You have been asked to size a water heating system for camping. the system is a simple black polyethylene bag filled with 1 gallon of water laid flat in the midday sun. the solar absorptivity of polyethylene black plastic is 0.94 and the emissivity to the sky is 0.92. the water is initially at 50°f and needs to be heated to 110°f in 4 hours. at 80°f the density of water and specific heat are 62.215 lbm/fts and 1.00 btu/lbm-°f, respectively. the radiative and convective losses will be higher at higher temperatures, as a result you will need to design the water heating bag based on the highest temperature. the bag is well insulated from the ground and there will no losses due to conduction to the ground it will be placed on folded sleeping bag). at the design conditions the convective heat transfer coefficient is 0.215 btu/ft2-h-°f, the air temperature is 60°f, the temperature of the sky is -15°f, the solar irradiation is 150 btu/ft2-h. a. how much energy is required to heat the water (btu)? b. what is the solar heat flux absorbed by the bag at design conditions (btu/h-ftz)? c. what are the convective heat flux losses of the bag at design conditions (btu/h-ft)? d. what are the radiative heat flux losses of the bag at design conditions (btu/h-ft)? e. how much usable heat flux is provided to the bag at design conditions (btu/ft2-h)? f. what should the exposed surface area of the bag be ( g. how long would it take to heat the bag if the convective heat transfer coefficient were 3 times larger (h)?

Iactually don’t know but i know someone you can ask

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.