lab report hari isnin hantar

SUMMARY / ABSTRACT

INTRODUCTION A cooling tower is a heat rejection device, which extracts waste heat to the atmosphere though the cooling of a water stream to a lower temperature. Common applications for cooling towers are providing cooled water for air-conditioning, manufacturing and electric power generation. The generic term "cooling tower" is used to describe both direct (open circuit) and indirect (closed circuit) heat rejection equipment. A direct, or open-circuit cooling tower is an enclosed structure with internal means to distribute the warm water fed to it over a labyrinth-like packing or "fill." The fill may consist of multiple, mainly vertical, wetted surfaces upon which a thin film of water spreads. An indirect, or closed circuit cooling tower involves no direct contact of the air and the fluid, usually water or a glycol mixture, being cooled. In a counter-flow cooling tower air travels upward through the fill or tube bundles, opposite to the downward motion of the water. In a cross-flow cooling tower air moves horizontally through the fill as the water moves downward. Cooling towers are also characterized by the means by which air is moved. Because evaporation consists of pure water, the concentration of dissolved minerals and other solids in circulating water will tend to increase unless some means of dissolved-solids control, such as blow-down, is provided. Some water is also lost by droplets being carried out with the exhaust air (drift).

AIM To determine the correlation of water to air mass flow ration with increasing water flow rate.

THEORY The theory behind the operation of the cooling tower is the First Law of Thermodynamics, which is the conservation of energy. In simpler terms, the energy that enters the system must exit the system; energy can neither be created nor destroyed, just transformed from one form to another.

Energy that enters the cooling tower is in the form of hot water. This hot water was cooled from temperature T1 to a temperature of T2. The cooling of the hot water was in the form of forced convection by which ambient air at T3 was blown over the hot water and exited the cooling tower at some temperature T2. Both the entrance and exit temperatures of the air and water were recorded. Once this data is recorded, an energy balance can be conducted on the system. An energy balance is a form of bookkeeping that accounts for the energy entering and leaving the system. The main component of the energy balance is enthalpy which is defined as: H = U + PV Where H is enthalpy, U is internal energy, P is pressure, and V is volume.

The combined terms U+PV is enthalpy, which means to heat. Enthalpy can be calculated or referenced from tables of data for the fluid being used. he fluids used by the cooling tower are air and water, whose enthalpy values can be obtained from a thermodynamics textbook. For example: Since both the initial and final temperatures of the input hot water and the output cool water were measured, the temperature T inlet can be referenced and the enthalpy (BTU/lbm, or KJ/kg) can be recorded. The enthalpy of the output cooled water can be similarly referenced and an energy balance can be conducted for the water. The equation below displays the general method to conduct an energy balance: in =

where

out

H = Hin- Hout. A similar method is employed for conducting the energy balance for air

entering and leaving the system.

The change in enthalpy for air can be determined form either of two methods. Since the air is at low pressure, it can be treated as an ideal gas and the enthalpy change can be calculated through the use of the following equation: H = Cp where

H is the change in enthalpy,

T

T is the change in temperature, and Cp is the specific

heat with respect to constant pressure.

Since the specific heat relation does not take into account the percent of water in the air, a psychrometric chart is used to determine the enthalpy change between the entrance and exit air. In order for the psychrometric chart to be used effectively, some information is needed about the input and output air.

The information needed to reference the psychrometric chart is the dry bulb and wet bulb temperatures of the inlet and outlet air. Both the input and output air flow is measured with a sling psychrometer. The sling psychrometer is an instrument that has two thermometers. The thermometer for measuring the wet bulb temperature has a wetted cotton sleeve over the bulb end, while the dry bulb thermometer is a regular thermometer. Once the wet and dry bulb temperatures of the inlet and outlet air have been measured, each can be referenced on the psychrometric chart and the enthalpies obtained. Once the enthalpies for the inlet and outlet water and air conditions are known, energy balance can be conducted on the system. Range is determined not by the cooling tower, but by the process it is serving. The range at the exchanger is determined entirely by the heat load and the water circulation rate through the exchanger and going to the cooling water. The range is a function of the heat load and the flow circulated through the system: Range 0C = Heat load (in kCal/hour) / Water circulation rate (l/hour) Cooling towers are usually specified to cool a certain flow rate from one temperature to another temperature at a certain wet bulb temperature. For example, the cooling tower might be specified to cool 4540 m3/hr from 48.9oC to 32.2oC at 26.7oC wet bulb temperature. 4.1.3 Approach As a general rule, the closer the approach to the wet bulb, the more expensive the cooling tower due to increased size. Usually a 2.8oC approach to the design wet bulb is the coldest

water temperature that cooling tower manufacturers will guarantee. When the size of the 4 Section

