Question

Please answer question 2.

Quastion 1 answer is already provided in the photos.

1. At an outdoor lot, there is a black-colored solar heat collection copper pipe. It is 50 meters long, 10 cm in inner diameter and 10.2 cm in outer diameter. The pipe is set horizontally. Assume that solar radiation in 1.0 kW/m2 shines on the entire surface of the pipe and convert 90% of the solar energy on the pipe into heat. There is water in 25 °C flowing in the pipe at a velocity of 0.05 m/s to be heated. The ambient air temperature is 25 °C. Also, radiation heat from tube goes to a surrounding of 25 °C. Please decide the temperature of the water at the exit of the pipe. Hint: Natural convection heat loss for horizontal pipes is available from class note or any Heat Transfer Textbooks. We can assume the water exit temperature, with which the heat can be calculated and thus the wall temperatures are calculated, and heat loss to outside is calculated. If heat loss and the heat going into the tube equals to absorbed heat, the calculation stops. Otherwise, assumption has to be made again. Take the entire tube as one section, as an example: 1) From C( ), let assume T to find the 0 and T, 2) with heat transfer coefficient, find T-= T, +a /(DLA, ) and then 2LK 3) Calculate QR-wo-rD,L*σ(T4-298.154) and QNC-rDLh,"(7,,-298.15) Where heat transfer coefficient is for pipe internal flow determined with Re, Pr. 4) If h is different from O, then need to assume T, one more time. 2. Extra problem for graduate student 0.9 1000- Cose- If the above heating system is used to heat water of 2000 kg from 25 °C to 50°C, how long time does it take? Hint: Consider that every At time, for example, 5 minutes, the heat obtained from the heater heats up the entire pool of water. It will raise the inlet tem perature of the heater for the next Δt time. This goes on and on. After certain number of At, the temperature of the pool of water will rise to the desired temperature. al 5om Copper pipe Lek Veloc:t o.os rys of Suonoundi a Temperatwe Heat thnough sola Heat loss ion 80ing ivko = through yodiakion the uoate Heat absosnbad b the ota Piooing into the tube Solan oiation rake o m conversion 90% tsians faned I kw Rackaton heat antien rate fevio Ppe in clatro block s -飞 IYるJY .18 w E 7.16 Kw 8.8S Rab (23.85-I3 2 1녀.sz ab 7.26 kw T a mop Cat) Pab 흖 le.lot)? xo.os x ooo.**18 s (76-1s") 4.5 32/4 11185 (76-25) 106S60 11 x2 35S 38 413s (7%- 2S)76q 418 S 石: 29.24 The temporatune of He octo ak exist empevatsane oP He 29. 24

Answer 1

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