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THERMOCOUPLESNOZZLES & DIFFUSERS

BALMES NAVALTA PUEBLOan electrical device that responds to a difference in temperature by producing an electric current.thermocoupleMeasurement JunctionMetal AMetal BReference JunctionWIRING TO SIGNAL CONDITIONING CIRCUITRYTypes of Thermocouple

Chromel90% nickel 10% chromium Alumel95% nickel 2% manganese 2% aluminum1% silicon

Constantan55% copper45% nickel

K-type ThermocoupleThe Most Commoninexpensive, accurate, reliable, and has a wide temperature range The Principlewhen any conductor is subjected to a thermal gradient, it will generate a voltage. This is now known as the thermoelectric effect or Seebeck effect.

Since the thermocouple is a differential device rather than an absolute temperature measurement device, the reference junction temperature must be known to get an accurate absolute temperature reading (the reference junction is kept at a fixed, known temperature). reference junction compensation (cold junction compensation) The Process

Advantages:

Wide Temperature RangeRobustRapid ResponseNo Self Heating

Disadvantages:

Complex Signal ConditioningSusceptible to Corrosion

ComplexityThermocouples are complex and have many sources of error. This is mostly due to their operation. Thermocouples use two dissimilar metals that have two different voltage readings produced from a change in temperatures on alternative ends of the metals. They also have a cold junction, which consists of copper wires to allow the metal to meet the instrumentation. They use various types of electronic compensation at the cold junction to allow for more accurate readings; this accounts for marginal errors, depending upon the type of thermocouple used.

8ApplicationsTemperature measurement for kilns, gas turbine exhaust, diesel engines

Gas appliance safety

Thermopile Radiation Sensors

Prototype Testing

Thermoelectric Cooling

Vacuum Gauge

gas-fed heating appliances such as ovens and water heaters make use of a pilot flame to ignite the main gas burner when required. If the pilot flame goes out, unburned gas may be released, which is an explosion risk and a health hazard. To prevent this, some appliances use a thermocouple in a fail-safe circuit to sense when the pilot light is burning. The tip of the thermocouple is placed in the pilot flame, generating a voltage which operates the supply valve which feeds gas to the pilot. So long as the pilot flame remains lit, the thermocouple remains hot, and the pilot gas valve is held open. If the pilot light goes out, the thermocouple temperature falls, causing the voltage across the thermocouple to drop and the valve to close.

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Insulated thermocouple

Thermocouple connectors

Industrial type thermocouple

Mineral Coated ThermocouplesNOZZLES vs. DIFFUSERSNozzleis a device designed to control the direction or characteristics of a fluid flow (especially to increase velocity) as it exits (or enters) an enclosed chamber or pipe.Types of NozzlesJetA gas jet, fluid jet, or hydro jet is a nozzle intended to eject gas or fluid in a coherent stream into a surrounding medium. Gas jets are commonly found in gas stoves, ovens, or barbecues.High velocityFrequently, the goal is to increase the kinetic energy of the flowing medium at the expense of its pressure and internal energy.PropellingA jet exhaust produces a net thrust from the energy obtained from combusting fuel which is added to the inducted air. This hot air passes through a high speed nozzle, a propelling nozzle, which enormously increases its kinetic energy.MagneticMagnetic nozzles have also been proposed for some types of propulsion, such as VASIMR, in which the flow of plasma is directed by magnetic fields instead of walls made of solid matter.Sprayis a precision device that facilitates dispersion of liquid into a sprayShapedSome nozzles are shaped to produce a stream that is of a particular shape

Diffusersa device that controls the characteristics of a fluid at the entrance to a thermodynamic open systemDiffusers are used to slow the fluid's velocity and to enhance its mixing into the surrounding fluid. In contrast, a nozzle is often intended to increase the discharge velocity and to direct the flow in one particular direction.HVACHeating Ventilating - Airconditioning

A nozzle is a device which accelerates fluid. During this process, velocity of fluid increases with decreasing pressure.A diffuser is a device which slows down fluid. That means, velocity of fluid decreases with increasing pressure.