Energy analysis plays a vital role in the industry due to the use of electrical energy, global warming, and economy crises. This paper describes the waste heat available in the exhaust of the steam turbine and beneficial use of the waste heat. The sugar industry steam turbine exhaust carries enthalpy of steam at 2500 kJ/kg, this thermal energy can be put into beneficial use as the heat source to the vapor absorption refrigeration system to compensate energy required for DC thyrist motor, and this can also be used for cold storage. Energy savings in terms of cost and fuels are calculated. Investigation on the heat and mass transfer in evaporator has been carried out in vapor absorption system by varying the operating parameter. Less circulation ratio is required to increase the coefficient of performance. The inlet temperature of the coolant should be less for achieving higher coefficient of performance.
Fixed-bed regenerator is a type of air-to-air energy exchanger and recently introduced for energy recovery application in HVAC systems because of their high heat transfer effectiveness. Testing of FBRs is essential for performance evaluation and product development. ASHRAE and CSA recently included guidelines for testing of FBRs in their respective test standards. The experiments on FBRs are challenging as they never attain a steady state condition, rather undergoes a quasi-steady state operation. Before reaching the quasi-steady state, FBRs undergo several transient cycles. Hence, the test standards recommend getting measurements after one hour of operation, assuming FBR attains the quasi-steady state regardless of test conditions. However, the exact duration of the initial transient cycles is unknown and not yet studied so far. Hence, in this paper, the duration of FBR's transient operation is investigated for a wide range of design and operating conditions. The test standards' recommendation for the transient duration is also verified. The major contributions of this paper are (i) quantifying the effect of design parameters (NTUo and Cr*) on the duration of transient operation and (ii) investigation of the effect of sensor time constant on the transient temperature measurements. The results will be useful to predict and understand the transient behavior of FBRs accurately.
A small-scale test facility is developed to determine the sensible effectiveness of a Fixed-Bed Regenerator (FBR) and the results are used to validate a numerical model. The numerical and experimental results for quasi-steady-state conditions are in a good agreement within the experimental uncertainty bounds. At quasi-steady-state condition, the outlet temperature of FBR varies with time but cyclically repeats itself; this is an important difference between FBR (regenerator) and recuperator heat exchangers. The outlet temperature of recuperator heat exchangers reaches a constant value during the steady-state operation. The quasi-steady-state temperature profile is used to determine the sensible effectiveness of FBRs.
However, FBRs undergo several cycles to reach the quasi-steady-state condition. The prediction of the duration of the transient duration of FBR is important for performance testing that could save money and time. CSA (Canadian Standards Association) recommends operating FBR for at least one hour to achieve a quasi-steady-state condition. This paper addresses the heat transfer behavior of FBRs during their transient operation. The initial transient cycles depend on the cycle period of FBR, air flow rate and the thermal condition of the exchanger at the beginning of the test. The small-scale FBR test facility is used to study the transient behavior of FBRs and this is the main focus of this paper.
The temperature profile during the transient condition of FBR is obtained and the results are compared with the numerical model. The effects of the mass flow rate of air and the cycle duration on the transient period of FBR are studied. The results show that FBR reaches a quasi-steady state operation in less than 30 minutes. The results will be useful for understanding the time required for performance testing, which will reduce the cost and time of each test.
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