1.2 is based on Cooling Towers. In: Energy Efficiency in Electrical Utilities. Chapter 7, pg 135 - 151. 2004, with the permission from Bureau of Energy Efficiency, Ministry of Power, India

Electrical Energy Equipment: Cooling Towers Energy Efficiency Guide for Industry in Asia – www.energyefficiencyasia.org ©UNEP 10

tower has to be chosen, then the approach is most important, closely followed by the flow rate, and the range and wet bulb would be of lesser importance. Approach (5.50C) = Cold-water temperature 32.2 0C – Wet bulb temperature (26.7 0C)

APPARATUS 1) The Bench Top Water Cooling Tower 2) Temperature calibration equipment 3) Stop Watch 4) Distilled Water

PROCEDURE 1. Make sure that the upper side of the water manometer is connected to the outlet located beneath the orifice and the other side is exposed to the atmosphere. 2. Turn on the fan to 0. 3. Make sure that the wicks of the wet-bulb thermometers are saturated with distilled water. These wicks tend to dry-up during the experiment. Make sure to re-check them from time to time and refill the wells with distilled water as needed. 4. Measure all the temperatures from T1,T2,T3,T4,T5,T6,T6A,T7, and T7A which include of inlet and outlet temperature of wet and dry bulb, ambient air, water in reserve tank, water leaving the collection tank, tower water inlet and outlet. 5. The first set of experiments will be conducted in the absence of any heat load. 6. Once you have turned on the water pump, monitor all temperatures as a function of time, i.e., measure this wet-bulb temperature after 10 minutes and record the time and temperature readings. 7. Once the temperature at 10 minutes recorded, start the stop watch and measure again all the temperatures at fan of 1,2,3,4,5,6,7,8,9 and 10.

8. Experiment is repeated again with setting up the tower inlet temperature to 30°C, 40°C and 50°C. 9. After 10 minutes, readings of all temperatures are recorded. 10. At the conclusion of the experiment, make sure to first turn off the heating load. Then turn off the liquid pump, the air fan, and the power to the entire experiment.

RESULT Variable = fan speed Water level ( 1cm = 0.3551) Initial = 30 cm 1st trial = 25.5 cm 2nd trial = 24.75 cm 3rd trial = 24.2 cm 4th trial = 23.9 cm 5th trial = 23.7 cm Fan Speed Tower Water Input (T1) 0 2 4 6 8 10 Water Flowmeter 205 204 206 204 208 206

Tower Water Outlet (T2)

25 25.4 22.6 20.9 20.2 19.8 Water in Reserve Tank (T4) 0 0 0 0 0 0

24.2 25.9 22.2 20.8 20.3 20.0

Input DryBulb (T6) 26.8 25.8 26.8 26.9 26.8 27.0

Water Leaving the Collection Tank (T5) 26.2 26.9 24.1 22.6 21.9 21.5

Input WetBulb (T6a) 25.9 26.9 25.8 25.9 25.9 26.0 Output Dry Bulb (T7) 27.8 29.3 26.3 25.6 25.1 25.0

Ambient Air (T3) 25.4 25.4 25.3 24.8 24.4 24.4 Output Wet Bulb (T7a) 25.2 24.4 23.3 22.2 21.6 21.4

Variable = Temperature Water level ( 1cm = 0.3551) Initial = 30 cm 1st trial = 23.2cm 2nd trial = 22.8 cm 3rd trial = 22.1 cm Temperature Tower Water Input (T1) 0 30 40 50 Water Flowmeter 201 204 206 204

Tower Water Outlet (T2)

