id Ir. Nanang Ruhyat MT. THERMODINAMIKA DASAR 1

3 http://www.mercubuana.ac.id Thermodinamika Ir. Nanang Ruhyat MT. PUSAT PENGEMBANGAN BAHAN AJAR-UMB http://www.mercubuana.ac.id Ir. Nanang Ruhyat MT. THERMODINAMIKA DASAR 3

Thermodinamika 5 http://www.mercubuana.ac.id Specific Enthalpy Specific enthalpy (h) is defined as h = u + P , where u is the specific internal energy (Btu/lbm) of the system being studied, P is the pressure of the system (lbf/ft2), and is the specific volume (ft3/lbm) of the system. Enthalpy is usually used in connection with an "open" system problem in thermodynamics. Enthalpy is a property of a substance, like pressure, temperature, and volume, but it cannot be measured directly. Normally, the enthalpy of a substance is given with respect to some reference value. For example, the specific enthalpy of water or steam is given using the reference that the specific enthalpy of water is zero at .01°C and normal atmospheric pressure. The fact that the absolute value of specific enthalpy is unknown is not a problem, however, because it is the change in specific enthalpy ( h) and not the absolute value that is important in practical problems. Steam tables include values of enthalpy as part of the information tabulated. Work Kinetic energy, potential energy, internal energy, and P-V energy are forms of energy that are properties of a system. Work is a form of energy, but it is energy in transit. Work is not a property of a system. Work is a process done by or on a system, but a system contains no work. This distinction between the forms of energy that are properties of a system and the forms of PUSAT PENGEMBANGAN BAHAN AJAR-UMB http://www.mercubuana.ac.id Ir. Nanang Ruhyat MT. THERMODINAMIKA DASAR 5