Marx's Insights on Nature, Labor, and Property
Karl Marx's writings in the mid-19th century delved into the interconnectedness of man with nature, the impact of alienated labor on private property, and the potential for intimate ties to resolve conflicts. Through his economic and philosophic manuscripts, Marx explored the universality of man and the essence of true personal property. His ideas on communism and humanism as resolutions of conflicts between man and nature offer thought-provoking perspectives on society and economics.
Download Presentation
Please find below an Image/Link to download the presentation.
The content on the website is provided AS IS for your information and personal use only. It may not be sold, licensed, or shared on other websites without obtaining consent from the author.If you encounter any issues during the download, it is possible that the publisher has removed the file from their server.
You are allowed to download the files provided on this website for personal or commercial use, subject to the condition that they are used lawfully. All files are the property of their respective owners.
The content on the website is provided AS IS for your information and personal use only. It may not be sold, licensed, or shared on other websites without obtaining consent from the author.
E N D
Presentation Transcript
Thermal Transfer Measurements Made With the Transient Line Heat Source Method With Information on Phase Change Materials Geoffrey Brown, Product Manager METER Group Inc. USA
Support from: Dr. Gaylon Campbell and Dr. Doug Cobos
Decagon Devices, Inc. (Pullman, WA, USA) + UMS Ag (Munich, Germany) = METER Group
Phoenix Scout Mission to Mars June 25, 2008 Oct., 2008 TECP: Thermal and electrical properties probe
Interesting Direct Applications Interesting Direct Applications Artificial skin Corneas Nanofluids Heat loss from buried power cables Cooking and sterilizing of foods Oils and coolants Greases and heat sink compounds Polymers
Outline Steady state conductivity measurement Line heat source conductivity measurement Improvements to the line heat source method Phase change materials testing Gels and liquids
Steady State Thermal Conductivity Measure heat flux density, H, temperatures and thickness Compute K from: H T1 T2 H x = k ( ) T T 1 2 x
Radial Test Cell For Steady State Thermal Conductivity ) / ln( 1 2 T T Heater & Temp. sensor q r r = k Soil in Copper or Aluminum tube 2 ( ) 1 2 r1 heater radius r2 tube radius T1 heater temp. T2 tube temp. q heat per unit length Temp. sensor Insulation
Steady State Methods for Determining k Good Simple calculations Large samples Direct method Bad Heat divergence Large samples Laboratory method Slow Thermally induced moisture redistribution Home made and/or expensive
Consequences of Thermally Induced Water Flow Steady state methods work well for measuring thermal conductivity in the laboratory on saturated or completely dry materials Steady state methods don't work for measuring thermal conductivity of unsaturated porous media
Line heat Source Methods for Thermal Properties Place a line heat source in the sample Apply heat to the source and measure its temperature over time Compare the measured response with the response predicted using the Fourier law model adjust k and D in the model until it matches the measurements
Equations for Line Heat Source Measurements q T 4 2 r = Ei During heating 4 k Dt 2 2 q r r = T Ei Ei ( m ) After heating 4 4 4 k D t t Dt 0 W ( / ) q is heat input r is radius of heater t is heating time o
Thermal Conductivity: Single Needle Method 0.6 Temperature Change (C) 0.5 k = 0.5 0.4 k = 1.0 0.3 k = 2.0 0.2 0.1 0 0.1 1 10 100 Time (s)
Why is the response linear with In t? q T 4 4 2 r = Ei k D t a = ( ) ( / )exp( 1 u du ) Ei a u = + + 2 ln / 4 ... a a a
Pulsed Infinite Line Source, Approximate Solution q T 4 2 r ln 24.5 4 k Dt 24.45 24.4 Temperature (C) 24.35 2 q r 24.3 = ln ln t 4 4 k DC 24.25 E 24.2 2 2.5 3 3.5 4 4.5 5 ln t q = k 4 slope
Example of k measurement 0.4 y = 0.0906x + 0.0564 R2 = 0.9998 r =153 C cm/W Temperature Rise (C) 0.3 0.2 y = 0.0853x + 0.008 R2 = 0.9996 0.1 r =144 C cm/W 0 0 1 2 3 4 ln t or ln t/(t-to) heating, excluded heating cooling cooling, excluded
Heated Needle as Transient Line Heat Source Ideally Source is infinitely long and infinitesimally small Medium is uniform Temperature is uniform and constant Source is in intimate contact with medium
Heated Needle as Transient Line Heat Source Reality: Source is 10cm long and 2.4 mm in diameter Temperature may vary in space and time Contact resistance between source and medium can occur Medium may not be uniform (no control)
Transient Methods for Determining k Good Small or large samples Fast Portable No thermally induced water flow In situ measurements Bad Destructive
Improvements on the Transient Method Blackwell solution to the differential equation Takes into account the finite probe size Takes into account contact resistance Other improvements Monitors temperature drift and correct the data
Thermal Dryout Curves The relationship between thermal conductivity and water content for a soil or other porous material Water content is an important variable, but density, mineralogy and temperature are also important. These need to be held constant
Dryout Curve of Sand 2.0 Thermal Conductivity (W/mK) 1.5 1.0 single sample 1 single sample 2 0.5 model single sample 0.0 0 0.1 0.2 0.3 0.4 0.5 Volumetric Water Content (m3/m3)
General PCM Info Transient line method can be used in liquids, solids, and gels. Sensors can be used in an environmental chamber Lab tech saves time with continuous read mode
Experiment in PCMs Tested liquids and gels Green product phase change occurs at 5 oC Orange product phase change occurs at 15 oC Gel samples retain shape at warmer temperatures
Test Setup Needle inserted into the gel and placed in an environmental chamber. Liquid samples placed in vial and thermal needle probe inserted into vial via septa in lid. Needles in vertical orientation
Results of 5oC Materials 1.800 1.600 Thermal Conductivity (W/mK) Green Gel Green Liquid 1.400 1.200 1.000 0.800 0.600 0.400 0.200 0.000 -30.00 -20.00 -10.00 0.00 10.00 20.00 30.00 40.00 50.00 Temperature (C)
Results of 17oC Materials 1.000 Orange Gel Scan 1 0.900 Orange Liquid 0.800 Thermal Conductivity (W/mK) 0.700 0.600 0.500 0.400 0.300 0.200 0.100 0.000 -30.00 -20.00 -10.00 0.00 10.00 20.00 30.00 40.00 50.00 Temperature (C)
Conclusion Steady state method is simple, but has flaws that can result in bad data Transient line source solves for some of those faults We are making improvements to make it even better Transient line method works well in PCMs
