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By Paul H. Johnson

Heap leaching is a simple means of recovering copper from oxide and oxide-sulfide ores. Although this method requires relatively low capital investment, it suffers from low copper recoveries and relatively high acid consumption. The objectives of this study were (1) to determine what factors influence these shortcomings, and (2) to establish a basis of correlation. between laboratory and field testing. The principal methods of leaching copper ores at the present time are heap, dump, in-place, and vat. A number of references are presented in the bibliography on the theoretical and practical aspects of these methods. In the heap-leaching method, crushed or uncrushed oxidized copper ore is placed on a prepared drainage pad. Acid leach solutions are dis¬tributed over the top of the heap, caused to percolate downward through the ore bed by gravity, and are drained from its base. The leach duration is generally a matter of a few months. Dump leaching is used to recover copper from very low-grade oxide-sulfide pit-waste materials. Here again, leach solutions are, percolated downward through a heap. However, in this method, little or no acid is added to the leach liquors, prepared drainage pads are not used and the leaching cycle is generally measured in terms of several years. Leaching agents are usually autogenously generated by the breakdown of sulfide minerals within the dump.

Jan 1, 1970

By W. Robert Rose, Randall Pyper, Carlos Mirabal, Jaime Eguivar

In 1984, work was started to determine the viability of heap leaching silver-containing waste dumps from Cerro Rico near Potosi - Bolivia, at an elevation of 4300 meters (14 100 it.). The result today is an unusual heap leach utilizing fine crushing, grinding, and agglomeration to process 1000 tonnes per day of ore containing 200 g/tonne silver. The unique metallurgical, economic, and political factors will be discussed which led to the decision to build a heap leach rather than a conventional agitation leach plant. Capital and operating costs will be given along with some of the uncommon process design and equipment problems encountered while developing the operation.

Jan 1, 1990

By R. Bruce Thorndycraft

This paper will describe several modifications to design of con­ventional oxide gold heap leaching. They are targeted at reduc­ing costs and simplifying heap operations. These modifications were conceptualized during consulting work on over 90 differ­ent heap leaches. In 1995, a unique opportunity arose to imme­diately apply all of these design concepts to the permitting and construction of a new facility at the American Girl Mine in southeastern California. American Girl Mine has operated since 1987. In April 1995, the mine faced a situation with grave consequences for cash flow. Approval for mining of a new ore zone, Oro Cruz, had just been granted, after lengthy delays by California regula­tors. All existing pad space would be filled by October. Only 6 months were available, and new pad siting and design were still undecided. Permitting of a new pad had not begun. Options were quickly reviewed. A strong criteria for pad site selection and design was ease of permitting. There was also a strong desire to install a system that would achieve better met­allurgical recovery and reduced operating costs, compared to previous heaps at this mine. One site offered the best chance for rapid permitting. It was the site of the original 1987-90 heap leach. This already dis­turbed ground contained 1.6 million tons of heaped ore. The old heap had just completed detoxification and was about to be signed off as a Group C waste, ready for reclamation. Instead of recontouring and revegetating the old heap, which the reclamation plan anticipated, we offered BLM and the County something even better. We proposed to off-load much of the detoxed old heap, and reuse the space. The off-loaded material would be back-filled into the original open pit, imme­diately adjacent. While the footprint of the proposed new pad was much larger, the reuse of disturbed ground, and backfilling of the open pit, had very strong appeal to the regulators. Our permitting strategy included the technical design of the proposed new facility. Many of the new design details also appealed to the regulators, particularly the "zero active ponds" concept.

Jan 1, 1996

By Thomas J. DeMull

Heap leaching was introduced to the precious metals mining industry approximately two decades ago as a simple, low cost method for recovering gold and silver from ores. Since that time, operational experience has contributed to knowledge and understanding of the process, making it a reliable alternative to conventional milling processes for low grade ores. At time of this writing, dozens of heap leach operations are active producing hundreds of thousands of ounces of gold and millions of ounces of silver annually. These successes have caused the popular press to acclaim heap leaching "high-tech" gold mining, but, despite the hype, the process remains a simple one. An example of simplicity in heap leaching is the operation established in 1986 at Amax Gold's Sleeper Mine. Starting with a simple goal, namely to produce gold from sub-mill grade ore at low cost, heap leaching was rapidly implemented at Sleeper; only five months after testwork started, leaching commenced on the first commercial scale, 50,000 ton heap of low grade ore. Sized at 600,000 tons per year to produce 10,500 oz gold per year, the low grade heap operation has performed beyond expectations. During the first year of production, 881,800 tons have been leached producing 15,665 oz of gold and 35,528 oz of silver. Operating ·costs for the first year have averaged $112 per oz gold produced ( or $95 per oz if silver credit is included). Successful implementation of heap leaching at Sleeper has had a dramatic impact on ore reserves and future operations.

