Answered step by step
Verified Expert Solution
Link Copied!

Question

1 Approved Answer

A large hot surface is positioned L = 0.2 m away from an equally large parallel surface with very low thermal conductivity. Previously. the

image

A large hot surface is positioned L = 0.2 m away from an equally large parallel surface with very low thermal conductivity. Previously. the hot surface was cooled by continuously pumping water along its surface using an 125 W pump. The electricity used to power the pump was priced at 0.39 per kWh. It is now proposed to add an array of equally-spaced fins to the hot surface, with the length of the fins equal to the gap between the two surfaces, such that the tip of each fin is just in contact with the surface with very low thermal conductivity, as shown in the figure. The fins will be manufactured from aluminium, which has a thermal conductivity of k = 180 W/mK. The temperature on the hot surface is 323 K, and the temperature of the surrounding air is 298 K. The heat transfer coefficient between the fins and the air is h = 20 W/mK. Surface with very low thermal conductivity Fins Hot surface Lm a) By considering maximum effectiveness, demonstrate whether circular- or square-cross section fins should be used. Assume that the cross sectional area is A = 0.0004 m for whichever geometry is chosen. Type your chosen cross section here (either circular or a) By considering maximum effectiveness, demonstrate whether circular- or square-cross section fins should be used. Assume that the cross sectional area is Ac = 0.0004 m for whichever geometry is chosen. Type your chosen cross section here (either circular or square): b) What is the efficiency of a single fin with the cross section chosen in part a)? Give your answer to the nearest whole number as a percentage (e.g. 54.32% would be given as 54): c) To maintain a constant temperature at the surface, 2500 W of heat must be removed by the fins (as this was previously removed by the water). Using the cross section identified in part a), how many fins will be required? Give your answer as a whole number: d) Given that aluminium costs 0.70 per kg, and its density is 2710 kg/m, how long will it take for the extra material cost to be paid back by the reduced operating cost when the fins replace the pumped water system? Give your answer to the nearest whole number of days:

Step by Step Solution

There are 3 Steps involved in it

Step: 1

blur-text-image

Get Instant Access to Expert-Tailored Solutions

See step-by-step solutions with expert insights and AI powered tools for academic success

Step: 2

blur-text-image_2

Step: 3

blur-text-image_3

Ace Your Homework with AI

Get the answers you need in no time with our AI-driven, step-by-step assistance

Get Started

Recommended Textbook for

Management Accounting

Authors: Leslie G. Eldenburg, Albie Brooks, Judy Oliver, Gillian Vesty, Rodney Dormer, Vijaya Murthy, Nick Pawsey

4th Edition

0730369382, 978-0730369387

More Books

Students also viewed these Mechanical Engineering questions

Question

1.10 Describe the medical model of abnormal behavior.

Answered: 1 week ago