LAB REPORT

Lab Report



Lab Report

Coolant heat load FRom steam power plants and process industries is transferred to ambient air in crossflow evaporative water cooling tower with multi-cell arrangement. Every cell consists of two identical sections, called here as cell halves. A number of cells are used operating in parallel and are situated in a row along the length side. Each cell half has a packing/fill for increasing the surface area of interaction between water and air, as well as, their residence time inside it. Fills are either of film or splash type, and are generally made from redwood or special plastics in different shapes. Double-flow designs are also available where each cell half independently has its own fan.

In general, the upgradation of a cell half will include water distribution system rectification, fill cleaning/repair, fan modification/troubleshooting and finally replacement of the existing fill by a new package. Further, with the availability of fill characteristic for individual cell halves, there exists a way for deriving better performance from the total system with or without partial upgradation. The normal style of supplying hot water at equal rate to all the cell halves results into a relatively high value of cooled water temperature exiting from the tower system than what may actually be feasible. It is possible to obtain cooled water at a temperature lower than the one mentioned just now through selective distribution of hot water by allowing larger portions of it to pass through such cell halves which have higher values of FC at any given FR.

Therefore, in order to accomplish economic upgradation and/or optimal use of an existing cooling tower system at a given time, it is essential to establish prevailing relationship between FC and FR through experiment and analysis for each cell half.

The conventional evaluation of FC for a particular cell half would require measurement of different sets of values for entry hot water temperature (twi), ambient air wet bulb temperature (WBT), mass flow rate of air (G'), mass flow rate of water (L'), and average exit cooled water temperature (two,avg). Measuring G' and two,avg for each cell half during multi-cell operation is not only complex and difficult, but it also needs a rather long time to complete the data set thus making FC deination away from its real value as all the required parameters cannot be held constant for the total time period.

Prasad has shown that while evaluating FC for a tower , air flow rate and water flow rate measurements can be replaced by that of a single additional temperature, the minimum exit water temperature occurring at fill bottom outer end (two,min). Nevertheless, recording of two,avg is a must in this case and cannot be dispensed with.

In a later work, Prasad has presented a scheme which deines FC for each cell half more efficiently by eliminating both the complicated measurements of G' and two,avg; and also of L'. Instead, it uses easily and quickly recorded two,min and two,max (the maximum exit water temperature occurring at fill bottom inner ...