Presentation is loading. Please wait.

Presentation is loading. Please wait.

KAUSAR AHMAD KULLIYYAH OF PHARMACY Heat Transfer By Conduction 1 PHM3133 Dosage Design 1 2010/11

Similar presentations


Presentation on theme: "KAUSAR AHMAD KULLIYYAH OF PHARMACY Heat Transfer By Conduction 1 PHM3133 Dosage Design 1 2010/11"— Presentation transcript:

1

2 KAUSAR AHMAD KULLIYYAH OF PHARMACY Heat Transfer By Conduction 1 PHM3133 Dosage Design /11

3 Contents 2 Practical heat transfer Heat transfer medium Heat transfer through multiple layers Heat transfer at boundary PHM3133 Dosage Design /11

4 Practical Heat Transfer 3 1.You stir some hot soup with a silver spoon and notice that the spoon warms up. 2.You stand watching a bonfire, but can’t get too close because of the heat. 3.It is hard for central air-conditioning in an old house to cool the attic. PHM3133 Dosage Design /11

5 Heat transfer medium Water ………………….…. Steam……………………. Oil………………..……… Thermal liquid………..…. Air……………………. Pebbles/Sand/Iron balls… ……. water-bath …….fluid energy mill …..oil-bath ……….???? …oven, spray drier …high temperature equipment PHM3133 Dosage Design /11 4

6 Thermal conductivity, k 5 k = “thermal conductivity” good thermal conductors ----  high k [k] = J/s-m-  C (  C or K) good thermal insulators … low k Exercise What is k for vacuum? Polystyrene cup? PHM3133 Dosage Design /11

7 Values of k (J/s-m-K) 6 MaterialTemperature/ K kUses Copper 373 (100  C) 379? Graphite 323 (50  C) 138? Glass wool Piping insulation Water circulation Air 473 (200  C) fluid Steam energy mill PHM3133 Dosage Design /11

8 Thermal conductivity of air PHM3133 Dosage Design /11 7 Temperature Thermal conductivity

9 Rate of heat transfer 8 H = Q/t = rate of heat transfer, Unit: J/s H = k A (T H -T C )/L Q/t = k A  T/  x T H Hot T C Cold L Area A PHM3133 Dosage Design /11

10 Find the rate of heat transfer 9 Q/t = k A  T/ xx   T = T H -T C = 25  C Plug in…. Q/t = x 35 x 25/0.02 H=3500 J/s H=3500 Watts Inside: T H = 25  C Outside: T C = 0  C Wood: thickness x = 0.02 m area A = 35 m 2 k = J/s ● m ●  C PHM3133 Dosage Design /11

11 Heat transfer through multiple layers 10 Air is better than wool! And cheaper!! Therefore important for insulation.Hence…layered clothing! Low k For effective heat transfer, choose material with high thermal conductivity. TT PHM3133 Dosage Design /11 Δx = x1 + x2 + x3

12 Examples: heat transfer through multiple layers 11 Heat transfer between fluids…..air heater Heat transfer through a wall ….pot on stove Heat transfer in pipes and tubes…. heat exchanger Heat exchange between a fluid and a solid boundary……fluidised bed PHM3133 Dosage Design /11

13 Find the rate of heat transfer in multiple layers 12 Assume H1 H1 = H2H2  k 1 A(T 0 -T C )/x 1 = k 2 A(T H -T 0 )/x 2 solve for T0 T0 = temp at junction  T 0 =2.27 C then solve for H 1 or H2H2  H=318 Watts x 2 = m A 1 = 35 m 2 k 1 = J/s-m-C Inside: T H = 25  C Outside: T C = 0  C PHM3133 Dosage Design /11 x 1 = 0.02 m A 1 = 35 m 2 k 1 = J/s-m-C

14 Thermal Resistance 13 Q/t = k A  T/  x H/A =  T k/  x =  T/R R =  x/k [Joules/s ● m 2 ], R is the thermal resistance R “adds” for multiple layers Q/tA =  T/ k  x =  T/(R 1 +R 2 +R ) R 1 = x 1 /k 1 etc PHM3133 Dosage Design /11

15 Insulation 14 Insulation for piping is critical to ensure minimum heat loss  Typical insulators are  Glass wool/rock wool  Aluminum sheets PHM3133 Dosage Design /11

16 Heat exchange between a fluid and a solid boundary 15 At the boundary, heat transfer is influenced by conduction and convection: H = hA(T 1 – T 1, wall ), h is the film coefficient A T1T1 T1, wall PHM3133 Dosage Design /11

17 Film coefficient, h (J/m 2 -s-K) 16 Fluidh Water (heat-exchanger) Gases Organic solvents Oils …….why? PHM3133 Dosage Design /11

18 Overall heat transfer coefficient 17 Taking into account k and h, k, thermal conductivity and h,film coefficient Q = U AdT U is the overall heat transfer coefficient PHM3133 Dosage Design /11

19 U values Overall heat transfer coefficient 18 Convection Sea-breeze….1 Radiation Else, heat from sun produces roasted human…… 2 Indirect i.e. through wall conduction House is our shelter…20 Contactive mechanism i.e. gaseous phase heat carrier passes directly through the solids bed200 PHM3133 Dosage Design /11

20 Common heat transport fluids 19 from Perry’s Chemical Engineers’ Handbook 6th Ed. PHM3133 Dosage Design /11

21 Heat transfer equipment: Fluidised bed dryer 20 Hence, drying of solids using fluidised bed technique is very popular! 0002?VNETCOOKIE=NO 0002?VNETCOOKIE=NO PHM3133 Dosage Design /11

22 Relationship between Energy and Temperature 21 Temperature (K) Energy PHM3133 Dosage Design /11

23 References 22 Aulton, M. E. (Ed.) (1988). Pharmaceutics – The Science of Dosage Form Design. Churchill Livingstone. PHM3133 Dosage Design /11


Download ppt "KAUSAR AHMAD KULLIYYAH OF PHARMACY Heat Transfer By Conduction 1 PHM3133 Dosage Design 1 2010/11"

Similar presentations


Ads by Google