Abstract
Very many food processing operations involve the transfer of heat: cooking, roasting, drying, evaporation, sterilisation (either of bulk liquids or of packaged foods), chilling and freezing are utilised to preserve food or to prepare it directly for eating. Thus the student of food engineering needs a thorough understanding of the mechanisms of the transfer of heat together with a knowledge of heat exchange equipment. Many applications of heat transfer to food processing require a knowledge of unsteady-state theory; this is particularly true of freezing, for example. However, it is undoubtedly easier to grasp the principles of heat transfer by studying steady-state processes first and, although steady state is simply a special case of the general unsteady-state theory, the approach adopted here is to study the former first. More complex problems will be introduced only when steady-state heat exchange has been covered in detail.
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Abbreviations
- a :
-
Coefficient
- A :
-
Area
- b :
-
Coefficient
- c :
-
Velocity of light; ratio of the yield stress to the shear stress at the wall
- c p :
-
Heat capacity at constant pressure
- c 1 :
-
Constant in Planck’s equation
- c 2 :
-
Constant in Planck’s equation
- C :
-
Coefficient
- d :
-
Diameter
- d o :
-
External tube diameter
- e :
-
Emissivity
- E :
-
Emissive power; field strength; electromotive force
- F :
-
Correction factor for multi-pass heat exchangers
- \({F_{mn}}\) :
-
View factor, fraction of radiation leaving at surface m and arriving at surface n
- g :
-
Acceleration due to gravity
- Gr :
-
Grashof number
- Gz :
-
Graetz number
- h :
-
Film heat transfer coefficient
- \({h_{{\textrm{fg}}}}\) :
-
Enthalpy of vaporisation
- h m :
-
Mean film heat transfer coefficient
- I :
-
Incident radiation rate
- k :
-
Thermal conductivity
- K :
-
Consistency coefficient
- L :
-
Pipe length; linear dimension characteristic of heat transfer geometry
- m :
-
Mass flow rate; index
- n :
-
Number of tubes; flow behaviour index; index
- Nu :
-
Nusselt number
- P :
-
Pressure; power
- P o :
-
Incident power
- Pr :
-
Prandtl number
- q :
-
Heat flux
- \({q_{\max }}\) :
-
Peak heat flux
- \({q_{1 \to 2}}\) :
-
Net radiant heat flux between surfaces 1 and 2
- Q :
-
Rate of heat transfer
- \({Q_{1 \to 2}}\) :
-
Net rate of radiant heat transfer between surfaces 1 and 2
- r :
-
Radius
- r a :
-
Arithmetic mean radius
- \({r_{{\textrm{critical}}}}\) :
-
Critical radius of insulation
- \({r_{{\textrm{lm}}}}\) :
-
Logarithmic mean radius
- r p :
-
Inner radius of insulation
- R :
-
Thermal resistance per unit area per unit length of pipe
- R f :
-
Fouling factor
- Re :
-
Reynolds number
- T :
-
Temperature
- T(r):
-
Temperature at radius r
- U :
-
Overall heat transfer coefficient
- V :
-
Volume
- x :
-
Length or thickness in the x-direction
- X :
-
Dimensionless temperature difference
- Y :
-
Dimensionless temperature difference
- z :
-
Penetration depth
- α :
-
Absorptivity; thermal diffusivity
- \(\alpha '\) :
-
Attenuation factor
- β :
-
Coefficient of linear expansion
- δ :
-
Group defined by Eq. (7.93)
- \(\tan \delta\) :
-
Loss tangent
- ΔT :
-
Temperature difference
- \(\Delta {T_{{\textrm{lm}}}}\) :
-
Logarithmic mean temperature difference
- \(\varepsilon '\) :
-
Relative dielectric constant
- \(\varepsilon ''\) :
-
Relative dielectric loss
- θ :
-
Tube-side temperature
- λ :
-
Wavelength
- λ m :
-
Wavelength at which energy emission is a maximum
- μ :
-
Viscosity
- ρ :
-
Density; reflectivity
- σ :
-
Surface tension; Stefan–Boltzmann constant
- τ :
-
Transmissivity
- υ :
-
Frequency
- Ψ :
-
Group defined by Eq. (7.88)
- b:
-
Bulk
- B:
-
Back body
- c:
-
‘Cold’ fluid
- h:
-
‘Hot’ fluid
- i:
-
Inner fluid; inlet
- L:
-
Liquid
- m :
-
Surface m
- n :
-
Surface n
- o:
-
Outer fluid; outlet
- w:
-
Wall
- V:
-
Vapour
Further Reading
Buffler, C. R. 1993. Microwave cooking and processing. New York, NY: Van Nostrand Rheinold.
Cornwell, K. 1977. The flow of heat. New York, NY: Van Nostrand Rheinold.
Decareau, R. V. and Peterson, R. A. 1986. Microwave processing and engineering. Chichester: Ellis Horwood.
Fryer, P. J., Pyle D. L., and Rielly, C. D., (eds.). 1997. Chemical engineering for the food industry. London: Chapman and Hall.
Hallstrom, B., Skjoldebrand, C., and Tragardh, C. 1988. Heat transfer and food products. London: Elsevier.
Heldman, D. R. and Lund, D. B. 2006. Handbook of food engineering. New York, NY: CRC.
Jackson, A. T. and Lamb, J. 1981. Calculations in food and chemical engineering, London: Macmillan.
Kern, D. Q. 1950. Process heat transfer. New York, NY: McGraw Hill.
McCabe, W. L. and Smith, J. C. 1993. Unit operations of chemical engineering, 5th ed. Singapore: McGraw-Hill.
Pitts, D. R. and Sissom, L. E. (1977). Heat transfer, Schaum’s outline series. New York, NY: McGraw-Hill.
Toledo, R. T. (1994). Fundamentals of food process engineering, 2nd ed. New York, NY: Chapman and Hall.
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Smith, P. (2011). Heat Processing of Foods. In: Introduction to Food Process Engineering. Food Science Text Series. Springer, Boston, MA. https://doi.org/10.1007/978-1-4419-7662-8_7
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DOI: https://doi.org/10.1007/978-1-4419-7662-8_7
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