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Published byNancy Bryan Modified over 9 years ago
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Objectives Heat exchangers Fluid mechanics (ducts and pitot tubes) Introduction to psychrometrics
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Any Questions/Administrative Issues? Syllabus Website Homework Lecture notes/videos Feedback? Is no PDF okay?
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Indoor Air 2005 Very successful and engaging conference Excellent talks and discussion Trends for the future Indoor secondary pollutants PCO (mixed feelings) Whole-building approaches/solutions Focus on lesser-developed nations
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Photo Album
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Heat Exchangers Counterflow Crossflow Cocurrent flow Ref: Incropera & Dewitt (2002)
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Shell-and-Tube Heat Exchanger Ref: Incropera & Dewitt (2002)
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Heat Exchanger Analysis
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We want to know the energy exchange between two fluids But, the temperature difference is not constant Q = UAΔt m The trick is coming up with appropriate expression for Δ t m Q= heat transferred (W, BTU/hr) UA = area × U-value (W/K, Btu/hr/F) Δt m = mean temperature difference (°F, °C)
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Heat Exchanger Analysis Counterflow Parallel
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Fluid Flow in Pipes Analogy to steady-flow energy equation Consider incompressible, isothermal flow What is friction loss?
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Pitot Tubes
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Summary Use relationships in text to solve conduction, convection, radiation, phase change, and mixed-mode heat transfer problems Calculate components of pressure for flow in pipes and ducts
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Any questions about review material? Where are we going? Psychrometrics Psychrometric terms Using tables for moist air Application of IGL Using psychrometric charts 7.1 – 7.5, 7.7
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Humidity Ratio, W W = m w /m a Degree of saturation, µ = W/W s Humidity ratio is hard to measure, but very useful in calculations What are units? Is W a function of temperature? What about W s ? W s = humidity ratio at saturation m a = mass of dry air m w = mass of water vapor
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Relative Humidity Φ = x w /x w,s = P w /P ws Function of T Easy to measure and useful in some contexts, but often need to know temperature as well x = mole fraction P = pressure μ = degree of saturation W = humidity ratio
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Summary Review material in chapter 2 Describe psychrometric quantities
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