Biological Physics: Thermodynamics lecture 1

Thermodynamics Overview

• Branch of Physics dealing with energy, thermal energy, and mechanical energy.
• Also covers transformations of energy (dynamics).
• Governed by the four laws of thermodynamics (0, 1, 2, 3).

Relevance to Biological Physics

• Biological processes are temperature dependent.
• The body uses temperature receptors to control its temperature within a tight window.
• Body temperature is determined and regulated via thermodynamics.
• Lectures teach how to quantitatively apply temperature, heat, and thermal energy concepts.
• Relevant reading material is in Biological Physics, Chapters 17-22.

Learning Objectives

• Become familiar with temperature, heat, and thermal expansion.
• Understand ideal gas properties, gas mixtures, and kinetic theory for gases/thermal energy.
• Real gases, phase change, specific & latent heat comprehension required.
• Learn moist-air properties, relative humidity, dry-bulb, dew-point, wet-bulb, and psychrometric charts.
• Grasp heat transfer by conduction, convection, and radiation.
• Study energy/metabolism, efficiency of energy processes, and thermoregulation of the body.
• Apply thermodynamic concepts with numerical calculations to biological systems through practice problems.

Thermo Summary: Lecture Outline

• Lecture One: Covers temperature, thermal energy, heat, energy conservation, and thermal expansion.
• Lecture Two: Focuses on ideal gases, Charles's, Boyle's, and Dalton's laws with kinetic theory/gas mixtures.
• Lecture Three: Centers on real gases, temperature and phase changes, specfic/latent heat, and energy conservation.
• Lecture Four: Discusses water vapor in the air: moisture content, humidity, and the psychrometric chart.
• Lecture Five: Covers heat transfer, energy balance in humans via conduction/convection/radiation, metabolism, and work efficiency.

Lecture 1 Key Objectives

• Develop an understanding of temperature and its measurement.
• Grasp the concept of thermal equilibrium and heat transfer.
• Learn to calculate thermal expansion amounts.

Temperature Basics

• Temperature relates to hot and cold awareness.
• Is a physical quantity to measure hot and cold.
• Enables understanding in terms of mass, velocity, and kinetic energy.
• Is related to thermal energy of a system
• Governs heat transfer between systems.

Constant-Volume Gas Thermometer

• Temperature is measured.
• A fundamental thermometer is the constant-volume gas thermometer
• Theory and Use will be covered
• Units are in kelvin (K)
• Zero kelvin (0 K) is absolute zero.

How to use Constant-Volume Gas Thermometer

• Put the gas thermometer bulb where you want to measure the temperature, T
• Let to settle, measure the pressure, P
• Measure the pressure, Ptp, with the triple-point cell with bulb (Ttp = 273.16 K)
• Based on constant volume,
  • T/Ttp = P/Ptp
• The temperature is then:
  • T = 273.16 x P/Ptp
• Triple point temperature, 273.16 K, defined as the temperature of a mixture of water liquid, vapor and ice, all in equilibrium

Celsius Scale

• Conversions
• T(°C) = T(K) – 273.15
• T(K) = T(°C) + 273.15
• Water freezes at 0 °C
• Water boils at 100 °C
• Triple point of water is 0.01 °C
• Example: 283 K corresponds to 9.85 °C; 293 K corresponds to 19.85 °C

Secondary Thermometers

• Measures like mercury thermometers can be used
• Can use electrical resistance (platinum resistance)
• Can use intensity of the infra-red radiation
• Can be calibrated against a primary thermometer tied to standard.

Thermal Energy Defined

• Atoms and molecules of matter move randomly
• Gases have energy through random translational movement
• Energy is typically in random atomic or molecular motions
• Thermal energy is "more motion"

Absolute Temperature (K)

• Measures average kinetic energy for an atom/molecule.

Heat Transfer

• Energy moves from hotter to colder objects when in contact.
• Heat transfer due to temperature difference.
• Continues to go until thermal equilibrium
• Energy moving this way is "heat".

Human Body Temperature

• The human body contains highly developed temperature regulation systems
• Body temperature varies, not one single temp
• Normally surface temperature is lower than the core temperature
• At night the core temp decreases while surface temp increases

Core Temps

• 33 °C or less: risk of hypothermia
• 35-36 °C: typical of early morning and considered a bit cold
• 36-37.5 °C: normal
• 38 °C: indicates moderate exercise, or active children
• 39-40 °C: indicates hard exercise or unwellness
• 42 °C→ may cause irreversible damage

Thermal Expansion

• Atoms move faster when temperature increases
• Objects expand as temperature increases
• At temperature T the length is L0
• At temperature T + ΔT the length becomes L0 + ΔL
  • where ΔL = L0 * α * ΔT

Thermal Expansion Cont.

• α (alpha) is the linear coefficient for thermal expansion.
• ΔT = (final temperature – initial temperature)
• Steel for example has an α = 12 × 10-6 °C-1
• Example: a 4 m sheet of steel at 10°C expands

Area and Volume

• The coefficient of surface expansion is 2α
• The coefficient of* volume expansion is 3α.
• Values of α at 20 °C: include
• Quartz 1 × 10-6 °C-1
• Pyrex glass 9 × 10-6 °C-1
• and more

Temperature Ranges

• Universe: 1 to 1012 K with range of 1,000,000,000,000 K
• Planet Earth: 185-330 K with range of 145 K
• Human body: 33-42 °C with range of 9 K