• ### How to calculate a non-steady state heat exchange between a heat source and a steady flow of cold water.?

Best answer: Let the temperature of the water leaving the pipe be T. This is a function of time t which we measure in minutes. Let the temperature of water in the tank be θ. This is also a function of t. How I tackle this problem depends strongly on how I interpret your term "efficiency of the heat exchanger". If the... show more
Best answer: Let the temperature of the water leaving the pipe be T. This is a function of time t which we measure in minutes. Let the temperature of water in the tank be θ. This is also a function of t. How I tackle this problem depends strongly on how I interpret your term "efficiency of the heat exchanger". If the "performance" (I think efficiency is an inappropriate term) of the heat exchanger were to be 100% then I'd understand that the water leaving bthe pipe would always be at T=θ which means that its temperature rise would be (θ – 10). I assume that "50% heat exchanger efficiency" means that the temperature rise of the water leaving the pipe is 50% of that value, i.e. ΔT= 0.5×(θ-10) giving: T=0.5×(θ-10)+10 = 0.5×θ+5 = 0.5×(θ+10) ......... (A) This means that the water initially (t=0) leaves the pipe at T(0) = 30˚C Now the rate of heat loss by the tank water is equal to the heat-flow rate in the pipe water i.e.: dθ/dt = -ΔT×10/100 ˚C /min. or: dθ/dt = -0.5×(θ-10)/10 or dθ/dt = 0.5 - 0.05θ Solving this linear, separable, first-order, differential equation gives the general solution: θ(t) = C.e^(-0.05t) + 10 where C is an arbitrary constant to be determined by the boundary conditions. obviously, to give θ(0) = 50, C must = 40 giving the particular solution for this problem as: θ(t) = 40.e^(-0.05t) + 10. Enter t = 10 into this formula and get the final value of θ = θ(10) Energy lost by water in 10 min = 100×[50-θ(10)]×s where s is the specific heat of water in J/kg/˚C. The final temperature of the water emerging from the pipe is found by entering θ(10) in any of the formulae A. I think you must be able easily to handle the substitutions and arithmetic. Please award one of your answers "Best Answer". We especially appreciate this particular small recognition of our efforts to assist
2 answers · Engineering · 12 months ago
• ### Is it possible to have dilatation without internal stress?

Best answer: Yes you can have expansion caused by heating (thermal expansion) but if, for example, the temperature is kept unifoirm throughout the body during the heating process, then there might well be no internal stress. Please award one of your answers "Best Answer". We especially appreciate this particular small recognition of our... show more
Best answer: Yes you can have expansion caused by heating (thermal expansion) but if, for example, the temperature is kept unifoirm throughout the body during the heating process, then there might well be no internal stress. Please award one of your answers "Best Answer". We especially appreciate this particular small recognition of our efforts to assist
1 answer · Engineering · 1 year ago
• ### Can you help me with Physics?

Best answer: Yes you're spot on! Note however that food Calories are already kilocalories, so in terms of food labelling and nutritional discussion, 4.4 Calories would be used. Thus food Calories (commonly written with a capital in an attempt to avoid confusion!) are kilocalories You're also correct in multiplying by 4 to account for the 25%... show more
Best answer: Yes you're spot on! Note however that food Calories are already kilocalories, so in terms of food labelling and nutritional discussion, 4.4 Calories would be used. Thus food Calories (commonly written with a capital in an attempt to avoid confusion!) are kilocalories You're also correct in multiplying by 4 to account for the 25% efficiency. Please award one of your answers "Best Answer". We especially appreciate this particular small recognition of our efforts to assist
2 answers · Engineering · 1 year ago
• ### How much does a rotor of a very large turbine generator weigh )ball park)?

Best answer: The largest steam driven turbogenerators are four pole 1800 rpm units used in large nuclear plants. Their rotors weigh around 200 metric tons. Large multi-pole generators for hydro-plants can be even heavier. They may need to be assembled on site. Manufacturers are GE, Siemens and possibly Mitsubishi. Formerly they were also built by... show more
Best answer: The largest steam driven turbogenerators are four pole 1800 rpm units used in large nuclear plants. Their rotors weigh around 200 metric tons. Large multi-pole generators for hydro-plants can be even heavier. They may need to be assembled on site. Manufacturers are GE, Siemens and possibly Mitsubishi. Formerly they were also built by ABB, Brown Boveri and Westinghouse but these names are now out of the business. Please award one of your answers "Best Answer". We especially appreciate this particular small recognition of our efforts to assist
6 answers · Engineering · 1 year ago
• ### Dynamics problem: In the cam-follower mechanism (shown in figure below), the slotted bar rotates with constant angular velocity w=20rad/s...?

