Design and Development of a Sustainable Shell and Tube Heat Exchanger for Use in a Higher Institution

Abstract

A heat exchanger can be defined as a thermo-fluid device that is used to transfer heat between two media, from a heat sink and to a heat source. This heat transfer is driven by the temperature differential between the former and the latter. The purpose of this work is to design, fabricate and test a shell and tube type heat exchanger which students can use to learn the basic principles of a heat exchanger. The heat exchanger was fabricated using gas wielding technique. It has two circuits – a hot water circuit and a cold water circuit. Two 1500 kW heaters serve as the source of heat for the hot water circuit which circulates under gravity when heated. The cold water circuit has an 0.55 kW (0.7375621 HP) centrifugal pump which effects water circulation. A digital thermometer was used to measure the temperature of fluids at specific intervals. The temperature of the cold water circuit increased on the average at 2.3oC while that of the hot water increased at 7oC. The LMTD was computed to be 4.690oC. While the effectiveness of the heat exchanger was 0.790. The results obtained from this work, was captured succinctly by Salby, (1999): The second law of thermodynamics is inspired by the observation that the quantity q/T (q is heat content and T is temperature) is independent of path under reversible conditions. One of the several statements of the second law, the Clausius inequality, has the consequences that pertain to the direction of thermodynamic processes: first, heat must be rejected to the environment somewhere during a cycle; second, under reversible conditions, more heat is exchanged at high temperature than at low temperature; and third, irreversibility reduces the net heat absorbed during a cycle. The first consequence precludes the possibility of a process that converts heat from a single source entirely into work: a perpetual motion machine of the second kind. The second consequence implies that net work is performed by the system during a cycle if heat is absorbed at high temperatures and rejected at low temperatures. The third consequence implies that irreversibility reduces the net work performed by the system, in the case of a heat engine, and increases the net work that must be performed on the system, in the case of a refrigerator.