Food-Processing-Plant-Design-layout

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Food Processing Plant Design & layoutQueuing theory provides a large number of alternative mathematical models for describingand solving waiting line problems.The economic balance between the cost of service and the cost associated with waiting canbe achieved at either by:1. providing more facilities at additional cost, or2. replacing less efficient service facilities by more efficient ones, or3. changing the pattern of arrival of customers for service, or4. changing the pattern of providing service, or5. effecting method improvements to reduce service time.Queuing problems can be solved basically either by mathematical or simulationapproaches.14.5.1 Elements of queuing systemThe basic queuing process (Queuing model) consists of:a) Input Sourceb) Queuec) Service discipline & mechanismThe 'Customers' requiring service are generated over time by an "input source". Thesecustomers enter the queuing system and join the queue. At certain times a member of thequeue is selected for service by some rule known as service discipline. The required serviceis then performed by the service mechanism, after which the customer leaves the queuingsystem.The various elements of the queuing system are: Input source (population), Waiting line(queue), Service discipline, Service mechanism, System output and Customer behaviour.14.5.1.1. Input sourceTwo important characteristics of the input source are: (i) its size and (ii) the pattern ofarrival.94 www.AgriMoon.com
Food Processing Plant Design & layoutThe size is the total number of customers that might require service from time to time. Thesize of the input source is generally assumed to be infinite. The railway reservation system,tax / toll both on highway etc. are the example of infinite queue.The arrival of the customers may be either at a constant rate or at random. Most arrivals ina service system are at random. This is when each arrival is independent of its previousarrivals. The exact prediction of any arrival in random system is not possible. Therefore, thenumber of arrivals per unit time (rate of arrival) is estimated by Poisson distribution.14.5.1.2. QueueA queue is characterized by the maximum permissible number of customers that itcontains. Units requiring service enter the system and join a queue. In some service systemsonly a limited number of customers are allowed in the system and new arrivals are notallowed to join the system unless the number becomes less than the limiting value.The important characteristics required to study the waiting line are:(i) Waiting time: It is the time that a customer spends in the queue before being taken upfor service.(ii) Service time: It is the time period between two successive services. It may be eitherconstant or variable.(iii) Waiting time in the system: It implies the time spent by the customer in the queuesystem. Waiting time in the system = Waiting time + Service time(iv) Queue length: It implies the number of customers waiting in the queue.(v) System length: System length is equal to the number of customers in the queue plusthose being served.14.5.1.3. Service discipline and mechanismService discipline refers to the order in which the customers waiting in queue are selectedfor service. It may be first-come-first-served, random or according to some priorityprocedure. The rules governing order of service may be.(i) FIFO. First-In-First-Out. (i.e., first-come-first-served): According to FIFO, the customersare served in the order of their arrival. Examples are bank counters, railway reservationcounters etc.(ii) LIFO. Last-In-First-Out. According to LIFO, the items arriving last are taken out first.Example, in big godowns/warehouses, the items arrived last are taken out first.(iii) SIRO. Service-In-Random-Order. (or Random and priority) Sometimes, certaincustomers are given priority for service i.e., the arriving customer is chosen for serviceahead of some other customers already in the queue. Example: Serious patients are givenpriority for treatment, vital machines are attended to first in the case of their breakdowns,important orders are given priority in production scheduling.First-come-first-served (FIFO) is usually implicitly assumed by queuing models unlessotherwise stated.95 www.AgriMoon.com
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