Evaporation heat transfer and pressure drop characteristics of R-600a in horizontal smooth and helically dimpled tubes

The use of hydrocarbons as natural refrigerants inside small diameter channels allows charge minimization and therefore it may be an interesting option in the refrigerating and heat pump technology. The aim of the present experimental work is to fully characterize the thermal performance of propane (R290) in minichannels by measuring frictional pressure drop, condensation and flow boiling heat transfer coefficients inside a circular cross section horizontal minichannel with an internal diameter of 0.96 mm and a rough inner surface. Measurements of frictional pressure drop during adiabatic two-phase flow have been performed at mass velocity ranging between 200 and 800 kg m−2 s−1. Local heat transfer coefficients have been measured during condensation and during flow boiling in the mass velocity range from 100 to 1000 kg m−2 s−1. The present database, including frictional pressure gradient, condensation and vaporization heat transfer coefficients, is compared against predicting correlations available in the open literature.

Comprehensive experimental investigation of two-phase heat transfer and pressure drop with propane in a minichannel

In the present paper, the refrigerant mixture R32/R290 (68%/32% by weight) is investigated as the drop-in replacement for R410A in household air conditioners. The GWP of it is only 22% of that of R410A. Theoretical and experimental investigations are conducted on the performance of the air conditioners working with both R32/R290 and R410A. Experimental results show that the refrigerant charge amount of R32/R290 is reduced by 30.0%–35.0%; the cooling and heating capacities are increased by 14.0%–23.7%. For further reducing charge amount and flammability, the micro-channel heat exchanger (condenser) is employed to replace the finned tube one. Compared with the R32/R290 system using finned tube heat exchanger, the R32/R290 charge amount and the power consumption are reduced by 34.1% and 0.4%, respectively; the cooling capacity and the COP are increased by 6.4% and 6.8%, respectively.

An experimental investigation of refrigerant mixture R32/R290 as drop-in replacement for HFC410A in household air conditioners.

Simulated and experimental performance of split packaged air conditioner using refrigerant HC-290 as a substitute for HCFC-22

Performance evaluation on an internal auto-cascade refrigeration cycle with mixture refrigerant R290/R600a

This article presents simulated and experimental performance evaluations of a few selected low global warming potential refrigerants as alternatives to HCFC-22 for room air conditioners. The alternatives considered are HC-290, HC-1270, HFC-161, HFC-32, and HFC-1234yf. The performance of each alternative has been evaluated by optimizing heat exchangers, compressors, and capillary for the maximum EERAC. Experiments were also conducted as per IS 1391 Part 1 for a few alternatives, including HC-290, HFC-161, and HFC-32. HC-290 and HFC-32 gave an EERAC of 3.7. The experiments indicate that HC-290 offers the best performance, and room air conditioners that have a capacity of less than 5.2 kW can meet the exiting safety standards. The discharge temperatures of HFC-32 are relatively high and need special attention in the compressor design. HFC-161 is also a potential ultra-low global warming potential alternative to HCFC-22, once its safety classification is established.

Low GWP refrigerants as alternatives to HCFC-22 in room air conditioners

An investigation was conducted to determine whether dimples on a heat sink fin can increase heat transfer for laminar airflows. This was accomplished by performing experimental studies using two different types of dimples: 1) circular (spherical) dimples, and 2) oval (elliptical) dimples. Dimples were placed on both sides of a aluminium plate with a relative pitch of S/D=1.21 and relative depth of δ/D=0.16 (e.g., circular dimples). For oval dimples, similar ratios with the same total depth and circular-edge-to-edge distance as the circular dimples were used. For those configurations the average heat transfer coefficient, pressure drop, thermal performance and Nusselt number ratio were determined experimentally. For circular and oval dimples, heat transfer enhancements (relative to a flat plate) were observed for Reynolds number range from 600 to 2000 (Reynolds number based on channel height). Also the results are validated analytically for Nusselt number and friction factor for plain vertical plate. This experiment was undertaken to provide the needed experimental data that fill the gap for the use of dimples for laminar flow conditions. Specifically, this investigation was conducted to determine whether or not the use of dimples can enhance heat transfer characteristics for heat sink applications. Dimples enhanced heat transfer from its surface for laminar air flows while the pressure drop was equivalent or smaller than that of the flat surface. These surfaces do indeed enhance thermal performance without the penalty associated with higher pressure drops.

