Efficiency Definition and 901 Threads

Homework Statement Superheated steam at a pressure of 40 bar and a temperature of 500°C is supplied to the turbine of a Rankine cycle. If the condenser pressure is 0.03 bar. Find the thermal efficiency of the cycle. (Neglect feed pump work). I used steam tables found...

Hi. I have a question about output torque and efficiency of a simple gear pair as shown on the picture. So, I have a pinion and a gear. I give an input torque Tp in the clockwise direction. Therefore, the pinion will rotate with ωp angular velocity in clockwise and the gear ωg in...

Hey guys, I ran into this paper talking about the Maximum power you can obtain from a Carnot cycle: http://aapt.scitation.org/doi/abs/10.1119/1.10023 From what I understood, there are two extremes. To achieve maximum efficiency you have to make sure that the temperature of the system is never...

Homework Statement An ideal gas with Cv = 5 2R, and γ = 1.4 starts at a volume of 1.5m3 , a pressure of 2.0×105Pa ,and a temperature of 300K. It undergoes an isobaric expansion until the volume is V , then undergoes an adiabatic expansion until the volume is 6.0m3 , and finally undergoes an...

Homework Statement You are tasked with designing an electrical circuit with a motor, a battery, and several 1ohm and 2ohm resistors. The motor is designed to run at a current of 20A and a voltage of 10V, but your battery supplies 15 V. The motor can then lift a 4kg mass 2.25 meters in...

Alright It's been over a year since I've posted and received amazing help the last time I did. Now I've a question I cannot seem to find an answer to. Say you have an electrical charge and use a transformer to step up the voltage high enough to where it arcs in air. Then you have a conductive...

So I have been looking into efficiency, My system is high radius with the motor located outside. This motor is small, and thus the gear being driven by the motor, is also small for space requirements. I have wanted to use a ratio of about 22:1 to make this system, and everything seems to work...

Homework Statement A step-down transformer has an efficiency of 90%, the voltage of it primary coil is 200V and its current is 0.5A, and its secondary coil has a voltage of 9V and a current of 10A and its number of turns is 90 turns. Calculate the number of turns of the primary coil. Homework...

What are the two methods for calculating large DC motor efficiency ?

Assuming a reverse Carnot engine (Heat Pump Achieve 353K after compression and 253K after evaporation) is cascaded to Rankine turbine such that heat rejection to a steam boiler and heat is collected from a thermally isolated compartment first (used as condensation by cooling) then from ambient...

Homework Statement I am trying to calculate the efficiency of this heat engine that has two step. an adiabatic compression, followed by a linear expansion back to the original point. I keep getting an efficiency of 1, which I know can't be right... Homework Equations ##e = \frac{W}{Q_H}## The...

The standard proof to show carnot efficiency cannot be exceeded is to couple a supposedly more efficient engine to a carnot refrigerator, and show that it would violate second law. However, isn't it true that we can make the same argument with any arbitrary efficiency? Some discussions on...

Suppose I heat a room directly by lighting a fire in the room, let's say it is a butane gas fire and it takes n BTU to raise the temperature by 10°C. Now, suppose I don't like the smell of burning gas fumes and decide instead to move the same gas fire outside and boil water to generate steam...

There's a youtube channel where someone nicknamed Thunderf00t is making fun of a water source that is supposed to be a wind-powered dehumidifier. He makes some arguments that don't look entirely valid. He argues that the energy needed is the evaporation heat of water, or some 2000 kJ/kg. In...

Hi. Sorting the exchanges of heat and mechanical work in a thermodynamic cycle by the signs and summarizing, I get ##Q_{in}>0##: heat transferred into the system ##Q_{out}<0##: heat transferred to the cold reservoir ##W_{out}<0##: work done by the system ##W_{in}>0##: work done on the system...

Homework Statement Consider the ##xyzzy## algorithm below. This algorithm takes a linear collection (e.g., a list or array) of size ##n## as an argument (i.e., as the input to the algorithm) and produces no return value (i.e., has no output, but might alter the linear collection). Note that the...

