|
|
GMAT Club Daily Prep
Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.
Customized
for You
Track
Your Progress
Practice
Pays
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
29 Apr 2015, 07:10
Kudos
Bookmarks
hello,
I have seen many GMAT experts recommend to use non-gmat content such as the economist ,to improve RC accuracy. I am having difficult time imprving my accuracy with RC.I subscribed for The economist digital subscription ,however I am not sure how to effectively use it. Do i just go ahead and start reaidng articles randomly.
Please let me know your views .Thanks in advance
I have seen many GMAT experts recommend to use non-gmat content such as the economist ,to improve RC accuracy. I am having difficult time imprving my accuracy with RC.I subscribed for The economist digital subscription ,however I am not sure how to effectively use it. Do i just go ahead and start reaidng articles randomly.
Please let me know your views .Thanks in advance
Archived Topic
Hi there,
This topic has been closed and archived due to inactivity or violation of community quality standards. No more replies are possible here.
Where to now? Join ongoing discussions on thousands of quality questions in our Verbal Questions Forum
Still interested in this question? Check out the "Best Topics" block below for a better discussion on this exact question, as well as several more related questions.
Thank you for understanding, and happy exploring!
09 May 2015, 05:40
Kudos
Bookmarks
Lets use a original Economist article in Science and Technology section posted for 9May 2015 for discussion.
- Q1: What is the main point of the passage?
- Q2: What is the purpose of the passage?
- Q3: What is the tone of the author?
COOL THINKING
LIQUID nitrogen seems a good place to start if you want to cool something down. If Peter Dearman, a British inventor, is correct, it might be even better than it looks. Mr Dearman is a man with a bee in his bonnet. He has dreamed, since he was 15, of making a useful motor powered by liquid nitrogen. Now, at 64, he thinks he has done it—not, as he had originally imagined, to run a car, but to run a refrigerator that promises to be more efficient and less polluting than conventional alternatives.
The Dearman engine works a bit like a steam, petrol or diesel engine. It uses heat to expand a gas (known as a working fluid), which drives a piston. The difference is that instead of starting at room temperature the working fluid ends up there, and starts instead at -196°C, the boiling point of nitrogen. That temperature change, and the expansion of the nitrogen it causes, is enough to do work equivalent to a more conventional heat engine—but not, sadly, much better than such an engine. Nitrogen engines have thus, for most of Mr Dearman’s life, been an idea looking for an application. Now, though, he thinks he has found a niche whose incumbent he can replace—the inefficient, pollution-generating diesel-powered refrigerators that keep the contents of food-delivery lorries cold.
The challenge was to extract more cooling power from liquid nitrogen via the engine than can be garnered by using it directly. Mr Dearman was able to do so by dividing the labour of cooling into two. First, instead of injecting liquid nitrogen directly into the engine’s cylinder, his system boils it by running it through a system of pipes called a heat exchanger. This apparatus is connected to the compartment to be refrigerated, and sucks heat out of that compartment and into the nitrogen, which turns from a liquid into a gas.
This process cools the compartment but does not raise the nitrogen’s temperature, which remains at -196°C. That is because the heat in question, known as latent heat of vaporisation, serves merely to change the nitrogen’s state, not to warm it up. The resultant cold, gaseous nitrogen is now injected into the engine’s cylinder (see diagram) along with a mixture of water and glycol, known as a heat-transfer liquid, that is at room temperature.
The heat-transfer liquid rapidly warms the nitrogen, causing it to expand and drive the piston—which powers a conventional refrigeration circuit that provides a second dose of cooling to the cold compartment. The piston’s return stroke then expels the gas and the now-cooled heat-transfer liquid. The nitrogen is vented to the air, and the heat just extracted from the cold compartment by the conventional refrigeration circuit is used to warm the heat-transfer liquid back to room temperature, ready to be used again.
