## Thermodynamics B/C

Test your knowledge of various Science Olympiad events.
Justin72835
Member
Posts: 170
Joined: June 25th, 2017, 7:06 am
Division: C
State: TX

### Re: Thermodynamics B/C

Crtomir wrote:
Justin72835 wrote:When you get out of a pool, even the slightest breeze will make you feel cold. Why is this?

Answer: Evaporation of water is an endothermic process, meaning it sucks in heat from the environment, which includes your skin which is at a higher temperature than the water. Since it sucks heat energy form your skin, you feel cold.

Next Question: (From Shortley and Williams Elements of Physics, 3rd Edition) A layer of ice on a pond is 2 cm thick. When the upper surface of the ice is at -15C and the temperature of the water just below the ice is 0C, at what rate does the ice become thicker? Express your answer in units of [cm/min.]. Show your work.

Tbh this is probably completely wrong but oh well
"The fault, dear Brutus, is not in our stars,
But in ourselves, that we are underlings."

Seven Lakes High School '19

Crtomir
Member
Posts: 148
Joined: April 11th, 2017, 1:24 pm
Division: B
State: OH
Location: Watts Middle School, Centerville, OH
Contact:

### Re: Thermodynamics B/C

Justin72835 wrote:
Crtomir wrote:
Justin72835 wrote:When you get out of a pool, even the slightest breeze will make you feel cold. Why is this?

Answer: Evaporation of water is an endothermic process, meaning it sucks in heat from the environment, which includes your skin which is at a higher temperature than the water. Since it sucks heat energy form your skin, you feel cold.

Next Question: (From Shortley and Williams Elements of Physics, 3rd Edition) A layer of ice on a pond is 2 cm thick. When the upper surface of the ice is at -15C and the temperature of the water just below the ice is 0C, at what rate does the ice become thicker? Express your answer in units of [cm/min.]. Show your work.

Tbh this is probably completely wrong but oh well

Correct. Nice Job!

Justin72835
Member
Posts: 170
Joined: June 25th, 2017, 7:06 am
Division: C
State: TX

### Re: Thermodynamics B/C

Great! Now it's my turn.

You have a piston filled with 8 moles of a monatomic ideal gas at a temperature of 278 K. It is completely insulated (meaning that there is no heat transfer between the walls of the piston) and it is at rest in a vacuum. The piston has a diameter of 25 cm and has a mass of 4.5 kg. You then apply 50 N of force to the top of the piston.

Determine the change in temperature of the gas.
"The fault, dear Brutus, is not in our stars,
But in ourselves, that we are underlings."

Seven Lakes High School '19

UTF-8 U+6211 U+662F
Exalted Member
Posts: 1473
Joined: January 18th, 2015, 7:42 am
Division: C
State: PA

### Re: Thermodynamics B/C

Justin72835 wrote:Great! Now it's my turn.

You have a piston filled with 8 moles of a monatomic ideal gas at a temperature of 278 K. It is completely insulated (meaning that there is no heat transfer between the walls of the piston) and it is at rest in a vacuum. The piston has a diameter of 25 cm and has a mass of 4.5 kg. You then apply 50 N of force to the top of the piston.

Determine the change in temperature of the gas.

Just a guess

Justin72835
Member
Posts: 170
Joined: June 25th, 2017, 7:06 am
Division: C
State: TX

### Re: Thermodynamics B/C

UTF-8 U+6211 U+662F wrote:
Justin72835 wrote:Great! Now it's my turn.

You have a piston filled with 8 moles of a monatomic ideal gas at a temperature of 278 K. It is completely insulated (meaning that there is no heat transfer between the walls of the piston) and it is at rest in a vacuum. The piston has a diameter of 25 cm and has a mass of 4.5 kg. You then apply 50 N of force to the top of the piston.

Determine the change in temperature of the gas.

Just a guess

You got it right, nice job!

One thing I noticed while looking through your work is that when you were calculating for pressure and area, you used the diameter instead of the radius of the piston. This didn't really matter in the end since the pressures got divided out in the final formula (causing the areas to cancel out), but it's something that you should definitely watch for.
"The fault, dear Brutus, is not in our stars,
But in ourselves, that we are underlings."

Seven Lakes High School '19

UTF-8 U+6211 U+662F
Exalted Member
Posts: 1473
Joined: January 18th, 2015, 7:42 am
Division: C
State: PA

### Re: Thermodynamics B/C

Someone else can go

kendreaditya
Member
Posts: 100
Joined: March 31st, 2016, 3:28 pm
Division: C
State: PA
Location: Mariana Trench

### Re: Thermodynamics B/C

This is my first time doing this so...

