Journal of Applied Science and Agriculture. Preliminary Data of Evaporation Characteristics foran Open Pond in East Malaysia

Transcription

1 AENSI Journals Journal of Applied Science and Agriculture ISSN Journal home page: Preliminary Data of Evaporation Characteristics foran Open Pond in East Malaysia Md. Ashikur Rahman, Md. Mizanur Rahman, Noor AjianMohd. Lair, Chi Ming Chu MechanicalEngineering Programme, Faculty of Engineering,Universiti Malaysia Sabah (UMS). A R T I C L E I N F O Article history: Received 11 October 2014 Received in revised form 21 November 2014 Accepted 25 December 2014 Available online 14 January 2015 Keywords: Evaporation rate Open pond Penman equation A B S T R A C T Evaporation is being considered as an alternative dewateringprocess of an increasing number of wastewater treatment applications and algae harvesting for biodiesel production. For simplicity, this paper presents work on modeling the performance of solar evaporation ponds. It will provide useful new technology towards commercial production of algal biodiesel. Evaporation is the combination of two phenomena involving the change of the phase from liquid into vapor, and the transfer of vapor. In open ponds, passive solar energy is used to the change of the phase from liquid to vapor. The ability to transfer vapor particles of open ponds in the air is a function of the relative humidity, wind speed, air temperature, water concentration, vapor pressure of air on water surface, pond size, water depth, among other things. The evaporation rate of an open pond of similar dimensions to modified class-a evaporation pan was measured over 15 days under typical East Malaysia climactic conditions. The experimental result is compared to the Penman evaporation method AENSI Publisher All rights reserved. To Cite This Article: Md. Ashikur Rahman, Md. Mizanur Rahman, Noor AjianMohd. Lair, Chi Ming Chu., Preliminary Data of Evaporation Characteristics foran Open Pond in East Malaysia. J. Appl. Sci. & Agric., 10(5): 6-12, 2015 INTRODUCTION An evaporation process occurs naturally in solar open ponds. Although the solar pond concept will be applied to harvesting algae, it can be in wastewater treatment as well. Solar evaporation ponds usually are limited by land availability and cost. The formulae available to estimate the water evaporation rate an open pond for concentrating waste products, sludge or for fish farming, are those developed for the application on fish ponds and lakes (Penman, 1948). The equation for evaporation given by Penman is: E = mr N +γe a 1 λ v ρ w m +γ where, E= Evaporation from open ponds in m/s; m = Slope of the saturation vapor pressure curve in Pa.K -1 ; R n = Net irradiance in W/m 2 ; E a = Parameter including wind velocity and saturated deficit in W/m 2 ; λ v = Latentheat of vaporization in J/kg ρ w = Density of water is equal to 1000 kg/m 3 γ = Psychrometric constant in Pa.K -1. The first term in the equation is the radiative component and the second term is the aerodynamic component. 1. Methodology: An evaporation pan that is considered to represent a solar heat pond was made by 25 Galvanized Iron sheets. Dimensions of the evaporation pan are 60cm, 54cm and 20cm in length, width and depth respectively. It was seated level to the ground in a grassy location, away from bushes, trees and other obstacles which obstruct natural airflow around the pan that is representing open water in an open area. A photograph of a pan that is representing open water in an open area is to show in the Figure 1. Corresponding Author: Chi Ming Chu, Chemical Engineering Programme, Faculty of Engineering, Universiti Malaysia Sabah (UMS), Kota Kinabalu, Sabah, Malaysia. Tel: ext 3135; chrischu@ums.sdu.my

2 7 Md. Ashikur Rahman et al, 2015 Fig. 1: Photograph of a pan, thus represented open water in an open area. 1.1 Instruments and accuracy: The methods for calculating evaporation from meteorological data require various climatological and physical parameters. Some of the data are measured directly by weather measurement instruments. Other parameters are related to commonly measuring data and can be derived with the help of empirical relationship. Air temperature, Wind speed, Relative humidity and atmospheric pressure were measured by a Kestrel 4000 Pocket Weather tracker at the experimental place in Universiti Malaysia Sabah (UMS). This type of weather measurement instrument has the capability to store up to 2000 points of weather data, enabling you to track changes in the environment over time. The wind speed is a daily average value in ms -1 typically; the wind function assumed wind speed was measured at 2m above the ground surface. The total daily expected solar radiation was taken from online solar insolation calculation software at 5 58ʹ north ( the location is Kota Kinabalu, Sabah. The water level in the pan was measured by a digital depth gauge and a float indicator. The fixed jay of the digital depth gauge was rigidly connected at the top of the pan rim. The sliding bar of the digital depth gauge was connected to the float indicator by a thin weight less aluminum bar. The float indicator was floating on the pan water, where the reduction in the water level caused the float indicator to move downward. The displacement of float indicators was taken from digital depth gauge display. The resolution of this level measurement instrument is 0.01mm.The daily rainfall was collected by a beaker. 1.2 Input Values for Penman Equation: Table 1 shows the input values of the Penman equation parameters. The experiment has done 9am to 5pm every consecutive day at Universiti Malaysia Sabah, (UMS). The place is situated in 5 58ʹ north. Table 1: Inputs values in Penman evaporation equation at UMS (5 58ʹ North). Mean The aerodynamic component (E Slope of the saturated Net solar a) Relative Day vapor pressure curve(m) radiation Wind function Vapor pressure in Pa/K (R N) in W/m 2 Humidity f(u) in m/s deficit in Pa Psychrometric constant (γ) in Pa/K (RH) in % The term (E a ) in the Penman equation isthe aerodynamic equation and represents the evaporative component due to turbulent transport of water vapor by an eddy diffusion process. It is defined as: E a = f u (e s e a ) 2 where, f(u)is a wind function typically of the form f(u) = 0.35(1+U 2 /160);and e s -e a is the vapor pressure deficit. Slope of the saturated vapor pressure curve in the Penman equation is calculated by the equation is: m = de s = 5336 dt a T 2 exp a T a

