On a summer day, the air temperature is 36°C and the relative humidity is 20%. Water...
On a summer day, the air temperature is 36°C and the relative
humidity is 20%. Water evaporates from the surface of a lake at a
rate of 0.20 kg/h per square metre of water surface area. The
temperature of water is 25°C.
(a) Determine the mass transfer coefficient. (10 marks)
(b) Determine the convective heat transfer coefficient. (10 marks)
(c) Determine the net heat loss (in W/m2) from the lake. (5 marks)
The specific volume of water vapour at 25°C is 43.40 m3/kg and
at 36°C is 23.97 m3/kg. The latent heat of evaporation at 25°C is
2441.8 kJ/kg and at 36°C is 2415.8 kJ/kg. The binary species
diffusivity of water vapour in air is 26×10-6 m2/s. At 30.5°C, the
density, constant pressure specific heat capacity and thermal
conductivity of air are 1.177 kg/m3, 1.0049 kJ/kg⋅K and 2.624×10-5
kW/m⋅K, respectively.
Homework Answers
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On a summer day, the air temperature is 36°C and the relative
humidity is 20%. Water...
1) 2.5 m3/s of air at 150°C is used to heat 0.342 kg/s of 20°C water....
1) 2.5 m3/s of air at 150°C is used to heat 0.342 kg/s of 20°C water. The heat exchanger is a finned-tube cross flow heat exchanger with both sides unmixed. The overall heat transfer coefficient associated with the hot side is 120 W/(m2°C). The hot-side area is 20 m2. Assume a constant specific heat for air and water of Crezia = 1.005 kJ/(kgº), Crewater = 4.2 kJ/(kg °C). The pressure of the hot air is P = 1.0 atm. The...
Question 5 (a) A sample of moist air at a temperature of 36 °C and total...
Question 5 (a) A sample of moist air at a temperature of 36 °C and total pressure 1.01 bar has 0.018 kg of moisture per kg of dry air. Calculate the relative humidity and the enthalpy (kJ/kg of dry air) of the air. (8 marks) (b) The air in (a) is cooled at constant total pressure until condensation of water just begins. Calculate the temperature and the enthalpy (kJ per kg of dry air) when condensation just begins. (6 marks)...
1) 2.5 m/s of air at 150°C is used to heat 0.35 kg/s of 20°C water....
1) 2.5 m/s of air at 150°C is used to heat 0.35 kg/s of 20°C water. The heat exchanger is a finned-tube cross flow heat exchanger with both sides unmixed. The overall heat transfer coefficient associated with the hot side is 120 W/(m2 °C). The hot-side area is 20 m². Assume a constant specific heat for air and water of Gezic = 1.005 kJ/(kg °C), Senator = 4.2 kJ/(kg °C). The pressure of the hot air is P = 1.0...
Moist air at 20°C, 1 atm, and 43% relative humidity and a volumetric flow rate of...
Moist air at 20°C, 1 atm, and 43% relative humidity and a volumetric flow rate of 900 m/hrs. enters a control volume at steady state and flow along a surface maintained at 65° C, through which heat transfer occurs. Liquid water at 20° C is injected at a rate of 5 kg/hr and evaporates into flowing stream. For the control volume, Wev =0, and kinetic and potential energy effects are negligible. Moist air exits at 32°C, 1 atm. (a) draw...
A) Determine the convection heat transfer coefficient for the flow of air. [W/m2·°C] B) Determine the...
A) Determine the convection
heat transfer coefficient for the flow of air.
[W/m2·°C]
B) Determine the convection heat transfer coefficient for water.
[W/m2·°C]
The velocity of the fluid is 9 m/s in an 8-cm diameter and 7-m-long tube when the tube is subjected to uniform heat flux from all surfaces. Use fluid properties at 25°C. Water or Air D 8 cm L=7 m Given: The properties of air at 25°C are: k 0.02551 W/m."C v 1.562 10-5 m2/s Pr =...
On a summer day the pressure is 1 atm, the temperature is 32°C, and the relative humidity is 95 percent. This air is to be conditioned to 24°C and 60 percent relative humidity. a) Determine the amount...
On a summer day the pressure is 1 atm, the temperature is 32°C,
and the relative humidity is 95 percent. This air is to be
conditioned to 24°C and 60 percent relative humidity.
a) Determine the amount of cooling, in kJ, required and
b) Water removed, in kg, per 1000 m3 of dry air processed at the
entrance to the system.
Cooling coils Ti 32С ф,-95% т,-24°C φ2 60% l atm Condensate
Cooling coils Ti 32С ф,-95% т,-24°C φ2 60%...
2. A separation column at a temperature of 100C is subjected for cooling for a certain...
2. A separation column at a temperature of 100C is subjected
for cooling for a certain period of time. If the separation column
is 1500 mm high and 18 cm in diameter, and eventually exposed to an
environment temperature of 35C, determine the following with a
neat diagram:
a) Heat Transfer Coefficient (in J/s m2C and kJ/s m2C)
b) Heat transfer Rate (in W and kW)
Assume the properties of air at mean temperature as density
(ρ) = 1.06 kg/m3,...
Moist air at 20° c, 1 atm, and 43% relative humidity and a volumetric flow rate...
Moist air at 20° c, 1 atm, and 43% relative humidity and a volumetric flow rate of 900 m/hrs. enters a control volume at steady state and flow along a surface maintained at 65 C, through which heat transfer occurs. Liquid water at 20" C is injected at a rate of 5 kg/hr and evaporates into flowing stream. For the control volume, Wa=0, and kinetic and potential energy effects are negligible. Moist air exits at 32c, 1 atm, (a) draw...