Jan 1, 1998

By Paul Chamberlin

Although performing a heap leach test is inherently simple, a lot of information beyond extraction, leach time, and reagent consumption can be obtained from a well designed test program. The following is a list of information to look for and acquire when performing column tests and field heap leach tests.

Jan 1, 1998

By Allan Neal, Jess W. Smith

FirstMiss Gold Inc., formerly FRM Minerals, Inc., is heap leaching gold from difficult, low grade ores at the Getchell Gold Mine in Humboldt County, Nevada. A two-thousand ton per day facility is leaching material from waste dumps from old operations and from small, satellite deposits around the main orebody. A three-thousand ton per day pressure oxidation mill is under construction to treat sulphide gold ores in the main deposit. The Getchell gold deposit occurs in a wide fault zone in carbonaceous, calcareous sediments and intrusive rocks. Intense clay alteration is typical within the mineralized zones. Silicification is a less dominant alteration phase within the ore. Gold in the upper oxide portion of the deposit occurs both in a free state which is leachable and complexed in fine disseminated pyrite which is not leachable. Gold in the lower sulphide portion of the deposit is almost entirely complexed in pyrite. Abundant arsenic sulphides and variable amounts of remobilized carbon are associated with the gold mineralization throughout the deposit. The waste dump material being heap leached was derived from the upper portions of the gold deposit. The dumps contain high quantitites of fines, clays and sulphides of iron, arsenic and other trace elements. No stockpiling of low grade materials was attempted during the old mining operations, therefore, the dump material is highly variable and unpredictable. A sample of representative material from one dump contained the following:

Jan 1, 1998

By E. A. Devuyst, G. H. Robbins

The Inco process can be retrofitted into a typical heap operation with minimum capital. Capital cost for a mid to large size heap would be less than 1 cent/ton. Operating costs are typically in the order of 8 cents/ton. Ammonium bisulphite is the preferred reagent. The process provides the equivalent of fresh water r?1s­ing and thus minimizes the time of the _nnse program. A typical heap (the Snow Caps Mine, California) was rinsed completely

Jan 1, 1996

By Robert G. Woolery

Union Carbide_ began looking seriously at heap leaching in 1971. At that time some 1.6 million tons of mineral averaging 0.040% U308 were stockpiled at various sites around the Gas Hills, Wyoming, uranium facility. Several alternatives for economically exploiting these reserves were considered and heap leaching seemed the most attractive. At the time, Western Nuclear Inc. was operating a heap leach project nearby in which the low-grade ore was leached with sulfuric acid, the product liquor treated in an on-site solvent extraction circuit, and the stripped product liquor re-acidified and recycled. They were most generous in allowing us to visit their site, answering our questions, and were helpful in discussing the problems associated with heap leaching. They confirmed our belief that, it was possible to operate a heap leach profitably on material too low grade for. conventional milling. Based largely on what we had learned from Western Nuclear's experience, a program was set up involving a laboratory study to determine the characteristics of the mineral stockpiles as related to heap leaching and to conduct a pilot heap leach adjoining our Gas Hills mill. Basically, the pilot heap construction and leach procedure were similar to those described in the literature(1,2) with certain modifications to permit detailed monitoring of the operation. In May, '1972, the decision was made to construct a test heap. The UCC plant at Gas Hills, Wyoming was selected as the most appropriate site for the follow¬ing reasons:

Jan 1, 1977

By A. D. Hammond

Until recently, the volumes delivered and unloaded from heap-leaching pads have been estimated by manual methods at Wharf Resources' South Dakota operation. In August 1989, the Engineering Department acquired the MINE-SURVEY software developed by GEM COM Services, Inc. of Vancouver, Canada, as part of a mine planning/grade control software package. The implementation of MINE-SURVEY for pad control resulted in a cost-effective tool to provide accurate and prompt estimates of ore delivered or unloaded from the pads. Volumes can be calculated in a matter of minutes as opposed to hours or days. Another benefit is the ease of comparison of as-build and designed volumes, plotting cross-section in any orientation, importing into AUTOCAD, validation of ore densities and truck factors. This paper describes the application of the MINE-SURVEY systems in heap leaching pad volumetrics.

