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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.

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Unit Operation and Process Heat Transfer

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  1. Unit Operation and ProcessHeat Transfer WideliaIkaPutri, 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 increasing 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. Hitungkecepatan transfer panasdaribahan 3x4 m, tebal 0,2m, disatusisi 0oC dandisisilainnya 35oC. Jikabahantersebutadalah: 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 daribahanberikutini: March 2012

  14. Steady State Conduction through a Single Slab March 2012

  15. Steady State Conduction through a Multilayer Slab March 2012

  16. Soal • Dindingdariruangpenyimpantersusundari 3 lapisan, dari yang terdalam: • Stainless steel, tebal 2mm • Thermal insulation, tebal 80mm (k = 0.03 J/s.m.K) • Beton, tebal 150mm Bilasisiterdalamadalah -18oC dansisiterluar 20oC, hitung flux panas yang melaluidinding? March 2012

  17. Steady State Conduction through a Cylinder Slab March 2012

  18. Soal 1. Pipabajaberdiameterluar 5cm membawauap air pada 150oC. Pipadisekatdenganlapisanpenyekatsilinderketebalan 3cm (k=0.03W/mK). Hitungkecepatanpanashilang per meter panjangpipa, jikasuhulapisanterluaradalah 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. Natural convection March 2012

  23. Soal • Papangabustebal 10 cm padasatusisibersuhu -12oC dansisi lain 21oC. Berapakecepatan transfer panasmelalui 1m2dinding? • Sebuah cold storage memilikidinding yang tersusundari: 11 cm batubata pd bag. terluar, kmdn 7,5 cm beton, dan 10 cm beton. Suhu rata2 di bag. dalam -18oC dandibagianluardinding 18oC. Hitungkecepatan transfer panasmelalui 1m2dinding? March 2012

  24. Soal 1. Hitungkecepatanpanas yang hilangdaridinding vertical suatu oven dengankonveksialami. Suhudinding 50oC dandiudara ambient 20oC. Tinggidinding 1.2m danlebar 3m? March 2012

  25. Forced convection March 2012

  26. Soal 1. Jus jeruk, didinginkan, mengalirdengankecepatan 4m3/jam melaluipipaberdiameter 0.05m. Sifatdari jus jerukpadasuhupengolahanadalah: ρ= 1060kg/m3; µ= 3.10-3Pa.s; cp= 3900J/kg.K; k= 0.54 W/m.K. Hitungkoeffisienpanaskonveksiantara jus jeruk yang mengalirdidalampipadengandindingpipa? March 2012

  27. 2. Gandumpipilandikeringkandenganudarapanasdalamaliran turbulent di fluidized bed dryer. Kecepatanudara 0.5m/s dengansuhu 93oC. Pipilangandumdiasumsikanberbentukbulatdengan diameter 1mm. Hitungkoeffisien transfer panaskonveksi? 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 denganradiasidarisebongkahrotidi oven padasuhu 177oC, jikaemissivitasnya 0,85 dgn total luas area 0.0645 m2dansuhu 100oC? March 2012

  32. Thank You !

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