Wet wood chips are dried in a continous rotary dryer that

Question

Problem 8.75

Wet wood chips are dried in a continous rotary dryer that operates at atmospheric pressure. The chips enter at 19C with a water content of 40 wt% and must leave with a moisture content of less than 15%. Hot air is fed to the dryer at a rate of 11.6 m3 (STP)/kg wet chips. To monitor the performance of the dryer by sampling the exiting chips and determining their moisture content directly would be a cumbersome procedure and almost impossible to automate. Instead. wet- and dry-bulb thermometers are mounted in both the inlet and outlet air lines. and the moisture content of the exiting chips is determined by a material balance. Moist air Wet chips. 19C 40 wt% H20 DRYER Air. 11.6 m3(STP)/kg wet chips Chips + reSidual mOisture ---- Encyclopedia Equipment humidifier Encyclopedia Equipment dryer After the unit goes on-stream, the inlet dry-bulb temperature is found to be 100C, and the wet-bulb temperature is low enough so that the moisture content of the air may be neglected. The dry-bulb temperature of the exiting air is found to be 38C, and the wet-bulb temperature is 29e. (a) Use the psychrometric chart to calculate the absolute humidity (kg H20/kg dry air) and specific enthalpy (kJ/kg dry air) of the outlet air stream. Then calculate the mass of water in the exiting air per kilogram of wet chips fed, assuming dry air has a molecular weight of 29.0. (b) Calculate the moisture content of the emerging chips and determine whether the design specification of less than 15% H2 0 has been achieved. (c) Ifthe unit is operating adiabatically and the heat capacity of the dry chips is 2.10 kJ/(kg'C), what is the exit temperature of the chips? (In estimating the specific enthalpy of the entering air, recall that the reference temperature for dry air used in constructing the psychrometric chart of Figure 8A-l is Oe.)

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Social Psychology: Chapter 12  How we behave around other people  How we think about/relate to influence one another o Someone present or watching (could be physical or implied presence)  Social Influence o Several different forms o Hitler, Stalin, David Koresh  One person’s impact can have an impact on people o Social norms  Face forward in elevator  Wait in lines  Certain places where you should smoke o Persuasion  Attitudes or beliefs influenced by another person’s communication  Systematic  Appeal to reason  Reasons why best presidential candidate / lay out facts  Heuristic  Appeal to emotion o Conformity  Tendency to what others do just because they are doing it  Why we conform  Normative influence (social norms) o Want to fit it, want others approval  Informative influence o Not sure how to act; look to others to see what to do  Asch’s study of Conformity o Conformity surprisingly high given:  Unambiguous  Strangers  Low stakes for being wrong o 24% participants never conformed  Personality characteristics/ factors  Desire for consistency o Changed either attitudes/beliefs or behavior o Foot in the Door Technique  Agree to small action; comply later with larger one  Safe driver study  17% consented to large, poorly lettered “Drive Carefully” sign  Almost 100% consented to 3-inch “Be a safe driver” sign  76% consented to the large sign  Cognitive Dissonance o Behaviors influence attitudes/beliefs o Cognitive Dissonance Theory  Festinger  Inconsistency leads to discomfort, change in attitude  Menial Task o Group 1 and 2  Tell others it’s fun o Group 1 gets $1 and group 2 gets $20  Which says it’s more enjoyable o Group 1  If unable to justify attitude change how they feel about the task o Obedience  Form of compliance  People follow direct commands, usually authority figure  Milgram Experiment  Test how people are really that evil (WWII and Holocaust time period)  Completely unethical so can’t be used today  26/40 (65%) completed the experiment  Factors that affect obedience o Yale vs. office building (48%) o Multiple “teachers”  Accomplices accepted orders (65%)  Accomplices defied orders (10%)  Group Behavior: 2 extremes  Diffusion of Responsibility o If alone, responsibility is yours, if others present, divided o Smoke filled room  Informational influence o Helping Behavior  People are less likely to help when in a group than when alone  75% help if alone  53% help in a group  Deindividuation o Large groups may increase impulsive, uninhibited behaviors o Less aware of individual values (take on values of the group)  Ex: Riots o Altruism  Behavior that helps other person  Unique to humans  Reciprocal altruism  Expect something in return (seen in animals) o Cooperation  Behavior that leads to mutual benefit  Studied quite a bit  Prisoner’s dilemma (game)  At first both remain silent, eventually one will confess (b/c people are thinking only of themselves  Tit-for-tat (iterative game)  Also one with forgiveness  Watch out for cheaters  Ultimatum game  2 people  offer and accept

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