Experiment on the Cause of Real Greenhouses’ Effect - Repeatability of Prof. Robert W. Wood’s experiment

By Nasif S. Nahle

University Professor, Scientist, Scientific Research Director at Biology Cabinet©
Monterrey, N. L., Mexico.


Quote: Nahle, Nasif S. Repeatability of Professor Robert W. Wood’s 1909 experiment on the Theory of the Greenhouse. June 12, 2011. Biology Cabinet Online, Academic Resources. Monterrey, N. L.


*The author is grateful to the Principia Scientific International team for their kind assistance with the text; nevertheless, any errors in the text are mine alone.
Abstract:

Through this controlled experiment, I demonstrate that the warming effect in a real greenhouse is not due to longwave infrared radiation trapped inside the building, but to the blockage of convective heat transfer with the surroundings, as proven by Professor Wood in his 1909 experiment.

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Introduction:

In 1909, Professor Wood conducted an experiment consisting of testing the effect of the longwave infrared radiation trapped inside a greenhouse with respect to the elevated temperature inside a greenhouse during insolation.

His experiment was described in an article that he published in the journal Philosophical Magazine, in 1909. (See reference [1]).

From his experiment, Professor Wood found that the increase in temperature inside a greenhouse was not due to trapped radiation but to the blockage of convective heat transfer between the interior of the greenhouse and the open atmosphere.

Given that there are no other documents by other scientists who have tried to repeat the experiment of Professor Wood, except the experiment by Professor Pratt [2], which contradicted the results of Professor Wood’s experiment, another science investigation by a third arbitrator is not only recommendable, but necessary. This is the reason that I decided to repeat the experiment of Professor Pratt to either falsify or verify his results and those of Professor Wood.

The following lines describe the experiments conducted by myself and their results.


FIRST EXPERIMENT


EQUIPMENT

2 Hanna Instruments® Digital Thermometers, Model HI98501. Range of Temperatures: -50 to 150 °C. Accuracy of ±0.3 °C (inside) and ±0.5 °C (outside). EMC deviation ±0.3 °C. [3]

3 CEM® Digital Thermometers, Model DT-131. Range of Temperatures: -40 to 250.  Accuracy of 0.03 °C. EMC deviation 0.1 °C.[4]

1 Sekonic® photometer.

Praktica® MTL-5B Professional Camera. Multi layered Lens 35 mm, F-1.8.

Sony® Digital Camera α 55. Multi-layered (ML) Zoom Lens Kit DT 18-55 mm; F 3.5-5.6 SAM.



MATERIALS

4 Lowe’s® corrugated cardboard  boxes, measuring 30 x 30 x 20 cm, thermal conductivity of 0.5 W/m K.[13]

1 impact modified acrylic plate Plaskolite®-Duraplex®, 3 mm thick. Solar near shortwave IR transmissivity index of 0.97 (0.94 in average) and Longwave transmission index of 0.12 (0.1 on average). Thermal Conductivity Coefficient of 0.18 W/m K.[5, 9]

1 silica glass panel, 3 mm thick. Solar near shortwave IR transmissivity index of 0.97 and longwave IR transmissivity coefficient of 0.1. Thermal Conductivity Coefficient of 1.2 W/m K.[4, 5, 6, 7]

Crystal Clear Polyethylene Film, 0.3 mm thick. Solar near shortwave IR transmissivity index of 0.98 and longwave IR transmissivity coefficient of 0.87. Thermal Conductivity Coefficient from 0.42 W/m K to 0.51 W/m K. [5, 10, 11, 12]

1 tube of white acrylic latex sealant for joints. Reflectivity of 0.94.[5]

1 tube of Qualtex® Silicone, translucent multipurpose silicone. TUGT-08347.[5]

Reynolds’ Wrap® aluminum foil. Reflectivity 98.4%. Thermal Conductivity Coefficient = 235 W/m K. [6, 7, 8]

White Glass Wool. Thermal Conductivity Coefficient of 0.04 W/m K. [6, 7, 8]

Quartet® Cork tiles. Thermal conductivity of 0.07 W/m K.[8]

Masking tape with similar absorptivity coefficient than that of corrugated cardboard (0.9).

Aluminum tape. Reflectivity 98.4%. Thermal Conductivity Coefficient = 235 W/m K. [5, 6, 7, 8]

Berel® Matte Black Paint. Reflectivity 0.005. [5]

Fuji® Film (ISO 400, ISO 200, and ISO 100).