The efficiency of a heat engine is defined as the ratio of what?

Justin72835
Member
Posts: 170
Joined: June 25th, 2017, 7:06 am
Division: C
State: TX

### Re: Thermodynamics B/C

kendreaditya wrote:This is my first time doing this so...

The efficiency of a heat engine is defined as the ratio of what?

There are a couple ways to define it:

Easy: (what you want)/(what you pay)

Mathematical: 1 - Qc/Qh = (Qh - Qc)/Qh = W/Qh
"The fault, dear Brutus, is not in our stars,
But in ourselves, that we are underlings."

Seven Lakes High School '19

Schrodingerscat
Administrator
Posts: 333
Joined: March 2nd, 2011, 7:10 pm
Division: Grad
State: KS
Location: Kansas City metro

### Re: Thermodynamics B/C

This may be more than anything I personally remember ever seeing on a thermo test, but yet still potentially a feasible test question (for C division at least), and I have recently developed an interest in boilers.

A sealed, perfectly insulated boiler is a cylinder with the (interior) dimensions of 1m in radius, 5m height and is 70% full of water at 25C. Assume ambient pressure of 1atm and ignore the heat capacity of the boiler. A furnace burns methane at a rate of 15MW and transfers 60% of the heat to the boiler.

a. What is the minimum stoichiometric air flow to the furnace in m^3/minute?

b. How fast will the furnace initially heat in degrees Celsius per minute? When will it reach boiling point?

c. Describe what happens inside the boiler as heat continues to be added.

d. Once the boiler reaches a pressure of 3MPa (absolute), a valve is kept opened such to maintain a constant pressure. Once most of the air is removed from the boiler, determine the following: the temperature of the boiler, the outflow rate of steam in kg/minute, an estimate of the time before the boiler runs dry (you may ignore factors like changing steam volume and water evaporated to reach steady state).

e. Feed water is now fed into the boiler at 20C and an equilibrium state with a water level of 50% is reached. Determine the new steam outflow rate.

f. What else can be done for the boiler to produce more steam without increasing the furnace output?

g. (Extra) The boiler fails catastrophically under full operating conditions. Estimate the size of the resulting steam cloud, neglecting the work done on the (former) boiler and the immediate surroundings.

Solutions
Last edited by Schrodingerscat on January 16th, 2018, 9:49 pm, edited 1 time in total.

UTF-8 U+6211 U+662F
Exalted Member
Posts: 1473
Joined: January 18th, 2015, 7:42 am
Division: C
State: PA

### Re: Thermodynamics B/C

Schrodingerscat wrote:This may be more than anything I personally remember ever seeing on a thermo test, but yet still potentially a feasible test question (for C division at least), and I have recently developed an interest in boilers.

A sealed, perfectly insulated boiler is a cylinder with the (interior) dimensions of 1m in radius, 5m height and is 70% full of water at 25C. Assume ambient pressure of 1atm and ignore the heat capacity of the boiler. A furnace burns methane at a rate of 15MW and transfers 60% of the heat to the boiler.

a. What is the minimum stoichiometric air flow to the furnace in m^3/minute?

b. How fast will the furnace initially heat in degrees Celsius per minute? When will it reach boiling point?

c. Describe what happens inside the boiler as heat continues to be added.

d. Once the boiler reaches a pressure of 3MPa (absolute), a valve is kept opened such to maintain a constant pressure. Once most of the air is removed from the boiler, determine the following: the temperature of the boiler, the outflow rate of steam in kg/minute, an estimate of the time before the boiler runs dry (you may ignore factors like changing steam volume and water evaporated to reach steady state).

e. Feed water is now fed into the boiler at 20C and an equilibrium state with a water level of 50% is reached. Determine the new steam outflow rate.

f. What else can be done for the boiler to produce more steam without increasing the furnace output?

g. (Extra) The boiler fails catastrophically under full operating conditions. Estimate the size of the resulting steam cloud, neglecting the work done on the (former) boiler and the immediate surroundings.

Ok... I think I know a, b, and c

Schrodingerscat
Administrator
Posts: 333
Joined: March 2nd, 2011, 7:10 pm
Division: Grad
State: KS
Location: Kansas City metro

### Re: Thermodynamics B/C

UTF-8 U+6211 U+662F wrote:
Schrodingerscat wrote:This may be more than anything I personally remember ever seeing on a thermo test, but yet still potentially a feasible test question (for C division at least), and I have recently developed an interest in boilers.

