List of top Dairy and Food Engineering Questions on Gas Refrigeration Cycle asked in GATE AG

The rotor shaft of an ice cream freezer consists of 3 scraper blades. The temperature difference between the ice cream mix and the refrigerant during freezing of ice cream is \(30^\circ C\). Density and latent heat of fusion of ice are 917 kg m\(^{-3}\) and 335 kJ kg\(^{-1}\), respectively. The overall heat transfer coefficient is 2000 kJ m\(^{-2}\) h\(^{-1}\) \(^{\circ}C^{-1}\). If the maximum thickness of ice formed before being scraped off is 10 μm, the minimum speed of the scraper shaft in rpm is:

The lighter liquid layer and the interphase layer in a basket centrifuge, rotating at a speed of 1000 rpm, are 0.1025 m and 0.105 m away from the center, respectively. Considering the densities of lighter and heavier liquids as 920 kg/m\(^3\) and 1015 kg/m\(^3\), the differential pressure in horizontal direction required to maintain the interphase layer in kPa is \underline{\hspace{3cm}} (rounded off to 3 decimal places, \(\pi = 3.14\)).

The upstream and downstream pressures in a homogenizer during homogenization of milk are maintained at 250 bar and 10 bar, respectively. If density of milk is 1030 kg/m\(^3\), then the velocity at which milk comes out of the homogenizing valve in m/s is \underline{\hspace{3cm}} (rounded off to 3 decimal places).

If the diameter of fat globule in a cream separator is reduced to half and the rotational speed of the centrifuge increased to three times, the terminal settling velocity of fat globule is:

A milk sample contains \(4 \times 10^5\) spores of \(C. botulinum\) (D value of 1.2 min at 121.1 °C) and \(7 \times 10^6\) spores of \(L. monocytogenes\) (D value of 0.9 min at 121.1 °C) per mL. If the milk is heated at a uniform temperature of 121.1 °C to obtain a probability of spoilage of 1 in 1000 cans, the minimum heating duration in minutes is _____. \textit{[Round off to two decimal places.]}