Temperature | Mechanical Engineering SSC JE (Technical) PDF Download

TEMPERATURE

Zeroth law of Thermodynamics
• The zeroth law of thermodynamics states that if two thermodynamic systems are each in thermal equilibrium with a third one, then they are in thermal equilibrium with each other.
• Zeroth law of thermodynamics is the basis of temperature measurement

ThermometerThermometric property
Constant vol. gas thermometerPressure (P)
Consant pressure gas thermometerVolume (V)
Resistance thermometer (Thermistor)Resistance (R)
Thermo coupleEMF (e)
Mercury in glass thermometerLength (L)

 

ThermometerTemp. range
Platinum resistance Thermometers–200ºC – 1200ºC
Thermoelectric thermometers–200ºC – 1600ºC
Radiation pyrometersabove 400ºC
Segar cone600ºC – 2000ºC
Optical pyrometersabove 650ºC
Gas Thermomenters–200ºC – 1200ºC
  • Thermocouple uses copper–constantan, platinum, rhodium, thodium, chromel alumel combinations.

Temperature

The temperature is a measure(degree) of hotness or coldness. (freezing cold, warm hot)

Temperature scales

  • They are related to absolute temperature scales.
  • The temperature scales used in the SI and English system are the kelvin scale and the Fahrenheit scale, respectively.
  • A scale of temperature independent of the thermometric substance is called a thermodynamic temperature scale.
  • Kelvin scale is related to celsius scale by

                              T(K) = T(C) + 273.16

  • Rankine scale is related to Fahrenheit scale by

                              T(R) = T(F) + 459.67

  • The temperature scales in the two unit systems are related by

                              T(R) = 1.8T(K)

                              T(0F) = 1.8T(0C) + 32

                              ΔT(0F) = 1.8ΔT(K) = ΔT(R)

The document Temperature | Mechanical Engineering SSC JE (Technical) is a part of the Mechanical Engineering Course Mechanical Engineering SSC JE (Technical).
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FAQs on Temperature - Mechanical Engineering SSC JE (Technical)

1. How is temperature measured in mechanical engineering?
Ans. Temperature in mechanical engineering is typically measured using various devices such as thermocouples, resistance temperature detectors (RTDs), and thermistors. These devices rely on the principle of thermal expansion or electrical resistance changes with temperature to provide accurate temperature readings.
2. What are the common units of temperature used in mechanical engineering?
Ans. In mechanical engineering, temperature is commonly measured in Celsius (°C) and Kelvin (K). Celsius is the most widely used unit for everyday temperature measurements, while Kelvin is often used in scientific and engineering applications where absolute temperature is required.
3. How does temperature affect the performance of mechanical systems?
Ans. Temperature plays a critical role in the performance of mechanical systems. For example, high temperatures can cause thermal expansion, which can lead to dimensional changes and potential failure of components. Temperature variations can also affect the viscosity of fluids, causing changes in flow rates and efficiency. Moreover, temperature can impact the efficiency and power output of engines and motors.
4. What is thermal stress and how does temperature contribute to it?
Ans. Thermal stress is the stress induced in a material due to temperature changes. When a material is subjected to different temperatures, it expands or contracts, causing internal stresses. These stresses can lead to deformation, cracking, or failure of the material. Temperature gradients across a structure or component can further contribute to thermal stress.
5. How is temperature control important in mechanical engineering applications?
Ans. Temperature control is crucial in mechanical engineering applications to ensure optimal performance, efficiency, and safety. It is essential in processes like heat treatment, welding, and casting to achieve desired material properties. In cooling systems, temperature control prevents overheating and maintains the system's stability. Additionally, precise temperature control is necessary in environmental chambers and testing equipment to simulate specific operating conditions.
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