SCHOOL OF MECHANICAL ENGINEERING SUMMER TERM II 2021-2022 DIGITAL ASSIGNMENT-II Course Code : MEE2005 Course Faculty : Prof. S. Senthur Prabu Course Name: Heat Transfer Do all the questions and submit on or before 8th July 2022 1. Two large parallel plates are maintained at a temperature of 600 K and 900 K and emissivity of 0.4 and 0.7 respectively. Determine heat transfer by radiation and also calculate percentage of reduction in heat transfer and shield temperature when another plate of emissivity 0.05 introduced in between them. 2. Sketch the boiling curve and indentifying key regimes explain various modes of pool boiling. What is the critical heat flux? 3. Air at 40oC flows over a tube with a velocity of 30 m/s. The tube surface temperature is 120oC, calculate the heat transfer coefficient for the following cases: (i) Tube could be square with a side of 6 cm (ii) Tube is circular cylinder of diameter 6 cm. 4. Explain the phenomenon of film-wise and drop-wise condensation with neat sketches. Mention essential differences between them. 5. A horizontal wire of 3 mm diameter is maintained at 100o C and is exposed to air at 20o C. Calculate the following: (i) Heat transfer coefficient (ii) Maximum current per unit length Take resistance of wire is 7 ohm/m. 6. In a counter flow heat exchanger, water is heated from 20o C to 80o C by an oil with a specific heat of 2.5 kJ/kg-K and mass flow rate of 0.5 kg/s. The oil is cooled from 110o C to 40o C. If the overall heat transfer co-efficient is 1400 W/m2K, find the following by using NTU method. (i) Mass flow rate of water (ii) Effectiveness of heat exchanger (iii) Surface area. 7. When 0.6 kg of water per minute is passed through a tube of 2 cm diameter, it is found to be heated from 20o C to 60o C. The heating is achieved by condensing steam on the surface of the tube and subsequently the surface temperature of the tube is maintained at 90o C. Determine the length of the tube required for fully developed flow. 8. Air at 0oC flows over a heated flat plate maintained at 100oC at a speed of 90 m/s. The plate is 60 cm long and 75 cm wide. Calculate the following i) Average friction coefficient, ii) Average heat transfer coefficient and iii) Rate of energy dissipation 9. Air at 15o C, 35 m/s, flows through a hollow cylinder of 4 cm inner diameter and 6 cm outer diameter and leaves at 45o C. Tube wall is maintained at 60o C. Calculate the heat transfer coefficient between the air and the inner tube. 10. Emissivities of two large parallel plates maintained at 800oC and 300oC are 0.3 and 0.5 respectively. Find net radiant heat exchange per square metre for these plates. Find the percentage reduction in heat transfer when a polished aluminum radiation shield of emissivity 0.06 is placed between them. Also find the temperature of the shield. 11. Air at 20oC, at a pressure of 1 bar is flowing over a flat plate at a velocity of 3 m/s. If the plate is maintained at 60oC, calculate the heat rate transfer per unit width of the plate taking the length of the plate along the flow of air is 2 m. 12. Air at 20oC, at atmospheric pressure flows over a flat plate of at a velocity of 3 m/s. If the plate is 1m wide and is at 80oC, calculate the following at x=300mm (i) Hydrodynamic boundary layer thickness, (ii) Thermal boundary layer thickness, (iii) Local friction coefficient, (iv) Average friction coefficient, (v) Local heat transfer coefficient, (vi) Average heat transfer coefficient, (vii) Heat transfer rate. 13. Air at 30oC, 0.2 m/s flows across a 120 W spherical electric bulb at 130oC. Find the heat transfer rate and power lost due to convection if bulb diameter is 70 mm. 14. Saturated steam at 126o C is condensing on the outer tube surface of a single pass heat exchanger. The heat exchanger heats 1050 kg/h of water from 20o C to 95o C. The overall heat transfer co-efficient is 1800 W/m2K. Calculate the following: (i) Area of heat exchanger (ii) Rate of condensation of steam Take hfg = 2185 kJ/kg. 15. A vertical plate of 0.75 m height is at 170o C and is exposed to air at a temperature of 105oC and one atmosphere. Calculate: (i) Mean heat transfer coefficient, (ii) Rate of heat transfer per unit width of the plate ****************************************************************************** ADHERE TO THE DEADLINE MENTIONED ABOVE.