4. A Cross-Flow Air-to-Water Heat Exchanger with an effectiveness of 0.58 is used to heat water, ...
4. A Cross-Flow Air-to-Water Heat Exchanger with an effectiveness of 0.58 is used to heat water, entering at 20°C at a rate of 4 kg/s, using hot air, entering at 127oC at a rate of 10 kg/s. The Overall Heat Transfer Coefficient for the Heat exchanger is 275 W/m'K. Assuming both fluids are unmixed, determine; (i) The Heat Capacity rates for both the air and the water (ii) The heat transfer surface area. ii) The exit temperature of the water...
Moist air at 20°C, 1 atm, and 43% relative humidity and a volumetric flow rate of...
Moist air at 20°C, 1 atm, and 43% relative humidity and a volumetric flow rate of 900 m²/hrs. enters a control volume at steady state and flow along a surface maintained at 65°C, through which heat transfer occurs. Liquid water at 20°C is injected at a rate of 5 kg/hr and evaporates into flowing stream. For the control volume, Wev=0, and kinetic and potential energy effects are negligible. Moist air exits at 32°C, 1 atm. (a) draw the system schematic...
1) 2.5 m3/s of air at 150°C is used to heat 0.342 kg/s of 20°C water. The heat exchanger is a finned-tube cross flow heat exchanger with both sides unmixed. The overall heat transfer coefficient associated with the hot side is 120 W/(m2°C). The hot-side area is 20 m2. Assume a constant specific heat for air and water of Crezia = 1.005 kJ/(kgº), Crewater = 4.2 kJ/(kg °C). The pressure of the hot air is P = 1.0 atm. The...
Question 5 (a) A sample of moist air at a temperature of 36 °C and total pressure 1.01 bar has 0.018 kg of moisture per kg of dry air. Calculate the relative humidity and the enthalpy (kJ/kg of dry air) of the air. (8 marks) (b) The air in (a) is cooled at constant total pressure until condensation of water just begins. Calculate the temperature and the enthalpy (kJ per kg of dry air) when condensation just begins. (6 marks)...
1) 2.5 m/s of air at 150°C is used to heat 0.35 kg/s of 20°C water. The heat exchanger is a finned-tube cross flow heat exchanger with both sides unmixed. The overall heat transfer coefficient associated with the hot side is 120 W/(m2 °C). The hot-side area is 20 m². Assume a constant specific heat for air and water of Gezic = 1.005 kJ/(kg °C), Senator = 4.2 kJ/(kg °C). The pressure of the hot air is P = 1.0...
Moist air at 20°C, 1 atm, and 43% relative humidity and a volumetric flow rate of 900 m/hrs. enters a control volume at steady state and flow along a surface maintained at 65° C, through which heat transfer occurs. Liquid water at 20° C is injected at a rate of 5 kg/hr and evaporates into flowing stream. For the control volume, Wev =0, and kinetic and potential energy effects are negligible. Moist air exits at 32°C, 1 atm. (a) draw...
A) Determine the convection
heat transfer coefficient for the flow of air.
[W/m2·°C]
B) Determine the convection heat transfer coefficient for water.
[W/m2·°C]
The velocity of the fluid is 9 m/s in an 8-cm diameter and 7-m-long tube when the tube is subjected to uniform heat flux from all surfaces. Use fluid properties at 25°C. Water or Air D 8 cm L=7 m Given: The properties of air at 25°C are: k 0.02551 W/m."C v 1.562 10-5 m2/s Pr =...
On a summer day the pressure is 1 atm, the temperature is 32°C,
and the relative humidity is 95 percent. This air is to be
conditioned to 24°C and 60 percent relative humidity.
a) Determine the amount of cooling, in kJ, required and
b) Water removed, in kg, per 1000 m3 of dry air processed at the
entrance to the system.
Cooling coils Ti 32С ф,-95% т,-24°C φ2 60% l atm Condensate
Cooling coils Ti 32С ф,-95% т,-24°C φ2 60%...
2. A separation column at a temperature of 100C is subjected
for cooling for a certain period of time. If the separation column
is 1500 mm high and 18 cm in diameter, and eventually exposed to an
environment temperature of 35C, determine the following with a
neat diagram:
a) Heat Transfer Coefficient (in J/s m2C and kJ/s m2C)
b) Heat transfer Rate (in W and kW)
Assume the properties of air at mean temperature as density
(ρ) = 1.06 kg/m3,...
Moist air at 20° c, 1 atm, and 43% relative humidity and a volumetric flow rate of 900 m/hrs. enters a control volume at steady state and flow along a surface maintained at 65 C, through which heat transfer occurs. Liquid water at 20" C is injected at a rate of 5 kg/hr and evaporates into flowing stream. For the control volume, Wa=0, and kinetic and potential energy effects are negligible. Moist air exits at 32c, 1 atm, (a) draw...
4. A Cross-Flow Air-to-Water Heat Exchanger with an effectiveness of 0.58 is used to heat water, entering at 20°C at a rate of 4 kg/s, using hot air, entering at 127oC at a rate of 10 kg/s. The Overall Heat Transfer Coefficient for the Heat exchanger is 275 W/m'K. Assuming both fluids are unmixed, determine; (i) The Heat Capacity rates for both the air and the water (ii) The heat transfer surface area. ii) The exit temperature of the water...
Moist air at 20°C, 1 atm, and 43% relative humidity and a volumetric flow rate of 900 m²/hrs. enters a control volume at steady state and flow along a surface maintained at 65°C, through which heat transfer occurs. Liquid water at 20°C is injected at a rate of 5 kg/hr and evaporates into flowing stream. For the control volume, Wev=0, and kinetic and potential energy effects are negligible. Moist air exits at 32°C, 1 atm. (a) draw the system schematic...
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