30.8 35.0 36.5 37.2 Water in Reserve Tank (T4) 0 0 0 0

27.5 31.3 32.3 32.5

Input DryBulb (T6) 27.2 27.9 28.1 28.6

Water Leaving the Collection Tank (T5) 32.1 36.2 31.6 38.2

Input WetBulb (T6a) 26.1 26.7 27.1 27.7 Output Dry Bulb (T7) 29.9 32.4 33.4 33.9

CALCULATION 1st trial To calculate range of the cooling tower, the following formula was used:

Ambient Air (T3) 24.1 24.6 25.1 25.6 Output Wet Bulb (T7a) 27.6 30.7 31.8 32.2

Range: Twater inlet-Twater outlet = 25.4ºC-25.9-ºC = -0.5 ºC The approach of the cooling tower was calculated using: Approach: Twater out-Twb inlet = 25.9-26.9= -1.0 Effectiveness of the cooling tower was calculated using the following formula: n = range/ (range+approach) = (-0.5)/(-0.5-1.0) = 33.333 % Humidity is gained from humidity chart; Twet bulb inlet average = 26.683 Tdry bulb inlet average = 26.067 Humidity, H = 0.0183 kg water vapor/kg dry air Humidity percentage, Hp = 81% Humid heat, cs = 1.005 + 0.45 (0.0183) = 1.0394 kJ/kg dry air.K Humid volume, vh = (2.83x10-3 + 4.56x10-3x0.0183)(26.067+273) = 0.8713 m3/kg dry air 2nd trial To calculate range of the cooling tower, the following formula was used: Range: Twater inlet-Twater outlet = 37.2ºC-32.5ºC = 4.7ºC The approach of the cooling tower was calculated using: Approach: Twater out-Twb inlet = 32.5-27.7= 4.8 Effectiveness of the cooling tower was calculated using the following formula: n = range/ (range+approach) = (4.8/(4.7+4.8) = 49.4736 % Humidity is gained from humidity chart; Twet bulb inlet average = 26.9 ºC Tdry bulb inlet average = 27.95 ºC

Humidity, H = 0.0178 kg water vapor/kg dry air Humidity percentage, Hp = 72% Humid heat, cs = 1.005 + 0.45 (0.0178) = 1.01301 kJ/kg dry air.K Humid volume, vh = (2.83x10-3 + 4.56x10-3 x 0.0178 )(26.9+273) = 0.8730 m3/kg dry air

DISCUSSION what could be include in this discussion is that reference result from http://www.seas.upenn.edu/~meam347/fall/347labmanual.pdf . We could compare their result and us. And boleh put some of information like this from this website The cooled water leaves the cooling tower and collects into the "load tank." Before reentering into the tank, the temperature of the exiting water is measured. Due to evaporation, the level of the water in the "load tank" tends to fall. This causes the float-operated needle valve to open and transfer water from the "make-up tank" into the load tank. Under steady-state conditions, the rate at which the water leaves the "make-up tank" is approximately equal to the rate of evaporation of the water in the tower. Then boleh letak ni dari http://www.irvindelapaz.com/blog/wp-content/uploads/Cooling-TowerLab.pdf - dlm ni go down to discussion. Ada some ideas plus ideas below 4.1.6 Relationship between range, flow and heat load The range increases when the quantity of circulated water and heat load increase. This means that increasing the range as a result of added heat load requires a larger tower. There are two possible causes for the increased range: � The inlet water temperature is increased (and the cold-water temperature at the exit remains the same). In this case it is economical to invest in removing the additional heat. � The exit water temperature is decreased (and the hot water temperature at the inlet

remains the same). In this case the tower size would have to be increased considerably because the approach is also reduced, and this is not always economical.

CONCLUSION

RECOMMENDATION 1. The temperature indicator needs to be fixed as it is not work properly. It is hard to set and take precise reading of the temperature. 2. Cooling tower effect can be verified through temperature, fan speed and types of packing column. For the next semester, use packing as the variable. 3. Type of packing column, water flow and temperature setting were confusing. In the future, need more explanation about it.

REFERENCES 1. 2. 3. 4.

http://www.cti.org/whatis/coolingtower.shtml http://chem.engr.utc.edu/webres/435F/3T-CT/3T-CT.html http://www.seas.upenn.edu/~meam347/fall/347labmanual.pdf http://www.mcilvainecompany.com/Cooling%20Tower%20Samples/cts%20sample1. htm

APPENDICES