Reference no: EM133141573

ENME2TH Thermodynamics

Problem Statement

If the operation of the standard Brayton heat engine cycle is reversed, it can be transformed into a refrigeration or heat pump cycle. Thus, instead of generating a net work output from a net heat input, this "reverse Brayton cycle" employs a net work input to transport heat from a cold environment to a warm environment.

Based on your own independent research, you are required to design a refrigerator that operates according to the reverse Brayton cycle, which is capable of removing heat from a liquid at -50 °C at a rate of 20 kW, and rejecting it to the external atmosphere, which has a temperature of 30 °C.

Your design should:
• Feature the following components: one compressor, one low temperature heat exchanger, one high temperature heat exchanger and one turbine
• Employ a gas which is suitable for use as a working fluid
• Operate as efficiently as possible
• Account for obvious non-ideal effects which would realistically reduce its efficiency

The design calculations you perform should enable the evaluation of the following key parameters:
• The pressure and temperature of the working fluid at the inlet of each component
• The change in the specific entropy of the working fluid across each component
• The mass flow rate of the working fluid
• The power developed by the turbine
• The pressure ratio of the compressor
• The rate at which heat is rejected by the refrigerator
• The refrigerator's coefficient of performance

Report Requirements

You are required to present your design in the form of a summary report, which should:
• Display all calculations performed

• Indicate all assumptions made in performing your calculations, including assumptions related to the components themselves, such as efficiencies, temperature drops, etc.
• Provide an explanation of the purpose of each calculation step
• Provide a fully-labelled schematic showing the layout of the refrigerator's components
• Provide a fully-labeled T-s diagram of the thermodynamic cycle associated with the refrigerator
• Provide confirmation that the refrigerator's operation will not violate the 2nd Law of Thermodynamics

The order in which the above information is presented in your report is left to your discretion, but it should be logical. Reports MUST be limited to a maximum of 5 pages in length, and MUST NOT contain a cover page, or introduction, discussion or conclusion sections. References must be provided where necessary.

The following report marking criteria should be also be considered (allotted marks are shown in brackets):
• Completeness - Does the report meet all of the requirements stated above?
• Presentation - Is the report free of spelling and/or grammatical errors? Are its contents delivered in a clear and logical manner? Are the diagrams that it includes clear and fully-labelled?
• Calculation accuracy - Do the calculations contain any significant errors? Are the units associated with each calculated value clearly stated and applied correctly?
• Explanations - Is the purpose of each calculation step clearly, concisely and accurately conveyed? Have all assumptions made been clearly identified and justified?
• Model sophistication - Does the thermodynamic model developed for the refrigerator adequately capture real-word non-idealities?
• Feasibility - Does the design make engineering sense? Would it be practical to implement?

Attachment:- Thermodynamics.rar