Heat Transfer and Fluid Mechanics Experiments

• The document details several experiments related to heat transfer and fluid mechanics, including cooling towers, rusting, heat exchangers, and thermal conductivity of bricks.

Experiment 1: Cooling Tower Loading Factor

• Objective: Calculate the loading factor of a cooling tower.
• Definition: A cooling tower is an open water recirculation device that uses fans or natural draft to cool water by evaporation, or a heat rejection device extracting waste heat to lower a water stream's temperature.
• Mechanism: Cooling towers exchange heat through water evaporation, bringing warm water into direct contact with cooler air; as air exits, it has a higher temperature and near-saturation moisture content.
• Cooling occurs because a temperature increase raises heat capacity, allowing more sensible heat to be absorbed.
• Heat rejection is evaporative, cooling a majority of water by evaporating a small portion into moving air.
• Heat transferred to the airstream raises the air's temperature and humidity to 100%, which is discharged.
• Cooling towers provide lower water temperatures more cost and energy-efficiently than air-cooled devices.
• Psychrometric Chart: Charts represent the physical properties of moist air at constant pressure, showing how properties relate.
• Dry-bulb Temperature: Measured via a standard thermometer.
• Relative Humidity: Reflects the amount of water air can hold at a given temperature relative to its saturation point.
• Humidity Ratio: Represents the mass of water in the air per unit mass of dry air; not temperature-dependent.
• Dewpoint Temperature: Indicates when water will begin to condense out of moist air as temperature decreases.
• Wet-bulb Temperature: The temperature at which water evaporates, saturating the air, assuming no heat is lost or gained.
• Enthalpy: Represents the heat energy content of moist air, useful in heating and cooling applications.
• Specific Volume: Reflects the space occupied by air.
• Design Considerations: Tower size depends on cooling range, approach to wet bulb temperature, mass flow rate of water, air velocity, and tower height.
• Loading Factor: The mass flow rate of makeup water.
• Drift: Water droplets carried out with the exhaust air, reduced by drift eliminators.
• Blow-out: Water droplets blown out by wind, limited by wind screens.
• Plume: The stream of saturated exhaust air leaving the cooling tower, may cause hazards.
• Blow-Down: Purging a portion of circulating water to control the amount of dissolved solids and other impurities at an acceptable level.
• Leaching: Loss of wood preservative chemicals in wood structure cooling towers.
• Noise: Sound energy emitted, caused by the impact of falling water, movement of air via fans, fan blades moving inside the structure as well as motors.

Experiment 2: Determining Rusting Time by Shrinking Core Method

• Objective: Find the time it takes for complete rusting using the shrinking core method.
• Gas-Solid Reactions: This involves heterogeneous reactions where a gas reacts with a solid, transforming it.
• Core reaction shrinks as process progresses.
• Progressive reaction converts material from outside in.
• Apparatus: Requires a weighing balance, oven, heater, iron rings with stand, and emery paper.

Experiment 3: Helical Coil Agitator Turns Calculation

• Objective: Determine the number of turns of coil in a helical coil agitator.
• Coil Design: Heats or cools tank contents, with helical, vertical, and plate coils as major types.
• Heat Transfer: Curved tubes are used for their heat transfer, suitable for chemical, food, and dairy processes; mechanical agitation improves heat transfer.
• Chilton, Drew, and Jebens offered an excellent correlation for heat transfer in jacketed vessels and coils.

Experiment 4: Heat Flow Rate Through Different Bricks

• Objective: Determine the heat flow rate through different types of bricks.
• Bricks: Ceramic structural material, traditionally hardened by drying but now fired in kilns.
• Heat Conduction: Heat transfer from a higher to a lower temperature region, equalizing temperature differences.
• Heat Flow Rate: It's expressed by Fourier's equation.
• Thermal Conductivity: Indicates the quantity of heat transmitted through a unit thickness.
• Fourier's Law: The rate of heat transfer is proportional to the negative temperature gradient.

Experiment 5: Heat Losses Comparison Through Insulations

• Objective: Calculate and compare heat losses of different insulations.
• Insulation: Materials that slow down heat flow, protect from damage, and enhance appearance.
• Insulating materials are designed to restrict heat flow, resist electric current, and offer high resistance to heat transfer.
• Multiple benefits include energy conservation, environmental protection, temperature control, condensation prevention, and increased system efficiency.

Experiment 6: Dirt Factor Determination for Double-Pipe Heat Exchanger

• Objective: Find the dirt factor of a double-pipe heat exchanger when cooling water flows co-current and counter-current.
• Fouling: Buildup of sediments on a heat exchanger's surface reduces heat transfer.
• The Dirt (Fouling) Factor is a measure of that fouling, and is a pre-determined number represents fouling amount and is used in calculation.
• Types of Fouling: Crystallization, Sedimentation, Biological Organic Growth, Chemical Reaction Coking, Corrosion, and Freezing.
• Fouling can be minimized through design and cleaned frequently.
• Mean Temperature Difference: Depends on the direction of fluid flows (parallel or counter-current).
• Logarithmic Mean Temperature Difference (LMTD): Is non-linear and can best be represented by a logarithmic calculation.
• Arithmetic Mean Temperature Difference (AMTD): An easier but less accurate way to calculate the mean temperature difference.

Exploration of heat transfer and fluid mechanics principles through experiments. Covers cooling towers, rusting processes, heat exchangers, and thermal conductivity in bricks. Includes calculations for cooling tower loading factors and mechanisms of heat rejection.