This double cycle extracts 40% more cooling power from liquid nitrogen than systems which use the stuff directly as a coolant. That makes it competitive with the conventional, diesel-powered refrigerators now used in chiller lorries. Its crucial advantage over diesel, though, is that it is pollution-free. Nitrogen is 78% of air, so a little more will make no difference. The tiny particles of soot that refrigerator diesel engines produce, by contrast, are a health hazard up with which regulators are increasingly unwilling to put. Mr Dearman’s engine, now undergoing trials, provides an alternative. If it proves itself, the bees in his bonnet may at last yield some honey.
- Q1: What is the main point of the passage?
- Q2: What is the purpose of the passage?
- Q3: What is the tone of the author?
COOL THINKING
LIQUID nitrogen seems a good place to start if you want to cool something down. If Peter Dearman, a British inventor, is correct, it might be even better than it looks. Mr Dearman is a man with a bee in his bonnet. He has dreamed, since he was 15, of making a useful motor powered by liquid nitrogen. Now, at 64, he thinks he has done it—not, as he had originally imagined, to run a car, but to run a refrigerator that promises to be more efficient and less polluting than conventional alternatives.
The Dearman engine works a bit like a steam, petrol or diesel engine. It uses heat to expand a gas (known as a working fluid), which drives a piston. The difference is that instead of starting at room temperature the working fluid ends up there, and starts instead at -196°C, the boiling point of nitrogen. That temperature change, and the expansion of the nitrogen it causes, is enough to do work equivalent to a more conventional heat engine—but not, sadly, much better than such an engine. Nitrogen engines have thus, for most of Mr Dearman’s life, been an idea looking for an application. Now, though, he thinks he has found a niche whose incumbent he can replace—the inefficient, pollution-generating diesel-powered refrigerators that keep the contents of food-delivery lorries cold.
The challenge was to extract more cooling power from liquid nitrogen via the engine than can be garnered by using it directly. Mr Dearman was able to do so by dividing the labour of cooling into two. First, instead of injecting liquid nitrogen directly into the engine’s cylinder, his system boils it by running it through a system of pipes called a heat exchanger. This apparatus is connected to the compartment to be refrigerated, and sucks heat out of that compartment and into the nitrogen, which turns from a liquid into a gas.
This process cools the compartment but does not raise the nitrogen’s temperature, which remains at -196°C. That is because the heat in question, known as latent heat of vaporisation, serves merely to change the nitrogen’s state, not to warm it up. The resultant cold, gaseous nitrogen is now injected into the engine’s cylinder (see diagram) along with a mixture of water and glycol, known as a heat-transfer liquid, that is at room temperature.
The heat-transfer liquid rapidly warms the nitrogen, causing it to expand and drive the piston—which powers a conventional refrigeration circuit that provides a second dose of cooling to the cold compartment. The piston’s return stroke then expels the gas and the now-cooled heat-transfer liquid. The nitrogen is vented to the air, and the heat just extracted from the cold compartment by the conventional refrigeration circuit is used to warm the heat-transfer liquid back to room temperature, ready to be used again.
This double cycle extracts 40% more cooling power from liquid nitrogen than systems which use the stuff directly as a coolant. That makes it competitive with the conventional, diesel-powered refrigerators now used in chiller lorries. Its crucial advantage over diesel, though, is that it is pollution-free. Nitrogen is 78% of air, so a little more will make no difference. The tiny particles of soot that refrigerator diesel engines produce, by contrast, are a health hazard up with which regulators are increasingly unwilling to put. Mr Dearman’s engine, now undergoing trials, provides an alternative. If it proves itself, the bees in his bonnet may at last yield some honey.
Archived Topic
Hi there,
This topic has been closed and archived due to inactivity or violation of community quality standards. No more replies are possible here.
Where to now? Join ongoing discussions on thousands of quality questions in our Verbal Questions Forum
Still interested in this question? Check out the "Best Topics" block above for a better discussion on this exact question, as well as several more related questions.
Thank you for understanding, and happy exploring!
Moderators:
509 posts
363 posts
