What is Mass balance: Definition and 35 Discussions

A mass balance, also called a material balance, is an application of conservation of mass to the analysis of physical systems. By accounting for material entering and leaving a system, mass flows can be identified which might have been unknown, or difficult to measure without this technique. The exact conservation law used in the analysis of the system depends on the context of the problem, but all revolve around mass conservation, i.e., that matter cannot disappear or be created spontaneously.Therefore, mass balances are used widely in engineering and environmental analyses. For example, mass balance theory is used to design chemical reactors, to analyse alternative processes to produce chemicals, as well as to model pollution dispersion and other processes of physical systems. Closely related and complementary analysis techniques include the population balance, energy balance and the somewhat more complex entropy balance. These techniques are required for thorough design and analysis of systems such as the refrigeration cycle.
In environmental monitoring the term budget calculations is used to describe mass balance equations where they are used to evaluate the monitoring data (comparing input and output, etc.). In biology the dynamic energy budget theory for metabolic organisation makes explicit use of mass and energy balance.

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  1. N

    Convert moment force at lever support

    I am trying to determine if a clamp holding a lever with a mass at one end can experience zero or reduced torque either by balancing the forces or converting the rotational torque into another form such as linear, I’ve looked at counterbalance with Steadicams etc. but I believe this just...
  2. Dario56

    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. Tapias5000

    How to solve this balancing exercise? (towing a boat with two ropes)

    This is the image of the problem I tried to solve it and I got the following is it correct?
  4. George26

    Conservation of mass: control volume approach question

    Summary:: Control volume question that has a brine solution entering a tank and mass accumulates over time. Hello, I'm currently struggling with a control volume approach question that has a brine solution entering a tank. I get to a point where I have a first order differential equation. I...
  5. R

    Mass Balance Approach for a 2-Stage Distillation Problem

    Homework Statement 180kmol/hr of a three component mixture made up of 60 mol % A, 25 mol % B and 15 mol %. Component A is the most volatile ,component C is the least volatile. The mixture is to be passed through a 2 stage distillation process. 80% of component C leaves the bottom of the first...
  6. A

    What Does Capital V Represent in Mass Balance Equations?

    Please tell me what capital V and v mean in this equation. And how can we derive the second equation from the first one.
  7. J

    Filling and emptying a barrel -- Bernoulli

    << Mentor Note -- thread moved from the schoolwork forums to ME for better views >> 1. Homework Statement Not really homework as this is for work. We are washing a cylindrical container (15.5 cm) with only one (1.8" dia) hole at the bottom the rest is sealed. Our machine sticks a .5" pipe with...
  8. W

    Mole balance issue with volume division

    Homework Statement Here we divide the mole balance by the volume ##4*\pi## ##*## r2##*##dr and take lim as dr->0(standard procedure) 1) How exactly he makes the transition from equation from 6 to 7? Exercise #2(see below please) Solution for Problem#2 2)Why does he divide here by...
  9. M

    Calculate Moles of Acetylene & O2 in C2H2+O2 Reaction at 60C, 10mmHg

    Acetylene (C2H2) is reacted with excess O2 in a container. After complete reaction, the volume of the gaseous mixture of the combustion products is 300ft3 at 60C and 10mmHg gauge pressure. P(atm) is 735mmHg. The relative humidity if the product gas is 100% with no condensed water present...
  10. mudweez0009

    Tank Mass Balance Calculation for Designing w/ Automatic Float Switch

    I'll be using a mass balance calc for a tank design at work. We are designing a tank that has an automatic float switch on it, attached to a valve which will start filling the tank when the water level drops below a certain point. This tank is intended to drain quickly (flow rate not known at...
  11. MexChemE

    How do I model mass transfer in a tubular reactor?

    Good evening, PF! I am supposed to model the following system. I will be using the same notation as in BSL. Fluid A enters the reaction zone at z = 0 at a concentration CA0. A reacts to form B in the first order reaction A → B at a rate of R_A = k_1''' C_A. We assume the whole mixture to be...
  12. M

    How to calculate mass of air in mass balance?

    What is the general procedure for calculating the mass of air in mass balance problems? what assumptions must be made? How do i convert this into mass from a percentage, e.g 21% oxygen & 79% nitrogen?
  13. MexChemE

    Mass balance with reaction -- Chemical kinetics POV

    Good evening, people of PF. Recently, while studying chemical kinetics, I have come across some questions about reaction rates and rate equations. I've noticed some inconsistencies between the chemical kinetics point of view, and the approach taken by chemical reaction engineering and reactor...
  14. MexChemE

    Unsteady state mass balance -- Draining of a tank

    Homework Statement A cylindrical tank, with a diameter Db, open to the atmosphere, is drained through an orifice in the bottom of the tank with a diameter Do. The speed of the fluid flowing through the orifice is given by v = \sqrt{2gh}, where h is the height of the liquid measured from the...
  15. MexChemE

    Pyrite roasting -- Mass balance with chemical reaction

    Homework Statement A certain pyrite ore contains 85% of FeS2 and 15% of inerts. This ore is introduced into a roasting furnace with 20% excess air, in order to oxidize the FeS2 in the reaction: \textrm{FeS}_2 + \frac{11}{4}\textrm{O}_2 \rightarrow \frac{1}{2}\textrm{Fe}_2 \textrm{O}_3 +...
  16. gfd43tg

    Mass balance for diffusion and analogy to heat conduction

    Hello, I just began learning mass transfer, and I am trying to use analogies from heat transfer to help me solve problems. For example, if you have one dimensional heat transfer through a plane wall, I would start with a general energy balance. $$\frac {dE}{dt} = \dot Q_{x} - \dot Q_{x + \Delta...
  17. M

