# What is Energy balance: Definition and 68 Discussions

In biology, energy homeostasis, or the homeostatic control of energy balance, is a biological process that involves the coordinated homeostatic regulation of food intake (energy inflow) and energy expenditure (energy outflow). The human brain, particularly the hypothalamus, plays a central role in regulating energy homeostasis and generating the sense of hunger by integrating a number of biochemical signals that transmit information about energy balance. Fifty percent of the energy from glucose metabolism is immediately converted to heat.Energy homeostasis is an important aspect of bioenergetics.

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1. ### A Is it possible to obtain excess energy from a Townsend discharge?

Let us assume a continuous flow of gas that can be ionized between the electrodes where an electric discharge is generated. According to the principle of conservation of energy, energy cannot be created or destroyed, but it can be transformed from one form to another with losses, e.g. in the...
2. ### Derivation of McCabe - Thiele Method

McCabe - Thiele method is used to find minimum number of separation stages or theoretical plates for a given efficiency of separation in distillation for two - component mixture if components have similar enthalpy of vaporization. If components have similar enthalpy of vaporization ,than on...
3. ### Invariant mass and energy balance

a) Two particles have energies E1 and E2, and momenta p1 and p2. Write down an expression for the invariant mass of this two-particle system. Leave your answer in terms of E1 and E2, and p1 and p2. b) A typical photon (γ) in the Cosmic Microwave Background (CMB) has an energy of kBTCMB, where...
4. ### Engineering Spring Deformation: Potential Energy Balance Incorrect?

In the initial position the spring is previously compressed, then the block adds a force, and the spring is again deformed. I think the energy balance is incorrect; the potential energy of the spring is repeated.
5. ### Solving for λ, a, and Vmax: An Analysis of Energy Balance and SHM

a) λ = 4/3 by considering the energy balance as P moves from A (2a) to B (1/2a). The E.E. at A changes into a gain in gravitational potential energy + build up of E.E. at B since the spring compresses. b) a = 5/3g by considering that the mass P is in dynamic equilibrium immediately after...
6. ### Thermodynamics energy balance for control volume

Why is energy balance for a control volume dE/dt = dQ/dt-dW/dt-dm/dt(ΔH+ΔKE+ΔPE) 0 = dQ/dt-dW/dt-dm/dt(ΔH+ΔKE+ΔPE) whereas for other systems it is ΔE =Q-W-(ΔU+ΔKE+ΔPE) 0 = Q-W-(ΔU+ΔKE+ΔPE) with enthalpy, h = u +pv, replaced by only the internal energy? How is the pv term accounted for...
7. ### Determining speed at an angle using an energy balance

I first found the height of the ball after it's passed the 45 degree angle by doing 4.12*sin(45) = 2.9133, and plugged in the rest of the variables (masses cancel) .5(m)(vo^2) = (.5)(m)(vf^2) + mgh (17.5^2)(.5) = (.5)(vf^2)(9.8*2.9133) vf = 15.7845, however this is incorrect I don't understand...
8. ### Am I missing out by not writing the energy balance?

Attempt: No clue what equations to use from here.

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### Atmospheric energy balance

Homework Statement Use the data in the energy balance diagram for the Earth shown below to determine numerical values for α, a and e. Assess your results by comparing them to the commonly used approximations α = 0.3, a = 0 and e = 1. Show your calculations. Homework Equations Look at the the...
14. H

### Transient Energy Balance for Heating a Tank of Water

Homework Statement In an industrial process, a tank containing 200 liters of water must be heated from a temperature of 293 K to 372 K at a constant pressure. There is a negligible change in the volume of the water. The water is stirred during this process to maintain a uniformly distributed...
15. ### I Why is first TD law different for chemical reactors

I've learned that first thermodynamic law for some open system is in the form of: where total change of system energy ##\frac{\partial E}{\partial \tau }## is equal to the transferred heat and work. Total change of system energy ##\frac{\partial E}{\partial \tau }## is equal to the energy...
16. D

### E-Balance for Jet Ejector

I am working on problem that has to deal with a jet ejector. For the life of me, I cannot figure out the E-Balance equation for it. Below is a cut away image of the ejector. The fluid is the same so using the ideal gas law I do not think should be included. Any help is greatly appreciated...
17. ### Thermodynamics Power Cycle Energy Balance

Homework Statement As shown in Fig. P5.39, a system undergoing a power cycle develops a net power output of 1 MW while receiving energy by heat transfer from steam condensing from saturated vapor to saturated liquid at a pressure of 100 kPa. Energy is discharged from the cycle by heat transfer...
18. ### Thermodynamics energy balance

Question A mass of 1.5 kg of air at 120 kPa and 24 C is contained in a piston-cylinder device. The air is compressed to a final pressure of 600 kPa. During the process heat is transferred from the air such that the temperature inside the cylinder remains constant. Calculate the work input...
19. ### Modeling a multiple inlet piping system

Hello, PF! I’m trying to model a real piping system, which has multiple inlets and one outlet, so I can’t use Bernoulli’s equation. Instead, I’m planning to use the generalized macroscopic energy balances as shown in BSL, which allow for any number of inlets and outlets. However, first I want...
20. ### Temperature change (first law of thermodynamics)

