1 / 21

HW2

HW2. AHU problems: Book: 8.5, 8.25, 8.27, 8.28, 8.22 Cooling Cycles Problems: - Book: 3.1 (page 69),  - Book: 3.5 ((page 70), - Out of book: Same like 3.5 for R22 with no intercooler - Book 3.9 (pages 70-71). Objectives. Learn about Cooling towers Cooling cycles. Cooling Tower.

keithallen
Download Presentation

HW2

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. HW2 AHU problems: Book: 8.5, 8.25, 8.27, 8.28, 8.22 Cooling Cycles Problems: - Book: 3.1 (page 69),  - Book: 3.5 ((page 70), - Out of book: Same like 3.5 for R22 with no intercooler- Book 3.9 (pages 70-71)

  2. Objectives Learn about Cooling towers Cooling cycles

  3. Cooling Tower • Similar to an evaporative cooler, but the purpose is often to cool water • Widely used for heat rejection in HVAC systems • Also used to reject industrial process heat

  4. Cooling Tower

  5. Solution • Can get from Stevens diagram (page 272) • Can also be used to determine • Minimum water temperature • Volume of tower required • Can be evaluated as a heat exchanger by conducting NTU analysis

  6. Summary • Heat rejection is often accomplished with devices that have direct contact between air and water • Evaporative cooling • Can construct analysis of these devices • Requires parameters which need to be measured for a specific system

  7. Vapor Compression Cycle Expansion Valve

  8. Efficiency • First Law • Coefficient of performance, COP • COP = useful refrigerating effect/net energy supplied • COP = qr/wnet • Second law • Refrigerating efficiency, ηR • ηR = COP/COPrev • Comparison to ideal reversible cycle

  9. Efficiency • First Law • Coefficient of performance, COP • COP = useful refrigerating effect/net energy supplied • COP = qr/wnet • Second law • Refrigerating efficiency, ηR • ηR = COP/COPrev • Comparison to ideal reversible cycle

  10. Carnot Cycle No cycle can have a higher COP • All reversible cycles operating at the same temperatures (T0, TR) will have the same COP • For constant temp processes • dq = Tds • COP = TR/(T0 – TR)

  11. Carnot Vapor-Compression Cycle • Figure 3.2

  12. Get Real • Assume no heat transfer or potential or kinetic energy transfer in expansion valve • COP = (h3-h2)/(h4-h3) • Compressor displacement = mv3

  13. Area Analysis of Work and Efficiency

  14. Comparison Between Single-Stage and Carnot Cycles

  15. Example • R-22 condensing temp of 30 °C (86F) and evaporating temp of 0°C (32 F) • Determine • qcarnot wcarnot • Diminished qR and excess w for real cycle caused by throttling and superheat horn • ηR

  16. Subcooling and Superheating • Refrigerant may be subcooled in condenser or in liquid line • Temperature goes below saturation temperature • Refrigerant may be superheated in evaporator or in vapor (suction) line • Temperature goes above saturation temperature

  17. Two stage systems

More Related