Hello, I have a question for you guys and gals. I am working on a Desalination project and am ironing out questions about efficiency. What would be the most efficient temperature to evaporate water? 50, 100, 110 degrees? Does it make a difference, or is the energy required to evaporate a fixed...

A problem I encounter when microwaving food is that the centre is no penetrated by the microwaves so remains cool and I have to wait for the heat to be conducted through which takes a long time and undermines one of the advantages of microwaving which is the speed of the process. Would it make...

It has been stated in previous threads that engine inefficiencies are caused by: Pumping losses (induction and exhaust) Frictional losses (in bores, bearings, and ancilliaries) Thermal losses to exhaust, coolant (jacket, charge and oil), and surroundings Does engine vibration have an effect on...

Hi Does anyone know of any papers about Increased efficiency Antimatter production, as I am interested in this area. Apologies if it's in the wrong area. Thanks.

Homework Statement In the year 2004 the USA produced 1787 TWh of electrical energy in conventional thermal plants and 476 TWh in nuclear plants. Assuming 30% efficiency for nuclear plants and 40% for conventional thermal plants, determine the (annual) volume of cooling water required to cool...

It is known that automotive engine efficiency (ie. fuel efficiency) is maximum at a specific range of medium loads. If we go higher than this range, the efficiency drops. If we go lower than these loads, the efficiency drops as well. Do we know the reasons for that? I am particularly interested...

Homework Statement Two identical bodies of constant heat capacity ##C_p## at temperatures ##T_1## and ##T_2## respectively are used as reservoirs for a heat engine. If the bodies remain at constant pressure, show that the amount of work obtainable is ##W = C_p (T_1 + T_2 − 2T_f)##, where...

I have to design a track for a skate boarder that is 50% efficient (friction must be present) from the start of the skater's drop-in, to his furthest point along the track. My skater's mass will be 75kg efficiency=energy output/energy input x100% I am not really sure where to go next and how...

Homework Statement [/B] A 12 Volt lead-acid car battery, engineered for "up to 500 or more charge/discharge cycles," has a rating of 330.0 Ampere-hours. It sells for $ 262.00. Part B: The battery has a mass of 32.7 kg. What total mass of such batteries would be required to deliver the same...

Homework Statement Ive looked through several published journals online trying to find an experiment that I can use as background research for my report, something I can compare my findings to but I am just wasting lots of time that I could be doing the rest of my report so what I am trying to...

You can burn a hole in paper using a magnifying glass and light. What would happen if you applied this large-scale on a solar panel?

I 've got a project, and I 've been searching all over to find an answer; what is the efficiency of the accelerometer itself (p.e. in its use in smart-devices as screen-orientation method)? Or do you know, what is the efficiency (approximately of a regular spring (NOT into void)? Thank you...

Homework Statement We did an experiment which included having an electric motor provide power to drive the compressor and we had instrumentation available to measure the compressor shaft torque and shaft rotational speed and 6 water filled manometer tubes were used as measurements of the...

Homework Statement To set-up an equation for the efficiency equation of single-phase toroidal transformer given the circuit with the following mesh equations (s*L1+R1)*I1 + (-s*M)*I2 = V1 (-s*M)*I1 + (s*L2+R2+RL)*I2 = 0 Homework Equations Efficiency equation(?), equation derived by The...

Homework Statement A motor lifts a block of mass 0.050kg at a constant velocity of 0.40m s-1. The current in the motor ia 85mA and the potential difference across it is 3.0V. Calculate the efficiency of the motor Homework Equations Ek = 1/2 x mv2 Electrical power = VIt The Attempt at a...

This is only a semi- serious thread, since I suspect there's a simple back-of-a-napkin calculation that shows this to be infeasible. The idea is the following: a lot of a car's efficiency gets lost in the form of air drag, I.e. forcing the air to go around the car. Could one upscale a...

Homework Statement Students used a speed gun to measure the final speed of slider at the bottom of the slide. They measure the height difference between the top and bottom of the slide to be 3.0 m. If the speed of a slider at the bottom of the slide is 5.0 m/s, what is the efficiency of the...