Best answer: r = 2+0.75cos(2θ) = 2+0.75×cos(2.ω.t) = 2 + 0.75×cos(40.t) θ = ω.t = 20.t radial acceleration = a = d²r/dt² - ω².r = -0.75×40×40×cos(40.t) - 20×20×[2 + 0.75×cos(40.t)] ...... (1) At θ = π/4, t = π/80 s. Plug t= π/80 into 1 to get the answer for the radial acceleration A at θ = 45˚ = π/4.. There is conveniently no angular acceleration so... show more
Best answer: r = 2+0.75cos(2θ) = 2+0.75×cos(2.ω.t) = 2 + 0.75×cos(40.t) θ = ω.t = 20.t radial acceleration = a = d²r/dt² - ω².r = -0.75×40×40×cos(40.t) - 20×20×[2 + 0.75×cos(40.t)] ...... (1) At θ = π/4, t = π/80 s. Plug t= π/80 into 1 to get the answer for the radial acceleration A at θ = 45˚ = π/4.. There is conveniently no angular acceleration so the x and y components of acceleration at θ = π/4 are each A/(√2). I let you crunch the numbers! Please award one of your responses Best Answer. We especially value this particular small recognition of our modest efforts to assist
1 answer · Engineering · 1 year ago
• ### Can anyone help me answer this problem on position analysis?

Best answer: Where I am located it's a bit too late for me to write all this out tonight. I shall do it tomorrow. Do you award Best Answer if you get a good one? The clue is in triangle O₂ O₄ A which will have a max deflection to the left when its angle at 3 is 90 degrees and also to the right under that same condition. The said triangle is... show more
Best answer: Where I am located it's a bit too late for me to write all this out tonight. I shall do it tomorrow. Do you award Best Answer if you get a good one? The clue is in triangle O₂ O₄ A which will have a max deflection to the left when its angle at 3 is 90 degrees and also to the right under that same condition. The said triangle is then a 3, 4, 5, making the angle to the vertical at O₄ equal to arccos(4/5) and therefore the total angular range of 4 = 2.arccos(4/5) = 73.74 degrees The slider stroke is then easy. Let me know meanwhile if you still can't do it. Slider stroke is then the horizontal distance moved by B = 2.O₂B.sin[arccos(4/5)] = 4 x 0.6 = 2.4 cm. Please don't forget the Best Answer award !! Thank you.
1 answer · Engineering · 1 year ago
• ### Where will I get a time machine?

Best answer: Any watch or clock shop the choice depending upon how much importance you attach to portability. Please award one of your answers "Best Answer". We especially appreciate this particular small recognition of our efforts to assist
Best answer: Any watch or clock shop the choice depending upon how much importance you attach to portability. Please award one of your answers "Best Answer". We especially appreciate this particular small recognition of our efforts to assist
4 answers · Engineering · 1 year ago
• ### Science question:True or False?

Best answer: 1) It does not become heavier but it will stop rising because the air outside it becomes less dense. So F & T. 2) T 3) T 4) F (if you mean fluid's speed and not speed's fluid) 5) F 6) T Please award one of your answers "Best Answer". We especially appreciate this particular small recognition of our efforts to... show more
Best answer: 1) It does not become heavier but it will stop rising because the air outside it becomes less dense. So F & T. 2) T 3) T 4) F (if you mean fluid's speed and not speed's fluid) 5) F 6) T Please award one of your answers "Best Answer". We especially appreciate this particular small recognition of our efforts to assist.
1 answer · Engineering · 1 year ago
• ### Why the resistance in dc distribution system for the length of 100 meters(length of distributer) is assumed as r/2?

Best answer: If something is an assumption then it is not open to question. It is already assumed. You cannot ask "why" unless the assumption conflicts with other given conditions of which you do not provide any. All of your other answers create such a conflict by also assuming two (one go and one return) conductors in series which gives... show more
Best answer: If something is an assumption then it is not open to question. It is already assumed. You cannot ask "why" unless the assumption conflicts with other given conditions of which you do not provide any. All of your other answers create such a conflict by also assuming two (one go and one return) conductors in series which gives 2r but you do not specify that. A valid implication of your assumption may be that r = the resistance of 400 m of conductor. Please award one of your answers "Best Answer". We especially appreciate this particular small recognition of our efforts to assist.
5 answers · Engineering · 2 years ago
• ### Multivariable calculus help PLEASE?