3 8 Md. Ashikur Rahman et al, 2015 Table 2: Input values for calculation of Net radiation at UMS (5 58ʹ North). Date Sunny day solar radiation(r A) in W/m 2 Incoming solar radiation (R C) in W/m 2 Air temperature (T) in C T max T min Mean actual vapor pressure (e d) in mb Available sunshine (n) in hour Sunny day sunshine (N) in hour 19 th Oct Full th Oct st Oct nd Oct rd Oct th Oct Full th Oct th Oct st Oct Full st Nov Full nd Nov Full th Nov th Nov th Nov th Nov Outgoing solar radiation (R L) in W/m 2 Where, m is the slope of the saturated vapor pressure curve in mmhg/k;t a is the mean air temperature in K. The net irradiance in the Penman equation is calculated by the equation is: R L = (1 r)r C R N 4 Where, R L is net long-wave (outgoing) radiation; R N is net incoming radiation; Rcis incoming (global) solar radiation; and r is reflection coefficient (albedo) value is (0.2~0.3). The incoming radiation predicted by the Angstrom equation in the energy balance term. R C = R A (a + b n N ) 5 where, R A is total possible solar radiation for the latitude and time of year;n is measured daily duration of bright sunshine; N is total possible daily duration of bright sunshine for the latitude and time of year; and a, b are regression constants. Taking a = 0.18 and 6 = 0.55 (Values used by Penman). The long-wave (outgoing) radiation produced by the equation R L = σ T max 4 +T 4 min e 2 a n N 6 Where, σt 4 a is theoretical black body radiation at a mean (air) temperature T a ; and e a is actual vapor pressure in kpa(wales-smith, 1979). RESULTS AND DISCUSSION Tables 3 and 4 show the prevailing ambient data over the water pan. The data were taken at UMS on a sunny day and on a rainy day respectively. Table 3: Prevailing Ambient Data for a Typical Sunny day at UMS (5 58ʹ North). Time Air temperature in C Wind speed in m/s Relative Humidity in % Saturated vapor pressure in Pa 9:00:00 AM :30:00 AM :00:00 AM :30:00 AM :00:00 AM :30:00 AM :00:00 PM :30:00 PM :00:00 PM :30:00 PM :00:00 PM :30:00 PM :00:00 PM :30:00 PM :00:00 PM :30:00 PM :00:00 PM

4 9 Md. Ashikur Rahman et al, 2015 Table 4: Prevailing Ambient Data for a Typical Rainy day at UMS (5 58ʹ North). Time Air Temperature in C Wind speed in m/s Relative Humidity in % Saturated vapor pressure in Pa 9:00:00 AM :30:00 AM :00:00 AM :30:00 AM :00:00 AM :30:00 AM :00:00 PM :30:00 PM :00:00 PM :30:00 PM :00:00 PM :30:00 PM :00:00 PM :30:00 PM :00:00 PM :30:00 PM :00:00 PM Relative Humidity and Air temperature: Figures 2 and 3 show the air temperature and relative humidity variation curve with time for open pan at UMS (5 58ʹ North) on a sunny day and a rainy day respectively. Fig. 2: Temperature and Relative Humidity curve with respect to time for a Sunny-day at UMS (5 58ʹ North). Fig. 3: Temperature and Relative Humidity curve with respect to time for a Rainy-day at UMS (5 58ʹ North). 2.2 Vapor pressure: Figures 4and 5 show the vapor pressure deficit (e s -e a )at UMS (5 58ʹ North) on a sunny day and a rainy day respectively. Fig. 4: Vapor pressure deficit curve with respect to time for a sunny-day at UMS.

