CEE 370 Environmental Engineering Principles Lecture #10 Energy - PDF document

CEE 370 Lecture #10 10/2/2019 Print version Updated: 2 October 2019 CEE 370 Environmental Engineering Principles Lecture #10 Energy Balances Reading: Mihelcic & Zimmerman, Section 4.2 & 4.3 Davis & Masten, Chapter 4 CEE 370 L#10 1 Conservation of Energy Generic: KNO 3 + C + S → K + + {S, SO 2 , SO 4 -2 } + {CO 2 , CO 3 -2 } + N 2 A specific example: 2 CEE 370 L#10 Lecture #10 Dave Reckhow 1

CEE 370 Lecture #10 10/2/2019 Energy Balance  First law of thermodynamics  Energy can be neither created nor destroyed  But the form can certainly change  Thermal Energy    H Mc T  Characterized by p  Temperature (T) and  Specific heat capacity (c p ) 3 CEE 370 L#13 David Reckhow Heat Transfer  Conduction  Transfer of energy without mass flux  Convection  Energy is carried by molecules in bulk motion 4 CEE 370 L#13 David Reckhow Lecture #10 Dave Reckhow 2

CEE 370 Lecture #10 10/2/2019 Energy Balances 5 CEE 370 L#10 Common Forms of Energy 6 CEE 370 L#10 Lecture #10 Dave Reckhow 3

CEE 370 Lecture #10 10/2/2019 Energy Balance  Much like material balances (Change in internal plus external energy per unit time) = (energy flux in) – (energy flux out) 𝑒𝐹 𝑒𝑢 � 𝐹 �� � 𝐹 ��� 7 CEE 370 L#10 Example 4.9  Heating Water: Scenario 1  40 gal capacity, cold water is 10C  5 kW is max heating rate  Flow is 2 gal/min  Assume 100% efficiency & steady state 𝑒𝐹 𝑒𝑢 � 0 � 𝐹 �� � 𝐹 ��� 0 � 𝑛 � � � 𝑑𝑈 �� � 5𝑙𝑋 � 𝑛 � � � 𝑑𝑈 ��� 8 CEE 370 L#10 Lecture #10 Dave Reckhow 4

CEE 370 Lecture #10 10/2/2019 Example 4.9 cont 0 � 𝑛 � � � 𝑑𝑈 �� � 5𝑙𝑋 � 𝑛 � � � 𝑑𝑈 ��� 0 � 𝑛 � � � 𝑑 𝑈 �� �𝑈 ��� � 5𝑙𝑋 Note error in book  Note that c=4184J/kg°C and 1W=1J/s 0 � 2 𝑕𝑏𝑚 𝐼 � 𝑃 𝑦 3.785 𝑀 𝑦 1.0 𝑙𝑕 𝑦 4184𝐾 𝑈 �� �𝑈 ��� � 5000𝐾 𝑦 60𝑡 𝑛𝑗𝑜 𝑕𝑏𝑚 𝑀 𝑙𝑕°𝐷 𝑡 𝑛𝑗𝑜 𝐾 𝐾 0 � 3.16𝑦10 � 𝑛𝑗𝑜°𝐷 𝑈 �� �𝑈 ��� � 3.00𝑦10 � 𝑛𝑗𝑜 𝑈 �� �𝑈 ��� � 3.00𝑦10 � 3.16𝑦10 � ℃ � 9.5℃ If T in is 10°C, then T out is 19.5°C ~67°F 9 CEE 370 L#10 Example 4.10  How long should you wait to get a temperature of 54°C (~129°F)? 10 CEE 370 L#10 Lecture #10 Dave Reckhow 5

CEE 370 Lecture #10 10/2/2019 11 CEE 370 L#10 GHG Effect • What are greenhouse gases? • What are affects of GHGs? • Are GHGs bad? 12 CEE 370 L#10 Lecture #10 Dave Reckhow 6

CEE 370 Lecture #10 10/2/2019 Solar Radiation & Climate Change 13 CEE 370 L#10 Global Average CO2 Concentration Trend Why? 14 CEE 370 L#10 Lecture #10 Dave Reckhow 7

CEE 370 Lecture #10 10/2/2019 Climate Change Scenarios 15 CEE 370 L#10 16 CEE 370 L#10 Lecture #10 Dave Reckhow 8

CEE 370 Lecture #10 10/2/2019 Rural vs. Urban Temperatures 17 CEE 370 L#10 Heat Distribution in Different Areas Why? 18 CEE 370 L#10 Lecture #10 Dave Reckhow 9

CEE 370 Lecture #10 10/2/2019 Urban Shallow Layer Energy Balance 19 CEE 370 L#10 20 CEE 370 L#10 Lecture #10 Dave Reckhow 10

CEE 370 Lecture #10 10/2/2019 Comparison of the American Home 21 CEE 370 L#10 Energy Use for Small vs. Large Homes 22 CEE 370 L#10 Lecture #10 Dave Reckhow 11

CEE 370 Lecture #10 10/2/2019 Sustainable Design for Temperature Regulation a) Thermal walls for heat transfer and dissipation b) Ventilation systems for natural heating c) Ventilation systems for natural cooling d) Overhangs to regulate effects from sun 23 CEE 370 L#10  To next lecture 24 CEE 370 L#10 Lecture #10 Dave Reckhow 12