10_TSH. Heat and Heat Transfer

Lecture Overview

• Heat & Heat Transfer Module

  • Topics: Thermoregulation, Special Senses, Endocrine System, Reproductive System

  • Code: TSH.10

  • Lecturer: Dr. Omar Mamad

Learning Outcomes

• TSH.10.01: Explain the mechanism of heat flow

• TSH.10.02: Demonstrate the basis of the main temperature scales: Celsius, Fahrenheit

• TSH.10.03: Recall the Kelvin scale; implications of Charles' law; thermometric properties; types of thermometer

• TSH.10.04: Explain normal body temperature variation with physiological state

• TSH.10.05: Define heat, specific heat capacity, thermal inertia

• TSH.10.06: Discuss mechanisms of heat transfer; define conduction and the conductive heat transfer equation

• TSH.10.07: Define convection, convective heat transfer equation; latent heat (fusion/vaporization), wind chill, turbo-oven effect

Section 1: Heat & Temperature Scales

• Heat vs. Temperature:

  • Same temperature can have different amounts of heat energy.

  • Heat flows from high temperature to low temperature.

• Units of Temperature:

  • S.I. scale is Kelvin (K), but Celsius (°C) is commonly used in clinical environments

  • Fahrenheit used primarily in the USA, Belize, Jamaica, Liberia, Marshall Islands

Temperature Conversion Table

Section 2: Temperature Measurement

• Thermometers:

  • Utilize different thermometric properties; physical properties that change with temperature (e.g., volume, electrical resistance)

  • Types of Thermometers:

    • Clinical mercury thermometer, bimetallic strip thermometer

Section 3: Changes in Temperature

• Heat Energy and Temperature Change:

  • To change the temperature of an object, heat energy must be added or removed

  • Formula:

    • Q = m * C * ΔT

    • Where Q = heat energy (J), m = mass (kg), C = specific heat capacity (J/kg/K), ΔT = change in temperature (K).

• Specific Heat Capacity:

  • Amount of heat energy required to change the temperature of 1 kg of a substance by 1 K

  • Water has high specific heat capacity, contributing to high thermal inertia of the human body.

Section 4: Mechanisms of Heat Transfer

• Methods of Heat Transfer:

  • Radiation:

    • Requires no medium; relies on photons

  • Convection:

    • Occurs in fluids; heated fluid becomes less dense and rises, cooler fluid sinks

    • Influences climate and weather patterns

  • Conduction:

    • Heat transfer in solids; involves direct contact

Conduction Formula

• H_cd = (k * A * ΔT) / L

  • Where:

    • k = thermal conductivity

    • A = area (m²)

    • ΔT = temperature difference (K)

    • L = thickness (m)

Practical Application in Insulation

• Examples of good insulators include air and materials with low thermal conductivity, while water is a poor conductor compared to air.

Section 5: Mechanisms of Heat Transfer Continued

• Convective Heat Flow Equation:

  • q = convective heat transfer constant

  • Affected by shape, orientation, type of surface

• Wind-chill Effect:

  • Wind can enhance the cooling effect, perceived lower temperatures than actual air temperature.

Section 6: Mechanisms of Heat Transfer via Radiation

• Radiation:

  • Heat transfer that occurs without a medium.

  • Concepts include emissivity and the Stefan-Boltzmann law:

    • e = emissivity (0 = bad, 1 = perfect)

    • s = Stefan's constant = 5.67 x 10^-8 W/m²K⁴

Thermometric Properties in Thermometers

Thermometers utilize thermometric properties, which are physical properties that change with temperature. These properties enable the measurement of temperature through different mechanisms. Common thermometric properties include:

• Volume: In liquid-in-glass thermometers, the volume of liquid expands or contracts with temperature changes, allowing for a direct reading on a calibrated scale.

• Electrical Resistance: In resistance thermometers, changes in temperature affect the electrical resistance of a material, which can be quantified to determine temperature.

• Pressure: Some thermometers measure the pressure of gases or liquids that change with temperature, using the ideal gas law to correlate pressure change with temperature.

Different types of thermometers leverage these properties for accurate measurement in various applications, highlighting their importance in temperature measurement.