Jan 1, 1991

By Frank P. Frandina, Michael J. Loehr, Paul E. Gabryszak

The Heartland Corridor Clearance Improvement Project is part of a regional Public-Private initiative to allow double stack container trains a direct route from the Port of Norfolk through Virginia, West Virginia, Eastern Kentucky and into Central Ohio. In the Preliminary Engineering stage, 30 existing tunnels were assessed and 28 were found to need clearance improvements to allow the use of double stack trains. Alternative tunnel enlargement methods were developed to achieve the desired clearance improvements, while maintaining structural integrity and minimizing disruption to train traffic. This paper summarizes the geometric and condition investigations of the existing tunnels, as well as describes the preferred methodologies to achieve the desired clearance. The clearance improvements will be implemented beginning in the summer of 2007.

Jan 1, 2007

By Frank P. Frandina

The Heartland Corridor Clearance Improvement Project is part of a regional Public-Private initiative to allow double stack container trains a direct route from the Port of Norfolk through Virginia, West Virginia, Eastern Kentucky and into Central Ohio. The project involves clearance improvements to twenty-eight tunnels, twenty-one of which require structural modification. With construction of the first Package of tunnels just underway at press time, this paper summarizes the program implementation from design through the initial stages of construction.

Jan 1, 2008

By I. Longson

As a longwall coalface advances a caved goaf or waste region is left behind. Air flow takes place through this permeable goaf due to the pressure differentials existing across it and en route this leakage air picks up both heat and moisture. A marked deterioration in climatic conditions occurs in the face area at all points downstream of where this leakage air rejoins the main air-stream. This goaf heat source can make a very significant contribution, typically 30-40% to the rate of total heat pickup on an advancing UK longwall coalface with a VST of 40°C and hence on the climatic conditions that prevail at the return end and in the return gate of the face. The magnitude of the rate of heat collection from the goaf depends on a number of factors but it has been established that it is particularly influenced by the prevailing virgin rock temperature and the total flow rate of the leakage air. This paper proposes a model for the goaf based on a packed bed analogy and other assumptions required in order to evaluate the rate of heat pickup are identified. The outlet condition of the leakage air predicted by the model have been shown to correlate with underground measurements taken for a range of different production patterns with the face cutter at various locations on the face. The sensitivity of these predictions to variations in the input data has been tested and is commented on. At this stage of the development the capabilities and predictive limitations of the model are discussed. Further areas of investigation are suggested in order to improve the predictive ability and to extend the versatility of the model.

Jan 1, 1989

By Donald Whittaker

Severe climatic conditions in mines are normally associated with working at depth. More precisely, it is a matter of working in regions of high strata temperature, since, for example, some coal mines in the Ruhr have strata temperatures at 1000 m which are matched only at 3 times that depth in the South African gold mines. In Britain we are perhaps fortunate in encountering strata temperatures in our deeper coal mines some 10-15 K lower than at the same depth in the hot mines of the Ruhr. Nevertheless the problems of high temperatures and humidities in UK mining operations, which in the past have been confined to a few specific sites, have in recent years become more widespread, and there is every reason to suppose that the trend will continue. Clearly strata temperature is not the only .causative factor. Long ventilation circuits serving districts remote from the shaft must also play a part, while the heavy use of machinery and the rapid, rates of excavation of modern mining methods are obviously important. It is necessary to understand the mechanisms of all such factors, and to measure their magnitudes and fluctuations, if remedial measures are to be properly designed or predictions made which are accurate enough to be of use in ventilation planning. This paper presents the results of a long-term (and continuing) investigation carried out in several mines to measure the major sources of heat and moisture on longwall districts and trunk conveyor roadways. The variation with time of these sources is reported, and the resultant effect on the climate is considered. In their investigations of the heat exchanges occurring in a whole mine Oakes and Hinsley (1955-56)1 listed and estimated the magnitudes of a large number of heat sources. Some of these, namely autocompression of the air in the shaft, diesel engines and compressed air mains, do not apply to the present investigations, which refer to longwall districts with conveyor transport and no compressed air supply. Others, such as oxidation of coal and, desorption of methane, have not been taken into account in the measurements, but are discussed later. One other source, the importance of which was pointed out by Gracie and Matthews (1975)2, is the coal on the conveyor, a form of strata heat emission, but one which is strongly dependent on the rate of coal production. The heat emissions measured in the present investigations were the energy consumed by electrical machinery, the heat conducted from the strata and the heat lost by the conveyed coal. Most of the emitted heat was removed from the district by the ventilation air, and was measured by continuously recording the enthalpy of the air at fixed stations. The heat removed by service water, supplied for machine cooling and dust suppression, was also measured. Account was of course taken of the relatively minor changes in level around the districts, in terms of the potential energy gained or lost by the coal and by the ventilation air (autocompression).

