Heat Transfer Homework

Heat Transfer Homework-29
Visit Stack Exchange I have huge vessel filled with $CH_4$ and another vessel filled with hydrogen. Assuming the heat transfer coefficients are same, the $CH_4$ would cool faster compared to the hydrogen vessel, this is because the hydrogen vessel has larger heat content and takes more time cool to ambient. Yes, it takes more energy (heat is a type of energy) to heat up the substance with the greater heat capacity, all other things (such as $\Delta T$, and mass) being equal.Lets assume they have the same mass of gas say kg$. Since the heat capacity of hydrogen is greater than that of $CH_4$ (for $H_2$ it is KJ/kg-K$ and for $CH_4$ it is .889KJ/kg-k$), the amount of heat absorbed to raise the temperature of hydrogen is greater than $CH_4$ This is because $Q=m C_P\Delta T$ and m and $\Delta T$ are same for both $H_2$ and $CH_4$, $C_P$ is higher for hydrogen. If both substances have the same heat transfer coefficient (measured in units of power per unit temperature per unit area), then the one with the greater heat capacity will cool down more slowly, all other things (critically geometry of container) being equal.

Visit Stack Exchange I have huge vessel filled with $CH_4$ and another vessel filled with hydrogen. Assuming the heat transfer coefficients are same, the $CH_4$ would cool faster compared to the hydrogen vessel, this is because the hydrogen vessel has larger heat content and takes more time cool to ambient. Yes, it takes more energy (heat is a type of energy) to heat up the substance with the greater heat capacity, all other things (such as $\Delta T$, and mass) being equal.Lets assume they have the same mass of gas say kg$. Since the heat capacity of hydrogen is greater than that of $CH_4$ (for $H_2$ it is KJ/kg-K$ and for $CH_4$ it is .889KJ/kg-k$), the amount of heat absorbed to raise the temperature of hydrogen is greater than $CH_4$ This is because $Q=m C_P\Delta T$ and m and $\Delta T$ are same for both $H_2$ and $CH_4$, $C_P$ is higher for hydrogen. If both substances have the same heat transfer coefficient (measured in units of power per unit temperature per unit area), then the one with the greater heat capacity will cool down more slowly, all other things (critically geometry of container) being equal.

FIND: (a) Equivalent thermal circuit, (b) Expression for heater temperature, (c) Ratio of outer and inner heat flows and conditions for which ratio is minimized.

ASSUMPTIONS: (1) One-dimensional, steady-state conduction, (2) Constant properties, (3) Isothermal heater, (4) Negligible contact resistance(s).

Convective coefficients on the inside and outside surfaces of a window are 20 W/m 2 - K and 15 W/m 2 - K, respectively.

What temperature drop will exist across each of the glass panes?

What will be the average temperature of the air between the glass panes? Ts =° 100 c Tcsurrounding= 25 ° Air space 0.8cm wide Window glass--0.32 cm thick Solution: q R Ri − ==× − ==× 3 0 − ==× q W ∑R Air space 0.8cm wide 250k hi 295k h 0 Window glass 0.32 cm thick Ti To Ri RGL RAS RGL Ro KNOWN: Hot water pipe covered with thick layer of insulation.

FIND: Sketch temperature distribution and give brief explanation to justify shape. Fw-300 #ya-qn-sort h2 /* Breadcrumb */ #ya-question-breadcrumb #ya-question-breadcrumb i #ya-question-breadcrumb a #bc .ya-q-full-text, .ya-q-text #ya-question-detail h1 html[lang="zh-Hant-TW"] .ya-q-full-text, html[lang="zh-Hant-TW"] .ya-q-text, html[lang="zh-Hant-HK"] .ya-q-full-text, html[lang="zh-Hant-HK"] .ya-q-text html[lang="zh-Hant-TW"] #ya-question-detail h1, html[lang="zh-Hant-HK"] #ya-question-detail h1 /* Trending Now */ /* Center Rail */ #ya-center-rail .profile-banner-default .ya-ba-title #Stencil . Bgc-lgr .tupwrap .comment-text /* Right Rail */ #Stencil . Fw-300 .qstn-title #ya-trending-questions-show-more, #ya-related-questions-show-more #ya-trending-questions-more, #ya-related-questions-more /* DMROS */ .SCHEMATIC: ASSUMPTIONS: (1) Steady-state conditions, (2) One-dimensional (radial) conduction, (3) No internal heat generation, (4) Insulation has uniform properties independent of temperature and position. 2.1, for this one-dimensional (cylindrical) radial system has the form This relation requires that the product of the radial temperature gradient, d T/dr, and the radius, r, remains constant throughout the insulation.For our situation, the temperature distribution must appear as shown in the sketch.FIND: Ratio KNOWN: Expression for the local heat transfer coefficient of air at prescribed velocity and temperature flowing over electronic elements on a circuit board and heat dissipation rate for a 4 ⋅ 4 mm chip located 120mm from the leading edge. SCHEMATIC: COMMENTS: (1) Note that the estimated value for Tf used to evaluate the air properties was reasonable.(2) Alternatively, we could have evaluated chip h by performing the integration of the local value, h(x).Don't show me this again This is one of over 2,200 courses on OCW. Find materials for this course in the pages linked along the left. Use OCW to guide your own life-long learning, or to teach others. KNOWN: A spherical shell with prescribed geometry and surface temperatures.FIND: Sketch temperature distribution and explain shape of the curve. 2 1 1 1 2 2 1 0 dd Tq r rdr dr k dd Tqr r dr dr k d T q rrc dr k d T q c dr k r d T r C dr qr c k 2 2 22 max 2 max 62 RR R R R R q R Tr R T C T k q TT R r a k TTr q R TT k 2 62 2 max surface qq V q Wmk T TK TKKKc TKb i  KNOWN: Conditions associated with a composite wall and a thin electric heater.

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