Hi, From the first law of thermodynamics it follows: Cp * (δT/δt) = (δQ/δt) where Cp = specific heat capacity, T = temperature, Q = heat, t = time From this formula, you would derive that temperature keeps on increasing as long as dQ/dt > 0. But if you, for example, look at the idealized...
21. ### A Oscillating Plane and Z axis - Energy Balance

Hello, I have a few questions regarding the osculating plane, which I understand to be the plane generated by the Principal unit tangent vector and principal unit normal vector (both are orthogonal), and the inertial Cartesian z-axis. Ultimately, I plan to understand the geometric/kinematic...
22. ### Potential energy in a Mass spring system

Why is the rate of change of potential energy always same the rate of change of kinetic energy in a mass spring system? Additiinally, How do we determine the rate of change of potential energy in such case?
23. ### Thermodynamics Energy balance equation for Non - Steady Flow

Hi, I am currently studying Thermodynamics and stumbled upon this equation and is slightly confused as to how this works. Hopefully someone can help me with the understanding. According to this text here, if I am not wrong e can be h + ke + pe or u + ke + pe depending on where i am looking...
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### Heat Equation and Energy Balance

Hi PF! For the longest time I thought an energy balance and the heat equation were identical procedures. However, recently I saw an example of a steady state, constant property, laminar flow of fluid between two flat surfaces where the top surface moves in the ##x## direction at ##V_1## and we...
25. ### Earth's Energy balance including a convective component

Hey guys, I'm really stuck right now 1. Homework Statement Habitable exoplanet: Now we will include a convective heat flux (H), with H being proportional to the difference between the atmospheric and ground surface temperature, $$H=c_p(T_a-T_p)$$ with c = 1.2 Wm−2K−1. Calculate the temperature...
26. ### Use of Entropy for a Control Volume in Energy Balance

Hi all, I'm having some trouble figuring out why entropy is used instead of enthalpy for an open system. From what I understand, an open system uses entropy to calculate internal energy. Since the control volume is constant (i.e. Δv = 0), wouldn't using : h = u + PΔv effectively be h = u? So...
27. ### Heat transfer -- one-dimensional energy balance for the heating of a fluid....

Homework Statement Perform a one-dimensional energy balance for the heating of a fluid through a hot pipe in order to develop a differential equation that governs the variation of the mean temperature of the fluid along the length pipe. The pipe has an inner diameter D and length L; its walls...
28. ### Energy Balance for closed rigid container

Homework Statement Water, initially saturated vapor at 4 bar, fills a closed, rigid container, The water is heated until its temperature is 400C. For the water, determine the heat transfer in KJ per kg of water . Homework EquationsThe Attempt at a Solution Assume potential and kinetic...
29. ### Solving the Energy Balance Problem

Hello, I was reading an article, and I found something unfamiliar(sorry I am not into heat transfer a lot) : For the energy balance of the fluid, I didn't understand the mCpθ where θ is the temperature and mCp(θ+dθ/dx θ) terms. I know that for a control volume, the energy balance for...
30. ### Calc ∆Ho & ∆Eo for CH3OH Reaction @ 298K

Homework Statement For the reaction CH3OH(l) → CH4 (g)+ 1/2 O2 (g)[/B] (a) Calculate ∆Ho298 (b) Calculate ∆Eo298 (c) Write an equation that would allow you to determine ∆H at 500°C and 1atm Homework Equations ∆H=∆E+∆(PV) ∆H=Σ∆Hproducts-Σ∆Hreactants The Attempt at a Solution a)...
31. ### Non-dimensionalization of the energy balance

Good evening people of PF! I have recently encountered a problem from Himmelblau's Basic Principles and Calculations in Chem. E. which asks to set up an energy balance for a tank, and then non-dimensionalize the differential equation before solving it. It's not the most complex task, but it's...
32. ### Classical mechanics - Energy balance confussion

Hi everyone. I'm confused with the balance of energy in this situation (I'm comparing the mechanical energy, initially, at rest, at a height = h, and then, at the end, at height = 0). It doesn't seem to be fine, maybe I missed something. I'd appreciate some help - Everything is in the .jpg...
33. ### Kinetic Energy - use a log scale or not?

