Share
Explore BrainMass

Heat Engines

A heat engine is a system that converts heat to mechanical work. It does this by bringing a fluid from a higher temperature to a lower temperature. A heat source will create thermal energy that brings the fluid to the high temperature. The fluid creates work in the engine while transferring heat to the colder sink until it reaches a low temperature state. During this process some of the thermal energy is converted into work by exploiting the properties of the working substance. The fluid can be any system with a non-zero heat capacity.

Heat engines are different from other engine types by the fact that the efficiency is defined by the Carnot’s theorem. Although the efficiency restriction is a negative, an advantage of heat engines is that most energy forms can be converted easily to heat. Since the heat source supplies energy to the engine, it can be powered by virtually any kind of energy. Heat engines have a wide range of applications. Some examples of heat engines include steam engines, diesel engines and gasoline engines in a car. These are powered by the expansion of heated gases.

Categories within Heat Engines

Second Law of Thermodynamics

Postings: 39

The second law of thermodynamics states that the entropy of the universe always increases in the course of every spontaneous change.

Isothermals

Postings: 22

Maintaining a process at constant temperature.

PV Diagrams

Postings: 7

A pressure volume temperature is used to describe corresponding changes in volume and pressure in a system.

Pressure difference between atmosphere and an evacuated tank.

It is proposed that a device be constructed to operate as follows: an evacuated tank of volume 1m3 is attached to the exhaust of an air-turbine-driven grinding wheel. Air at atmospheric pressure and 300K will be allowed to enter the turban inlet, while the pressure drop between the atmosphere and the tank serves to operate the t

Heat and Net Work Problem

An inventor claims to have invented a heat engine that receives 750kJ of heat from a source at 400K and produces 250kJ of net work while rejecting the waste heat to a sink at 300K. Is this a reasonable claim? Why?

Engine Operations and Maximum Possible Efficiency

Suppose you have a heat engine operating between 230 degress C and 100.0 C. It acieves 20.0% of the maximum possible efficiency (Carnot Efficiency). What energy input will enable the engine to perform 12.0 kJ of work?

Heat Engine Problem and Effficiency

A heat engine operating between temperatures of 500 K and 300 K is used to supply a constant 392 watts of power. If the engine were to operate at the maximum possible efficiency, determine the following. i. The rate at which the hot reservoir supplies heat to the engine, and ii. The rate at which heat is exhausted to t

Heat Engine Efficiency

A metal rod of length L and cross sectional area A connects two thermal reservoirs of temperatures T1 and T2. How would you describe the relationship between A, L and the amount of heat transferred through the rod per unit time?

Determining Maximum Cycle Temperature

A high speed compression ignition engine operates on the dual combustion cycle with a compression ratio of 20 to 1.Air is taken in at a pressure of 1.01 bar and at a temperature of 20celcius. The maximum cycle pressure is 70bar (cp=1.005kJ kg-1K-1, cv=0.718kJ kg-1K-1). Determine the maximum cycle temperature assuming that th

Carnot Heat engines operating in series

Consider two Carnot heat engines operating in series. The first engine receives heat from the reservoir at 1800 K, and rejects the waste heat to another reservoir at temperature T. The second engine receives the energy rejected by the first one, converts some of it into work, and rejects the rest to a reservoir at 300 K. If the

Carnot Cycle for an Ideal Gas

In our work with the Carnot cycle for an ideal gas, an equation similar to (1) below was derived, where q2 is the heat taken in at T2 and q1 is the heat expelled at T1. See attached files for full problem description.

Thermodynamics - Change in efficiency of an engine

Thermodynamics: Due to design changes, the efficiency of an engine decreases from 0.23 to 0.42. For the same input heat Qh. These changes increase the work done by the more efficient engine and reduce the amount of heat rejected to the cold reservoir. Find the ratio of heat rejected to the cold reservoir.

Carnot Cycle - Efficiency of heat engines

A Carnot engine operating at 30% efficiency exhausts heat into a heat sink at 283 K. By how much would the temperature of the heat reservoir need to be raised to increase the efficiency of the engine to 45% I believe the answer is 111 K. I need to see each step and formula to solve this question. Please assume I know nothing

Hurricanes

USING THE SCIENTIFIC METHOD EXPLAIN THE CYCLE OF A HURRICANE, HOW IT FORMS AND HOW IT BREAKS UP.

Tension, Work and Energy Consumption

1. A 200 lb metal object is suspended in a liquid with a specific gravity of 1.6. The metal object has a weight density of 150 lb/ft^3. If the object is only 3/4 submerged, what is the tension in the support cable? 2. A vertical cylinder is closed by a freely moving piston at its top. The piston has a mass of 5 kg and an area

Carnot Heat Engine

Question: The exhaust temperature of a carnot heat engine is 350 degrees Celsius.What is the intake temperature if the efficiency is 25%? a) 400 b) 543 c) 558 d) 830

Fuel consumption of multicylinder gasoline engine

The rate of revolution of a multicylinder gasoline engine in an airplane, operating at 2500 rev/min, takes in energy 7.89*10^3 J and exhausts 4.58*10^3 J for each revolution of the crankshaft. How many liters of fuel does it consume in 1.00 h of operation if the heat of combustion is 4.03 * 10^7 J/L, and what is the torque exert

Thermodynamics: Change in entropy for a heat engine

A heat engine operates between two reservoirs at T_2= 600K and T_1= 350K. It takes in 1000J of energy from the higher-temperature reservoir and performed 250 J of work. Find the entropy change of the universe and the work that could have been done by an ideal Carnot engine operating between these two reservoirs. I've tried

Carnot Engine

A 20% efficient real engine is used to speed up a train from rest to 5.00 m/s. It is known that an ideal (Carnot) engine using the same cold and hot reservoirs would accelerate the same train from rest to a speed of 6.50 m/s using the same amount of fuel. The engines use air at 300 K as a cold reservoir. Find the Temperature

Reversible heat engine with multiple reservoirs

The heat engine in the atachment operates reversibly and draws 1200 KJ of heat from the 200 K reservoir. The work produced is 200 KJ. Determine the amount and direction of heat interactions with the other reservoirs.

Steam plant: Estimate the amount of cooling water circulated in the condenser

In a steam plant the steam leaves the boiler at 2000kpa+250C deg. It is then expanded in an engine + finally exhausted into a condenser. The press+ condition of the steam at entry to the condenser are 15kpa+0.82 dry respectively. Assume the whole of this heat drop is converted into useful work in the engine. Show engine powe

Calculating Efficiency and Power in a Carnot Engine

A Carnot engine is used in a nuclear power plant. It receives 1500 MW by heat transfer with a source at 340C, and it rejects thermal waste to a nearby river at 27C. The river temperature rises by 3C. Determine the: (i) Efficiency of the power plant (ii) Power output of the power plant.