A sealed, perfectly insulated boiler is a cylinder with the (interior) dimensions of 1m in radius, 5m height and is 70% full of water at 25C. Assume ambient pressure of 1atm and ignore the heat capacity of the boiler. A furnace burns methane at a rate of 15MW and transfers 60% of the heat to the boiler.

a. What is the minimum stoichiometric air flow to the furnace in m^3/minute?

b. How fast will the furnace initially heat in degrees Celsius per minute? When will it reach boiling point?

c. Describe what happens inside the boiler as heat continues to be added.

d. Once the boiler reaches a pressure of 3MPa (absolute), a valve is kept opened such to maintain a constant pressure. Once most of the air is removed from the boiler, determine the following: the temperature of the boiler, the outflow rate of steam in kg/minute, an estimate of the time before the boiler runs dry (you may ignore factors like changing steam volume and water evaporated to reach steady state).

e. Feed water is now fed into the boiler at 20C and an equilibrium state with a water level of 50% is reached. Determine the new steam outflow rate.

f. What else can be done for the boiler to produce more steam without increasing the furnace output?

g. (Extra) The boiler fails catastrophically under full operating conditions. Estimate the size of the resulting steam cloud, neglecting the work done on the (former) boiler and the immediate surroundings.

Ok... I think I know a, b, and c

Guess I did overlook a few things not fully calculating it myself first. I had just assumed standard temperature and pressure air, and I adjusted the power to get a larger equilibrium steam flow but forgot to consider the effects on the heat-up phase.

Edit: Actually you accidentally added a factor of 60, making it slightly more reasonable.

Tailsfan101
Exalted Member
Posts: 621
Joined: April 14th, 2017, 4:33 pm
Division: C
State: ID
Location: Philippians 3:20a "For our citizenship is in heaven"
Contact:

### Re: Thermodynamics B/C

Cat's questions only further the reason I would never want to do Thermodynamics.
Over my head...
2019 Treasure Valley Homeschool Wiki
2018

2019

Possible 2020 events: DD, GLM, Code, WIDI, 4N6

Assassinator for games #118 and 136

Alex-RCHS
Member
Posts: 530
Joined: November 4th, 2016, 3:46 pm
Division: C
State: NC
Location: Raleigh, NC

### Re: Thermodynamics B/C

Tailsfan101 wrote:Cat's questions only further the reason I would never want to do Thermodynamics.
Over my head...

I used to feel this way about Physics too, but once you understand the concepts involved formerly impossible questions appear quite simple, and the whole learning process becomes very fulfilling.
About me!
Raleigh Charter HS (NC) 2018
UNC-Chapel Hill 2022

WhatScience?
Member
Posts: 394
Joined: July 16th, 2017, 4:03 pm
Division: C
State: NJ

### Re: Thermodynamics B/C

Alex-RCHS wrote:
Tailsfan101 wrote:Cat's questions only further the reason I would never want to do Thermodynamics.
Over my head...

I used to feel this way about Physics too, but once you understand the concepts involved formerly impossible questions appear quite simple, and the whole learning process becomes very fulfilling.

This is why I like physics more than bio.

I dropped A and P and Microbes because it was just too much memorization. Thermo at least feels more like a science, where everything has a logical solution.
"When you clean your room, you are increasing the total chaos of the universe" - Hank Green Crash Course (Entropy)

Events 2018

Thermodynamics, Potions and Poisons, Disease Detectives, Optics, and Towers

Alex-RCHS
Member
Posts: 530
Joined: November 4th, 2016, 3:46 pm
Division: C
State: NC
Location: Raleigh, NC

### Re: Thermodynamics B/C

WhatScience? wrote:
Alex-RCHS wrote:
Tailsfan101 wrote:Cat's questions only further the reason I would never want to do Thermodynamics.
Over my head...

I used to feel this way about Physics too, but once you understand the concepts involved formerly impossible questions appear quite simple, and the whole learning process becomes very fulfilling.

This is why I like physics more than bio.

I dropped A and P and Microbes because it was just too much memorization. Thermo at least feels more like a science, where everything has a logical solution.

Did you just...
imply...
that microbio...
isn’t a science...
About me!
Raleigh Charter HS (NC) 2018
UNC-Chapel Hill 2022

Return to “2018 Question Marathons”

### Who is online

Users browsing this forum: No registered users and 2 guests