TOOLS

Bit saw, carpenter’s saw, wood stripes, hammer, 2 acrylic cutters, reamer, 4 drill bits, ¼ kg nails, 8 screws, Black & Decker® screwdriver and Black & Decker® Kit.


PROCEDURE FOR THE FIRST STAGE OF THE EXPERIMENT

Four identical boxes of corrugated cardboard, by Lowe's®, were constructed by me.

The joints of the walls were sealed with white acrylic latex sealant. (Picture 01)

The inner walls of the boxes were painted with matte-black paint by Berel®, with a reflectivity of 0.3 and an absorbency of 0.97 (Picture 02). The reflectivity of the inner walls was confirmed with a Sekonic® photometer.

To test the seal around the edges, I placed a box in sunshine and observed the air expanding to make the polythene sheeting bulge (Picture 03)

The five exterior surfaces of the boxes were covered with Reynolds’ Wrap® aluminum foil. (Picture 04)

I adhered a square of Reynolds’ Wrap® aluminum foil to each of the glass and acrylic plates and the polyethylene film covering the open sides of the four boxes, exactly at the center, in order to avoid direct solar radiation having an effect on the rods of the digital thermometers so that overheating of the rods would not give false readings. (Picture 05)

I placed a sheet of clear acrylic Duraplex® by Plaskolite® with a cut-out window of 5 x 5 cm to cover the open side of the box no. 1 (Picture 06), which was then sealed with translucent silicon glue on the free edges of the corrugated cardboard walls.

I placed a plate of silica glass cover on the open side of box no. 2, which was then sealed with translucent silicon glue on the free edges of the corrugated cardboard walls.

I placed a plate of clear acrylic Duraplex® by Plaskolite® to cover the open side of box no. 3, which was then sealed with translucent silicon glue on the free edges of the corrugated cardboard walls.

I placed two sheets of Crystal Clear Polyethylene Film to cover the open side of the box 4 (Picture 07), which was then sealed with translucent silicon glue on the free edges of the corrugated cardboard walls. (Two sheets to reduce disproportionate conductive heat loss)

To test the reliability of the experiment the four boxes were placed under direct sunlight at 19 hr UTC (13:00 hr CST). The first segment of the experiment was then conducted the next day at 10:00 hrs (CST), as detailed below.

The four boxes were placed on a white table at an angle of 23° 15’ so that the solar radiation would strike perpendicularly on the boxes, thus avoiding shadowing.

The four boxes were initially covered with a blanket of Aluminum Plastic with a reflectivity of 97% before they were exposed to the sunbeams. (Picture 08)

I conducted the first segment of the experiment on May 20, 2011.

I started the experiment at 10:00 hr (CST).

I finished the experiment at 11:00 hr (CST).

The coordinates of the location where the experiment was carried out were:

Location: San Nicolas de los Garza, Nuevo Leon, Mexico.

Latitude: 25º 48´ North

Longitude: 100º 19' West

Altitude: 513 meters above sea level.
RESULTS

The instantaneous measurements of temperatures recorded during the first stage of the experiment were as follows:


I have plotted the results in the following graph:

OBSERVATIONS

1. The initial temperatures of the boxes in the shadow were higher than the ambient temperature. The cause is that the black walls of the boxes absorb thermal energy emitted by the surface where the boxes were placed and convection was not permitted, except for the box covered with a holed plate of acrylic, which caused a lower temperature than the boxes covered by glass and uncut acrylic because it permitted the free flow of air currents between the inside of the box and its surroundings.

2. After 1 minute of direct exposure to insolation (not graphed), the temperature in all boxes increased by approximately two degrees inside each box.

a) I observed that the temperature inside the box with a holed acrylic plate remained lower than the temperature inside the boxes covered with Polyethylene and acrylic uncut plates.

b) I observed that the temperature inside the box covered with the holed acrylic plate was the same than the temperature inside the box covered with the glass plate.

c) I observed that the temperature inside the box covered with Polyethylene film was lower than the temperature inside the box covered with an uncut acrylic plate.