Best answer: i = V/R Using differentiation of a quotient we obtain: di/dt = [R.dV/dt-V.dR/dt]/R² = [-2 - 1×0.01]/10⁴ = - 20.1×10⁻³ A/s Please award one of your answers "Best Answer". We especially appreciate this particular small recognition of our efforts to assist
Best answer: i = V/R Using differentiation of a quotient we obtain: di/dt = [R.dV/dt-V.dR/dt]/R² = [-2 - 1×0.01]/10⁴ = - 20.1×10⁻³ A/s Please award one of your answers "Best Answer". We especially appreciate this particular small recognition of our efforts to assist
1 answer · Engineering · 2 years ago
• ### How many cubic meters of water needs to flow, per second, over a 180 meter drop to produce 5kW of electricity?

Best answer: Weight of 1m³ of water = 9810 N. Potential energy of 1m³ at 180 m elevation = 180×9810 = 1.766 ×10⁶. Joules 5 kW = 5000 J/s Therefore m³/s required for 5 kW is V = 5000/(1.766×10⁶) = 2.83 × 10⁻³ m³/s = 2.83 litres per s. This is the theoretical amount. If you suppose an efficiency number for the set up a more realistic value might be... show more
Best answer: Weight of 1m³ of water = 9810 N. Potential energy of 1m³ at 180 m elevation = 180×9810 = 1.766 ×10⁶. Joules 5 kW = 5000 J/s Therefore m³/s required for 5 kW is V = 5000/(1.766×10⁶) = 2.83 × 10⁻³ m³/s = 2.83 litres per s. This is the theoretical amount. If you suppose an efficiency number for the set up a more realistic value might be around 4 litres per s if the 5 kW is to be in electrical form. The efficiency of hydraulic turbines is very high (>90%) but this is such a small one it might at best be around 70%, probably a bit lower. Please award one of your answers "Best Answer". We especially appreciate this particular small recognition of our efforts to assist
3 answers · Engineering · 2 years ago
• ### The value of youngs modulus for a perfectly rigid body is?

Best answer: Infinity. That's due to division by zero in the Young's modulus quotient. A perfectly rigid body would exhibit zero strain. Please award one of your answers "Best Answer". We especially appreciate this particular small recognition of our efforts to assist
Best answer: Infinity. That's due to division by zero in the Young's modulus quotient. A perfectly rigid body would exhibit zero strain. Please award one of your answers "Best Answer". We especially appreciate this particular small recognition of our efforts to assist
4 answers · Engineering · 2 years ago
• ### A hollow pipe is to be enclosed so it can be used as a storage bin. The two circular ends will be cut from a rectangular piece which has an?

Best answer: If, pursuing common sense, we choose a rectangular piece which will allow us to cut two circles of radius r with minimum wastage, then this occurs when the said rectangle piece has a length of 4r and a width of 2r. Hence : 2.r.4.r = 8.r² = 3362 giving r = √[3362/8] = 20.5 cm. giving diameter = 2.r = 41 cm. Curved surface area = 2.π.r.h... show more
Best answer: If, pursuing common sense, we choose a rectangular piece which will allow us to cut two circles of radius r with minimum wastage, then this occurs when the said rectangle piece has a length of 4r and a width of 2r. Hence : 2.r.4.r = 8.r² = 3362 giving r = √[3362/8] = 20.5 cm. giving diameter = 2.r = 41 cm. Curved surface area = 2.π.r.h = 18000 where h is the requested height. h = 18000/[π×41] = 139.75 cm. Please award one of your answers "Best Answer". We especially appreciate this particular small recognition of our efforts to assist.
2 answers · Engineering · 2 years ago
• ### What will happened if I install fan on closed strong box to pull air outside the box? does fan won't produce air flue? fan will damage?

Best answer: The fan will reduce the pressure in the box. There will be little or no air flow (because the box is closed) except due to edge effects at the hub and around the blade tips where some small amount of air can re-circulate. The fan will run but if the motor, which drives the fan, is cooled by some of the fan's (normal) air flow, then... show more
Best answer: The fan will reduce the pressure in the box. There will be little or no air flow (because the box is closed) except due to edge effects at the hub and around the blade tips where some small amount of air can re-circulate. The fan will run but if the motor, which drives the fan, is cooled by some of the fan's (normal) air flow, then it may be starved of cooling and overheat.
3 answers · Engineering · 2 years ago
• ### Is it true that engineers like girls who study law and philosophy more than women of their profession?