5 10 Md. Ashikur Rahman et al, 2015 Fig. 5: Vapor pressure deficit curve with respect to time for a Rainy-day at UMS. 2.3 Wind velocity: Figures 6 and 7 show the air speed with respect to time. The wind speed was taken 2m above from the ground surface at UMS (5 58ʹNorth) for a Sunny-day and a Rainy-day. The air flow over the open pan is a function of the climactic environment. The air flow over the open pan is therefore unstable. Fig. 6: Wind speed for a Sunny-day at UMS (5 58ʹ North). Fig. 7: Wind speed for a Rainy-day at UMS (5 58ʹ North). 2.4 Evaporation Rate: Table 5 shows the two sets of evaporation rate data: the Penman evaporation predicted data and the open pond evaporation data collected at Universiti Malaysia Sabah (UMS) for 15 consecutive days. The three main parameters that control the evaporation rate of a body of water are: the temperature, the partial pressure of water in the air, the surface area. Additional factors are both of the heat available in the liquid and the strength of the inter-molecular forces between the molecules. On a warm sunny day, the atoms in the water absorb energy from the surrounding air and the sun, which increases the energy of the atoms causing them to evaporate faster. Evaporation can faster on sunny days not just because of the extra heat, but also because sunny days are often drier and so have lower relative humidity. While on a cold day the molecules are moving slower this causes it to evaporate more slowly and find it more difficult to escape from the liquid. The partial pressure of water in the air is a measure of how much water is already in the air. From the Penman equation, the rate of evaporation is directly related to the partial pressure of water in the air or vapor pressure deficit of water in the air. As a body of water gets more spread out, then more of the water particles are exposed to the air and will therefore be given more of a chance to evaporate. Finally, we can realize the evaporation is influenced bythe temperature of the air at the water surface; the humidity of the air; the area of the air-water surface: The temperature of the air. In a real-world situation of evaporating water, none of these four quantities above remain constant because the process of evaporation itself changes them. The Penman evaporation rate is much maximized. Where the rainfall is 1.2mm maximum there the evaporation rate is 0.71mm minimum at the open

6 11 Md. Ashikur Rahman et al, 2015 pond. The comparison between the Penman predictions and the experimental evaporation rate from a pan will be reduced by the control of air flow over the evaporation pan. For future work, proposal to use natural draft solar chimney to enhance flow will bring the air flow velocity over the pond under control. Table 5: Penman-Predicted and experimental evaporation rates for a Class-A type Open Pond during 19 th Oct to 20 th NovatUniversiti Malaysia Sabah, (UMS)in East Malaysia Day Penman evaporation rate in (mm) Pan evaporation in (mm) Rainfall in (mm) Fig. 8: Penman-Predicted and experimental evaporation rates for a Class-A type Open Pond in at UMS (5 58ʹ North) East Malaysia (UMS). Conclusion: In summary, the evaporation rate varied with the wind speed, vapor pressure deficit and the area of the water bodyto spread of the air. From the Penman evaporation equation, the rate of evaporation is high at the higher vapor pressure deficit and at higher wind flow. Natural draft solar chimney could be engaged to control the air flow velocity. REFERENCES Penman, H.L., Natural evaporation from open water, bare soil and grass, Proc. Roy. Soc. Lon., A, 193: McMahon, T.A., M.C. Peel, L. Lowe, R. Srikanthan and T.R. McVicar, Estimating actual, potential, reference crop and pan evaporation using standard meteorological data: a pragmatic synthesis, 17: ,Hydrology and Earth System Sciences. Malika, F., B. Abdenour and M. Saighi, Evaluation of two methods for estimation of evaporation from Dams water in arid and semi-arid areas in Algeria, 2: , International Journal of Application or Innovation in Engineering & Management (IJAIEM). Suat, I. and Z.H. Dorota, Evaluation Of Five Methods For Estimating Class-A Pan Evaporation In Humid Climate, Florida Agriculture Experiment Station Journal Series R Lim, W.H., L. Roderick Michael, M.T. Hobbins, W.S. Chin, F.D. Graham, The energy balance of a US Class A evaporation pan, Series , July, pp Agricultural and Forest Meteorology. Liu, H., A.W. Duan, F.S. Li, J.S. Sun, Y.C. Wang and C.T. Sun, Drip Irrigation Scheduling for Tomato Grown in Solar Greenhouse Based on Pan Evaporation in North China Plain, 12(3): , Journal of Integrative Agriculture. Chu, C.R., M.H. Li, Y.Y. Chen, Y.H. Kuo, A wind tunnel experiment on the evaporation rate of Class A evaporation pan, vol. 381, November, pp: Journal of Hydrology. Ozgyr, K., Evolutionary neural networks for monthly pan evaporation modeling, vol. 498, June, pp , Journal of Hydrology.

7 12 Md. Ashikur Rahman et al, 2015 Chu, C.R., M.H. Li, Y.F. Chang, T.C. Liu and Y.Y. Chen, Wind-induced splash in Class A evaporation pan, Vol. 117, January, D11101, Journal of Geophysical Research, Wales-Smith, B.G., Estimates of net radiation for evaporation calculations, Hydrological Sciences- Bulletin-des Sciences Hydrologiques, 25, 3, 9/1980