Thermodynamics and Heat Transfer Lecture Notes

These flashcards cover key concepts from the thermodynamics and heat transfer lecture, focusing on power absorption, emissivity, heat engines, and changes in internal energy.

What happens to the power absorbed by an object if its radius is halved and temperature is doubled?

The power reduces from 100 W to 25 W.

How is power absorbed from the walls calculated?

Pabs = AseσT, where A is the area, se is the emissivity, and T is the temperature.

Which object gains heat the most quickly in a warm chamber?

A brick with high emissivity in a chamber filled with air whose inside walls have high emissivity.

What contributes to faster heat absorption in the context of emissivity?

Higher emissivity allows objects to emit and absorb more electromagnetic energy.

What is the approximate percentage of power of radiation from a lightbulb radiated between 600nm and 800nm?

Approximately 36%.

How much more power does a radiation source produce in visible light compared to infrared, if the IR region has double the width and height?

It emits four times as much power in visible light compared to infrared.

What is true about work done (W) and heat supplied (Q) during processes A and C of an ideal gas?

QA > WA and QC > WC.

Given an ideal gas with C = 3R/2, what is the change in internal energy when pressure and volume are doubled?

The change in internal energy is 45 kJ.

During an adiabatic expansion of a gas, how does work compare to isothermal expansion?

The work done during adiabatic expansion is typically greater than during isothermal expansion.

What is the heat absorbed by an engine operating on a cycle with given heat input and output?

The efficiency can be calculated as the output work divided by heat input.

In a system with rigid walls versus one with a movable piston, which container will have more ice melted when cooled?

More ice melts in the case with the movable piston.

What is the efficiency of an engine consuming 4000 J and expelling 3000 J of heat?

The efficiency is 0.25.

In a thermodynamic cycle, how is maximum efficiency defined?

Maximum efficiency is defined by the Carnot efficiency formula based on temperature differences.

What can be said about the work done on a gas during isobaric, isothermal, and adiabatic processes?

ΔU is largest for the isothermal process if work done is the same.

What is the heat transfer |Q| along different paths in a PV diagram if state B has lower internal energy than state A?

|Q| is the greatest for the path exhibiting the largest work done.

In a system at mechanical equilibrium where two pistons are freely movable, what can be concluded about the mass?

The mass of the happy brick can be determined based on the pressure balance.

When heating different moles of gas under constant volume versus constant pressure, how does energy requirement differ?

Heating at constant volume requires less energy than heating at constant pressure.