Best answer: Law and philosophy have no particular relevance to engineers' likings. Male and female engineers might find it comparatively a little more difficult than average to "hit it off" often because of heavy chips on some of the female shoulders, due to their minority status in that profession. The female ones seem, amongst... show more
Best answer: Law and philosophy have no particular relevance to engineers' likings. Male and female engineers might find it comparatively a little more difficult than average to "hit it off" often because of heavy chips on some of the female shoulders, due to their minority status in that profession. The female ones seem, amongst themselves, to "get along" quite well. Please award one of your answers "Best Answer". We especially appreciate this particular small recognition of our efforts to assist
6 answers · Engineering · 2 years ago
• ### How do you describe the main types of feedbacks including voltage, current, series and shunt.?

Best answer: Proportional, integral, derivative, positive and negative and the main adjectives describing various configurations of feedback. Voltage, current, series and shunt are not terms used in describing types of feedback. Feedback will increase closed loop gain if positive and reduce closed loop gain if negative. Please award one of your... show more
Best answer: Proportional, integral, derivative, positive and negative and the main adjectives describing various configurations of feedback. Voltage, current, series and shunt are not terms used in describing types of feedback. Feedback will increase closed loop gain if positive and reduce closed loop gain if negative. Please award one of your answers "Best Answer". We especially appreciate this particular small recognition of our efforts to assist
2 answers · Engineering · 2 years ago
• ### "The hoop stress is minimum at the outer surface and maximum at inner surface of a thick cylinder." Prove this statement.?

Best answer: The truth or otherwise of the statement depends on the configuration of the applied loading. It is not universally true therefore it is generally untrue unless its validity is restricted to certain defined load configurations. Please award one of your answers "Best Answer". We especially appreciate this particular small recognition of our efforts to assist
1 answer · Engineering · 2 years ago
• ### Thermodynamics?

Best answer: I hope you will award one of your responses with Best Answer. So many people just take our help and walk away without any sign of thanks. We do appreciate this small token of thanks. Anyway, to your problem: 1. Surely the convection coefficient should be 10 W/(m².K). Assuming this is so, I proceed: 2. Where d is the required... show more
Best answer: I hope you will award one of your responses with Best Answer. So many people just take our help and walk away without any sign of thanks. We do appreciate this small token of thanks. Anyway, to your problem: 1. Surely the convection coefficient should be 10 W/(m².K). Assuming this is so, I proceed: 2. Where d is the required thickness: Considering the whole "sandwich": Energy flow rate per m² = Q = (300-60)/[0.08/d + (60-30)×10] Considering only the insulation: Q = (60-30).d/0.08 Thus we may write: 240/[0.08/d + 300] = 375×d Multiply both sides by d to get: 240 = 375×(0.08+300d)×d Solving the quadratic 300d² + 0.08d -0.64 = 0 we obtain d = 0.04605 m. (the other root being negative and therefore irrelevant). By the way, this is simple heat transfer and not thermodynamics.
1 answer · Engineering · 2 years ago
• ### The equivalent power consumption in series and parallel ? ?

Best answer: If, in each connection case, P1, P2 and P3 represent the respective power consumptions in elements 1, 2 and 3 then in both cases the sum is simply P1+P2+P3, independent of their connection. Please award one of your answers "Best Answer". We especially appreciate this particular small recognition of our efforts to assist show more
Best answer: If, in each connection case, P1, P2 and P3 represent the respective power consumptions in elements 1, 2 and 3 then in both cases the sum is simply P1+P2+P3, independent of their connection. Please award one of your answers "Best Answer". We especially appreciate this particular small recognition of our efforts to assist
1 answer · Engineering · 2 years ago
• ### Applications of second order ODE's in real world?

Best answer: They are a step on the way to more exciting topics, although what it may take for you not to be bored is something I cannot estimate. 1+1 = 2 is also boring as time goes by but you do need to know the basics. Try fluid flow problems, electric field, heat flow or vibration problems, eg using Bessel functions. And take them into... show more
Best answer: They are a step on the way to more exciting topics, although what it may take for you not to be bored is something I cannot estimate. 1+1 = 2 is also boring as time goes by but you do need to know the basics. Try fluid flow problems, electric field, heat flow or vibration problems, eg using Bessel functions. And take them into multi-dimensional transient analysis if you need even more spice! I've always had difficulty to understand that some people find engineering boring. I acknowledge it might be thought negative for its environmental effects but boring? I just can't see it! Please award one of your answers "Best Answer". We especially appreciate this particular small recognition of our efforts to assist.
1 answer · Engineering · 2 years ago