Annealing is a process by which steel is reheated and then cooled to make it less brittle. consider the reheat stage for a 100 mm thick plate (r = 7830 kg/m3, cp = 550 j/kg k, k = 48 w/m k). the plate initially is at 200 oc and is to be heated to a minimum temperature of 550 oc. heating is effected in a gas-fired furnace where the products of combustion at t[infinity] = 800 oc maintain a convection heat transfer coefficient of h = 250 w/m k on both surfaces of the plate.

(a) calculate the biot number for this heat transfer process.

(b) can the lumped-capacitance approximation be used to analyze this transient heat transfer process?

(c) assuming that the lowest temperature in the plate is at its midplane, calculate the dimensionless temperature at the midplane of the plate when temperature is 550 oc

(d) using the one-term approximate solution for convective heat transfer into a semi-infinite medium, calculate the fourier number required to achieve a temperature of 550 oc in the steel

(e) calculate the time required to achieve a temperature of 550 oc at the midplane of the plate.

Infrared sensor is most used sensor in wireless technology where remote controlling functions and detection of surrounding objects/ obstacles are involved. this post will discuss about what is infrared sensor, its working principle, how it works, types, applications, advantages and disadvantages. what is infrared sensor

ir sensor is a simple electronic device which emits and detects ir radiation in order to find out certain objects/obstacles in its range. some of its features are heat and motion sensing.

ir sensors use infrared radiation of wavelength between 0.75 to 1000µm which falls between visible and microwave regions of electromagnetic spectrum. ir region is not visible to human eyes. infrared spectrum is categorized into three regions based on its wavelength i.e. near infrared, mid infrared, far infrared.

wavelength regions of infrared spectrum

near ir – 0.75µm to 3 µm
mid ir – 3 µm to 6 µm
far ir – > 6 µm
1 introduction to infrared sensor

fig. 1 – introduction to infrared sensor

working principle of infrared sensor

infrared sensors works on three fundamental physics laws:

planck’s radiation law: any object whose temperature is not equal to absolute zero (0 kelvin) emits radiation.
stephan boltzmann law: the total energy emitted at all wavelengths by a black body is related to the absolute temperature.
wein’s displacement law: objects of different temperature emit spectra that peak at different wavelengths that is inversely proportional to temperature.
key elements of infrared detection system

the key elements of infrared detection system are:

ir transmitter

ir transmitter acts as source for ir radiation. according to plank’s radiation law, every object is a source of ir radiation at temp t above 0 kelvin. in most cases black body radiators, tungsten lamps, silicon carbide, infrared lasers, leds of infrared wavelength are used as sources.

transmission medium

as the name suggests, transmission medium provides passage for the radiation to reach from ir transmitter to ir receiver. vacuum, atmosphere and optical fibers are used as medium.

ir receiver

generally ir receivers are photo diode and photo transistors. they are capable of detecting infrared radiation. hence ir receiver is also called as ir detector. variety of receivers are available based on wavelength, voltage and package.

ir transmitter and receivers are selected with matching parameters. some of deciding specifications of receivers are photosensitivity or responsivity, noise equivalent power and detectivity.

Difference Between Series and Parallel Circuits. The major difference is that the series circuits have the same amount of current flow through all the components placed in it. ... On the other hand, in parallel circuits, the components are placed in parallel with each other. This circuit splits the current flow.