Introduction to Food Physics - Chapter 4

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Questions and Answers

What is the relationship between the Celsius and Kelvin temperature scales?

  • The Kelvin scale is shifted 273.15 units higher than the Celsius scale. (correct)
  • They have the same size degree.
  • The Celsius scale is shifted 273.15 units higher than the Kelvin scale.
  • They have the same starting point.

According to the information provided, what is the formula for converting degrees Celsius to degrees Fahrenheit?

  • $T_C = T_K - 273.15$
  • $T_F = T_R - 459.67$
  • $T_F = 5T_C + 32$
  • $T_F = \frac{9}{5}T_C + 32$ (correct)

What is the difference between the Celsius and Fahrenheit temperature scales?

  • They have the same starting point but different size degrees.
  • They have different starting points but the same size degrees.
  • They have different starting points and different size degrees. (correct)
  • They have the same starting point and the same size degrees.

What is the significance of the zero point on the Kelvin scale?

<p>It represents the temperature at which all molecular motion ceases. (A)</p> Signup and view all the answers

What is the relationship between the Kelvin and Rankine temperature scales?

<p>They have different starting points but the same size degree. (C)</p> Signup and view all the answers

Why is the Kelvin scale considered an absolute temperature scale?

<p>It starts at the theoretical point where all molecular motion ceases. (C)</p> Signup and view all the answers

Which of the following is a correct conversion from degrees Celsius to degrees Kelvin?

<p>100°C = 373.15 K (C)</p> Signup and view all the answers

According to the provided information, which of the following is a correct formula for converting degrees Fahrenheit to degrees Rankine?

<p>$T_F = T_R - 459.67$ (B)</p> Signup and view all the answers

What is the primary focus of thermal properties in the food industry?

<p>To perform various heat transfer calculations (B)</p> Signup and view all the answers

Which of the following is NOT a thermal property related to food processing?

<p>Nutritional analysis (B)</p> Signup and view all the answers

What does heat transfer in food primarily help with?

<p>Estimating process time for thermal processing (A)</p> Signup and view all the answers

Which thermal property would be most relevant for designing refrigeration equipment?

<p>Thermal diffusivity (B)</p> Signup and view all the answers

What principle is primarily utilized to solve problems associated with thermal properties of food?

<p>Thermodynamics (D)</p> Signup and view all the answers

What is the approximate specific heat capacity of unfrozen water?

<p>4186-4200 J/kg.°C (D)</p> Signup and view all the answers

What must be considered when calculating the specific heat of frozen foods?

<p>Both sensible and latent heat effects (C)</p> Signup and view all the answers

Which of the following models was NOT used to estimate the specific heat of unfrozen food?

<p>Thompson's approximation (1990) (B)</p> Signup and view all the answers

What happens to the specific heat capacity of food as temperature decreases below its freezing point?

<p>There is a large decrease in specific heat (A)</p> Signup and view all the answers

What does the variable $cp$ represent in the equation $cp = \sum_{i=1}^{n} c_{pi} X_i$?

<p>Specific heat capacity of the materials (C)</p> Signup and view all the answers

Which method is used for the proximate analysis of protein content in food?

<p>Kjedahl method (D)</p> Signup and view all the answers

What type of model did Choi and Okos propose in 1986 for predicting specific heat?

<p>A comprehensive model based on composition and temperature (C)</p> Signup and view all the answers

In the equation for specific heat capacity, how is the contribution of each component represented?

<p>By the specific heat of the ith component multiplied by its mass fraction (C)</p> Signup and view all the answers

What content is analyzed using Soxhlet extraction?

<p>Fat (D)</p> Signup and view all the answers

What is the purpose of conducting a proximate analysis on food?

<p>To obtain the nutritional composition (D)</p> Signup and view all the answers

What is the primary purpose of calorimetry?

<p>To quantitatively measure heat exchange (C)</p> Signup and view all the answers

In the calorimetry example, what is the final temperature of the system?

<p>30.5°C (B)</p> Signup and view all the answers

Which equation accurately represents the principle of calorimetry?

