Lecture on Heat and Heat Transfer

TSH.10.01: Explain the mechanism of heat flow

• Heat flows from areas of high temperature to areas of low temperature due to the temperature gradient between the two locations. This movement continues until thermal equilibrium is reached, meaning both areas are at the same temperature.

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

• The Celsius scale (°C) is used widely in clinical settings and is based on the freezing and boiling points of water (0°C and 100°C respectively). The Fahrenheit scale (°F) is primarily used in the USA and is based on a mixture of ice, water, and salt being 0°F and body temperature being approximately 98.6°F.

TSH.10.03: Recall the Kelvin scale and the implications of Charles' Law; Explain thermometric properties; List the types of thermometers

• The Kelvin scale (K) is the SI unit of temperature, where 0 K is absolute zero, the point at which molecular motion ceases.

• Charles' Law states that the volume of a gas increases with temperature at constant pressure, graphically represented as a straight line on volume vs. temperature graphs.

• Thermometric properties involve measurable characteristics (like volume, color, electrical resistance) of substances that change with temperature. Common thermometers include clinical thermometers, bimetallic thermometers, and Galilean thermometers.

TSH.10.04: Explain variation in body temperature in a normal healthy human; Variation with physiological state

• Body temperature can fluctuate based on several factors:   - Normal Variations: Average oral temperature is approximately 37°C.   - Physiological Influences: Factors like time of day (diurnal variation), physical activity, emotions, age, smoking, and hormonal changes can cause body temperature to vary.   - Measurements: Different methods, such as oral, rectal, or axillary, yield slightly different temperatures based on core body temperature.

TSH.10.05: Define heat; specific heat capacity; thermal inertia

• Heat: The transfer of thermal energy from one body to another due to a difference in temperature.

• Specific Heat Capacity (C): The amount of heat required to raise the temperature of 1 kg of a substance by 1 K. Water, for instance, has a high specific heat capacity, which means it can absorb significant amounts of heat without a large temperature increase, contributing to thermal inertia.

• Thermal Inertia: The property of a substance to resist changes in temperature, crucial for maintaining stable internal conditions in organisms.

TSH.10.06: Discuss mechanisms of heat transfer; define conduction; state the conductive heat transfer equation; explain thermal conductivity

• Mechanisms of Heat Transfer: Primarily conduction, convection, and radiation.   - Conduction: Heat transfer through direct contact of particles. The equation for conductive heat transfer is $Q = kA\frac{ΔT}{L}$, where $k$ is thermal conductivity, $A$ is area, $ΔT$ is temperature difference, and $L$ is length.   - Thermal conductivities vary by material; for instance, water conducts heat 24 times better than air.

TSH.10.07: Define convection; state the convective heat transfer equation; Define latent heat, latent heat fusion, latent heat vaporization; Define wind chill and the turbo-oven effect

• Convection: The transfer of heat within fluids due to variations in density; warmer (less dense) fluid rises, while cooler (more dense) fluid sinks.

• Convective Heat Flow Rate: Generally summarized as $q$, the flow rate's typical value for humans is approximately $7.1W m^{-2}K^{-1}$.

• Latent Heat: The heat required to change the phase of a substance without changing its temperature.   - Latent Heat of Fusion: Energy needed to change a substance from solid to liquid.   - Latent Heat of Vaporization: Energy needed to change from liquid to gas.

• Wind Chill Effect: In windy conditions, convection increases the rate of heat loss, causing temperatures to feel colder than they are. The turbo-oven effect refers to increased heat transfer through forced convection created by fans in ovens, leading to more rapid cooking.