Method of determination of thermal conductivity of timber

IS 10754: Scope - Key Points & Specifications

• Purpose: Defines test methods for thermal insulation materials using a guarded hot plate apparatus.
• Rounding off results: Final calculated/observed values must be rounded as per IS 2-1960, retaining the same significant figures as the standard values.
• Terminology: Uses definitions from IS 3069-1965 (thermal insulation) and IS 707-1976 (timber technology).
• International Coordination: Aligns with global standards while considering Indian practices.
• Temperature Measurement:
  • Use thermocouples embedded in grooves or under working surfaces of heating/cooling units.
  • Detect temperature imbalances between central and guard plates.
  • Refer IS 3346-1980 for thermocouple number, placement, and specs.

Apparatus Features (Fig. 1 Summary)

Rounding Rule (IS 2-1960)

• Round off to the same number of significant figures as specified in the standard.
• Example: If standard value = 0.123 (3 sig. figs), report 0.123 or rounded accordingly.

flowchart LR
    A[Central Heater] --> B[Central Surface Plates]
    C[Guard Heater] --> D[Guard Surface Plates]
    B --> F[Differential Thermocouples]
    D --> F
    E[Cooling Units] --> Es[Cooling Unit Surface Plates]
    G[Heating Unit Thermocouples] --> B
    H[Cooling Unit Thermocouples] --> Es
    I[Test Specimens] --> B

This ensures accurate thermal conductivity measurement per IS 10754 scope.

IS 10754 - Definitions & Key Specifications Summary

• Reference Definitions:
  Definitions are primarily from:

  • IS 3069-1965 (Thermal insulation materials glossary)
  • IS 707-1976 (Timber technology glossary)
  • IS 3346-1980 (Thermocouples and temperature measurement)

• Temperature Measurement Setup (Clause 3.4):

  • Thermocouples must be placed in grooves or beneath working surfaces of central heating and cooling units.
  • Used to detect temperature imbalance between central and guard surface plates.
  • Number and placement per IS 3346-1980.

• Rounding Off Results (Clause 4):

  • Final test values must be rounded as per IS 2-1960.
  • Retain significant figures equal to those in the specified value.

Key Terminology (from IS 10754 Fig.1):

Important Notes:

• Use two slab guarded hot-plate method (IS 707) for thermal conductivity testing.
• Follow IS 2-1960 for rounding off numerical results.

flowchart LR
    A[Central Heater] --> B[Central Surface Plates]
    C[Guard Heater] --> D[Guard Surface Plates]
    B & D --> F[Differential Thermocouples]
    E[Cooling Units] --> Es[Cooling Unit Surface Plates]
    G[Heating Unit Surface Thermocouples] & H[Cooling Unit Surface Thermocouples] --> I[Test Specimens]

This setup ensures accurate temperature measurement and compliance with IS 10754 requirements.

IS 10754: Apparatus and Equipment Key Points

Measurement Precision (Clause 5.1)

• Specimen thickness: ±10⁻⁵ m
• Other dimensions: ±10⁻⁴ m
• Weight: ±10⁻⁴ kg
• Hot plate temperature: 300–310 K
• Pressure: Constant, enough for thermal contact but no specimen deformation
• Power supply: Stabilized to avoid fluctuations

Temperature Measurement (Clause 3.4)

• Use thermocouples embedded in grooves under central and guard plates.
• Refer IS 3346-1980 for thermocouple number and placement.
• Ensure temperature uniformity between guard and central sections.

Specimen Handling (Clause 5.6)

• Weigh specimens before and after testing.
• Dry in oven at 100 ± 2°C until constant mass.

Data Recorded (Clause 5.4)

• Temperature difference across specimen (ΔT in K)
• Electrical power input: Voltage (V) and Current (A)
• Hot and cold plate temperatures
• Centre-to-guard temperature balance (K)

Typical Formula for Thermal Conductivity (k):

[ k = \frac{Q \times d}{A \times \Delta T} ]

Where:

• ( Q = V \times I ) (Power input in Watts)
• ( d ) = specimen thickness (m)
• ( A ) = cross-sectional area (m²)
• ( \Delta T ) = temperature difference across specimen (K)

Apparatus Schematic (Simplified)

graph LR
  A[Central Heater] --> B[Central Surface Plates]
  B --> I[Test Specimens]
  I --> E[Cooling Units]
  C[Guard Heater] --> D[Guard Surface Plates]
  F[Thermocouples] --> B
  F --> D
  G[Heating Unit Surface Thermocouples]
  H[Cooling Unit Surface Thermocouples]

Summary: IS 10754 emphasizes precise measurement, stable temperature control, and proper specimen handling to ensure accurate thermal conductivity testing using a guarded hot-plate apparatus.

IS 10754: Specimen Preparation and Conditioning Summary

Specimen Dimensions & Preparation (Clauses 4.1 & 4.2)

• Thickness: 0.02 m (± precision 10⁻⁵ m)
• Shape: Square or disc with side/diameter 0.15 m (± precision 10⁻⁴ m)
• Surface: Smooth, plane for good thermal contact
• Orientation: Radial/tangential (plank) or longitudinal (log cross-section)
• Sample Sets: Minimum 10 sets; each set has 2 identical samples with equal thickness; 3 sets must be longitudinal thickness
• Heating Unit Dimensions: Minimum linear dimension 0.10 m; guard area width 0.05 m

Conditioning (Clause 4.2)

• Condition specimens to constant mass at:
  • Relative Humidity: 60 ± 5%
  • Temperature: 27 ± 1°C

Measurement & Testing (Clause 5.1 & 5.6)

• Weigh specimens to precision 10⁻⁴ kg before and after test
• Apply constant pressure on specimen plates without affecting thickness
• Heating unit temperature: 300–310 K
• Use stabilizer to avoid power fluctuations
• After test, dry specimens in oven at 100 ± 2°C until constant mass

Key Specifications Table

Notes:

• Ensure **thermal contact pressure

IS 10754 - Test Procedure Key Points

Measurement & Instrumentation

• Use thermocouples embedded in grooves or under working surfaces to measure surface temperatures of central heating and cooling units (Clause 3.4).
• Thermocouples detect temperature imbalance between central and guard surface plates.
• Refer IS:3346-1980 for thermocouple specifications and placement.