<p>Heat lost = Heat gained (B)</p> Signup and view all the answers

What assumption is made about the calorimeter in the specific heat calculation example?

<p>Air space between the jacket and cup insulates well (B)</p> Signup and view all the answers

What is the mass of the sample alloy heated in the example?

<p>0.150 kg (B)</p> Signup and view all the answers

Which of the following components contributes to the heat exchange in the system?

<p>The alloy and water combined (A)</p> Signup and view all the answers

What specific heat capacity value is given for water in the example?

<p>$4186 , rac{J}{kg , °C}$ (D)</p> Signup and view all the answers

What type of calorimeter is mentioned in the context provided?

<p>O2 bomb calorimeter (B)</p> Signup and view all the answers

What does the 0th law of thermodynamics state?

<p>Two systems in equilibrium with a third are in equilibrium with each other. (D)</p> Signup and view all the answers

What occurs when two objects are in thermal equilibrium?

<p>They do not exchange energy by heat or radiation. (B)</p> Signup and view all the answers

Which of the following best describes thermal contact?

<p>Transfer of energy due to temperature difference. (D)</p> Signup and view all the answers

If object A and object B are each in thermal equilibrium with object C, what can be inferred about A and B?

<p>They must be at the same temperature. (A)</p> Signup and view all the answers

What conclusion can be drawn from the relationship between thermal equilibrium and temperature?

<p>The same temperature signifies thermal equilibrium. (D)</p> Signup and view all the answers

Why is the SI unit for temperature Kelvin?

<p>Kelvin is based on absolute zero and thermodynamic principles. (C)</p> Signup and view all the answers

Which of the following is NOT a characteristic of thermal dynamic systems?

<p>They must have temperature differences. (A)</p> Signup and view all the answers

What is the effect of placing two objects at the same temperature on energy exchange?

<p>No energy will be exchanged between the objects. (C)</p> Signup and view all the answers

How is the concept of thermal contact related to energy exchange?

<p>Temperature differences must exist to allow energy exchange. (B)</p> Signup and view all the answers

Which concept explains that two objects will not exchange energy when in thermal equilibrium?

<p>0th law of thermodynamics (A)</p> Signup and view all the answers

Flashcards

0th Law of Thermodynamics

States that if two systems are in thermal equilibrium with a third, they are in equilibrium with each other.

Thermal Equilibrium

Condition where two objects exchange no energy by heat or radiation.

Thermal Contact

When two objects can exchange energy due to temperature difference.

Temperature Scale

A system that indicates temperature measurement, e.g., Celsius, Kelvin.

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Unit Conversion of Temperature

The process of changing temperature from one scale to another.

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Equilibrium with a Third System

The concept that two systems can be in equilibrium through a shared system.

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Energy Exchange

The transfer of thermal energy between objects due to temperature differences.

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Same Temperature

Condition when two objects do not exchange energy and are in thermal equilibrium.

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Kelvin Scale

An absolute temperature scale starting at absolute zero, used in science.

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Thermodynamic Systems

Systems that can exchange energy or matter with their surroundings.

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Temperature

A measure of how hot or cold something is, affecting food processing.

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Heat Capacity

The amount of heat needed to change a food's temperature by one degree Celsius.

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Thermal Conductivity

The ability of a food material to conduct heat.

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Enthalpy

A measure of energy used in heating and phase changes of food during processing.

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Heat Transfer in Food

The process of moving heat in or out of food during cooking or storage.

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Specific heat capacity of water (unfrozen)

The amount of heat required to raise the temperature of water by 1°C, approximately 4186-4200 J/kg.°C.

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Latent heat

The heat released or absorbed during a phase change, such as freezing or melting, without changing temperature.

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Apparent specific heat

An effective specific heat that combines sensible heat and latent heat effects during phase changes.

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Specific heat of unfrozen food

The thermal property of unfrozen food estimating how much heat is needed to change its temperature.

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Choi and Okos model (1986)

A model that predicts the specific heat of unfrozen foods based on their composition and temperature.

