센겔 앤 볼스 열역학 5th 솔루션4-2

소개글

센겔 앤 볼스 열역학 5th 솔루션입니다.

목차

Closed System Energy Analysis: Solids and Liquids

본문내용

4-74 A number of brass balls are to be quenched in a water bath at a specified rate. The rate at which heat needs to be removed from the water in order to keep its temperature constant is to be determined.
Assumptions 1 The thermal properties of the balls are constant. 2 The balls are at a uniform temperature before and after quenching. 3 The changes in kinetic and potential energies are negligible.
Properties The density and specific heat of the brass balls are given to be ρ = 8522 kg/m3 and cp = 0.385 kJ/kg.°C.
Analysis We take a single ball as the system. The energy balance for this closed system can be expressed as
)()(21out12balloutenergies etc. potential, kinetic, internal,in Changesystemmass and work,heat,by nsferenergy traNet outinTTmCQuumUQEEE−=−=Δ=−Δ=−4342143421
The total amount of heat transfer from a ball is
kJ/ball 88.9C)74120(C)kJ/kg. 385.0)(kg 558.0()(kg 558.06m) 05.0()kg/m 8522(621out333=°−°=−=====TTmcQDmππρρV
Waterbath,50°C
Brassballs,120°C
Then the rate of heat transfer from the balls to the water becomes
kJ/min 988=×==)kJ/ball 88.9(balls/min) 100(ballballtotalQnQ&&
Therefore, heat must be removed from the water at a rate of 988 kJ/min in order to keep its temperature constant at 50°C since energy input must be equal to energy output for a system whose energy level remains constant. That is, .

참고 자료

없음