Jan 1, 1980

By M. L. Gupta, S. P. Banerjee, D. C. Panigrahi

The paper describes the computer simulation of climatic conditions in the longwall workings in India. For this simulation work the longwall panels have been divided into two segments, viz; the intake gate segment and face segment. Two computer models, one based upon transient heat and moisture transfer algorithm of McPherson (1986) and the other on quasi-steady algorithm of Starfield and Bleloch (1983), have been developed for intake gate segments. Similarly two computer models, one based upon the transient heat flow in cylindrical tunnel with certain modifications of McPherson algorithm (1986) and the other on linear heat flow concept, have been developed for face segment. The models incorporate the necessary running and spot heat sources present in their respective segments. In addition to this the goaf heat flow parameters have been incorporated in the models for the face segments. Continuous recording of important thermal parameters have been carried out in several longwall faces in India to validate these models and the results have been presented.

Jan 1, 1993

By S. J. Bluhm

INTRODUCTION Lesotho is a mountainous area of southern Africa from which water is to be exported in an extensive tunnel system, to industrial regions inland. The related tunnelling project has involved a num- ber of drives using tunnel boring machines [TBMs] to excavate about 100 km of 5 m diameter water tunnels [von Glehn and Bluhm, 1995). This paper describes the ventilation and cooling of some of the tunnel drives from both the operational and design points-of-view with a particular focus on heat generation. There were many common features in all of the drives but this paper is focused mainly on the Hlotse drive which was 18,4 km long. The drives were ventilated using forced ventilation systems to provide appropriate air flow throughout the tunnels and face zones. In addition, the Hlotse drive required refrigeration equip- ment which provided chilled water to the tunnel. While the sec- ondary ventilation systems play an important role in gas and dust handling, the paper concentrates on the primary ventilation and cooling issues. The ventilation of these tunnels was an exacting exercise be- cause: • Rock temperatures and geothermal heat flow were high. • TBMs with relatively high power ratings were used. • Diesel locomotives were used. • Drives were relatively long. • High altitude meant a low air density. An important feature was the simulation and monitoring of the ventilation and heat flow components and the project was characterised by analysis, monitoring and ongoing tactical decision-making throughout the progress. The thermodynamics of the systems were complex because there were many interactive effects and analyses were carried out using special computer pro- grams. The monitoring confirmed the accuracy of the models, and in this manner it was possible to confidently ensure healthy and safe working conditions and still minimise costs. Local ambient climate conditions range from temperatures higher than 35 "C in summer to below -10 OC in winter. Based on available statistical data and the thermal storage/damping effects in the system, design summer ambient conditions were taken as 15 OC/25 "C wet-bulb/dry-bulb. The barometric pressure was 80 kPa and due to the altitude, the ambient air density was only 0,9 kg/m3. The local Authority specified a maximum in-tunnel wet- bulb temperature [at any point] of 32,O OC and a mean wet-bulb temperature [from all locations] of 27,5 OC maximum. The maxi- mum height of ground cover above the tunnel was 1 200 m and the maximum virgin rock temperature was 41 OC; see Figure 1. Diesel dilution criteria specified by the local Authority was a minimum of 0.1 m3/s per rated kW of diesel engine. Other requirements related to gases such as CO, CO2, NOx and CH4 [and the need for intrinsically safe equipment] but these are not of direct relevance to this paper. The actual average face advance was about 30 m/d with good days achieving 60 m/d and good months achieving 1 000 m [23 working days]. The original design tunnelling rate was 50 m/d. DESCRIPTION OF HLOTSE DRIVE VENTILATION AND COOLING SYSTEM The ventilation requirements in the tunnels were dictated by heat and diesel dilution needs. The best ventilation and cooling policy is generally a balance between using increased quantities of fresh air or refrigeration [or both]. In this particular scenario it turned out that, since the diesel emission criteria required large quantities of air, the refrigeration needs were modest. The drive was ventilated using a ducted, forced ventilation system from fans located at the portal. The maximum ventilation requirement was 51 m3/s when the drive was at 18.4 km. From a heat flow point of view, the worst scenario was a heat load of 3.5 MW when the drive was at 7 km. This was cooled by the ventilation air and a supply of chilled water to the tunnel. Refrigeration and chilled water system In the design phase, a detailed comparison was carried out between two general alternatives for providing refrigeration. First, was a system in which refrigeration sets and air coolers are installed on the TBM train; the refrigeration sets are cooled by condenser water piped to and from cooling towers at the portal. Second, was a system in which refrigeration water chillers are in- stalled at the portal and chilled water is piped into the tunnel. The detailed comparison indicated that the capital and running costs of the second system were at least 60 % lower than the in-tunnel plant. There were also many obvious practical benefits for favouring the portal system. The refrigeration plant supplied 23 11s of cold water at a temperature of 10 OC. After providing the cooling effect in the drive, the water returned to the portal where it was initially cooled in open-circuit evaporative pre-cooling towers, chilled in the refrigeration plant and then returned to the tunnel. The cold water flowed into the tunnel in an insulated supply pipe and returned in an uninsulated pipe; the water was simply circulated to the end of the pipe and returned. The cooling effect in the tunnel was achieved entirely through heat transfer from the pipe [long linear heat exchanger] and no air coils or other heat exchangers were required. The cooling requirements were satisfied by the heat transfer to the returns chilled water steel pipe [200 mm]. The pipes were eventually installed to a maximum distance of 10,8 km in what was considered a very practical and cost effective solution.