3. After 5 minutes of direct exposure to insolation, the temperature in all boxes increased around 20 degrees.

a) I observed that the temperature inside the box with a holed acrylic plate was lower than the temperature inside the remainder boxes.

b) I observed that the temperature inside the box covered with Polyethylene film was higher than the temperature inside the box covered with a glass pane and the temperature inside the box covered with a holed acrylic pane.

c) I observed that the temperature in the box covered with a holed acrylic plate was lower than the temperature inside the remaining boxes.

d) I observed that the temperature inside the box covered with glass was almost the same than the temperature inside the box covered with polyethylene film.

4. After 10 minutes of direct exposure to insolation, the temperature continued increasing inside the four boxes.

a) I observed that the temperature inside the box covered with a glass plate was lower than the temperature inside the box covered with Polyethylene film.

b) I observed that the temperature inside the box covered with the holed acrylic plate was lower than the temperature inside the remainder boxes due to the free flow of air between the inside of the box covered with the holed acrylic plate and its surroundings.

c) I observed that the temperature inside the box covered with the uncut acrylic plate was higher than the temperature inside the remaining boxes.

5. After 15 minutes, the temperature inside the four boxes continued increasing.

a) I observed that the temperature inside the box covered with silica glass was almost the same than the temperature inside the box covered with Polyethylene film. This matching behavior repeats in the subsequent minutes, up to 60 minutes.

b) I observed that the temperature inside the box covered with the holed acrylic plate was lower than the temperature inside the remaining boxes.

c) I observed that the temperature inside the box covered with uncut acrylic plate continued being higher than in the remainder boxes.

6. After 40 minutes of direct exposure to insolation, the temperature inside the four boxes continued increasing.

a) I observed that the trend of increase of temperature inside the four boxes continued in a quasi-stable way.

b) I observed that the temperature inside the box covered with a glass plate was slightly higher than the temperature inside the box covered with polyethylene film. This trend was maintained up to 60 minutes of exposure to insolation.

c) I observed that the temperature inside the box covered with the uncut acrylic plate continued being higher than the temperature of the remainder boxes.

d) I observed that the temperature inside the box covered with a holed acrylic plate was lower than the temperature in the boxes covered with glass, acrylic, and Polyethylene film.

7. After 1 hour of direct exposure to insolation, I took off the Polyethylene sheet from the box labeled as “Polyethylene Film”, waited for 10 minutes, and inspected the temperature inside the box. I found that the temperature had decreased dramatically from 70.1 °C down to 45.4 °C due to convective heat transfer with the open atmosphere.


GENERAL CONCLUSIONS:

The greenhouse effect inside greenhouses is due to the blockage of convective heat transfer with the environment and it is not related, neither obeys, to any kind of “trapped” radiation. Therefore, the greenhouse effect does not exist as it is described in many didactic books and articles.

The experiment performed by Prof. Robert W. Wood in 1909 is absolutely valid and systematically repeatable.

In average, the blockage of convective heat transfer with the surroundings causes an increase of temperature inside the greenhouses of 10.03 °C with respect to the surroundings temperature.

PLEASE, READ THE PDF OF A WHOLE DESCRIPTION OF THE EXPERIMENT.



REFERENCES:

1. http://www.tech-know.eu/uploads/Note_on_the_Theory_of_the_Greenhouse.pdf

2. http://boole.stanford.edu/WoodExpt/

3. http://www.hannainst.com/manuals/manHI_98501_02_05_06.pdf

4. http://cemszmkpl.en.makepolo.com/productshow/4569429.html

5. Manufacturers' specifications.

6. Pitts, Donald and Sissom, Leighton. Heat Transfer. 1998. McGraw-Hill

7. Modest, Michael F. Radiative Heat Transfer-Second Edition. 2003. Elsevier Science, USA and Academic Press, UK.

8. http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html

9. http://www.atoglas.com/literature/pdf/81.pdf

10. http://people.csail.mit.edu/jaffer/FreeSnell/polyethylene.html

11. http://www.fao.org/docrep/T0455E/T0455E0o.html

12. http://web.archive.org/web/20061213003555/http://chem.arizona.edu/courses/chem245/polyeth.html

13. http://www.koverholt.com/pubs/Overholt_CSSCIpaper_2009.pdf

14. http://en.wikipedia.org/wiki/File:Polycarbonate_IR_transmission.png

15.  http://www.astm.org/Standards/D2103.htm


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IMPORTANT NOTE: THIS ARTICLE IS ONLY AN INTRODUCTION TO THE COMPLETE EXPERIMENT. PLEASE, READ THE PDF OF A WHOLE DESCRIPTION OF THE EXPERIMENT.