GATE Agricultural Engineering Dairy and Food Engineering Syllabus

Dairy and Food Engineering syllabus — full chapter and topic list

Expand any chapter to see its topics and sub-topics. This is the whole examinable outline for Dairy and Food Engineering in GATE Agricultural Engineering, not a summary of it.

1. 1

   Heat and Mass Transfer

   7 topics

   • Steady state heat transfer
     • Conduction
     • Convection
     • Radiation
   • Transient heat transfer
     • Simple geometry
   • Working principles of heat exchangers
   • Diffusive and convective mass transfer
   • Simultaneous heat and mass transfer in agricultural processing operations
   • Material and energy balances in food processing systems
   • Water activity, sorption and desorption isotherms
2. 2

   Preservation of Food

   3 topics

   • Kinetics of microbial death
     • Pasteurization
     • Sterilization of milk and other liquid foods
   • Preservation of food by cooling and freezing
   • Refrigeration and cold storage basics and applications

Dairy and Food Engineering flashcards for GATE Agricultural Engineering

19 of 52 cards from the Dairy and Food Engineering deck — real questions with worked answers.

1. What is steady-state heat transfer?

   Heat transfer in which the temperature at any point in the body does not change with time, i.e. $\frac{\partial T}{\partial t}=0$. The rate of heat in equals the rate of heat out and the temperature distribution is constant over time.

2. State Fourier's law of one-dimensional steady-state conduction.

   $$q=-kA\frac{dT}{dx}$$ where $q$ is heat flow rate (W), $k$ is thermal conductivity (W/m·K), $A$ is area, and $\frac{dT}{dx}$ is the temperature gradient. The negative sign indicates heat flows down the temperature gradient.

3. What is the conduction resistance for a plane wall, and how is it used?

   $$R_{cond}=\frac{L}{kA}$$ Heat flow is then $q=\frac{\Delta T}{R}$, analogous to Ohm's law where $\Delta T$ is the driving potential and $R$ the thermal resistance.

4. Write the steady-state conduction equation for a hollow cylinder (radial).

   $$q=\frac{2\pi k L (T_1-T_2)}{\ln(r_2/r_1)}$$ The conduction resistance is $R=\dfrac{\ln(r_2/r_1)}{2\pi k L}$.

5. Write the steady-state radial conduction rate through a hollow sphere.

   $$q=\frac{4\pi k (T_1-T_2)}{\frac{1}{r_1}-\frac{1}{r_2}}$$ with resistance $R=\dfrac{1}{4\pi k}\left(\dfrac{1}{r_1}-\dfrac{1}{r_2}\right)$.

6. State Newton's law of cooling for convection.

   $$q=hA(T_s-T_\infty)$$ where $h$ is the convective heat transfer coefficient (W/m²·K), $A$ the surface area, $T_s$ the surface temperature and $T_\infty$ the bulk fluid temperature. The convective resistance is $R=\frac{1}{hA}$.

7. Distinguish natural (free) convection from forced convection.

   Natural convection: fluid motion is driven by buoyancy from density differences caused by temperature gradients (no external device). Forced convection: fluid motion is produced by an external means such as a pump, fan or stirrer. Forced convection generally gives much higher $h$ values.

8. Define the Nusselt number and state its physical meaning.

   $$Nu=\frac{hL}{k}$$ It is the ratio of convective to conductive heat transfer across a fluid layer. $Nu=1$ implies pure conduction; larger values indicate stronger convection.

9. Define the Prandtl, Reynolds, and Grashof numbers.

   $$Pr=\frac{\mu c_p}{k}=\frac{\nu}{\alpha},\quad Re=\frac{\rho v L}{\mu},\quad Gr=\frac{g\beta\Delta T L^{3}}{\nu^{2}}$$ $Pr$ relates momentum to thermal diffusivity, $Re$ inertial to viscous forces (forced convection), $Gr$ buoyancy to viscous forces (natural convection).

10. State the Stefan-Boltzmann law for radiation from a body.

    $$q=\varepsilon\sigma A T^{4}$$ where $\varepsilon$ is emissivity, $\sigma=5.67\times10^{-8}\ \text{W/m}^2\text{K}^4$ is the Stefan-Boltzmann constant, and $T$ is the absolute temperature (K). Net exchange between a surface and surroundings: $q=\varepsilon\sigma A(T_s^{4}-T_{surr}^{4})$.

11. Define emissivity and what value a blackbody has.

    Emissivity $\varepsilon$ is the ratio of radiation emitted by a surface to that emitted by a blackbody at the same temperature, $0\le\varepsilon\le1$. A perfect blackbody has $\varepsilon=1$ (also absorbs all incident radiation, $\alpha=1$).

12. State Kirchhoff's law of thermal radiation.

    At thermal equilibrium, the emissivity of a surface equals its absorptivity: $\varepsilon=\alpha$. Good emitters are good absorbers.

13. What is transient (unsteady-state) heat transfer?

    Heat transfer in which temperature varies with both position and time, $\frac{\partial T}{\partial t}\neq0$. It occurs during heating or cooling before steady state is reached, e.g. during cooking, freezing, or thermal processing of foods.

14. Define the Biot number and state the lumped-system criterion.

    $$Bi=\frac{hL_c}{k}$$ where $L_c=V/A$ is the characteristic length. If $Bi<0.1$, internal conduction resistance is negligible and lumped-capacitance (uniform internal temperature) analysis applies.

15. Give the lumped-capacitance temperature-time response.

    $$\frac{T-T_\infty}{T_i-T_\infty}=e^{-\frac{hA}{\rho V c_p}t}=e^{-t/\tau}$$ where the time constant $\tau=\dfrac{\rho V c_p}{hA}$.

16. Define the Fourier number and its role in transient conduction.

    $$Fo=\frac{\alpha t}{L_c^{2}}$$ where $\alpha=\frac{k}{\rho c_p}$ is thermal diffusivity. It is dimensionless time governing transient conduction; large $Fo$ means heat penetrates deeply / approaches steady state.

17. What tool relates dimensionless temperature, $Bi$, and $Fo$ for simple shapes in transient conduction?

    Heisler charts (and Gröber charts), which give the dimensionless centre temperature and heat transferred for an infinite slab, infinite cylinder, and sphere as functions of $Bi$ and $Fo$ when $Bi>0.1$.

18. Define thermal diffusivity and give its formula.

    $$\alpha=\frac{k}{\rho c_p}\ \ (\text{m}^2/\text{s})$$ It measures how quickly a material responds thermally — how fast heat diffuses relative to heat storage. High $\alpha$ means rapid temperature equalization.

19. Compare parallel-flow and counter-flow heat exchangers.

    Parallel-flow: both fluids enter the same end and flow in the same direction; outlet temperatures approach each other but the cold fluid can never exceed the hot outlet. Counter-flow: fluids flow in opposite directions; gives a larger mean temperature difference, higher effectiveness, and the cold outlet can exceed the hot outlet temperature.

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