Performance evaluation of hot-gas by-pass capacity control schemes for refrigeration and air-conditioning systems

M. Yaqub, Syed M. Zubair*, Jameel Ur Rehman Khan

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

30 Scopus citations


The capacity control of a vapor-compression refrigeration system is investigated by injecting hot gas and liquid refrigerant into the suction side of the compressor. Three different possibilities for the by-pass schemes are investigated for HFC-134a by considering finite size of the components that are used in the refrigeration systems. The model considers the finite-temperature difference in the heat exchangers, thus allowing the variations in the condenser and evaporator temperatures with respect to capacity and external-fluid inlet temperatures. It is demonstrated that the compressor discharge temperatures increase significantly when the hot-gas from the compressor discharge is extracted and injected (without any liquid injection) directly into the suction side of the compressor. A comparative study is also performed of these schemes in terms of the system coefficient of performance (COP), operating temperatures and the refrigerant by-pass fraction as a function of the percentage capacity reduction.COP Coefficient of performanceh Enthalpy (ṁ Mass-flow rate of refrigerant (kg.s-1)Q̇ Capacity of the evaporator or condenser (kJ.s-1)R Liquid to total by-pass ratio of the refrigerantT or t Temperature (°C)y By-pass fraction of refrigerant(εĊ) Product of heat-exchanger effectiveness and fluid-capacitance rate (kW.K-1)η Compressor efficiencySubscripts1 to 6 state pointscond condenseref,c external-fluid condenseref,e external-fluid evaporatorevap evaporatorref refrigerantSuperscriptin inlet

Original languageEnglish
Pages (from-to)543-561
Number of pages19
Issue number6
StatePublished - Jun 2000

Bibliographical note

Funding Information:
The authors acknowledge support provided by King Fahd University of Petroleum and Minerals for this research project.

ASJC Scopus subject areas

  • Civil and Structural Engineering
  • Building and Construction
  • Pollution
  • Mechanical Engineering
  • Industrial and Manufacturing Engineering
  • Electrical and Electronic Engineering


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