    Mass balance on oxidation of ammonia for production of nitric acid

    Homework Statement The following chemical reaction takes place inside a reactor where 80% conversion is obtained with an equimolar mixture of NH3 and O2 fed at the flow rate of 100 mol/h. 4NH3 + 5O2 ⇔ 4NO + 6H2O What are the output rates of all species? There's a diagram shown where...
  18. M

    Steady State mass balance for separation of cyclopentadiene

    Hello, Here is a homework problem that I have been working on. I am wondering if for the mass balance of substance A, do I include the terms in the reaction rate that involve species R and B? Also, wouldn't A and B start reacting in the pipe before they even go into the CSTR? (I guess put in...
  19. W

    Equilibrium, Charge Balance, Mass Balance

    Homework Statement Write the charge balance for a solution containing H(+), OH(-), Ca^(2+). HCO3(-). CO3^(2-) , Ca(HCO3)+, Ca(OH)+, K+, and CIO4(-).Homework Equations Also, I am having a trouble understanding the concepts of mass balance and charge balance. The Attempt at a Solution The...
  20. C

    Beta plus decay: mass balance?

    Hi: I am taking a radiochemistry class, and I am confused by beta plus decay. (1) p --> n + positron + electron-neutrino The mass of a proton is less than the mass of a neutron. In addition, the neutrino has mass as does the positron. (2) E = mc2 There must be come sort of...
  21. T

    How Much Hydrogen Can Be Produced From Biomass?

    The Problem: Bio fuels are receiving more and more attention. For biomass waste materials (cellulose, manure etc.), the first step in the process is typically to convert the biomass to sugar (glucose, C6H12O6). This first step is only able to produce 0.1 g glucose per g of biomass. The...
  22. C

    Momentum and mass balance in fluid mechanics

    When I am reading the paper in fluid mechanics, I found a paragraph and two equations: "Since the fluid is considered Newtonian and incompress- ible of density ρ and constant viscosity μ, the dimensionless mass and momentum balance equations are:" \nabla \cdot \mathbf{v} = 0...
  23. W

    How Do You Calculate the Bottoms Ethanol Fraction in Distillation?

    Haven't taken a course in distillation in a long time and now myself and some others are working on getting a fuel ethanol still going and wanted to do the calculations before we moved forward. We have a beer that is 12% alcohol and reaching a purity of 90% EtOH in the distillate. The mass...
  24. I

    Mass Balance and Enviromental Reactor

    Homework Statement 1) A spill of 5kg of a soluble pesticide takes place into a well-mixed pond. The pesticide is subject to volatilization that can be characterized by the first order flux J=VvC, where Vv = volatilization mass-transfer coefficient of 0.01m/d. Other parameters for the pond...
  25. B

    Help with transient mass balance for desalination by destillation

    Homework Statement Homework Equations ordinary mass balance The Attempt at a Solution So far I have gotten: d[rhob*V]/dt = Min - ?
  26. L

    Process engineering mass balance in the douglas aproach

    Hey guys i was hoping for some help with the mass balance of the equations for the production of styrene from ethylbenzene. I have attached my problem sheet and my answer sheet, q 7 is what i am stuck on please help me i am confused
  27. S

    Euler's Method With Mass Balance o.d.e's

    Hi I'm doing a practice paper for a past mathematical modelling exam. I've attached the problem What I'm having trouble with is simplifying the equations and variables into a differential equation that is solvable with Euler's Method. What I have currently is the sqrt(h1-h2) in the...
  28. G

    Chemical Engineering Mass Balance with matrix

    Homework Statement Ethane reacts with chlorine to make ethyl chloride and hydrogen chloride, and ethylene reacts with hydrogen chloride to form ethyl chloride. C2h6+ Cl2 > C2H5Cl + HCL C2H4 + HCl > C2H5Cl I post an image of flow chart and rest of description Based on my reading...
  29. B

    How Much Chemical Solution Is Needed for Proper Dosing in Water Treatment?

    Hello everybody.. I have aquestion and hope to get help..please bear with me and try to finish reading my question.. Thank u very much for your time. My question is I have a pilot plant filter.. and i need to add some chemicals to the raw water before entering the filter..say for...
  30. D

    How to Solve a Mass Balance Problem for Homework

    Homework Statement A tank used to prepare 10% salt solution was shut down for the day. The next day, you were told that the effluent concentration should be 5 wt %. The tank volume is 1000 m^3, and it is completely filled with 10% solution. You decide to run pure water and remove the...
  31. D

    How Long to Dilute a 10% Salt Solution to 5% in a 1000 m³ Tank?

    Mass Balance Question - Please HELP! Homework Statement A tank used to prepare 10% salt solution was shut down for the day. The next day, you were told that the effluent concentration should be 5 wt %. The tank volume is 1000 m^3, and it is completely filled with 10% solution. You decide to...
  32. J

    Need help with a unsteady state mass balance problem

    if anybody can help, the problem is finding out the amount of time it takes to drain a 12oz soda can through the shotgun method. this method of draining involves opening the tab on top of the can and then punching a hole at the bottom to drain the soda out.the velocity out obviously changes as...
  33. C

    Mass Balance & Waste generation

    Hello everyone! So I'm working on constructing a simple mass balance for a cake. I didn't have any problems doing that, but I was asked about waste that is generated in the process of making the cake. Is there really a waste generated in this kind of process? I've also been asked to...
  34. K

    Static Mass Balancing: Procedure for Assemblies of 2.5-10kg

    What is the procedure of static Mass Balancing of any assembly which has a total mass of 100 kg with subsystems which would assemble in it is ranging from 2.5 to 10 kg ... i think to hang the complete system freely in air and then checking the placement of exact cenetr is an appropriate method...