Homework Statement Lets say we have a series of balls and an eggs. All items have equal mass but are traveling at different velocities. Thus they have differing kinetic energies. Now, for each 'ball' object we have, we want to find an egg object with a similar kinetic energy. Let's say...
34. ### Transient state energy balance -- Variable volume system

Hello PF! I have some questions regarding the accumulation term for the energy balance on a variable volume system. Suppose we have a tank storing a liquid substance. The tank has a moving boundary at the top, which can expand unlimitedly. The system has a mass input \dot{m}_1 and mass output...
35. ### Energy balance on metallurgical furnace

Homework Statement Pure iron sulfide (FeS2) is fed into an Herreshoff furnace at 25 °C. An 83% of excess air is also fed into the furnace at 25 °C. The solid product consists only of Fe2O3. The solid product reaches a temperature of 1832 °C, and the exhaust gases (8.7% SO2, 9.8% O2, 81.5% N2)...
36. ### Motion, Energy balance, momentum question

Homework Statement A block of mass m= 10kg rests on a horizontal table. The coefficient of friction between the block and the table is 0.05. When hit by a bullet of mass 50 g moving with speed v, that gets embedded in it, the block moves and comes to stop after moving a distance of 2m on the...
37. ### Thermo - Simple Energy balance equation

The General Energy balance equation is: ∑ENin - ∑ENout + Egen = Est (in rate form - don't know how to put the dot above) I know that Est is 0 when the system operates at Steady State Steady Flow (SSSF). I have 2 formulas for ΔE in "Q-W = ΔE" 1) ΔE = ΔU + ΔKE + ΔPE 2) ΔE = m[h2 - h1...
38. ### Energy balance -- Physical interpretation of Q

Hello PF! I have a simple question on energy balances. Suppose you have an isothermal reactor where you want to have an exothermic reaction happening at 450 °C. The simplified energy balance for the reactor is Q = ΔH. Supposing ΔH = -150 kcal, then Q = -150 kcal. Does this mean that, a) in order...
39. ### Energy Balance of Beta+ Decay of $^{22}_{11}Na$

Homework Statement If we have a beta + deca: $$^{22}_{11}Na(3^+)\rightarrow ^{22}_{10}Ne(2^+)+ e^+ +\nu$$ with $t_{1/2}=2.6 years$, what is the energy balance at this decay, if you know that $^{22}_{10}Ne(2^+)$ is an excited state of $^{22}_{10}Ne$ with $1.25 MeV$ larger energy. Homework...
40. ### Energy conservation in Special Relativity

Homework Statement A train is traveling in the x direction at a speed of v. On the train, a passenger is playing darts and fires a dart in the y direction with a speed of Uy. The dart hits the target and stops abruptly. What is the difference in the mass of the dart as observed by a person on...
41. ### Thermodynamics problem - Compressing the air. Energy Balance

MODERATOR NOTE: THIS THREAD WAS ORIGINALLY POSTED SOMEWHERE ELSE, SO THERE IS NO TEMPLATE. Dear! I have a problem with one, complex exercise. I’ve divided it into three parts just to simplify finding the answer. So let’s start. The air is sucked from the atmosphere by a compressor. Atmospheric...
42. ### Energy and momentum in a car accident

Two identical cars collide with equal and opposite velocity to each other. What happens to the energy? What happens to the momentum? Answer: energy is converted into heat and momentum disappears. But what has that to do with force?
43. ### Enthelpy balance equation

Hello PF! I have a very short question. We're currently doing enthalpy balances for chemical reactions in our Thermo class. We are using the simple enthalpy balance equation: \Delta H_{\textrm{Reaction}}^0 = \sum \Delta H_{\textrm{Products}}^0 - \sum \Delta H_{\textrm{Reactants}}^0 My question...
44. ### Steady Flow Energy Equation basics

Right, I'm sure this is bread and butter to a lot of you but I have just been introduced to the SFEE. mgz+0.5mC^2+H +Q = mgz + 0.5mC^2 +H+W Where Q is the heat transfer, W is work done and H is enthalpy. Where is it assumed that the heat energy is in the energy balance? If heat is added where...
45. ### Energy Balance Spring Slider system

I am currently looking facing a problem concerning a spring slider system. The system consists of a electro engine that pulls on a spring with a constant velocity. The spring is attached to a block that sticks to the surface, but after a certain force is applied (by the spring) starts to slip...
46. ### Energy Balance of Isothermal Energy Storage Tank

Homework Statement Using unsteady state energy balances, discuss why storing cold water will be better in a larger tank rather than a smaller one. Assume the initial state where the tank is full. The Attempt at a Solution I've tried to make this an algebraic exercise where I created...
47. ### Concentric Tube Heat Exchanger - Clarification on Energy Balance

I'm trying to model a Transfer function for the response of the deviation in temperature of water coming out of the concentric tube heat exchanger in response to an input velocity of water function. THE PROBLEM I start the derivation with a couple equations in Seborg's Process Dynamics...
48. ### Thermodynamics Closed System Energy Balance

Hi everyone, I am currently reviewing for a thermodynamics exam and have come across a difficult problem while studying. Here it is: An insulated tank containing helium, a monatomic gas, at P1t = 1000kPa and T1 = 800K is connected to an initially evacuated insulated piston-cylinder device...
49. ### Pre big bang energy balance

Several articles I've read describing one theory of how everything could have started from nothing. State that all the energy of nothing equals zero as gravity is negative energy. One of those articles was written by Stephen Hawkings. He also stated that quantum fluctations will always exist...
50. ### Finding the energy balance of a hydroelectric power generator

finding the "energy balance" of a hydroelectric power generator I proposed a new hydroelectric energy idea to somebody and they asked me for a "energy balance". I know nothing about physics or anything relevant to calculating something like this. If somebody asked you for the energy balance of...