Mechanical engineer interviews questions

Pasteurization requires that the milk is in custody for a specified time. The appropriate length for the holding tube can be calculated by the flow rate (Q) of milk and the diameter (D) of the holding tube using the formula: Length of holding tube, L = Q x holding time/A x η A = Area = pi/4 x sqr D Where an efficiency factor, η, of 0.85 is used in the model.

Power input into the motor compressor is obtained by the following formula: Power Pcomp =M x (h2 - h1) Power Pcomp = Power input into the motor compressor M = The mass flow rate of the refrigerant h1 = Enthalpy at inlet to the process, h2 = Enthalpy at outlet to the process,

The work done to compress the refrigerant vapor is obtained by applying to the compression process: Work done Wcomp= h2 - h1 Wcomp = Work done during the process h1 = Enthalpy at inlet to the process, h2 = Enthalpy at outlet to the process, This is the work done by compressor per kg of the refrigerant.

Ammonia is a toxic gas that used in various industries. It can be extremely dangerous if not handled properly at the time of leak or spill. It can pose a serious risk to human health and the environment also if it leak or spill. Ammonia is a colorless, strong, pungent odor gas and it is difficult to detect leak without specialized equipment. Ammonia can generate white cloud, irritation in throat, eye or nose, coughing, vomiting and difficult to breathing if leaks. Exposure to 300ppm is immediately dangerous to health and life. If the possibility of exposure more than 300ppm, use NIOSH approved self breathing apparatus(SCBA). Ammonia is flammable at concentrations of 15 to 28% by volume in air.  An Emergency Action Plan(EAP) is a written document required by OSHA standard. Emergency procedure is providing to workers with detailed directions in case of an emergency. The written emergency procedures must consist of specific details pertaining to the following: Location of the sy...

Pure ammonia comes in two forms: gas and liquid. Ammonia is a naturally occurring substance that has been successfully used as a refrigerant in industrial refrigeration plants for more than 140 years. Liquid ammonia is a clear fluid, colorless that evaporates quickly at room temperature. Liquid ammonia also has a high compression ratio. The ratio of liquid to gas is 1 to 800, which means that 1 litre of liquid ammonia  expands to form 800 litres of gas. It is a colorless, strong gas that liquefies under pressure and has a pungent odor. It is also much lighter than air. If ammonia gas escapes from a refrigeration system or a storage container, it tends to collect in high areas or ceilings. Ammonia has negligible environmental impact with zero ozone depleting potential (ODP= 0), no direct global warming potential (GWP = 0) and low operational emissions due to high efficiencies.  GWP = 0, ODP = 0 Ammonia carries a B2 safety classification, meaning that it has a mediu...

The average COP of the major compressor available in the market is given below: Compressor Type Capacity COP-Avg. rating Open Reciprocating type 5 kw to 225 kw 3.2 Screw type 80 kw to 2000 kw 4.5 Hermetic Scroll type 3 kw to 50 kw 3.5 Hermetic reciprocating type 1 kw to 50 kw 3.0

Cooling capacity of bulk-milk cooler find out by the following formula: Q=V x Rho x Cp x (T1 – T2)/t Where; Q - Cooling capacity of bulk-milk cooler, kcal/h V - milk volume inside bulk-milk cooler, cum Rho - milk density, kg/m3 Cp - milk specific heat, kcal/kg.C T1 - milk temperature at any loading time, in degree C T2 - milk temperature at the time which gives the temperature of safe storage, in degree C and t - cooling hours, h.

Example- One cold store dimensions is -10 m x 10 m × 5 m = 500 Sq mtr, External store surface area is 385.75 Sq mtr, Storage temperature is minus 20 Degree C, maximum ambient temperature is 35 Degree C. Insulation thickness is 250 mm. Consider two men are working inside the cold room. Calculate total calculated refrigeration load. Calculation: (1) Insulation heat leak through walls, floor and roof Conductivity of polystyrene 0.033 kcal/h m C Surface area of store = 385.75 Sq mtr Temperature difference between ambient and store 35 Deg C and -20 Deg C = 55 Deg C Thickness of polystyrene = 250 mm Heat leak in Kcal/hr = 385.75 x 55 x 0.033/ 0.250 = 2800 kcal/hr (2) Product load 5.5 kcal/kg for fresh fish load at an average temperature of -20 Deg C Fish loaded per day 25 000 kg Product load = 25000 x 5.5 / 24 = 5729 kcal/hr (3) Fan load 2 x 200 W = 400 kcal/hr (4) Air changes Average of 2.5 air changes in 24 h Store volume = 500 Cum Heat gain (35 C and 60% R.H. air) 40 ...

A container in which water is boiled or a sealed vessel where water is converted to steam. Hindi meaning Bhatti . Water boiler is a closed vessel or arrangement of enclosed tubes in which water is heated and circulated, either as hot water or as steam, for heating or to supply steam to drive an engine or turbine. Industrial Boilers must be constructed in accordance with the ASME Boiler and Pressure Vessel Code: Section I is for the high-pressure boilers. Section II for materials. Section IV for heating boilers. Section VIII for rules for the construction of pressure vessels. Section IX welding and brazing qualifications. Section XIII for rules for overpressure protection etc. Additionally, ASME B31.1 is the required code for power piping installation for high-pressure boilers. Section IV is for low-pressure steam and hot water heating, and hot water supply boilers. Note:-ASME means American Society of Mechanical Engineers.