Experimental Study for Heat Transfer Enhancement Due To Surface Roughness at Laminar Flow

As per the accelerated phase out schedule of Montreal Protocol, HCFC-22 has to be phase out by 2020 in Article 5 countries and 2030 in non Article 5 countries. Being natural substance, HC-290 is considered as alternative to HCFC-22. In the case of HC-290, the consideration must be given to flammability. After achieving the reduction in charge of HC-290 up to 30% lower that of HCFC-22, this paper focuses on simulation studies for further reduction of HC-290 charge for air conditioners both window and split air conditioner using IMST ART v3.3. A 5.16 kW capacity window air conditioner and 4.95 kW capacity split air conditioners designed for HCFC-22 are considered. The air conditions considered are as per the Indian Standard IS 1391 (1992) Part I. First the baseline performance is established with HCFC-22 for both the air conditioners. The performance of HC-290 is predicted under drop-in condition. Under drop-in test, (replacing HCFC-22 with HC-290 without any other system changes) for both air conditioners, the cooling capacity is lower and COP is higher than that of HCFC-22. The optimized charge of HC-290 is in the range 48 to 50% that of HCFC-22 by weight. Standards like EN 378 specify the allowable charge of HC-290 in a closed space to avoid risk due to flammability. The condenser is the major component of air conditioner which contains the large amount of refrigerant. Therefore, the various combinations of low size condenser tube OD, ranging from 9.52 to 3.18 mm is considered to reduce charge with performance equivalent to HCFC-22. The lowest HC-290 charge is with 4.75 mm tube OD condenser for both window air conditioner as well as split air conditioner. For window air conditioner with 4.75 mm OD tube, the cooling capacity is 9.2% lower than that of HCFC-22 and COP is 2.9% higher than that of HCFC-22. For split air conditioner with 4.75 mm OD tube, the cooling capacity is 5.8% lower than that of HCFC-22 and COP is 7.1% higher than that of HCFC-22.

Simulated performance of HC-290 in air conditioners.

HFC-161 is being considered as an alternative to HCFC-22 in air conditioner. Thermo physical properties of HFC-161 are closer to HCFC-22. The flammability of HFC-161 needs to be addressed while using in air conditioner. A typical split packaged air conditioner with nominal cooling capacity of 5.2 kW that was originally designed for HCFC-22 was selected for performance evaluation in psychrometric chamber. Test conditions considered are as per IS 1391 part 1. Air conditioner performance was evaluated for capacity rating test conditions. Initially, baseline performance was established with HCFC-22. Then HFC-161 was used as drop-in for HCFC-22. Under drop-in test, the cooling capacity of HFC-161 was 10.1% lower than that of HCFC-22 and EER was 19.7% higher compared to HCFC-22. The optimized HFC-161 charge under drop-in was 385g. This was 51% of HCFC-22. In order to achieve equivalent cooling capacity of HCFC-22, modified capillary was considered in another test. In this test, HFC-161 gave 7.1% lower cooling capacity and 17.7% higher EER than that of HCFC-22.

Kundlik V. Mali

Papers

Simulated and experimental performance of split packaged air conditioner using refrigerant HC-290 as a substitute for HCFC-22

Low GWP refrigerants as alternatives to HCFC-22 in room air conditioners

Experimental Study for Heat Transfer Enhancement Due To Surface Roughness at Laminar Flow

Simulated performance of HC-290 in air conditioners.

Performance assessment of air conditioner using HFC-161.