Specimen Preparation & Measurement (Clause 5.1)

• Thickness measured to ±10⁻⁵ m; other dimensions to ±10⁻⁴ m.
• Weight measured to ±10⁻⁴ kg.
• Apply constant pressure on specimen to ensure good thermal contact without altering thickness.
• Heating unit temperature set between 300 K and 310 K.
• Use stabilizer to maintain constant electrical power (voltage & current).

Data to Record (Clause 5.4)

• Temperature difference across specimen (K).
• Electrical power input (volts × amperes).
• Hot and cold plate temperatures.
• Centre-to-guard temperature balance (K).

Rounding Off Results (Clause 0.4)

• Round off test results as per IS 2-1960.
• Retain significant figures equal to those in the standard's specified values.

Simplified schematic of temperature zones in hot plate apparatus:

graph LR
A[Central Heater] --> B[Central Surface Plates]
B --> I[Test Specimen]
I --> E[Cooling Units]
C[Guard Heater] --> D[Guard Surface Plates]
D --> I
F[Differential Thermocouples] --> B
G[Heating Unit Thermocouples] --> B
H[Cooling Unit Thermocouples] --> E

This ensures precise thermal conductivity measurement using guarded hot plate method per IS 10754.

IS 10754 - Key Calculations for Thermal Conductivity

Thermal Conductivity Formula (Clause 6.2)

[ K = \frac{2 A (T_h - T_c)}{I \times V \times l} ]

Where:

• K = Thermal conductivity (W/m·K)
• A = Specimen area enclosed by boundary midway through air gap (m²)
• Tₕ = Hot face temperature (K)
• T𝑐 = Cold face temperature (K)
• I = Current through central heater (A)
• V = Potential drop across heater (V)
• l = Thickness of specimen (m)

Additional Specifications:

• Specimens must be oven-dried at 100 ± 2°C to constant mass before weighing (Clause 5.6).
• Rounding off values should follow IS 2-1960 rules, maintaining the same number of significant figures as specified.

Summary Table:

flowchart LR
    A[Heater Current (I)] --> B[Power Input (I × V)]
    B --> C[Heat Flow through Specimen]
    C --> D[Temperature Difference (Tₕ - T𝑐)]
    D --> E[Calculate K using formula]

This formula and procedure ensure accurate determination of thermal conductivity using the guarded hot-plate method as per IS 10754.

IS 10754 – Reporting of Results: Key Points & Specifications

• Rounding Off (Clause 0.4):
  Final test or analysis results must be rounded as per IS 2:1960 (Rules for rounding off numerical values).

  • Retain the same number of significant figures as the specified value in the standard.
  • Example: If specified value = 0.123 (3 significant figures), report result as 0.456, not 0.46.

• Specimen Handling (Clause 5.6):
  After testing, specimens are:

  • Weighed immediately.
  • Dried in a well-ventilated oven at 100 ± 2°C until constant mass is achieved.
    This ensures moisture content consistency for accurate reporting.

• Calculations (Clause 6):
  While details are not provided here, calculations typically involve:

  • Thermal conductivity via guarded hot-plate method.
  • Use of mass difference before and after drying for moisture content.

Summary Table: Rounding Off Rules (per IS 2:1960)

flowchart TD
    A[Test/Analysis Result] --> B[Round off as per IS 2:1960]
    B --> C[Report with same significant figures]
    A --> D[Specimen weighed post-test]
    D --> E[Oven dry at 100±2°C until constant mass]
    E --> F[Final weight for moisture calculation]

Note: Always cross-check with IS 10754 full text for detailed calculation methods and reporting formats.

IS 10754: Precautions and Notes Summary

Key Points from Clause 3.4 (Thermocouple Placement & Temperature Measurement)

• Thermocouples must be embedded in grooves or beneath working surfaces of central heating and cooling units.
• Use multiple thermocouples to detect temperature imbalance between central and guard surface plates.
• Refer to IS 3346-1980 for:
  • Number of thermocouples required at various locations.
  • Thermocouple specifications.
  • Equipment details.

Important Specifications & Practices

• Temperature measurement must ensure uniformity across the test surface.
• Use differential thermocouples to accurately monitor temperature gradients.
• Maintain guard heaters and plates to minimize heat loss and ensure steady-state conditions.

Rounding Off Results (per IS 2-1960)

• Final test values must be rounded off to the same number of significant figures as the specified standard values.

Typical Thermocouple Arrangement (Fig. 1 Conceptual)

graph LR
  A[Central Heater] --> B[Central Surface Plates]
  B --> F[Differential Thermocouples]
  C[Guard Heater] --> D[Guard Surface Plates]
  E[Cooling Units] --> Es[Cooling Surface Plates]
  G[Heating Unit Surface Thermocouples]
  H[Cooling Unit Surface Thermocouples]
  I[Test Specimens]

Reference Standards

• IS 3346-1980: Thermocouple details and placement.
• IS 2-1960: Rounding off numerical values.
• Method: Two slab guarded hot-plate for thermal conductivity.

Summary: Ensure proper thermocouple placement per IS 3346, use differential thermocouples to detect temperature imbalance, maintain guard heaters, and round off results as per IS 2.