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Absolute Zero

The lowest possible temperature where no thermal energy exists, defined as 0 Kelvin.

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Conversion from Celsius to Kelvin

To convert Celsius (°C) to Kelvin (K), add 273.15.

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Celsius to Fahrenheit Conversion

To convert Celsius to Fahrenheit, use the formula T℉ = 5T℃/9 + 32.

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Temperature Change Equivalence

The change in temperature (∆T) is the same for Celsius and Kelvin scales but differs in Fahrenheit.

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Boiling Point in Celsius

The boiling point of water is 100°C, a common reference in temperature discussions.

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Pressure vs Temperature Graph

A graph plotting pressure against temperature, showing the behavior of gases.

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Gay-Lussac’s Law

A gas law stating that the pressure of a gas is directly proportional to its absolute temperature at constant volume.

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Specific Heat Capacity

The amount of heat needed to change the temperature of a material per unit mass.

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Proximate Analysis

A method to determine the moisture, fat, protein, fiber, carbohydrate, and mineral content in food.

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Moisture Content

The amount of water present in food, often measured in proximate analysis.

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Soxhlet Extraction

A method for extracting fat from food samples in proximate analysis.

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Kjeldahl Method

A technique to determine the protein content in a food sample.

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Chen's Model

An expansion of Siebel's equation for specific heat.

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Calorimetry

The quantitative measurement of heat exchange between systems.

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Calorimeter

A device used to measure heat transfer or heat exchange.

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Specific Heat

The amount of heat needed to raise the temperature of a substance by one degree Celsius.

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Heat Transfer Calculation

Calculating heat lost or gained in calorimetry experiments.

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System Temperature

The final temperature in a calorimetric process.

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Metal Alloy in Calorimetry

Specific heat determination using a heated metal sample.

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Study Notes

Introduction to Food Physics - Chapter 4: Thermal Properties

  • This chapter covers thermal properties applicable in food processing.
  • Key learning outcomes include explaining thermal properties, principles, and laws, along with solving problems related to food thermal properties.
  • Applications in the food industry involve various heat transfer calculations, equipment design, process time estimation, microbial inactivation, thermal processing of foods/beverages, and process control optimization.

Temperature

  • Zeroth law of thermodynamics governs thermal contact, equilibrium.
  • Thermal equilibrium implies no net heat exchange between objects at the same temperature.
  • Temperature scales exist, and unit conversions are essential.

Thermal Equilibrium

  • If two systems are each in thermal equilibrium with a third, they are in thermal equilibrium with each other.
  • This principle is fundamental to temperature measurement and understanding heat transfer.

Temperature Scales

  • The text discusses Kelvin as the absolute temperature scale, as well as the conversion of units between different temperature scales.

Thermal Properties in Food Processing

  • Calculations for heat transfer are needed for storage, refrigeration, freezing, heating, drying, microbial inactivation, and other thermal processing methods.
  • These calculations help optimize food processing procedures.
  • Various models exist to estimate specific heat capacity in different food types.
  • Techniques for specific heat measurements or proximate analysis methods are used.

Heat Capacity

  • Heat capacity is a material's ability to hold and store heat.
  • The amount of energy required to change the temperature of the material by 1°C (or 1 K) defines heat capacity.
  • Calculating specific heat capacity can aid in understanding required energy for heating/cooling processes.
  • Various food models or equations aid in calculating specific heat in food products in specific conditions.
  • Specific heat capacity values are essential for different materials in thermal calculations.

Specific Heat Capacity of Food

  • Specific heat capacity of frozen or unfrozen food vary.
  • A larger decrease in specific heat occurs as temperatures decrease for frozen foods.
  • The latent heat from temperature change and fusion of water must be considered at freezing points.

Specific Heat Measurement Techniques

  • Proximate analysis methods include measuring water content, fat, protein, fiber, carbohydrates, and minerals to determine specific heat using models.
  • Calorimetry is a direct technique for measuring heat exchange.
  • Measuring calorimeter can determine unknown specific heat of materials.

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IMK114 Introduction to Food Physics Chapter 4: Thermal Properties PDF

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