Homework Statement A Carnot engine absorbed 1.0 kJ of heat at 300 K, and exhausted 400 J of heat at the end of the cycle. What is the temperature at the end of the cycle? Homework Equations The efficiency of a Carnot engine is given by the formula Efficiency = 1 – Qc/Qh = 1 –...

What is the difference between thermal efficiency and mechanical efficiency of an engine...and which engine is more efficient ..petrol or diesel

Homework Statement http://i.imgur.com/SQ6jx94.png (sorry for the low resolution~ it's already the best i can make it~) Homework Equations U=Q+W the three variables of isobaric, isochoric, adiabatic process (can i save my effort from typing all of them out?) e=(Qh-Qc)/Qh The Attempt at a...

Will a four cycle, internal combustion engine have greater thermal efficiency with a relatively cool jacket water temperature, say 160 degrees F, or a relatively hot water jacket temperature, say 190 degrees F? These specific numbers are only important in as much as they are commonly available...

Hi, I have developed a 2KW hydro turbine prototype with a generator connected. Generator Type - Brushless DC Permanent Magnet (16Pol-18Slot) (2000Watts, 2000 RPM, 54VDC) Generator test report (by manufacturer) is given below; RPM Volts Current 1000 29.8...

Will a rankine cycle have efficiency equal to the carnot cycle, if the mean temperature of heat addition in rankine cycle is equal to the source temperature of Carnot cycle, and the mean temperature of heat rejection is equal to the sink temperature of carnot cycle. My understanding is that in...

I learned that brushless DC motor windings have an algorithm for winding depending on several variables... When I google image search BLDC stator, I expect to see this : But I see a lot more of this : Is this second one still a brushless DC? If so, do they just lose efficiency by winding...

I'm Brazilian, and until a few years ago most commercial electric fans sold in the country looked like this: But then one company started making them with 6 blades, claiming it had better wind output and made less noise than the 3-bladed fans (they didn't directly made this claim; it was...

I know theoretically fuel cell efficiency decreases as temperature increases. But in practice it is vice versa. What is the reason of that? I couldn't find enough sources. Any kind of help is much appreciated.

i wonder if it is possible to get the efficiency of an LED just by knowing the radiant power an the outside temperatur. i also know the temperatur of the emmited light. well they say the LED has an efficiency >1 because it takes heat from the out side and turns it into rays. so these two things...

Homework Statement Evaluate the experiment below, identifying energy loss and errors, and access their effect on the efficiency? The experiment was 'Determining the efficiency of energy conversion of boiling water in an electric kettle'. The method/system - 1. Weigh accurately 1000g of water...

Hello, I am wondering if anyone can help me with the following question. I want to find out how the size of the core in an inductor influences the current induced in the secondary coil, and whether a smaller core is more efficient if efficiency is defined as inducing the highest current in the...

Homework Statement Consider a Buck-Boost converter. If in addition to the transistor on resistance (R_{ON}), the converter diode has a voltage drop (V_{D_0}), symbolically derive an expression for the efficiency, η of the converter, where η = 100* PO/PIN. Verify that that when R_{ON} and...

Hey all, I'm a bit of a food geek and a DIY nut and I'm looking to build my own vacuum sealer for as cheap as possible. My question to you guys, is what is the cheapest material I can use that will still withstand the pressure as well as maintain the airtight seal needed? I am looking to get a...

I was just wondering how we can find out the efficiency of a rotary engine? Obvious, it is more efficient than a gasoline/diesel engine.For example the RX8 on 1.3 L in 2 rotors get 250 hp which is quite impressive for that capacity,also it works in 4 stroke,and the power to weight ratio is...

Homework Statement What is the clearance of an ideal otto engine if the efficiency is 46.4% and k=1.3 Homework Equations efficiency = Worknet/Heat Added k=1.3 hot air T= 1900kThe Attempt at a Solution i don't know how to start

Homework Statement I'm doing an investigation for my physics class, where we were told to investigate the relationship between current flowing through and the efficiency of an immersion heater. My hypothesis was that as current increased, the efficiency would decrease due to the relationship...