辅导 BRE2031 – Environmental Science 1 Tutorial 1 – Introduction to Environmental Science and Thermody

Subject: BRE2031 – Environmental Science

Tutorial 1 – Introduction to Environmental Science and Thermodynamics

1. Consider two identical rooms, one with a refrigerator in it and the other without one. If all the doors and windows are closed, will the room that contains the refrigerator be cooler or warmer than the other room? Why?

If the door of the refrigerator is opened, will the room air temperature be lower or higher than the other room without the refrigerator? Why?

2. A student living in a 4m x 6m x 6m dormitory room turns his 150 W fan on before he leaves his room on a summer day hoping that the room will be cooler when he comes back in the evening. Assuming all the doors and windows are tightly closed and neglecting any thermal energy transfer to/through the walls and windows, determine the temperature of air in the room when he comes back 10 hours later. Neglect the pressure change of the indoor air. The specific heat capacity of air is 1007 J/kg.K. The temperature in the morning is 15oC. The density of air can be treated as constant as 1.2kg/m3.

3. Water is heated in an insulated, constant diameter tube by a 7kW electric resistance heater. If the water enters the heater steadily at 15oC and leaves at 70oC, determine the mass flow rate of water. (heat capacity of water: 4190 J/kg.K)

4. A storage tank measuring 2m by 2m is filled to a depth of 1.5m in 5 minutes by a

supply pipe with a diameter of 100 mm which runs full bore. (a) Calculate the flow rate in the pipe;

(b) Determine the mean velocity of flow in the pipe.

5. A given gas sample occupies a volume of 3 liters at 20oC and 1atm. What volume will this sample occupy at 40oC at 1atm?

6. A given gas sample occupies a volume of 3 liters at 20oC at 1atm. What will be the pressure of the gas sample if it’sheated to 40oC with fixed volume?

7. The specific heat capacity ( cp ) of air at a constant pressure at 25oC is 1005 J/kg.K. At the same temperature, the specific heat capacity of air at a constant volume ( cv ) is 718J/kg.K. The molar mass of air is about 29 g/mol. Assuming the volume of gas at 25oC is 22.4 liters/mol, the density of air at 25oC is about 1.2 kg/m3. Suppose we have an air sample (initially at 1atm) contained in a container measured by 1m x 1m x 1m. Determine the amount of heat that is needed to increase the air temperature from 25oC to 26oC – (a) At constant volume (1m3); (b) At constant pressure (1atm, consider the top cover can move freely);