Heat Exchanger And Design Of Thermal Systems: Heat Exchanger Design Essay

Question:

Discuss about the Report for Heat Exchanger and Design of Thermal Systems of Heat Exchanger Design.

Answer:

Introduction

The report is about the design of a condenser for 100 cubic meter cool room at 3 Degrees Celsius and R134a. A condenser is a kind of heat exchanger in which vapors are changed into liquid state by removing the latent heat with the aid of a coolant like water. There are two main types of condensers namely the type where the coolant and condensing vapor come into direct contact and the type where the coolant and condensate stream are differentiated by a solid surface, specifically a tube wall.

Problem Statement

The is need to attain a proper design of a condenser as a form of heat exchange with a fliud that optimizes the heat generated and provides the best result. The rationale for choosing the R134a revolves around its various advantages over other possible selections. Such advantages include the idea that it uses low price of the fluid (Caputo, Pelagagge, & Salini, 2008). In addition, R134a employs the technology that is already generally studied and entrenched, and with verified formulas for condensation experiments (Tarrad & Altameemi, 2015). Further, the R134a condenser is efficient because it utilizes the economic turbines for the expansion that is already available in the market. Moreover, the fluid used by the R134a condenser does not have the uppermost efficiency measures, both for the heat exchange and the generation of energy (Laskowski, 2012).

Operating conditions and parameters based on worst scenario

Design of Shell and Tube Heat Exchangers

Several methods can be used in this design such as:

i. Kern method

This method does not cater for the bypass and leakage streams

It is simple to apply and precise enough for preliminary design computations

It is usually restricted to a fixed baffle cut of about 25 percent

ii. Bell-Delaware method

This is the most widely used method that considers the leakage through the openings between tubes and baffles and the baffles and shell and bypassing of flow of the fluid around the gap between tube bundle and the shell.

iii. Stream Analysis method

This is a more rigorous and generic method that is appropriate for computer estimations and forms the basis for most of the commercial computer codes.

Construction Details

i. The Tube Dimensions

The Tube diameters in the range 16 mm and 50 mm

Smaller diameters of up to 2.54 cm are preferred since this produces a compact and affordable heat exchanger

The larger tubes are used mainly for heavily fouling fluids

The suitable steel tubes are BS 3606 although other tubes can be used such as the BS 3274

The Preferred tube lengths range between 6 ft and 24 ft

The optimum tube length to shell diameter ratio is approximately between 5 and 10

An estimated value of 19 mm is the suitable tube diameter for the worst scenario cases

ii. The Tube Arrangements

The tubes normally arranged in equilateral triangular, rotated square patterns or square

The Tube pitch, Pt, is computed as OD multiplied by 1.25

iii. The Shells

The Shell will be put at a close fit to the tube bundle to minimize bypassing

The Shell-bundle clearance will be based on the type of heat exchanger (R134a)

iv. Shell-Bundle Clearance

The chosen Bundle diameter depends on not only number of tubes but also the number of tube passes

The other parameters for the design include

Nt = the number of tubes

Db = the bundle diameter

D0 = tube outside diameter

Moreover, n1 and K1 are constants

v. The Baffles

The single segmental baffle will be used for the purpose of

Directing the fluid stream across the tubes (Bhatnagar & Bartaria, 2012)

Increasing the fluid velocity

Improving the rate of transfer

The optimal baffle cut for the design is 45%

Literature Review

All air conditioners have four fundamental constituents and these include an expansion valve, a pump, an evaporator, and a condenser. In addition, they operate using a working fluid as a prinary medium and another opposing fluid medium. It implies that two air conditioners may seem completely different in configuration, size, shape but they would operate in essentially in a similar manner (Bhatnagar & Bartaria, 2012). This is due to the broad range of applications and energy sources existing. Most air conditioners obtain their power from a combination of an electrically-driven motor and pump to circulate or pump the refrigerant fluid. A number of natural chillers that are gas-driven couple the pump with a gas engine to produce considerably additional torque.

It is also worth mentioning that as the refrigerant or working fluid circulates through the air conditioning system at significantly evelated pressure through the pump, it jets into an evaporator whereby it transforms to achieve a gaseous state. In the process, the working fluid takes away heat from the opposing fluid medium and operates in the same way as the heat exchanger (Bell, 2004). The working refrigenrant subdesuently enters into to the condenser, where it releases heat to the ambient by condensing back into a liquid state (Laskowski & Lewandowski, 2015). The working fluid attains its former low pressure state after passing through an expansion valve. When the cooling medium that can be a fluid or air passes close to the evaporator, substantive quantity of heat is drawn to the evaporator. As a result, the process efficiently cools the opposing medium thereby aiding in the localized cooling within the building (Capata & Zangrillo, 2014). The olden times air conditioners used freon as their working refrigenrant, but due to the harmful effects freon poses to the environment, it is no longer widely used. The contemporary designs have met stern challenges to develop the efficiency of a unit, while utilizing a substandard substitute for the freon as a refrigerant (Walawade, Barve, & Kulkarni, 2012).

Design Drawing

The drawing of the design of the condenser is as shown below.

The parts of the design are as shown below

The geometry of the baffle is as shown in the drawing below

Materials List

Part

Use

Plastic

used to reduce weight and cost

Copper or aluminum tubing

provides better-quality thermal properties and a positive impact on the efficiency of the system

Paint or powder coating

to protect sheet metal

Water as a working fluid

Is the fluid that circulates through the air-conditioning setup

References

Bell, K. (2004). Heat Exchanger Design for the Process Industries. J. Heat Transfer, 126(6), 877.

Bhatnagar, P., & Bartaria, V. N. (2012). Numerical Analysis of a Surface Condenser Design. International Journal of Innovative Research and Development ISSN 2278– 0211, 1(5), 223-231.

Bhatnagar, P., & Bartaria, V. N. (2012). Surface Condenser Design-A Review. International Journal of Innovative Research and Development ISSN 2278–0211, 1(5), 438-449.

Capata, R. & Zangrillo, E. (2014). Preliminary Design of Compact Condenser in an Organic Rankine Cycle System for the Low Grade Waste Heat Recovery. Energies, 7(12), 8008-8035.

Caputo, A., Pelagagge, P., & Salini, P. (2008). Heat exchanger design based on economic optimisation.Applied Thermal Engineering, 28(10), 1151-1159.

Laskowski, R. M. (2012). A mathematical model of a steam condenser in off-design operation. J. Power Technol, 92(2), 101-108.

Laskowski, R., & Lewandowski, J. (2015). Simplified correlation for steam condenser effectiveness under off-design conditions as a function of inlet parameters. Journal of Power Technologies.

Tarrad, H., & Ali Farhan Altameemi, A. (2015). Experimental and Numerical Model for Thermal Design of Air Cooled Condenser. Global Journal of Research In Engineering, 15(3).

Walawade, S. C., Barve, B. R., & Kulkarni, P. R. (2012). Design and Development of Waste Heat Recovery System for Domestic Refrigerator.IOSR Journal of Mechanical and Civil Engineering, 28-32.

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