IAP 2001, Presentation 4, PART 2:

MEASUREMENT OF CASE EXCHANGE RATES AND THE USE OF SUCH MEASUREMENTS

Hubertus Ankersmit +, Maximiliano Lebidinsky, Simon F. Watts

School of Biological and Molecular Sciences, Oxford Brookes University
Instituut Collectie Nederland / Netherlands Institute for Cultural Heritage (ICN) +

PART 2: SLIDES FROM PRESENTATION:

IAP 2001

Observations from a Museum Case

Simon Watts, Max Libedinsky and Hubertus Ankersmit*

School of Biological and Molecular Sciences, Oxford Brookes University

*The Netherlands Institute for Cultural Heritage

Oxford-Brookes

Structure

  • Aims of this work
    - inter-relationship with other work
    - case models

  • The experimental set-up
    - the case
    - RH, T and N2O measurement

  • Results
    - sample
    - obvious things
    - less obvious things

  • Conclusions

Style of Talk

style of talk

Please interrupt with questions about the leaves!

Aims of this work

  • To study intra-case differences of some chemical and physical parameters

  • To identify appropriate parameters for case function description

  • To test the Michalski type model for exchange processes

Inter-relationship with other work

  • Frank Ligterink, Maarten van Bommel & Hubertus Ankersmit
    (Institute for Cultural Heritage, Amsterdam)

  • Andrew Calver (Museum of London)

Slide 3

The "Case"

  • Dimensions 1m x 1m x 1.5 m

  • Steel with plastic fixing and 4mm polycarbonate sides

  • Corners with silicon sealant

Case

"Case" Specifications

case specifications

  • Holes
    - 1 cm diameter

  • Cracks (along top)
    - 0.7 and 2.5 cm width

  • Sealed with "Duck" tape

"Case" Layout

  • Monitoring the "Case"

    - Meaco Museum Control System
         RH, T at 3 points in case
         - top front LHS corner
         - centre
         - bottom RHS corner
         - outside bottom LHS corner

    - Analox N2O "Buddy"
         N2O, T at 1 point in case
         - mid front

  • N2O inlet middle LHS and computer
    fan bottom LHS front corner

The working "Case" I

The experiments involve injecting N2O into the case
and watching the loss under varying conditions

The working case

The "Case" Geography

  • Differences in temperature between four probes
    (A) ~ 0.5°C
    (B) ~ 3°C

  • Tells us that inside the case is not well mixed (hotter at top)

temperature difference

The working "Case" II

Decay curve

  • Decay curve from fully closed case

  • Slope (rate of exchange) gets progressively less

  • Need a model or mathematical description before analysis & comparison

Interpretation

Decay curve

  • The "Why" of a model

  • Not a good fit to any of the expected models - NOT continuous curve

  • Approximate N2O lifetime in case ~27 hours (CER 0.89 d-1)

The working model I

  • Observations
    - Temperature differences mean stratification inside case
    - such stability implies separate air-masses

    - Would explain "kinks" in curves and areas of decreasing slope

  • Guessed two reservoirs - two stage box-model
    (Truesdale, V.W. Watts, S.F. [2001] Deep Sea Research) **

The working model II

no10

no11

a & b are constants, t is time, and [N2O] is N2O concentration

First Test

  • Use of fan should make case atmosphere uniform, shorter lifetimes, higher CER.

  • Fan should fit standard model, this graph second order (!)

  • Mauve without fan, black with fan. Steeper line, higher CER

First test

Implications

  • Fan increases CER by ~ 30%

  • Fan straightens out kinks, better fit to standard models (second order not understood!)

    Normal museum cases do not have fans - hence CERs better than predicted
    - Michalski's model does not comprehend second box

Affect on CER of holes

  • Tests limited
    - holes at same level
    - holes at different level
    - no cracks (yet!)

Cross-sectional hole area
/ 106 m2 		Height
Difference
/ m 		Slope of
1/[N2O] vs t line
/ 106 ppm-1
Fixed* Variable
(planned holes)		 Total
(Fixed + Variable)
30078.6037800.004
300157.14571.400.008
300157.145700.007
300314.2614.21.400.010
* (CER 0.88 d-1; Case volume 1.5 m3;Ps = 0.25 Pa.)

Conclusions

  • From this work (in progress)

    - intra - case effects are important for medium sized cases

    - Michalski model does not seem to deal with
    inhomogeneous air masses within cases very well

    - More work is required to validate the entrainment type model

Back to Part 1: Abstract

Ankersmit, H.
Instituut Collectie Nederland
Gabriel Metsustraat 8
Postbus 76709
1070 KA Amsterdam

Lebidinsky, M. and Watts, S.F.*
School of Biological and Molecular Sciences
Oxford Brookes University
Headington, Oxford, UK
OX3 0BP
E-mail: sfwatts@brookes.ac.uk*

(*): Author to whom correspondence may be addressed:

horizontal ruler

Index of presentations at IAP 2001 meeting

[ Page up ]     [ IAP Group homepage ]     [ Main IAQ in Museums homepage ]     [ Search site ]

Webmaster

Indoor Air Quality in Museums and Archives
© January 04th, 2002

Valid HTML 3.2!