Define effectiveness of heat exchanger, minimum fluid, fouling resistance, and heat capacity rate.
When is NTU method better than LMTD method? Why is higher heat transfer occurred in counter flow than in parallel flow arrangement? Explain.
A double pipe heat exchanger is used to heat an oil with cp=2.1c_p = 2.1 kJ/kg-K from 50°C to 100°C. The other fluid is water having cp=4.2c_p = 4.2 kJ/kg-K enters the heat exchanger at 160°C and leaves at 90°C. The arrangement is counter flow. UU value is 320 W/m2^2-°C. Calculate the area and effectiveness of the heat exchanger for a total heat transfer rate is 400 kW.
Define mass transfer, mass diffusion coefficient. Explain the mechanism of mass transfer.
Define Lewis number, Sherwood number, and Schemidt number. Explain the physical significance of these.
Draw NTU versus ϵ\epsilon for counter and parallel flow. Is there any limit for effective design of exchanger based on NTU versus ϵ\epsilon? Explain.
In which case NTU method is preferable than LMTD? Why heat transfer is higher in counter flow heat exchanger than in parallel flow arrangement? Explain.
Define optimum spacing for natural convection with finned surface. A 12m wide and 18cm high vertical hot surface in 25°C air is to be cooled by a heat sink with equally spaced fins of rectangular profile. The fins are 0.1 cm thick, 18 cm long in the vertical direction, and have a height of 2.4 em from the base. Determine the optimum fin spacing and the rate of heat transfer by natural convection from the sink if the base temperature is 80°C.
Hot oil is to be cooled by water in a 1 shell pass and 8 tubes passes heat exchanger. The tubes are thin walled and are made of copper with an internal diameter of 1.4 cm. The length of heat exchanger is 6m where U = 300 W/m²-K. Water flows through the tubes at rate of 0.2 kg/s and the oil through the shell at a rate of 0.3 kg/s. The water and the oil enter at temperatures of 20°C and 160°C, respectively. Determine the rate of heat transfer in the heat exchanger and the outlet temperature of water and oil.
Define heat capacity rate, minimum fluid and heat exchanger effectiveness. Explain the effects of NTU on effectiveness.
A double-pipe heat exchanger is constructed of a Cu inner tube of internal diameter (Dᵢ) = 1.2cm, external diameter (D₀) = 1.6cm and an outer tube of diameter 3 cm. Determine
Why is correction factor needed?
Why LMTD is used instead of arithmetic mean of temperature? Between counter and parallel flow which one has higher heat transfer and why?
Define NTU method, effectiveness, minimum fluid. Upon what factors effectiveness depends? Explain.
A counter flow double pipe heat exchanger is to heat water from 25°C to 85°C at the rate of 1.2 kg/s. The heating is accomplished by geothermal water available at 160°C at a mass flow rate of 1 kg/s. The inner tube is thin-walled and has a diameter of 15 cm. If the overall heat transfer coefficient of the heat exchanger is 620 W/m²°C, determine the length of the heat exchanger required to achieve the desired heating.
Why is higher heat transfer experienced in counter flow than in parallel flow?
Under what conditions is the thermal resistance of the tube in a heat exchanger negligible?
A double pipe heat exchanger is used to heat an oil with cp_p = 2.1 kJ/kg.°C from 50 °C to 100 °C. The other fluid in water having cp_p = 4.2 kJ/kg.°C enters the heat exchanger at 160 °C and leave at 90 °C. The arrangement is counter flow. U = 320 w/m²°C. Calculate the area and effectiveness of the heat exchanger for a total heat transfer rate 500 kW.
When is LMTD method applied? Define minimum fluid and effectiveness of heat exchanger. Between counter and parallel flow which one has higher heat transfer? Why?
Under what conditions will the temperature rise of the cold fluid in a heat exchanger be equal to the temperature drop of the hot fluid?
A double-pipe heat exchanger is used to heat an oil with C = 2.2 KJ/Kg. °C from 50 °C to 100 °C. The other fluid having C = 4.2 KJ/Kg. °C enters the heat exchange at 160 °C and leaves at 90 °C. The overall heat transfer coefficient is 300 W/m².°C. Calculate the area and effectiveness of the heat exchange for a total heat transfer rate of 600 KW.