Jan 1, 1997

By J. Jorge, J. Mariño-Salguero, B. Álvarez-Rodriguez, J. M. Menéndez-Aguado, J. J. de Felipe

"This work focuses on the characterization of heat generation during dry fracture by direct impact of a tantalum ore. Moreover, an attempt was made to quantify the heat energy loss to the environment during the grinding process of a ball mill. The study was carried out using mineral samples from a Spanish mine that were characterized by measuring their density and specific heat. During the experiments, increases of temperature ranging from 5.9 to 7.3 °C after the fracturing process were observed. A numerical model was then applied to calculate temperature distributions through the mill wall. Three possible combinations of heat transfer coefficients were analyzed, from (1) Kapakyulu and Moys, (2) Duda and (3) the heat transfer laboratory of Universitat Politècnica de Catalunya. The models with the coefficients from Kapakyulu and Moys and the heat transfer laboratory of Universitat Politècnica de Catalunya were found to provide results that were in best agreement with the experimental data. IntroductionEvery year, several billion tons of metallic ores, minerals, cement and other solids used in the ceramic and chemical industries are subjected to size reduction in ball mills around the world. The U.S. Department of Energy (2005) reported that in the United States about 29 percent of the total energy used by the mining industry, or 0.4 percent of total U.S. energy consumption, is used in comminution. In Canada and Australia, comminution is responsible for about 2 percent and 1.5 percent of total energy use, respectively. In nonindustrialized countries where mining constitutes higher fractions of their industrial sectors, comminution costs represent a significant contribution to mine operating costs. The specific energy consumption values for the grinding of these materials typically range from 5 to 50 kWh/t. Thus, a significant amount of electrical energy is consumed in the ball mill grinding operation (Aguado et al., 2006; Gupta and Sharma, 2014). Grinding can represent up to 50 percent of the direct operating cost in a mineral processing plant, especially as comminution devices operate in highly inefficient ranges of 4 to 8 percent (Wang, Yang and Yu, 2012)."

Jan 1, 2017

By Paloma Lazaro, Moe Momayez

Interactions between human beings and their work environment require the body to regulate its temperature by balancing heat production and loss. Comfortable environmental conditions are crucial for keeping workers safe and healthy and to maintain a suitable level of productivity. However, achieving a proper core body temperature may become challenging under different conditions, especially in high heat-generating workplaces such as hot underground mines. Because hot underground mines have the potential to expose workers to heat stress, compliance with standardized and regulated indices and criteria is distinctly required. The objective of this paper is to provide an overview of the current research on heat stress and strain in hot underground mines, collected from published and specialized literature. General definitions, statistics of heat-related accidents in mining, overview of the indices, standards, and recommendations for heat stress are provided herein.

