1 / 36

Unit Operation and Process Heat Transfer

Unit Operation and Process Heat Transfer . Widelia Ika Putri, S.T.P., M.Sc. Pasteurization of milk, juice, etc. Refrigeration of fruits and vegetables. Meat freezing. Thermal sterilization in canned food. Evaporation Distillation Drying . Heat transfer.

wilmet
Download Presentation

Unit Operation and Process Heat Transfer

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Unit Operation and ProcessHeat Transfer Widelia Ika Putri, S.T.P., M.Sc.

  2. Pasteurization of milk, juice, etc. • Refrigeration of fruits and vegetables. • Meat freezing. • Thermal sterilization in canned food. • Evaporation • Distillation • Drying March 2012

  3. Heat transfer • A dynamic process in which heat is transferred spontaneously from one body to another a lower temperature body. • The rate of heat transfer depends upon the differences between the bodies, the greater the difference in temperature, the greater the rate of heat transfer. • Temperature difference between the source of heat and the receiver of heat is therefore the driving force in heat transfer. • An increase in the temperature difference increases the driving force and therefore increases the rate of heat transfer. March 2012

  4. Heat transfer Conduction Convection Radiation March 2012

  5. Rate of transfer = driving force / resistance • Rate of heat transfer = temperature difference / heat flow resistance of medium. March 2012

  6. Ohm’s Law • The rate of transport (the quantity transported per unit time) is proportional to the driving force and inversely proportional to the resistance of the medium to the transport. March 2012

  7. q = dQ/dt = the rate of heat transfer • F = driving force • R = resistance of the medium to heat transfer • k = conductance of the medium to heat transfer • Heat flux (J) = the rate of transport proportional to the area A available to the transport (the rate of transport per unit area) => q/A March 2012

  8. Steady State Conductive Heat Transfer • Steady state => all the properties that define the ‘state’ of the system (temperature, pressure, chemical composition, etc.) remain constant with time. • Fourier’s 1st Law March 2012

  9. Q = heat transferred (J) • T = temperature (K) • t = time (s) • k = thermal conductivity of the medium (J/s.m.K)(W/m.K) • z = distance in the direction of the transport (m) March 2012

  10. March 2012

  11. Soal 1. Hitung kecepatan transfer panas dari bahan 3x4 m, tebal 0,2m, di satu sisi 0oC dan di sisi lainnya 35oC. Jika bahan tersebut adalah: a. alumunium; b. kuningan; c. besi; d. tembaga; e. karet March 2012

  12. Sweat (1986) • k = 0.25Xc+ 0.155Xp + 0.16Xf + 0.135Xa + 0.58Xw • X = mass fraction • c = carbohydrate • p = protein • f = fat • a = ash • w = water March 2012

  13. Soal • Hitung thermal conductivity dari bahan berikut ini: March 2012

  14. Steady State Conduction through a Single Slab March 2012

  15. Steady State Conduction through a Multilayer Slab March 2012

  16. Soal • Dinding dari ruang penyimpan tersusun dari 3 lapisan, dari yang terdalam: • Stainless steel, tebal 2mm • Thermal insulation, tebal 80mm (k = 0.03 J/s.m.C) • Beton, tebal 150mm Bila sisi terdalam adalah -18oC dan sisi terluar 20oC, hitung flux panas yang melalui dinding? March 2012

  17. Steady State Conduction through a Cylinder Slab March 2012

  18. Soal 1. Pipa baja berdiameter 5cm membawa uap air pada 150oC. Pipa disekat dengan lapisan penyekat silinder ketebalan 3cm (k=0.03W/mK). Hitung kecepatan panas hilang per meter panjang pipa, jika suhu lapisan terluar adalah 35oC? Company Logo

  19. Steady State Convective Heat Transfer Convection Natural Convection The movement is caused by heat transfer itself. Forced Convection The movement is caused by factor independent of the transfer. March 2012

  20. A stationary layer (film) of fluid which in contact with the solid’s surface -> thickness δ • Temperature in the bulk -> T2; temperature in the boundary layer -> T1 • A coefficient convective of heat transfer -> March 2012

  21. h -> depends on the properties of the fluid (specific heat, viscosity, density, and thermal conductivity), the turbulence (average velocity), and the geometry of the system -> these parameters are dimensionless group used in heat transfer. March 2012

  22. vertical Natural convection sphere March 2012

  23. Soal • Papan gabus tebal 10 cm pada satu sisi bersuhu -12oC dan sisi lain 21oC. Berapa kecepatan transfer panas melalui 1m2 dinding? • Sebuah cold storage memiliki dinding yang tersusun dari: 11 cm batu bata pd bag. terluar, kmdn 7,5 cm beton, dan 10 cm gabus. Suhu rata2 di bag. dalam -18oC dan di bagian luar dinding 18oC. Hitung kecepatan transfer panas melalui 1m2 dinding? March 2012

  24. Soal 1. Hitung kecepatan panas yang hilang dari dinding vertical suatu oven dengan konveksi alami. Suhu dinding 50oC dan di udara ambient 20oC. Tinggi dinding 1.2m dan lebar 3m? March 2012

  25. turbulent viscous Forced convection sphere March 2012

  26. Soal 1. Jus jeruk, didinginkan, mengalir dengan kecepatan 4m3/jam melalui pipa berdiameter 0.05m. Sifat dari jus jeruk pada suhu pengolahan adalah: ρ= 1060kg/m3; µ= 3.10-3Pa.s; cp= 3900J/kg.K; k= 0.54 W/m.K. Hitung koeffisien panas konveksi antara jus jeruk yang mengalir di dalam pipa dengan dinding pipa? March 2012

  27. 2. Gandum pipilan dikeringkan dengan udara panas dalam aliran turbulent di fluidized bed dryer. Kecepatan udara 0.5m/s dengan suhu 93oC. Pipilan gandum diasumsikan berbentuk bulat dengan diameter 1mm. Hitung koeffisien transfer panas konveksi? March 2012

  28. Radiation • Radiation covers a vast array of phenomena that involve energy transport in the form of waves, in the wavelength range of 10-7 to 10-4 m. • Radiation => cooling the emitting body and heating the receiving body. • > 0oK => all substances emit electromagnetic radiation. • Heat transfer by radiation does not require the presence of material medium. March 2012

  29. Black body => a body that absorb the incident radiation totally; the absorbtivity of black body is unity and its reflectivity and transmissivity are both zero. March 2012

  30. Emmisivity (ε) => the ratio of emissive power of a real body to that of a black body at the same temperature; always less than unity. March 2012

  31. Soal 1. Hitung net heat transfer dengan radiasi dari sebongkah roti di oven pada suhu 177oC, jika emissivitasnya 0,85 dgn total luas area 0.0645 m2 dan suhu 100oC? March 2012

  32. Heat Exchanger • Device for the exchange of heat between two fluids separated by partition. • The partition is a heat conducting solid wall, usually made of metal. • Extensively used in the food industry for heating (e.g. pasteurizer), cooling (chilled water generator), and heat induced phase change (freezing, evaporation). Company Logo

  33. 1 2 3 Parallel flow Countercurrent flow Cross flow Flow Pattern Company Logo

  34. Company Logo

  35. Company Logo

  36. Thank You !

More Related