CLec2

Lecture 2: Fluid/Physical Properties of Waters : 

Lecture 2: Fluid/Physical Properties of Waters Dr. Robert Vega MARI-5421 August 30, 2006

Water as a Fluid : 

Water as a Fluid Air and water are the two fluids we are most concerned with. Fluid: a substance consisting of particles that change their position relative to one another. Other definition: a substance that will continuously deform when a shear stress is applied. Water is a relatively incompressible fluid, at least for most aquaculture applications.

Fluid Properties: Specific Weight: 

Fluid Properties: Specific Weight Specific weight: the gravitational force exerted on a unit volume of water (weight per unit volume). Formula = Formula: specific weight = density x force due to gravity Expressed as lb/ft3 or N/m3 As temperature increases, specific weight decreases (see table) N = 9.8 kg

Temp vs. Specific Wt./Density: 

Temp vs. Specific Wt./Density

Fluid Properties: Density () : 

Fluid Properties: Density () Density = specific weight/acceleration due to gravity (g). Density of water does not change much. Water is incompressible and can be assumed to have a relatively constant density (0oC = 0.99987 g/cm3; 30oC = 0.99568 g/cm3). Very high levels of pressure are required to change the density of water. Not so with air. () = rho

Density and Temperature: 

Density and Temperature ????

Fluid Properties: Specific Gravity (SG): 

Fluid Properties: Specific Gravity (SG) Usually considered a comparison of the specific weight of water to the same volume of water under different conditions (e.g., temperature). Often used to determine salinity via a hydrometer. SG for water is usually 1.0 and, since it is dimensionless, has no units.

Fluid Properties: Viscosity (µ): 

Fluid Properties: Viscosity (µ) Viscosity = a fluid’s resistance to shear or deformation. Probably water’s most important physical property. Viscous fluids flow more slowly when shear or stress is applied to them. Increased temperature = decreased viscosity. µ = mu

Viscosity of Water vs. Temp: 

Viscosity of Water vs. Temp

Part 2: Physical Properties of Water: 

Part 2: Physical Properties of Water

Physical Variables: Temperature vs. Animal: 

Physical Variables: Temperature vs. Animal Environmental parameter having the greatest impact on aquaculture species. Primary factor affecting economic viability. Impractical to control in large-scale (pond) situations. Pond culture implies proper geographical location. Temperature affects rates of physiological processes and levels of other parameters. Metabolism is the engine, temp controls rate of engine.

Physical Variables: Temperature vs. Animal: 

Physical Variables: Temperature vs. Animal Physiological processes affected: Respiratory rate (metabolic rate) metabolic rate increases with temperature fish consume oxygen 2-3x faster at 300C vs. 200C Conclusion? Efficiency of feeding/assimilation Growth Behavior Reproduction

Physical Variables: Temperature vs. Animal: 

Physical Variables: Temperature vs. Animal Temperature sets the pace of metabolism by controlling molecular dynamics (diffusion, solubility, fluidity). Resting, fasted fish’s demand for oxygen (std metabolism) increases exponentially with temp. However, physiological capacity to provide oxygen rises sigmoidally. Stressors can reduce metabolic scope at all temps and shift optimum temperature: growth is affected.

Physical Variables: Temperature vs. Animal: 

Physical Variables: Temperature vs. Animal Beyond lower and upper extremes of temperature, fish can’t grow or live. Specific relationship depends on species (perhaps also age/size), past thermal experience, general condition of the individual and levels of non-thermal factors (e.g., salinity).

Physical Variables: Temperature vs. Animal: 

Physical Variables: Temperature vs. Animal Each species has a characteristic growth curve with an optimum range. Also have upper and lower temperature limits (lower lethal limit, upper lethal limit). Outside tolerable temperature range, disease and stress become more prevalent. Brook trout 7-13 Chinook salmon 10-14 Tilapia 28-30 Pacific white shrimp 26-32 oC

Physical Variables: Temperature Classifications: 

Physical Variables: Temperature Classifications Aquaculture species are often classified as either cold-water, cool-water or warm-water. Some are referred to as “tropical”. However, much overlap Often species of different classifications are found in the same place at the same time. Poikilothermic: having same body temperature as surrounding medium. What energy source drives this?

Marine Climatic Zones: 

Marine Climatic Zones From Sumich; page 26

Physical Variables: Temperature & Salinity: 

Physical Variables: Temperature & Salinity Pond water temperature is also responsible for the physical effect known as thermal stratification. Epilimnion: upper thermal layer, warmer, less dense. Hypolimnion: lower thermal layer, cooler, more dense, often problematic. Thermocline: thin layer between both. Mixing often occurs when surface waters cool at night, especially in shallow ponds. Problems with thermoclines?

Variations in Temperature: 

Variations in Temperature From Sumich, page 27

Properties of Pure Water: 

Properties of Pure Water Latent heat of fusion: water requires a large loss of energy to pass from liquid to solid phase. Reverse is true for latent heat of vaporization. Meaning: large bodies of water resist changes in temperature, life processes remain constant. From Sumich, page 19

Physical Variables: Density: 

Physical Variables: Density Already mentioned as an aspect of fluids. Pure water is most dense at 4oC. Below this it becomes less dense and freezes at 0oC. When you add impurities to water (e.g., salt), its density increases. Thus, seawater freezes at a lower temp (-1.4oC). If seawater can freeze, why doesn’t it accumulate at the bottom of the ocean?

Density Variations: 

Density Variations From Sumich, page 27

Physical Variables: Freezing : 

Physical Variables: Freezing Often mentioned as a separate phenomenon. Water is unusual in its freezing characteristics compared to other liquids. Change in hydrogen bond angles expands volume of water molecule (e.g., ice floats). Also causes lakes and ponds to freeze from the top down. What would happen if a lowering of temp caused bond angles to decrease?

For Next Time…Lecture 3: 

For Next Time… Lecture 3 Continue with physical properties of water: Salinity, Electrical Conductance, Turbidity, Color, and Total Gas Pressure Readings = Boyd 2000 (44-49, 63-65, 99-103)