Oct 6, 2020

By Siddhartha Roy, Hemant Agrawal, Ram Madhab Bhattacharjee, Devi Prasad Mishra

Heat stress is a major concern for the health, safety and productivity of miners working in hot and humid underground mines. At greater depth, heat inside underground mines increases due to geothermal gradient, heat released from high-capacity machinery, exposed rock surface, auto-compression of air, human metabolism, etc. Prolonged physical work in thermal environments severely affects the health, safety and efficiency of miners. In order to address this important issue, a systematic literature review (SLR) has been conducted. This SLR aimed to identify the research gap in the area of heat stress effect on underground miners and its control. An extensive literature search was carried out on numerous digital databases, grey literature and conference proceedings to identify relevant research work for this review. Moreover, the impactful studies, methodologies and preventive measures undertaken during the past five decades on the effect of heat stress on underground miners were retrospectively analysed, with a broader aim to explore the need for further research on this pertinent topic. Overall, 571 references were identified from the literature review, out of which 51 research articles addressing the sources of heat, heat stress effects on miners, heat stress indices and control measures for heat stress in underground mines were selected as primary papers for detailed review. Pre-developed fatigue is one of the prime causes of health hazard, safety and productivity loss of miners working in underground high heat stress zones. Hence, development of a better heat stress index integrating personal, environmental parameters and pre-developed fatigue (PDF) of miners is essential.

Jan 14, 2022

By P. C. Schutte, A. J. Kielblock

INTRODUCTION Certain activities, such as emergency work and rescue operations, often have to be undertaken in environments where heat loads often exceed limits prescribed for routine work. This is particularly relevant to the South African mining industry where heat stress-induced fatalities are not uncommon during rescue operations. In this regard an excessively hot environment is defined as one where either the dry-bulb temperature exceeds 37,0°C or the wet-bulb temperature exceeds 32,5"C, and it is therefore not surprising that heat stroke mortality escalates rapidly when these limits are exceeded. A review of both local and international standards indicated that the available information on safe exposure times under abnormal heat stress conditions is very limited. Where available, such standards are aimed at the general population, including both sexes, irrespective of age and also the least heat tolerant worker, and not at a medically-screened, all-male population free of grossly heat intolerant individuals, as is the case in the South African mining industry. It is suggested that available norms and limits are too conservative for local application and, therefore, unrealistic. In view of the definite need to protect workers when exposed to abnormally high environmental temperatures, the present study was undertaken to establish a scientifically derived data base. applicable to local conditions, to determine safe exposure times: Any exposure limit, especially in an emergency situation, should be easy to administer, valid and reliable. These aspects, there- fore, form an integral part of this paper. FORMULATION OF HEAT STRESS LIMITS The formulation of heat stress limits was based on the criterion that a heat exposed individual should experience a negligible risk of developing dangerously elevated body temperatures. In order to provide a database for risk assessment, certain physiological responses of heat tolerant men were determined at various combinations of thermal conditions and work rate in a climatic chamber. These physiological responses were analysed statistically in order to predict safe survival and tolerance times as a function of thermal conditions and work rate. EXPERIMENTAL DESIGN A total of 202 randomly selected, medically fit mine workers volunteered for the study on the basis of informed consent. These men were considered to be inherently heat tolerant in as far as they had successfully completed a heat tolerance test (Anon., 1991) or the standard climatic room acclimatisation procedure used on many South African gold mines (Anon., 1989). The subjects were allocated randomly to 14 experimental groups and each group was exposed in a climatic room to one of

Jan 1, 1997

By M. McPherson, P. Mousset-Jones, G. Danko

Calculation of the sensible heat transfer between the rock surface and the flowing air in an underground airway is still fraught with problems. There are only a few results available in the literature for the calculation of the convection in tunnels with naturally rough surfaces. Some of them are purely empirical, while others use a theoretical approach, based on the analogy between heat and momentum transfer, expressing the heat transfer coefficient as a function of the friction factor. A review and evaluation of these results are presented. The heat transfer equations obtained using the different assumptions, vary over a wide range, so that experimental results are needed to determine the formulae and constants applicable to mine airways. In situ measurements of the "physical" and "technical" heat transfer coefficient carried out in deep mines are described. The statistical distribution of the convective heat transfer coefficient on rough surfaces, as well as the regression between the Nusselt and Reynolds numbers in the turbulent flow region, are presented. Radiative heat transfer between the surface and the moist air flowing in a duct of relatively large hydraulic diameter has been taken into account during evaluation. The results will be a definite refinement of those calculations presently used in mine climate simulation models.

Jan 1, 1987