ICAR AIEEA PG 2024 - Agricultural Engineering and Technology

According to Newton's Law of Cooling for convective heat transfer:

Given parameters:
Heat transfer coefficient,

Converting to kilowatts:

For a counter-flow heat exchanger, fluids flow in opposite directions:

• At End 1 (Hot fluid inlet & Cold fluid outlet):
  \[ \Delta T_1 = T_{h, \text{in}} - T_{c, \text{out}} = 22^\circ\text{C} - 3^\circ\text{C} = 19^\circ\text{C} \]
• At End 2 (Hot fluid outlet & Cold fluid inlet):
  \[ \Delta T_2 = T_{h, \text{out}} - T_{c, \text{in}} = 6^\circ\text{C} - (-2^\circ\text{C}) = 6 + 2 = 8^\circ\text{C} \]
• The Logarithmic Mean Temperature Difference (LMTD, \(\Delta T_m\)) is defined as: \[ \Delta T_m = \frac{\Delta T_1 - \Delta T_2}{\ln\left(\frac{\Delta T_1}{\Delta T_2}\right)} = \frac{19 - 8}{\ln\left(\frac{19}{8}\right)} \]

Correct definitions of fluid types in fluid mechanics:
(A) Ideal fluid: A theoretical fluid that is incompressible and has zero viscosity (\(\mu = 0\))\lt /strong\gt \(\rightarrow\) (I).
(B) Newtonian fluid: Obeys Newton's law of viscosity, where shear stress is linearly proportional to shear strain rate (\(\tau = \mu \frac{du}{dy}\))\lt /strong\gt \(\rightarrow\) (II) (e.g., water, air, light oils).
(C) Real fluid: Any actual physical fluid that possesses viscosity (\(\mu > 0\))\lt /strong\gt and exhibits friction \(\rightarrow\) (IV).
(D) Non-Newtonian fluid: Fluid where shear stress is not linearly proportional to shear rate \(\rightarrow\) \lt strong\gt (III)\lt /strong\gt (e.g., paint, starch suspensions, blood). \lt strong\gt (E) Ideal plastic fluid (Bingham plastic)\lt /strong\gt : Does not deform until a definite \lt strong\gt yield stress (\(\tau_0\)) is exceeded, after which shear stress is proportional to shear strain rate \(\rightarrow\) (V) (e.g., toothpaste, sewage sludge).